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

Systematic variation in plant-available water at different landscape p ositions is thought to be one of the most important factors controllin g crop production. The objectives of this study were to evaluate varia bility in equivalent depth of soil water, plant;available water, and s oil water pressure as a function of landscape position and their effec ts on corn (Zea mays L.) silage production. Soil water content to a de pth 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 int ervals on an 80-m-long transect using neutron attenuation and tensiome ters, respectively. Plant-available water at g given time was cal calc ulated as field measured soil water content minus the soil water conte nt at - 1500 kPa. Corn silage yield was measured on 13.5-m(2) plots ce n centered at 5- or 10-m intervals and grouped by landscape position. The foot slope position had the lowest total water content on both tra nsects, but the greatest amount of plant-available water on the longer transect. Equivalent depth of soil water in the upper 1 m of soil dec reased from the interfluve to the footslope position and was negativel y correlated with silage yield. Soil water pressures were greater at t he footslope than the other landscape positions and were positively co rrelated with silage yield in the shorter transect.