Round the carbon cycle with Sangeeta

A soil scientist discusses her findings in conservation agriculture and the deteriorating soil health in India.
By | Published on Dec 15, 2017
WHO? Sangeeta Lenka, 41
WHAT? Agricultural scientist
WHERE? ICAR – Indian Institute of Soil Science, Bhopal

Reported by Aashima Dogra

Agriculture, combined with forestry and other land use, is the second biggest contributor to climate change, after energy production. Around 45 percent of India’s land is used for agriculture. Predominant farming practices release an alarming amount of greenhouse gases not only messing up the carbon cycle contributing to global warming but also hampering soil health. These losses are for the farmers to bear. This is the central theme of Sangeeta Lenka’s work.

“My area of research is conservation agriculture. I focus on ways to conserve resources, especially carbon sequestration, and other farm management practices that reduce greenhouse gas emissions from agriculture,’’ Sangeeta said, during an interview in her office at the sprawling Indian Institute of Soil Science campus in Bhopal.

Contributors to atmospheric Co2 emissions. AFOLU stands for Agriculture, Forestry and other Land Use
Source: 2014 IPCC Report on Climate Change

Carbon sequestration – locking in the carbon

To understand carbon’s role in climate change, we have to keep in mind the carbon cycle. Carbon exists in the atmosphere as inorganic carbon dioxide – a molecule which has the optical properties to increase warming of the planet. Through respiration of forests and other phenomena, this carbon dioxide is transformed into organic compounds and transferred to the earth’s surface. In the earth, it might be used (temporarily) by (and as) living things – plants, microbes or humans and then locked in the soil stored ultimately as organic fossil fuels. Throughout the carbon cycle, it is the same carbon that travels very very slowly in various forms from the thin airy atmosphere into the dense living earth.

How long the carbon spends in each ‘carbon pool’ depends on the turnover time of that form of carbon; the turnover time is related to the half-life, the elemental property of every substance in the universe. This also decides how much carbon is in each carbon pool. The overuse of earth-locked carbon has led to too much carbon in the atmosphere. The balance that we rely on for predicting the climate has been tipped. And hence the changing change.

Source: Kansas State University, Soil Carbon Center

Carbon sequestration is the process of capturing atmospheric carbon and locking it into a carbon pool whose turnover time is very high. Soil is one such carbon pool holding on to 1,500 gigatonnes of organic carbon – more than the amount of carbon in vegetation and the atmosphere. It is also Sangeeta’s favourite.

‘‘Plants convert inorganic carbon dioxide in the atmosphere to an organic form through photosynthesis. As plants live and die, this organic form of carbon stays in the soil as a complex organic compound,’’ she explained. “Carbon compounds have different turnover times; some are slow cycling – resistant to decomposition, and others are very actively decomposed by microbes. Both types are beneficial to mitigate climate change but the active form, which is easily decomposable, is also helpful for the nutrition of the soil.”

The goal of conservation agriculturists like Sangeeta is to find ways to retain the carbon in the soil for a longer time. “If it is released back to the atmosphere (by burning crop residues and forest clearing, for example), the concentration of carbon dioxide is going to increase, increasing the pool of greenhouse gases in the atmosphere and ultimately affecting global warming.”

“Sequestering carbon (by farming in different ways) is one of the ways of retaining the carbon. And it is very eco-friendly.”

Sangeeta’s field trials test different farming practices for their sequestration skills. She examines if and how the soil’s organic carbon pool is being built up; is it an active, slow or passive carbon pool? “We observe these pools to tell where the carbon is going and how the management practice is affecting these pools. Does one farm management practice have more turnover time than the other or is the carbon being lost to the atmosphere? These are the things are being evaluated,’’ she said, describing her current work on sequestration.

Harmful farming practices

Unfortunately, farming is not so sophisticated in our country yet. Labour intensive tillage and ploughing are the main management practices on Indian farms. “Tillage oxidises soil carbon to inorganic carbon, which is lost to the atmosphere. For sequestering carbon we want to avoid this. But, the farmers go for a minimum three tillage before sowing. It is the first management practice farmers follow.”

Tillage and Ploughing

“In conservation agriculture, our first focus is to ask the farmers to reduce their number of tillage.” This is an important carbon sequestration strategy as it reduces the loss of carbon into the atmosphere. Another farming practice helpful in sequestering carbon is the management of nutrients in the soil. ‘‘When the plant grows, it withdraws nutrients from the soil.’’ The plant material is then harvested, the carbon with it. Unless the soil is replenished, it will not be productive.

