Reduced Nitrogen Mineralization and Litter Decomposition in Unfertilized Smooth Bromegrass Pastures

Abstract

ABSTRACTNitrogen fertilization has been shown to affect herbage accumulation, litter deposition, litter N return, and presence of weeds in smooth bromegrass (Bromus inermis Leyss.) pastures. The objective of this study was to evaluate the effect of pasture management strategies that varied amount and form of N input on soil N mineralization, litter decomposition, and litter N release in smooth bromegrass pasture. Management strategies included: (i) nitrogen‐fertilized pasture grazed with unsupplemented beef cattle (FERT); (ii) unfertilized pasture grazed with unsupplemented beef cattle (CONT); and (iii) unfertilized pasture grazed with dried distillers grains plus solubles (DDGS)‐supplemented beef cattle (SUPP). After 210 d of aerobic soil incubation, cumulative soil N mineralization was 155.1 ± 9.8, 170.5 ± 15.6, and 180.2 ± 13.8 mg N kg–1 soil for CONT, SUPP, and FERT pastures, respectively, which represented a supply of 254, 279, and 294 kg N ha–1 for the 0‐ to 15‐cm soil depth, respectively. Decomposition day models incorporating precipitation and temperature generally were the best predictors of litter decomposition. Regardless of the model used, there was no difference in litter decomposition among management strategies in 2010, while in 2011, both leaf and stem litter decomposed faster in FERT than CONT and SUPP pastures. After 8 yr of management, cessation of N fertilization in CONT and SUPP resulted in a soil environment that supported less litter decomposition than FERT.