Water footprints of cellulosic bioenergy crops

MZ Hussain, S Hamilton, A Bharadwaj, B Basso, and GP Robertson
W.K. Kellogg Biological Station; Department of Plant, Soil, and Microbial Sciences; Great Lakes Bioenergy Research Center; Department of Geological Sciences; Department of Integrative Biology, Michigan State University; Central Soil Salinity Research Institute, Indian Council of Agricultural Research

Presented at the All Scientist Meeting (2015-04-15 to 2015-04-16 )

Water use by plant communities across years of varying water availability indicates 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. We measured growing-season evapotranspiration (ET) 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 (480-610 mm) whereas 2012 was a drought year (210 mm). Over all four years, mean (±SEM) growing-season ET for perennial systems did not greatly differ from corn (496±21 mm), averaging 559 (±14), 458 (±31), 573 (±37), 519 (±30), and 492 (±58) mm for switchgrass, miscanthus, native grasses, prairie, and poplar, respectively. Differences in biomass production largely determined variation in water use efficiency (WUE). Miscanthus had the highest WUE in both normal and drought years (52-67 and 43 kg dry biomass ha-1 mm-1, respectively), followed by maize (40-59 and 29 kg ha-1 mm-1); the native grasses and prairie were lower and poplar was intermediate. That measured water use by perennial systems was similar to maize across normal and drought years contrasts with earlier modeling studies and suggests that rain-fed perennial biomass crops in this climate will not much alter landscape water balances, whether replacing rain-fed corn on arable lands or successional vegetation on marginal lands. Results also suggest that crop ET rates, and thus groundwater recharge, streamflow, and lake levels, may be less sensitive to climate change than has been assumed.

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