Relationship of apparent soil electrical conductivity to claypan soil properties

Understanding relationships between sensor-based measurements and soil properties related to soil quality may help in developing site-specific management. The primary objective of this research was to examine whether sensor-based apparent soil electrical conductivity (EC.) could he used to predict soil properties for claypan soil. Soil samples were obtained at three depths intervals (0- to 7.5-, 7.5- to 15-, and 15- to 30-cm depths) at 65 locations within a 4-ha area of an agricultural field located in north central Missouri in 2002. Samples were analyzed for numerous physical, chemical, and microbiological properties that serve as soil quality indicators. The EC, measurements were also collected at the coring locations with an electromagnetic induction-based sensor. A combine equipped with a commercial yield-sensing, GPS based recording system was used to map corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields from 1993 to 2002. At the deepest sampling depth, soil bulk density (D,,), clay, silt, cation exchange capacity (CEC), and Bray-1 P were the most significantly correlated (r > 0.55) with ECa. Soil properties were regressed against ECa, and R-2 values were often improved using a quadratic term of ECa, especially at the 0- to 7.5-cm depth. Selected regression models were validated with an independent soil sample data set (n = 20). Soil properties were similar between measured and predicted. Some soil properties (e.g., clay and CEC) and EC, that were positively correlated to yield in years with average or greater than average cumulative July to August precipitation (> 15 cm) were negatively correlated to yield for years with less than average precipitation (< 15 cm). Our results suggest that sensor-based EC, can be a quick and economical way of estimating some claypan soil quality measurements.