Crop residue burning in India
S. Bhuvaneshwari, Hiroshan Hettiarachchi and Jay N. Meegoda
The agricultural industry plays a major role in the overall economic growth of the world. However, there is limited discussion on the management of agricultural waste in the published literature. It could be related to the fact that agriculture industry is not regulated as the municipal solid waste (MSW). The MSW is mainly governed by public entities such as municipalities and hence the generation and management data are collected, recorded, and analyzed in the public domain. Agricultural waste is predominantly handled by the owners of the agricultural land which is predominantly in the private sector, with little public sector involvement.
Waste materials derived from various agricultural operations are defined as agricultural wastes. As per the United Nations, agricultural waste usually includes manure and other wastes from farms, poultry houses and slaughterhouses; harvest waste; fertilizer run-off from fields; pesticides that enter water, air or soils; salt and silt drained from fields. According to the world energy council, in addition to all above, agricultural waste can also comprise of spoiled food waste. The harvest waste, which is more popularly termed as crop residue can contain both the field residues that are left in an agricultural field or orchard after the crop has been harvested and the process residues that are left after the crop is processed into a usable resource. Stalks and stubble (stems), leaves, and seed pods are some common examples for field residues. Sugarcane bagasse and molasses are some good examples for process residue.
According to the Indian Ministry of New and Renewable Energy (MNRE), India generates on an average 500 Million tons (Mt here after) of crop residue per year. The same report shows that a majority of this crop residue is in fact used as fodder, fuel for other domestic and industrial purposes. However, there is still a surplus of 140 Mt out of which 92 Mt is burned each year. The table below compares the agricultural waste generated by selected Asian countries in Mt/year. It is also interesting to note that the portion burnt as agricultural waste in India, in volume is much larger than the entire production of agricultural waste in other countries in the region.
Agricultural waste generation in India compared to other select nations in the same region:
Country Agricultural Waste Generated (million tons/year)
Waste from the agricultural industry can be beneficially utilized in various agro-based applications and other industrial processing. However, the cost of collection, processing and transportation can be much higher than the revenue from the beneficial use of such waste. The classic example of how economic reasons have prevented attaining the sustainable use of agricultural waste and led to environmental chaos in India, is the focus of this manuscript. This topic is important to the wider audience beyond India for two reasons: first, crop residues are an important constituent of agricultural waste that can actually be used for the benefit of the society due to its organic composition. The other important reason is that the volumes of crop residue, with unsustainable management practices create high adverse environmental impacts that go far beyond India. Specifically, India is the second largest producer of rice and wheat in the world, two crops that usually produce large volume of residue.
Crop Residue: Composition and Decomposing Mechanisms
General types of crop residues produced by the main cereal crops and sugar cane are a natural resource that traditionally contributed to the soil stability and fertility through ploughing directly into the soil, or by composting. Good management of field residues can also increase irrigation efficiency and erosion control. However, the mass scale and rapid pace of crop production have imposed economic and practical limitations to such traditional sustainable practices. It is a common practice in many of the developing countries, especially in Asia to burn the surplus crop residue. While burning creates environmental issues, ploughing field residue into the ground for millions of hectares within a short time requires new and expensive technical assistance.
Crop residues produced by major crops:
Rice Husk, bran
Wheat Bran, straw
Maize Stover, husk, skins
Sugarcane Sugarcane tops, bagasse, molasses
The crop residues generated due to agricultural activities are exploited by several countries in different ways. The possible options include its use as animal feed, composting, production of bio-energy and deployment in other extended agricultural activities such as mushroom cultivation. According to Lohan et al., many countries such as China, Indonesia, Nepal, Thailand, Malaysia, Japan, Nigeria and Philippines utilize their crop residues to generate bio energy and compost. The management of agricultural waste using microbes could also be an excellent option for the detoxification of the soil and mitigation of environmental pollution. Microbial populations degrade the complex substances present in the biomass to simpler ones that can be reused or recycled through environmental processes. The techniques adopted can either be aerobic or anaerobic, depending on the nature of bacteria, fungi or algae involved in the degradation. The microbial degradation techniques reduce the soil toxicity, promote plant growth through provision of growth accelerating metabolites and provide plant nutrients through sequestration from soil. Thus, the bioremediation of the agricultural waste could be effectively carried out by anaerobic and aerobic processes, through some of the associated techniques like composting, vermicomposting, biogas production, bio-methanation and bio pile farming.
