Response of Soybean to Defoliation in a Limit Grazing System.

Limited grazing is a form of supplemental grazing that provides livestock access to a high-quality forage on a restricted basis in order to satisfy a dietary requirement. Although forages are typically used in limited grazing systems, there are areas in the United States where grain crops may be incorporated into these systems to meet the dietary needs of the livestock while still allowing for harvest of grain. There is considerable research on the response of soybean [Glycine max ] defoliation, little has been done from an animals perspective. The goal of this experiment was to observe the impact of simulated limited grazing on soybean grain and forage yield. Soybean (MG = 4.4) were exposed to simulated grazing at two levels of defoliation (1/3 and 2/3 of canopy) and three stages of maturity (R1, R2, or R3). Biomass was collected before and following grazing to determine yields of available forage and was analyzed for forage nutritive value. The yield of available forage did not differ between the levels of defoliation when harvested at R1 but were higher when 2/3 of the canopy was removed in later harvest. Additionally, the forage harvested at R3 and R2 displayed a lower leaf-to-stem ratio which suggest a lower nutritive value compared to R1 and was lower for the higher level of defoliation. There was no difference in the amount of floral components removed via defoliation during the first two harvest, but nearly 50% was removed at R3 and increased with level of defoliation. Grain yields will be determined in the fall following grain maturity. Once the grain yields are collected, data will be analyzed to determine if a compromise exists where soybeans may be utilized as a feed for livestock without causing significant sacrifices in grain yields.