“No race can prosper till it learns there is as much
dignity in tilling a field as in writing a poem”. – Bookert T. Washington
Agriculture, ‘the backbone of our country’, holds its meaning ‘Activities on the Ground for Raising Intended Crops for Uplifting Livelihoods Through Use of Rechargeable Energies’, contributes a GDP of 15.4 % (2017). For decades, agriculture dealt only with the production of essential food crops but at present it involves forestry, dairy, fruit cultivation, poultry, bee keeping, mushroom, arbitary, etc. According to World Bank 2017, employment in agriculture (% of total employment) was reported to be 42.74% in India.
Out of 328 m ha of geographical area, India has gross cropped area and net sown area of 195 m ha and 141 m ha respectively. A popular saying by Jill Shukla tells “Everything has its own advantages and disadvantages. What matters is the way you perceive it’”. Agriculture having tonnes of significance has its own disadvantages with the major contributing to air pollution. Changes in equipment and technology caused a greater impact to the nature of farming and environment. Management practices can help in reducing pollutants entering from field to our atmosphere.
There are two major sources of air pollution from agriculture: livestock, which produces methane and ammonia, and the burning of agricultural waste. Around 24 percent of all greenhouse gases emitted worldwide come agriculture, forestry and other land-use.
AIR POLLUTANTS FROM AGRICULTURE
The major pollutants from agriculture are
1. Methane from rice fields
Methane accounts for 15% of the total enhanced global warming. Rice grown in anaerobic conditions release methane by methanogenic bacteria of which rice plant act as chimneys for transferring methane from rhizosphere to atmosphere.
2. Nitrous oxide
Nitrogen, the new carbon is 300 times more potent than CO2. India consumes 17 million tonnes of nitrogen fertilizer annually. Only 33% is taken up by the plants and the remaining 67% remains in the soil and poses threat to environment.
Ammonia enters as a gas through heavily fertilized fields and livestock wastes. In atmosphere, it reacts with gases like sulphur dioxide and nitrogen dioxide to form ammonium containing fine Particulate Matter (PM) which causes negative impact on cardiovascular and respiratory health.
4. Inorganics used in agriculture
Usage of inorganics has been increasing at a highest trend. Inorganics such as pesticides, fungicides, herbicides, etc. when sprayed can directly hit the non-target vegetation and sometimes it may get volatilized and contaminate air, water, soil and some non-target plants.
5. Animal agriculture
Around 400 different harmful gases enter into the atmosphere through animal wastes like urine and manure. Some of the gases include nitrous oxide, ammonia, particulate matter, endotoxins and hydrogen sulphide. Animal agriculture releases nearly one-fifth of the world’s greenhouse gas emissions.
6. Burning of crop residues
India generates a large quantity of agricultural wastes. Of which their disposal is a major challenge. A large portion of un-utilized wastes are left in the field. Thus in order to clear the field for next crop cultivation they are being burnt in the field in situ which acts as an inexpensive measure by farmers. But burning of agricultural wastes results in emission of many significant air pollutants like CO2, N2O and CH4.
- Water regime has a direct effect on methane emissions. Promoting mid- season aeration by short term drainage can help in lowering methane emissions from rice fields.
- Promoting aerobic degradation through composting or incorporation into soil during off-season drained period is another technique.
- Usage of sulphate containing fertilizers can reduce CH4 emissions because sulphate-reducing bacteria act as a strong competitor for CH4 producing bacteria thus reducing its outcome.
- Application of fermented manure like bio gas slurry instead of other organic amendments helps in reducing emissions.
- Cyanobacteria and azolla when applied to flood water oxidizes methane thus reducing methane emissions.
- Direct crop establishment instead of transplanting technique can reduce emissions.
- Use of low C:N organic manures such as chicken manure and rice straw compost helps in reducing methane emissions.
- Instead of burning the agricultural wastes it can be put to various productive usage like incorporation in field, bio-energy, etc. Awareness must be conducted about the negative impacts of crop residue burning to the farmers and the importance of crop incorporation in soil for maintaining sustainable agricultural productivity.
- Nitrous oxide emissions can be reduced by low usage of nitrogenous fertilizers. Split application of nitrogen fertilizers can increase the use efficiency to plants thus reducing its entry to environment by various loses.
- Crop rotation with leguminous crops can help in reducing the usage of nitrogen fertilizers because of their ability to fix nitrogen in plants.
- Under waterlogging, nitrate can be denitrified to nitrous oxide and nitrogen gas by soil bacteria. Prevent waterlogging to reduce emissions.
- Using nitrification inhibitors reduces nitrous oxide emissions by reducing nitrification which subsequently reduces nitrate leaching and production of nitrous oxide.
Nitrous oxide has 300 times the global warming potential of CO2 which means avoiding the release of 1 tonne of nitrous oxide would be eligible to create nearly 300 carbon dioxide equivalent offset units.
- Most of the ammonia emissions from agriculture is from livestock. Nearly 85% of nitrogen consumed by farm animals is excreted in faeces and urine as nitrogen compounds thus increasing emissions. Thus limiting the excess protein fed to animals by maximizing the portion of protein that animals can metabolize and reducing the fractions that they cannot metabolize helps in reducing ammonia emissions.
- The greater the surface area of manure is exposed to air, the greater is the ammonia loss. Thus when livestock are kept indoors, ammonia loss can be minimised by designing the facilities they are housed with.
- Traditionally manure is spread by broadcast application which causes high levels of ammonia released to the environment. Thus many other techniques can be used to reduce manure- air contact by incorporating manure into the soil.
- Reduced usage of excessive synthetic fertilizers can reduce ammonia emissions. Urea- based fertilizers can be replaced with ammonium nitrate.
Inorganics used in Agriculture
- Data on the occurrence of pesticide-related illnesses among defined populations in developing countries are scanty. Pesticides being inexpensive, quick and easy has contaminated almost every part of our environment. Spraying insecticides, pesticides and herbicides poses threat to human on inhalation. The book “Silent Spring” by Rachael Carson gives a brief understanding on the impact of synthetic chemicals to plants and human.
- Reduction of inorganics and usage of organic amendments helps to create a safer environment to both plants and humans.
- Crop rotation, crop incorporation, etc. can be adopted and predatory insects like lady bird beetle, etc can be introduced to pest infested crops which is environmental safety.
- Mulching practices can be employed in areas of weed infestation instead of herbicides which might pose severe threat to non-target plants and humans.
- Crop rotation and incorporation of green manures and green leaf manuring can reduce the usage of synthetic fertilizers.
- Applying nutrients at right time, right method, right amount and right placement is essential.
- Design objectives for managing manure do not include minimization of emissions of ammonia, methane, or other gaseous compounds, but rather focus on odour and dust control, avoidance of direct discharge to surface water, and land application at rates that are beneficial to growing crops.
- High standards of cleanliness can reduce ammonia emissions.
- For poultry, ammonia emissions can be reduced by ensuring droppings are able to dry rapidly. By maintaining dry and crumbly litter and managing drinking systems can reduce gaseous emissions to atmosphere.
With around two-third of the Indian population dependent directly or indirectly on agriculture, it is considered to be the basis of the country’s economic development. It is not just known to be a source of livelihood in India but a way of life. Without food there is no life. Air pollution from agriculture can be arrested in several disciplines. People take measures which are quick, inexpensive and easy but never consider the consequences. Thus awareness must be created to ensure safety to environment and human health. It is our own responsibility to preserve and conserve the world where we live in.
Author, Keerthana R is a Post graduate in Soil Science and Agricultural Chemistry from TamilNadu Agricultural University, Coimbatore. email@example.com