As hotter weather, droughts, and depleting aquifers threaten food crop yields in South Asia, scientists have successfully tested a greener and more profitable way for India’s farmers to manage irrigated rice-wheat rotations.
Based on two years of field trials comparing innovative versus established practices, the best system for the rice-wheat rotation turned out to feature underground drip irrigation with fertilizer in the water, or ‘fertigation,’ as well as conservation agriculture practices — such as sowing both crops without tillage, keeping a crop residue mulch on the soil, and growing rice without flooding.
“A suite of these methods raised overall farm profitability by nearly 30%, while requiring 70% less irrigation water than the conventional approaches of intensive soil preparation for rice and wheat, flood irrigation, and growing rice in puddled paddies,” said M.L. Jat, a cropping systems agronomist at the International Maize and Wheat Improvement Center (CIMMYT) and co-author of a 2019 Nature Scientific Reports article on the study.
Variants of the rice-wheat rotation are practiced on about 13.5 million hectares in South Asia, sustaining hundreds of millions of people but also draining water reserves, generating greenhouse gases, and churning out deadly smoke from farmers’ custom of burning crop residues.
“Fertigation in our study reduced nitrogen fertilizer needs by 20% while increasing crop yields,” explained Harminder S. Sidhu, a principal research engineer at the Borlaug Institute for South Asia (BISA) and co-author of the Nature Scientific Reports paper. “In medium textured soils, non-flooded rice yielded about 14% less than flooded rice, but the total system productivity of the rice-wheat rotation was higher and growing rice-wheat with fertigation saved labor, time, water, and energy — all of which means costs savings for farmers,” Sidhu explained. “It can also help reduce yearly paddy rice emissions of methane — a greenhouse gas with 25 times the global warming potential of carbon dioxide — which are as high as 4.9 million tons in South Asia.”
Retaining crop residues as mulch, instead of burning them, improves long-term soil health and crop yields, saves water and mitigates extreme pollution in cities such as New Delhi, according to Sidhu.
Given the mounting challenges in northwest India for flooded rice production — including depletion of water tables, soils being degraded from puddling, and the shortage of labor — researchers and policymakers are exploring more sustainable alternatives. Maize, which is grown elsewhere in India and imported to the northwest to feed poultry, offers an option.
In this study, when maize was substituted for rice in rotation with wheat under sub-surface drip fertigation and the conservation agriculture suite of practices, the result was 20% higher system productivity, 49% greater farmer profits, and 85% savings in irrigation water, over the conventional rice-wheat system. “There is also space for quick-growing legumes in our system, adding to profits and nutrition,” said P.C. Sharma, Director of the Central Soil Salinity Research Institute (CSSRI) and co-author of the Nature Scientific Reports paper.
National and state policies in India support practices that save water and avoid residue burning, as well as promoting technologies such as sub-surface drip irrigation systems, said Balwinder Singh Sidhu, Commissioner of Agriculture in the Government of Punjab.
Partners and funders
Funding was provided by the CGIAR Research Program on Wheat (WHEAT), the Indian Council of Agricultural Research (ICAR), the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) and the Government of Punjab, India. We acknowledge the CGIAR Fund Council, the Australian Centre for International Agricultural Research (ACIAR), Irish Aid, the European Union, the International Fund for Agricultural Development (IFAD), the Netherlands, New Zealand, Switzerland, the United Kingdom, USAID, and Thailand for their funding to CCAFS. The basic infrastructure for the study provided by ICAR’s Central Soil Salinity Research Institute (CSSRI) is thankfully acknowledged. BISA and CIMMYT field staff in Karnal, Haryana state, and Ludhiana, Punjab state, greatly contributed to the research.