Anaerobic digesters can turn biomass into biogas, a renewable energy source, containing approximately 50% methane, and a final solid residue usable as a fertilizer rich in nutrients. Anaerobic digestion is a promising valorization technology due to its ability to convert almost all sources of biomass, including different types of organic waste, slurry and manure into highly energetic biogas. It is an effective and environmentally attractive pathway and promising option for recycling agricultural by-products because these contain high percentage of biodegradable materials. Anaerobic digestion involves microbial conversion in aqueous environment and could be processed without any pretreatment. The past governmental interventions mainly focus on the use of crop residue as a source of energy: in the form of biogas as well as a supplement for thermal power plants. Biogas generated through anaerobic biodegradation of municipal solid waste and agricultural waste, contains around 40–70% methane, this is usually augmented to natural gas quality with a methane content of 70–99%. Further it can be injected into the natural gas grid or used as fuel for transportation. The methane production potential of wheat straw ranges from 0.145 m3/kg to 0.390 m3/kg for dry organic mass fed to the digester. Rice straw has a methane production potential ranging from 0.241 m3/kg to 0.367 m3/kg. Deublin and Steinhauser reported a biogas production potential of around 0.550 to 0.620 m3/kg for rice straw biomass with around 50% methane content. Similarly, the reported biochemical methane production from sugarcane biomass varies from 0.266–0.314 m3/kg .
Crop Residue Burning in India: Statistics
India, with 17% of the world population and an agrarian background, generates large volumes of food grains such as rice and wheat for domestic consumption as well as for export. Of the various crops grown, majority crop residue of rice, wheat and sugarcane are burned. These crops have large returns on investment making it highly impossible for the farmers to find alternative crops, which produces lower crop residues. National policy for management of crop residues (NPMCR) provides the details of the state-wise statistics of crop residue generated and excess residue burned. Based on NPMCR, it is evident that the generation of crop residues is highest in the state of Uttar Pradesh (60 Mt) followed by the other states Punjab (51 Mt) and Maharashtra (46 Mt) with a grand total of 500 Mt per year out of which 92 Mt is burned. Rice and wheat contribute nearly 70% of the crop residues. Out of the total waste generated, the surplus residue refers to the waste that remains after utilizing the residue for various other purposes. A part of the surplus waste is burned, and the remains are left in the field.
Based on Jain et al., and the Intergovernmental Panel on Climate Change (IPCC), the highest contribution to the amount of residue burned on the farm is from the states of Uttar Pradesh, followed by Punjab and Haryana. According to IPCC, over 25% of the total crop residues were burnt on the farm. Jain et al. also reported that the fraction of crop residue burned ranged from 8–80% for paddy waste across all states. Among different crop residue, major contribution was 43% of rice, followed by wheat to around 21%, sugarcane to 19% and oilseed crops around 5%. The Ministry of Agriculture attributes the increase in the on-farm crop residue burning to the shortage of human labor. Jitendra et al. reported that 80% of the crop residue burning took place during the post-harvest period of April-May and November-December. The reason behind this is attributed to the crop patterns used to ensure higher economic returns which leave limited time between two consecutive crop cultivations. Some farmers even resort to a cycle of three crops a year with a short gap between harvesting and sowing.
Adverse Impact of Crop Residue Burning on the Environment
The burning of crop residues generates numerous environmental problems. The main adverse effects of crop residue burning include the emission of greenhouse gases (GHGs) that contributes to the global warming, increased levels of particulate matter (PM) and smog that cause health hazards, loss of biodiversity of agricultural lands, and the deterioration of soil fertility. The PM emitted from burning of crop residues in Delhi is 17 times that from all other sources such as vehicle emissions, garbage burning and industries. As such the residue burning in the northwest part of India contributes to about 20% of organic carbon and elemental carbon towards the overall national budget of emission from agricultural waste burning. Crop burning increases the PM in the atmosphere and contributes significantly to climate change. One contributor to global climate change is the release of fine black and also brown carbon (primary and secondary) that contributes to the change in light absorption. Usually PM in the air is categorized as PM2.5 and PM10 based on the aerodynamic diameter and chemical composition (PM2.5 or fine, particulate matter with aerodynamic diameter <2.5 µm and PM10 or coarse, particulate matter with aerodynamic diameter <10 µm). Lightweight particulate matter can stay suspended in the air for a longer time and can travel a longer distance with the wind. The effect of particulate matter gets worsened by the weather conditions, as the particles are lightweight, stay in air for a longer time and causes smog. The annual contribution of PM2.5 due to burning of paddy residue in the Patiala district of Punjab was estimated to be around 60 to 390 mg/m3. During the period of October, smoke from crop residue burning in Punjab and Haryana blows across northern India and Pakistan. With the onset of cooler weather in November, the smoke, mixed with fog, dust, and industrial pollution, forms a thick haze. Wind usually helps disperse air pollution, and the lack of it, worsens the problem for several days as was the case during November 2017. Several major cities—including Lahore, New Delhi, Lucknow, and Kanpur—faced elevated levels of pollution.
