The Aman season is almost going to end by the last week of November. Only some of the late planted varieties like BR22, BR23 and BRRI dhan46 will be harvest by the middle of the next month (15 December).
To be hurry to establish the upcoming Rabi (winter) crops some of the farmers might burn the stubbles (leftover straw in the field) of the previous Aman crop. A general conception goes like this: A crop cannot be established properly in the stubbles. In fact, stubble is not a problem for the leguminous crops like Lathyrus, peas etc. even under zero tillage condition. Even a rice crop could be established in the stubbles of the previous crops. But some crops like wheat, millet onion or garlic is grown in the traditional way, needs cleaning of the rubbishes to prepare the appropriate tilth.
The burning of rice stubbles or straw was a normal practice when deepwater rice (DWR) was cultivated throughout the country. Now the coverage of DWR rice has reduced to some small pocket areas of the country and the practice of straw-burning is not much noteworthy. But burning in some emergency cases is prescribed by the Department of Agricultural Extension (DAE) to get rid of the pests and pathogens like Brown Plant Hopper for rice, Blast for wheat etc.
The famous IRRI scientists Felix Ponnamperuma in the early 1980s was in favour of open-field burning of rice straw. He said that the practice was the effective way of removing large volume of biomass and to control the weeds and pests. Even many of the present day scientists of the developed countries believe that the process of straw burning is an easy way to destroy the roots of pest and pathogens. Recently, many farmers of the developing countries like India, the Philippines, and Thailand are getting more interested to burn their straw or stubbles in the field as they do not keep any cattle to till their land. They now till their land by a power tiller or a tractor. The crops are no more cut at the base as they do not have to thatch there house with rice straw. The poor people are supposed to collect the rice stubbles to use as fuel. But they are kept away from the rich farmers’ field nowadays. The farmers know that the incorporation of stubble is good for the soil. As the job is tedious and need some financial involvement, some farmers prefer to burn the stubbles considering at least they would get some benefit from the ashes. Even, the idea of clean cultivation works in their mind as suggested by the extension agents of the earlier days. However, still the open-field burning of rice straw is not widely practiced in Bangladesh. But the farmers’ might consider the practice for their convenience as the country is approaching towards mechanization. Some of the developing countries like the Philippines burn the rice stubbles in the field. In India (northwestern part of the country) the farmers nowadays are using combine harvester to harvest their rice crop. For the sake of saving the turnaround time in between the Kharif (summer) and the Rabi crop season they have to go for land preparation just by burning the stubbles. Lately farmers from the adjacent states are blamed of causing smog over the Indian capital, Delhi. The farmers Malaysia are doing the same practice. It might happen anywhere in any of the rice growing countries. The practice is profitable in terms of farm practices but detrimental in terms of environment and health perspectives. The straw or stubble burning is helpful to increase the cropping intensity. In contrast, it directly involve in reducing nutrient from the field. As per IRRI, the rice straw burning is liable not only to nutrient loss but also to soil organic matter depletion and reduction of soil biota. An estimate says, 40% of Nitrogen, 80-85% of Potash, 30-35% of Phosphorous, 40-50% of Sulpher left in the stubble or straw after harvest. All the nitrogen remained in the straw was lost in the air with burning. Potash and Phosphorous are lost around 20-25% in the same way. The loss of Sulpher varies from 5-60%. The loss of these elements can be minimized to some extent if the straw is burnt no sooner than harvest. But there is no way to reduce the loss of Nitrogen. The similar loss is also recorded from wheat straw. The burning of wheat straw resulted almost 100 % loss of nitrogen, 70-90% loss of Sulpher and 20-40% loss of phosphorous and potassium in the USA. In addition to that, IRRI referred to the reports of Oanh et al., 2011 and Jenkins et al., 2003 that the open-field burning of rice straw is considered one of the factors of polluting the environment as one kg of the straw has the potentiality to produce 4.1g of Methane, and 0.019-0.057g of nitrous oxide. The open-burning is a process of incomplete combustion good for emitting a huge amount of pollutants like Sulpher dioxide, Nitric oxide and Hydrochloride acid, including toxics gases like carbon monoxides, dioxins and furans volatile organic compounds, carcinogenic polycyclic aromatic compounds in nature. It is thought that the atmospheric brown cloud is responsible for poor air quality, atmospheric visibility and the climate is formed due the burning of agricultural wastages. IRRI also cited the reports of Chang et al., and 2013, Engling et al., 2009 that rice straw was the source of aerosol particles affecting the air quality, and the radiation budget of the earth. IRRI also mentioned that the particles were hazardous to human health also. So in many countries the open-field burning is brought under the legal bindings. More so, rice has a significant contribution in emitting greenhouse gases. Rice straw contributes 0.05%, 0.18% and 0.56% of the total amount of greenhouse gas emissions in India, Thailand and the Philippines, respectively (Gadde, et al., 2009). It’s a great concern to the scientists and environmentalists.
