With the introduction of green revolution technologies, the modern agriculture is getting more and more dependent upon the steady supply of synthetic inputs. Intensive agriculture with the use of chemical fertilizers in large amount has, no doubt, resulted in manifold increase in the productivity of farm commodities but the adverse effect of these chemicals are clearly visible on soil structure, micro flora, quality of water, food and fodder. At this critical juncture, biofertilizers are useful supplement to chemical fertilizers. Organic farming has emerged as the only answer to bring sustainability to agriculture and environment. Biofertilizers is also an ideal for practicing organic farming.
Biofertilizers are the most advanced biotechnology necessary to support developing organic Agriculture, sustainable agriculture, green agriculture and non-pollution agriculture. Bio Fertilizer are natural and organic fertilizer that helps to keep in the soil with all the nutrients and live microorganisms required for the benefits of the plants. Today product like biofertilizers using the biotechnology techniques have proved that biological control is widely regarded as a desirable technique for controlling insects and pests, due to its minimal environmental impact and its avoidance of problems of resistance in the vectors and agricultural pests.
The increasing demand for biofertilizers and the awareness among farmers and planters in the use of biofertilizers have paved way for the fertilizer manufacturers and new entrepreneurs to get into biofertilizers production. It is one of the important components of integrated nutrient management, as they are cost effective and renewable source of plant nutrients to supplement the chemical fertilizers for sustainable agriculture.
This book gives a detailed process on manufacture of biofertilizers & organic farming. It contains chapters on biofertilizers, role of biofertilizer in crop production, production and distribution of biofertilizer, organic farming, method of organic farming, weed and pest management, and many more. This book will be very helpful to soil scientists, microbiologists, biologists, students, new entrepreneurs, fertilizer industry, organization engaged in biofertilizers production, training centres and to all those interested in the efficient use and recycling of wastes, resource management and sustainable farming.
1. BIOLOGICAL WASTES AS SOURCES OF BIOFERTILIZERS
Significance of Waste Recycling, Chemical Characteristics of Wastes and Utilisation, Hydraulic loading is calculated as follows:, Heavy Metals and Associated Problems, Pathogens and Health Hazards, Effect on Crops Yield and Soil Properties, Effect on Crop Yields, NPK Through Fertilizer, Effect on Soil Properties, Problems in Waste Utilization, Future Research Needs
2. A NOTE ON BIOFERTILIZERS
Rhizobium, Production of Rhizobium Inoculants, Isolation of Rhizobium, Identification of Rhizobium, Establishing the Starter Culture, Mass culture of Rhizobium, Making the Carrier-based Inoculant, Packing and Storage, Field Application of Rhizobium Inoculant, Crop Respons, Azotobacter, Production of Azotobacter Inoculant, Field Applications, Seed Treatment, Seedling Treatment, Pouring of Slurry, Top Dressing, Beneficial Roles of Azotobacter, Azospirillum, Production of Azospirillum Inoculant, Isolation of Azospirillum, Confirmation of Azospirillum, Making the Starter Culture, Mass Culture, Carrier-Based Inoculant, Field Use of Azospirillum, Seed Treatment, Seedling Treatment, Top Dressing, Crop Response, Blue - Green Algae (BGA) Biofertilizer, Production of BGA Inoculant, Isolation of BGA, Starter Culture, Mass Culture of BGA, Storage, Field Use of BGA Inoculants, Crop Response, Phosphate Biofertilizers, Isolation of Phosphate Solubilizers, Mass Production, Field Application, Vesicular - Arbuscular Mycorrhizal Fungi, Genera of VAM Fungi, Morphology of VAM, Isolation of VAM spores, Mass Production of VAM, Field Application, Important of VAM Fungi, Azolla: A Green Manure Cum Biofertilizer, Mass Cultivation of Azolla, Field Application of Azolla, Azolla As A Green Manure, Azolla As A Dual Crop
3. ROLE OF BIOFERTILIZER IN CROP PRODUCTION
Nitrogen-fixing Bacterial Inoculants, Rhizobium, Classification, Need for Inoculation, Competitiveness and Effectiveness of Strains, Factors Affecting Performance of Inoculant Strains, Yield Response to Inoculation, Azotobacter and Azospirillum, Yield Responses to Inoculation, Effect of Soil Nutrients, Frequency of Inoculation, Phosphate Solubilizing Microorganisms, Mechanism of Action, Yield Responses to Inoculation, Vesicular-Arbuscular Mycorrhizae (VAM), Mechanism of Action, Root Colonisation, Yield Responses to Inoculation, Preparation of Inoculum, Plant Growth Promoting Rhizobacteria, Mode of Action, Yield Response to Inoculation, Future Research Needs, Strategy for Successful Use of Biofertilizers
4. BIOFERTILIZERS FOR RICE ECOSYSTEM
Azolla, Growth and N-fixation, Factors Affecting Growth and N-fixation, Water, Mineral Nutrients, Light, pH and Salinity, Management Practices, Rate and Time of Inoculation, Fertilizer Application, Method of Rice Planting, Insects, Diseases and Weeds, Method of Utilization, Impact on Rice Yield and Soil Fertility, Availability of Azolla-N to Rice, Effects on Rice Yield and Soil Fertility, Economic Aspects, Suitable Agroclimatic Conditions, Adoption Constraints and Future Research Needs, Blue-Green Algae (BGA), Nitrogen Fixing Potential and N-input, Factors Affecting Growth and N-fixation, Management Practices, Fertilizer Application, Method of Rice Planting, Insects, Diseases and Weeds, Method of Inoculum Production, Method of Utilization, Impact on Rice Yield and Soil Fertility, Availability of BGA-N to Rice, Effect on Rice Yield, Economic Aspects, Suitable Agroclimatic Conditions, Adoption Constraints and Future Research Needs, Conclusions
5. GREEN MANURING
Green Manures, Leguminous Green Manures, Non-grain Legumes, Grain Legumes, Perennial Trees and Shrubs, Role of Green Manuring in Cropping Systems, Rice-based Systems, Sugurcane-based System, Cotton-based Systems, Potato-based Systems, Rainfed/dryland Systems, Plantation Crops, Fate of Green Manures on Application to Soils, Availability of Essential Nutrients, Crop Responses and Residual Effects, Green Manure Management, Residual and Long-term Effects, Maize yield (t/ha) Corresponding N input, Economics of Green Manuring, Constraints of Green Manuring, Future Research Needs, Conclusions
6. PRODUCTION AND DISTRIBUTION OF BIOFERTILIZERS
Definition and Classification, Practical Significance of Biofertilizers, Requirement of Biofertilizers, Production Technology of Biofertilizers, Rhizobium, Sources of Mother Cultures, Carriers, Production of Biofertilizers, Rhizobium, Azospirillum & Azotobacter, Blue Green Algae, Standards and Quality Control, Government Support and Programmes, Constraints, Production and Distribution Level Constraints, Storage and Distribution, Constraints at Field Level, Market Level Constraints, Areas for Future Development, Training, Improvement in production technology, Need for preparation of biofertilizer map, Region-specific effective strains, Necessary quality control acts, Proper storage facilities, Conclusions
7. BIOLOGICAL NITROGEN FIXATION
Non-symbiotic Nitrogen Fixation, Features Favourable for Non-symbiotic Nitrogen Fixation, Special Separation of Nitrogen Fixing Cells, Protein-Nitrogenase Association, High Rate of Respiration, Time Specific Nitrogenase Activity, Association With Rapid Oxygen Consumers, Presence of Hydrogenase, Colonizarion, Nitrogenase, Basic Requirements For Nitrogen Fixation, Mechanism of Nitrogen Reduction, Assimilation of Ammonia, Symbiotic Nitrogen Fixation, Root Nodulation, Mechanism of Nitrogen Fixation, Nitrogenase, Requirements For Nitrogen Reduction, Assimilation of Ammonia, Genetics of Nitrogen Fixation, Nif-genes of Klebsiella Pneumoniae, Regulation of Nif Genes, Nif-genes of Azotobacter, Nif-genes of Anabaena, Rhizobial Genes, Legume Nodulin Genes, Overall Regulation of Genes, Gene Transfer for Nitrogen Fixation, Transfer of Nif genes to Non-nitrogen Fixing Bacteria, Transfer of Nif genes to Plants, Transfer of Nif-genes fo Pfanfs, Transfer of Nod Genes, Transfer of Hup Genes
8. THE SOURCE OF ORGANIC MATTER
The Root-system of Crops Soil Algae, Green-manures, Farmyard Manure, Artificial Farmyard Manure
9. THE CHIEF FACTORS IN INDORE PROCESS 159
The Continuous Supply of Mixed Vegetable Wastes, Composting Single Materials, Nitrogen Requirements, The Amount of Water Needed, The Supply of Air, The Maintenance of the General Reaction, The Fermentation Processes, Gains and Losses of Nitrogen, The Character of the Final Product
10. MANUFACTURE OF BIOFERTILIZER BY THE INDORE METHOD
The Compost Factory, Collection And Storage of the Raw Material, Plant Residues, Urine Earth and Wood Ashes, Water and Air, ARrangement and Disposal of the Bedding under the Work Cattle, Charging the Compost Pits, Turning the Compost, Time-table of Operations, Output, Manurial Value of Indore Compost
11. ORGANIC MATTER AND SOIL FERTILITY
Soil Humus, its Origin and Nature, The Formation of Humus as a Result of the Synthesizing Activities of Micro-organisms, The Role of Humus in the Soil, The Washington Symposium on Soil Organic Matter
12. WEED MANAGEMENT IN ORGANIC FARMING
Cultural Methods of Weed Control, Tillage, Tillage combined with irrigation, Timing, Seeding rates and cultivar selection, Cropping systems, Use of animals, Flooding, Mulching, Fire, Composting, Hoeing and hand weeding, Farmer’s care, Straw disposal, Biological Control of Weeds Using Insects, Weed suitability to biological control, Classical approach, Characteristics of weeds and problems, Weed survey for Natural enemies, Introduction of
natural enemies, Use of Pathogens in Weed Suppression, Mycoherbicides, Characteristics of good Mvcoherbicide, Use of seed-borne and seed infecting microorganisms, Parasitic Weeds, Management strategies for parasitic weeds, Biological control, Ecological Principles, Research Needs
13. PEST MANAGEMENT IN ORGANIC FARMING
Pest Management Methods, Biological alternatives, Organically acceptable chemical alternatives, Cultural alternatives, Biological Control, Advantages of Bio-control:, Botanical pesticides, Bacterial insecticides, Viral insecticides, Microbial antibiotics, Biological control in field crops, Other Crops, Botanics for Storage Pest Control, Seed treatment with materials of plant origin for insect control, Active principles, Cultural Practices/Ecological Methods, Optimum site conditions, Diversity over Time, Rotations, Diversity in space, Habitant enhancement, Role of Non-crop vegetation, Trap crops, Constructed traps, Plant resistance to pests, Traditional Practices for Pest Control, Other Management Practices
14. RICE-FISH INTEGRATION OF ORGANIC FARMING
Externalities of Green Revolution, Rice Productivity in States of India, Lowland Rice Ecologies, Diversification- IPS Approaches, A fish harvest from rice field, Vanishing rice lands - Economic sustainability issues, Pokkali system-the classic example, Rice-Fish, Harnessing complementarities, Group Fish Farming (GFF), Environmental Superiority, Economic sustainability, Win-Win Land use Model
15. CHOICE OF VARIETIES FOR ORGANIC FARMING
What is organic Agriculture?, Selection of rice varieties for organic farming, Weed Control, Soil fertility, Insects and Diseases, Speciality rices for organic farming, Varieties for Special systems of cultivation, Pokkali, Koottumundakan cultivation.
