Long-Term Study Alleviates Water-Use Concern for Biofuel Crops
Potential water requirements are a significant concern for large-scale production of biofuel crops. Studying water use for plant communities across years of varying water availability can indicate how terrestrial water balances will respond to climate change and variability as well as to land cover change. Perennial biofuel crops, likely grown mainly on marginal lands of limited water availability, provide an example of a potentially extensive future land-cover conversion. Researchers at the Department of Energy’s Great Lakes Bioenergy Research Center measured growing-season evapotranspiration based on daily changes in soil profile water contents in five perennial systems—switchgrass, Miscanthus, native grasses, restored prairie, and hybrid poplar—and in annual maize (corn) in a temperate humid climate (Michigan, USA). Three study years (2010, 2011, and 2013) had normal growing-season rainfall, whereas 2012 was a drought year with about half to a third normal rainfall. Overall growing-season mean evapotranspiration for the four years did not vary significantly among corn and the perennial systems. Differences in biomass production largely determined variation in water-use efficiency. Miscanthus had the highest water-use efficiency in both normal and drought years, followed by maize; the native grasses and prairie were lower and poplar was intermediate. Measured water use by perennial systems was similar to maize across normal and drought years and contrasts with earlier modeling studies suggesting that rain-fed perennial biomass crops in this climate have little impact on landscape water balances, whether replacing rain-fed maize on arable lands or successional vegetation on marginal lands. Results also suggest that crop evapotranspiration rates, and thus groundwater recharge, streamflow, and lake levels, may be less sensitive to climate change than has been assumed.
Hamilton, S. K., M. Z. Hussain, A. K. Bhardwaj, B. Basso, and G. P. Robertson. 2015. “Comparative Water Use by Maize, Perennial Crops, Restored Prairie, and Poplar Trees in the U.S. Midwest,” Environmental Research Letters 10, 064015. DOI:10.1088/1748-9326/10/6/064015.