Soils and carbon for reduced emissions
A healthy soil is productive, sustainable and resilient to withstand the impacts of farm management practices and changing climatic conditions. Healthy soils undertake many functions for healthy plant growth, including storing and providing water and nutrients, maintaining biological activity, maintaining good soil structure and the ability to resist erosion.
Soils can store carbon and soil carbon is strongly linked to soil quality and productivity. How much and for how long varies depending on factors such as soil texture (the clay and fine silt fraction), climate — temperature and annual rainfall (amount and distribution over the year), soil moisture and importantly farm management practices.
Soil organic matter makes up a small component of the soil mass, yet it has an important role in the functioning of the physical, chemical, and biological properties of the soil. Soil organic carbon is a measure of the carbon contained within soil organic matter. Soil carbon provides a source of nutrients through mineralisation, helps to aggregate soil particles (structure) to provide resilience to physical degradation, increases microbial activity, increases water storage and availability to plants, and protects soil from erosion. Ultimately, increasing soil carbon levels can lead to better plant establishment and growth. While increasing soil carbon is highly desirable, it is also easily lost, so maintaining what you have is important. Climate is a strong driver, affecting accumulations and decomposition of soil organic matter in soils.
The following management options aim to improve soil condition by improving soil structure, reducing losses of carbon and nitrogen from the soil and building soil organic matter. Improving soil condition will enhance a plant’s ability to access the nutrients it needs, capture and retain soil moisture for longer and reduce losses of nitrogen to the atmosphere, groundwater and waterways.
There are ways to increase soil carbon while also increasing productivity, water holding capacity and nutrient cycling. This will reduce input costs and produce wider natural resource management benefits.
Monitor soil nutrient levels:
- test your soil to check the nutrient status and structure of your soil and develop a plan to improve constraints to nutrient and water access e.g. physical (structure, compaction, drainage), chemical (pH, salinity, toxicities/deficiencies), biological (micro-organisms).
- monitor soil organic matter/soil organic carbon over time via testing.
- complete a nutrient balance/budget to match fertiliser requirements to crop/pasture demand.
- manage soil structure to maximise water infiltration and retention for plant uptake and aeration.
Consider application of soil amendments:
- addition of organic amendments (manure, crop residues) where practical and economically viable. Know the quality of any products, have them tested and ensure any claimed benefits are supported by sound evidence and research.
- manage application of gypsum on sodic soils to maintain/improve soil structure.
- manage livestock manure (dung and urine) to minimise nitrous oxide emissions — see Livestock section for further details.
Manage the soil resource:
- use direct drill, minimum/conservation tillage and controlled traffic techniques in cropping operations to avoid compacting soils and losing carbon and nutrients through soil cultivation and erosion.
- avoid burning crop residues and retain where possible.
- cultivate soils at an appropriate moisture content — not too moist for soils to smear, or too dry that the soil is pulverised.
- avoid bare fallows and have continuous plant cover where possible e.g. green/brown manure crops between seasons and crops can maintain groundcover, provide active root material and organic matter as well as use available nitrogen and avoid losses by leaching.
- manage irrigation and soil drainage to avoid waterlogging. Use irrigation scheduling and monitoring.
- rotate crops and include perennial pastures and legumes phases in rotations. In general, perennial pastures will improve or stabilise soil carbon more than annuals can.
- do not overgraze pastures. Ensure there is sufficient groundcover throughout the year (>50 percent cover). Consider stock containment areas to ensure improved pasture and groundcover management options.
- manage livestock movement and paddock rotations to distribute animal deposited dung and urine evenly and reduce compaction from hoof traffic.
Keep an eye on policy changes relating to potential incentive payments for carbon stored in soil. Always seek legal and financial advice first.
The Soil Carbon Snapshot booklet was produced by Agriculture Victoria to explain what we know about soil carbon. The short video provides a summary of what we know about soil carbon.
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