Studying crop yield constraints from space in Punjab, India
Though it's difficult to predict the exact rate of population growth in the coming years, most published studies agree that the number of people on Earth will continue to rise in the near future, likely reaching 9 billion by the middle of this century. The implications of this continual crowding of the planet will be many and varied, but perhaps one of the most basic problems is the question of how to feed an extra 2+ billion people.
Increasing food production, while at the same time preserving natural ecosystems, will require further increases in production on existing croplands. Crop yield, generally measured in tonnes/hectare, depends on many variables, some of which farmers and scientists understand well, and some of which are still relatively unstudied. Society has directed considerable energy and resources to improving crop varieties, conferring on them resistance to pests and diseases, tolerance to drought and heat, and the ability to allocate more of the photosynthetic energy they capture into the grains we consume. Through breeding, and through the development of new fertilizers, irrigation systems, and pesticides, we've seen substantial increases in the maximum potential yields of our main food crops.
But in farmers' fields, we still observe vast variation in the yields actually achieved. Although a casual observer might say that all fields look the same, for example when driving through the Central United States, in fact yields often vary by a factor of two or more between nearby fields. The gap between the potential yields of these crops and the yields actually achieved represents food we could be producing but aren't, stomachs that could be filled but instead go empty. The focus of this project is to determine what factors are contributing to this yield gap in selected regions around the world, and at what magnitude, so that we can better understand where to direct future research aimed at closing that gap.
One region of interest is the Indian Punjab, one of the most intensive and important wheat growing regions in the world. The first image below shows satellite-based yield estimates for a six district area in the Punjab covering over 1 million hectares. The second image shows a closer look at the full resolution (28.5 m) of the data. Red indicates fields with yields near 5 ton/ha, while blue indicates yields of roughly half this value. We can use these maps for several years, combined with data on climate, soil type, and geographic and manmade features such as waterways and roads, to increase our understanding of the factors affecting grain yield in the Punjab. These techniques are transferable to other regions of the world, so in time we may be able to diagnose yield gaps across the globe, leveraging the power of remote sensing to help produce more food and potentially use less water and other inputs in the process.