Tillage and Canopy Cover Effects on Interrill Erosion from First-Year Alfalfa

Alfalfa (Medicago sativa L.) establishment techniques commonly produce a soil surface susceptible to high runoff and soil losses prior to crop canopy development. Limited data are available on the erodibility and productivity of alfalfa seedbeds established with conservation tillage systems. Four alfalfa establishment techniques were investigated for runoff, erosion, and forage yield over two growing seasons on a Plano silt loam soil (fine-silty, mixed, mesic Typic Argiudoll) with a 5% slope in south-central Wisconsin. Alfalfa seedbeds were established on cropland previously in no-till (NT) corn (Zea mays L.). Five simulated rainfalls were applied to moldboard (MB), moldboard-nurse crop (MB/nc), chisel (CH), and NT alfalfa seedbeds. An additional seedbed investigated was no-till with surface residue removed (NT/wo) immediately prior to rainfall simulation. Relative to MB, CH treatments reduced runoff volumes by 23 to 72% and NT treatments reduced volumes 59 to 100%. Soil-loss reductions of 24 to 64% from CH and 71 to 100% from NT relative to MB were observed. Runoff volumes from NT/wo were the largest of all treatments for four of the five rainfall simulations. Soil losses from NT/wo were statistically similar (P = 0.05) to MB for all rainfall simulations. Comparisons of MB to MB/nc runoff volumes did not indicate an influence of canopy cover on runoff. A MB/nc soil loss of 87% less than MB at a rainfall simulation with MB/nc canopy cover of 93% relative to MB canopy cover of 47% did indicate a canopy effect on soil loss. No significant influence of canopy development on runoff volumes from similar treatments over time was evident. Canopy development contributed to reduced soil losses within all treatments, with a maximum reduction of 96% observed for MB/nc canopy cover of 93% relative to MB/nc soil loss at 0% canopy. Establishment year alfalfa yield and quality did not vary among MB, CH, and NT treatments at a significance level of P = 0.05. Research supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison.