Grassland Defoliation Strategies to Minimize Nitrogen Losses from Appalachian Beef Stocker Grazing Systems.

Societal concern about the negative environmental impacts of nitrogen (N) losses from agricultural systems has expanded farm N use regulations. Nitrous oxide is a potent greenhouse gas. Ammonia reduces air quality. Nitrate leaching causes eutrophication of water bodies and contamination of groundwater. Research results filled some knowledge gaps that improved the sustainability of ruminant livestock systems. However, there are knowledge gaps relative to the identification of defoliation strategies to reduce the environmental impact of N losses from Appalachian stocker grazing systems. This research focuses on this knowledge gap.

Specifically, ranges of defoliation strategies in association with a modeling approach to quantitate N balance, characterize N use efficiency (NUE), and evaluate the environmental impacts of N losses were evaluated. The hypotheses of this research are: A 35-day regrowth interval improves NUE compared with 28- and 42-days, because it avoids respectively excess N intake and consumption of forage that limits intake and the efficiency of N utilization. The improvement of NUE of 35-days in comparison with the 28- or 42-days is independent of proportional removal of intial sward height, because forage nutritive value is affected essentially by frequency of defoliation.

Appalachian grazing systems will sooner or later be called upon to reduce environmental impacts. This research indicates defoliation strategies that reduce N losses and improve NUE while in balance to maintain high livestock production from grasslands systems. In association with the Integrated Farm System Model, information to select the best environmental scenario for productive Appalachian beef stocker grazing systems at farm level will be provided.