So what would be the alternative method to the open-field straw burning? The better option is to incorporate the stubbles or straw into the soil. But the incorporation of straw under an irrigated condition would take a longer time to decompose and not convenient to the farmer who wanted to take the advantage of short turn-around time in between the two cropping seasons. In addition to that the anaerobic decomposition under the submerged condition enhances the production of methane and nitrous oxide (greenhouse gases). The amount of carbon dioxide equivalent (3, 500kg/ha) emitted as a greenhouse gas from this kind of straw incorporated field is 1.5 times higher than that of the field where straw is removed. The aerobic decomposition is better and faster. So it is better to avoid incorporation of the stubbles into the soil under submerged condition. The recent practice of spraying with Trichoderma (a kind of fungi) spore could be a solution to enhance faster decomposition. But it needs a more research to recommend in the country like us. The other way is to collect the stubbles to produce cattle feed-stuffs or energy under the care of government or public-private interventions. In those cases, the system might not be economic as the straws or stubbles have to carry to the point of processing. Even the processing industry might emit significantly more (15 times for India, 10 times for Thailand and 8 times for the Philippines) greenhouse gases as compared to that of the in-situ burning in the field (Gedde et al., 2009: see above). The preparation of compost from that straw through aerobic decomposition method may be an alternative approach. However, those specific straw-cleaned fields must be replenished with the compost or by any other organic fertiliser before the next growing season starts. Unless the field might lose not only the organic matter but also the other essential elements over the time.
The conversion of the removed straw or stubbles into “biochar” could be an alternative but an efficient way. Biochar is a kind of charcoal produced burning rice husks or straw almost under anaerobic conditions to keep the carbon intact. Just the reverse condition of open field burning where straw is burnt in the presence of oxygen to produce a lot of carbon dioxide. Thus biochar has limited opportunity to contribute to the greenhouse gas as carbon dioxide. It helps the soil to accommodate more amounts of nutrient and water with its large surface area and pore volume. Even biochar could act as an absorbent of pesticide or pollutants in its surface area to keep the nearby water source safe by restricting the leaching loss of the pollutants.
Bangladesh is producing around 60 million metric tonnes (of rice straw. Straw burning in the open field is a sporadic practice in Bangladesh, I mentioned earlier. But with the development of the economy, it might be a significant problem in the near future. Nowadays a considerable amount of straw is still used as fuel for cooking stoves, mulching in the potato fields and as cattle feed. The rest are allowed to compose in the field but may not be flowing appropriate procedure. Therefore, no matter how it is used, rice straw has a significant contribution in the greenhouse gas emission in environment. On the other hand, there is a huge potentiality of rice straw to be used as a raw material for the preparation of compost and methane as well under controlled condition to use as a fuel in the rural area. Then there will be no need to burn the straw in the field or allowed to decompose anaerobically and the rice agriculture cannot be blamed for the emission of greenhouse gases, unilaterally. So it is better to find a mechanism to recycle the agricultural wastes for the purpose of agricultural production only without any harm to the ecology. Unfortunately, we do not have any of the activities like this in Bangladesh. But in the Philippines, there is some farmers’ organisation working to stop burning of rice straw through a festival called Dayami Festival. Some are campaigning for the preparation charcoal and its use. Phil Rice is acting as the key-advisor behind this movement through the scientific logic of the gains and losses of the rice straw burning. I think still we have the scope to initiate debate on the issue among the scientists, environmentalists and philanthropists the kind supervision of the government.
The writer is the Director General (retired), Bangladesh Rice Research Institute, Gazipur