Effects of thirty years of irrigation on the genesis and morphology of two semiarid soils in Kansas

Widespread adoption of irrigation began to occur in western Kansas in the 1950s. The western third of the state is in the ustic moisture regime, receiving about 400 to 500 ram of precipitation per year. Irrigation adds an additional 300 to 600 mm of water per year and effectively alters the natural climate. The Richfield and Keith soil series were investigated to determine if irrigation has caused changes in soil properties and morphology, affecting the genesis of irrigated soils. For each series, 10 long-term (28-31 yr) irrigated pedons and 10 adjacent pedons that had never been irrigated were sampled. The pH of the surface horizons of the irrigated Keith and Richfield pedons was 1.0 pH unit higher than the dryland pedons. Exchangeable sodium percentage (ESP) was also higher in irrigated pedons. Irrigation did not significantly affect organic C content or the calcium carbonate equivalent (CCE). Irrigated pedons contained significantly higher amounts of total clay and showed an altered clay distribution within the profile. They also exhibited more strongly expressed argillic horizon properties in the field and in thin section than nonirrigated pedons. The data indicate that =30 yr of irrigation increased clay illuviation and mineral weathering, altered the surface horizon pH and ESP, and modified the natural genetic processes by increasing the rate of pedogenic activity.