Nitrous oxide emission from agriculture has risen sharply over 30 years, finds study

Fertiliser pricing policies – influencing farmers’ preference towards specific chemical combinations – need to be mapped to the officially prescribed nitrogen, phosphate and potassium ratio to curb excess non-carbon dioxide emission from India’s cropland based agriculture, research has suggested.

The agricultural sector is the world’s largest source of non-CO2 greenhouse gas emissions such as methane and nitrous oxide, both of which contribute significantly to climate change.

Cropland-based agricultural activities account for 24.17% of India’s total methane and 95.84% of the total nitrous oxide emission from the agricultural sector.

In 2010, India adopted the National Mission for Sustainable Agriculture as one of the eight missions listed under National Action Plan on Climate Change. One of the objectives of the mission is to reduce agricultural greenhouse gas emission.

Slightly less methane but more nitrous oxide emissions

While methane emission from paddy cultivation has shown a slow and slight decline, the lopsided use of nitrogen-based fertiliser in India has released more and more of nitrous oxide into the atmosphere in the past three decades, a study has found.

The research by Jadavpur University, Kolkata and Thailand’s Asian Institute of Technology scientists reveals that “nitrous oxide emission from nitrogen-fertiliser use increases by around 358 percent, growing at a “statistically significant rate of 5100 tonnes per year” from 1980-1981 to 2014-2015.

The total non-carbon dioxide emission from cropland-based agricultural activities, mainly due to nitrous oxide, has gone up by approximately 49% in the past three decades, according to the analysis authored by Shreya Some, Joyashree Roy and Arpita Ghose.

“The marginal decline (a rate of 200 tonnes per year) in methane emission is mainly due to a switch to less water-intensive paddy cultivation under flooded land conditions. Irrigation facilities have also improved, coupled with technological advances,” Joyashree Roy told Mongabay-India.

The rise in non-CO2 emission from increasing use of nitrogen-based fertiliser could be clearly attributed to the link between fertiliser pricing policy and disproportionately higher use of nitrogen fertiliser going beyond officially prescribed ratios, the authors write in the study.

Nitrous oxide emission from agricultural soil is due to the natural biochemical process in the nitrogen cycle. Application of nitrogen-based fertilisers stimulates microbes in the soil to convert nitrogen to nitrous oxide at a faster rate than normal. So, controlling nitrogen fertiliser use can help in the reduction of nitrous oxide emission.

Pricing-driven fertiliser application

“We looked deeper into the factors which drive methane emission and nitrogen oxide emission from the agricultural sector. While we saw that methane emission from agriculture is coming down slowly, nitrous oxide is increasing and there is an imbalance in the ideal and actual ratio of NPK [nitrogen, phosphate and potassium] use by farmers,” Roy explained.

As against the ideal nitrogen, phosphate and potassium ratio of 4:2:1 (around 57% of nitrogen, 29% of phosphate and 14% of potassium) for India, the ratio during the study period worked out to be 6.5: 2.5:1.

Roy and co-authors were surprised to discover ups and downs in nitrogen-based fertiliser use over the study period in India where 77% of the emission from agricultural soil comes from nitrogen-based fertiliser use in India.

“We were curious to understand that although there is the whole scientific concept of optimum use of NPK and the prescribed ratio for balanced use then why are farmers not following that and why do we observe swings in nitrogen-based fertiliser use during the period,” she said.

Roy pointed out whenever the price for nitrogen-based fertiliser has gone down, farmers deployed more of it and vice versa.

“We found that the years in which the fertiliser policy and relative prices changed, the farmers reacted immediately to the market prices and changed their behaviour in using more amount of the cheaper fertiliser,” explained Roy.

According to the study: “The years of fertiliser price reforms which made N [nitrohgen]-fertiliser relatively cheaper than P [phosphate] and K [potassium], use of a higher proportion of N-fertiliser by farmers could be detected very clearly.”

For instance, in 2010, India announced the nutrient-based subsidy policy to ensure application of fertilisers in a balanced way and control the falling marginal productivity of fertiliser.

“Under this, two major changes took place. First, a fixed rate of subsidy was given to the farmers based on the nutrient content of the fertiliser used and second, the Maximum Retail Price on P and K fertilisers were decontrolled and fertiliser manufacturers were allowed to fix the MRP at reasonable rates.”

“However, these led to an immediate rise in the prices of P and K fertilisers leading to a decrease in their use. More N fertiliser were used, distorting the NPK ratio to 6.9:3:1 in 2010-11 and further to 8.2:3.2:1 in 2011-12 as compared to 4.6:2:1 in 2008-09. This also drove up N2O emission,” the study showed.

However, the analysis goes on to show the total fertiliser consumption decreased steeply by 14 percent per year from 2011 to 12 to 2013-14. “Sudden fall in N-fertiliser use in 2000, 2002, 2009 and 2012 coincides with drought years in India. As a matter of fact, N2O emission also declined.”

This has a very strong policy-relevant message for rationalising fertiliser pricing policy that can be designed to incentivise farmers towards the use of the officially prescribed science-based ratio of various fertiliser types.

“So fertiliser policy interventions have played a very important role in driving farmers’ behaviour towards fertiliser use which means that policy processes need to match with the NPK balance prescribed so farmers apply in right proportions as per prescribed standards. This would have mitigating effects on emissions and soil health,” Roy said.

The findings are relevant to key global policy processes.

Need more ways to mitigate non-CO2 emissions

To be consistent with the Paris agreement of global warming of 1.5 degree Celsius above pre-industrial level there is a need for accelerated mitigation actions. The agricultural sector contributes 10 percent of the global direct greenhouse gas emission.

Indian agriculture contributes seven percent of the global emission from the agricultural sector. To explore mitigation options from Indian cropland based agriculture, comprehensive understanding of the past emissions from this sector and drivers of change are necessary.

“If you look at the IPCC [Intergovernmental Panel on Climate Change] 2018 report, it stresses that total emission comes down as fast as possible in alignment with the Paris agreement. You can’t do justice to the amount of reduction in the short period of time if you only consider carbon dioxide emissions. You have to also look at non-carbon dioxide emissions,” Roy said.

Although the component is not large compared to CO2, it is also not negligible.

“Non-carbon dioxide emissions are under research and we really need to find out what are the ways and means to mitigate them. The bottom line is we have to simultaneously try to reduce emissions in all possible ways and from all possible sources. No potential should be left out,” Roy added.

This article first appeared on Mongabay.