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SOIL & WATER

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

^a Dep. of Environmental Sci., 2323 Geology Bldg., Univ. of California, Riverside, CA 92521
^b 269 Agric. Eng. Bldg., USDA-ARS, Cropping Systems and Water Quality Research Unit, Columbia, MO 65211
^c 302 ABNR Bldg., Dep. of Soil, Environmental and Atmospheric Sci., Univ. of Missouri, Columbia, MO 65211

^* Corresponding author (pingping.jiang{at}ucr.edu).

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 r² 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.

Abbreviations: EC_a, bulk soil apparent electrical conductivity • PAW, plant available water • PAW_c, plant available water capacity • PAW_1.2, plant available water capacity for a 1.2 m soil profile • VPD, vapor pressure deficit • SIYM, simple inverse yield model

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Received for publication June 19, 2007.