Effects of pasture treatments on detached pasture litter mass, quality, litter loss, decomposition rates, and residence time in northern New South Wales

Abstract

Few data are available on litter quantity and quality and decomposition rates over time and what effects stocking rate, grazing method, legume introduction, and fertiliser application may have. Studies were conducted from spring 1997 to 2001 at 3 pasture sites in northern New South Wales to provide such data by examining the effects of pasture treatments on detached litter mass (kg DM/ha) and quality data (percent carbon (C), nitrogen (N) and C : N ratio) collected at 9 sampling times in 2 replicates of 5 (native pasture) or 4 (sown pasture) treatments and examined for differences over time using cubic spline analyses. For each site, decomposition bags were also used to assess differences among treatments for initial and final detached litter mass, organic matter (OM), N values, the relative rate of decomposition (g/g.day), and residence time (days) for periods March to June 1998, June to September 1998, and September to November 1998. Initial and final data were also collected for detached resident and subterranean clover ('Trifolium subterraneum') litter for 6 sampling times from September 1998 to January 1999 for a reduced range of treatments at each site. Similar data were collected at each site for resident litter and grass green leaf material from January to April 1999. Detached litter mass declined (P < 0.05) in unfertilised continuously grazed treatments (Barraba native pasture) and with high continuous stocking rate in the Nundle sown pasture. Litter quality was only significantly affected by grazing treatment at the Barraba native pasture site where the fertilised treatment oversown with subterranean clover tended to have low percent C and a lower C : N ratio and higher percent N and microbial biomass C than other treatments. From autumn to spring 1998, the fertilised, oversown treatment at both native pasture sites generally had high litter DM, OM, and N losses and relative rates of decomposition compared with continuously grazed, unfertilised pasture. For the same period, at the Nundle sown pasture site, OM and N losses and the relative rate of decomposition were consistently higher, and residence time lower, in the continuously grazed, high stocking rate treatment compared with all other treatments. Compared with resident detached litter, both subterranean clover litter and green leaf material at the native pasture sites had higher relative decomposition rates and lower residence times. The implications of these data for the management of both native and sown pastures are discussed.