Sheep dung disappearance from grazed hill country landscapes
Two experiments were conducted to examine the effects of biological (composition and site history) and topographic (slope and aspect) factors affecting sheep dung disappearance rates in hill country pastures. We used three of the farmlets that have been receiving 0 (NF), 125 (LF) or 375 (HF) kg of single superphosphate (SSP)/ha since 1980) from the long-term phosphorus fertiliser trial at Ballantrae. Experiment one examined the effect of farmlet, slope (low and medium slope class), and aspect (E, SW, NW), whereas Experiment two examined the effect of farmlet, both as a source of dung (from LF or HF farmlets) and as a site in the landscape (on LF or HF farmlets). In both experiments, disappearance of dung followed a quadratic curve, and no improvements were made using higher-order polynomials. Despite a lower fibre concentration, dung from sheep grazing the HF farmlet did not disappear at a faster rate than dung from the other farmlets, but soil activity in situ (placement) was pivotal to the rate of dung disappearance. A faster rate of dung disappearance on the HF farmlet is consistent with a greater capacity for turnover of plant biomass and animal excreta in this high fertility environment. These experiments contribute to our understanding of the influence of biological and topographic drivers of dung disappearance rates, and enable further advances to be made in the modelling of nutrients in these topographically complex agroecosystems.
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