THE USE OF A WATER BUDGET MODEL AND YIELD MAPS TO CHARACTERIZE WATER AVAILABILITY IN A LANDSCAPE

Authors: Timlin, Dennis; Pachepsky, Yakov; Walthall, Charles; LOECHEL, S - UNIVERSITY OF MARYLAND

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2000
Publication Date: 1/10/2001
Citation: N/A

Interpretive Summary: Combine yield monitors allow growers to map corn grain yields in fine detail. These crop yield maps may contain substantial corollary information regarding the distribution of the yield related soil properties across a landscape. One of these properties is water holding capacity (WHC). Since WHC is critical for crop yields, our objective was to determine if WHC could be estimated by using measured yields from yield map data. Soil water holding capacity was estimated by using a simple water budget to estimate the available water needed to produce crop yields. This was measured using the combine yield monitor. Field data on soil water holding capacity and corn plant growth and development was measured in an 8-acre field over a period of 2 years. During both years, rainfall was not sufficient to meet the plants' need for water and severe water stress was observed. The soil textures in the field varied from sandy loam to loamy sand. These data verified that a relationship between available water and grain yields existed in the field. The spatial distribution of available water in the field, estimated using 1997 yield data, was similar to the distribution estimated using 1998 yield data. Use of multiple years of yield data is required to give stable results for estimated water holding capacities. This information could be used in a farm management plan by allowing a producer to classify a field into areas which are buffered against drought and areas more susceptible to drought.

Technical Abstract: Crop yield maps may contain information regarding the distribution of yield related soil properties across a landscape. One of these properties is water holding capacity (WHC). Since WHC is critical for crop yield, our objective was to determine if WHC could be estimated by matching simulated yield with yield map data. We collected soil and plant data from 60-plots on four transects, over the 1997 and 1998 growing seasons. Soil cores were also sampled on 40 other locations on a grid pattern. We utilized a simple water budget model which uses the relative transpiration ratio to calculate relative yield from available water in the soil profile. Rainfall, potential evapotranspiration, and soil water holding capacity were input. An optimization program varied the WHC to produce a grain yield similar to the one from the yield map at a specific location. This analysis was carried out over several scales by averaging yields over 55 by 71m, 27 by 35m, and 11 by 14m areas. Yields from the transects in both years were significantly related to measured WHC in the surface 0-10 cm of soil. The calculated stress indices from the water budget model and estimated available WHC calculated for the 1997 data were similar to those calculated for the 1998 data where data was aggregated in 27 by 35 m or larger blocks. The contour map of estimated WHC was similar to the map of measured WHC for some features though there were also some differences. The use of multiple years of yield data are required to give stable results for estimated WHC. This information could be used in a farm management plan by allowing a producer to classify a field into areas that are buffered against drought and areas more susceptible to drought.