Hydroretentive polymers, or hydrogels, are materials consisting of large molecules composed of polymer chains parallel to each other, rich in cross-links, forming a network of hydrophilic groups, capable of absorbing water or solutions. In the Italian agricultural scene, their use has been hampered by their cost and technical limitations related to their manipulability.

However, recent technological progress has made it possible to significantly reduce their production cost and to develop new, better performing and totally biodegradable products. A first category is synthetic polymers based on salts of polyacrylic acid, containing sodium (sodium polyacrylate) or potassium (potassium polyacrylate), formulated in powder or granule form. In addition, super-absorbent hydrogels made from organic material are now available. The latter, of plant origin, can be sourced, for example, from waste from the wood industry (cellulose) or the textile industry (cotton), and be allowed under organic regimes.

In this specific case, the experimental trials of the PSR IN+VITE project (www.inviteproject.eu) were conducted on three different hydrogels in relation to limiting water conditions for vine development. In particular, potassium polyacrylate-based H1 and H2, respectively, and organic-based H3 were used (Fig. 1).

Fig.1 Hydroretentive polymers from left to right .

Photosynthesis response curve

During 2023, the efficacy of the two different hydrogels was tested on Sangiovese plants grown in pots under semi-controlled conditions at an outdoor space of the Department of Sustainable Plant Production Sciences (Università Cattolica del Sacro Cuore, Piacenza). Specifically, vines to which potassium polyacrylate-based hydrogel (H1) was applied and vines to which organic derivative-based hydrogel (H3) was applied were compared to an untreated Control.
During these trials, in addition to evaluating vine response as a function of progressive water deficit, the response curve of photosynthesis to increasing values of photosynthetically active light (PAR) was characterized before and after a period of particularly severe water deficit imposed artificially by suspending irrigation.In the period before the severe water stress, the leaves of H1 vines showed higher photosynthesis values than those of the control leaves. In particular, the difference between theses increased progressively at PAR values > 400 μmol m-2 s-1. At light saturation (PAR > 1200 μmol m -2 s -1), the vines with H1 had a net photosynthesis of 15 μmol m -2 s -1, the vines with H3 had a net photosynthesis of 13 μmol m -2 s -1, while in the control, assimilation did not exceed 11 μmol m -2 s -1 (Fig.2). Following severe water stress, despite restoration of full water volumes, the leaves of the control were unable to take up positive photosynthetic rates, and even at light saturation, net assimilation was less than 1 μmol m -2 s -1. In the vines with SH1 and SH3, although the leaves did not exhibit net assimilation values comparable to the pre-water stress period, net photosynthesis was still significantly higher than the control for any PAR threshold examined, up to values close to 8 μmol m- -2 s -1.Thus, the trial conducted demonstrated that the application to the plant of SH1 and SH3 allows for increased net assimilation and dry matter partitioning under nonlimiting conditions, and, consequently, shoot growth rate, as well as for the maintenance of improved physiological function following particularly dry periods.

Fig. 2 Correlation between net leaf photosynthesis and light intensity that reaches leaves, before a period of severe stress (top) and following the stress period (bottom), in vines to which H1 and H3 polymers were applied at planting and Control vines.