Plough stubble back into soil

Manjit S Kang
Former VC, PAU, Ludhiana, and Adjunct Professor, Kansas State University, Manhattan (USA)

Agriculture is the backbone of India's economy. In 2015, it contributed to GDP about 16 per cent and to exports 10 per cent. Because of diverse climatic zones, various types of crops are grown. According to the Agriculture Ministry, in 2011-12, the production of some major crops was as follows: 104.6 million tonnes of rice, 93.9 million tonnes of wheat, 21.6 million tonnes of maize, 20.7 million tonnes of bajra (millet), 358 million tonnes of sugarcane, 8 million tonnes of fibre crops (jute, cotton, etc), 17 million tonnes of pulses, and 30 million tonnes of oil-seed crops.

Therefore, it is natural that much on-farm and off-farm crop residue is generated. About 500-550 million tonnes of crop residue is produced annually. Some of it is fed to animals, and some used as mulch and bio-fertiliser in crop production. Crop residue may also be used in rural areas to build roofs and some for producing energy.

Among the largest crop residue-producing states are UP (60 million tonnes), Punjab (51 million tonnes), and Maharashtra (46 million tonnes). The largest amount of crop residue (70 per cent or 352 million tonnes) is produced by cereal crops, of which 34 per cent is contributed by paddy and 22 per cent by wheat. Each kilogram of milled rice produced results in 0.7-1.4 kg of rice straw, depending on varieties, cutting height, and moisture content during harvest.

About 50 per cent of the paddy residue is fed to animals and the rest burned in fields. According to International Rice Research Institute (IRRI), paddy straw contains a high amount of silica, which wears out components in processing machines, such as conveyers or grinders. Silica also makes paddy straw less digestible for livestock.

Though the crop residue is valuable for the farmers, they burn it to quickly vacate the field for the sowing of the next crop (generally wheat), as sowing must be accomplished in about three weeks after paddy harvest. Straw is also burnt due to shortage of farm labour, use of combines that leave much stubble behind and high cost of removing the crop residue from the fields via traditional means.

Consequences of burning crop residue

It is ironic that, on the one hand, the country faces a shortage of food/feed/forage for animals and on the other hand, crop residue is burned in the fields. This is one of the reasons for the high prices of forages.

In the food bowl states of Punjab, Haryana, and western UP, after the paddy harvest, because of stubble burning,  air is polluted and leads to breathing problems.

The burning emits such gases as carbon dioxide, methane, carbon monoxide, nitrous oxide and sulphur oxide, and particulate matter; all of which adversely impact the environment. It can exacerbate problems of asthma and heart disease. The greenhouse gases are responsible for global warming and climate change, which impact, among other things, all aspects of agriculture, food security, and livelihoods.

In October, 2012, the stubble burning problem attracted international attention. The National Aeronautics and Space Administration showed satellite images of stubble burning on lakhs of hectares of farms in north-western India. In Punjab alone, 12 million tonnes of paddy stubble is burned every year. 

According to the International Crops Research Institute for the Semi-Arid Topics (ICRISAT), Hyderabad, in burning crop residue, Punjab farmers lose $18 million worth of urea and $30-35 million worth of all nutrients. In addition, stubble burning kills essential soil microorganisms and farm-friendly insects. 

Some solutions

Agricultural universities are developing short-season rice varieties to enable a larger window of time between paddy harvest and sowing of the next crop (wheat). Rice varieties containing reduced levels of silica must be bred so that their straw can be made more palatable for livestock. 

The main principle of sustainable agriculture is to return to the soil what has been taken out of it. Farmers must be encouraged to adopt conservation practices. Crop residue should be incorporated into the soil. This would enhance soil health and crop production and reduce pollution. The problem of burning of rice straw can be mitigated by reducing the rice area in Punjab from 2.7 million hectares to 1.5 million hectares, as suggested by noted rice expert, Dr Gurdev S Khush. The extra area could be diverted to other crops that use lesser water. 

Some practices that can be adopted 

Happy Seeder: Punjab Agricultural University (PAU) has developed, in collaboration with Australian scientists, a seeding drill called "Happy Seeder", which lets farmers to plant wheat directly in the standing paddy stubble. This drill, with modification, can now be operated with a small tractor. The Punjab Government provides a 60 per cent subsidy on the Happy Seeder. However, all farmers are not making use of it.

Compost from residue: PAU and ICRISAT scientists have developed a simple method of producing compost from crop residue in 45 days. Containing about 2 per cent nitrogen, 1.5 per cent phosphorus and 1.5 per cent potassium, the compost can increase crop production by 4-9 per cent. But it requires much labour. Indian Agricultural Research Institute has also developed a method of making compost from crop residue. With the help of microorganisms, compost can be readied in 75-90 days. 

Mulching: Crop residue is spread on the ground for decomposition by earthworms, thus increasing soil fertility. 

Biofuel: Punjab Biomass Power Ltd, Patiala, has established a plant in which paddy straw is used to produce electricity. The company intends to set up several plants in Punjab. India has the capacity of generating 17,000 megawatts of power from paddy straw. But it goes against the principle of sustainable agriculture, ie paddy straw should be incorporated into the soil. The electricity so generated will benefit a few people, while incorporation of straw into the soil will improve soil and help many people. 

To ensure food security and good health for all, paddy straw should best be incorporated into the soil as per conservation practices. Farmers must be educated about viable alternatives to stubble burning.