Controlled Traffic Impacts on Physical and Hydraulic Properties in an Intensively Cropped No-Till Soil

Changes in soil properties with wheel traffic involving intensive cropping systems under no-till (NT) are not well understood. We assessed the 8-yr impacts of intensive cropping systems and wheel traffic on soil physical and hydraulic properties and their relationships under NT on a Ladysmith silty clay loam (a fine, smectitic, mesic Udertic Argiustoll) near Hesston, KS. Winter wheat ( Triticum aestivum L.) (W), grain sorghum [Sorghum bicolor (L.) Moench] (S), double-crop grain sorghum (*S), soybean [Glycine max (L.) Merr.] (B), and double-crop soybean (*B) arranged in S-S-S, W*S-S-B, W-S-B, and W*B-S-B rotations were studied. In doubled crops, sorghum or soybean was planted immediately after wheat harvest. Cropping systems had less of an effect on soil properties than wheel traffic. Wheel traffic increased bulk density (rho(b)) from 1.16 +/- 0.06 (mean +/- SD) to 1.38 +/- 0.03 Mg m(-3), cone index (CI) from 1.78 +/- 0.29 to 3.10 +/- 0.15 MPa, shear strength (SHEAR) from 23 +/- 2.2 to 61 +/- 5.2 kPa, and aggregate tensile strength from 377 +/- 80 to 955 +/- 148 kPa over nontrafficked rows in the 0- to 7.5-cm depth. Wheel compaction reduced cumulative infiltration by 40 to 120 times except in S-S-S. It also reduced the logarithm of the saturated hydraulic conductivity (log K-sat), soil water retention at 0 kPa, plant-available water, effective porosity (phi(e)), and the volume of >50-mu m pores. An increase in rho(b) CI, and SHEAR linearly reduced phi(e) (r > -0.74), which, in turn, reduced cumulative infiltration and log K-sat (r > 0.74). Data strongly support the need for using controlled traffic to reduce the adverse impacts of wheel traffic on soil physical quality.