Rapid Composting Technique for Rice Straw
Authors: Seema, Rekha Sodani, Jyoti Chauhan, Sunil Kumar

A simple, rapid composting technique to convert huge piles of rice straw into an organically rich soil amendment has been developed by a soil microbiologist at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru nearHyderabad. It is an aerobic composting method using a native soil fungus. This method is designed to be a rural enterprise for the educated unemployed youth. This eco-technology will save huge volumes of rice and wheat straw that are being burnt in parts of India,Vietnam, Sri Lanka, Philippines and Indonesia, and conserve the valuable nitrogen and other nutrients contained in the straw,explains Dr. O.P Rupela, ICRISATs Soil Microbiologist, who developed this technology.

The burning of the straw is a serious environmental issue in many Asian countries. The damage caused by the soot in the atmosphereis considered very serious. According to a study in 1998, in Punjab about 12 million tonnes of rice and wheat straw were burnt.The loss of nitrogen in that process was estimated at US $ 18 millions. The new eco-friendly technology, which is well suited to the semi-arid tropics of world, will not only prevent such losses but also significantly contribute to employment and income generation in the rural areas, according to Dr. Rupela.In this method, dry rice straw should be bundled into convenient sizes of 5 to 10 kg each, and dipped in a soaking solution for two to three minutes. The soaking solution is prepared by mixing one ml of fungal (Aspergillus awamori) spore suspension and one gram of urea for every litre of water. With each soaking, thedry straw bundle will soak up to 1.5 times its weight of the solution. For instance, a 10-kg bundle will use up about 15 litres of the solution. The wet straw bundle should be drained over a polythene sheet spread over a sloping surface for about 20 minutes. This will facilitate the drained solution to flow to the lowest point from where it can be collected and re-used.

The well-drained bundles are sprinkled with 6 per cent powdered rock phosphate and placed layer by layer over dried twigs. The dried twigs will help in aeration between the soil and the strawlayers, to form a large heap of 5 metres length, 1.5 metres width and 1.5 metres height. Each of such large heaps will accommodate about 500 kg dry straw soaking 750 litres of the solution. The whole heap is then covered with a 20 to 30 cm layer of untreated straw to retain the moisture.

Care should be taken to maintain the moisture regimen of the heap. To penetrate the interior layers, an indigenously designed injection-pipe lance is used. It is thrusted into the heap and allowed to deliver 10 to 40 litres of water a minute. The first watering is done on the 7 th day and about 100 litres water is added. On the 15th day, the heap is turned well, and about 240litres is added. On the 20 th day about 150 litres of water is added, and the final turning and watering is done on the 30 th day, when about 200 litres of water will be required.

The temperature in the center of the heap reaches 60 degrees Celsius within four days. The base of the heap remains 4 to 6 degrees Celsius above the ambient temperature. On the 45 th day,the entire heap will be completely composted, which is indicated by sweet, earthy smell, and the dark colouration of the straw.The straw strands will still be visible, but will break easily. The soft compost will then be ready for application in the field.

The compost has been found to contain 1.7 to 2.1 per cent nitrogen, 1.3 to 1.5 per cent phosphorus and 1.4 to 1.6 per cent potassium. The compost is evaluated and field-tested by the scientists at the Punjab Agricultural University (PAU), Ludhiana. The economics of the eco-friendly rapid composting technique is being worked out in collaboration with PAU scientists. In the field experiments conducted in Punjab, the scientists found that crop raised with this compost yielded 4 to 9 per cent higher than those raised with equivalent quantity of burnt rice straw, according to him.

About Author / Additional Info:
I am currently pursuing ph.D in Plant Physiology from Banaras Hindu University