For growers and agronomists across South East South Australia, Central Victoria and Western Victoria, soil carbon is a practical indicator of soil function. It affects structure, water movement, nutrient cycling, root growth and long-term resilience.
Soil organic carbon is the carbon held in soil organic matter as plants, roots, microbes, manures and other organic materials break down. It generally makes up about 50–58% of soil organic matter, making it a useful indicator of soil health.
The South Australian Department for Environment and Water notes that soil with 1.5% organic carbon to a depth of 30 cm and a bulk density of 1.3 g/cm³ contains about 58.5 tonnes of carbon per hectare. Regional targets should be based on rainfall and soil texture, not a blanket figure.
A sandy soil near Penola, a red clay loam around Newbridge, a pasture soil near Mount Gambier and a vineyard soil on the Limestone Coast will behave differently. The common goal is improved water holding, nutrient cycling and plant growth.
Organic matter helps bind soil particles into stable aggregates, improving porosity, aeration and water movement. For growers, this can mean better infiltration, stronger roots, improved water-holding capacity and greater resistance to crusting and erosion.
Soil carbon supports nutrient cycling, retention and availability. It does not replace a fertiliser program, but it can help the soil make better use of nutrients already present or applied.
As organic matter breaks down, soil microbes release nutrients in plant-available forms. Soil carbon also increases cation exchange capacity, helping soils retain nutrients such as calcium, magnesium and potassium.
Healthier soil generally supports healthier plants. Better aggregation helps roots move more freely, while improved infiltration and water storage help plants keep growing between rainfall or irrigation events.
More carbon does not automatically translate to higher yields. Soil type, rainfall, nutrition, compaction, pH, crop choice and management all influence outcomes. However, soil carbon can create better conditions for root growth, nutrient uptake, water-use efficiency and more stable production.
Bio Gro’s fieldwork adds local, first-hand context across broadacre and pasture systems in South East SA, Central Victoria and Western Victoria.
In a barley trial in Central Victoria near Newbridge, AgriGro compost at about 6 t/ha increased grain yield by 31% compared with the control. AgriGro+ increased yield by 20%. The report noted below-average rainfall in 2024 and said further investigation was required.
In a permanent pasture trial south-east of Mount Gambier, AgriGro compost increased pasture dry matter by 115 kg/ha. It delivered higher digestibility and metabolisable energy than single superphosphate, at the same economic value. [biogro.com.au]
Near Branxholme/Hamilton, compost improved pasture growth in both sandy loam and clay soils, with the strongest early response in sandy loam and more sustained gains in clay when compost was combined with gypsum. [biogro.com.au]
These are field examples, not universal guarantees. They show how compost-based amendments can support soil function when matched to soil type, season and agronomic goals.
Compost is a practical way to return organic matter - and therefore carbon - to agricultural soils. It adds nutrients, improves soil structure, supports soil biology and helps improve water retention over time.
Compost works best as part of an integrated fertility program, alongside soil tests, paddock history, production goals, soil constraints, seasonal timing and nutrient budgets.
AgriGro: compost-based formulations for practical soil improvement
Bio Gro agricultural soil amendments combine processed compost, manures and mineral elements, with nutrient analysis to help growers select formulations suited to their soils and production goals.
AgriGro is Bio Gro’s certified organic, 100% compost-based soil additive. It is suited to horticultural, broadacre and pasture systems, with typical organic carbon of 24–30% and organic matter of 42–52%.
In practice, AgriGro can support:
Broadacre: applied before sowing to support soil structure, nutrient cycling and early crop establishment.
Pasture: used as a topdress to support dry-matter production, feed quality and longer-term soil condition.
Horticulture: incorporated where soil structure, nutrient retention and microbial activity are critical to crop performance.
Viticulture: applied under-vine or in targeted strips to support water retention, infiltration and soil biological activity.
Bio Gro can also match formulations to constraints such as nutrient demand, pH correction, soil structure, or sodicity, using soil testing and constraint analysis.
The right amendment depends on soil type, rainfall, enterprise, application window, logistics, nutrient requirements, and return on investment.
Building soil carbon is not a quick fix. It is a long-term strategy for soil function that can improve structure, infiltration, water-holding capacity, nutrient retention, biological activity, root growth and production resilience.
For growers and agronomists across South East SA, Central Victoria and Western Victoria, compost-based amendments such as AgriGro offer a practical, locally available way to build soil carbon and improve soil function, working alongside conventional fertiliser programs where required.
Healthy soils do more work. They hold more water, cycle more nutrients and support stronger plants - for the next crop, grazing rotation or season.
Contact Bio Gro to talk with our agronomy team about your farming operation, soil goals, and how Bio Gro can help.