16. COASTAL AGRO-ECO SYSTEM IN ORGANIC RICE FARMING
Organic farming - the truths vs. myths, Organic food tastes better and is of superior quality, Organic food is more nutritious and safer, Organic farming is eco-friendly, Organics as a source of Plant nutrients, Organic Farming and Food Security, Organic Farming- a lesson from China, Biodynamic Farming, System Of Rice Intensification (SRI)
17. MICROORGANISM FOR ORGANIC FARMING
Biological nitrogen fixers, Legume - Rhizobium symbiosis, Azospirillum, Different methods of application of Azospirillum in the field, Cyanobacteria (Blue green algae - BGA), Mass Production of BGA in the field, Anabaena - Azolla Symbiosis, Utilisation of Azolla for rice, Mass production of Azolla in the field, Phosphorus solubilising microorganisms, Arbuscular Mucorrhizal Fungi (AMF), Silicate solubilising bacteria, Zinc solubilising bacteria, Plant Growth Promoting Rhizobacteria (PGPR), Efficacy of PGPR in rice, Methods of application of Pseudomonas fluorescens in rice, Seedling root dip, Soil application, Foliar spray, Microbial consortium for rice
WASTES AS SOURCES OF BIOFERTILIZERS
order to meet the nutrient needs of agriculture in the coming years,
the Government of India’s working group on fertilizers has estimated
that 6.5 million tonnes (mt) of N + P2O5 + K2O will be needed by
2007-08 and 60 mt by 2010. On no account can fertilizers, or any single
input provide such large quantities of plant nutrients. All available
nutrient sources have to be made use of. In addition, integrated use of
mineral, organics and recyclable wastes is accepted as the most
appropriate strategy for sustaining high crop yields, minimising soil
depletion and value-added disposal of what are traditionally labelled
chapter present a current assesment of biological and industrial wastes
as sources of plant nutrients and analyses various factors which
determine their usefulness. Among biological wastes, materials covered
are sewage sludge, biogas slurry, waste water, fish pond effluent and
some wastes of food processing industry. Pressmud and phosphogypsum
(biproduct of fertilizer industry) are also dealt with.
of Waste Recycling
and water being major constraints in the development of Indian
agriculture, harvesting the nutrient energy of biological and
industrial wastes is of prime importance for maximising the food, feed,
fodder and fuel production in the country. Further, when these wastes
are recycled through land for crop production, due to the degradative
and assimilative capacity of soil the pollution of streams and/or
rivers receiving these wastes can be minimised to a large extent as
compared their direct disposal in water resources. Role of 4 R cycles
in harvesting the nutrient energy of waste. Domestic and industrial
waste waters are disposed on land (i) to use the nutrient potential for
biomass production (ii) provide safe disposal to the waste water
through the soil and (iii) prevent the pollution of streams and rivers.
potential for the exploitation of manurial value of biological and
industrial wastes exists in India. Even at 50% collection of the total
agro forest waste, more than 14.5 in ha of land can be manured at the
rate of 10 t/ha annually. Further, the productivity of more than 48 m
ha land can be improved through biogas slurry manure at 50% collection
domestic and industrial wastewaters amenable for crop production can
help to increase the irrigated area by 170.4 x 103 hectares in the
country. The prevention of environmental pollution through recycling of
waste is difficult to quantify but it will be several times valuable as
clean environment is today’s need. Nutrient potential of different
biological and industrial wastes has been summarised in Table 1. The
major sources are crop residues, animal excreta, rural compost (of
which dung is again a major component) domestic and industrial waste
water, forest litter, and city refuse. Since dung is a major component
of rural compost, nutrient potential can be over estimated if cattle
dung and rural compost are taken as independent materials which they
are not. If 60% of the total dung available is fed into biogas plants,
this can generate 470 mt of organic manure. Under the National
Programme on Biogas Development about 350,000 biogas plants were set up
during 2000 which produced 7.1 mt. of manure. Biogas manure is richer
in plants nutrients compared to FYM and contains 1.65-1.84% N,
1.08-1.18% P2O5 and 1.24-1.83% K2O.
NOTE ON BIOFERTILIZERS
carrier based microbial inoculants being added to the soil to enrich
the soil fertility are called biofertilizers. They are often known as
microbial fertilizers or microbial inoculants. A biofertilizer may
contain nitrogen fixing microbes or phosphate solubilizing microbes or
spores of VAM fungi. It is supplied to the soil either by seed
treatment or by spreading it over the field during cultivation.
Biofertilizers reduce the use of chemical fertilizers in agriculture
and cost of production.
nitrogen biofertilizer may have nitrogen fixing bacteria or blue-green
algae. The nitrogen fixing bacteria include Rhizobium, Azospirillum,
Azotobacter Azotococcus, etc. Blue green algae such as Anabaena,
Aulosira, Nostoc, Plectonema and Tolypothrix are used as nitrogen
of phosphate solubilizing bacteria such Bacillus megatherium, B,
subtilis, Xanthomonas and Pseudomonas, are used as phosphate
spores of VAM fungi like Glomus, Gigaspora, Acaulospora, Sclerocystis
and Endogone are used as VAM biofertilizers.
have the following advantages-
reduce the use of chemical fertilizers in agriculture.
never cause pollution in air, water and land.
secrete plant growth hormones to increase the plant growth.
reduce the attack by soil-borne pathogens,
improve the quality of soil for more productivity.
can be mass produced by using renewable wastes.
special care is required while using biofertilizers.
farmers themselves can grow BGA biofertilizers and
in their own lands.
Rhizobium is a
gram negative, aerobic, rod-shaped bacterium. It contains a refractive
granule. It is a soil bacterium present in large numbers in rhizosphere
of legume roots.
roots of legumes and forms nodules on the roots. Inside the root
nodules, the bacteria exist in various pleomorphic forms called
bacterioids. The bacterioids fix the atmospheric nitrogen into ammonia.
They provide the fixed nitrogen for plant’s use and draw nourishments
from the root cells. This type of association is called symbiosis.
species of Rhizobium can fix 50-200 kg nitrogen/ha/ year in leguminous
crops. Therefore, they have been recommended as nitrogen biofertilizers
species of Rhizobium show a great degree of host specificity. Hence
they can be used as biofertilizers only for the specific crops-
meliloti (Medic-Rhizobium): Lucerne
trifolii (Clover-Rhizbium): Egyptian
Leguminosarum (Pea-Rhizobium): Lentil, pea,
khesri (Lathyrus) and vetch.
Phaseoli (Bean-Rhizobium) : Bean,
kidney bean and French bean,
lupini (Lupin-Rhizobium): Lupines
and white lupines.
japonicum (Soybean-Rhizobium): Soyabean.
sps. (Chickpea-Rhizobium): Chickpea
: Sunnhemp, cluster bean,
peanut, jack bean, lablab, horsegram, moth bean, green gram, blackgram
of Rhizobium Inoculants
of Rhizobium inoculant involves-
Isolation of Rhizobium
Identification of Rhizobium
Establishment of starter culture
Mixing with carrier
Packaging and storage.
Isolation of Rhizobium
occurs in the soil as well as in the root nodules of selective legumes.
Rhizobium in the root nodules has least contaminants. Therefore, it is
isolated from root nodules of a proper leguminous plant.
leguminous plant is carefully uprooted from the soil and the root
system is washed with running water to remove the soil particles. Firm,
undamaged, pink-coloured root nodules are selected visually and excised
from the roots.
root nodules are kept immersed in 0.1% potassium chloride solution or
in 0.1% acidified mercuric chloride solution for 5 minutes to sterilize
the surface of the nodules.
sterilized root nodules are then washed 5 or 6 times with distilled
water. They are once again sterilized by immersing them in 90% ethyl
alcohol for 10 seconds and washed repeatedly with distilled water.
root nodules are crushed gently in a small amount of distilled water
using a pestle and mortar to get a suspension.
suspension is diluted and inoculated onto YEMA (Yeast extract mannitol
agar) medium in petri dishes. The culture plates are incubated at 28°C
for about 10 days. Rhizobial cells form gummy colonies on the medium.
of YEMA medium
NaCl -0.1 g
water -1000 ml.
Identification of Rhizobium: YEMA
medium is suitable for the growth of Rhizobium as well as
Agrobacterium. Rhizobial colonies are identified from the culture in
the following methods:
CRYEMA Test: A
2.5 ml of congo red dye is mixed with a litre of YEMA medium to prepare
CRYEMA medium. Bacterial colonies on the YEMA medium are streaked on
the CRYEMA medium and the petri dishes are incubated at 28 ± 2°C for
cells uptake congo red very weakly so they 27-BT form white, circular,
entire, raised, convex colonies. Agrobacterium colonies, if any, look
like Rhizobial colonies, but show characteristic colour of congo red.
The white colonies are picked up to produce Rhizobium inoculant.
Microscopic Observation : Bacterial
cells in the CRYEMA medium are stained with carbol fuschin and
visualized under a compound microscope. This dye stains the
-polyhydroxybutyrate granule in the Rhizobium. The cells of those
colonies having -polyhydroxybutyrate granule are picked up to
establish Rhizobium inoculant.
Peptone Agar Test (GPA Test): Rhizobial
colonies are streaked on YEMA medium and a master plate is made.
Colonies in the master plate are transferred to GPA medium in a petri
dish by replica plating. Rhizobium cannot grow in the medium, but
Agrobacteria, if present in the colonies, grow into colonies. Those
colonies in the master plate failed to grow in the replica plate are
pure rhizobial colonies. They are picked up and grown in YEMA medium.
This test is the confirmative test to test the purity of Rhizobial
same species of legume from which Rhizobia were isolated, is grown in
sterile soil in sterile jars. Nutrient solution that lacks nitrogen
source, is supplied through a hole at the base of the jars by inserting
a cotton thread immersed in the solution. Each pure Rhizobial culture
is then inoculated near the root of legume growing in a jar. After 3 or
4 weeks, the plants are carefully uprooted from the jars and visualized
for root nodules. Presence of more root nodules indicates that it is
the right strain of Rhizobium for that legume.
Establishing the Starter Culture: Pure
rhizobial colony is transferred to a flask containing YEMA medium. The
flask is kept on a rotary shaker system in a constant temperature room
at 28±2°C. Pure culture of rhizobium appears within a week. It is known
as starter culture or mother culture. A starter culture is frequently
sub-cultured for maintaining it for a long time.
Mass culture of Rhizobium: Rhizobium
is mass cultured in large bioreactors (fermenter) to prepare inoculant.
YEM medium * or sucrose-mannitol medium is used for this purpose.
suitable medium is formulated and filled into the bioreactor after
proper sterilization. One litre of starter culture for 100 litres of
medium is inoculated into the bioreactor.
temperature inside the reactor is maintained at 28± 2°C. Sterile air is
continuously supplied to the broth with the help of a proper device.
The broth is stirred continuously by a stirrer system kept in the
counting is done a regular intervals to assess the growth rate of
Rhizobium. Having reached 108-109 cells/ml, the broth is harvested to
use as inoculant. Further maintenance of the broth in the bioreactor
may lead to death of rhizobial cells due to the deficiency of enough
OF BIOFERTILIZER IN CROP PRODUCTION
have an important role to play in improving the nutrient supplies and
their crop-availability in upland crop production. Although Rhizobium
is the most researched and well known among these, there are a number
of microbial inoculants with possible practical application in upland
crops where they can serve as useful components of integrated plant
nutrient supply systems. Such inoculants may help in increasing crop
productivity by way of increased biological nitrogen fixation (BNF),
increased availability or uptake of nutrients through solubilization or
increased absorption, stimulation of plant growth through hormonal
action or antibiosis, or by decomposition of organic residues.
scope of this chapter is confined to microbial inoculants of N2-fixing
bacteria, vesicular arbuscular mycorrhizae (VAM), phosphate
solubilizers and plant-growth promoting rhizobacteria (PGPR) and their
role in production of upland crops. Aspects determining the success of
inoculant technology are discussed here rather than presenting an
up-to-date account of literature on the performance of biofertilizers.
Rhizobial inoculants are dealt with in detail as a general example and
for others, our discussion is restricted to those points which are
specific to a particular group of inoculants.
every hectare of land at sea level, there are 78,000 tonnes of inert
nitrogen gas (N2). Nitrogen is the most limiting nutrient for
increasing crop productivity. Only a few procaryotic organisms are able
to “fix” N2 directly through a biological process. Annually BNF is
estimated to be around 175 million tons of which close to 79% is
accounted for by terrestrial fixation. The N2 fixers involved are
metabolically diverse but the process is similar and depends upon (i)
nitrogenase (N2ase) enzyme complex, (ii) a high energy requirement
(ATP) (iii) anaerobic conditions (for N2ase activity) and, (iv) source
of strong reductant. Amongst N2-fixing bacteria viz; Rhizobium,
Azospirillum, and Azotobacter, the most widely used inoculant is
N2-fixation by Rhizobium with legumes contributes substantially to
total BNF. Rhizobium inoculation is a well known agronomic practice to
ensure an adequate nitrogen nutrition of legumes in place of fertilizer
of nitrogen fixed by some legumes.
Crop Nitrogen fixed (kg/ha) Crop Nitrogen fixed (kg/ha)
Alfalfa 100-300 Lentil 35-100
Clover 100-150 Green gram 50-55
Chickpea 26-63 Pigonpea 68-200
bean 37-196 Soybean 49-130
Cowpea 53-S5 Peas 46
Groundnut 112-152 Fenugreek 44
genus Rhizobium consists of six distinct species based largely on the
cross inoculation group concept. The assumption in this classification
is that those leguminous plants falling within a particular infection
group were nodulated by a particular species of nodule bacteria. More
than twenty cross-inoculation groups have been established, but only
seven have achieved prominence. The validity of the cross-inoculation
groups has been questioned as many legumes are nodulated by rhizobia of
other host-bacterial groups. With repeated evidence of anomalous
cross-infection among the different plant groups, new classification
has been proposed. The slow-growing rhizobia are grouped under the
genus Bradyrhizobium and the fast growers under the genus Rhizobium.
new classification is more complex as the same host may be nodulated by
fast and slow-growing strains. Moreover, the agricultural significance
of the cross inoculation groups still remains a key feature of the
established taxonomic system. In this article we have used the
classification based on cross-inoculation groups. The cross-inoculation
groups and Rhizobium-host plant associations are listed below:
inoculation Rhizobium Host Legumes group species genera included
group R. meliloti Medicago Alfalfa
Melilotus Sweet clover
group R. trifolii Trifolium Clovers
group R. leguminosarum Pisum Pea
Lathyrus Sweet pea
group R. Phascoli Phaseolus Beans
lupini Lupinus Lupines
group R. japonicum Glycine Soybean
group Rhizobium sp. Vigna Cowpea
Phaseolus Lima bean
for Inoculation: The
most important point is do we need inoculation of legumes in a region
where these crops have been grown over long periods? Development of an inoculant
industry in many countries has been largely motivated by
the desire to introduce legume species to new areas. Most cultivated tropical soils
are assumed to have relatively large populations (> 100/g dry
soil) of rhizobia capable of nodulating the legumes grown in such
soils. The need to inoculate the legumes grown on cultivated soils must
be assessed by considering the interacting factors between the soil,
the host plant and Rhizobium.
of nodules on plant roots does not necessarily mean that sufficient N2 is being
fixed for maximum benefit to the host plant. In groundnut or pigeonpea nodulation occurs naturally
at most locations due to the cross-species promiscuity of the cowpea
rhizobia. However, the ability to fix high amounts of N (efficiency) is
governed by the symbiotic capability between Rhizobium and
the host plant. Hence, it may be necessary to introduce superior (more
competitive and efficient) strains of Rhizobium to
ensure adequate N2fixation
for maximum growth and yield of the host plant. In a survey of
groundnut crops grown in farmers’ fields in southern India, 52 out of
95 fields showed inadequate nodulation with less than 10 per cent N2-fixing
(acetylene reducing) activity of what can be obtained under reasonable
The results of surveys of farmer’s gain and fodder legume crops also
revealed poor nodulation in large areas and good noduation only in a
few pockets. Poor nodulation in farmer’s fields could be due to several lactors eg. lack of
appropriate rhizobia in soil, deficiency or toxicity of a nutrient,
unfavourable conditions like prolonged water logging, unsuitable pH,
abundance of bacterial predators, pests and disease
attack, etc. Although adequate nodulation was observed in some parts, ineffective nodules
exceeded the number of effective nodules. Out of 87 groundnutrhizobial
strains isolated from different parts of India, only 5 were found to be effective.
