Soil Available Water as Influenced by Landscape Position and Aspect1

Abstract

In dryland farming, stored soil water is an essential source of water for crop production. The amount of water available for storage and crop use in a particular soil in hillslope topography is affected by its position on the landscape. The effect of slope aspect and position on soil water and its changes throughout the year in dryland farming were studied in southeast Nebraska. North, south, and east‐facing slopes of Wymore silty clay loam (Aquic Argiudolls fine, montmorillonitic mesic) were selected for study. Four positions on each slope including summit, shoulder, backslope, and footslope were identified. Water content of the soil from 0 to 150 cm depth in 30 cm increments was measured weekly by neutron scattering for 2 years. Daily precipitation was recorded. Twenty percent more water was available in soils on the north‐facing slope than in soils on the south‐facing slope at planting and throughout the year. Soils on the east‐facing slope were the driest. They contained 50% less available water than did those on the north‐facing slope. Within slope positions, soils on the footslopes and backslopes contained an average of 4 cm more available water than soils on the summits and shoulders. Soil water sampling at planting time for crop management and yield prediction models should be done according to slope position.