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Irrigation’s yield advantage

The yield gap between irrigated vs. rainfed crops spreads.

A 65-year-long comparison finds the gaps between irrigated and non-irrigated crop yields are widening.

University of Nebraska’s Suat Irmak and Meetpal Kukal analyzed the annual yields of nine crops on a county-by-county basis over a 65-year period starting in the 1950s. They found that the differences in food produced with irrigation vs. rainfall alone generally widened over that span, a trend they suspect stems partly from climate change and technological advances in irrigation management.

“You get more yield from irrigated than rainfed (agriculture), but the magnitude of yield increase is a function of several variables,” Irmak notes. “It’s not surprising that as precipitation increases, the yield gap decreases.”

Corn benefits the most from irrigation, experiencing a massive 170% gain in yields. On the other hand, the unique growing season of winter wheat, for example, meant that its yields rose only nominally with irrigation. Yet even crop-specific yield gaps varied noticeably by location. Two corn-growing areas separated by about 700 miles, for instance, saw a sevenfold difference in irrigation-related yield gains.

Having mapped such differences across roughly 80% of cultivated land in the United States, the researchers say the findings can help guide future crop production while calibrating water management and irrigation use nationwide.

“Irrigation on 24% of the cultivated land produces 40% of the total global food supply,” Irmak points out. “If we stopped irrigating today, more people would suffer due to substantially reduced food, fiber, and feed production, especially in areas that are already experiencing a significant shortage of supplies.”

Minimizing negatives 

Irmak adds that researchers looked at reducing the negative environmental impact of irrigation. “I do acknowledge that irrigation may have some negative environmental effects when management is not practiced properly,” he says.

Irmak says he regularly encounters irrigation-related pushback from colleagues who study environmental issues, including irrigation’s role in ferrying nitrogen and other fertilizer components into groundwater. He quickly points out, however, that irrigation contributes substantially to food production.

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