FOR RICE ECOSYSTEM
is grown in about 42 m.ha in India. It contributes 75 mt, (44%) to the
total foodgrain production of 170 mt. Apart from water management,
supply of nitrogen is a key factor in the realisation of potential
yields from modern high yielding varieties. The rice plant absorbs
about 20 kg N/t paddy produced. Due to the poor N-status of soils, N
application is a must for harvesting moderate-high yields. Rice is
estimated to receive 40% of the total fertilizer N applied in India.
however, is not exclusively dependent on fertilizers or FYM for
external N supplies because the crop can receive sizable N input from
green manures and certain biofertilizers. The most important
biofertilizers for flooded rice are Azolla and Blue-Green Algae (EGA).
Both can grow along side rice. In addition, Azolla can also be used as
a green manure.
chapter takes stock of available information on Azolla and BGA for
flooded rice ecosystem. Any integrated N-supply system for flooded rice
must feature one of these biofertilizers which have the potential to
contribute 20-68 kg N/ha depending on the intensity of multiplication.
Sustainability of rice production will depend on how well these inputs
have been integrated with other sources of N. Both these biofertilizers
are members of the plant kingdom and they themselves require certain
inputs at optimum level for growth and N-fixation.
aquatic fern Azolla is distributed in both temperate and tropical rice
growing regions, and fixes atmospheric nitrogen (N2) in symbiotic
association with a heterocystous BGA, Anabaena azollae. Azolla contains
0.2-0.3% N on fresh weight basis and
3-5% N on dry weight basis. Azolla has been used as a fertilizer for
rice in Vietnam and China for centuries. However, its use as a
biofertilizer for rice in other countries is a relatively recent
development. About 90 strains belonging to seven species are being
maintained at CRRI, Cuttack which is the premier centre for Azolla
research in India. Of the seven species, Azolla pinnata is most widely
distributed in India.
growth rate, total biomass and N content of Azolla provide the estimate
of its potential for agricultural use. The environmental conditions and
nutrient availability greatly influence fern growth. In India, the
fresh weight of A. pinnata increases 2-6 fold in a week. The BGA in the
Azolla cavities is very efficient in N-fixation and can meet the fern’s
total N requirement. However, the fern is able to utilize both fixed N
and soil N simultaneously and maintains a high rate of N-fixation in
presence of combined N. Under ideal conditions, it has a potential of
fixing more than 10 kg N/ ha/day. At Cuttack, A.pinnata fixed 75 mg N/g
dry wt./day and produced a biomass of 347 t fresh wt/ha in a year which
contained 868 kg N, as much as in 1900 kg urea. About 30-100 kg N/ha
can be fixed
in a month.
variability is observed among Azolla strains with regard to growth and
N fixation. Among different A. pinnata strains, the Vietnam green and
Bangkok strains performed better than the India (Cuttack) strain. One
strain of A. caroliniana is found to fix more N than many A. pinnata
strains. This A. caroliniana strain can grow round the year in rice
fields and has better tolerance to snails, other pests and diseases.
One crop of Azolla provides 20-40 kg N/ha to the rice in about 20-25
days. Even though the estimates of N input vary considerably, the
N-fixing potential of Azolla is fully established.
Affecting Growth and N-fixation
prefers to grow in a free-floating state. Good water control is
desirable for its successful multiplication. The multiplication rate is
drastically reduced if the soil is just moist and the fern dies upon
complete drying. However, one strain of A. caroliniana is found to
survive on the moist soil for a longer period as compared to the
strains of other species. A water depth of 5-10 cm is recommended for
good growth but depths upto 30 cm do not have any adverse effect.
requires all the essential plant nutrients for normal growth. Because
of its aquatic nature, these elements must be available in the water.
The deficiency of any one element adversely affects its growth and
N-fixation. In these respects Azolla behaves as an agricultural crop.
Phosphorus is a key element and its deficiency results in poor growth,
pink or red colouration, curling of roots and reduced N content. The
effect of P and Ca deficiency on the growth and N-fixation is more
intense than that of K or Mg deficiency. Threshold level of P in Azolla
is about 0.2%-0.3% P on dry weight basis and its uptake by the plants
increases with increasing levels of P in the growth medium as described
later. Under favourable conditions, addition of one kg P results in
fixation of about 5-10 kg N.
is considered to be an efficient scavenger of potassium and may serve
as a K-source for rice in K-deficient soils. Iron is also important and
deficient ferns turn yellowish, due to decreased chlorophyll content.
Cobalt and molybdenum are required for efficient functioning of the
N-fixing system. The deficiency of one element affects the uptake of
others for example, P-deficiency results in increased uptake of Fe and
Zn whereas Mg deficiency reduces the uptake of K but increases the
uptake of Fe, Co and Mn.
the partners of the fern-alga association carry out photosynthesis
which helps it to maintain a high rate of N-fixation. Growth and
N-fixation of Azolla are influenced by both quality and intensity of
light. Azolla prefers a certain degree of shading, particularly during
summer, and reaches its full at 25-50% of full sun light. When the fern
and rice are grown together in a dual cropping system, Azolla growth is
below its potential due to shading by rice canopy which increases with
the advancement of rice growth. The shading effect is more in the wet
season than the dry season. A. caroliniana is more tolerant to shading
than other species. The growth of Azolla dual crop thus depends on leaf
area index of rice, weather conditions and fertility status of flood
water. The day length also affects the growth of Azolla. The growth is
better at higher latitudes than in the tropics as a result of longer
days during the Azolla growing season.
Temperature is perhaps the most important environmental factor that
limits the growth of Azolla and 25-30°C is optimum for most species.
A.pinnata is successfully grown in the rice fields at Cuttack round the
year (14-35°C) but its growth is better during July to December. Azolla
growth and N accumulation in relation to water temperature and solar
radiation are presented in Fig.2. The diurnal variation in temperature
is important in determining the temperature response of Azolla. The
temperature response varies among Azolla species/strains.
A.filiculoides and A, rubra are cold tolerant whereas A. mexicana, A.
microphylla, A. caroliniana, A. nilotica and some varieties of
A.pinnata have better tolerance to high temperature. A. filiculoides
does not grow well at high temperature but it can tolerate low
temperature upto 5°C.
appears to be a synergistic relation between tolerance to high
temperature and light intensity. At high light intensities the optimum
temperature for its growth shifts upwards. Temperature response is also
influenced by population density. Tolerance to high temperature is low
when Azolla attains a stationary phase. The high temperature causes a
severe damage to Azolla indirectly through its stimulatory effects on
population of Azolla pests. The extreme temperatures result in reddish
brown colouration in Azolla but change in colour usually does not
affect its N-fixing activity. The high temperature damage on Azolla can
be reduced by shading, draining the field or flushing.
role of green manures in improving soil fertility and supplying a part
of the nutrient requirement of crops is well known. Their use in crop
production is recorded to have been practised in China as early as 1134
B.C. These are one of the main components of integrated nutrient supply
system alongwith inorganic fertilizers and biofertilizers. In India, an
estimated 6.2 million ha were green manured during 1988-89 (4% of the
net sown area). Andhra Pradesh (AP) and Uttar Pradesh (UP) account for
60% of green manured area and 88% treated area was in the six states of
A.P., Karnataka, Madhya Pradesh, Orissa, Punjab and U.P.
chapter provides an overall assessment of green manures, their
significance and various management aspects in modern agriculture.
Green manures can meet a part of the nutrient needs (particularly N) of
crops for optimum production and to that extent can result in savings
in fertilizer costs. These cannot completely replace fertilizer N if
the goal is to harvest moderate-high yields on sustained basis.
manure refers to fresh plant matter which is added to the soil largely
for supplying the nutrients contained in its biomass. Such biomass can
either be grown in situ and incorporated or grown elsewhere and brought
in for incorporation in the field to be manured. Just any plant cannot
be used as a green manure in practical farming. Green manures may be
plants of grain legumes such as pigeonpea, greengram, cowpea, soybean,
or groundnut; perennial woody multipurpose legumes viz.,Leucaena
leucocephala (subabul), Gliricidia sepium. Cassia stamea or non-grain
legumes like Crotalaria, Sesbania, Centrosema, Stylosanthes and
plants are largely used as green manures due to their symbiotic N
fixing capacity. Some non-leguminous plants are also occasionally used
for the purpose due to local availability, drought tolerance, quick
growth and adaptation to adverse conditions.
ideal green manure should posses the following traits.
early establishment and high seedling vigour
tolerant to drought, shade, flood and adverse temperature.
early onset of N Fixation and its efficient sustenance.
an ability to accumulate large biomass and N in 4-6 weeks
easy to incorporate.
tolerant to pests and diseases.
Green Manures : These
differ widely in nitrogen concentration and yield. Among 86 species
used in India as green manures for rice their N contents ranged from
2.0 to 4.9% N. Earlierresults
on the performance of some important green manure crops in lowland rice
showed N-fixation of 74-134 kg/ha and about 200% increase on paddy
yield over unmanured plots.
manure crops suitable for various cropping situations prevailing in
India are listed in Table 1. Abundant availability of water and
sufficiently long fallow period before raising the rice crop have made
the green manuring a widely adopted practice in lowland rice
ecosystems. Common green manure crops in rice fields of India and their
potential of biomass and N contribution in 45-60 days of growth are
1: Green manures suitable for some field crops
Sesbania and Wild indigo (Indigofera
Potato Lupin (Lupinus
Cowpea, Guar, Buck wheat (Fagopyrum
evaluation of some of the promising green manure crops at Coimbatore
potential of already popular dhaincha and
ths newly introduced stem nodulating S.
rostrata. The exotic stem nodulating
S. rostrata of
Senegalese origin has much promise for lowland rice especially with
adequate irrigation. Another promising stem nodulating introduction
from Madagascar is Aeschynomene
is capable of withstanding water stress to some extent. Its potential
under Indian conditions has not been fully explored.
purpurea and Phaseolus
rather slowly and accumulate much less N than Sesbania, they
are more adapted to drought T.
the additional advantage of self-sowing and is not browsed by cattle.
Hence in deltaic areas
common leguminous green manure crops for rice fields and their
potential N contribution.
in 45-60 days
Local Botanical Growing Green matter Nitrogen name name season (t/ha) contribution
Sunnhemp Crotolaria juncea Wet 21.2 91
Dhaincha Sesbania aculeata Wet 20.2 86
Pillipesara Phaseolus trilobus Wet 18.3 201
Greengram Vigna radiata Wet 8.0 42
sinensis Wet 15.0 74
Guar Cyamopsis tetragonoloba Wet 20.0 68
Senji Melilotus alba Dry 28.6 163
Khesari Lathyrus sativus Dry 12.3 66
Berseem Trifolium alexandrium Dry 15.5 67
3: Evaluation of green manures for rice based cropping systems
in 60 days
manures Biomass N
(t/ha) kg/ha kg/ha/day
juncea 16.8 159 2.65 Quick
growing, easy seed
aculeata 26.3 185 3.08 High
rostrata 24.9 219 3.65 Stem
nodulating, tolerant to
purpurea 16.8 115 1.92 Drought
tolerant, self seeding
trilobus 17.6 126 2.10 Green
a single rice crop is grown due to limited water availability, T.
purpurea is raised in the long rice fallow season without irrigation.
After 3-4 months, it sheds seeds in the field which germinate after
rice harvest in the next year. The green manure is incorporated 7-10
days before rice transplanting. Another drought tolerant green manure
crop suitable for rainfed rice is wild indigo. It can contribute 62-
182 kg N/ha to the succeeding rice crop, depending on soil, climatic
and cropping conditions.
annual grain legume crops are also used as green manure, after all or
part of the grain is harvested. Greengram stover incorporated in the
soil after pod harvest contributed about 60 kg N/ha to the succeeding
rice crop. Evaluation of several grain legumes with Sesbania and
Crotolaria showed that greegram was the best, yielding about 11 grain
and 2.5t dry matter/ha equivalent to 50 kg N/ha. Greengram, blackgram
(Phaseolus mungo) and cowpea could provide about 50-60 kg N/ha for the
succeeding rice crop.
studies at Coimbatore cowpea was the best among the grain legumes
tested, contributing about 65 kg N/ha in addition to about 500 kg
grain/ha. Its residues can also be used to supplement N-supplies for
rice. Hence after grain harvest the legume stover grown in the pre-rice
season could be incorporated as green manure to meet the partial
requirement of N, provided there is no competing demand for the stover
as cattle feed.
a comparison, S.rostrata produced more biomass and contained 2.5-3
times more N than grain legumes in 60 days. Where grains are harvested,
the N-benefit to the following crop is reduced to the extent that
absorbed N is taken away with the grains.
