Brisbane, Australia
Brisbane, Australia

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Segoli M.,CSIRO | Allen D.,Landscape science ESP | Dalal R.,Landscape science ESP | Watson I.,CSIRO | And 2 more authors.
Soil Research | Year: 2015

Extensive cattle grazing is the dominant land use in northern Australia. It has been suggested that grazing intensity and rainfall have profound effects on the dynamics of soil nutrients in northern Australia's semi-arid rangelands. Previous studies have found positive, neutral and negative effects of grazing pressure on soil nutrients. These inconsistencies could be due to short-term experiments that do not capture the slow dynamics of some soil nutrients and the effects of interannual variability in rainfall. In a long-term cattle grazing trial in northern Australia on Brown Sodosol-Yellow Kandosol complex, we analysed soil organic matter and mineral nitrogen in surface soils (0-10cm depth) 11, 12 and 16 years after trial establishment on experimental plots representing moderate stocking (stocked at the long-term carrying capacity for the region) and heavy stocking (stocked at twice the long-term carrying capacity). Higher soil organic matter was found under heavy stocking, although grazing treatment had little effect on mineral and total soil nitrogen. Interannual variability had a large effect on soil mineral nitrogen, but not on soil organic matter, suggesting that soil nitrogen levels observed in this soil complex may be affected by other indirect pathways, such as climate. The effect of interannual variability in rainfall and the effects of other soil types need to be explored further. © CSIRO 2015.

Allen D.E.,Landscape science ESP | Pringle M.J.,Landscape science ESP | Bray S.,Agri Science Queensland | Hall T.J.,Science Engagement | And 5 more authors.
Soil Research | Year: 2013

This study aimed to unravel the effects of climate, topography, soil, and grazing management on soil organic carbon (SOC) stocks in the grazing lands of north-eastern Australia. We sampled for SOC stocks at 98 sites from 18 grazing properties across Queensland, Australia. These samples covered four nominal grazing management classes (Continuous, Rotational, Cell, and Exclosure), eight broad soil types, and a strong tropical to subtropical climatic gradient. Temperature and vapour-pressure deficit explained >80% of the variability of SOC stocks at cumulative equivalent mineral masses nominally representing 0-0.1 and 0-0.3m depths. Once detrended of climatic effects, SOC stocks were strongly influenced by total standing dry matter, soil type, and the dominant grass species. At 0-0.3m depth only, there was a weak negative association between stocking rate and climate-detrended SOC stocks, and Cell grazing was associated with smaller SOC stocks than Continuous grazing and Exclosure. In future, collection of quantitative information on stocking intensity, frequency, and duration may help to improve understanding of the effect of grazing management on SOC stocks. Further exploration of the links between grazing management and above- and below-ground biomass, perhaps inferred through remote sensing and/or simulation modelling, may assist large-area mapping of SOC stocks in northern Australia. © CSIRO 2013.

Pringle M.J.,Landscape science ESP | Allen D.E.,Landscape science ESP | Payne J.E.,Landscape science ESP | Dalal R.C.,Landscape science ESP | Marchant B.P.,Rothamsted Research
Digital Soil Assessments and Beyond - Proceedings of the Fifth Global Workshop on Digital Soil Mapping | Year: 2012

The natural abundance ratio of soil 15N to 14N (δ 15Nis a useful measure of the extent of the N cycling in an ecosystem. The aim of this study was to model the effects of soil type and grazing management on soil δ 15N using samples collected from a farm-scale cattle-grazing trial in the tropical rangelands of northern Australia. We used a statistical model, fitted with robust geostatistical methods due to a systematic sampling design and the presence of outlying values, to improve the understanding of N cycling. The model revealed a consistent interaction between soil type and grazing pressure on δ 15N For a Grey Vertosol and a complex of Brown Sodosol and Yellow Kandosol, heavy grazing was associated with relatively small values of δ 15N in contrast, for a (coarse-textured) Red Kandosol, heavy grazing was associated with relatively large values of δ 15N. This suggests that, at heavy stocking rates, N cycling is particularly fast on the coarse-textured soil. Information such as this could help graziers minimize environmental impacts in tropical grazing systems. Using an existing soil map as a basis, we extrapolate our findings to the region about the study site, in a first attempt to locate at-risk areas. © 2012 Taylor & Francis Group.

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