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BS Dhillon
VC, PAU, Ludhiana
Punjab agriculture is facing the challenges of conservation of natural resources and environment. Paddy straw management has emerged as an important issue therein. Unlike other sources of air pollution, the paddy straw-burning events are compressed into a short span of time, causing an intense impact. Paddy straw management, thus, becomes a burning problem and needs to be tackled by all-round efforts by all stakeholders.
Several research institutions, including the PAU, have been alive to the issue. The PAU has adhered to the multiple-option mantra. The options include the use of paddy straw for biogas and biochar production, mulching and mushroom cultivation. The university has also developed machinery for in situ management, ie in the field itself, employing both surface retention and soil incorporation approaches, and is working on in situ biodegradation with microbes.
Scientific strategy
A paddy straw management strategy was rolled out after deliberations among the governments of the Union and states (Punjab, Haryana, Uttar Pradesh, Rajasthan, Delhi) in which research institutions, including the Indian Council of Agricultural Research, were also involved. Scientific information obtained from more than a decade of research, practical experience, infrastructure and resources were considered and a strategy based on in situ surface retention and soil incorporation, besides support to baling the straw for demand-driven supply to power plants and other industries, was finalised. Thus, the strategy has a sound footing and is suitable for immediate adoption.
The PAU held a workshop on crop residue management on September 6 to keep track of new developments, including the bio-CNG option. The consensus was that managing 20 million tonnes of paddy straw in Punjab in just about three weeks to enable sowing of the next crop is a gigantic task for which all options should be explored. In situ management has an edge as removing the straw is costly. It was agreed that work on the other options, including bio-CNG, needs to be continued and relative economics worked out under different scenarios.
Some unfounded apprehensions are now being raised about the strategy. It seems to be an attempt to sabotage the campaign on paddy straw management. A news item entitled "Ploughing straw back won't do, say experts" (The Tribune dated October 3) carries statements like "government-sponsored in situ paddy straw management is a short-sighted approach and is sure to deplete Punjab's precarious soil health" and "this technique approved and adopted in Punjab and other paddy-growing states may result in 'invisible' soil pollution which may impact productivity and sustainability".
In situ residue management
Paddy straw management options being promoted are not only scientifically sound and environmentally positive, but also the most economical at present.
The in situ options include both incorporation of paddy straw in the soil or its retention on the surface. To retain straw on surface, harvesters fitted with straw management systems and Happy Seeders are used. Soil incorporation is pursued with rotavators through wet mixing or mulchers and mouldboard plough. This option is particularly relevant for potato, pea and other vegetable crop sowing. In this case, the farmer has no other option because of the time constraint.
In situ residue management is of significance in our intensive cropping system, where about 70 per cent of the produce moves out of the state. It provides the most convenient mode of recycling of organic carbon and nutrients, thereby positively impacting the soil health and crop performance. Improved soil organic carbon is the most important soil health parameter.
Surface retention as a mulch is an integral component of conservation agriculture. It helps in moisture conservation, weed management, soil temperature regime moderation in favour of crops and soil microorganisms. Further, minimised ploughing reduces fossil fuel use and emission of greenhouse gases. Retaining crop residue in the field is its integral component. It has been adopted in 180 million ha worldwide.
Methane emission has been cited as the flip side of in situ management. Our experiments show that there is no significant enhancement of methane emission from wheat field with paddy residue managed in situ, over that receiving only inorganic fertiliser with no crop residues. Since ages, a large area has been under forests where leaves and other biomass residues have been decomposing on the soil surface.
In the perspective of environmental safety of the region, the union and state governments and research institutions have shaped the programme after a year of wide-ranging deliberations. The government has also made significant financial assistance available.
For straw management, the PAU has also worked on another front: the development of high-yielding varieties namely PR 121, PR 126 and PB 1509 which have lesser biomass load.
The bio-CNG option
The bio-CNG option is not new. The PAU-designed and piloted paddy straw-based biogas plants produce biogas with 60 per cent methane. The bio-CNG technology, however, envisages purification of biogas with more than 90 per cent methane. bio-CNG has potential, but the infrastructure for baling, transportation, pre-treatment, leak-proof digestion, purification of biogas to produce bio-CNG, bottling and dispensing units are non-existent. Further, there is need to work out combinations of feed material, their pretreatments and size reduction and determine the C-N ratio for optimal bio-CNG production. To cite one component of resources required for bio-CNG production, low density paddy straw has to be baled in the field and baling per se costs two times that of the Happy Seeder option. The compost coming out of bio-CNG plant is expected to be costlier than the equally effective FYM and rice straw compost.
When it comes to biofuels, bio-CNG is one of the options along with drop-in-fuel, bio-hydrogen, bio-methanol, di-methyl ether etc. Indian Oil Corporation Limited is installing bio-CNG production plants whereas Hindustan Petroleum Corporation Limited is setting up bio-ethanol plants in Punjab. Evidently, all options are being explored.
As per the National Bio Fuels Policy notified by the Ministry of Petroleum and Natural Gas in June 2018, the Task Force on Waste to Energy has estimated that 62 MMT of municipal solid waste annually generated in the country, and this waste has huge potential for biogas generation. Producing bio-CNG from such sources, going totally waste at the moment with little scope of being ploughed back into the fields for nutrient cycling, may be the priority.
The campaign for paddy straw management has entered a decisive phase. So, efforts must be aimed at seeking logical consent and positive action by all stakeholders. Any action which creates confusion among the stakeholders at this stage is unwelcome. We must not lose focus as the stakes are too high and we also know what to do. Deviations and distractions in this critical phase can prove disastrous.
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