Influence of foliar applications of humic acids on yield and fruit quality of table grape cv. Italia

Aims: The responses in growth, yield and quality components of a Vitis vinifera cultivar (Italia) to the foliar applications of two humic acids extracted from a soil and a compost have been studied. Methods and results: The foliar applications of the two humic acids were performed in two years and six different dates of the season. Both humic acids were tested at two different concentrations, 5 and 20 mg/L. Throughout the trial, different analyses were performed (SPAD, chlorophyll content, titrable acidity, soluble sugars, pH, yield). Grapevines treated with the two humic acids exhibited both significant increases in total chlorophyll content and reductions of the chlorophyll a/b ratio. Application of humic acids significantly decreased titrable acidity and increased °Brix/acidity ratio. Generally, the treatments with humic acids significantly increased berry size, and as a consequence the yield. Conclusions: Humic acids exerted some positive effects (chlorophyll content, acidity, berry size) in Italia table grape. Better results were obtained when the compost humic acid was sprayed. Significance and impact of study: This study gives new information about the positive effects of foliar application of humic acids, active components of soil and compost organic matter, on yield and fruit quality of table grape. In organic viticulture humic acids may find a valid and appropriate application for a technical and economical use.