A solution for improving the productivity of our soils came to a young independent India in the 1960s, with the launch of the much-lauded Green Revolution. Yields of Indian crops increased thanks to the use of hybrid seeds, chemical fertilisers and pesticides. India managed to be self-sufficient in grains and the gratitude for Norman Borlaug, who introduced the techniques poured from Indian hearts.

Sangeeta’s findings hint that perhaps it is time for Indians to reconsider this perception. The Green Revolution may have been phenomenal in it’s right and it’s time, but the legacy it leaves is disastrous. A revolution in food distribution is the need of the hour, reviews have suggested.

The benefits of the integrated use of chemical and organic fertilisers are multifold: increasing sequestration of carbon, reducing the emission from agriculture and also keeping the yields high.

“Our slogan is ‘Produce More’, isn’t it?” Sangeeta remarked. “But to produce more they are using more fertilisers. These fertilisers have not only increased the mineralisation of the organic carbon compounds present in the soil, but also emissions of dangerous nitrogenous greenhouse gases like nitrous oxide,” she said, adding that nitrous oxide is 310 times stronger than carbon dioxide in its greenhouse effect… meaning it is 310 times better at global warming.

Sangeeta agrees that we have to produce more to feed the growing population, but in the same breath, she pushes for a balance between the indiscriminate use of fertilisers and sustainable farming. 

“Farmers tend to apply more and more urea, DAP (Diammonium phosphate) or other nitrogenous fertilisers; they don’t opt for organic fertilisers like manure or vermicompost.” Balanced fertilisation is the way to go, according to Sangeeta. Organic fertilisers increase the soil organic carbon by sequestering more carbon into the soil and increasing soil health for productivity. “Inorganic fertilisers may produce yields, but in the long run, soil health deteriorates. Organic fertilisers also improve soil microbial diversity, which is most important in the whole cycle of decomposition. This is what releases the locked nutrients for the plants. These things are all interrelated.’’

The benefits of the integrated use of chemical and organic fertilisers are multifold: increasing sequestration of carbon, reducing the emission from agriculture and also keeping the yields high.

Farmer adaptation is the challenge ahead

Based on her experience in conservation agriculture for the last 10 years, Sangeeta is able to see very clearly the hurdles in modernising Indian agriculture. The biggest one is convincing farmers to take up new research-based farm management strategies. The recent smog in Delhi resulting from farm residue burning was the visible and breathable evidence of this difficult challenge.

Delhi on a smoggy night in 2017

‘‘The farmers have been asked repeatedly to stop the burning of residues and instead use the residue, leave it there and incorporate it into the soil. Conservation agriculture scientists have found that this will increase soil carbon and soil health. But farmers are yet to adapt,” Sangeeta said. “You can ask farmers to reduce the number of tillage, but they are not going to take up your advice immediately. They have been doing it for a long time. If the farmer doesn’t see the benefits of the recommendations (in the short term) and is then bombarded with other recommendations like reducing fertiliser use…and then again is asked to replace old practices with new ones…it is not going to work. Convincing the farmer is difficult.’’

So what is the way forward? Firstly, Sangeeta feels that the government should improve policies. She cited an example: “Farmers used urea since they were getting it at a low price. Now, the urea subsidy has been reduced.”

Secondly, she stressed the urgent need for awareness along with incentives to motivate farmers to participate. “When electricity was provided for free or subsidised, farmers used it to withdraw groundwater for irrigation without understanding that the groundwater was getting depleted.”

Thirdly, the right machinery needs to be made available for modernised conservation farming. “Why does the farmer practise burning? We have to understand that it is because he saves on labour costs that are required to clear the land. There is machinery available for this, but only in institutes. The government could help provide the farmer with the right machinery to work with the residue. Without this, how will the farmer adapt?’’

The megaproject

These days Sangeeta works inside a hybrid between a laboratory and the open field called ‘open top chamber’. It is a greenhouse-like facility where Sangeeta and other scientists at the institute study the effect of climate change on soil properties. “We have taken up this mega project to see the impact of elevated carbon dioxide and temperature on crop productivity and soil health.”

