Nutrient management in organic crop products
- Part 2 -

DJ Rajkhowa *

Components of soil fertility in organic farming

1. Use of crop rotations
2. Green manures
3. Bio- fertilizer
4. Managing crop residues
5. Use of agro-industry wastes
6. Oilcakes and other organic manures
7. Use of composted animal manures
8. Naturally occurring mineral amendments (e.g. Rock phosphate, potassium sulphate, Calcite lime, Dolomite lime etc.

In organic farming plants have to convert the unavailable nutrients to available forms and that happens due to organic acids produced by the microbes. Livestock keeping at farms is an age-old practice. Livestock keeping at farms is an age-old practice. Livestock play a major role in organic agriculture as the intermediary between the utilization of crop residues or fodder produced at the fans and the return of nutrients as manure.

Animal dung, crop residues, green manure, biofertilizers and bio-solids from agro-industries and food processing wastes are some of the potential sources of nutrients of organic farming. Technologies to enrich the nutrient supply potential from manure, including farmyard manure three to four times are being widely used in organic farms. Organic farms and food production systems are quite distinct from conventional farms in terms of nutrient management strategies.

Organic systems adopt management options with the primary aim to develop holistic farms, like a living organism with balanced growth, in both crops and livestock holding. Thus nutrient cycle is closed as far as possible. Only nutrients in the form of food are exported out of the farm. Crop residues burning is prohibited, so also the unscientific storage o animal wastes and its application in the fields.

It is, therefore, considered more environments friendly and sustainable than the conventional system. Crop rotations and varieties are selected to suit local conditions having the potential to sufficiently balance the nitrogen demand of crops. Requirements for phosphorus, potash sulphur and micro-nutrients are met with local, preferably renewable resources.

Organic agriculture is therefore, often termed as knowledge-based rather than input-based agriculture. Some of the important features of organic farming in the context of soil health and environmental protection are given below. In organic farming, the supply of nutrients is more balanced, which keeps the plant more healthy and improve the biological activity of soil, which in turn improves nutrient mobilization from organic matter and native soil reserves and minimizes the losses of nutrients, thus protecting the environment.

Microorganisms have a good feeding base and create a stable soil structure. Inclusion of legumes or cover crops mulching, intercropping and agro-forestry, plays an important role in protection against soil erosion and degradation.

Management practices to conserve nutrients and enhance soil quality
Application of corn-posted animal manure and other organic residue to form a more uniform corn-posted material.

Use of crop rotations to help trap and recycle nuttiernts in the soil profile, increase soil tilth, and provide a diversity of crop residues. Crop rotations is an essential component of any organic farming system, creating diversity in space and time that disrupts the growth and development of weed, pests and disease populations.

Use of green manures and cover cropping is a standard practice in organic farming

Use of compost is beneficial because it contains antibiotics and antagonists to soil pests allowing for increased plant resistance to attacks, increases crop yields is important in weed control and build up soil organic matter

Use of annual soil tests to help calculate appropriate amounts of organic manure to add.
Avoidance of surface application of manure prior to rain or irrigation

Use of farming practices that enhance soil quality and reduce the potential for water runoff and wind erosion

Use of vegetative buffers or filters between cropping areas and water bodies to protect against nutrient loss.

Improving nutrient use efficiency is a key challenge for all agricultural production systems. The need to reduce losses and make the optimum use of applied nutrients has been driven by both economic and environmental concerns.

Enrichment of compost

The nutrient content in the compost produced from different biowaste is generally low and mainly depends on the nature of biowaste used. Hence, it is important to improve such compost in terms of its nutrient content. This will also help in minimizing fertilizer requirement and will be of immense utility particularly for nutrient management under organic farming.

Development of several compost production technologies like vermicomposting, microbes mediated, phosphor composting, N-enriched phosphocomposting etc. improves the quality of composts through enrichment with nutrient bearing minerals and other additives. These manures have the capacity of firlfil nutrient demand of the crops adequately. Inoculation of efficient nitrogen fixing and P solubilizing microorganisms, mineral amendments are some of the ways to increase the nutrient content in the compost.

One of the possible ways of improving nutrient content in the compost is by inoculating nitrogen fixing microorganisms and phosphate solubilizing microorganisms. The culture of efficient strains of nitrogen fixing bacteria such as Azotobanter, Azospirillum, Pseudomonas etc. can be inoculated in the compost either during composting or in the final compost to increase the nitrogen content in the compost. Similarly, phosphate solubilizing microorganisms such as Asp.gillus avvamori are inoculated to enhance P content in the compost.

Inoculation of compost with Azotobacter and phosphate solubilizing culture along with 1% rock phosphate is beneficial to obtain good quality compost rich in nitrogenandphosphate. Compost quality interim of nutrient content can also be improved through addition of rock phosphate etc. during the process ofcomposting. Oilcalces, bone meal, bio gas slurry etc. canals° be usedfor enrichment ofcompost quality.

