Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2017
Publication Date: 6/22/2017
Citation: Conway, L., Yost, M.A., Kitchen, N.R., Sudduth, K.A. 2017. Using topsoil thickness to improve site-specific phosphorus and potassium management on claypan soil. Agronomy Journal. 109(5):2291-2301. doi:10.2134/agronj2017.01.0038.
Interpretive Summary: Substantial soil loss after years of annual row crop production on claypan soils has led to varying topsoil thickness across fields in Missouri, resulting in complex nutrient dynamics across landscapes. Determining how this erosion has affected the soil’s ability to buffer against change is crucial for maximizing grower fertilizer inputs. Research was conducted near Columbia, MO from 2009 to 2016 to determine if accounting for topsoil thickness could enhance fertility management of corn, soybean, and switchgrass. Results indicated that soil test phosphorus and the amount of fertilizer required to raise soil test potassium increased as topsoil thickness increased. Conversely, soil test potassium decreased as topsoil thickness increased. These findings demonstrate that adjusting fertility rates based upon topsoil thickness could result in more efficient use of phosphorus and potassium fertilizers on claypan soils. This information will help retailers and producers in determining the most accurate fertilizer amount to apply at a specific location within a field.
Technical Abstract: Precise P and K fertilizer management on claypan soils can be difficult due to variable topsoil thickness, or depth to claypan (DTC), across landscapes, nutrient supply from subsoils, and crop removal. Therefore, a study was performed to determine if DTC could be used to improve P and K management for corn (Zea mays L.), soybean [Glycine max (L.)], and switchgrass (Panicum virgatum L.). Research was conducted on a claypan soil at the University of Missouri’s (MU) South Farm Research Center in Columbia, MO, from 2009 to 2016. Corn, soybean, and switchgrass were grown each year on 16 plots with constructed DTC ranging from 0 to 94 cm. Surface soil samples for soil test phosphorus (STP) and potassium (STK) were collected in the early spring of 2009, 2015, and 2016. Fertilizer was applied shortly after soil sampling in 2009 and 2015 based on the MU buildup recommendation. Results in the spring of 2015 showed that STP increased 0.53, STK decreased 4.4, and the phosphorus buffering index (BIP) decreased 0.94 kg ha–1 with each 1 cm increase in DTC. Most importantly, across the 2015 growing season the amount of fertilizer K needed to raise soil test potassium by 1 kg ha–1 (REQK) was four times greater at DTC of 44 than 0 cm. These relationships show that accounting for DTC could improve current fertility guidelines by applying more, or more frequent P, and less K on shallow soils.