Previous PageTable Of ContentsNext Page

Climate change – identifying the impacts on soil health in Victoria.

James Nuttall13, Roger Armstrong1 and Michael Crawford2

1 Department of Primary Industries, PB 260, Horsham, Vic 3401.
2.
Department of Primary Industries, PO Box 3100, Bendigo, Vic 3554
3
Correspondence: email James.Nuttall@dpi.vic.gov.au

Abstract

Soil health will play a critical role in the response of agricultural production to climate change. In a review of the potential impacts of climate change on soil health in Victoria, climate change is expected to result in drier springs (up to 14% decrease in rainfall by 2030 and 40% decrease by 2070 compared with 1996) and hotter summers (up to 2.0C increase in temperature by 2030 and 6.0C increase by 2070 relative to 1996). Soil carbon levels and quality of fraction are expected to decrease due to reduced net primary production (NPP). Although overseas studies suggest that NPP increases under elevated CO2 as a result of greater transpiration efficiency by plants, it is unclear to what extent this effect will be outweighed by an overall reduction in growing season rainfall and potentially progressive nitrogen limitation for different land uses in south-eastern Australia. Additionally, increased risk of soil erosion and nutrient loss due to reduced vegetation cover in combination with episodic rainfall and greater wind intensities is expected. Fires will reduce ground cover and soil stability, particularly in the sub-alpine regions, and increase risk of soil and nutrient export into waterways. For Victoria’s agricultural production systems to remain financially viable in the future, there is an urgent need for better predictions of the likely impact of climate change on different farming systems that preserve the soil resource and more water efficient plant production that compensates for the predicted reductions in available water.

Key Words

Soil quality, greenhouse effect

Introduction

The increasing concern around the greenhouse effect over at least the last 20 years is related to the rapid increase in anthropogenic contribution of carbon dioxide, methane and nitrous oxides to the atmosphere through increased rates of industrialisation, the consumption of fossil fuels and land clearing, resulting in rapid climate change. The impact of these changes will not only have direct effects on society and infrastructure, such as threat of rising sea level on coastal occupation or changes in climate conditions on living standards, but will also impact on the stability of many biological systems, both natural and agricultural. In particular, climate change will shift the equilibrium of numerous soil processes including carbon and nitrogen cycling, acidification, risk of erosion and salinisation. Overall climate change is expected to have a major impact on Victoria’s agricultural sector where economic viability and environmental amenity depend heavily on ‘soil health’ and function. In this context, farming systems may either be part of the solution or problem in soil health maintenance. This paper summarises the likely impact on Victoria’s climate as predicted by global circulation models and then assesses how these predicted changes alter soil processes and health in the context of land use.

Methods

Predictions of future climatic conditions across Victoria were derived from Whettin et al. (2002). The high resolution assessment of Victoria uses the CSIRO DARLEM model and the assumptions of CO2 emissions and concentrations from the IS92a mid-case scenario used by the IPCC in 1996. Land-use zones of Victoria were resolved to coincide with the pixel size of the CSIRO high resolution regional assessment model (DARLAM) at a pixel resolution of 60 60 km. This allowed cross referencing between temperature and rainfall predictions (Whettin et al. 2002) and land-use zones within Victoria. For predicted temperature shifts, change was divided into 3 classes (2030: low 0.2 to 1.4C, medium 0.3 to 1.7C and high 0.3 to 2.0C and for 2070: low 0.7 to 4.3C, medium 0.8 to 5.2C and high 0.8 to 6.0C). These represent average daily temperature. For rainfall predictions, seven classes were condensed into four, where two mid-case scenarios were combined and the 3 ‘unknown’ categories were pooled, (2030: dry: -14 to 7%; drier: -13 to 3%; driest: -14 to -3% and for 2070: dry: -40 to 25%; drier: -30 to 5%; driest: -40 to -10% and unknown). These values represent percent changes in average seasonal precipitation.

