CONTROLLED WHEEL TRAFFIC EFFECTS ON SOIL PROPERTIES IN RIDGE-TILLAGE

Ridge-till is pining widespread use on highly erodible land. Matched-w idth equipment has allowed producers to establish permanent traffic la nes in ridge-till. The establishment of permanent traffic lanes and a lack of preplant tillage has increased concern about soil compaction. The purpose of our study was to assess the effects of long-term contro lled tractor wheel traffic on soil properties of a ridge tillage syste m. This research was conducted on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) in southeastern Nebraska. A s plit-split-plot design was employed to evaluate differences in soil pr operties among corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] crops; row, trafficked interrow, and nontrafficked interrow positions ; and depths of 0 to 7.5, 7.5 to 15, and 15 to 30 cm. Axle load of the tractor used on the plots was 4 Mg. Sampling was conducted in the sum mer after ridging. Most variability in soil properties among positions was confined to the 0- to 7.5-cm depth. Bulk density, soil strength, aggregate mean weight diameter (MWD), water content at field capacity (FC), and water content at wilting point (WP) tended to be highest in the trafficked interrow and least in the row. Saturated water content and gravitational water (GW) were generally highest in the row and lea st in the trafficked interrow. Soil strength in the trafficked interro w was 56% greater than the nontrafficked interrow and 104% greater tha n the row. Similar, but less pronounced differences among positions we re also observed for bulk density. Aggregate mean weight diameter in t he trafficked interrow indicated that wheel traffic resulted in larger aggregates while ridging resulted in smaller aggregates in the 0- to 7.5-cm depth of the row. Mean saturated hydraulic conductivity (K(sat) ) in the trafficked interrow was approximately one-quarter of the mean value for the nontrafficked interrow and row. Organic C and TN were g reater in the row than the interrow positions. The influence of tracto r wheel traffic on soil properties was largely dissipated by the 15- t o 30-cm depth. Because of the dissimilarity in soil properties among p ositions, ridge-tilled fields should be conceptualized and managed as three distinct soil zones, not as a single unit.