Composted Animal Manure as Source of Crop Nutrients

Animal manure is an organic by-product of livestock industry containing many valuable macro (N, P, K) and micro nutrients (boron, calcium, copper, iron, magnesium, manganese, molybdenum, sulfur, zinc). It is one of the most economical sources of crop nutrients. The organic matter (an important component of soil fertility) and plant nutrients added to soil through animal manures can prove an asset rather than a liability for producers. Organic matter improves soil tilth, increases water-holding capacity, lessens erosion, improves soil aeration and has a beneficial effect on soil microorganisms and plants. There are about 1.3 billion cattle worldwide, slightly more than 1 billion sheep, around 1 billion pigs, 800 million goats and 17 billion chickens (FAO). As per estimates they produce around 13 billion tons of fecal matter each year. Untreated manures can cause (i) leaching of nitrates and pathogens into groundwater (ii) their direct application to soil can result in oversupply of nutrients that can damage the soil fertility. In many parts of Asia as much as 25 % of the entire crop have already suffered from excess phosphorous added through animal manures. The effective management of animal manures is a matter of concern and needs some low labor intensive economical technology.

Composting is an effective manure management tool that recycles nutrients and stabilizes them, reduces volume, kills pathogens and weeds seeds. The process of composting involves the aerobic decomposition of organic materials by different group of microorganisms under controlled conditions. During the decomposition of organic-by products, the microorganisms feed on organic matter while using oxygen. The heat generated during the active process of composting can kill Escherichia coli, Salmonella and Listeria monocytogenes, the commonly found pathogens. However, the high moisture content, the low C: N ratio and low porosity are some of the physical characteristics that need to be taken care of before composting solid animal manures. The mixing of animal manures (in appropriate ratio) with some bulking agent such as cereals straw (C: N ratio > 80 :1) can reduce the high C:N ratio of latter to 50:1 (desirable ratio to initiate decomposition). In addition, the high moisture content and low porosity of animal manures gets amended by mixing them with cereal straw, thereby improving the physical structure of composting mixture. Urban residues such as leaves and grass clippings can also be used as co-composting substrates to produce soil amendments high in organic-matter content. The process of composting can be carried out in pits or heaps depending upon the availability of space and the process can be accelerated by inoculation with cellulolytic /lignolytic microbial consortium (Aspergillus sp., Phanerochaete chrysosporium, Pleuretus sajor caju and Polyphorus varsicolor, Trichoderma sp.). The moisture content of the composting mixture should be around 60-65 % and air needs to be incorporated routinely by turning the mixture at fortnightly intervals. The compost with high humus content gets ready with in 90 days. However, the quality of the compost is very important, to avoid phytotoxicity and nitrogen immobilization. Ultimately it is the quality of compost that supports soil fertility in organic agriculture. The proper use of composted animal manures can improve the physico-chemical and biological properties of soil, retain nutrients and help in proliferation of beneficial microbial communities besides reducing wind and water erosion.

Application of straw-manure compost to cultivable soil should be based on the nutrient requirements of the crop. Most crops need a nitrogen-to-phosphorus (N: P) ratio of 7- 10: 1, whereas composted manures commonly have an N : P ratio of 1-2: 1. To prevent nutrient loading and high levels of phosphorus that can accumulate when manure application is ill managed and not properly monitored, nutrient management plans may be based upon phosphorus management.

The influence of compost can vary depending on its quality, the soil parameters, and the utilization strategy. Testing soil for nutrients can alleviate nutrient loading.

• Analyze the soil for pH, residual N, available P and K.
• Analyze manure for dry matter contents as well as N, P, and K contents.
• Applying composted manure just before planting or at peak growing stages gives plants the best opportunity to use the nutrients. It also reduces the chance of nutrient run off.
• Too much manure may be harmful to the water supply and too little may not meet the crop requirements.
• Use supplemental fertilizer if needed: If application rates are based on phosphorus, extra N may be needed. P and K can buildup in the soil if manure is used to meet the N needs of a crop.

About Author / Additional Info: