EROSION FROM ALFALFA ESTABLISHED WITH OAT UNDER CONSERVATION TILLAGE

Conservation tillage (CT) methods reduce soil erosion, but effects on establishing alfalfa (Medicago sativa L.) are not well known. Oat (Ave na sativa L.) is often planted with alfalfa to reduce erosion during e stablishment, but results are not well documented. We hypothesized tha t the inclusion of oat during establishment would not be as effective as CT at reducing soil erosion. Moldboard plowing (MB) was compared wi th two CT practices of disking (DK) and no-till (NT), with alfalfa pla nted alone (SOLO) or with a companion oat crop (COMP). The study was c onducted in 1992 and 1993 on Rozetta silt loam soils (fine-silty, mixe d, mesic Typic Hapludalfs) following corn (Zea mays L.) each year. Sim ulated rainfall, 72 mm h-1 for 1 h, was applied twice per growing seas on, at planting (1 wk) and during oat canopy development (4 wk). Runof f was reduced from 28 mm in MB plots to 13 mm in CT plots at planting in 1992. Four weeks after planting in 1993, runoff was reduced from 47 mm in SOLO to 44 mm in COMP. Averaged across all simulations, sedimen t concentration was 23.3 g L-1 for MB and 3.2 g L-1 for CT. The 2-yr m ean soil loss dropped from 644 g m-2 in MB to 94 g m-2 in CT at planti ng. Mean treatment erosion was reduced 85% by canopy in 1992, a dry ye ar. The wet 1993 growing season had several severe crusting rainstorms that induced large MB soil loss (2173 g m-2) 4 wk after planting. Com panion cropping reduced MB soil loss 46% (from 2827 to 1520 g m-2) in 1993 and DK and NT further reduced soil loss to 235 and 123 g m-2. For age biomass was unaffected by treatment in 1992.