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Measurement of Cover Crop Evapotranspiration and Impacts on Water Management in Crop Production Systems

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2012 Dallas, Texas, July 29 - August 1, 2012  121337007.(doi:10.13031/2013.41727)
Authors:   Christopher H Hay, Brett Hankerson, Jeppe H Kjaersgaard
Keywords:   Evapotranspiration, cover crop, Bowen ratio, remote sensing, METRIC

The use of cover crops is an increasingly popular sustainable farming practice that provides many benefits to the soil and subsequent cash crops. This research examines how the water usage of a cover crop affects the water availability within a crop rotation. The objective was to evaluate evapotranspiration (ET) of a cover crop mixture within a crop rotation in eastern South Dakota using field measurements and remote sensing. ET of spring wheat followed by a cover crop mixture was measured using a Bowen ratio energy balance system, and the METRIC model was used to estimate ET using Landsat images for two dates during the growing season of 2011. The results show that the cover crop used 136 mm of water from planting until the first hard freeze, while the spring wheat crop used 382 mm of water from the date of instrument installation until harvest. Calculated midseason crop coefficient values for the spring wheat were 1.5 and 1.2 for grass and alfalfa reference surfaces, respectively, which are higher than typical values and may be due to calculations based on measurements over a non-standard surface. METRIC estimated ET on 6 July compared well with BREBS-measured wheat ET, but there was less agreement for the 2 October image that included the cover crop surface.

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