Among the major cropping systems in India is rice-wheat. Rice straw management is one of the major concerns of this cropping system. Each year, millions of tonnes of straw are produced from rice and wheat cultivation. Straw from wheat is used to feed cattle.
However, rice straw remains a major problem for farmers. Approximately 220 lakh tonnes (22 million tonnes) of straw are generated only from paddy fields in Punjab alone every year, and 90 percent of that is burned in the fields. There is a very short time span between harvesting of rice and sowing of wheat in rice-wheat cropping system. This unfortunately leads to farmers opting for rice crop stubble burning to quickly prepare the field for wheat sowing. For farmers, stubble burning practice is the easiest way to manage rice residue. However, stubble burning has enormous environment degrading consequences.
Stubble burning involves setting fire to crop residue to remove it from the field for sowing the next crop. The method is used in areas where the ‘combine harvesting method’ is used. A combine harvester is a machine that harvests, threshes (meaning separates the grain), and also cleans the grains. However while using this machine; the machine does not cut close enough to the ground, leaving behind stubble that is useless to farmers. It is important for farmers to plant the next crop in time for it to yield a full yield and also maximum profit. Hence, burning the stubble is the fastest and cheapest way to clear the field according to the farmers
Although farmers are discouraged by the government from burning stubble, they still prefer it because it is cheap and less time consuming. Due to a lack of financial and technological resources, it is not feasible for farmers to consider alternatives to stubble burning, such as plowing it or investing it for other purposes.
The uprooting, cutting, burying, and watering of the stubble takes almost two days. Once the stubble is turned, it takes almost 45 days for it to turn into manure. Planting the next crop at the right time (mostly November-end) is critical. Furthermore, this process costs farmers Rs 500-700 per acre per day while setting fire to the stubble hardly costs them anything. In dairy farms, the majority of cereal and forage crop residue is used as cattle feed. However, rice straw is not preferred as cattle feed in northern regions due to its high silica, lingo-cellulose, and limited protein content (2-7%), which prevents it from being taken to the dairy. Despite this, basmati rice feed is sometimes preferred by cattle due to its high palatability.
Among the potential greenhouse gases produced by burning crop residues are methane, carbon monoxide, nitrous oxide, and other hydrocarbons, which are chemically and radioactively dangerous. This causes damage to the ozone and environmental pollution. It is estimated that rice straw burning releases carbon(C) as CO2 (70%), CO (7%) and CH4 (0.66%) while nitrogen (N) is released as N2O (2.09%).Furthermore, burning agriculture waste also emits a great deal of particulate matter, which contains a large number of organic and inorganic organisms. Biomass smoke contains a variety of known or suspected carcinogens that can cause lung diseases when they are inhaled in large quantities.
Pollutants, after being released into the atmosphere, disperse in the surrounding areas, undergo physical and chemical transformations, and eventually adversely affect human health. Human well-being is directly impacted by stubble burning. The reason for this is that all the toxic gases and heavy metals released by residue burning act as slow poisons in the human body. Studies have found that air pollution increases the risk of health problems in pregnant women, infants, the elderly, and people with a history of illnesses. The exposure of humans to these potentially hazardous gases has been associated with a wide range of respiratory, cardiovascular, neurological, skin and optical diseases.
The loss of soil nutrients occurs as a result of straw burning. In general, burning of one ton of rice straw will result in losses of 400 kilograms of organic carbon, 5.5 kilograms of nitrogen, 2.3 kilograms of phosphorus, 25 kilograms of potash, and 1.2 kilograms of sulfur. In addition, the heat generated by paddy straw burning kills useful microbes in the soil. Thus, burning straw negatively affects soil fertility and health.
Burning of stubble in Punjab, Rajasthan and Haryana causes a thick blanket of smog that poses not only a serious health risk to the population of Delhi and surrounding areas during winter but also visibility problems.
Transport problems are caused by the smoke screen that results after burning. Every day, numerous accidents result in the loss of valuable lives and wealth. The burning of straw destroys trees and plants around fields and along roadsides, thus destroying biodiversity.
