Animal manure recycling technology for P enriched compost
By - SUNITA GAIND

Phosphorus (P) is essential for food production. Its low availability in soil restricts the plant growth and affects the crop yield severely. To meet the nutritional needs of the crop plants, water soluble P in the form of super-phosphate has to be applied to soil in quantity in excess of the crop requirement. This not only increases the cost of cultivation and puts financial constraint on the marginal farmer but also affects the soil fertility. Sustainable resource management of P fertilizer is critical for global food security. There is need to develop new technologies for P recovery from agricultural and animal residues that have huge potential for recycling of nutrients. Live stock by products such as cattle manure, poultry manure and farm yard manure are the economical sources of nitrogen (N) and P. Approximately 65 % of the P excreted from animal waste is not utilized and lost. Recovery from such organic wastes is one of the likely sources of P recycling for global sustainability. The concept of P reuse is important for sustainable crop production and environment protection. The P recovery from manures using techniques that produce concentrated by-products with nutrient value competitive with mineral fertilizers is highly desired.

Need for effective utilization of animal manure

Land application of fresh animal manure is the most common practice for manure disposal. However, the amount of N and P in manure exceeds the amount of nutrient required by the crops. High levels of ammonia or ammonium in fresh manure can be detrimental to germinating seeds. Poultry manure contains high level of water soluble P (2000 mg kg-1). Run off of the dissolved P from field receiving poultry manure can occur even when the best management practices are used. Water soluble P gets transported to run off water during rain fall. It is an environmental concern often associated with excess P in soil and potential water pollution. Transportation of raw poultry litter is less economical. The bio-conversion of P and N rich animal residue to a stable product such as compost by blending it with high C: N plant residue offers an attractive technology for recycling and conservation of nutrients. It also represents an alternative means of waste management that can result in P enriched manure. The application of P enriched compost to soil can reduce the input of chemical fertilizer besides maintaining the biological activity.

Methodology

Take a plastic/metal composting bin of 50- 60 liters capacity. Add carbon-rich substrate such as crop plant residues, grass clippings, paddy straw (cut into small pieces of about 1-2 inches) or dried leaves to poultry manure in the ratio of 6:1 (w/w) to achieve a carbon-to-nitrogen ratio of 30:1. A combination of 30 part of carbon to one part of nitrogen creates the best environment for initiation of microbial degradation of crop residues. Mixing of bulking agent with poultry manure also improves the physical characteristics of composting mixture. Add water to keep the moisture level between 40- 50 percent (it will feel like a damp sponge when squeezed). Mix it thoroughly and cover the bin with lid having placed newspaper inside. This will absorb the foul odour emission during decomposition. Allow the composting mixture to decompose. As the organic matter decomposition begins, the internal temperature of the substrate mixture will start rising within 3-4 days of decomposition process and will remain about 50-55oC for two to three weeks. This high temperature kills the weed seeds and pathogens (E.coli, Salmonella sp.) present in composting mixture. A fortnight turning of composting mixture should be done to ensure the even distribution of the heat. Continue to turn the pile every 2 weeks for about four months, until the compost is dark brown, crumbly and uniform. The dark brown color of compost is due to high humus content. Analyze mature compost for phyto-toxicity by mustard seeds germination test to ensure its safe application to the field for crop cultivation.
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Animal manure-based composts are rich in plant nutrients such as Nitrogen (N), phosphorous (P) and potassium (K) and provide organic matter that conditions the soil. While they can make excellent soil amendments for the soil, it is important to use them effectively and safely. In particular, these materials often contain more phosphorus than nitrogen. Thus, enough application of these materials to meet nitrogen needs for crops will result in application of far more phosphorus than is needed. Over the time, this can lead to very high levels of soil phosphorus. Very high soil phosphorus when moves into surface waters, can lead to algal blooms, which pollute water quality and affect the aquatic life. Therefore, to use manures and composts effectively and responsibly, pH and nutrient status test especially available P is necessary for both soil and compost to avoid the overdose of fertilizer.

The recovered P reuse technology will not only help to minimize the manure P losses into environment but will simultaneously promote long term sustainability of livestock industry and poultry production.

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