Tillage and Cropping System Effects on Nutrient Availability and Stratification in the Central Great Plains.

Conventionally tilled winter wheat is a dominant component of dryland cropping systems in the central Great Plains. However, row-crop introduction to cropping systems is increasing with adoption of no-till agriculture. Changes in cropping systems and tillage impact nutrient inputs, uptake, and soil mixing. The objectives of this study were to determine the effects of cropping and tillage changes on nutrient availability and stratification. A long-term (10-year) study on a Ladysmith silty clay loam soil was conducted to evaluate the effects of tillage on corn and soybean production versus grain sorghum in an annual rotation with winter wheat and to compare these rotations with monoculture wheat and grain sorghum. Soils were sampled at 0-5, 5-10, and 10-15 cm prior to and following the study period. No-till production decreased surface pH more than reduced till, but did not influence pH below 10 cm. Wheat-soybean cropping systems had the highest soil pH, likely due to decreased N fertilizer inputs to those systems. No-till increased soil test P concentrations compared to reduced-till in all crop rotations except continuous wheat. Tillage effects on P concentration were only observed at 0-5 cm. No-till production also resulted in higher soil organic matter content. Tillage effects on soil organic matter were more pronounced in continuous wheat, wheat-sorghum, and wheat-soybean crop rotations. Cropping these plots for over 20 years without K inputs has decreased exchangeable K by over 50%, but K concentrations are still in excess of crop requirements. Results of this study suggest that changes in cropping systems and tillage will affect the long-term fertility status of soils.