Crop residue effects on electrical conductivity of Tennessee Valley soils

Electrical conductivity (ECa) measurements taken with soil-contact sensors are commonly used to evaluate field-scale soil variability. Several studies have evaluated soil property effects on ECa, however, relatively few studies have evaluated the impacts of crop residues on these measurements. Crop residues may impact ECa readings, thus affecting the ability of ECa to depict spatial patterns of static soil properties. Residue effects on ECa measurements were evaluated in the intensively cropped Tennessee Valley region of Alabama where the adoption of conservation tillage practices that utilize cover crops is increasing. Ten transects (3.1 m wide by 73.2 m long) were established within a 0.22 ha (30.5 m x 73.2 m) no-till field in a corn (Zea mays L.)-wheat (Triticum aestivum L.)-soybean (Glycine max L.) rotation. Soils classified in fine-loamy, siliceous, semiaetive, thermic Typic Paleudults. Geo-referenced ECa measurements (at 0-30 and 30-90cm depths) collected with a coulter mounted direct-contact sensor were taken with 1) crop residue (3789 +/- 955 kg ha(-1)) in place, 2) residue removed from five randomly selected transects, and 3) residue incorporated through shallow disking (5 to similar to 10 cm). Measurements were taken at operating speeds of 2.2 and 4.4 ms(-1). Sand and clay content and gravimetric water content (theta(g)) were highly correlated with ECa, and regression equations using measured soil properties were developed that explained between 56% and 86% of the ECa variability. Difference in operating speeds had minimal effects on ECa measurements. Significant differences were observed between ECa values for residue remaining vs residue removed, but differences were small (similar to 0.5 mS m(-1)). When compared within two groups stratified by clay content (< or > 200 g kg(-1)), larger differences in ECa(0-30cm) values for residue removed vs residue remaining were observed. Minimal differences in geostatistical parameters were observed. Overall, for the residue quantities and soils evaluated in this study, residue had minimal impacts on ECa values.