Turnip growers and vegetable producers take note — a new preprint study published on SSRN reports that wood vinegar application promoted turnip (Brassica rapa var. rapa) growth by enhancing nitrogen uptake and improving photosynthetic activity. The research found wood vinegar enhanced fertiliser efficiency, with treated plants accumulating significantly higher nitrate-nitrogen levels in both leaves and edible roots without additional nitrogen input.

Researchers grew turnip plants in soil treated with wood vinegar solutions at concentrations of 0.001%, 0.01%, and 0.1% over periods of one to six weeks, measuring growth parameters, nitrogen levels, gene expression, chlorophyll content, photosynthetic activity, and glucose accumulation at each stage.

The key findings were striking. Edible root fresh weight increased significantly at the 0.01% application rate after three weeks, with growth promotion continuing through to six weeks. Nitrate-nitrogen concentrations rose significantly in the leaves at three weeks across all application rates, and in the edible roots at both the 0.001% and 0.01% rates after six weeks — without any corresponding increase in potassium, suggesting the effect was specific to nitrogen dynamics rather than a general ionic response.

To understand the mechanism, the researchers examined the expression of nitrate transporter genes — the molecular machinery plants use to absorb nitrogen from soil. Wood vinegar treatment enhanced the expression of both NRT1.1 and NRT2.1 homologs in turnip roots. These two transporters operate across different nitrate concentration ranges, suggesting wood vinegar may broaden the plant’s effective nitrogen uptake capacity rather than simply stimulating a single pathway.

On the photosynthesis side, two-week-old plants treated with wood vinegar showed increased chlorophyll content, higher steady-state PSII quantum yield, and a decreasing trend in non-photochemical quenching. In plain terms: the treated plants were using light energy more efficiently for photosynthesis and wasting less as heat. Glucose accumulation in leaves also increased, indicating stronger carbon assimilation — which the researchers linked to the enhanced edible root development seen at later growth stages.

The authors propose that wood vinegar promotes turnip growth through two coordinated mechanisms: improved nitrogen acquisition via upregulated transporter gene expression, and enhanced photosynthetic carbon assimilation that drives photoassimilate allocation to the storage root. The 0.01% concentration emerged as the optimal rate for edible root promotion in this study.

For Australian vegetable growers, the nitrogen use efficiency finding is the headline result. The research suggests wood vinegar could support nitrogen uptake without increasing fertiliser input — a meaningful outcome given the cost and environmental concerns associated with nitrogen fertilisation. The photosynthetic improvements add a second dimension, pointing to broader effects on plant metabolism beyond simple nutrient availability.

It’s worth noting this study is a preprint and has not yet completed peer review. The findings are preliminary but consistent with a growing body of research examining wood vinegar’s role as a biostimulant across a range of crop species.

Source: Wood vinegar application improves Brassica rapa var. rapa growth by enhancing nitrogen uptake and promoting photosynthetic activity — Nakai et al., SSRN Preprint, 2026 (https://ssrn.com/abstract=6410159)

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