Evapotranspiration of Annual and Perennial Biofuel Crops

Cellulosic feedstocks in the US are expected to contribute about half of the 2022 bioethanol target. However, there is a concern that cellulosic perennial biofuel crops consume more water than corn grain as a biofuel crop. We previously studied evapotranspiration (ET) from corn, switchgrass and restored prairie fields three years after they were converted from Conservation Reserve Program (CRP) grasslands and agricultural lands. We also had one CRP grassland (CRP-Ref) that was maintained in brome grass. However, in that study the perennial biofuel crops were in their establishment phase. In this study, we have added four years of data to include post-establishment ET from the perennial biofuel crops. Over all years, the ET from the CRP-Ref field was consistently higher than the ET from all the converted biofuel crops. Within the biofuel crops, there was no single crop that had consistently higher ET than all the other fields. ET in the first two years after conversion was higher at AGR than at CRP fields for each crop. ET during the drought year 2012 was the lowest and similar at all converted fields, irrespective of land use history. Post 2012, the ET at CRP lands was higher than the ET at AGR lands for the perennials but it was similar at both CRP and AGR fields for corn. In sum, there was no consistently clear difference in ET between the annual corn and perennial biofuel crops. Large-scale conversion of annual row-crops to perennial grasses, therefore, may not drastically alter watershed water balance.