AND DISTRIBUTION OF BIOFERTILIZERS
routes of improving soil fertility for optimum crop production are
vital components of integrated nutrient supply systems. These routes
are operated by microorganisms who either synthesise plant- usable
forms of nutrients (N2 to NH4) or increase the availability and root
accessibility of nutrients already present in the soil, as in case of
P. Though most of these organisms are present in the soil and have been
on the job for centuries, as manageable agricultural inputs they have
received attention only during the 20th century. Due to several
reasons, their importance is on the increase and therefore their
production and distribution aspects assume practical significance.
microorganisms have somehow come to be called as “biofertilizers” a
term which many consider to be arbitrary, a misnomer and even slangish
but nevertheless widely used. In the strictest sense, real
biofertilizers are the green manures and organics (materials of
biological origin which are added to deliver the nutrients contained in
them). We believe that what are commonly referred to as biofertilizers
should be referred to as inoculants after the name of microorganism
they contain viz Rhizobium inoculant or Azospirillum inoculant.
chapter deals with the various aspects of production, promotion and
distribution of biofertilizers in the Indian context.
inoculants are biologically active products containing active strains
of specific bacteria, algae, fungi, alone or in combination, which may
help in increasing crop productivity by way of helping in the
biological nitrogen fixation, solubilization of insoluble fertilizer
materials, stimulating plant growth or in decomposition of plant
residues. A number of biofertilizers are now available in India.
Depending upon the nutrients provided, these can be broadly classified
for legumes NBF
for cereals Phosphate Phosphate
Rhizobium Azospirillum, Solubiliser Absorber
BGA Pseudomonas VA-mycorrhiza
India, systematic study on biofertilizers started 70 year ago with the
first report of the isolation and identification of Rhizobium from
different cultivated legumes by Joshi in 1920. This was followed by
extensive research by Gangulee, Sarkaria and Madhok on the physiology
of the nodule bacteria and its inoculation for better crop production.
Important milestones in production, development and promotion of
biofertilizers in India are presented in Table 1.
Rhizobium and Blue-Green Algae can be considered as established
biofertilizers; Azolla, Azospirillum and Azotobacter are at an
intermediate stage and the rest are potential materials.
Significance of Biofertilizers
N-fixation accounts for 69% of total N-fixation (including fertilizer
industry) in the world and non-biological processes for 31%.
Inoculation with Rhizobium can help legumes to meet upto 80-90% of
their N needs and the treatment increases grain yield by 10-15% under
on-farm condilions. Benefits of symbiotic BNF by legume to subsequent
cereal crops are common and measurable. Legume residues are usually
high in N, have a narrow C: N ratio and generally mineralise faster to
benefit subsequent crops.
green algae can add about 20-25 kg N/ha to rice fields and to that
extent fertilizer N can be saved or supplemented. In addition, BGA have
been shown to benefit the rice plants by supplying growth promoting
substances such as gibberellic and indole acetic acid. Temperature and
available P are two most important factors which determine the success
of Azolla. Azospirillum and Azotobacter have also shown promise as
biofertilizers. At present there is a great demand for Azospirillum
from farmers of Tamil Nadu as they have obtained significant responses
in rice and sugarcane due to its inoculation.
with P-solubilising microorganisms invariably show that inoculation of
seeds with these increases grain yield. These also have the
potentiality of being used as co-inoculants for
legumes which have high P requirement. VAM-fungi facilitate the
accumulation of P by plants through mycelial network, but the
multiplication of VAM on commercial scale is yet to arrive.
tonne Rhizobium inoculant is equivalent to 100 t of fertilizer N
(considering minimum N-fixation of 50 kg/ha and 0.5 kg/ha application
dose) and 1 tonne of BGA is equivalent to 2 t of fertilizer N
(considering minimum N-fixation of 20 kg/ha from 10 kg/ha application
dose). Monetary benefits derived from the use of biofertilizers are
presented in Table 2.
annual requirement of Rhizobium innoculum varies from 1,250 to 15,000t.
Highest requirements are apparently based on an over-simplified
approach multiplying the total legume area by dosage/ha. If 25% of area
is annually treated, 3750t inoculum is needed for 30 m ha,. Present
production is about one-fourth of this.
requirement of BGA varies from 168,000t for treating 16.8 m ha under
wetland rice to 230,000t for treating 23.6 m ha of rice in eight major
states to as high as 400,000t apparently for inoculating the entire
rice area in India with 10
kg/ha. The authors have also arrived at an estimate closer to that of
Venkataraman. Present production is less than 0.1% of this.
estimates should actually be based on the native bacterial population
per unit soil, nodulation map for Rhizobium, natural distribution of
microorganisms, environments offering greatest potential and presence
of any major constraints such as nutrient deficiencies. Requirements
based on multiplication of total area by dosage/ha do not serve any
purpose and provide exaggerated estimates which cannot be used as a
basis for planning or setting up production facilities.
Technology of Biofertilizers
on the physical nature and carrier materials used, various types of
biofertilizers are manufactured by different producers. These are
carrier based inoculant, agar based inoculant, broth culture and dried
culture. New developments in biofertilizer productions like (i)
freeze-dried inoculants (e.g. BAIF, IARI. India) (ii) Rhizobium-paste
(e.g. KALO Inc. USA), (iii)granular inoculant (e.g. Soil implant of
Nitragin , USA) (iv) pelleting (e.g. Pelinoc of Nitragin), (v)
Polyacrylamide entrapped rhizobia (e.g. Agrosoke) and (vi) Pre-coated
seeds (e.g. Prillcote of New Zealand) appear to be more promising for
inoculation success in tropical legumes. Advantages and disadvantages
of most of the types mentioned above have been critically examined and
carrier based inoculant has been regarded as most suitable for
commercial purposes. Since different species of Rhizobium bacteria
infect different legumes, a whole range of inoculants are needed. Their
production technology is however the same.
India, septic methods of production of Rhizobium biofertilizer is
followed comprising mixing of broth with unsterilised carrier.
Sterilisation of carrier in’bulk is done in autoclave by most of the
producers, where complete sterilisation is not achieved. The fool proof
method of sterilisation of carrier material is through gam-a radiation
but such facility is lacking. To achieve production of quality
biofertilizer, carrier should be sterilised in sterilisable poly
propylene pouches, inoculum introduced by injecting and cured for at
least two weeks at 27-30°C before despatch.
SOURCE OF ORGANIC MATTER
number of sources of soil organic matter exist, namely: (1) the roots
of crops left behind at harvest, including the weeds turned under in
the course of cultivation; (2) the algae met with in large quantities
in rice fields, on the surface of the soils of tropical countries
during the rainy season and to some extent in all soil; (3)
green-manure; (4) farmyard manure; (5) artificial farmyard manure. In
addition to these supplied, certain by-products of industries, such as
oil-cakes and wool-waste, are also employed as sources of organic
matter. These, however, are small in total amount and need not be
considered. Except in China and Japan and to a limited extent in India,
little or no use is made of night soil in crop production.
ROOT-SYSTEM OF CROPS
is not always realized that about half of every crop the root-system
remains in the ground at harvest time and thus provides automatically a
continuous return of organic matter to the soil. The weed sand their
roots turned in during the ordinary course of cultivation add to this
supply. When these residues, supplemented by the fixation of nitrogen
from the atmosphere, are accompanied by skilful soil management, crop
production can be maintained at a moderate level without the addition
of any manure whatsoever. A good example of such a system of farming
without manure is to be found on the alluvial soils of the United
Provinces, where the field records of ten centuries prove that the land
produces fair crops year after year without any falling off in
fertility. A perfect balance has been reached between the manurial
requirements of the crops harvested and the natural processes which
recuperate fertility. A similar, although not so striking a result, is
afforded by the permanent wheat plot at Rothamsted, where this crop has
been grown every year on the same land without manure since 1844. This
plot, showed a slow decline in production for the -first eighteen years
after which the yield has been practically constant. Systems of soil
management such as these provide, as it were, the base line for the
would-be improver. Nothing exists in the world’s agriculture below this
level. At the worst, therefore, the organic matter of a soil,
constantly cropped without manure, does not disappear altogether. The
wheel of life slows down. It does not stop.
source of readily decomposable organic matter, which is available in
India just at the moment when the cold season crops need it, is to be
found in the shape of a thick algal film on the surface of cultivated
soils during the second half of the rains. This film has also been
observed in Africa, Ceylon and Java, and is probably universal during
the rainy season in all parts of the tropics. As is well known, there
are two periods in India when the crop is in greatest need of combined
nitrogen: (1) at the break of the monsoon in June and July, and (2)
when the cold season crops are sown in October after the rains. These
latter are planted at a time when the available nitrogen in the surface
soil is likely to be in great defect. The land has been exposed to
heavy rain for long periods; the surface soil is often waterlogged.
Nitrates under such conditions are easily lost by leaching and also by
de-nitrification. The conditions are therefore altogether unfavourable
for any approach towards and ample supply of nitrate when sowing time
comes round in early October. How do the cold weather crops obtain a
sufficient supply of this essential food material? It is more than
probable that the deficiency is made up for, in part at least, by the
rapid decay of the algal film (which also appears to be one of the
factors in nitrogen fixation) during the last cultivations preceding
the sowing of the cold weather crop in October. It is possible that
some changes may have to be made in soil management with a view to
stimulating the growth of this algal film. One of the beneficial
effects of growing a green-manure crop like sann hemp for composting,
during the early rains, may prove to be due to the favourable
environment provided for the rapid establishment of the algal film. On
monsoon fallow land it will probably be found best to suspend surface
cultivation during the second half of the rains when the film is most
active. There is already among the cultivators of India a tendency to
stop stirring the surfaced, from the middle to the end of the rains,
even when this involves the growth of weeds. This coincides with the
period when the algal film is most noticeable. The indigenous practices
may therefore prove to be based on sound scientific principles. Here
are ready to hand several interesting subjects which urgently call for
study under actual tropical conditions. When this is undertaken, the
investigation should include: (1) the conditions most favourable for
the establishment of the algal film; (2) the part played by algae and
associated bacteria in nitrogen fixation; (3) the role of algae in
banking easily destroyed combined nitrogen during the rains; and (4)
the supply of easily decomposable and easily nitrifiable organic matter
for the use of the cold weather crops. In the rice fields of the
tropics, the algal carpet is even more evident than on ordinary
cultivated soils. The total weight of organic matter added every year
to each acre of rice land in the shape of algal remains must be
considerable and must serve as a useful addition to the store of
organic matter. Apart from the fixation of nitrogen from the air, it
may help to explain why such heavy crops of paddy can be obtained in
India, year after on the same land, without manure.
the investigations of Schulz-Lupitz first showed how open sandy soils
in Germany can be rapidly improved in texture by the incorporation of
green-manures, the future possibilities of this method of enriching the
land became apparent to the investigators of the Occident. After the
role of the nodules (found on the roots of leguminous plants) in the
fixation of atmospheric nitrogen was proved, the problems of
green-manuring have naturally centred round the utilization of the
leguminous crop in adding to the store of organic matter and combined
nitrogen in the soil. At the end of the last century it seemed so easy,
by merely turning in a leguminous crop, to settle at one stroke and in
a very economical fashion the great problem of maintaining soil
fertility. At the expenditure of a very little trouble, the soil might
be made to manure itself. A supply of combined nitrogen, as well as a
fair quantity of organic matter, might be provided without any serious
interference with ordinary cropping. These expectations have led to
innumerable green-manuring experiment all over the world with
practically every species of leguminous crop. The results however have
left much to be desired. In a few cases, particularly on open soils and
where the rainfall, after the ploughing in of the green crop, is well
distributed, the results have been satisfactory. On rice lands, where
abundance of water ensures the maintenance of swamp conditions,
somewhat similar results have been obtained. In the vast majority of
cases, however, green-manuring has been disappointing. As a general
method of soil improvement, the game is hardly worth the candle. On the
monsoon fed areas of India the rainfall is often so uncertain, after
the green crop is ploughed in, that for long periods decay is arrested.
Sowing time arrives at a stage when the soil contains a mass of
half-rotted material, with insufficient combined nitrogen and moisture
for the growth of a crop. Failure results the crops raised after
green-manure are worse than those obtained on similar land left fallow.
For this reason green-manuring has not been taken up by the people in
India, in spite of the experiments and propaganda of the Agricultural
CHIEF FACTORS IN INDORE PROCESS
Indore process enables the Indian cultivator to transform his mixed
vegetable wastes into humus; in other words to become a chemical
manufacturer. The reactions involved are those which take place under
aerobic conditions during the natural decay of organic residues in the
soil. The object of the process is to bring these changes under strict
control and then to intensify them. A knowledge of the chemical
processes involved and of their relative importance is therefore
essential in applying the process to other conditions. These matters
form the subject of the present chapter.
