Soils and Land
Soil is important to the south-west for its important environmental and economic roles and as a result is a fundamental base for all life. Soil acts as medium for the region’s native plants and farming crops, it recycles nutrients and organic wastes, it acts as a filter to improve water quality and is habitat for many important organisms that in turn play important roles in both natural and farming ecosystems.
For the South West region, climate change modelling and projections indicate that increasingly hotter and drier conditions can be expected. Temperature is expected to increase in all seasons with an increasing number of hot days and fewer very cold days overall. Average annual temperatures are projected to rise by between 0.5 and 1.1 degrees by 2030. Winter rainfall is likely to decrease and summer rainfall expected to increase. Despite an overall decrease in rainfall by up to 7% by 2030, the intensity of extreme rainfall events is likely to increase. Because of the natural variability in rainfall across the region, the overall trends may be masked for decades to come, particularly in summer.
Despite these changes, the impact of climate change on agriculture is expected to be less damaging to South-West Victoria than other parts of the State. Temperatures are expected to remain moderate while rainfall is anticipated to remain adequate in the medium term, particularly in the region’s south. It is likely that the area most suitable for grain production (mainly wheat and barley) will move southward. As such, the region may become more attractive to agricultural producers in northern Victoria, who may experience more negative production impacts due to climate change and wish to relocate. An increase in cropping has already occurred within the region; from 1990 to 2010 an average of 12,000 ha per year of grazing pastures were converted to cropping.
Climate has a direct impact on soil health and has its most severe impacts in extremes of dryness leading to wind erosion and, in extremes of wetness, leading to sheet, rill and gully erosion. Soil erosion is likely to be exacerbated due to an overall reduction in precipitation in combination with increases in intense rainfall events occurring on dry, denuded soils. In combination, drier soils, reduced vegetation cover and more intense rainfall will present significant challenges to soil conservation even with moderate climate change.
Soil health is also linked to climate benefits on a global scale because soils can store carbon, leading to improved soil quality and reduced greenhouse impacts. Carbon within the terrestrial biosphere can behave either as a source or sink for atmospheric CO2 depending on land management, thus potentially mitigating or accelerating the greenhouse effect. Soil carbon in the region is expected to decrease under climate change due to decreased net primary production. Any gains by increased efficiency of plant water use, due to elevated CO2, are likely to be outweighed by increased carbon mineralisation after episodic rainfall and reduced annual and growing season rainfall. In addition, shifts in land suitability for farming may lead to increased and significant land-use change.
Soil biology and microbial populations are also expected to change under conditions of elevated CO2 and changed moisture and temperature regimes. As soil biology regulates nutrient dynamics and many disease risks, nutrient availability to crops and pastures could change as could the exposure to soil-borne diseases.
More information on the region’s soil can be found in the Soil Health Knowledgebase at www.ccma.vic.gov.au/soilhealth/
