Wood Vinegar Boosts Phosphorus Availability in Soil, New Research Shows

Australian growers looking to improve fertiliser efficiency have new evidence to consider. Research published in the Journal of Soils and Sediments found that wood vinegar application significantly reduced phosphorus adsorption in soil — meaning more phosphorus remains available for plants rather than being locked up in soil particles. When combined with biochar at a 3% rate, wood vinegar reduced phosphorus adsorption by up to 28%.

Phosphorus is one of the most critical nutrients for crop production, but it’s also notoriously inefficient. Much of the phosphorus applied as fertiliser quickly binds to soil particles in a process called adsorption, making it unavailable to plants. This means growers often apply more phosphorus than crops actually use, increasing costs and environmental risks.

Researchers tested biochar and wood vinegar both separately and in combination, applying them at various ratios to soil samples and measuring how much phosphorus the soil absorbed. Biochar alone reduced phosphorus adsorption by 2.93% to 26.65% depending on the application rate. When wood vinegar was added to the biochar treatments, phosphorus adsorption dropped even further — by 4.43% to 28.02%.

The mechanism appears straightforward: organic acid anions in wood vinegar compete with phosphorus for binding sites on soil particles. When these organic acids occupy the sites, phosphorus remains in solution where plant roots can access it.

The optimal combination tested was 3% biochar with wood vinegar. This ratio effectively enhanced soil phosphorus availability by preventing phosphorus from binding tightly to soil minerals. The researchers noted that the combined application was more effective than either amendment alone, suggesting a synergistic effect between biochar’s physical properties and wood vinegar’s chemical activity.

This research adds to a growing body of evidence showing wood vinegar’s potential role in nutrient management. Earlier studies have documented wood vinegar’s effects on soil pH, microbial activity, and nitrogen availability. The phosphorus findings are particularly relevant for Australian soils, many of which are naturally phosphorus-deficient and prone to strong phosphorus fixation.

For growers managing tight input budgets, any improvement in phosphorus efficiency represents real value. Less phosphorus locked away in soil means better return on fertiliser investment and potentially reduced application rates over time.

Source: Enhanced soil phosphorus availability via combined biochar and wood vinegar application — Journal of Soils and Sediments, 2025

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