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More Planning Needed for Water Use in Biofuel Crops

Miscanthus (Oak Ridge National Lab)

Miscanthus (Oak Ridge National Lab)

An overlooked factor in planning for prairie grasses as biofuel feedstocks is their use of water, according to a new study by researchers in the U.S. and Germany. Their findings appear this week in the journal Proceedings of the National Academy of Sciences (paid subscription required).

Engineers Praveen Kumar and Phong Le at University of Illinois in Champaign-Urbana and former postdoc Darren Drewry now at the Max-Planck-Institut für Biogeochemie in Jena, Germany investigated the water needs of second generation bioenergy crops such as miscanthus and switchgrass. They developed a mathematical model to estimate water requirements, taking into account the crops’ foliage density and length of growing season, as well as environmental factors, such as changes in rainfall and temperature from climate change.

In their National Science Foundation-funded study, Kumar’s team notes that miscanthus and switchgrass cover more surface area and much denser growth than corn, which makes them good for increasing biomass. But they also intercept light and rain differently from corn and lose more water through transpiration, causing them to pull more water from the soil.

These impacts on water supplies are affected further by climate change, characterized by higher concentrations of carbon dioxide in the atmosphere, higher temperatures, and changing rainfall patterns. Higher levels of carbon dioxide can make the plants more water-efficient, since their pores are open less time to absorb carbon dioxide.

But this gain in efficiency if offset by rising temperatures. Plants will transpire more while their pores are open, losing more water than they save, which compounds the increase in water usage from land conversion.

In the U.S. Midwest, says Kumar, rainfall should remain sufficient to meet water demand. However, areas that rely on irrigation could find they have less water to meet higher demands, which could increase the net cost of large-scale land conversion and put pressure on already stressed water resources.

Water is “already a scarce resource across the globe, and the need for it is only going to increase,” notes Kumar. “The cost of that should be factored in to the decision making.”

Read more: Long-Term Impacts of Biofuels on Land Analyzed

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