Climate change, wheat production and erosion risk

The Agricultural Production System simulator (APSIM) was used for this study. This platform contains a suit of modules and a range of plant, animal, soil, climate and management components that can be incorporated into modelling agricultural outcomes.

This case study used the following soil properties: surface texture and plant available water holding capacity (PAWC), along with mapped attributes of water erosion and wind erosion potential. These mapped attributes were used as a basis for establishing ‘critical ground cover’ required for adequate protection against erosion.

Representative historic long-term climate datasets were used in the modelling, along with hypothetical climate change scenarios (consistent with projections to 2030) to explore simulated regional impacts under drying, warming and increasing carbon dioxide levels.

• Shallow clayey soils are most vulnerable to poor yields and low stubble cover in dry years.
• In low rainfall environments, higher rates of evaporation and the inherent higher wilting point moisture levels in clay surface soils increases the risk of moisture stress and terminal drought (early crop senescence), compared to sandy surface soils.
• Sandy surface soils with large PAWC (e.g. deep sands or some sandy surfaced texture-contrast soils) are the most resilient for cropping in drier environments.
• Low rainfall cropping environments appear most vulnerable to reducing grain yields and increasing erosion risk, if rainfall declines.
• The modelling suggests that for some areas there will be a general trade-off between grain yield and residual crop biomass (available to protect soils) under declining rainfall. This lower biomass is the result of earlier flowering and grain production triggered in some wheat varieties by the warming climate, giving the plant less time to invest in growing its biomass (i.e. shorter growing period).
• Meanwhile, cropping systems in the wetter parts of the State are likely to benefit from a warming, drying climate. In these situations, where moisture is not a limiting factor, the increased CO₂ and temperature (in historically cool regions) have the opportunity to boost plant and crop production levels.
• Erosion risk is a gradational problem, increasing in extent with poorer seasons and increasing in frequency with a drying climate.
• The erosion risk maps highlight a patchwork of areas that will need to be monitored if projections of a drying climate become a reality, to identify any emerging and recurrent erosion risk issues.

If climate changes in line with current projections, farmers and other natural resource managers will need to adopt a range of adaptation strategies. These may include incremental shifts and flexible risk management approaches through to more fundamental practice changes over generational timeframes. Farm management practices

• Continue to improve water use efficiency to optimise grain and biomass production.
• Adopt a range of climate risk management strategies (e.g. flexible and responsive farming techniques; using seasonal indicators to base management decisions).
• Consider soil and land types in management decisions (e.g. farming to land capability, including inherent production potential and risk; assessing required stubble cover and quality; grazing management).
• Retain cereal stubbles for soil protection, helping to minimise erosion risk after harvest and into the following season.
• Use crop species that leave greater amounts of protective biomass after harvest (particularly in the case of grain legumes).
• Continue uptake of reduced tillage and ‘no-till’ farming techniques.
• Investigate alternative land use or management on areas of land prone to higher frequencies of poor crop growth, low economic returns and elevated erosion risk.
• Use spatial analogues to consider adaptation options (learn from what farmers are doing in warmer and drier locations).

Refer to the full report for recommendations for a) research and development, b) state and regional planning and policy development, c) industry adaptation and education, and d) future scenario modelling.