The WHO standard for permissible levels of PM2.5 in the air is 10 µg/m3, and according to the India’s National Ambient Air Quality Standard, the permissible level for PM2.5 is set at 40 µg/m3. However, the National Capital territory of Delhi recorded a mean value of 98 µg/m3, which is at least twice more than the Indian standard and ten times higher than the WHO standard. In addition to the emission of gases and aerosols, there is continuous deterioration of soil fertility due to burning. Heat from burning of residues raises the soil temperature and causes depletion of the bacterial and fungal population. The residue burning increases the subsoil temperatures to nearly 33.8–42.2 °C at 10 mm depth, and long-term effects can even reach up to 15 cm of the top soil. Frequent burning reduces nitrogen and carbon potential of the soil and kills the micro flora and fauna beneficial to the soil, and further removes the large portion of the organic matter. With crop burning the carbon-nitrogen equilibrium of the soil is completely lost. According to NPMCR, it is reported that burning of one ton of straw accounts for the loss of entire amount of organic carbon, 5.5 kg of nitrogen, 2.3 kg of phosphorous, 25 kg of potassium and 1.2 kg of sulphur. On an average crop residue of different crops contain approximately 80% of nitrogen (N), 25% of phosphorus (P), 50% of sulphur (S) and 20% of potassium (K). If the crop residue is retained in the soil itself, it can enrich the soil with C, N, P and K as well.
Stringent measures to mitigate crop burning and further to regulate crop waste management require involvement of the appropriate Government agencies. Several attempts were made by the Government of India to introduce and educate the agricultural community about the best practices of agricultural waste management through Government-initiated projects. Numerous forums and proposals were also formulated by environmentalists and Government officials to curb crop residue burning and to promote the usage of alternative sustainable management methods. Some of the laws that are in operation pertaining to crop residue burning are: The Section 144 of the Civil Procedure Code (CPC) to ban burning of paddy; The Air Prevention and Control of Pollution Act, 1981; The Environment Protection Act, 1986; The National Tribunal Act, 1995; and The National Environment Appellate Authority Act, 1997. Particularly, in the states of Rajasthan, Uttar Pradesh, Haryana and Punjab stringent measures have been taken by the National Green Tribunal (NGT) to limit the crop residue burning.
Initiative towards Biogas Plants
Biogas plants are a progressive step taken by the Government of India to curb crop burning and to prevent pollution. The biogas technologies have been in vogue since the 1970s and several programs are run by the National Biogas and Manure Management Program-off grid biogas power generation program to provide renewable energy for electricity generation, cooking and lighting purpose. These programs were implemented by the Government under the “waste to energy mission”. This is also a part of India’s action plan on climate change. Large scale industrial biogas plants generate 5000 m3 of bio gas per day. Nearly 400 off-grid biogas power plants have been set up with a power generation capacity of 5.5 MW. Currently there are 56 biogas-based power plants operational in India, the majority of them are in the states of Maharashtra, Kerala and Karnataka. Small family type biogas plants have also been introduced in the rural areas, which can generate 1 to 10 m3 biogas per day. Nearly five million family biogas plants have been installed by MNRE under the biogas development program.
Recent developments in technology have opened the possibility of using paddy straw and other crop residue other than dung and vegetable waste for biogas generation in an integrated approach. Urja reported the setting up of a biogas plant combined with commercial farms and processing units that was set up in Fazilka, Punjab as a novel initiative towards green energy. This plant generates biogas using rice straw through bio-methanation technology. The biogas plant having been certified by the premier academic institutes like the Indian Institute of Technology, Delhi and Punjab Agricultural University, generates around 4000 m3 of biogas from 10 tons of agricultural residue. In another biogas enterprise, a 12 MW rice-straw power plant can consume 120,000 tons of stubble collected from nearly 15,000 farmers. These private enterprises generated around 700,000 jobs for the farming population.
