Comparison of Corn Transpiration, Eddy Covariance, and Soil Water Loss

Abstract

Sap flow gages are used to estimate plant transpiration (an indirect form of soil water loss), but relatively few studies compare transpiration with other measures of soil water loss. The purpose of this study was to compare two landscape positions for transpiration (T) from sap flow measurements, soil water changes estimated by daily neutron probe readings, and evapotranspiration (ET) determined via eddy covariance and associated microclimate measurements. Monitoring at backslope and toeslope positions occurred for 2 wk during the corn (Zea mays L.) early reproductive stage. Evaporation from soil (E) and potential ET were calculated from microclimate measurements. The T from sap flow measurements plus calculated soil E was significantly higher at the backslope position than the toeslope position. Grain yields were within 3% (9020 vs. 8774 kg ha−1) for the toeslope and backslope positions. At the backslope position, crop development was delayed at the milk stage and leaf area index was larger compared with corn at the toeslope position. For July 18th through August 4th, the water table was 0.65 to 0.85 m deep at the toeslope position but 1.70 to 2.28 m deep at the backslope position. Higher water table depths at the toeslope position would supply extra water during dry times compared with the backslope position but could also have caused low temperature stress early in the season. The backslope faced south and could have experienced higher wind speed causing water stress during dry periods. The mid to late 2011 growing season was dry enough to detect landscape position effects.