Organic Vineyard Fertilization: Soil Carbon and Nitrogen in Southern Brazil

In recent years, vineyard areas in organic production system have been increasing significatively, in both develop and developing nations. This trend aligns with the growing concerns of people and governments. They are increasingly worried about health issues and the environmental impact of conventional agriculture and horticulture. In contrast, agroecology and organic fertilization have the potential to offer safe products and promote carbon (C) sequestration in the soil. The latter benefit is also a crucial strategy to mitigate the climate effects of greenhouse gas emissions. This aligns with the UN's guidelines for carbon-neutral production systems However, in vineyard agroecosystems, there is limited technical information about the impact of organic fertilizers and plant CO₂ fixation on carbon levels. This is especially true in subtropical climates. Therefore, this research aimed to evaluate how different fertilization systems affect soil organic carbon (SOC) and soil organic nitrogen (SON). An experiment was set up in a commercial organic vineyard with two different cultivars: ‘Isabella’ (Vitis labrusca x V. vinifera) and ‘Chardonnay’ (V. vinifera), in Veranópolis (Cfa climate), in Southern Brazil. The soil in the experiment was classified as Cambisol (WRB). Since 2020, the following fertilization systems have been applied yearly: no fertilization (T), grape pomace vermicompost (GPV), grape pomace compost (GPC), GPV plus mineral fertilizers (GPV+MF), GPC plus mineral fertilizers (GPC+MF), and mineral fertilizers only (MF). The organic fertilizers were applied in the dose of 40 kg of N ha^-1, on the surface beneath grapevine canopies. The mineral fertilizers consisted of natural phosphate and potassium sulphate, in the doses of 160 and 100 kg ha^-1 of P₂O₅ and K₂O, respectively. In 2023, soil samples were collected from 0 to 5, 5 to 10, 10 to 20 and 20 to 40 cm layers, at bud burst (August), and analyzed for SOC and SON, via combustion followed by gas chromatography. No fertilization system increased SOC or SON in layers up until 20 cm deep after three years of treatment. In 20 to 40 cm layer, there was variability among treatments; however, that is probably main to natural variation. Mean C:N ratio of soil organic matter was 12,0. In light of this, we suggest the evaluation of SOC and SON after a longer period of treatment application, since their low increase in humid subtropical regions, which presents hot and wet summers.