Impact of environmental changes and land management practices on wheat production in India

Spring wheat is a major food crop that is a staple for a large number of people in India and the world. To address the issue of food security, it is essential to understand how the productivity of spring wheat varies with changes in environmental conditions and agricultural management practices. The goal of this study is to quantify the role of different environmental factors and management practices on wheat production in India in recent years (1980 to 2016). Elevated atmospheric CO2 concentration ([CO2]) and climate change are identified as two major factors that represent changes in the environment. The addition of nitrogen fertilizers and irrigation practices are the two land management factors considered in this study. To study the effects of these factors on wheat growth and production, we developed crop growth processes for spring wheat in India and implemented them in the Integrated Science Assessment Model (ISAM), a state-of-the-art land model. The model is able to simulate the observed leaf area index (LAI) at the site scale and observed production at the country scale. Numerical experiments are conducted with the model to quantify the effect of each factor on wheat production on a country scale for India. Our results show that elevated [CO2] levels, water availability through irrigation, and nitrogen fertilizers have led to an increase in annual wheat production at 0.67, 0.25, and 0.26 Mt yr(-1), respectively, averaged over the time period 1980-2016. However, elevated temperatures have reduced the total wheat production at a rate of 0.39 Mt yr(-1) during the study period. Overall, the [CO2], irrigation, fertilizers, and temperature forcings have led to 22 Mt (30 %), 8.47 Mt (12 %), 10.63 Mt (15 %), and -13 Mt (-18 %) changes in countrywide production, respectively. The magnitudes of these factors spatially vary across the country thereby affecting production at regional scales. Results show that favourable growing season temperatures, moderate to high fertilizer application, high availability of irrigation facilities, and moderate water demand make the Indo-Gangetic Plain the most productive region, while the arid north-western region is the least productive due to high temperatures and lack of irrigation facilities to meet the high water demand.