Results

Emissions scenarios – IPCC

The Intergovernmental Panel on Climate Change (IPCC) has developed a set of scenarios which the human populaces may evolve and so influence climate change through different rates of the greenhouse gas emissions (Nakicenovic et al 2000). The scenarios are described by 4 main categories defined as A1, A2, B1 and B2 family lines. Of these, the A1 family is further subdivided into 3 sub-groups A1F1, A1T and A1B. The A1B is most concordant with the previously defined mid-case scenario, ISA92a. Its predicted outcomes are that CO2 concentrations in 2030 and 2070 will increase to 425 ppm and 590 ppm, respectively, compared with the present level, 370 ppm. These increases will be associated with median global temperature increases of 0.8 and 2.5 C, respectively.

Climate change over Victoria’s land use zones

Victoria’s land use was split into 3 major categories; dryland cropping (26%), dryland pasture (32%) and public land (37%). The remaining 5% incorporates urban and agricultural irrigation districts (Fig 1).

Figure 1. Land use zones for Victoria, Australia. Zones have been resolved to coincide with pixel size (60 60 km) of the CSIRO high resolution regional assessment model (DARLAM) for estimating climate change.

Within Victoria, the effects of climate change will be most strongly felt as drier springs (up to 14% decrease in seasonal rainfall by 2030 and 40% decrease by 2070 compared with 1996) and hotter summers (up to 2.0C increase in temperature by 2030 and 6.0C increase by 2070 relative to 1996) (Fig. 2). The largest component of the reduction in annual rainfall is expected to occur via reduced spring rainfall across all three land use zones examined. In contrast, the most extreme temperature forecasts for summer are restricted to the dryland cropping and public land regions.

Soil health

Of the potential indicators used to infer soil health status, soil carbon is particularly important (Burke et al 1989, Dalal & Chan 2001). Organic matter is vital because it supports many soil processes that are associated with fertility and physical stability of soil across the various ecosystem services. Cycling of soil organic carbon is strongly influenced by moisture and temperature, two factors which are predicted to change under global warming.

Figure 2. Projected changes in seasonal temperature and rainfall relative to 1996 for three land use zones in Victoria under the IS92a scenario. Temperature increase by 2030; low: 0.2 to 1.4C, med: 0.3 to 1.7C, high: 0.3 to 2.0C; and by 2070; low: 0.7 to 4.5C, med: 0.8 to 5.2C, high: 0.8 to 6.0C by 2070. Rainfall change; dry: -14 to 7%; drier: -13 to 3%; driest: -14 to -3% by 2030 and dry: -40 to 25%; drier: -30 to 5%; driest: -40 to -10% by 2070; Unkwn, unknown.

Soil carbon (C) levels within cropping and pasture systems of north-western Victoria may possibly decline due to decreased net primary production (NPP) (Fig. 3). Despite potential benefits of elevated CO2 such as increased water use efficiency of plants (Kimball 2003), greater allocation of carbon and nitrogen into roots (Xu et al. 2007) and increased carbon sequestration into soil microaggregates (Jastrow et al. 2005), these benefits are likely to be outweighed by greater frequency and severity of drought in some environments (Xu et al. 2007), progressive nitrogen limitation (De Graff et al. 2008) and reduced rates of soil organic carbon turnover (Cardon et al. 2001). These possible effects are based on international observations for a range of pasture, crop and forest systems but have yet to be tested for Australian conditions. There is also the potential for increased risk of soil erosion and nutrient loss if vegetation cover is reduced in combination with greater frequency of extreme rainfall events and greater wind intensities. Transient salinity may increase where leaching during episodic rainfall events may be limited due to surface sealing and capillary rise of salts dominate. Conversely, the severity of saline scalds due to secondary salinisation may abate as groundwater levels fall in line with reduced rainfall. Water quality may be impacted by increased bush fire frequency and intensity (Hennessy et al. 2005). Within sub-alpine regions fires will reduce ground cover and soil stability and increase risk of soil and nutrient export into waterways.