CONTINUOUS SUPPLY OF MIXED VEGETABLE WASTES
continuous supply of mixed vegetable wastes throughout the year, in a
proper state of division, is the chief factor in the process. The ideal
chemical composition of these materials should be such that, after the
bedding stage, the carbon-nitrogen ratio is in the neighbourhood of
33:1. The material should also be in such a physical condition that the
fungi and bacteria can obtain ready access to, and break down the
tissues without delay. The bark, which is the natural protection of the
celluloses and ligning against the inroads of fungi and bacteria, must
first be destroyed. This is the reason why all woody materials-such as
cotton-stalks, pigeon-pea stalks and sann hemp are laid on the roads
the crushed by the traffic into a fine state of division before
composting. Still more refractory residues like the stumps of
sugar-cane and millets, shavings, sawdust, waste paper and packing
materials, old gunny bags and similar substances, must either be
steeped in water for forty-eight hours or mixed with moist earth in a
pit for a few days before passing, in small quantities daily, into the
vegetable wastes which have been utilized at Indore for the last six
years are the following:-
available in large quantities: Cotton stalks, sann hemp either as green
plants reaped before the flowering stage or as dried stems of the crop
kept for seed, pigeon-pea stalks, sugar-cane trash, weeds, fallen
available in moderate quantities: Mixed dried grass, gram stalks, wheat
straw, uneaten and decayed silage, millet stalks damaged by rain,
residues of the safflower crop, groundnut husks, ground-nut stalks and
leaves damaged by rain, sugar-cane and millet stumps.
available in small quantities: Waste paper and packing materials,
shavings, sawdust, worn out gunny bags, old canvas, worn out uniforms,
old leather belting.
chemical composition of the above or of similar materials is given in
will be seen that the raw materials available at Indore differ greatly
in chemical composition and particularly in the percentage of nitrogen.
Many of these wastes, such as cotton-stalks, the stems of sann hemp and
of the pigeon-pea, and cane trash, are too low in nitrogen for rapid
composting. Others such as green hemp, reaped just before flowering,
ground-nut residues and leguminous and other weeds contain higher
percentages of nitrogen, a portion of which is certain to be lost
during the process if these materials are composted singly.
proper mixture of the various materials available, so that the nitrogen
content of the mass throughout the year is kept uniform and
sufficiently high, is the first conditions of success. For this reason
it is necessary to collect and stack the various residues in such a
manner that a regular supply of dry, mixed, vegetable wastes (as
already stated with a carbon-nitrogen ratio in the neighbourhood of
33:1 after the material has been used as bedding) is available right
through the year. This could only be accomplished at Indore: (1) by
cutting the cotton-stalks soon after picking is over so as to secure
the maximum number of leaves; (2) by growing a large area of sann hemp,
which contains when withered as much as 2.3 per cent of nitrogen; and
(3) by securing as much green weeds, ground-nut residues and fallen
leaves as possible for the mixture. All these materials are rich in
nitrogen, and help to bring the carbon-nitrogen ratio near the required
standard. By stacking the various constituents in layers, not more than
one foot thick, and by a judicious admixture with the residues richest
in nitrogen, it is possible to provide a continuous supply of dry mixed
material of the correct chemical composition. During the rains, a good
deal of the raw material is in the form of fresh green weeds, rich in
nitrogen and soluble carbo-hydrates. These must be spread, in thin
layers, on the grass borders of the
fields alongside the roads and withered, before being carried to the
stack or used as one of the constituents of the bedding. Only in this
way can the most be made of this valuable material. Collecting weeds in
temporary heaps on the borders of fields leads to serious waste of the
soluble carbo-hydrates and also of the nitrogen.
OF BIOFERTILIZER BY THE INDORE METHOD
aim of the Indore method of manufacturing compost is by means of a
simple process to unite the advantages of three very different
things: (1) the results of scientific research on the transformation of plant
residues; (2) the agricultural experience of
the past, and (3) the ideal line of advance in the soil management of
the future in such a manner that all the by
products of agriculture can be systematically converted into humus. An essential feature
of this synthesis is the avoidance of anything
in the nature of fragmentation of the factors. All available vegetable matter,
including the soiled bedding from the cattle-shed, all unconsumed crop
residues, fallen leaves and other forest wastes, farmyard manure,
green-manures and weeds pass systematically through the compost
factory, which also utilizes the urine earth from the floor of the
cattle-shed together with the available supply of wood ashes from the
and the workmen’s quarters. The only other materials employed are air and water.
This manufacture is continuous right through
the year, including the rainy season, when a slight modification has to be made
to ensure sufficient aeration. The product is a finely divided
leaf-mould, of high nitrifying power, ready for immediate use. The fine
state of division enables the compost to be rapidly incorporated and to
exert its maximum influence on a very large area of the internal
surface of the soil.
Indore process thus utilizes all the by-products of agriculture and
produces an essential manure. Besides doing this any successful system of
manufacturing compost must also fulfill the following conditions:-
labour required must be reduced to a minimum. The process must fit in with
the care of the work cattle and with the ordinary working of the farm.
suitable and also a regular carbon-nitrogen ratio must be produced by
well mixing the vegetable residues before going into
the compost pits. Unless
this is arranged for, decay is always retarded. The mixing of these
residues, combined with the proper breaking up of all refractory
materials is essential for rapid and
vigorous fermentation and for uniformity throughout the process.
process must be rapid. To achieve this it must be aerobic throughout,
and must include arrangements for an adequate supply
of water and for inoculation, at the right moment, with the proper
fungi and bacteria. The general reaction of the mass must be
maintained, within the optimum range, by means
of earth and wood ashes. The maintenance of the proper relationship between
air and water, so that no delay takes
place in the manufacture, proved to be the greatest practical difficulty when
evolving the process.
should be no losses of nitrogen at any stage; if possible, matters
should be so arranged that fixation takes place in the compost factory
itself and afterwards in the field. To conserve the
nitrogen, the manufacture must stop as soon as the compost reaches the
nitrification stage, when it must either be used for banked. It can
best be used as a top dressing for irrigated crops; it can be
preserved, as money is kept in a bank, by applying it to the fields
when dilution with the large volume of soil arrests further changes
till the next rains.
must be no serious competition between the last stages of
the decay of the compost and the work of the soil in growing a crop.
This is accomplished by carrying the manufacture of humus up to
the point when nitrification is about to begin. In this way the Chinese
principle of dividing the growing of a crop into two separate processes
(1) the preparation of the food materials outside the field, and (2)
the actual growing of the crop can be introduced into general
compost should not only add to the store of organic matter and provide combined
nitrogen for the soil solution but should also stimulate the
manufacture must be a cleanly and a sanitary process from the point of
view both the man and also of his crops. There must be no smell at any
stage; flies must not breed in the compost pits or in the earth under
the work cattle. Theseeds
of weeds, the spores of harmful fungi, the eggs of noxious insects must first
be destroyed and then utilized as raw material for more compost. All
this is achieved by the combination, in the compost pits during long
periods, of high temperature and high humidity with adequate aeration.
MATTER AND SOIL FERTILITY
ancients and the moderns are in the completest agreement as to the
importance of organic matter in maintaining the fertility of the soil.
This is evident when the methods of crop production in the time of the
Romans are compared with the views now held by many of the leading
experiment station workers in the Unites States and other parts of the
world. In Roman times, the management of the manure heap had already
reached an advanced stage. In 40 B.C. Varro drew attention to the great
importance of the complete decay of manure before it was applied to the
land. To bring this about,
the manure heap, during the period of storage, had to be kept moist. In
A.D. 90 Columella emphasized the importance of constructing the pits
(in which farmyard manure was stored) in such a manner that drying out
was impossible. He mentions the need of turning this material in summer
to facilitate decay, and suggested that ripened manure should always be
used for corn, while the fresh material could be applied with safety to
grass land. The Romans therefore not only understood the importance of
organic matter in crop production but had gone a long way towards
mastering the principle that, to obtain the best results, it is
necessary to arrange for the decay of armyard
manure before it is applied to arable land.
exception, the investigators who took part in this conference laid the
greatest emphasis on the importance of keeping up the supply of organic
matter in the soil, and on discovering the most effective and the most
economical method of doing this under the various conditions, as
regards moisture, which the soils of the United States present.
the 2,000 years which have elapsed since Varro wrote in 40 B.C. and the
American investigators met there has occurred only one brief period
during which the role of organic matter was to some extent forgotten.
This took place after Liebig’s Chemistry in its Application to
Agriculture and Physiology first appeared in 1840. Liebig emphasized
the fact that plants derive their carbon from the carbon dioxide of the
atmosphere and advanced the view that, in order that a soil may remain
fertile, all that is necessary is to return to it, in the form of
manure, the mineral constituents and the nitrogen that have been taken
away in the crop. The discovery of the true origin of the carbon of
plants not unnaturally suggested that the organic matter in the soil
was of little consequence. Nitrogen and minerals only remained, the
latter being found in the plant ashes. When therefore analyses of the
crops had been made, it would be possible to draw up tables showing the
farmer what he must add in the way of nitrogen and mineral sin any
particular case. These views and the controversies to which they gave
rise, combined with the results of the Rothamsted experiments led to
the adoption of artificial manures by many of the farmers of Europe.
The Rothamsted experiments undoubtedly proved that if the proper
quantities of combined nitrogen, phosphates and potash are added to the
soil, satisfactory crops for many years can be obtained without the
addition of organic matter beyond that afforded by the roots of the
crops grown. Further, the results of hundreds of trials, in the course
of ordinary farming practice, confirmed the fact that the judicious
addition of nitrogenous artificial fertilizers can, in the great
majority of cases, be relied on to increase the yield. It was only
natural that results of this kind, combined with the important fact
that the application of artificials often pays in practice, produced a
marked effect on current opinion and also on teaching. For nearly a
century after Liebig’s ideas first appeared, the majority of
agricultural chemists held that all that mattered in obtaining maximum
yields .was the addition of so many pounds of nitrogen, phosphorus and
potassium to the acre. Beyond this the only other factor of importance
was the liming of acid soils. The great development of the artificial
manure industry followed as a matter of course.
place of organic matter in the soil economy was forgotten. The old
methods of maintaining soil fertility naturally fell into the
a time all seemed to go well. It is only in comparatively recent years
that experiment station workers have begun to understand the part
played in crop production by the micro organisms of the soil and to
realize that the supply of artificials is not the whole story.
Something more is needed. The need for the maintenance of the supply of
organic matter soon became apparent. The view now beginning to be held
is that, only after the supply of organic matter has been adequately
provided for, will the full benefit of artificials be realized. There
appears to be a great field for future experiment in the judicious use
of artificials to land already in a fair state of fertility.
all this however there was one important exception. In the Orient, the
artificial manure phase had practically no influence on indigenous
practice and passed unheeded. The Liebig tradition failed to influence
the farmers of forty centuries. No demand for these products of the
west exists in China. At the present day it would be difficult to
purchase such a substance as sulphate of ammonia in the bazaars of
HUMUS, ITS ORIGIN AND NATURE
is the origin and nature of the organic matter or soil ‘humus’ and what
part does it pay in soil fertility? These matters form the subject of
the present chapter.
organic matter found in the soil consists of two very different classes
of material: (1) the constituents of plants and animals which have been
introduced into the soil and are undergoing decomposition; various
unstable intermediate products which have been formed under certain
environmental conditions; substances like lignified cellulose which are
more resistant to decomposition and which may persist in the soil for
some time; and (2) a number of valuable materials which have been
synthesized by the numerous groups of micro-organisms which form the
soil population. The soil organic matter is thus a heterogeneous mass
of substances which is constantly undergoing changes in composition.
When its composition reaches a certain stage of equilibrium, it becomes
more or less homogeneous and is then incorporated into the soil as
‘humus’. This definition of soil organic matter, which is due to
Waksman, is of great importance. Soil organic matter or ‘humus’ is not
merely the residue left when vegetable and animal residues decay. It
contains in addition the valuable materials synthesized and left behind
by the fungi and bacteria of the soil population. Moreover it is a
product of the general soil conditions which obtain in any particular
locality, and therefore varies in composition and character from one
soil type to another. It is not the same all over the world. The soil
humus for example of the black cotton soils of India is not identical
with that of the alluvium of the Indo-Gangetic plain.
various steps in the formation of soil organic matter are somewhat as
follows. When the fresh remains of plants or animals are added to the
soil, a portion of this organic matter is at once attacked by a large
number of the microorganisms present. Rapid and intense decomposition
ensues. The nature of these organisms depends on the soil conditions
(mechanical and chemical composition and physical condition) and on the
soil environment (moisture content, reaction and aeration, and the
presence of available minerals). The decomposition processes can best
be followed by measuring one of the end products of the reaction-carbon
dioxide. The rate of evolution of this gas depends on the nature of the
organic matter, on the organisms which take part in the process and on
the soil environmental conditions. As soon as the readily decomposable
constituents of the plant and animal remains (sugars, starches,
pectins, celluloses, proteins, amino-acids) have disappeared, the speed
of decomposition diminishes and a condition of equilibrium tends to
become established. At this stage only those constituents of the
original organic matter, such as the lignins which are acted upon
slowly, are left. These and the substances synthesized by the
micro-organisms together form the soil humus and then undergo only a
slow transformation during which a moderate but constant stream of
carbon dioxide is liberated. At the same time the nitrogen of this soil
humus is similarly converted into ammonia which, under favourable
conditions, is then transformed into nitrate. It will be clear
therefore that the soil organic matter or humus is a manufactured
product and that its composition is not every where the same, but will
vary with the soil conditions under which it is produced. Like all
manufactured articles, it must be properly made if it is to be really
effective. Too much attention therefore cannot be paid to its
FORMATION OF HUMUS AS A RESULT OF THE SYNTHESIZING ACTIVITIES OF
the important part played by micro-organisms in the formation of soil
humus has only very recently been fully understood, nevertheless the
older literature contains a number of useful contributions to the
subject. Most of these early papers appeared towards the end of the
last century; many of them related to other branches of knowledge and
were not written from the point of view of agriculture. They have been
summed up by Waksman, from whose paper the following account has been
and Muller considered that the ‘humus’ bodies obtained from soil often
consist of the chitinous remains of insects and animal excreta.
