Long-Term Conservation Tillage Effects On Physical Properties and Productivity of Southeastern U.S. Piedmont Ultisols.

The southeastern U.S. piedmont region includes approximately 16 million ha of upland soils dominated by Typic Kanhapludults derived from felsic crystalline rock. Row crops are grown on sloping sandy to sandy clay loam soils with low C, aggregate stability, and water holding capacity; and prone to erosion, crusting, and compaction. We summarize two long-term (1984-present) trials testing the impact of contrasting tillage (e.g., no-till, in-row subsoiling, chisel, disk, chisel plus disk, moldboard) on: 1) soil C, pore size distribution, infiltration, Ksat, bulk density, aggregate stability (1-4 mm), and available water capacity in the Ap horizon; and 2) corn (Zea mays L.) and soybean (Glycine max L. Merr.) productivity. These RCB experiments with controlled traffic have been in corn or a corn-soybean rotation on fine, kaolinitic, thermic Typic Kanhapludults at the Upper Piedmont Research Station, Reidsville, NC. Differences in corn and soybean productivity due to tillage systems were more strongly associated with residue-cover differences than with differences in bulk density, porosity, or C.  Aggregate stability and C were positively related and sensitive to tillage; however, the overall low percentage of water stable aggregates suggests that unprotected Ultisols in the southeastern Piedmont remain highly susceptible to crusting, erosion, and runoff. Infiltration and runoff under simulated rainfall provided further evidence of rapid surface sealing associated with weak aggregate structure. Beginning 2008, we used a multi-depth capacitance probe to monitor soil profile moisture weekly at five depths in selected treatments. This on-going work attempts to characterize soil profile moisture dynamics in different tillage systems and their relationship to short- and long-term productivity. Capacitance probe soil moisture and its variance differed as a function of tillage system and soil depth. Higher yields, reduced environmental costs, and greater farm profitability can be realized on fragile southeastern piedmont Ultisols by conservation practices that reduce or eliminate tillage and maximize residue cover of soil.