- Authors:
- Eckard, R.
- Barker-Reid, F.
- Chen, D.
- Li, Y.
- Source: Plant and Soil
- Volume: 309
- Issue: 1-2
- Year: 2008
- Authors:
- Edis, R. B.
- Park, K.
- Meyer, M.
- Kirkby, C.
- Chen, D.
- Wang, G.
- Turner, D. A.
- Source: Australian Journal of Experimental Agriculture
- Volume: 48
- Issue: 3
- Year: 2008
- Authors:
- Krull, E.
- Woodbury, P.
- Coleman, K.
- Falloon, P.
- Barson, M.
- Carter, J.
- Sohi, S.
- Skjemstad, J.
- Lehmann, J.
- Source: Nature Geoscience
- Volume: 1
- Issue: 12
- Year: 2008
- Summary: Annual emissions of carbon dioxide from soil organic carbon are an order of magnitude greater than all anthropogenic carbon dioxide emissions taken together. Global warming is likely to increase the decomposition of soil organic carbon, and thus the release of carbon dioxide from soils, creating a positive feedback. Current models of global climate change that recognize this soil carbon feedback are inaccurate if a larger fraction of soil organic carbon than postulated has a very slow decomposition rate. Here we show that by including realistic stocks of black carbon in prediction models, carbon dioxide emissions are reduced by 18.3 and 24.4% in two Australian savannah regions in response to a warming of 3 degrees C over 100 years(1). This reduction in temperature sensitivity, and thus the magnitude of the positive feedback, results from the long mean residence time of black carbon, which we estimate to be approximately 1,300 and 2,600 years, respectively. The inclusion of black carbon in climate models is likely to require spatially explicit information about its distribution, given that the black carbon content of soils ranged from 0 to 82% of soil organic carbon in a continental-scale analysis of Australia. We conclude that accurate information about the distribution of black carbon in soils is important for projections of future climate change.
- Authors:
- McMahon,Thomas A.
- Kiem,Anthony S.
- Peel,Murray C.
- Jordan,Phillip W.
- Pegram,Geoffrey G. S.
- Source: Journal of Hydrometeorology
- Volume: 9
- Issue: 6
- Year: 2008
- Summary: This paper introduces a new approach to stochastically generating rainfall sequences that can take into account natural climate phenomena, such as the El Nino-Southern Oscillation and the interdecadal Pacific oscillation. The approach is also amenable to modeling projected affects of anthropogenic climate change. The method uses a relatively new technique, empirical mode decomposition (EMD), to decompose a historical rainfall series into several independent time series that have different average periods and amplitudes. These time series are then recombined to form an intradecadal time series and an interdecadal time series. After separate stochastic generation of these two series, because they are independent, they can be recombined by summation to form a replicate equivalent to the historical data. The approach was applied to generate 6-monthly rainfall totals for six rainfall stations located near Canberra, Australia. The cross correlations were preserved by carrying out the stochastic analysis using the Matalas multisite model. The results were compared with those obtained using a traditional autoregressive lag-one [AR(1)], and it was found that the new EMD stochastic model performed satisfactorily. The new approach is able to realistically reproduce multiyear-multidecadal dry and wet epochs that are characteristic of Australia's climate and are not satisfactorily modeled using traditional stochastic rainfall generation methods. The method has two advantages over the traditional AR(1) approach, namely, that it can simulate nonstationarity characteristics in the historical time series, and it is easy to alter the decomposed time series components to examine the impact of anthropogenic climate change.
- Authors:
- Radford, B. J.
- Yule, D. F.
- McGarry, D.
- Playford, C.
- Source: Soil & Tillage Research
- Volume: 97
- Issue: 2
- Year: 2007
- Summary: Heavy wheel traffic causes soil compaction, which adversely affects crop production and may persist for several years. We applied known compaction forces to entire plots annually for 5 years, and then determined the duration of the adverse effects on the properties of a Vertisol and the performance of maize and sorghum crops under no-till dryland cropping with residue retention. For up to 5 years after a final treatment with a 10 Mg axle load on wet soil, soil shear strength at 70-100 mm and cone index at 180-360 mm were significantly ( P<0.05) higher than in a control treatment, and soil water storage and grain yield were lower. We conclude that compaction effects persisted because (1) there were insufficient wet-dry cycles to swell and shrink the entire compacted layer, (2) soil loosening by tillage was absent and (3) there were fewer earthworms in the compacted soil. Compaction of dry soil with 6 Mg had little effect at any time, indicating that by using wheel traffic only when the soil is dry, problems can be avoided. Unfortunately such a restriction is not always possible because sowing, tillage and harvest operations often need to be done when the soil is wet. A more generally applicable solution, which also ensures timely operations, is the permanent separation of wheel zones and crop zones in the field-the practice known as controlled traffic farming. Where a compacted layer already exists, even on a clay soil, management options to hasten repair should be considered, e.g. tillage, deep ripping, sowing a ley pasture or sowing crop species more effective at repairing compacted soil.
- Authors:
- Denmead, O. T.
- Macdonald, B. C. T.
- Bryant, G.
- Wang, W.
- White, I.
- Moody, P.
- Source: Proceedings of the Australian Society of Sugar Cane Technologists
- Volume: 29
- Year: 2007
- Authors:
- Source: Healthy Soils Symposium
- Year: 2007
- Authors:
- Grace, P.
- Rochester, I.
- Crothers, B.
- Chen, D.
- Weier, K.
- Rowlings, D.
- Kiese, R.
- Butterbach-Bahl, K.
- Li, Y.
- Source: Non-CO2 Greenhouse Gas Fluxes in Australian-New Zealand Landscapes
- Year: 2007
- Authors:
- Grace, P.
- Rowlings, D.
- Peterson, N.
- Weier, K.
- Kiese, R.
- Butterbach-Bahl, K.
- Source: Non-CO2 Greenhouse Gas Fluxes in Australian-New Zealand Landscapes
- Year: 2007
