By: Dr Som Dutt
Farmers opt for straw burning and clear the field from straw and stubble after the harvest of preceding crop because there is shortage of time period between harvesting of preceding crop and sowing of succeeding crop.
Nowadays, burning of straw of rice or wheat, in agricultural fields emits a large amount of pollutants including toxic gasses like carbon monoxide, volatile organic compound, and carcinogenic polycyclic aromatic hydrocarbons and fine inhalable partials. These are very dangerous to humans and other fauna and flora too. The burning of straw contributes significantly to emission of greenhouse gases like CO2, ammonia, methane and other pollutants, consequently contributing to the global warming.
Intensive burning of agricultural waste substantially contributes to the formation of the atmospheric brown cloud and that affects the local air quality, atmospheric visibility and the earth climate. In India, about 141.2 million tonnes straw is in use and from that about 7.0 lakh tonnes nitrogen, 8.4 lakh tonnes phosphorous and 21 lakh tonnes potassium are supplied. About 25% of nitrogen, 25% phosphorus, 50% of sulphur and 75% potassium uptake by cereal crops are retained in residues, making the valuable sources of nutrients. If considering 50% crop residue is utilized as animal feed, the rest can be recycled. The various applications of residues other than animal feed are used in composting, thatching for rural homes and fuel for domestic and industrial use.
But, the current practice of burning crop residues in fields is one of the most significant activities of global biomass burning bio fuels and contributes substantially to air pollution. After harvesting, the waste straw is frequently burned in the open regions with insufficient time before planting the next crop. Most of the stubble burning takes place over three weeks in October-November, releasing particulates and smog-forming carbon monoxide and nitrogen oxide, which drift from the fields over almost the entire Indo-Gangetic plain.
This pollution contributes around 12-60 per cent of particulate concentrations depending on the generation of other pollutants in different locations, winds, temperature and other local factors. Farmers themselves are doubly harmed, by the local air pollution caused, and by the loss of soil nutrients such as nitrogen, potassium, phosphorous and sulphur due to the burning. However, in contrast to closed burning, the open burning of straw is an uncontrolled combustion process in which the products of burning are emitted into the atmosphere, such as CO2, CO, CH4, PM, NOx, and SO2, influencing both the local air quality and global climate.
Punjab and Haryana alone contribute 48% of this total and is subject to open field burning which contributed about 20% to Delhi’s pollution due to heavy pollutant transportation in the atmosphere. Complete burning of the rice and wheat straw resulted in 100, 20.1, 19.8 and 80.2 % and 100, 22.2, 21.8 and 75.0 % losses of N, P, K and S respectively.
The burning of straw (crop residue) is not desirable. But large-scale burning of crop straw of rice and wheat system in Punjab, Haryana and western Uttar Pradesh has become a matter of serious concern not only for greenhouse gas emission but also for problems of pollution, health hazards and loss of nutrients. There is a need to validate the emission estimates experimentally and the associated uncertainty in the estimates.
The residues can be put to various productive usage such as incorporation in the fields, bioenergy etc. This is possible only if residues are collected and managed properly. Awareness must be created among farming communities about the negative impact of crop biomass burning and importance of crop residues incorporation in soil for maintaining sustainable agricultural productivity.
Farmers opt for straw burning and clear the field from straw and stubble after the harvest of preceding crop because there is shortage of time period between harvesting of preceding crop and sowing of succeeding crop. Thus, for timely agronomic practices residue burning becomes necessary practice. Residue burning is a more economical and inexpensive because sufficient labour force is required for manual removal of residues.
Rice straw burning has been linked to increased asthma attack in children and even in adults. Due to smoke and soot suspended in the air, affected people are prone to diseases like cough, cold, T.B., cancer, irritation in eyes, allergies, choking of lungs and problems in breathing and other respiratory problems.
The waste types that can be disposed of by burning without an environmental permit are restricted to vegetation, untreated wood and untreated timber, logs and branches from fallen or felled trees, untreated timber from fence mending, hedge trimmings, crops and vegetation and leaves and bark. The crop residue management can have a significant impact on C and N levels and the C/N ratio, which directly affects top soil layer due to the straw burning. Residue retention significantly increases the amount of mineralizable C and N in the soil as compared to situation where the residue is repeatedly burnt.
This also increases the activity of rapid decomposition and ensures turnover of organic matter, resulting in greater amount of available nutrient over times, conserving moisture and improve soil health and controling atmospheric pollution. There are some advantages of burning straw like it quickly clears the field and is cheap method for next sowing. It kills weeds, including those resistant to herbicide, kills slugs and other pests and reduces nitrogen tie-up. Some harmful effects are loss of nutrients, bad impact on soil microbes and fauna, increase in erosion (wind and water), loss of carbon, reduction in soil structure (soil aggregate stability) and increase in acidity over the time.