As Green Revolution was started in India during 1965, enormous increase in agricultural production led India to become self sufficient in food grains. This increased agricultural production is contributing significantly to increase in green house gases (GHG) concentration in the atmosphere due to excessive tillage, use of fertilizer and improper crop residue management practices. The mechanization of Indian agriculture has resulted in development and adoption of combine harvester, which leaves residue of harvested crop in the field. This residue can be managed in three ways; first, it can be collected and transported from field to be used as dry fodder for animals. Second, it can be used for producing electricity and third it can be used in paper industry, card board industry etc.
According to the study conducted by the National Physical Laboratory, New Delhi in 1994, Madhya Pradesh stood third in the list of the crop residue producing states of India with a production of 18.84 million tonnes of rice and wheat residues. As any worthwhile use of such a high quantity of crop residue is not introduced to farmer, lack of user friendly recycling tools, expensive labour and moreover farmers are in a hurry to sow the next crop; the practice which is widely accepted is the burning of this crop residue in the open field. Wheat and rice crops are major contributors to burning of crop residues in open field with small contributions from sugarcane, cotton, jute, millets, maize, rapeseed and mustard crops. The division of Environmental Sciences of IARI, New Delhi reported that wheat contributed the highest in GHG emission of 24% of methane and nitrous oxide emissions in 2007. The GHG emission due to crop residue burning was around 5 Mt CO2 eq in 1995-96 and within a decade it increased to more than 7 Mt CO2 eq in 2006-07.
Crop residue burning has been identified as one of the key factor for unsustainability, rapid CO2 emission and disturbing soil’s natural properties that contribute adversely to the fertility of the soil. This burning of crop residue in open fields is not only harming the atmosphere but is also a big threat to soil fertility and productivity. These long term ill effects if not checked now will cause a great loss to crop productivity and environment.
Residues when burnt result in the production of aerosols (particulates that arise from organic and inorganic species) which are harmful to atmospheric chemistry, radiation budget, human health and crop yield. Major and trace gases like CO, NOx, CH4, CO2 and N2O contribute to air pollution and global warming. Indias contribution in CO2 emission due to burning of agricultural residues in open field is approximately 18%. Madhya Pradesh contributes to CO2 emission of 7% from open field burning of wheat residue and 6% from rice residue.
Soil temperature, pH, moisture, available phosphorus and soil organic matter are some of the soils properties that are greatly affected due to burning. Microbial population of soil is also governed by the factors like soils temperature, pH, moisture content and organic matter. Thus, burning not only disturbs soils natural environment but also have an adverse effect on microbial population of soil. During burning of crop residue, soils temperature increase up to 33.8°C-42.2°C. Most of the soil microorganisms are mesophilic having 37°C as their optimum temperature. The sudden increase in temperature during burning results in decline of microbial population up to a depth of 25 mm. Low microbial declines organic matter decomposition which affects aggregate formation and stability.
Water plays an important role in seed germination, plant growth, and nutrient supply to plants. It serves as a source of H/O to the microorganisms. Burning results in a rapid loss of moisture in the form of vapours. This results in lowering of moisture content of soils, which takes a lot of time to regain. The absence of adequate moisture in soil results in death of some of the microbes due to tissue dehydration. Therefore, optimum soil moisture should be there for better microbial population and low moisture content results in decrease in seed germination and growth in plants.
Burning of residues also results in ash production, which is rich in Ca, Mg and K ions. These contribute to rise in pH. This shift from normal pH of soil adversely affects microbial activities. These effects become more prominent when burning is practiced continuously for many years. Fire also results in abrupt release of nutrients which in absence of fire would only have become gradually available through the slow decay of plant litter. Studies have shown a decline of 30-50% in bacterial population on repeated burning. Long term burning of crop residues results in lowering of total N and C by 27-73% up to a depth of 150 mm and 2.4 kg/t of N is lost from burning of wheat residue. This lowering of nitrogen will affect plant growth and excessive use of nitrogen containing fertilizer is again a non eco-friendly practice. Decline in carbon content of soil results in less stable aggregate formation.
Although burning is not a good farming practice, yet it is being continued as a matter of convenience. Apart from its impact on GHG emissions and degradation of soil, it also affects human health in a number of ways. Stubble burning produces large amount of fine particles that can be carried for long distances suspended in the wind. Studies have indicated that short term exposure to low level increase in particles in the air is associated with an increase in illness and death, particularly in individuals with heart and lung ailments. People with lung ailments such as asthma and chronic obstructive pulmonary disease are more quickly affected by these tiny particles entering their breathing system. For persons with allergies, smoke in the air can cause annoying symptoms such as sore throat, sore eyes, coughing, nasal and sinus congestion.
Keeping the above points in consideration, there is an immediate need to put an end to the practice of burning of crop residues in open field. This can be done by adoption of tractor drawn PTO operated straw baler which has been developed for efficient collection of straw from field in the form of cubes which can be easily transported. CIAE, Bhopal has also developed a tractor operated straw reaper (combine) which is used to recover wheat straw after combine operation and is operated by a tractor. Straw collected by a straw combine is cut into pieces and is collected in the trolley. The field capacity of machine is 0.4 ha/h at a speed of 2.5 km/h and straw eco very is about 55-60%. The cost of operation is `1200/ha. The machine can cover about 75-100 ha/year. The quality of bhusa is comparable with mechanical thresher. There is an additional grain recovery of 50-100 kg/ha. The cost of grain removal is almost equal to amount paid for hiring the machine. The collected crop residues can be effectively utilized in preparation of briquettes which is a renewable source of energy. Retention or incorporation is another most beneficial residue management practice. It has many advantages like, it sustains the productivity of soil as it can hold and supply the nutrients, reduce soil erosion from water and wind, act as mulch and modify soil temperature and improve physical condition of soil. It has been observed that residue retention on field increased crop yield from 5.37 to 5.81 tonnes/ha as compared to residue removal. The government should monitor and discourage burning through incentives and technology transfer. Efficient machinery developed should be popularised and researchers farmers interactive sessions should be held for discussion of pros and cons of burning practice.
The increase in agricultural production in India has contributed significantly to increase in GHG concentration in the atmosphere due to excessive tillage, use of fertilizer and improper crop residue management practices. The mechanization of Indian agriculture has also resulted in development and adoption of combine harvester, which leaves residue of harvested crop in the field. This crop residue is normally burnt in the open field leading to rapid GHG emissions and disturbing soils natural properties that contribute adversely to the fertility of the soil. It also affects human health in a number of ways. There is a need to discourage burning through Government incentives and technology transfer. Efficient machinery developed should be popularised and researchers farmers interactive sessions should be held for discussion of pros and cons of burning practice.
Author is presently working in the Agricultural Production Department, Kashmir, Bandipora, J&K,