Understanding soil water dynamics and evapotranspiration (ET) is imperative to predict the interactions between bioenergy cropping systems and water resources; yet measurements of these variables under bioenergy crops in the U.S. Southern Great Plains (SGP) are limited. The objectives of this study were to quantify and compare soil water dynamics and ET under switchgrass (Panicum virgatum L.), biomass sorghum [Sorghum bicolor (L.) Moench], and mixed perennial grasses managed for biofuel production. Soil water content was measured from 2011 through 2013 at Stillwater, OK, and from 2012 through 2013 at Chickasha, OK, and ET was estimated using the soil water balance approach. For these crops, soil water depletion occurred mainly above the 2.0-m depth, suggesting negligible root water uptake below 2.0 m. Growing season soil water depletion ranged from 4 to 287 mm and was greater ( alpha =0.10) for sorghum than switchgrass in 2 out of 5 site-yr, while mixed grasses exhibited the greatest soil water depletion in 1 out of 3 yr. Growing season soil water depletion was positively related to initial soil water content. Crop year ET ranged from 493 to 846 mm and was greater for switchgrass than sorghum in 2 out of 3 site-yr. At Stillwater, average crop year ET measured for 2 yr was 676 mm for switchgrass, 630 mm for sorghum, and 717 mm for mixed grasses. In the SGP, rainfed bioenergy production systems based on biomass sorghum may consume less water per unit land area than systems based on perennial grasses.
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