Submitted to: North Central Extension Industry Soil Fertility Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/16/2000
Publication Date: N/A
Technical Abstract: Soil sampling for fertilizer recommendations is most often from the surface 15 to 20 cm. However, the nutrient pool available to crops might be quite variable when considering the spatial variation in the sub-soil nutrient pool. The objective of this research was to assess the potential interaction between claypan soil topsoil thickness (i.e., depth to the claypan) and soil-test phosphorus (P) and potassium (K) on corn and soybea crop response. Plots were established in 1996 on a corn-soybean field near Centralia, MO with varying topsoil thickness (5 to 119 cm). A range of soil-test P and K values was achieved with fertilization in the springs of 1996 and 1999. Both soil-test P and K decreased dramatically over the 1997 and 1998 cropping period, indicating minimal buffering capacity of the surface soil for fertilizer additions. Erosion classes based on topsoil depth significantly explained the majority of corn yield variation in 1997 and 1999. In three crop-years yield response to higher soil test values was best in areas of enhanced topsoil thickness. Generally, sub-soil P and K were negatively correlated with topsoil thickness, an explanation for why we observed a recurring crop response to surface soil-test P and K in areas with greater topsoil thickness.