The Biochar challenge in Mediterranean viticulture: results from 10 years of field experiment

There are extensive reports and scientific articles in literature on the applicability of biochar as soil amendment in agriculture and on the benefits that this practice can bring in terms of soil improvement and optimization of water resources. The use of biochar as a soil amendment in agriculture is a suitable option that helps to mitigate the effects of climate change. Biochar has an approximate mean residence time in the soil over 1,000 years and this long-term stability is a fundamental prerequisite for considering biochar as a suitable method for carbon sequestration. Unfortunately, most literature provides results based on one-year trials. Not enough for a soil amendment to be able to claim effectiveness for many decades and not enough for a soil treatment to be considered irreversible. An effective option to fill this knowledge gap is represented by long-term field experiments. In this study, we investigated the effect of biochar application on plant water relations and soil properties during 10 years in a field experiment in Central Italy on Vitis vinifera. Biochar was applied at a rate of 22 t ha-1 in two consecutive growing seasons: 2009 and 2010. The results obtained during these years on biochar treatment compared to the control treatment are exciting: we demonstrated an increase in grape production, up to 66%, without a decrease of the grape quality, an increase in plant-soil water relations, no effects on the concentrations of soil PAHs, no eco-toxicity soil effect and a positive effect on soil chemical and biological parameters. Surprisingly, after 10 years the biochar effect continued to demonstrate significant differences among treatments, in particular: a significant increase of soil biological quality, decrease in soil bulk density coupled with a corresponding increase in saturated hydraulic conductivity, an enhance in soil available water content and a significant improvement of plant water status. The modification of plant water availability induced by biochar application increase the resilience of vineyards to droughts, as demonstrated by the lower leaf potential and higher stomatal conductance. This effect has a significant impact on quantity and quality of grape production after 10 years. Moreover, in the long-term perspective the biochar demonstrates to have an effect on soil biological communities that resulted sensitive to biochar with positive increase of abundance of species related to soil moisture content and enhance of biodiversity index. According to these results, the viticulture is now in the position to provide an effective contribution to mitigate climate change and we expect that this will be an example for other Mediterranean countries.