Wettstein and Winterstein showed that chitin is characteristic of
various fungi and not of bacteria. Schemook advanced the view that he
protein nitrogen in the soil was mostly present in the bodies of
bacteria and protozoa. Trussov showed that he proto and protozoa.
Trussov showed that the protoplasm of fungi is a source of humus in the
soil. Schreiner and Storey suggested that various characteristic
constituents of the soil are probably synthesized by micro organisms.
early work on this subject has been considerably developed, first by
Falck and more recently by Waksman. Falck showed that organic matter in
forest soils can be transformed into different types of humus in at
least three ways: (1) The yearly additions of raw organic matter are
completely decomposed by fungi (microcriny) accompanied by the
synthesis of fungus protoplasm, which serves as an excellent fertilizer
for the forest trees. In this process the celluloses are decomposed
completely, whereas the lignins are more resistant. (2) The
decomposition of the organic matter is begun by fungi and then carried
on by lower invertebrates and bacteria (anthracriny). The fungus
mycelium as well as the original organic matter are devoured by various
larvae producing a dark ‘humus’ mass which, in the presence of bases,
is oxidized by bacteria with the ultimate liberation of carbon dioxide
and the formation of nitrate. (3) The formation of peat (anthrogeny),
which Falck explains as resulting from the absence of an abundant
fungus development. Waksman carried the subject still further and
called attention to the similarity between the carbon-nitrogen ratio of
the soil organic matter and that of the protoplasm of the soil fungi
and other micro-organisms, and suggested that these probably make up a
large part of the soil ‘humus’. He further pointed out that when
cellulose is added to the soil, it decomposes only in proportion to the
available combined nitrogen present. This is because the decomposition
is brought about the fungi and bacteria, both of which require combined
nitrogen. The ratio between the amount of cellulose decomposed and the
nitrogen required is about 30:1, so that, for every thirty parts of
cellulose decomposed by the fungi and bacteria, one part of inorganic
nitrogen (ammonium salt or nitrate) will be built up into microbial
protoplasm. In the presence of sufficient combined nitrogen and under
aerobic conditions, the decomposition of cellulose is very rapid. The
same is true of vegetable wastes like straw, maize stalks, wood
products and other materials rich in celluloses, pentosans and lower
carbohydrates but poor in nitrogen. These facts explain the injurious
effects on crop growth which follow the addition of straw and
green-manure to the soil. The decomposition of these materials removed
large quantities of combined nitrogen from the soil solution. The
nitrogen is then temporarily stored in the form of microbial
protoplasm, when for a time it is placed beyond the reach of the
Waksman’s paper appeared in 1926, an important contribution to this
subject has recently been made by Phillips, Weite and Smith. The result
of these investigators (which agree with our experience at Indore) has
removed the impression that lignin is comparatively resistant to the
action of microorganisms. Under suitable conditions, soil organisms
are capable of decomposing lignin as found in lignified plant materials
(corn-stalks, oat hulls, corn cobs and wheat straw), the rate of
decomposition being as great as that of cellulose and pentosans.
ROLE OF HUMUS IN THE SOIL
the immediately practical point of view, the actual role of humus in
the soil is of even greater interest than its formation, nature and
decomposition. This material influences soil fertility in the following
physical properties of humus exert a favourable influence on the tilth,
moisture-retaining capacity and temperature of the soil as well as on
the nature of the soil solution.
chemical properties of humus enable it to combine with the soil bases,
and to interact with various salts. It thereby influences the general
soil reaction, either acting directly as a weak organic acid or by
combining with bases liberating the more highly dissociating organic
biological properties of humus offer not only a habitat but also a
source of energy, nitrogen and minerals for various micro-organisms.
properties physical, chemical and biological confer upon humus a place
apart in the general work of the soil including crop production. It is
not too much to say that this material provides the very basis of
successful soil management and of agricultural practice.
MANAGEMENT IN ORGANIC FARMING
have been defined in various ways, but the most commonly used
definition is: “A weed is a plant that in a given situation is more
determintal to agriculture than beneficial”. It is common knowledge
that weeds compete with crop plants for light, air, moisture and
nutrients. But the full extent of economic harm which they cause and
their direct effects on crop fields, are not generally realised. Weed
problems have been accentuated with the increase in the use of inputs
like seeds of high yielding varieties, fertilizer and irrigation. In
cropped areas these inputs help in good growth of weeds, thereby
causing severe competition between crops and
weeds. In the non-cropped area, the weed problems have been observed in various types
of aquatic environments, forests, railways, highways,
industrial sites, airport and places
of aesthetic value. Presence of weeds is a constraint and the effect is
further accentuated by their improper management. In assured water conditions, where
irrigation facilities are available, farmers use high doses
of fertilizer, quality seeds and improved pest management techniques. High fertility
accompanied by high moisture provides a situation
where the intensity and growth of weeds are high and in many cases may
adversely the affect the production potential of crops.
estimated crop losses due to weeds, diseases, insect pests, etc. were
nearly Rs.6000 million and Rs. 1,84,000 million during 1973-74 and
1989-90 respectively. Yield losses caused by weeds in some crop plants are given
of weeds is an important component of production techniques as
elimination of weeds is expensive and hard to achieve. The
basic approach is to minimise production losses caused by weeds, though weeds may
exist as a part of the whole ecosystem. A number
of mechanical, ecological and chemical methods of weed control have been developed
over centuries of experience. Weeds ‘are aggressive,
persistent and ubiquitous. In order to prevent the accumulation of
chemical residues in the soil to a dangerous level and to prevent shift
in weed population, it is necessary to find alternative weed management
techniques leading to minimum loss in crop production and
least disturbance to the ecosystem.
METHODS OF WEED CONTROL
methods are less expensive and less dangerous to neighbouring crops and
orchards. As the long term and indirect efforts of weed control due
to implementation of systematic changes become apparent, less intensive
control is required.
after the advent of chemical weed killers, tillage methods are still
used in many situations as the most effective and economical methods
of weed control. Most of the farmers in the developing countries practice some
form of minimum tillage where mould board plough is used for the
perennial weed control or for breaking sod in a crop-sod rotation.
Ploughing, cultivating and harrowing make possible weed control before
sowing the crop and there are appropriate
tools that can do a satisfactory job even after weed emergence. The disc harrow
and chisel plough are used for primary tillage operations. Discs,
cultivators and harrows are used for seed bed
preparation and cultivators, discs, rodweeders, harrow and rotary hoes for
post-seeding weed control. New types of minimum tillage implements that
cut and incorporate residues and ridge the soil in one operation are
strongly advocated for organic agriculture. Discs are used for weed
control in orchards and to a lesser extent rotavators. Roto tillers are
used in smaller row crop operations. The younger and smaller the weeds
are, the most efficient and economical will be their control. The role
of tillage in weed control consists
the germination of weed seeds, which can, then, be easily destroyed by
roots or stolons to the soil surface where they will dry out under the
cultivation, thereby depleting the food reserve of the plant, and,
or smothering the weeds with soil.
combined with irrigation
of the most effective means of weed control is irrigation before sowing with a
quantity water just sufficient to wet the soil to the
full depth of the future root system. Then cultivating the field
superficially, before or during sowing (if a combined-tillage and sowing operation is carried
out) will destroy the weeds that have germinated following irrigation.
The crop seeds are sown in moist soil at a
depth that is sufficient to ensure germination without additional irrigation. The surface
soil dries out, effectively preventing germination of
additional weeds with next irrigation. In view of the earlier
irrigations in depth, the next irrigation can be delayed somewhat so
that the crop has an edge in growth when the next wave of weeds appears, making selective
of field operation is very important. It is better to incorporate
residues as soon as possible after harvest. It is believed that this
process conserves the more readily metabolised and leachable carbon
substrates. There are two strategies for planting of field crops; which
one is followed depends on the crop, the regional climate and the
climatic conditions or other variables in a particular year. The first
strategy is to plant the crop as early as possible to get a head start
on weeds; the other is to plant the crop later. In both the cases, it
is common to cultivate from once to many times after seeding to set
back the weed growth relative to the crop, and to reduce the seed bank.
For grains, weeds are commonly harrowed or rotary tilled at least once
before the crop germinates and then one to several times after the crop
has germinated and is well rooted. The interval between operations is
timed to allow germination and some growth of a new generation of
weeds. Hence, the objective in the timing of all the operations is to
set weeds back long enough, or to start the crop sufficiently ahead of
weeds, so that crop can maintain its advantage without assistance.
Appropriate timing is crucial for controlling perennials. In theory,
frequent mowing and tillage starves roots, taproots and rhizomes, but
if a harrow is used and the soil is wet, target weeds may multiply. Use
of deeper working implements and working in dry weather can be
successful. Mowing operations are commonly timed to reduce seed set by
annuals rather than as an efficient method of weed eradication.
Frequent and regular mowing of perennial weeds exhausts the food
reserves of the underground storage organs, weaken the plants and may
occasionally lead to their death, when environmental conditions become
rates and cultivar selection
is a common practice in organic farming to exceed the recommended rates
of seeding by upto 25 per cent to allow for losses during cultivation.
Higher seeding rates, closer crop spacing ad use of cultivars the
achieve canopy closure earlier than other varieties or that have a more
competitive architecture (eg. are taller or have more tillers) are
other strategies that enhance the suppression of weeds by crops. It is
important to select varieties that emerge quickly and that have a thick
and full canopy. Some crops such as forage crops are able to compete
successfully with weeds; their inclusion in the cropping systems,
especially if the weeds start active growth at time when the cultivated
crop is already well developed. One of the traditional methods used for
combating weeds is sowing a thick stand of the crop. Heavy seed rate
gives the crop a distinct competitive advantage over the weed
population in the field. However, where a relatively low plant
population is one of the major means of adjustment to limited soil
moisture supply, this method of weed control cannot be adopted.
important principles in designing organic farming systems are to
maximize diversity and soil coverage. A succession of different crops
facilitates weed control. Certain weeds are almost obligatory
association of specific crop plants and if these are sown continuously,
effective weed control my become impossible. Weeds, whose growth and
propagation is favoured by a certain crop, may be weakened or checked
by an appropriate succeeding crop. Annual weeds which thrive in the
winter cereal are easily destroyed during a winter fallow proceeding
the summer crop. The following principles may be followed for effective
of competitive crops (eg. forage grass or maize) and non-competitive crops (eg.
cotton or pulses).
of perennial phases in crop rotation combined with moving or intensive
rotational grazing to control perennials.
of weed suppressing crops as cover crops.
cereals with fodder legumes
there are very heavy infestation of weeds - summer fallowing
of catch crop or trap crop: These are used for the control of parasitic
weeds such as witch weed. A catch crop that is host to the
parasite is sown and ploughed under before the parasite produces seeds.
A crop plant that is not a host to weed but induces it to germinate is
called as trap crop.
monoculture cropping systems, several manipulable management and
environmental factors have been shown to affect competitive suppression of
weeds. Crop density, spatial arrangement,
species and genotype and soil fertility are probably important for controlling
weeds in intercropping systems.
MANAGEMENT IN ORGANIC FARMING
are chemical or natural substances that control pest populations by
killing the pest organisms, be they insects, diseases, weeds or
animals. In 1985, roughly 2300 million kg of chemicalpesticides were used
worldwide. About 15 per cent of this, including 30
per cent of all insecticides, is used in the third world. During the traditional technology
period in India, the use of synthetic pesticides was
negligible and reserved for the high value crops only. The traditional
crop varieties did not face much problem of pests and diseases and in
the event of their occurrence traditional practices were able to reduce the
menace. However, with the advent of green revolution,
the new crop varieties and cropping sequences for intensive agriculture
brought to the forefront problems of pests which caused tremendous
losses to various crops and their produces. Pesticide
consumption in India has shown steady increase from the mid-fifties both in
quantity and coverage. The quantity of pesticides used rose from 200
tonnes in 1955 to 72000 tonnes in 1987 and the plant protection
coverage increased from 2.4 million hectares in 1956 to 18 million
hectares in 1984. However, use of these toxic substances, although
essential, requires adequate caution and safety measures.
