Soil electrical conductivity as a crop productivity measure for claypan soils

Inexpensive and accurate methods for spatially measuring soil properties are needed that enhance interpretation of yield maps and improve planning for site-specific management. This study was conducted to investigate the relationship of apparent profile soil electrical conductivity (ECa) and grain yield on claypan soils (Udollic Ochraqualfs). Grain yield data were obtained by combine yield monitoring and ECa by a mobile, on-the-go electromagnetic (EM) induction meter. Investigations were made on four claypan fields between 1993 and 1997 for a total of 13 site-years. Crops included five site-years of corn (Zea mays L.), seven site-years of soybean [Glycine max (L.) Merr.], and one site-year of grain sorghum [Sorghum bicolor (L) Moench]. Transformed ECa (1/ECa) was regressed to topsoil thickness giving r(2) values > 0.75 for three of the four fields. The relationship between grain yield and ECa was examined for each site-year in scatter plots. A boundary line using a log-normal function was fit to the upper edge of data in the scatter plots. A significant relationship between grain yield and ECa (boundary lines with r(2) > 0.25 in nine out of 13 site-years) was apparent, but climate, crop type, and specific field information was needed to explain the shape of the potential yield by ECa interaction. Boundary line data of each site-year fell into one of four condition categories: Condition 1-site-years where yield increased with decreasing ECa; Condition 2-site-years where yield decreased with decreasing ECa; Condition 3-where yield was less at low and high ECa values and highest at some mid-range values of ECa; and Condition 4-site-years where yield variation was mostly unrelated to ECa. Soil ECa provided a measure of the within-field soil differences associated with topsoil thickness, which for these claypan soils is a measure of root-zone suitability for crop growth and yield.