Nutrients and heavy metals in a vineyard soil under organic, biodynamic and conventional management

Abstract

Context and purpose of the study – Promoting sustainable agricultural practices is one of the challenges of the last decades. Organic and biodynamic viticulture can be an alternative to intensive viticulture, furthermore contributing to reduction of impact on environment and human health and guaranteeing soil preservation and quality products.
The aim of this experimentation was to evaluate the medium and long-term effects of different agronomic practices in viticulture on nutrient availability and heavy metal accumulation in soil.

Material and methods – In 2011 an intensive vineyard in north-eastern Italy (Trentino) was subjected to three different managements: integrated pest management (IPM), organic management (OM) and biodynamic management (BM). The experimental vineyard (1.5 ha) was divided in twelve plots, four per management with a randomized scheme. BM plots were subjected to green manure between alternate rows (BM+GM). Every autumn, from 2012 to 2018, soil was sampled in four repetitions per management. Air dried soils were analyzed. Exchangeable K and Mg (extraction in 1 M ammonium acetate pH 7 for 1 hour – 1:20 p/v) and bioavailable heavy metals (extraction in DTPA/CaCl2/TEA pH 7.3 for 2 hours – 1:2 w/v) were determined with ICP-OES. TOC and total N were analyzed with elemental analyzer and assimilable P with Olsen method2. Statistical analysis were performed using the RStudio software.

Results – Exchangeable K is the nutrient that exhibited mainly significant differences (P<0.001) among the managements. In detail, OM and IPM showed on average the highest values, proving that manure is a good supplier of K, which is a promoter of photosynthesis3, is involved in sugar translocation from leaf to fruit3,4 and plays an important role in determining the size of the berries, influencing the final yield of crop4. The lower values in biodynamic managements (BM and BM+GM) were due to lack of K supply. Total N did not show significant differences among the three managements. This result highlights how organic manure and leguminosus plants of green manure provide enough nitrogen for the crop needs, as well as conventional practices. Bioavailable heavy metal content was similar among the managements. Although Cu was used (<5 kg/ha) during the whole experimentation on all the plots, it was not found an increase of the bioavailable concentrations in the years, as expected for the accumulation of this metal in soil. The high Cu content in the soil, due to the abuse of this fungicide in the past decades, means that its use at the doses allowed by current regulations does not cause a significant increase in soil concentrations. These results valorize organic and biodynamic practices, being more compatible alternatives to protection of environment and human health than conventional viticulture.