Estimating Plant‐Available Water Using the Simple Inverse Yield Model for Claypan Landscapes

Plant‐available water (PAW) is one of the fundamental soil factors affecting crop yield, yet quantitative determination of plant‐available water capacity (PAW c ) at a field scale has been challenging. A simple inverse yield model (SIYM) has been devised and shown to be successful in estimating PAW c at a field scale for well‐drained soils by matching simulated corn ( Zea mays L.) yield with measured yield. For other soils, however, SIYM is yet to be tested. Our objective was to evaluate SIYM performance in estimating PAW c for poorly‐drained claypan‐soil landscapes. Soil PAW c to a depth of 1.2 m (PAW 1.2 ) was measured at 19 and 18 sampling locations for two claypan‐soil fields, Fields 1 and 2, respectively. Corn yield maps of the two fields (nine site‐years between 1993 and 2003) were used with the model to estimate PAW c Yield reduction associated with low precipitation and high vapor‐pressure deficit during corn reproductive stages, and large yield variation in dry years were indications available water was the main yield‐limiting factor. The regression r 2 values between SIYM‐estimated PAW c and the measured PAW 1.2 were 0.43 for Field 1 and 0.31 for Field 2 with estimating errors of 18 and 50 mm, respectively. In Field 2, SIYM estimated markedly lower PAW c compared with the PAW 1.2 at the most‐eroded backslope areas, where claypan characteristics were most prevalent. The SIYM‐PAW c estimates would be more informative in assessing soil productivity because they are based on crop‐water relations and not solely on soil texture.