- Agriculture supports roughly half of India’s population and is the key to its food security. We have, indeed, avoided the spectre of food shortages, thanks to our farmers increasing production using modern inputs and technology developed by agriculture scientists. But there has been a collateral cost to this — in the form of overexploitation of our natural resources, especially soil and water — which has brought issues of sustainability to the fore.
Soil organic carbon (SOC)
- It is extremely important for agriculture. About 58% of organic matter mass exists in the form of carbon. The percentage of organic matter in the soil can, thus, be estimated by simply multiplying the SOC% by a conversion factor of 1.72 (100/58). While farmers may apply urea or di-ammonium phosphate, adequate SOC levels is what makes the nitrogen and phosphorous from these chemical fertilisers bio-available to crops. Organic matter is also the source of food for the microorganisms that help increase the porosity and aeration of soils. The soil’s moisture holding capacity, too, goes up with higher carbon levels, thereby reducing water runoff.
Importance of SOC
- While farmers may apply urea or di-ammonium phosphate, adequate SOC levels is what makes the nitrogen and phosphorous from these chemical fertilizers bio-available to crops.
- Organic matter is also the source of food for the microorganisms that help increase the porosity and aeration of soils.
- The soil’s moisture holding capacity, too, goes up with higher carbon levels, thereby reducing water runoff.
- Simply put, SOC levels have direct correlation with soil productivity and, by extension, sustainability of agriculture.
How it is linked to Climate Change?
- Atmospheric carbon dioxide is stored in the form of SOC through the process of absorption in crop production and plant residue retention in soil.
- This sequestration of atmospheric carbon dioxide can, indeed, be a powerful mitigating measure for climate change.
- But in the last four years, based on sample testing results under the Centre’s Soil Health Card Scheme, the picture emerging isn’t all that encouraging.
- SOC levels are found to be very low in most parts of India.
- The soils in temperate climates have better carbon levels. It is quite the opposite in hot and tropical atmospheric areas such as ours, where the soils tend to lose carbon through decomposition (mineralization) of plant residues.
- Rising temperatures from climate change further aggravates the situation.
How to ascertain adequate SOC levels?
- SOC levels matter can be raised through higher retention of farm residue and adding organic matter from outside.
Step I: Proper crop selection
- Plants, we know, take atmospheric carbon dioxide and convert it into food through photosynthesis process.
- Ideally, only crops producing more aboveground and root mass – which contribute to long-term productivity by enhancing soil organic matter – should be grown.
- But farmers, being rational economic agents, will go only for crops that give higher and assured returns, even if in the short run.
- A change in cropping patterns, to ensure high SOC and long-term productivity, will not take place unless the desired alternative crops are remunerative.
- It calls for appropriate policy intervention, including encouragement to set up agri-processing units for such crops, which will, in turn, make it profitable for farmers to grow them.
Step II: Proper retention of farm residues
- Even the aboveground mass remaining after harvesting of the grain and dried stalks needed for fodder should be returned to the soil as much as possible.
- This requires scientific crop residue management.
- Burning of crop stubble has a negative impact not just on environment and human health, but also on soil fertility.
- The crop residue when burnt, instead of raising SOC through mixing with the soil, gets converted into carbon dioxide.
- A strategy focused on both in situ and ex situ management of residue is necessary today.
- Currently, it is being sought to address the issue through subsidised provision of implements such as Happy Seeder, Super-Straw Management System attachment, mulcher and chopper-shredder.
- But all this is mostly in areas closer to the national capital. For sustainable farming and improving soil health, we need all states to pitch in.
Step III: Adding organic matter from external sources
- Use of compost must be promoted.
- There is definitely a case to subsidize building of vermicompost pits or ‘Nadep’ mud/clay brick tanks using money from MGNREGA and other schemes.
- Even urban green waste and manure from sewage treatment plants can be returned to farm soils.
- There is clear evidence that when nitrogen, phosphorus and potassium is used in conjunction with farm yard manure, the fertilizer response ratio itself goes up with rising SOC levels.
Step IV: Crop Rotation
- Farmers, however, are hesitant to cultivate pulses for lack of a proper system of government procurement at minimum support prices, unlike that for wheat and paddy.
- In the rice-wheat system, planting of legumes, either as a summer or full replacement crop in the kharif/rabi season, is most needed.
- Legumes have root nodules harbouring rhizobium bacteria that fix nitrogen from the atmosphere.
- This nitrogen also helps bind and retain carbon in the soil for a longer time.
- Inclusion of pulses in the public distribution system would go a long way in promoting the cause of soil health as well as nutritional security for our masses.
Step V: Promoting Zero Tillage
- The use of no-till implements deserves a big push. Organic carbon is retained in large soil aggregates.
- Deep ploughing equipment that break these aggregates cause SOC loss, whether through runoff with water or evaporation as carbon dioxide.
- Zero-till seed drills, Happy Seeders and Direct Seeded Rice machines will ensure minimal disturbance of aggregates and less depletion of organic matter.
- We need to launch a comprehensive awareness programme for enhancing the organic matter content of soils, with specified and time-bound targets.
- The very act of monitoring and measuring outcomes will help focus attention on this important aspect.
- Farming should, of course, be profitable. But it must also be sustainable.