Corn stover harvest and tillage impacts on near-surface soil physical quality

Excessive harvest of corn (Zea mays L.) stover for ethanol production has raised concerns regarding negative consequences on soil physical quality. Our objective was to quantify the impact of two tillage practices and three levels of corn stover harvest on near-surface soil physical quality through the Least Limiting Water Range (LLWR). We evaluated no harvest, moderate and high stover harvest treatments within no-tillage and chisel plow plots following seven years of continuous corn production. Forty undisturbed soil samples were taken from the 0–7.5cm deep layer within each treatment and used to determine water retention curves, soil resistance to penetration and bulk density values (Bd). No-tillage plots had higher average soil bulk density and resistance to penetration values, and were more affected by stover harvest than chisel plow plots. The results confirmed that soil resistance to penetration determined the lower limit of the LLWR regardless of tillage or stover treatment, whereas soil aeration controlled the upper limit only at Bd>1.45 and Bd>1.55Mgm−3 for chisel plow and no-tillage, respectively. The LLWR was smallest for no-tillage with moderate or high corn stover harvest, indicating poor soil physical condition for plant growth, while the largest LLWR occurred with moderate stover harvest and chisel plowing. The introduction of alfalfa (Medicago sativa L.) into an extended rotation with no-tillage improved the LLWR by reducing the potential crop growth restriction due to resistance to penetration. Although bulk density values were only occasionally higher than the critical level (Bd=1.60Mgm−3 for chisel plow and Bd=1.64Mgm−3 for no-tillage), lower soil structure quality was evident with no-tillage under moderate or high stover harvest and with chisel plowing under high stover removal. The LLWR was more sensitive than available soil water content for detecting tillage and stover harvest effects on soil structural degradation.