Influence of topsoil removal and fertilizer application on spring wheat yields

Topsoil loss by wind and water erosion has reduced crop productivity and created soil management problems. Crop yield-soil loss relationships vary, depending on soil, climate, crop, and management practices. The purpose of this study was to determine the relationships among the surface soil removal and additions of nitrogen (N) and phosphorus (P) fertilizer on spring wheat yields and yield components. Soil was mechanically removed from the surface of a Williams loam (fine-loamy mixed, Typic Argiboroll) to 0.00-, 0.06-, 0.12-, and 0.18-m depths in a spring wheat (Triticum aestivum L.)-fallow rotation. Three levels of N (0, 35, and 70 kg ha-1) and three levels of P (0, 20, and 40 kg ha-1) were applied in all combinations to each soil removal treatment prior to seeding a spring wheat crop. In 3 of 5 years, soil removal treatments reduced spring wheat yields an average of 9, 28, and 45% for 0.06-, 0.12- and 0.18-m soil removal treatments, respectively, when averaged over all fertilizer treatments compared to 0.00-m soil removal treatment. The other 2 years were water limiting and soil removal treatments were not a factor. Application of 20 and 40 kg ha-1 of P fertilizer increased grain yields 75 to 400 kg ha-1 with yield increase associated with in increase in heads m-2 and kernels head-1. Phosphorus application tended to decrease grain N concentration because grain yields were increased which caused a dilution in grain N concentrations. Application of 35 and 70 kg ha-1 of N, in combination with either 20 or 40 kg ha-1 of P, resulted in greater grain yield increases when compared to N application without P. Generally 70 kg ha-1 of N and 20 kg ha-1 of P increased grain yields on 0.06-, 0.12-, and 0.18-m soil removal treatments to at least the same yield as 0.00-m soil removal treatment without N or P fertilizer. These data suggest P was the most limiting nutrient and additions of N fertilizer without P resulted in small yield increases.