Organic nutrient management

The primary goal of Organic farming is to optimize the health and productivity of interdependent communities of soil life, plants, animals and people.

In simple words, it can be defined as a farming system which makes no use or limited use of any chemical fertilizers, pesticides, growth regulators and genetically modified organisms (GMOs).

Nutrient Management in Organic Farming:
The management of nutrients in organic farming systems presents a formidable challenge, as the use of inorganic fertilizers is not permitted. Therefore, organic farming must optimize a range of soil, crop rotation and manure managements to ensure a nutrient supply which will guarantee optimum crop yields and minimize losses to the environment. To achieve this objective, an appreciation of the nutrient cycles in farming systems is essential which is possible through various practices as mentioned below:

• Crop rotation:
  It is the very basic building blocks of organic farming systems. It is a practice of growing a sequence of plant species on the same piece of land. The succession of crops to be grown is carefully designed to ensure soil nutrients are sustained, pest populations are controlled, weeds are suppressed and soil health is built.
  
  The exact sequence of crops will vary depending on local circumstances, with the critical design element being an understanding of what each crop contributes and takes from the soil. For instance, nitrogen depleting crop should be preceded by a nitrogen-fixing crop (Legumes).

A crop rotation will cycle through cash crops (such as vegetables), cover crops (grasses and cereals) and green manures (often legumes). The exact sequence of crops will vary depending on local circumstances, with the critical design element being an understanding of what each crop contributes and takes from the soil. For instance, nitrogen depleting crop should be preceded by a nitrogen-fixing crop (Legumes). The central idea is to have the crops themselves sustain soil health, rather than planting the same crop year in, year out, and then repairing soil health through fertilizers, pesticides and herbicides.

A well-designed crop rotation makes land both more productive and more environmentally sustainable. It improves the financial viability of a farm by increasing productivity whilst reducing chemical input costs. Key advantages of crop rotation are: Improved soil fertility and structure, disease control, pest control, weed control, Increased Soil Organic Matter, Erosion Control, Increased yield, Reduced commercial risk, improved biodiversity etc.

• Cover Cropping:
  Cover crops are the plants which are usually planted for the benefit of the soil rather than the crops. Cover crops slow erosion enhances water availability, smother weeds, improves soil health, help control pests and diseases and increases biodiversity. Thus, we can consider cover crops as a long-term investment for improving soil health and farm management. They begin to pay for themselves in the first year of use, or it may take a few years for them to lead to a net positive return. Cover crops also help to attract pollinators and provide resilience in the face of erratic and increasingly intensive rainfall, as well as under drought conditions. Buckwheat, cowpea, mustards, radish, alfalfa, sunflower, sun hemp are beloved by bees and beneficial crops. Stacking these pollinator plants in one field can lengthen the bloom period.

Cover crops can be either be sown after harvest of a cash crop, or they can be sewn into a standing crop (Over-seeding). Over-seeding is most commonly used to give cover crops a head start before the winter in regions with a short growing season.

The cover plants that fit for our crop field varies by location and purpose. Different cover crops have different strengths. While selecting cover crops for pollinators flowering broadleaf species are a must. Grass cover crops pollen contains lower protein and does not provide nectar while broadleaf cover plants higher nectar content and pollen contains more protein.

While selecting cover crops we should avoid the plants that serve as an alternate host for plant diseases. For e.g., if we are growing a brassica vegetable then it wouldn’t be clever to select cover crop of the same family because it would support similar pest.

Non-leguminous cover crops, typically grasses or small grains, do not fix nitrogen but can be effective in recovering mineralized nitrogen from the soil after crops are harvested. When legume or grass cover crops are killed and incorporated into the soil, living microorganisms in the soil start to decompose plant residues. The biomass Nitrogen is mineralized and converted first to ammonium (NH₄) and then to nitrate compounds (NO₃) that plant roots can take up and use.

• Addition of Compost/FYM:
  Composting is a biological process that requires careful monitoring of air and moisture levels in compost piles or windows to produce specific temperature ranges (113 to 160 degree Fahrenheit) that promotes the growth of beneficial microorganisms. Organic residues (manure, animal carcass, straw, grass, etc.) are the constituents of good compost. Compost mainly contains 2 per cent Nitrogen, 0.5 – 1 per cent Phosphorous, and about 2 per cent Potassium. Nitrogen fertilizers and manure may be added to speed decomposition.