Plant material rich in nitrogen such as legume Stover(greengram, black gram, cowpea, Cassiabiomassetc. mayalsobe mixed with other plant biomass such as rice straw, wheat straw etc.to enhance composting and also to obtain compost with higher nitrogen content. Oil cakes , bone meal etc. can also beused for enrichment of compost Efficient use of organic manure Since, the availability of organic manure is limited in terms of quantity and time, therefore, its efficient application is very much important.

Fourth, efficient use of such manure also minimizes weed infestations. Application of organic manure at proper time, dose and by following appropriate method (s) is important for maximum use efficiency. Well decomposed organic manure, free from weed seed and other toxic substance should be used in field. Partially decomposed organic manure should be applied at least 15-20 days before sowing or planting of a crop when the soil has sufficient moisture so that the nutrient is released as per the crop requirement.

Application of such manure long before sowing of a crop will lead to loss of manurial value, particularly the loss of nitrogen. Well rotten manure however, should be applied just before sowing or planting of a crop particularly in sandy soil to avoid loss of nitrogen. Such organic manure with narrow carbon: nitrogen ratio can also be applied in the standing crop also preferably at grand growth period.

In case of perennial crops like tea, coconut, citrus etc, application of organic manure once at the time of onset of monsoon and the other at the time of cessation of monsoon is beneficial. Rate of application of organic manure is depend on soil nutrient status including humus content, crop grown, availability of mamires, nutrient status in the manure or the quality of manure etc. In general, 5 to 10 t manure (FYM, Compost etc.) is to be applied per hectare, while, vermicompost (containing relatively higher nutrient content) may be applied @ 1 to 2.5 Vha.

However, higher rate of organic manure may be applied for crops grown organically. Under rain fed condition, organic manure may be applied at 1 t/ ha while, under irrigated condition, 5 to 1 Mn of organic manure may be applied per hectare depending upon the availability. Under limited availability, organic manure may be applied to one third or fourth of the field at usual rate in rotation every year so that all arts of the field receive the manure regularly once in 3 to 4 years. Organic manure applied in scattered heaps in the field without incorporation should not be practiced as it leads to deterioration of manorial value.

Incorporation of organic manure after application is always beneficial. Application of manure without incorporation will result in significant loss of nutrients. Light irrigation following organic manure application is beneficial. For field crops, organic manure should be unifonnly applied in soil and incorporated well For row crops, organic manure should preferably be applied in crop rows or in the root zone.

This will also reduce weed infestation. For orchard plants, organic manure can be applied around the base of the plants followed by light forking or incorporation. The growing of leguminous crops in rotation improves soil fertility by way of fixing atmospheric nitrogen. Such practice also improves the mineral nitrogen content and N availability in soil besides improving soil physical properties and microbiocidal activity.

In general, a leguminous green manure can add 100-200 kg nitrogen per hectare besides adding considerable amount of organic matter. Such crops also act as mulch and checks soil and water loss. Such crops can add 4-5 t/ha of dry biomass in about 50-60 days when managed properly. These crops are also well suited to most of the cropping systems. Practiced in different parts of the country, more particularly in rice based cropping systems. Summer is the best season for growing green manure crops.

Green manuring crops can also be grown as intercrop in between the space of the main crop and when the green manure crops reach 45-50 days, the plants can be cut and used as mulching. This practice will also help in reducing weed infestations besides adding organic matter and plant nutrients. Nitrogen supplied through green manure crops is readily available to the subsequent crops because of its low C:N ratio and easy mineralization. Apparent recovery of green manure N in different crops varies from 30-58%.

The success of organic farming depends to a great extent on the efficiency of agronomic management adopted to stimulate and augment the underlying productivity of soil resource. Organic agriculture lays emphasis on appropriate cropping and farming system models, ensuring on farm diversity and nutrient cycling, conservation and use of organic/biological resources of nutrients, cultural practices conducive to the conservation of soil and water resources.

Some issues To meet the food requirement of alanningly increasing population, large scale conversion to organic agriculture is not feasible. Identification of potential areas and crops is most important to reap the benefits of organic farming. High value crops having export potential may be good options on priority basis to produce organically. There is necessity to standardize location specific manurial schedules.

As the supplies of organic manures are not adequate, these need to be augmented by developing a strong component of dairying, piggery, poultry etc. There is need to enrich the organic manures in terms of nutrient content. The bio-fertilizers need to be popularized. Location specific, appropriate cropping/fanning systems need to be developed.

Some of the issues to be considered for promoting organic farming are
Awareness
Conversion period
Increase productivity
Appropriate technology
Certification process
Market infrastructure
Institutional support

Concluded ....