From samosas to chapatis, and bhajis to naan, wheat is an essential ingredient in Indian cooking, and estimated to provide as much as one-fifth of household calories. India is the second-largest producer of wheat globally. The Indo-Gangetic Plains acts as the nation’s breadbasket, supplying 80% of its wheat. However, projections indicate that warming temperatures could reduce wheat yields by as much as one third by mid-century, potentially creating a food crisis for India.

Already, wheat yields are stagnating in many regions, but some areas are producing much higher yields than others. To identify both the size of existing yield gaps and the causes behind them, Meha Jain from the University of Michigan, US, and colleagues used satellite data to produce 30 metre-resolution yield maps from 2001 to 2015 across the Indo-Gangetic Plains.

Using a method known as the Scalable Crop Yield Mapper (SCYM), which uses crop model simulations to train algorithms that translate satellite vegetation indices – measure of the greenness of the crop – into wheat yields, Jain and her colleagues were able to observe the differences in yield across India's breadbasket region without ever setting foot in a field. "This method is exciting because it requires no training data on the ground, which is important for modelling yield in smallholder systems where such field level data may not exist," explained Jain.

The results show a huge difference in wheat yield across the Indo-Gangetic Plains, with the highest yields occurring in the west and the lowest yields in the east. The researchers point out that this difference is partially explained by the cooler climate of the west, along with factors such as subsidized electricity to pump groundwater and better access to irrigation in western regions such as Punjab. But this doesn't explain it all.

Jain and her colleagues also show that if the eastern Indo-Gangetic Plains adopted some of the current best practices used in each district, yields could be increased by as much as 32%. More specifically, if the current best practices from the highest yielding state of Punjab were implemented in the eastern regions, yields could more than double with increases of up to 110%.

"We find that the factors that most explain yield variation across the Indo-Gangetic Plains are temperature and sow date," said Jain. The effect of temperature is not surprising, with previous studies having shown a clear link between warmer temperatures and lower wheat yields. But in this case the researchers find that sow date is often more important than temperature in explaining yield variation. "This is because if wheat is sown late it is more negatively impacted by warm temperatures at the end of the growing season, since the crop has not matured prior to this end of season heat stress," explained Jain.

By improving management strategies, including sowing wheat earlier in the season, farmers in the Indo-Gangetic Plains may stand a chance of beating the heat and, in the eastern plains at least, even increasing their yields.

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