Managing soil organic carbon on Western Australian farms

• Slow increase in carbon (less than 0.2tC/ha for each tonne extra grain yield)
• Higher fertiliser inputs may increase decomposition rate.

• Where harvest index maintained profit and organic matter should increase.

• Higher nutrient cycling capacity and biological fertility.
• Lower erosion risk.

• Cost neutral long-term.

• Decrease in particulate organic matter and nutrient cycling.

• Can be positive or negative.
• Where high weed pressure exists, should increase yield.
• Burning leads to loss in soil fertility, which could decrease yield.

Increasing rotational diversity

• Supports a more diverse microbial community.
• Provides disease break options.

• Can be positive or negative.
• Lack of profitable break crop options in low rainfall may constrain potential for profit.

• Positive provided no water deficit occurs in cash crops.
• Potential for green bridge to increase disease risk.

• Mixed pastures provide best quality inputs and capitalise on longer growing season.
• Well established perennials with high biomass production or deeper carbon allocation.
• Perennial systems tend to be dominant in high rainfall areas.

• Positive where good pasture establishment and weed and erosion risks are managed.
• Dependent on stock/meat/wool prices.
• Pasture cropping could influence moisture availability in subsequent crop.

• Lower grazing pressure to decrease erosion risk and increase organic matter inputs.
• In theory, rotational grazing increases productivity and residues turnover.

• Dependent on stock/meat/wool prices.

• One-off cover crops etc. likely to have little impact.
• Impact greater if able to support two or more crop/pasture phases in a year.
• Pasture cropping where organic matter inputs are effectively extended (higher net primary productivity).

• Significant cash flow deficit in year of implementation for green manures.
• Viability dependent on opportunity and operational costs and subsequent seasonal conditions.
• Carefully consider the area to be targeted.

• Carbon in manure and compost is more stable than fresh residues.
• While possible to generate enough biomass to raise soil carbon, often external sources of organic matter (manure, compost) are required.
• Amendments vary widely in properties and effect on crops and soils.

• Negative in the short-term with high application cost, with little evidence of long-term profit outcome.
• Economic outcomes likely to be constrained by rate of application and costs, including transport.
• Agronomic responses vary widely and can be negative. Seek local trial data.
• Consider any potential environmental risks.

• Small, if any benefit to soil organic matter. Long-term adoption can promote soil aggregation and slow decomposition rates.
• Direct drilling decreases erosion risk and helps maintain soil structure, slowing decomposition.
• Organic residues on the soil surface tend to provide only minor contributions to stable soil organic carbon fractions.

• Effect on structured or aggregated soils greater than on coarse textured sand.
• Increased reliance on herbicides can contribute to negative profit base.

• Fallow contributes to soil carbon losses because no additional biomass is generated and erosion risk increases.

• While short-term economic responses to fallow can be positive, longer term profit outcomes are often negative.

• Low cost practices available.
• Likely to be positive though dependent on current losses and the intervention required.

• All organic matter (minus natural loss) returned to the soil, with replanting of native species on degraded land.

• There are direct and indirect costs in retiring agricultural land. Economic viability dependent on foregone opportunity costs, carbon price and market opportunities.

• Large potential for carbon storage through the establishment of forests, trees and other perennial vegetation.
• Less erosion potential.

• Opportunity costs over the long-term should be considered. Economic viability dependent on carbon price and market opportunities.

• Higher biomass production.
• Increased frequency of crops and pastures supports higher soil organic carbon.
• Irrigating when warm can increase decomposition rate.

• Large on-farm impact.
• Potential trade-off between higher carbon inputs and increased decomposition rates.