Testing The Water For Bioenergy Crops

Many energy researchers and environmental advocates are excited about the prospect of gaining more efficient large-scale biofuel production by using large grasses like miscanthus or switchgrass rather than corn. They have investigated yields, land use, economics and more, but one key factor of agriculture has been overlooked: water. "While we are looking for solutions for energy through bioenergy crops, dependence on water gets ignored, and water can be a significant limiting factor," said Praveen Kumar, the Lovell Professor of civil and environmental engineering at the University of Illinois. "There are many countries around the world that are looking into biofuel energy, but if they are adopting these (large grasses) into their regular policy, then they need to take into account the considerations for the associated demand for water."

Kumar led a study, published in the Proceedings of the National Academy of Sciences Early Edition, detailing effects to the hydrologic cycle of large-scale land conversion, both now and as growing conditions change in the future.

Miscanthus and switchgrass have a very different above-ground foliage structure from corn -- more surface area and much denser growth. This is good for maximizing the amount of biomass that an acre of land can produce, but it also increases water use. Miscanthus and switchgrass intercept light and rain differently from corn, and lose more water through transpiration, causing them to pull more water from the soil. The result of large-scale adoption would be a reduction in soil moisture and runoff, but an increase in atmospheric humidity.

"All these together account for the changes in hydrology, just from land-use change," said Kumar, who also is affiliated with the department of atmospheric sciences. "Then, if you impose further -- higher carbon dioxide in the atmosphere, higher temperatures and changes in rainfall patterns -- they add further modulation to the water use pattern."