21 Sep Is there a way out of rice stubble burning?
Rice is one of the most important food crops in Asia. Globally, India ranks second in both annual rice production (118.87 million metric tons, 2019/20) and consumption (106.5 million metric tons, 2020/21). Rice cultivation involves the production of large amounts of straw as residues, with one hectare of rice generating approximately five tons of residues. In India, major portion of such residues are burnt on open fields owing to shorter turnaround time between 2-3 crops sown in a year. Residue burning not only results in a loss of nutrients and soil organic matter but also causes severe smog conditions all over the Indo-Gangetic plains. Breathing such air has adverse impacts on human, animal and vegetation health. A recent study titled ‘State of Global Air 2019’ states that air pollution is third biggest cause of death and kills 1.2 million Indians in a year. Therefore, crop residue management becomes critical step for sustainable rice cultivation. Currently, multiple research organizations are working on developing improved rice residue management solutions that can help reduce the adverse environmental impacts of and increase returns from rice production. Some of the current practices have been listed below –
Surface retention and mulching: This technique is most suitable in regions where conservation tillage practices are prevalent and direct drilling of seeds is done. Crop residues are cut and left on soil surface as mulch without any form of incorporation. The residues usually degrade on its own in five to six months on its own. The main requirement is that the straw be chopped and spread evenly across the field after threshing. Farm machinery with devices called the SMS (straw management system) or Happy Seeders can be used for the activity. Surface retention helps in weed suppression, protecting the fertile surface soil against wind and water erosion, improves soil moisture and decreases fertilizer needs after third to fourth season
Residue incorporation: Crop residues can be incorporated partially or completely into the soil depending upon methods of cultivation. This can be easily done by ploughing the land using machinery like Rotavator or Superseeder. Residue incorporation usually helps improve
SOM and soil N, P and K contents. However, in crops like wheat, a major concern of farmers that has been observed is that incorrect incorporation of cereal straw can lead to N-deficiency by immobilizing the inorganic N in the soil leading to reduced yields. However, experts state that this problem can be easily rectified. Farmers just need to follow proper complementary fertilizer management techniques like applying urea while sowing, and not later at the time of irrigation; increase the dosage of N fertilizer application; or place Nitrogen fertilzer below the soil surface (Urea deep placement) after incorporation of crop residue to prevent N deficiency.
Composting using microbial or fungal inoculums: In India, adoption of crop residue incorporation also fails because the rate of decomposition of rice straw is very slow. There is very little time between two crop seasons and waiting for the straw to properly decompose can adversely delay next season’s sowing. To combat this research institutes like IARI and PUSA have tried to speed up the decomposition process by using fungal and microbial inoculums (e.g. Pusa decomposer, Waste Decomposer). However, even with these decomposers, atleast 7-8 weeks are needed to completely degrade the stubble for it to be mixed with the soil. Hence, another option is to clear, collect and compost the stubble at one corner or on the bunds of the field with animal manure and the inoculums. When ready it can be spread on farmer’s fields as a farm yard manure rich in nutrients and soil organic carbon.
Diversifying use of straw in on and off farm activites: Surplus rice residues can be used for a number of different off and on farm purposes including as a livestock feed additive, livestock bedding, fuel, mushroom cultivation, bedding for vegetables such as cucumber etc., mulching for orchards and other crops and as a building and packing material. Using rice straw for mushroom cultivation is a particularly interesting and cost effective solution. Mushrooms are an indoor crop and the construction cost of cropping sheds/ growing houses and bedding substrate are a significant cost factor for mushroom cultivation. Paddy straw can be conveniently used for making low cost mushroom growing houses and it also serves as the perfect substrate for growing the mushrooms. Furthermore, paddy straw is locally available and can be easily accessed even by landless, small and marginal farmers including women farmers interested in cultivating mushrooms.
All the above options clearly highlight that the scenario for managing paddy straw is not all that bleak. Awareness generation, proper nudges and helping farmers select the correct option best suited for their needs can help prevent stubble burning and turn paddy straw from being considered a useless waste to a useful resource.
Images from DownToEarth
Sudeshna Maya Sen
Deputy Manager – Climate Change