The use of a water budget model and yield maps to characterize water availability in a landscape

Crop yield maps may contain substantial corollary information regarding the distribution of yield related soil properties across a landscape. One of t hese properties is water holding capacity (WHC). Since WHC is an important parameter for crop models and is also critical for crop yield, our objectiv e was to determine if WHC could be estimated by matching simulated yield wi th yield map data. We collected soil cores for water retention measurements and recorded plant phenological stages from 60 plots on four transects ove r two growing seasons (1997 and 1998), Soil cores were also sampled on 40 o ther locations set out on a grid pattern. We utilized a simple water budget model that uses the relative transpiration ratio to calculate relative yie ld from available water in the soil profile. Rainfall, potential evapotrans piration and soil water holding capacity are input. An optimization program varies the WHC to produce a grain yield similar to the one from the yield map at a particular location. This analysis was carried out over several sc ales by averaging yields over 55 m x 71 m, 27 m x 35 m, and 11 m x 14 m are as. Yield data from 2 years were used. Yields from the transects in both ye ars were significantly related to measured WHC in the surface 0-10 cm of so il. The calculated stress indices from the water budget model and estimated available WHC calculated for the 1997 data were similar to those calculate d for the 1998 data where data were aggregated in 27 by 35 m or larger bloc ks. The contour map of estimated WHC was similar to the map of measured WHC for some features though there were also some differences. Use of multiple years of yield data are required to give stable results for estimated wate r holding capacities.. This information could be used in a farm management plan by allowing a producer to classify a field into areas that are buffere d against drought and areas more susceptible to drought. Published by Elsev ier Science B.V.