Experts focus on water use

Irrigation and productivity


Producing higher yields using less water would feed more people

LINDELL BEACH, B.C. — Climate change is starting to focus on water productivity and the amount of food produced in relation to the amount of water consumed.

These issues will become even bigger for farmers and consumers as precipitation patterns change and the global population increases.

Scientists with the University of Minnesota’s Institute on the Environment (IonE) and the University of Bonn’s Institute of Crop Science and Resource Conservation (INRES) have analyzed crop production, water use and productivity of 16 staple crops grown in 20 climatic zones around the world.

Crops included wheat, corn, rice, barley, rye, millet, sorghum, soybean, sunflower, potato, cassava, sugar cane, sugar beet, oil palm, rapeseed and groundnut. They represent 56 percent of global crop production by tonnage, account for 65 percent of crop water consumed and are grown on 68 percent of all cropland.

“What we looked at was how much food is being produced in relation to how much water is used,” said Kate Brauman, global landscapes initiative postdoctoral fellow with IonE and the lead author of the report.

“What was the crop yield and how much water was used during the growing period, (including) how much water was evaporated from the ground or from the crop during that growing period.”

The team’s report, Improvements in crop water productivity increase water sustainability and food security — a global analysis, was published online in Environmental Research Letters.

“Reducing the amount of water required for crop production and increasing crop water productivity is a key strategy for achieving food security and water sustainability in a world with growing demands for both,” Brauman wrote.

“If, for example, low water productivity in precipitation-limited regions were raised to the 20th percentile, the total rain-fed food production in Africa could be increased by more than 10 percent without exploiting additional cropland.

“Similar improvements in water productivity on irrigated cropland could reduce total water consumption by eight to 15 percent in precipitation-limited regions of Africa, Asia, Europe, and South America.”

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Brauman defined the 20th percentile as a baseline for the least amount of productivity to grow a crop.

“The 20 percent is a survival guide. The number means that even if we just try to intervene at this level, we get results. If we get farmers to the 20 percent baseline, they will increase food production with less water and more food as a result.”

The use of irrigation consumes more water than any other human activity. For the 16 crops studied, 52 percent of rainwater consumption (by irrigated and rain fed crops) and 82 percent of irrigation water consumption occur in regions of limited rainfall.

However, water consumption can be disproportionately large for the volume of food produced.

“On the least water-productive rain-fed cropland in precipitation-limited regions, over 46 percent of water was consumed in the production of just 20 per cent of maize calories,” Brauman wrote.

The team looked at locations where crops are irrigated and where crops are rain fed. In rain-fed areas, re-searchers explored how to get more food out of the same area.

Researchers accounted for different evaporation and humidity rates and addressed the level of variation in a climate zone as they adjusted for the influence of microclimates.

She said it is reasonable to irrigate, but the issue comes down to what is being irrigated and how a limited resource such as water is being used.

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“We looked at ratios of kilocalories to water,” she said.

“If you are growing crops but not getting a very good yield, a lot of the time you are using the same amount of water. You are still growing plants, but the ratios would be different.”

She said those ratios vary not only because of microclimates but also because of management practices such as the use of fertilizer, weed problems, pests, and the application of conservation tillage.

Improving water use efficiency by 20 percent would measurably increase food production but researchers estimate a 30 percent increase is possible in precipitation-limited regions, providing food for more than 110 million people annually.

On irrigated cropland, increasing the lowest water productivity in low rainfall regions would save water consumption without reducing food production. The water savings would amount to more than 25 percent of the current water consumption and would be enough to meet the annual domestic water demand of potentially 1.4 billion people.

“The power of a global study like this is that it tells you what is possible and relatively where you sit,” said Brauman.

“It does not tell you the specifics of technology, but it shows that you can do better and points you in the right direction. In Canada and the U.S., we do pretty well and get high yields. But there are lots of places where yields like ours do not happen.”

Brauman said a lot of the water issues will involve hard political decisions of reallocation and changes in economics.

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“People are starting to really think about water and think about the future. There are a lot of pieces to the puzzle, but we have to start using water more efficiently.”