Their influence in upsetting the ecological balance and polluting the
environment is being increasingly felt. The following are the known dangers of
year thousands of people are poisoned by pesticides, about half of them in the
third world. In 1983 a total of about 2 million people suffered from
pesticide poisoning and 40000 of the cases were fatal. Because of their
toxicity, many pesticides like
DDT have been banned in industrialised countries, but they are still being used
in many developing countries.
a period of time, pests build up resistance to pesticides, which must
then, be used in even higher doses to have toxic effect. Pest resistance
builds up more rapidly in tropical than in temperate
countries as biological processes are more rapid at higher
temperatures. Resistance to pesticides was known for 447 insects and mites, 100
plant pathogens,55 kinds of weeds,2 kinds of nematodes and 5 kinds of
kill not only organisms that,cause damage to crops but also useful
organisms, such as natural enemies of pests. The incidence of pest
attacks and secondary pest attacks may increase after pesticides have
killed the natural enemies.
a small portion of pesticides applied in field reaches the organisms
that are supposed to be controlled. The major part reaches the air, soil, or
water, where it has a damaging effect on living organisms. Aquatic
organisms are particularly sensitive to pesticides.
that do not break down easily are absorbed in the food chain and cause
considerable damage to insect-consuming animals,
prey birds and ultimately human beings.
to population increase the problem today is food and nutrition security
to mankind. Even though agrochemicals and pesticides are important
tools in enhancing food supplies, excessive use
of these chemicals has led to toxicity and pollution in the environment. The world
pesticide market in 1981 was reported to be worth
about US $ 13,000 million (user value, of which 20 per cent was from
developing countries and 10 per cent market was from India).
1. Pesticide market in the world
Pesticide Million per cent
US$ of total
Herbicide 8,600 42
Insecticide 6,100 31
Fungicide 4,100 21
(Fumigants defoliants, and desiccators etc.) 1200 6
Total 20,000 100
growing disillusionment with highly toxic, broad spectrum synthetic
pesticides and the expanding global awareness to avoid environmental
degradation has shifted the pest management strategy from application
of pesticides, to manage the pests with permanent, self-sustained,
self-regulating, and ecofriendly biological pesticides without
environmental backlashes. World wide, an estimated 67000 different pest
species attack agricultural crops. In general, less than 5 per cent are
considered to be serious pests. From 30 to 80 per cent of the pests in
any geographic region are native to that region. In most instances, the
pests which are specific for each region have moved from feeding on
native crop to feeding on crops that were introduced into the region.
For nearly a century and a half, various parasitic and predacious
species have been used as biological control agents for a wide variety
of pest species. Although approximately 3000 out of 67000 pest species
in the world have been targets, of biological control, only 120 pest
species have been effectively controlled. As the remaining species have
been only moderately or partially controlled, additional measures are
continued to be used to control them. All the developmental stages of
most of the insect pests of crop are subjected to attack by
entomo-phagous insects, belonging to 224 families of 15 orders.
the present approach is to develop new molecules which are highly
effective at low active ingredient dosage level, less persistent and
rapidly biodegradable, selective in action and safer to human beings
and environment. These new concepts and technologies can be broadly
grouped as follows:
new class of highly activated insecticides/compounds that provide
plants with resistance to insects.
mobile and less volatile formulation to reduce hazard to man and the
environment avoiding leaching and contamination to water sources.
The exploitation of microorganisms in pest control has been receiving
greater attention in the recent years and commercial products are now
available. In 1988, the world microbial pesticide market was valued at
US $ 70 million accounting for less than 0.5 per cent of the total
Pheromones of around 800 insect species worldwide have been identified.
Of these, over 400 are sexual attractants or aggregations. Pheromones
have been synthesi-sed and are being marketed widely.
techniques to establish pest resistance to insecticides
management methods can be categorised as biological, cultural and
organically accepted chemical alternatives, with further subdivisions.
control by multicellular organisms including release of exotic
parasites and predators, conservation and augmentation of natural
enemies, genetic improvement and allelopathy.
control by microbial agents-application of beneficial or antagonistic
microorganisms or toxins synthesized by microbes.
practices, including natural mulches, living mulches, trap crops and
cover crops to enhance the population of natural enemies.
acceptable chemical alternatives
and soaps —some horticultural oils and various fatty acids
— toxins derived from plants such as pyretherum and ryania.
— pheromones, allomones and kairomones including sex attractants,
feeding attractants and repellents produced by insects and affecting
the behaviour of other insects.
or elemental compounds such as elemental sulphur and some copper
rotation - rotation of crops and fallow periods
controls - such as tillage, mowing, chopping and flaming
- removing non-crop hosts and infected hosts.
and canopy management - physically manipulating the structure of the host
management-controlling water application and drainage.
choices - choice of field, location, planting and intended harvest
dates, vigorous cultivars. Plant density, transplanting etc.,
- including mandatory host - free periods, host free zones, crop
termination, seed indexing and detection.
INTEGRATION OF ORGANIC FARMING
and fish are the staples for the people in most Asian countries. Over
90 per cent of the world’s area under rice, equivalent to approximately
134 million hectares, is grown under flooded conditions providing not
only home to a wide range of aquatic organisms, but also offering
opportunities for their enhancement and culture. Asia is the largest
producer of rice (91%) with an average productivity of 3.9 t/ha. India
has the maximum rice area, 44.5 Mha, although China with second largest
area under rice, 30.5 Mha, is the world’s largest producer of rice,
with average productivity of over 6 t/ha. However, the productivity of
the irrigated rice ecosystem, that accounts over 76% of the global rice
production under continuous and intensive cropping conditions is either
stagnating or declining.
of Green Revolution
the introduction of high yielding technology although rice yield has
increased substantially in irrigated rice tracts in India, there has
been no significant increase in yield under rain fed and lowland rice
ecologies that account for over 50 percent of rice area. Consequently,
in states like Assam, Bihar, Orissa and Madhya Pradesh and Kerala the
realized yield have been very low as compared to irrigated ecologies.
There is a strong view that the Green Revolution paradigm adopted in
these places in tune with the National agenda has been inappropriate
owing to the complete neglect of the natural situations. The technology
supposed to be scale and resource neutral has therefore been confined
to the regions with favorable farming situation. It is argued that in
states likn Kerala, the increase in productivity with the advent of
high yielding technologies was not commensurate as compared to
escalation in cost of production. This has been partly attributed to
the high rainfall situations, undulating topography, and water logged
rice-growing situations in high rainfall tropics at variance from that
of the semi arid irrigated areas. These unique situations call for
technologies tailored to the specific environmental conditions.
of the second generation problems in regions of high productivity have
been identified as 1) declining or plateauing of farm productivity due
to depletion of organic matter, coupled with depletion of soil
fertility due to over mining of native nutrient reserve.2) declining
fertilizer use efficiency, groundwater depletion due to
overexploitation in utter disregard to level of natural recharge
ability.3) increasing problems of salinity- alkalinity in the command
areas due to excessive and indiscriminate use of irrigation water and
4)build up of disease— pest pressure by continuous cropping and
increased varietal uniformity and excessive dependence of on
indiscriminate use of pesticides that eventual emergence and resurgence
of pests thereby increased cost on plant protection.
with high rainfall, undulating topography, and water logged situations,
the rice growing situations in high rainfall tropics are at variance
from that of the semi arid irrigated areas. These unique situations
call for technologies tailored to the specific environmental conditions
in fragile rice ecologies. Over centuries, our forefathers have
therefore evolved a farming strategy in consonance with the rigid
environmental conditions such as saline to acid soil and rising flood
conditions in these places. This calls for a shift to an ideal
cropping/ farming system that ensure high productivity, reasonable
economic returns and least risk to natural endowments. It has been
highlighted that the high yielding technologies were highly productive
and profitable in rotation with varied crops and cropping sequences.
farming is the biological process of transformation of solar energy in
to biomass involving the major resources, land and water, approaches
that facilitate scientific and optimum utilization of production
potentials of natural and human resources must be the primary
considerations for sustainable development. Full utilization of the
production potentials through intensification and diversification will
not only provide income and employment opportunities but also help to
ensure the livelihood security of the people who subsist on them.
of crops and livestock has been a sustainable and traditional practice
in Kerala for over centuries. Under the homestead, approach prevalent,
animals used to be raised on agricultural waste; animal power was used
for agricultural operations; and animal dung was used as manure and
fuel. During sixties and seventies with the advent of modern practices
in farming involving extensive use of irrigation and agrochemicals, new
vistas for increased crop productivity was opened. But there is strong
view that in the process, the essential foundation for sustaining this
production such as soil, water, forest and biodiversity has got eroded.
The initial spurt in yield rate was also not sustained. These concerns
lead us to the search for technologies that blend productivity,
economic efficiency and ecological sus-tainability.
rice lands - Economic sustainability issues
holds the key to food security in Kerala. The gross are a under rice
which was 8.75 lakh ha in 1975 has come down to 3.01 lakh ha in
2002-03. Out of the annual rice requirement of 37 lakh tons presently a
little over 18 per cent, 6.8 lakh tons is produced internally. Out of
the major 15 rice producing states in the country, Kerala ranks 8th in
terms of productivity and ranks 14th in terms of area. In terms of cost
of production of rice, Kerala ranks first with Rs.523/qtl of rice,
while cost of production of rice in Punjab is only Rs. 183/ Qtl and
National average being Rs.268/ Qtl. In a study conducted in Kuttanad,
the major rice-growing tract in Kerala, it was demonstrated that with
the introduction of high yielding technology, the cost of production of
rice has increased disproportionate to the value of output. While the
cost increased 254 per cent during the last 10 years, the output price
of paddy increased only by 95 per cent. This mismatch between the input
cost and value of output is indicated by the paddy equivalence cost
(PEC) of rice cultivation. The Paddy Equivalence Cost of cultivation
for the base year 1988 was 1983 kg per ha, which increased to 3239 kg
per ha in 1998. This means that a minimum yield of 32 quintals per ha
is necessary to breakeven paddy cultivation in Kuttanad. And out of the
53 samples surveyed only 19 samples were observed to conform to the
level of productivity. This has led to a drastic reduction in cropping
intensity despite heavy investments to boost rice production. The
average cropping intensity of rice in coastal wetlands in places such
as Kuttanad in Kerala is barely 120 per cent which means that only 20
per cent of rice fields are utilized for more than one crop a year.
These lands remain under utilized for most part of the year. By
integrating aquaculture, these under utilized wetlands can be brought
to farming with enhanced profitability. Such an enterprise
diversification would decease dependency of farmers on one crop alone
for income, thus reducing the risks presently associated with rice
1 : Changes in cost and return (Rs/ha) of rice cultivation in Kuttanad,
Item 1988 1998 Hike Percentage
Seed 483 1026 544 112.86
Fertilizer 1174 2249 1075 91.57
protection 434 799 365 84.10
Manure 5 55 50 1000.00
power 371 101 -270 -72.78
Machine 215 1244 1029 478.60
Labour 2105 9786 7681 364.89
Inputs 256 871 615 240.23
Total 4560 1613 11571 253.75
Output 8129 1588 7755 95.40
return +3087 -247
Yield (kg/ha) 3266 3320 54 1.65
being the staple food of the people in these places, and the internal
production is barely eighteen per cent of our requirement, this decline
in area under paddy raise concern to food security. The labor
opportunity for dependent labor is hampered as rice cultivation
generates over 70 man-days of labor per ha. Located in the valley
bottom wetlands and lowlands in the steep and undulating topography in
these places the paddy lands in these places have a unique ecological
function, like forest, by promoting recharge of ground water. However,
with the poor profitability of paddy cultivation, the very existence
and livelihood of the farmer is at stake. The options available for the
State is to make paddy cultivation competitively profitable with the
aid of technical inputs or to let the farmers adopt a sustainable
integrated farming system, wherever possible. A combination of the
above approaches is the one most desirable.
of fish along with rice is considered in this perspective for ensuring
the diversity of food basket with out compromising on the sociological
and environmental functions of these wetlands. In Kerala rice is
cultivated mainly in lowlands and valley bottom areas of highlands and
midlands and the coastal lowlands classified as niloms, or wetlands. In
each of these locations, the paddy field or wetland plays a unique
ecological function. In the coastal lowlands, paddy is often cultivated
in locations where nothing else can be cultivated. Some spots are so
hostile that even paddy can hardly survive eg. the Kari land of
Kuttanad. However, the coastal wetlands comprising of Kuttanad, Kole,
Poklkali lands constitute approximately 24 per cent of the paddy lands
in the state and contribute to over 37 per cent of the rice output.
Being close to the sea and exposed to the monsoon floods, diurnal and
tidal flushing, the environment is even more hostile to for paddy in
seaward locations such as karilands in Kuttanad and pokkali lands.
However a unique symbiosis of paddy during monsoon season and
fish/prawn during high saline months has been developed and practiced
in pokkali lands in tune with the nature’s rhythm.
OF VARIETIES FOR ORGANIC FARMING
use of improved rice varieties since the 1960s has reduced food prices,
for the poor and prevented millions of cases of childhood malnutrition.
Without the development of the high yielding varieties, prices for
developing country consumers would likely be as much as 40 per cent
higher than they are today. The new varieties have also reduced costly
food imports by almost 8 per cent and have eliminated the need to
convert millions of hectares of forestland to agricultural uses as
would have otherwise been required had yields remained at 1960 levels.