Sustainable Management Practices for Crop Residue
Composting: Composting is not a new concept to India. While small scale backyard composting and making compost from organic material in MSW is common, there is no information in the literature to prove that it is also the case for the agriculture industry in India. The high organic content in crop residue makes it an ideal raw material for compost similar to animal manure and food waste. Composting is the natural process of rotting or decomposition of organic matter by micro-organisms under controlled conditions. As a rich source of organic matter, compost plays an important role in sustaining soil fertility and thereby helping to achieve sustainable agricultural productivity.
Production of Biochar: As a measure for controlling GHG emissions, the agricultural research community is constantly looking for ways to effectively enhance natural rates of carbon sequestration in the soil. This has made an increased interest in applying charcoal, black carbon and biochar as soil amendment to stabilize soil organic content. Biochar is a fine-grained carbon rich porous product obtained from the thermo-chemical conversion called the pyrolysis at low temperatures in an oxygen free environment. It is a mix of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulphur (S) and ash in different proportions. When amended to soil, highly porous nature of the biochar helps in improved water retention and increased soil surface area. It mainly interacts with the soil matrix, soil microbes, and plant roots, helps in nutrient retention and sets off a wide range of biogeochemical processes. Many researchers have reported an increase in pH, increase in earthworm population and decreased fertilizer usage. Specifically, biochar is used in various application such as the water treatment, construction industry, food industry, cosmetic industry, metallurgy, treatment of waste water and many other chemical applications. In India currently, the biochar application is limited and mainly seen in villages and small towns. Based on its wide applicability, it could be more valuable to promote biochar method in India.
In-Situ Management with Mechanical Intensification: In-situ application of the crop residue is adopted by many farmers as it is a natural process. This method also imparts certain benefits to the soil. There are two main way of conducting field applications, but both methods involve leaving crop residue on the farmland after harvesting. How they differ is based on what happens with tillage in the next season. In the first method, planting in the next season is carried out without tillage or with less tillage and in the other method crop residue is incorporated into the soil by mechanical means during tillage. While in-situ management of crop residues can offer long-term cost savings on equipment and labor, both methods need special (new) equipment, e.g., machinery for crop residue incorporation into soils or no-till seeing equipment. This method has many advantages for the soil such as cooling effect, increased moisture, source of carbon, and erosion protection. However, this method also finds some negative implications for example, microbial infestation, formation of phytotoxins and nutrient immobilization. This results in a reduced yield which may warrant additional use of agricultural chemicals. For improving the soil organic matter, crop residue is incorporated into the soil by plowing. Adding nitrogen fertilizers while plowing at a depth of 20–30 cm can enrich the soil with humus and prevent nitrogen depression.
The smog experienced by millions of people in the country each year clearly suggests that the crop burning issue has not been sufficiently addressed by any of the previous interventions. The question that needs to be asked is “why not?” The answers to this question will help identify better alternatives for implementation. There are three key policy-related and/or functionality issues related crop residue management that need to be taken into consideration for any future interventions. They are: (1) The need to think of a self-running mechanism, rather than isolated ones; (2) Empowering stakeholders; and (3) Avoiding sectorial thinking, and if possible, lean towards nexus thinking. Individual small-scale farmers do not have the capacity to establish a long-lasting solution. The local government, the municipality, or a farmers’ association should fill this void and launch community programs to assist such as equipment rentals, waste transportation, and possible linking of waste to where it can be needed as raw materials. Educating the farming community and other related stakeholders is crucially important to bring them out of generational thinking that they are used to that the waste management is not their responsibility. It is even more important to empower them with technical as well as socioeconomic assistance. They should be educated about the advantage of reduced agrochemical cost due to the utilization of compost and the extra revenue they can receive through other type of recovery programs such as energy production. The last, but perhaps the most important piece of the puzzle is the sectorial thinking of the curtailing of the crop residue burning issues only to agricultural sector and energy, even though it touches upon many other sectors, such as environment, economy, social aspects, and education. This sectorial thinking can be overcome by embracing nexus thinking, which promotes a higher-level integration that goes beyond the disciplinary boundaries.