Assessment of total and available heavy metal contents in vineyards managed under different agriculture practices

Land degradation is a major challenge, particularly in intensive agriculture areas such as typical vineyards. Soil contamination with heavy metals is a widespread phenomenon in vineyards, due to the intensive use of pesticides, fertilizers, manure and slurry. As a result, vineyard soils have accumulated heavy metals and other trace elements that may be phytotoxic, non-biodegradable and persistent, which represents a long term threat to the crop system and to the food chain. In Portugal, vineyard area represents the fourth largest area in Europe (178770 ha), being one of the most relevant crops. Different approaches, such as, environmental programs and innovative management practices have been adopted over the last years, in order to minimize soil contamination by heavy metals. However, the establishment of quality standards for heavy metals in agriculture soils are mainly based on their total content, which is insufficient to estimate their environmental potential risk. The toxicity of metals does not depend only on their total concentration, but rather on their availability. Nevertheless, knowledge on the “bioavailable fraction” of heavy metals on agriculture soils, and particularly in vineyards, is still limited. This study, developed under iSQAPER research project, aims to assess the total and available heavy metal content in vineyards managed under different management practices: (1) no tillage, (2) integrated production, and (3) conventional farming. The integrated production and the conventional farming in the study sites have been intensively managed for more than 5 years, and more than 30 years in the no tillage vineyard.  The study was performed in 2018, based on soil sampling before and after pesticide application (April and July, respectively). Soil samples were also analyzed for pH, soil organic matter content (SOM), total and available (DTPA-extractable) heavy metals content (Cu, Cd, Cr, Pb, Zn and Ni). Preliminary results show higher content of total Cu, Pb, Cr and Ni in the vineyard managed under no tillage than in the farms with conventional and integrated production practices. Cupper is the heavy metal with highest total concentrations, mainly due to the intensive application of Cu-based fungicides. In the vineyards with no tillage, the long term practices have led to total levels of Cu above the soil quality standards. Moreover, similar contents in total Zn were also observed in no- tillage and integrated production practices. The higher content of SOM observed in vineyards under integrated production may have favored the Zn accumulation in the topsoil layer of vineyards. Higher content of organic matter, were found in integrated production farming than in no-tillage and conventional practices, 2.6%, 1.3% and 1.2%, respectively. Understanding total and bioavailable fraction of heavy metals in vineyards is crucial to assess their potential toxicity on plants, animals and humans. The assessment of the best agricultural management practices is a key factor to mitigate land degradation in vineyards.