Soil electrical conductivity as a crop productivity measure for claypan soils

Inexpensive and accurate methods for spatially measuring soil properties ar e needed that enhance interpretation of yield maps and improve planning for site-specific management. This study was conducted to investigate the rela tionship of apparent profile soil electrical conductivity (ECa) and grain y ield 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 betw een 1993 and 1997 for a total of 13 site-years. Crops included five site-ye ars of corn (Zea mays L.), seven site-years of soybean [Glycine max (L.) Me rr.], and one site-year of grain sorghum [Sorghum bicolor (L) Moench]. Tran sformed 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 an d ECa was examined for each site-year in scatter plots. A boundary line usi ng a log-normal function was fit to the upper edge of data in the scatter p lots. A significant relationship between grain yield and ECa (boundary line s 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 whe re 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 pr ovided a measure of the within-field soil differences associated with topso il thickness, which for these claypan soils is a measure of root-zone suita bility for crop growth and yield.