The availability of high yielding varieties has prompted many of the
world’s poorest countries to invest in plant breeding programs and
produce varieties suited to local environments and markets. The new
plant types have also prompted massive government investments in
agricultural infrastructure such as irrigation and fertilizer delivery
spite of the advantages of high yielding varieties, it should not be
forgotten that the adoption of high yielding has led to the
substitution of a large quantity of species for only a few and uniform
varieties from a genetic point of view, which has caused a significant
reduction in the genetic inheritance of cultivated species. Many
agricultural species, varieties and breeds which have played an
important role in the human diet and traditional cultures have
practically disappeared over the last century.
the last decade, the adoption of organic agriculture has indirectly
established a rescue process of species, varieties and breeds
threatened by under-use or extinction. Stronger collabora tion has
been evident among movements aiming to defend biodiversity and the
organic agriculture movement. This is especially the case now that
there is interest in traditional, speciality and organic products. For
the rescue of varieties threatened by extinction, the development of a
market is fundamental and it is here that organic agriculture plays an
important role as the price premium gives an additional value to the
product. The restoration and enhancement of under-utilized species and
varieties has been motivated by a food demand concerned with health and
culinary traditions. Organic agriculture has allowed the maintenance
and improvement of species and varieties that otherwise would suffer
strong genetic erosion or extinction
is organic Agriculture?
systems avoid the use of synthetic fertilizers, pesticides, and growth
regulators. Instead they rely on crop rotations, crop residues, animal
manures, legumes, green manures, off-farm wastes, mechanical
cultivation, mineral-bearing rocks, and biological pest control to
maintain soil health, supply plant nutrients, and minimize insects,
weeds, and other pests.
of rice varieties for organic farming
general, rice planting dates, seeding rates, preferred varieties, and
harvesting methods vary among regions, but they are largely the same
for conventional and organic systems While choosing varieties for organic
farming, the special considerations relevant to organic rice
production has to be duly recognized. Weed control, management of soil
fertility and minimizing pests and diseases are the
principal challenges associated with organic rice production and
according to the needs and requirements in each, varieties have to be chosen.
are a problem in both wetland rice as well as up lands, but it is more
hazardous under up land conditions. Direct seeding of rice is receiving
much attention in recent times since it reducesproduction costs. As
cultural practices for rice shift from transplanted
to direct seeded rice, weed problems will increase because rice and
weeds can emerge together. Many weeds of irrigated ecosystems like
Barnyard grass (Echinocloa
become more important /harmful in direct seeded rice since they are
adapted for better growth under dry than wet conditions. While choosing
varieties for upland rice, care should be taken to select varieties
with initial vigour and increased growth rate so that they can compete with
weeds and come up well. Short duration varieties
are preferred for direct seeding in uplands, since they have higher
growth rate compared to medium or long duration varieties.
et.al. (2002) while evaluating upland varieties for their weed
competitiveness at Regional Agricultural Research Station, Pat-tambi,
noticed distinct difference in the weed suppression ability of the
cultivars tested. Based on this, they classified the rice varieties
into three groups viz., 1. Varieties, which can completely smother the
weeds, 2. Varieties that show moderate tolerance and 3. Varieties that
are smothered by competing weeds. Improved traditional varieties like
PTB 28, PTB 29 and PTB 30 and land races like Karanellu belong to the
first group. The improved upland varieties could grow fast and produce
large no. of tillers, there by preventing the growth of weeds in
between. Land races like Karanellu had long and droopy leaves, which
prevented light interception by weeds there by reducing their growth.
Research is underway to transfer the weed competitiveness of these
varieties to high yielding varieties.
transplanted rice in lowlands, crop rotations, land leveling, seedbed
preparation, water management, and rotary hoeing are the primary
weed-control practices followed to take care of the weeds. Here also,
varieties having natural weed fighting capacity could be chosen to
reduce the hazards from high weed growth. Use of allelopathic rice
varieties having activity against a broad spectrum of target weeds
could be a desirable choice. Cultivars that show allelopathic potential
against important rice weeds have been identified in many countries
viz., United States, Japan, Egypt and the Philippines. In the United
States, evaluated more than 10000 accessions of rice for allelopathic
effects against aquatic weeds like duck salad and red stem and could
identify around 190 promising accessions. This included rice varieties
from many countries including India. A list of Indian rice varieties
showing allelopathic effects against duck salad and red stem are
furnished in Table 1. Allelopathic cultivars that strongly inhibit root
elongation of barnyard grass but weakly affect the shoot have been
identified by Olofsdotter. In Egypt, identified Indian rice varieties
that expressed allelopathic effects on Echinocloa cruss-galli and
Cyperus difformis. L. at 3-4-leaf stage by inhibiting root development
and emergence of the first or second leaf of both weeds. Kim and Shin,
1998 identified promising rice germplasm for allelopathic activity in
Korea and new cultivars are being generated using them.
soil fertility in organic cropping typically involves some combination of crop
rotation with deep-rooted legume crops or
green manure/cover crops, and applying rock minerals, animal manures,
composts, and other approved organic amendments. Green manures have proven
their positive influence in enhancing rice
yields. Leguminous green-manure crops can supply 30 to 50 per cent of
the nitrogen needs of high yielding rice varieties. The availability of
green-manure nitrogen depends on the quantity, quality, and type of
green-manure crop; the time and method of application; soil fertility;
and cropping method. It has been observed that green manuring with
Sunnhemp or Cowpea grown during summer months and
incorporated in soil before transplanting rice could save about 60 kg
N/ha for rice crop. Recent studies on economizing
chemical fertilizers through organic manures in selected cropping systems
under All India Co-ordinated Agronomic Research
Project have shown that 25-50% N requirement of rice during Kharif season could
be met through organic sources without any
adverse effect on rice productivity. Yield response of rice varieties
to organics indicated varietal differences to organic farming. Some
varieties responded more to organics than to chemical fertilizers.
Similarly, certain rice varieties responded to chemical fertilizers than
of trace gases especially Methane from flooded rice fields has become a
serious concern world over. Methane emission from lowland
rice has been identified as resulting from organic matter fermentation
and factors like incorporation of crop residues like rice straw can
enhance the process. Varieties with low methane emission potential
could reduce ‘hazards resulting from high methane emission and could be
more rewarding under organic farming.
both rain fed and irrigated is infested by a variety of pests and
diseases. Intensive cropping of modern varieties under high inputs
provided a favourable environment for many pests as a limited number of
modern varieties began to be widely cultivated, the populations and
economic importance of their associated pests increased and new
pathogen strains and insect biotypes developed. The major insect pe.sts
viz., Plant hoppers gall midge, stem borer, leaf rollers, rice bug,
along with minor pests like case worm, thrips, ear cutting caterpillar,
whorl maggot etc., cause serious damage to the rice crop in the
tropics. Similarly, fungal diseases (leaf blast, sheath blight, brown
spot, sheath rot, bacterial diseases (bacterial blight) and viral
diseases (Tungro Virus, Grassy Stunt Virus) etc., can also devastate
the crop. Excessive nitrogen levels are rarely a problem in organic
production, since use of synthetic fertilizers is avoided, but timely
control measures are a must to keep the damage under economic threshold
levels. Timely planting, variety selection, and cultural practices to
suppress weeds and encourage dense stands of rice will help control
most of the biotic stresses mentioned above.
of resistant varieties can prove to be consistently and significantly
more productive under high pest or disease pressure. Varieties with
moderate resistance are a better choice since they allow pest
populations to be maintained at levels that do not result in
significant damage. Varieties with strong resistance reduce the
populations of natural enemies that feed on the pest and could
ultimately lead to resurgence of the pest. Table 3 gives a list of high
yielding varieties combining resistance to various biotic stresses
released by the Central Seed Subcommittee on Crop Standards,
Notification and Release of Varieties. The different states have also
released a number of varieties resistant to various biotic stresses. A
list of high yielding rice varieties with multiple resistances
developed by Kerala Agricultural University is furnished in Table 4 as
to guide in choosing varieties for a particular situation.
varieties possessing multiple resistances could make the programme more
effective. Again, the economic loss associated with each stress should
be assessed before selecting a variety and high priority should be
assigned to varieties resistant to a particular stress for which
biological control measures are not available, and low priority could
be given for varieties resistant to such stresses where other low cost
control methods are available. For eg. Use of varieties resistant to
Bph and gall midge and adopting biological control measures for stem
borer and leaf roller could take care of all the above pests.
Similarly, selecting a blast resistant variety along with biological
control measure for sheath blight could be a more effective method for
controlling the two diseases rather than going for varieties resistant
AGRO-ECO SYSTEM IN ORGANIC RICE FARMING
is well known to be a semi-aquatic plant grown under flooded condition
almost throughout the season. The rice ecosystem is thus characterised
by puddled (de-structured) soil with standing water. The practice of
puddling itself causes at least two ill effects viz soil erosion and
hard pan formation just below the plough layer. Thus preparation of
land itself for growing rice causes continuous loss of fertile topsoil,
especially during the first crop season of southwest monsoon The only
advantage of this type of cultivation practice is effective weed
control. Efficient fertilizer management is also a problem in rice soil
specifically in case of N and K fertilizers due to their high
solubility and leaching which in turn may cause pollution of ground
water and/or neighboring water bodies. During the green revolution era,
the substantial increase in production was due to the use of fertilizer
responsive high yielding varieties. Thus fertilizers had an equal role
in enhancing the production along with high yielding varieties.
farming as promoted in the present form is aiming at demolishing the
above main pillars of green revolution. Whether the newly constructed
“organic pillar” can withstand the pressure of sustainability in terms
of fertility, productivity, profitability and food security and
ecological safety is the big question to be answered immediately since
a long gap can cause stagnation in production which in turn cannot be
afforded in the context of increasing population. In this protext, the
real objective of the farming system should be to have an “evergreen
rice farming and nutrient management in such an ecosystem should be
viewed against this background. Sus-tainability should aim at
developing farming systems that are productive and profitable, conserve
the natural resource base, protect the environment from pollution and
enhance health and safety on a long term basis or rather indefinitely.
Organic farming without the use of inorganic synthetic chemicals in
terms of fertilizers and pesticides is argued to be sustainable.
However this statement should be critically analyzed to realize whether
it is a truth or a myth.
farming - the truths vs. myths
in his R.V Tamhane memorial lecture during the annual convention of Indian
Society of Soil Science has shown with data
how certain myths got a walkover over reality in process of
popularisation of organic farming According to him the myths are:
food tastes better and is of superior quality: The traditional belief that
organic manure promotes quality while mineral
fertilizers promote quantity was shown to be over simplistic by Schuphan on
the basis of trials conducted for
over a decade. This is because irrespective of the source, plants
absorb nutrients as ions and then metabolised into compounds, which
determine the quality of produce such as flavour and shelf life which
in turn is a genetically inherited property.
food is more nutritious and safer : The
mineral composition of a product is independent of the cultivation
practice and slight variations are due to environmental and cultural
factors. This concept may be derived from the belief that the hazards in the
food are mainly derived from agrochemicals.
In fact the microbes are the main culprits of food borne diseases and
organic manures from animal sources have more chances of
pathogen risk such as that of Salmonella, Esherichia
farming is eco-friendly :
It is believed that organic farming keeps the soil healthy and does not pollute environment.
At the same time one should remember that the end product of manure
decomposition is nitrate and if one recommends manures on
nitrogen equivalent basis, the release of
these nitrates will not synchronies with crop demand and uptake and so can
accumulate in soil or water causing pollution. Further,
addition of large amount of organic manure under submerged condition can
of green house gases like methane and carbon dioxide. Further, organic
manures from animal sources and sewage and sludge contain at times very
high concentrations of trace elements and heavy metals.
farming improves soil fertility and chemical fertilizers deteriorate
it. Long-term fertilizer experiments have proved beyond doubt that
balanced application of fertilizers along with manures sustained yield.
farming sustain higher yields : On long-term basis, partial
substitution of fertilizers with organic sources was found to reduce
the grain yield of rice significantly.
organics are available to replace chemical fertilizers. Projections on
the availability of plant nutrients from organic sources in India as
worked out by Tandon (1997) as given in table-3 and the projected plant
nutrient addition and removal show that all tapable nutrients from
organic sources will barely able to meet the deficit of nutrients in
soil after crop removal at the present level of crop production and
fertilizer application. So what to say of replacing chemical
fertilizers presently used.
as a source of Plant nutrients
is an established fact that without improving organic carbon status of
the soil it is not possible to improve nitrogen status because of the
constancy of CN ratio. Thus for effective nitrogen management organic
manures are a must. This can be achieved by inclusion of legumes in the
crop rotation in a rice- rice - legume rotation. Legume can also grown
as a companion crop during dry sowing in first crop season and when
flooded afterwards with the onset of southwest monsoon, legume may get
incorporated as a manure to rice. Organic matter can also be added
through FYM, compost @ about 4 - 6 t ha–1 Cattle manure being widely
used as fuel for cooking in rural areas, alternate source of energy is
to be found out or biogas plants must be established so as to tap
energy without reducing the manurial value of cattle dung. But release
of methane from the biogas plants from exposed parts of the
fermentation well is a built in hazard of these plants.
fertilizers enhance soil fertility by fixing atmospheric nitrogen,
mobilising sparingly soluble forms of P, Zn etc. and also by enhancing
decomposition of crop residues. Blue green algae (BGA) in rice field
are contributing nitrogen to rice. BGA can fix even to the tune of 120
- 150 kg N ha if suitable temperature (25 - 30 °C) and good
availability of P is assured. This is most suitable for coastal areas
where the annual mean temperature is in the range of 25-30ºC.
experiments on effect of P solubilizing organisms on crop yield that
5-10% yield increase svas obtained over uninoculated plots.
Vesicular-arboscular mycorrhizae can help in skipping about 15 kg P
ha–1 and also there is a carry over of VAM inoculums through rice
stubbles to the succeeding wheat crop. It must be noted that the
nitrogen fixation or nutrient release by microbes consume energy for
the growth and multiplication of microbes which is released either from
the host plant affecting its yield potential or as in the case of free
living ones from the organic matter decomposition in the soil which in
turn make the process inefficient and causes depletion of organic
matter in tropical soils.
and sludge and industrial effluents contain variable quantities of
plant nutrients and organic matter besides some toxic elements
depending upon the source or origin.