Best out of agricultural waste

Dr Chinmoy Kumar Sarma

(The writer can be reached at drcksarma@gmail.com)

Agriculture remains the largest sector of the Indian Economy as a source of livelihood and almost half of the workforce in India still remains dependent on agriculture and therefore, progress in the agriculture sector will decide the condition of the low-income group in our country. The targeted year for doubling the farmers' income is 2022 and, if anything is to be doubled within this period, the annual growth rate in the agricultural sector must be enhanced which can be achieved by taking strong measures to harness all possible sources of growth in farmers' income such as improvement in productivity, increased resource use efficiency, increase in cropping intensity, diversification towards high-value crops etc. Expanding agricultural activities has naturally resulted in increased quantities of agricultural crop residues, livestock waste and agro-industrial by-products. As developing countries continue to intensify farming systems to meet their food requirement, there is likely to be a significant increase in agricultural wastes globally. In India, emphasis has been given on raising farm income, so farmers need to pay attention not only to primary agriculture but also to secondary, wherein they enhance the value of the product and utilize all possible by-products.

Huge quantities of agricultural wastes are produced in Indian farm fields every year and approximately, it exceeds 620 million tonnes per year of which, almost 50 per cent finds applications in various agricultural and industrial activities like animal feedstock, paper industry, roofing material and energy generation. However, a major portion of the on-farm agricultural residues to which farmers generally treat as wastes is burnt in the field itself as it is a low cost and easy means of agro-waste disposal. Crop residue burning is a major problem in some parts of our country. The farmers have to burn huge quantities of biomass because of time constraints to accommodate the next crop which contributes to great haze and global warming. With a small turnaround window of hardly 20 days between rice harvesting and the optimal sowing of wheat, the flexibility to clear the field of leftover straw whether by manual removal or in situ incorporation is limited. The least-cost and most time-saving option are to simply burn. Crop residue burning is mainly confined to the areas where farmers grow paddy and wheat and harvest these using combined harvesters. In manual harvesting, the crop is cut close to the ground using a sickle and the paddy straw left after threshing can be used as fodder or packaging material. Combine harvester which harvests, threshes and cleans the separated grain at one go, operates at 50-60 cm above the ground which generates 40-50 cm of loose straw and 50-60 cm of standing stubble. Disposal of this residue isn't easy as normal paddy straw fetches very low rate as it cannot be finely cut or made into chaff and so, burning is the only option left with the farmers. Crop residue burning has a great negative impact on the agro-ecosystem as it is responsible for the formation of smog, smoke that causes air pollution, and disturbs soil physical, chemical and biological structure including microbial population as well as microflora and microfauna. Conventionally, locally available natural materials like crop residues, weeds, cow dung etc., have been used as manure by the farmers since early days and with the advent of input-intensive agricultural technology, chemical fertilizers have become an integral component in the production system in view of fast growth and good yield. The use of chemicals as fertilizer is not only expensive but also goes on accumulating in soil, crops, undergoes bio-magnification which leads to health disorders. In organic agriculture or integrated plant nutrient management system, agro wastes can be the important sources of plant nutrients which on decomposition give good nutrients to plants. As per an estimate, almost 50 per cent of the total agricultural residues are produced mainly by rice, wheat and oilseeds and this could turn out to be a major source of minerals. Approximately, 6.5 million tons which equate to almost 30 per cent of the total nitrogen, phosphorus and potassium mineral consumption in India is contained in the form of these farm residues even after assuming that almost 50 per cent of all the overall content per year is being utilized in different ways. Experimental observations suggest that direct application of crop residues in the fields may have its own negative implications. Recycling is an eco-friendly technology through which we can convert organic waste into a product that is rich in nutrient content and can replace chemical fertilizer. Composting is one of the best methods by which agricultural solid waste can be recycled. Recycled waste products could be bio-composts, which may be fortified with microbial consortia and organic material to produce bio-organic farm inputs at a commercial scale which could ultimately generate economic livelihood to the rural society also. Vermicomposting technology has the considerable economic potential of using earthworms to convert a wide range of organic agricultural waste and city garbage into valuable plant growth media. In this process, excess worms can be converted into vermi protein which can be utilised as feed for poultry, fish, etc. Waste from livestock activities includes solid waste such as dung, litter, organic materials in the slaughterhouse, wastewater such as urine, cage wash water, wastewater from the bathing of animals and from maintaining sanitation in slaughterhouses. The utilization of animal manures for fertilizer has a definite impact on input energy requirements at the farm level. Methane gas which is used for heating purposes as in boiler operation, water heating, grain drying etc., can be produced from agricultural wastes particularly from manures. Anaerobic digestion makes the treatment and disposal of large poultry, swine and dairy waste feasible, minimizing the odour problem. It stabilizes the waste and the digested sludge is relatively odour-free and yet retains the fertilizer value of the original waste.

Agriculture as a whole has placed more emphasis on crops rather than livestock production. In general, livestock in the region is primarily raised on small farms rather than in big, commercial herds. Crop residues, plant parts and various agro-industrial by-products are utilized conventionally as feed materials in small farms but advancement in nutritional science provides opportunities for improving their feeding values. Nowadays biomasses produced from agricultural waste are used to generate energy because it carries great potential to convert into energy. The utilization of agricultural waste is gaining importance especially when the world scenario of the energy demand gap is reported. Production of energy from biomass can provide farmers with new prospects and possibilities to diversify agricultural activities. The "waste-to-energy" conversion processes for heat and power generation and in some cases for transport fuel production can have good economic and market potential. Indian farmers are also turning wastes into gold. The husks, weeds and other agricultural wastes they thought useless are being converted into sustainable, non-polluting and cheap energy that is lighting up villages and irrevocably changing lives in some parts of the country. Agricultural biomass can also be converted into some commercial products. In the year 2016, studies showed the feasibility of utilizing the coffee waste in the production of bricks and proved the feasibility of utilizing wheat bran to produce bio-alcohol. Industrialization and urbanization pose a serious threat to the environment through the release of heavy metals and in recent years, agricultural wastes have proven to be a low-cost alternative for the treatment of effluents containing heavy metals. The low-cost agricultural waste such as sugarcane bagasse, rice husk, sawdust, coconut husk, oil palm shell, neem bark etc., for the elimination of heavy metals from wastewater has been investigated by various researchers.

As seen from the literature, various uses of biomass and agricultural waste are in practice and newer development in technology in process development and in product development is necessary to increase the economic values of products. More conversion of this waste requires more research and renovation in the existing technologies.