Soil Erosion and Macronutrient Fluxes Under Simulated Rainfall: The Effects of Tillage and Crop Residue Removal.

Erosion by water is a principal process of soil degradation in agricultural lands. The majority of agricultural soil erosion occurs during high intensity rainfall events.  Soil erosion also influences the storage and fluxes of C and key macronutrients N and P in soil surface layers, and erosion can lead to stoichiometric shifts which may in turn influence the turnover of organic matter and the supply of plant nutrients. No till (NT) crop management, a practice that favors the return of crop residues to the soil surface, significantly reduces erosion on susceptible landscapes. The selective removal of crop residues for bioenergy production from no-till systems has been suggested as a secondary crop, but the effect of this practice on the benefits of NT (i.e. reduced rates of soil erosion) has not been quantified. Therefore, this study was initiated in spring 2012 to examine the effects of soil management practices on erosion and associated macronutrient fluxes under simulated rainfall at the North Appalachian Experimental Watershed (NAEW) in Coshocton, OH. The hypothesis being tested was that water runoff and sediment loss, as well as runoff and sediment borne C and macronutrient fluxes, would be larger in soils under crop residue removal and conventional tillage.  We explored the impact of contrasting tillage management in a nested experiment within a 42 year old NT corn (Zea mays) plot. The treatments were: (1) long term NT with 100% crop residue (NT 100%), (2) NT with 50% crop reside (NT 50%), (3) NT with complete crop residue removal (NT 0%), (4) long term conventional tillage (CT), and (5) long term no-tillage plots that were cultivated (TNT) prior to the rainfall simulation.  A field rainfall simulator was utilized to apply rainfall at an intensity of 7 cm hr^-1 for 30 minutes. We observed significant differences among treatments in total run-off, suspended solids and C:N:P ratios in dissolved (<0.45 μm) and solid (>0.45 μm) residues of eroded sediments between treatments. The data support the conclusion that NT management with residue mulch reduces soil erosion potential, but that its benefit is drastically impaired by crop residue removal.