Environmental and grazing management drivers of soil condition

Domestic livestock grazing is one of the dominant forms of land use globally. However, there are variable findings concerning the impacts of different grazing regimes on soil condition. We quantified the impacts of contrasting livestock grazing regimes on soil properties within nationally endangered temperate box-gum woodlands in south-eastern Australia. We sampled total soil nitrogen, phosphorus, carbon and bulk density at 65 woodland sites with a history of either continuous, strategic or rotational livestock grazing, as well as livestock grazing exclusion. We evaluated the influence of both historical and current management practices upon soil properties in the context of broad-scale soil forming factors such as climate, geology and topography. We found evidence of a strong relationship between total soil phosphorus and nitrogen, while phosphorus also was influenced by site-scale native tree cover. Total soil phosphorus and nitrogen were related to the combined effects of pasture type and long-term fertilizer history (>10 years prior to sampling). No significant differences in soil nutrients or bulk density were detected between different grazing treatments, likely due to the importance of total grazing pressure (i.e. from all exotic and native herbivores) and the level of environmental variation between sites. However, total soil phosphorus was significantly higher in soils sampled in the season following a grazing event, irrespective of grazing intensity or duration. Total soil nitrogen and carbon exhibited a similar pattern. This is likely a result of multiple processes such as direct input of organic matter to the soil and stimulation of soil microbial communities. These findings have important implications for the strategic management of woodland understorey vegetation as soil nutrients have been identified as important drivers of native plant diversity.