Nitrogen Use Efficiency and Cycling in Pastures Managed with Reduced Nitrogen Inputs.

Increasingly, management strategies that reduce N fertilizer inputs are emphasized to enhance N use efficiency, reduce N losses, and improve pasture grazing economics.  In 2005, a long-term experiment was initiated at the Univ. of Nebraska-Lincoln to evaluate beef cattle performance and N cycling in 1) N-fertilized pasture grazed with unsupplemented beef cattle (FERT); 2) unfertilized pasture grazed with unsupplemented beef cattle (CONT); and 3) unfertilized pasture grazed with dried distillers grains plus solubles (DDGS)-supplemented beef cattle (SUPP).  Research partners included agricultural economists, animal scientists, ecologists, and soil scientists.  Across the 10-yr experiment, the research showed steers in SUPP had better body weight gains and used N more efficiently than steers in CONT and FERT, and SUPP produced greater economic returns because of reduced N fertilizer costs and improved animal performance. Cessation of annual N fertilization in CONT and SUPP, however, decreased annual herbage accumulation, litter deposition, and root and rhizome mass, soil N mineralization and litter decomposition compared to FERT, indicting the importance of N fertilization to sustaining pasture productivity.The accumulation of these results also shows that importance of partnering and long-term experiments to further understanding of nutrient cycles in managed grassland ecosystems.