Using a novel N-15 natural abundance approach to quantify soil nitrogen transformations in biochar-treated vineyard soils.

The increased frequency and intensity of climate extremes challenges vineyards to adapt and mitigate to ensure the survival of grape vines (Vitis vinifera) to meet the growing demand for quality wine.  Regenerative Viticulture (RV) is a novel approach with a strong focus on increasing soil carbon (C) stocks to regenerate vineyard soil that is largely degraded and in poor health.  When soil health and fertility is low, this impacts vine health and reduces its ability to fight disease and pests and withstand extreme climatic events. We hypothesised that biochar would increase nitrogen (N) cycling and retention and that these would differ in relation to the distinct physiochemical properties of the two vineyard soils.   Conscious of contributing to a sustainable circular economy, we utilised viticulture industry waste to produce biochar’s to compare with standard pine biochar.  Biochar was produced with three feedstocks at different pyrolysis temperatures, grape marc (475°C), vine pruning (450°C) and pine (600°C).  Soil (0 - 10 cm depth) was collected from under vines from vineyards at the South Burnett (heavy texture) and Granite Belt (sandy texture) regions in Queensland, Australia. We used a novel ¹⁵N natural abundance approach in a laboratory incubation experiment to investigate the potential of using biochar, a C-dense material produced by high temperature pyrolysis of organic materials in limited oxygen conditions as a suitable climate smart RV method for vineyard soils.  A short three-day laboratory incubation followed by microdiffusion was conducted to quantify the impacts of the three biochars on N transformations in the two soils.  Soil moisture was controlled at 60% and 90% water holding capacity (WHC) and biochar applied at 0% and 10% (w/w), with samples harvested on incubation days 0 and 3. Preliminary results indicate that in the short term for both experimental soils, biochar stimulated microbial activity, increased N availability and water use efficiency and reduced N loss through denitrification.  The results indicate that fungicides use in vineyards impacted the underlying soil health and microbial communities and influencing N cycling.  For the long term impact, the potential to use biochar for increase biodiversity and ecosystem recovery as a climate smart RV method in vineyards needs to be trialled in the field.  This is to establish the long-term effects of C accumulation and improved N cycling on soil health, biodiversity, vine resilience under extreme natural weather events, and on wine grape quality and quantity.