Soil Electrical Conductivity as a Crop Productivity Measure for Claypan Soils

Abstract

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 (EC a ) and grain yield on claypan soils (Udollic Ochraqualfs). Grain yield data were obtained by combine yield monitoring and EC a 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 EC a (1/EC a ) was regressed to topsoil thickness giving r 2 values > 0.75 for three of the four fields. The relationship between grain yield and EC a 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 EC a (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 EC a interaction. Boundary line data of each site-year fell into one of four condition categories: Condition 1-site-years where yield increased with decreasing EC a ; Condition 2-site-years where yield decreased with decreasing EC a ; Condition 3-where yield was less at low and high EC a values and highest at some mid-range values of EC a ; and Condition 4-site-years where yield variation was mostly unrelated to EC a . Soil EC, 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.