New bio-based super-absorbent hydrogels, a game-changing tool for organic vineyards water management and adaptation to drought

Hydrogels are soil-conditioning materials capable of absorbing substantial amounts of water relative to their weight. Their use in agriculture is rapidly expanding and new bio-based hydrogels allowed in organic agriculture are now available, but their effects on grapevines at transplanting has until now not been explored. This study compared the localised root-zone application to soil of a potassium polyacrylate hydrogel (SH1) and an organic hydrogel (SH2) at vine transplanting, with an untreated control (C) in two experiments: one on potted vines under semi-controlled conditions and the other in a newly established rainfed vineyard. Both SH1 and SH2 increased soil field capacity and maximum available water. In the potted vines, they improved water status under drought conditions, delaying the decline of stem water potential (+ 0.25 MPa on the last day before rewatering) and enhancing leaf gas exchange (+ 9 and + 8 μmol m –2 s –1 for SH1 and SH2, respectively, as compared to C). By the end of the second season after transplanting, SH1 and SH2-treated vines exhibited greater leaf area, higher yield (+ 29 % and + 26 % relative to C, respectively), and a lower leaf-to-fruit ratio, resulting in reduced fruit sugars (–2.0 and –2.2 °Brix respectively) and anthocyanin levels. In the field, shoot growth and final leaf area after two years were higher in SH1- and SH2-treated vines (+ 25 %). SH1 accelerated the transition to a productive stage, while SH2 reduced the number of vines requiring two-nodes pruning. Our findings indicate that bio-based hydrogels are promising tools for organic vineyard water management. Their incorporation at transplanting could help shorten unproductive stages and accelerate full crop development.