Soybean varietal response to liquid swine manure application

Applying manure to soybean [Glycine max (L.) Merr.] as a routine management practice requires additional information about cultivar-dependent responses. Our objective was to determine seed yield, dry matter accumulation, N accumulation, and lodging responses for a cross-section of adapted public and private soybean cultivars when liquid swine (Sus scrofa) manure was applied. Field studies were conducted at seven locations in southern Minnesota during 1996 and 1997. Whole-plot treatments included three swine manure rates (zero, Iow, and high) injected with sweeps to a soil depth of 13 cm before planting. Split-plot treatments consisted of 12 public and private soybean cultivars. Average seed yield for all cultivars at three of seven locations was generally positive, increasing on average 1.4 kg kg^-1 of applied available N. A significant manure rate × cultivar interaction was observed for lodging scores, but increased lodging was not related to any change in yield. Seed yield decreased with increasing manure rates at a seventh location, where there was a history of white mold [Sclerotinia sclerotiorum (lib.) d. By.] incidence. At this location, seed yield for the control was 0.20 Mg ha^-1 greater than seed yield from either manure rate, and response to manure application was not the same for every cultivar. Except for this latter site, seed yield response to increasing manure rate was either favorable or innocuous, despite increased lodging. Manure application to soybean appears to be an acceptable management practice regardless of cultivar, except when the application exacerbated an already present disease pressure.