Litter Deposition and Decomposition In Smooth Bromegrass Pastures.

Litter may constitute a significant organic matter pool in pastures.  Our objectives were to evaluate how management affects litter deposition and decomposition rates in smooth bromegrass (Bromus inermis L.) pastures.  We hypothesized that increasing N inputs to pastures would increase litter deposition and decomposition rates.  From 2010-2011, we measured standing crop, litter mass, litter deposition rates, and litter decomposition rates within an ongoing experiment where yearling beef cattle gains were evaluated on (1) fertilized (90 kg N ha^-1) pastures (FERT); (2) unfertilized pastures where cattle were supplemented with dry distillers grains plus solubles (DDGS); and (3) unfertilized pastures (CONT).  Spring standing crop averaged 4734, 3685, and 2699 kg DM ha^-1 in FERT, DDGS, and CONT pastures, respectively.  By late summer, standing crop declined to 1907 kg DM ha^-1 across treatments.  Across the season, standing crop N concentrations averaged 18.4, 17.1, and 16.8 g kg^-1 among FERT, DDGS, and CONT pastures, respectively.  Despite these differences, N addition to the pastures had no effects on litter mass, litter deposition, or litter decomposition.  Pastures contained on average 2000-3000 kg DM ha^-1 of litter and litter deposition averaged 10 kg ha^-1 d^-1.  Litter decomposition, evaluated through placement of litter in screen bags on pasture soil, lost 30% of DM from 29 July to 3 Nov.  Management effects on litter deposition and decomposition were mostly likely a function of grazing pressure.  Use of put-and-take stocking to increase cattle gains ha^-1 in FERT and DDGS pastures resulted in similar end of season standing crop among all pasture treatments, and thus, similar effects on litter were observed.  Although grazing pressures were equal, cattle trampling would have been on the order of 20 times greater within the FERT and DDGS pastures, but apparently it had no effect.