For Victoria’s agricultural production to be viable into the future, there is a need to identify farming systems that are climate change compatible, where productivity and soil health are maintained. Computer simulation studies and appropriate verification experimentation are needed to assess the relevance of international observations of elevated CO2 effects on the interaction between future climate scenerios and land use systems in south-eastern Australia. It is likely however, that rain-fed plant production systems will require more prudent water budgeting to compensate for reduced water availability. This may require a shift in agronomic management practices within current farming systems or the enterprise itself. Increasing crop adaptation may also be assisted by increasing drought tolerance of crop and pastures through genetic control, although this may be a less realistic option (Passioura 2006). A shift in land suitability for farming based on soil texture and plant/soil water dynamics and plant available water is also vitally important.

Figure 3. Schematic representation of the potential links between climate change and soil health

Conclusion

Future climatic conditions within the arable regions of Victoria are likely to be come hotter and drier. To facilitate adaptation to these new climates, management practices used within current farming systems as well as possible changes in the enterprise will need to change accordingly. Current assessments of the suitability of land for farming may need to be reassessed due to a greater significance of soil texture on plant/soil water dynamics and plant available water in the future. Maintaining plant production will ensure both the supply of organic carbon to the soil, which is strongly linked to soil health and potentially mitigation of climate change through carbon sequestration. Maintaining groundcover will be important for protecting the soil from both water and wind erosion. To meet these challenges, climate-change-compatible farming systems need to be identified to allow the adaptation process by landholders and industry to commence.

References

Burke IC, Yonker CM, Parton WJ, Cole CV, Flach K, Schimel DS (1989) Texture, climate, and cultivation effects on soil organic matter content in U.S. grassland soils. Soil Science Society of America Journal 53, 800-805.

Cardon ZG, Hungate BA, Cambardella CA, Chapin FS, Field CB, Holland EA, Mooney HA (2001) Contrasting effects of elevated CO2 on old and new soil carbon pools. Soil Biology & Biochemistry 33 365-373.

Dalal R, Chan KY (2001) Soil organic matter in rainfed cropping systems of the Australian cereal belt. Australian Journal of Soil Research 39, 435-464.

De Graff M, van Kessel C, Six J (2008) The impact of long term elevated CO2 on C and N retention in stable SOM pools. Plant and Soil 303 311-321.

Hennessy K, Lucas C, Nicholls N, Bathols J, Suppiah R, Ricketts J (2005) 'Climate change impacts on fire-weather in south-east Australia.' CSIRO, Melbourne.

Jastrow JD, Miller RM, Matamala R, Norby RJ, Boutton TW, Rice CW, Owensby CE (2005) Elevated atmospheric carbon dioxide increases soil carbon. Global Change Biology 11 2057-2064.

Kimball BA (2003) Response of plants to elevated atmospheric CO2. Indian Journal of Plant Physiology (Special Issue) 18-24.

Nakicenovic N, Davidson O, Davis G, Grubler A, Kram T, La Rovere EL, Metz B, Morita T, Pepper W, Pitcher H, Sankovski A, Shukla P, Swart R, Watson R, Dadi Z (2000) 'IPCC Special report, emissions scenarios - Summary for policymakers.' Intergovernmental panel on climate change.

Passioura J. 2006. Increasing crop productivity when water is scarce - from breeding to field management. Agricultural Water Management. 80: 176-196.

Whetton PH, Suppiah R, McInnes KL, Hennessy KJ, Jones RN (2002) 'Climate change in Victoria - High resolution regional assessment of climate change impacts.' CSIRO Atmospheric Research, Melbourne.

Xu Z, Zhou G, Wang Y (2007) Combine effects of elevated CO2 and soil drought on carbon and nitrogen allocation of the desert shrub Caragana intermedia. Plant and Soil. 301:87-97.

Previous PageTop Of PageNext Page