EFFECT OF LANDSCAPE POSITION ON SOIL-WATER AND CORN-SILAGE YIELD

Systematic variation in plant-available water at different landscape positions is thought to be one of the most important factors controlling crop production. The objectives of this study were to evaluate variability in equivalent depth of soil water, plant;available water, and soil water pressure as a function of landscape position and their effects on corn (Zea mays L.) silage production. Soil water content to a depth of 1 m and sail water pressure at depths of 30, 45, and 60 cm were monitored at 5-m intervals on an 110-m-long transect, and at 10-m intervals on an 80-m-long transect using neutron attenuation and tensiometers, respectively. Plant-available water at g given time was cal calculated as field measured soil water content minus the soil water content at - 1500 kPa. Corn silage yield was measured on 13.5-m(2) plots cen centered at 5- or 10-m intervals and grouped by landscape position. The foot slope position had the lowest total water content on both transects, but the greatest amount of plant-available water on the longer transect. Equivalent depth of soil water in the upper 1 m of soil decreased from the interfluve to the footslope position and was negatively correlated with silage yield. Soil water pressures were greater at the footslope than the other landscape positions and were positively correlated with silage yield in the shorter transect.