RUNOFF, EROSION, AND FORAGE PRODUCTION FROM ESTABLISHED ALFALFA AND SMOOTH BROMEGRASS

Surface sealing of soils in established alfalfa (Medicago sativa L.) m ay produce runoff during intensive rainstorms, resulting in soil loss and reduced yield. We hypothesized that smooth bromegrass (Bromus iner mus Leyss.) grown in mixture with alfalfa would reduce on-site runoff and soil loss, and that this should offset any negative effect on fora ge quality. Alfalfa, smooth bromegrass, and an alfalfa-smooth bromegra ss mixture were established in 1992 on Rozetta silt loam (moderately w ell drained, fine-silty, mixed, mesic Typic Hapludalfs) near Lancaster , WI. A 72-mm h(-1) simulated rainfall was applied for 1 h during the growing seasons of 1993 and 1994 to forage regrowth at 4 and 6 wk afte r first harvest and immediately after second harvest. The addition of smooth bromegrass to alfalfa did not significantly reduce runoff volum e, sediment concentration, or total soil loss at any rainfall event at any stage of regrowth in either year. Furthermore, forage yield and c oncentrations of acid-detergent fiber and crude protein in the forage were not affected. Averaged over both years and the three sward types, runoff at 6 wk was significantly less than at 0 wk, which was signifi cantly less than at 4 wk. Total soil loss from all sward types summed over six simulated rainstorms was between 0.19 and 0.61 Mg ha(-1), muc h less than the 11.2 Mg ha(-1) yr(-1) considered tolerable for this so il. Neutral-detergent fiber (NDF) concentration of bromegrass (534 g k g(-1)) was greater than either the mixture (441 g kg(-1)) or alfalfa ( 404 g kg(-1)). Soil loss and forage quality results do not support add ing smooth bromegrass to alfalfa, especially since increased NDF resul ts in lower forage intake by ruminants and reduced milk yield in dairy tattle (Bos taunts); however livestock operations that could efficien tly utilize smooth bromegrass monocultures could reduce soil loss and runoff by doing so.