Tillage and residue effects on runoff and erosion dynamics

The carry-over effects from one year to the next of surface residue and tillage management decisions on runoff and erosion are not clear. The dynamics of runoff and erosion processes during rainfall events are likely dependent on the tillage and residue management system. The objective of this study was to elucidate the effects of tillage practices and residue management, by removal of residue cover, on the properties that describe the dynamics of the runoff and erosion processes. Six-row, 12.2 m long x 5.5 m wide, plots under conventional tillage (CT) or no tillage (NT) corn (Zea mays L.) for nine years were used in this study. Plots had an average slope of 5.7% on a Grenada silt loam (Glossic Fragiudalf) soil. Rainfall simulations were conducted on a 10.7 m x 3.7 m area within each plot at a rate of 65 mm h-1 for 1 h under natural antecedent soil-water conditions (dry run), followed by a 0.5 h simulation 4 h later (wet run), and another 0.5 h application 30 min later (very wet run). The ten treatments consisted of an incomplete 2 x 2 x 3 factorial arrangement of two tillage histories (CTh and NTh), two tillage levels (tilled and not tilled), and three residue management levels (residue left, residue removed just prior to simulated rainfall, and residue removed one year prior to simulated rainfall). The missing treatments were the NTh-tilled and CTh-not tilled with residue left. The time of runoff initiation, maximum runoff rate, flow velocity, and maximum sediment concentration were used to describe differences in runoff and erosion dynamics. Residue removal resulted in significantly sooner runoff with the NT system. There was a significant carry-over effect of residue removal with runoff initiated 35% sooner the subsequent year of removal and sediment concentrations increasing by >100%. Maximum sediment concentrations were lower for the CTh land that was not tilled than for the tilled despite the untilled land experiencing sooner runoff and higher runoff rates. Tilling NTh land resulted in significantly lower sediment concentrations than tilling CTh land, suggesting that the soil quality of NT was not immediately lost when tilled, but these beneficial properties were fully lost within one year of residue removal.