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Title: Field estimation of specific yield in a Central Iowa crop field

item Logsdon, Sally
item SCHILLING, KEITH - Iowa Department Of Natural Resources
item Hernandez Ramirez, Guillermo
item Prueger, John
item Hatfield, Jerry
item Sauer, Thomas

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2009
Publication Date: 4/23/2010
Citation: Logsdon, S.D., Schilling, K.E., Hernandez Ramirez, G., Prueger, J.H., Hatfield, J.L., Sauer, T.J. 2010. Field estimation of specific yield in a Central Iowa crop field. Hydrological Processes. 24(10):1369-1377.

Interpretive Summary: In non-irrigated areas, the water for the crops comes from rain and from the soil and groundwater. We need to know how much water is available in the soil and groundwater to sustain the crop during periods between rains. This study showed how much water drained to the groundwater in response to rain and how much water moved up from the groundwater in response to evaporation. When crops were growing, we needed to know the loss or gain of water in the root zone to get an accurate estimate of water gain or loss from the water table. After the growing season, the former root zone was rewetted with early rains, and was not affected much by later fall rains. Then the water drained more rapidly and completely to the water table. This information is important for scientists who study soil water, and for farmers and advisors that want to maximize crop use of rainfall in non-irrigated agriculture.

Technical Abstract: The specific yield (Sy) is the gain or loss of water associated with water table rise or fall. Rain is partially intercepted by the canopy, refills the soil pore system, or may be taken up by plant roots growing in the soil pores before reaching the water table. Water lost from the root zone may be replenished from a shallow water table, so water table loss is indirectly tied to evapotranspiration (ET). The purpose of this study was to use automated data for back-calculating Sy from the different components of the water cycle for both wetting and drying conditions. Two time periods were considered for a toeslope site in an Iowa corn (Zea mays L.) field: actively-transpiring plant during 22 June to 10 July 2007, and post season 13 to 30 October 2007. The field was instrumented with Eddy covariance for ET estimates, tipping bucket rain gauge, automated well-depth recorder, and water content reflectometers (CS616s) for soil water content. There were few day-night differences in water table changes, indicating not much net lateral addition or loss. The day-night differential root zone water losses were apparent after a few days during the time of active crop growth but not post-season. During drying in the active crop growth period, mean Sy was 0.19. During wetting, estimates of Sy were improved when soil water increase was subtracted from total rainfall; then the mean wetting Sy was 0.052. The water balance procedure was useful to provide Sy estimates.