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Climate change impacts on our soils

Key points

  • Soils are essential to plant life, supporting ecosystems and agriculture. 
  • Climate change will affect soils, leading to changes in soil erosion, organic carbon, nutrients and alkalinity. 
  • Decreasing soil carbon due to climate change also has implications for accounting of carbon emissions from the land, which is an important avenue for NSW to meet its Net Zero Emissions by 2050 target.   
  • Agricultural managers may be able to limit the impact of these changes and manage their land to maximise soil health by using sustainable soil management principles. Principles include choosing appropriate crops, managing nutrient and water cycles and reforestation. 

The importance of soils in NSW

Soils support the growth of most plant life. They are a crucial element of land-based ecosystems and agriculture. In NSW, the gross value of agricultural production was $11.2 billion in 2019–20. 

Because soils form extremely slowly, protecting our soils and their health is essential. Important measures of soil health include: 

  • soil structure and porosity 

  • topsoil thickness 

  • carbon and nutrient content 

  • acidity (pH) 

  • salinity. 

How soils are affected by climate change in NSW

Many soil properties are affected by changes in temperature and rainfall. Projected changes to our climate will therefore affect our soils.  

Degradation of our soils will have environmental impacts on our vegetation and water quality. It will also affect our agricultural production.

Soil erosion

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 terrains have a high erosion risk while flat terrains have low erosion risk.  

Hillslope erosion in NSW is predicted to increase by 7–21% in the next 60 years. The areas most affected are those with already high erosion risk, namely the Great Dividing Range, Central Coast, North Coast and Hunter regions. 

Soil organic carbon

Soil organic carbon (SOC) is a key indicator of soil health. It is associated with many desirable attributes 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 and soil structure, aeration and water-holding capacity. Agricultural productivity may decrease in affected regions, unless remediating measures are undertaken. 

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, thus contributing to climate change. 

Soil nutrients

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

Acidity and alkalinity (pH)

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. pH levels also influence the availability of nutrients and toxic elements, 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 increased slightly (become more alkaline), typically up to 0.3 pH units, and generally increasing from east to west. The far southern alpine region has the greatest increase, of 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 farm 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, which have normally established under particular pH ranges. This issue may need to be considered and addressed by ecosystems managers. 

How will soil erosion change in NSW?

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How will soil properties change in NSW?

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Adapting to changes in the soil in NSW

Careful soil management will be needed to minimise the effects of climate change on our soils, environment and economy. 

Using sustainable soil management principles can help landholders and managers to maximise soil health. Principles include: 

  • Protect soil from physical, chemical and biological degradation, limit erosion and avoid deforestation (for example, the best way to combat soil erosion is to maintain vegetation to cover at least 70% of the soil.) 

  • Restore soils on degraded lands (for example, increase organic matter levels). 

  • Maintain soil-based ecosystem services, water availability and quality (for example, create buffers between agricultural lands and waters). 

  • Enhance soil productivity according to its natural capacity (for example, choose appropriate crops for the soil type and replace nutrients removed by harvest). 

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