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.

An Indian farmer spreading fertiliser over a crop. Photo credit: Kiran Kumar/Wikimedia Commons [Licensed under CC BY 2.0]
An Indian farmer spreading fertiliser over a crop. Photo credit: Kiran Kumar/Wikimedia Commons [Licensed under CC BY 2.0]
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.