Compost has many benefits to the soil. Fertility, water-holding capacity, bulk density and biological properties are improved by the use of compost in our field. The regular addition of compost is one of the best ways to enhance soil organic and humic content, which helps to build a fertile soil structure. Addition of FYM/compost to the field improves microorganism population in the soil which makes the soil alive with productivity and enables plants to battle diseases and pests. It is found that the soil with 4% OM contains 4000 lbs total Nitrogen/acre and the Nitrogen from compost becomes available to the plants at a slower rate, which reduces leaching and extends availability over the whole growing season.

• Application of Green Manures:
  It is a simple practice of ploughing or turning specific plant or crop varieties into the soil to improve overall quality. The green manure crop can be cut and then ploughed into the soil or simply left in the ground for an extended period prior to tilling. The main objective of applying green manures to the soil is to add organic matter and thus, enrich it with Nitrogen.

Types of Green Manuring:

1. Green manuring in-situ:
   When green manure crops are grown in the field itself either as a pure crop or as an intercrop with the main crop and buried in the field, it is known as Green Manuring In-situ. E.g. Dhaicha, Cowpea, Berseem, Mung, Sunn hemp, etc.

2. Green Leaf Manuring:
   It is the practice of turning the green leaves and tender green twigs collected from shrubs and trees grown on bunds, wastelands and nearby forest area into the soil with an objective to improve soil OM and Nitrogen content. For e.g. Wild Dhaicha, Glyricidia, Karanj, Neem, water hyacinth, etc. It is a beneficial practice, usually in the Hilly parts of the country. 

• Application of Crop Residues:
  Crop residues are the leftover parts of crops on cultivated land after the crop has been harvested. Straw, stubbles, twigs, leaves, roots, stalks, etc. are common crop residues. It acts as soil cover as well as a source of organic matter. These residues act as an anti-soil erosion measure in the soil. Moreover, crop residues can improve soil structure, increase organic matter content in the soil, fix CO₂ into the soil and reduce evaporation.

The amount of manure produced and their nature varies between crop types. For e.g. cereal straw contains only around 35 kg N/ha and has a wide C: N ratio while some green vegetables contain more than 150 kg N/ha along with a narrow C: N ratio. The narrow C: N ratio of green leafy residues means that N is released much more rapidly than from cereal straw.

• Supplemental application of organically approved amendments:
  Soil amendments are the materials added to the soil to improve its physical properties, such as water retention, water infiltration, drainage, permeability, aeration and structure. They are also known as soil conditioners. The main aim of using soil amendments is to provide a better environment for roots. Organic amendments are the safest and most effective means to promote soil fertility. Organic amendments include sphagnum peat, grass clippings, straw, compost, manure, wood chips, sawdust, wood ash, alpha pellets, leaf moulds and biosolids.

   

• Animal Manures:
  Animal manures include a mixture of animal faeces, urine, bedding materials (e.g. straw, wood chips, rice hulls, sawdust), and other materials associated with animal production, such as wash water, waste feed etc. Poultry and animal manures have been used to improve soil productivity since the dawn of civilizations and are the primary soil amendment. It improves soil physical and biological properties through the addition of organic matter. Fresh manure, especially slurry and poultry manure, contains a considerable proportion of Nitrogen in readily (principally Ammonium-N) forms, which can be easily and rapidly lost to the atmosphere.

   

• Bio-Fertilizers:
  Biofertilizers are the substances that contain microorganisms, which, when added to the soil, improves its fertility status and promotes plant growth. It is one of the important components of Integrated Nutrient Management. It is a cost-effective and renewable source of plant nutrients to supplement the chemical fertilizers for sustainable agriculture. Mycorrhizal fungi, Blue-Green Algae, and bacteria are the common biofertilizers. Several microorganisms and their association with crop plants are being exploited in the production of biofertilizers.

For e.g.-
N₂ fixing biofertilizers: Anabaena, Azotobacter, Rhizobium, Azollae, Azospirillum

P Solubilizing Biofertilizers: Bacillus spps, Pseudomonas striata, Penicillium sp, Aspergillus

P Mobilizing Biofertilizers: Acaulospora sp, Glomus sp, Amanita sp, Rhizoctinia solani

Optimizing soil health is the foundation of organic agriculture. Organic aims to ‘feed the soil to feed the crop’ by maintaining soil biology and nutrients at optimum levels throughout the rotation rather than the non-organic approach of applying nutrients to feed the crop to maximize yield. Organics, therefore, is a long term, whole-farm approach to nutrient management.

Organic Agriculture is the ultimate solution to combat the global food crisis and sustain agriculture for future generations. Thus, proper organic fertilizer management is crucial for high productivity of crops.

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