In the open top chamber, all atmospheric variables are monitored, specifically carbon dioxide concentration and temperature. These things are hard to experiment in the open field as there are too many physical parameters to consider. Experiments have been on for around two years. “We tested with different concentrations of carbon dioxide – ambient and 550 ppm. As expected, elevated carbon dioxide levels are good for the plants because it increases photosynthesis.’’ But not for long.

Sangeeta’s results indicate that global warming does not simply benefit crop yields. The science is more complicated. “Carbon dioxide doesn’t increase alone; it will also raise the atmospheric temperature. Increasing temperature beyond a threshold reverts the yield to normal.’’

According to their initial results, the temperature increase of more than two or three degrees will be detrimental but on increases of around 0.5 degrees improves yields to 10 to 15 percent. Sangeeta is careful about interpreting these results. ‘‘We can’t say the positive effect of increased Carbon dioxide is totally nullified. We do an experiment on a small scale, so we cannot expect totally similar results upon extrapolating to larger scales.”

Benefits of a two-body boon

Like many women scientists interviewed by, Sangeeta is also married to a scientist. Often, married scientists face the so-called ‘two-body problem’, where couples find it difficult to find jobs in the same institute, but Sangeeta and her husband have been lucky. Her husband works at the same institute and Sangeeta considers this a blessing.

“Since we are both in the same field, he understands the nature of my work. Sometimes, we get late if we have some work in the lab, sometimes we go to present our work to conferences… we know each other’s struggles very well. It takes time to establish yourself in science. If my husband was in a different field, maybe he would not have understood why I needed to go to Australia for my postdoc with a fellowship from the Australian government. He understood that this was a big opportunity.”

Science is a demanding profession and how you manage home and work is crucial for many working women. The two body boon gave Sangeeta an added advantage over her peers during graduation and post graduation, she believes. “When we were studying together, my friends were studious. But after they got married, they discontinued and are now housewives. I am the only from my batch who is doing science. Maybe the lack of support is the reason for most girls to drop out. I was lucky.”

‘‘I got married in the first year of my PhD and a pregnancy soon followed. So I took a while to complete my PhD.’’ Sangeeta had her in-laws and parents pitch in while her son was very young so she could carry on her research. But these days she wonders if she gives him enough attention. “He is now 13 years old. This is the time to guide him to his future,” she said.

After schooling, Sangeeta signed up for a degree in agriculture at Orissa University of Agriculture and Technology in Bhubaneswar. Thanks to good teachers in the soil science module, Sangeeta developed an affinity to the subject. A masters at Tamil Nadu Agricultural University in Coimbatore, a PhD from Indian Agricultural Research Institute in Delhi and a recent postdoc in Sydney followed.

Sangeeta grew up in Bhubaneswar, Orissa. But every summer, the family visited their native village where she would watch her uncles work on the fields, till the soil and sow seeds. Farming was fascinating, but not a special interest until much later. “It did not happen until I came to this profession.” And so goes the story of science. You might not discover your passion until you study something deep enough.

About the author(s)

Aashima is a freelance science communicator, author and editor. She co-founded in 2016.

4 responses to "Round the carbon cycle with Sangeeta"

    Hari says:

    Greetings. Congrats on this initiative that I have come to know thanks to the Wire. I have a question about the use of combined organic/chemical fertilisers being advocated in this article. Is this better than organic farming that uses no chemical fertiliser, or a mid-way solution going towards completely organic farming?

    tlos says:

    Hi Hari, thanks for your encouragement. Combined use is suggested as a midway solution in the current scenario where the possibility to completely moving away from chemical fertilizers is scant. These are comments made in general based on Sangeetas work in Indian agriculture, fertilizer use for each farm needs to be looked at separately.

    Pratibha says:

    Thanks for forum for women scientist . I’m microbiogist from Osmania university for organic farming.. my research on a bacterium from fish is close to bacterium found on vehicle sent to Mars.. reviews from various I conclude that same bacterium is found in cow dung. Now once again we can emphasize our traditional method of agriculture.dung domesticated animals and kitchen waste when mivedd. With jaggery , gram flour , curd milk and ghee on fermentation is good fertiliser and pestcide

    Pratibha says:

    Fermentation of cowdung with medicinal plants like calotropus, pungami , , besan, milk products gives good yeild of bacterium, has good growth factors and Anti fungal factors . So we can say organic farming can be propagated or facilitated by cowism

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