Punjab farmers burn straw after harvest. It is time to exploit the potential of this agro-waste
Not a waste until wasted
Plumes of smoke arising from the fields is a common sight in Punjab during rice harvesting season. In the months of October-November it almost asphyxiates anyone who ventures out of house, be it a village or city. Reason: paddy stubble burning.
Burning of rice straw remains emits trace gases like carbon dioxide, meth ane, carbon monoxide, nitrogen oxide, sulphur oxide and large amount of particulate matters, which adversely affect human health as well as the environment. Last year, the magnitude of stubble burning was so high that it received international attention. The National Aeronautics and Space Administration (NASA) released a satellite image showing large number of fires across millions of hectares of agriculture fields in Punjab.
Farmers in the state complain that rice straw is a huge problem for them because they follow mechanised agriculture. “When you harvest rice by a combine harvester, it leaves a significant length of straw on the field,” says Rajinder Kumar Sama, a farmer from Abohar district. So crop residues in combine-harvested fields are burnt. Besides, explains Sarabjit Singh from Ghanaour village in Patiala district, both wheat and rice are long-duration crops. With a short period available between rice harvesting and wheat plantation, burning is the easiest and quickest way to get rid of rice straw. Singh adds that increasing labour cost is another reason farmers prefer setting fire to their vast swathes of paddy fields after they have harvested the crop.
After China, India is the world’s largest producer of paddy. India produces 98 million tonnes of paddy with roughly 130 million tonnes of straw. Of this, about half is used as animal fodder. The rest is mostly burned in the fields, though a small amount is also consumed by brick kilns and paper and packaging industry. Despite such huge amou nts of rice straw generation, farmers in the country are yet to realise the potential of this agro-waste in terms of manure and as a profitable raw material for various industries.
Where’s the profit?
Sama says on an average one gets about two tonnes of rice straw per acre (0.4 hectare). “The combine owner or operator charges an additional Rs 850 per acre for harvesting that leftover portion which is of no use to us,” says Sama. It cannot be even fed to the cattle. Blades of fodder cutter easily get blunt by the thick and sharp straw.
Sama adds that in his area only brick kilns buy rice straw, but they are limited. Besides, selling rice straw to kilns is not profitable. “They pay us Rs 600-Rs 700 a tonne, which means we get Rs 1,200-Rs 1,400 per acre. Now subtract Rs 850 rental cost of the combine harvester and transportation cost of Rs 300, which is borne by the farmer, from the amount. All we get is between Rs 50 and Rs 250. Where is the profit?”
Daljeet Singh, another farmer from Patiala says, “Of late, power companies are approaching us to buy rice straw. They are offering between Rs 500 and Rs 700 a tonne. Last year, the paper and packaging industry had bought straw for Rs 1,400-Rs 1,700 a tonne.” That was a one-off deal though. In the absence of assured returns, farmers find stubble burning an economic way of managing the agro-waste.
Back in soil
Every year about 12 million tonnes of rice straw is burned in Punjab. Accor ding to O P Rupela, former soil microbiologist at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), this leads to nutrient loss from the soil which is equivalent to US $18 million worth of urea. Rupela, along with scientists from Punjab Agricultural University (PAU), has developed a simple and rapid composting technique to convert huge piles of rice straw into organically rich soil.
|Rice straw compost can
increase crop yield by
4-9%. When applied as
mulch it helps maintain
|O P Rupela,
former soil microbiologist, ICRISAT
|We pay Rs 900 a tonne for non-basmati rice straw and Rs 1,500 for basmati rice straw|
|S Y Mehta, head,
Punjab Biomass Power Ltd
|Rice straw to power ...
Agents appointed by the company approach farmers to harvest their rice straw. The harvesting is followed by cutting, baling and transporting the bales to company depots where it is stored. The plant, set up at the cost of Rs 80 crore, is based on the simple principle of combustion. It has a furnace, a boiler and a steam turbine. There are also a set of machines that cut open the bales and shred the straw into small pieces to ensure uniform combustion. The shredded straw is then fed into the boiler using a conveyor belt. A conventional steam turbine then generates electricity. An electrostatic precipitator to collect ash ensures minimal atmospheric pollution. Although there will be some emissions from combustion, the project is eco-friendly and aims to earn substantial carbon credits.
What about the ash produced by the plant every day? S Y Mehta, head of Punjab Biomass Power Limited (PBPL), says we are trying our best to find ways of utilising the ash by selling it for production of bricks and other construction materials. For the time being a contractor has been hired who dumps the ash in landfills or depressions created at brick kilns.
Apart from combustion, Mehta informs, there are other technologies to produce power from rice straw, such as anaerobic digestion (biogas), pyrolysis (bio-oil) and gasification (sygas). The last two are under research and development as they are not economically viable, Mehta adds. PBPL has signed an MoU with the Punjab State Power Corporation for selling electricity at Rs 5.18 per unit. The other rice straw plants which are in the inception stage will supply electricity at Rs 5.83 per unit. PBPL now plans to introduce a rice straw power plant in Bihar.
... and to compost
Take dry rice straw bundled in sizes of 5 to 10 kg and soak them in solution prepared by mixing one milliliter of fungal (Aspergillus awamori) spore suspension and one gramme of urea with water for every one litre of solution. The dry straw bundle will soak up to one-and-a-half times its weight of the solution. For instance, a 5 kg bundle will use up 7.5 to 8 litres of the solution. The wet straw bundle is then drained over a polythene sheet spread over a sloping surface for about 20 minutes. The drained solution can be re-collected and re-used.
The well-drained bundles are then sprinkled with powdered rock phosphate and placed layer by layer over dried twigs to form a heap. The gap between soil and the straw bundles will help in aeration. The heap should be ideally 1.5 metre high and wide, and 5 metres long. Such a heap is likely to accommodate 500 kg of straw soaked in 750 litres of solution. The heap is then covered with a layer of dry straw to ensure moisture retention in the heap.
The heap now needs water supply at regular intervals. For this, an injection-pipe is designed, which is thrust into the heap and delivers 10 to 40 litres of water a minute. The first watering of 100 litres is done on the seventh day. Then the heap is turned well on the 15th day and 240 litres of water is poured into it. On the 30th day, the heap is turned again and 200 litres of water is added. Following these procedures, the temperature at the centre of the heap reaches 60oC within four days, while temperature at the base of the heap remains 4oC to 6oC. The heap will be composted by the 45th day, which is indicated by dark colouration and sweet earthy smell of the heap. Though straw strands will be visible, they will break easily. The soft compost is ready.
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