Topsoil Thickness Effects on Corn, Soybean, and Switchgrass Production on Claypan Soils

Core Ideas Grain relative yield increased with depth to claypan, while switchgrass relative yield was unaffected. Grain yield was twice as temporally variable as switchgrass yield. Grain crops generally were more profitable than switchgrass across depth to claypan. Switchgrass has the capacity to reduce yield variability caused by depth to claypan.Diminished topsoil thickness, or depth to claypan (DTC), is a major cause of yield and profit depression in corn ( Zea mays L.) and to a lesser extent in soybean [ Glycine max (L.) Merr.] production on claypan soils in the U.S. Midwest. Perennial grasses, such as switchgrass ( Panicum virgatum L.), may be more resilient to reduced DTC than grain crops. Therefore, a study was conducted on a Missouri claypan soil to compare production and profitability of switchgrass grown for bioenergy to corn and soybean grain over varying DTC. Corn, soybean, and switchgrass yield were measured from 2009 to 2015 on plots constructed with DTC representative of those found on claypan landscapes. Yield, annual by‐crop relative yield (RY), yield coefficient of variation (CV), and return to land and management (net return) were evaluated by year, within wet and dry year categories, and across all years. Results indicate that corn and soybean RY across years increased to a maximum of 82 and 79% at DTC of 32 and 21 cm, respectively. Switchgrass RY was unresponsive and averaged 72% across DTC. Corn, soybean, and switchgrass yield CV averaged 46, 35, and 17%, respectively. Corn and switchgrass net return increased with DTC to a maximum of US$386 and $134 ha −1 at DTC of 31 and 32 cm, respectively, while soybean net return averaged $634 ha −1 across DTC. In general, switchgrass yield was less variable than grain production across DTC, and switchgrass could compete economically with corn on shallow DTC (<3 cm).