Recycling crop and animal waste is a win for green farming

Low domestic production and reliance on imports for pulses, legumes and leguminous oilseeds have seriously affected India’s nutritional security. The green revolution was tweaked to a starch/carbohydrate one, a shift that continues despite rising diabetes incidence, while limiting India’s self-sufficiency in producing proteins and edible oils.

Skewed government procurement at minimum support prices (MSP), and preference of farmers to grow crops to sell at MSP, made matters worse with steadily rising input costs and falling output prices. Farmers continue to have low incomes, while consumers face increasing food prices.

Crop and livestock farming are ecologically interconnected, and the waste from one is a resource for the other. Farm waste is used as animal feed or is composted, while animal dung, poultry droppings serve as manure, saving the spend on fertilizers.

Crop farmers who don’t rear cattle must buy their manure or fertilizer, and livestock farmers must buy grass or commercial feed. In the process, waste management becomes a common problem for both, leading to air and water pollution.

Fertilizer-based emissions of nitrous oxide and ammonia from burning residue and dung cakes contribute to air pollution, while water pollution is caused by the loss of nitrogenous or phosphatic compounds from fertilizers or manure into the soil and water bodies.

Nutrients form a huge proportion of the wastewater (untreated or partially treated) that is dumped into lakes and rivers causing pollution and eutrophication.

Mitigation is possible by adopting simple measures for both input and output management.

Legume-based cropping systems

Nitrogen compounds constitute the predominant input for crops, whether as manure, compost or fertilizer such as urea. Legume crops including pulses and oilseed legumes like groundnut, soybean and sesame have natural capability to fix atmospheric nitrogen with the help of symbiotic N-fixing microbes in their root nodules.

These crops can not only survive without nitrogenous fertilizers, but also leave behind usable nitrogen and other residual nutrients sufficient to support non-legumes in the vicinity or in the next crop. The green revolution increased the dependence on fertilizers and hampered self-reliance in pulses and oilseeds. Crop diversification is necessary for sustainable agriculture in both economic and ecological terms, but it needs diverse buying policies of pulses and oilseed legumes at MSP for sustainable self-reliance.

Wastewater and solid waste are important sources of nutrients but India’s current capacity for their recovery and recycling is barely 20%. Though technologies and best practices exist to recycle livestock and crop wastes, there is little administrative commitment or investment to take appropriate measures.

In the process, of 65,250 metric tonnes of nutrients contained in more than 150 billion litres of wastewater produced per day in India, 84% is lost every day.

Forty percent of average daily fertilizer consumption of about 1,37,000 metric tonnes could be saved if recoverable nutrients from wastewater could be recycled. Similarly, recycling all of the 15kg manure produced per animal per day and 15-20 litres of urine per animal per day, by an estimated 191 million cattle, and all wastewater, could yield nutrients to the tune of 3,35,000 metric tonnes, which is 60% more than India’s daily fertilizer consumption.

Legume-based multi-cropping and inter-cropping systems would further reduce the demand for fertilizers and manure. Recycling nutrients would reduce air and water pollution, and improve economic yields.