It is easy to manage stubbles by incorporating them into the field. Farmers, however, do not prefer in-situ incorporation since the stubble takes time to decompose. There are various ways this may adversely affect wheat productivity, including late wheat sowing and nitrogen immobilization, which results in inadequate nitrogen supply. In combine harvested paddy fields, the Happy seeder is used to sow wheat without removing the straw. It is critical to spread the loose straw uniformly in the field for the happy seeder to work properly.
The paddy should be harvested using a combine harvester equipped with the PAU super straw management system (SMS). Paddy Straw Chopper-cum-Spreader is a machine developed by the PAU for chopping and spreading rice straw and stubble in the field. Rotating tillers can be used to mix the chopped straw into the soil after applying a light irrigation. Effective decomposition can substitute for straw burning. Straw decomposition requires cellulose and lignin-degrading microorganisms.
By decomposing rice straw, carbon, nitrogen, and other nutrients are recycled back into the soil, restoring soil fertility. Microbial processes may occur both under aerobic and anaerobic conditions. However, aerobic pathways are more critical for most soils than anaerobic ones. Feeding animals with rice residues is an option. Electricity can also be generated from rice residue. Biomass is the fuel used in the thermoelectric plants.
Research conducted by the Department of Livestock Production and Management of the College of Veterinary Sciences of Punjab Agricultural University found that paddy straw can be used as bedding material during winter by farmers. This bedding increases the quality and quantity of milk by providing comfort to the animals, udder health, and leg health. Rice straw is also an ideal raw material for making paper and pulp boards.
Paper is also produced from paddy straw combined with wheat straw. Paper mills are already using this technology to meet 60 percent of their energy needs. Paddy straw can also be used as growing medium for mushroom cultivation, including Agaricus bisporus, Volvariella volvacea, and Pleurotus spp. The yield of these mushrooms is 300, 120–150, and 600 g per kilogram of paddy straw, respectively.
Mushrooms grown on paddy straw are called paddy straw mushrooms (Volvariella volvacea).A variety of agricultural wastes can also be used to prepare the substrate for growing this mushroom, such as dried banana leaves, water hyacinth, oil palm bunch waste, cotton and wood waste. Composting is a traditional method of preparing organic matter enriched with beneficial nutrients.
The process of composting is a natural breakdown of organic materials involving microorganisms such as bacteria that break down animal waste, crop residues, vegetable waste, and some municipal waste. When decomposition is complete, it can be used as natural organic fertilizer.
In addition to its physical, chemical, and biological properties, this natural fertilizer increases soil fertility. Paddy straw produces almost 3.2 tonnes of nutrient-rich FYM per hectare. Agricultural wastes can be converted into biogas for use as an alternative energy source. The main source of lignocellulose for biogas production is crop residues, such as rice straw. Using rice straw as a mulch in the field has so many benefits. Mulching maintains soil moisture, controls weeds, and stabilizes soil temperature, which promotes healthy plant growth.
A model of a paddy straw geyser has been developed by the Punjab University that uses straw bales as fuel for water heating in order to properly utilize rice residue.
In November 2015, the National Green Tribunal ordered Delhi and its neighboring states to cease the practice of stubble burning. However, the order had little effect. The Centre approved a scheme worth Rs 1,151 crore aimed at promoting in-situ crop residue management through the provision of subsidized THS machines. There are currently seven plants in operation with a total capacity of 62.5 megawatts. Small and marginal farmers in Punjab were offered a ‘stubble-burry’ scheme to curb stubble burning with the Under the Mahatma Gandhi National Rural Employment Guarantee Act (MGNREGA) the District Administration is responsible for providing workers to farmers to dig up the compost pits.
Researchers developed perennial rice by hybridizing Asian domesticated annual rice with wild perennial rice from Africa. Taking advantage of modern genetic tools to fast-track the process, the team identified a promising hybrid in 2007, planted large-scale field experiments in 2016, and released the first commercial perennial rice variety, PR23, in 2018.
Farmers in China and Uganda have shifted to using long-lived perennial rice that is both high-yielding and cost-effective, and its success has provided us with a good opportunity to ponder the possible benefits of sowing this variety in India and help to solve stubble burning problem since it can be planted once in two years, thus burden of stubble can be reduced.