Climate change impacts on our soils

Climate change will affect rates of soil erosion. This is because: 

• reduced rainfall in southern states may lead to drier topsoils and reduce soil structure
• more frequent extreme weather events will bring heavy downpours. 

Downpours – heavy rain that falls in a short period of time – are a major cause of soil erosion. If the rain is heavy enough, the soil cannot absorb it and water flows across the surface, taking a layer of topsoil with it. 

The risk of soil erosion varies across NSW because of changes in terrain. For example, steep terrain has a high erosion risk, while flat terrain has a low erosion risk. 

Hillslope erosion in NSW is projected to increase by 7–21% in the next 60 years. The areas most affected will be those in which the erosion risk is already high: the Great Dividing Range, Central Coast, North Coast and Hunter regions. 

Soil organic carbon (SOC) is a key indicator of soil health. It is associated with many desirable qualities including nutrient availability, high biological activity, soil physical structure, water-holding capacity and aeration. 

NSW is projected to experience an overall decline in SOC in both the near (2030) and far (2070) future. This will affect nutrient supply, soil structure, aeration and water-holding capacity, which have negative impacts on agricultural productivity. 

SOC also has a role in climate change mitigation. Changes in the quantity of carbon stored in the soil can affect the global carbon cycle and alter carbon dioxide levels in the atmosphere. Thus, decreases in soil carbon may raise greenhouse gas levels in the atmosphere, contributing to climate change. 

Soil is the major source of the nutrients needed by plants for growth. Higher levels of nutrients indicate more fertile soils and contribute to increased agricultural productivity. 

NSW is projected to experience an overall increase in soil macronutrients, including calcium, magnesium, potassium and sodium. Soil nutrients normally increase in upper soil layers with rising temperatures and declining rainfall, as is expected over much of NSW. 

The rise in soil macronutrients over most of the state could generally benefit agriculture. However, intensive agricultural land use may reduce nutrient levels. 

Changes in nutrient levels will also affect natural ecosystems. These ecosystems often have narrow and typically low requirements for nutrients, so increased nutrients may be harmful. These are issues that may need to be considered and addressed in land management. 

Soil pH is a measure of acidity or alkalinity. All plants, including both agricultural and native vegetation species, have particular ranges of pH that they find suitable, beyond which they will suffer. Some plants have a broad range while others may have a relatively narrow range. The availability of nutrients and toxic elements are also influenced by pH levels, which affect plant growth. 

Currently, pH varies across NSW from less than 4.5 to greater than 8.0 pH units. NSW pH levels are projected to increase slightly (become more alkaline), typically up to 0.3 pH units, and generally increasing from east to west. The far southern alpine region will see the greatest increase – up to 0.5 pH units or more. 

Over most of the state, the changes are quite small and not likely to significantly affect agricultural practices. But they may still need to be considered by land managers, especially where their crop or pasture species require a narrow pH range, for example some varieties of wheat. 

Changes in soil pH may also affect natural ecosystems that have been established within particular pH ranges. This issue may need to be considered and addressed by land managers.