Polímero hidroretentor alternativo para horticultura em condições salinas

Abstract

Water retention by superabsorbent hydrogels is affected by salinity, and there is interest in developing salt-tolerant materials for use in agriculture. This study was conducted to prove that an alternative calcium carbonate based hydrogel retains more water in the soil and favors the lettuce crop when compared to a commercial acrylamide and potassium acrylate based hydrogel without calcium carbonate under water deficit conditions, leading to more favorable results compared to no polymer in response to increasing salinity. Two experiments were set up: one in the laboratory and the other in the greenhouse, both with a fully randomized design, in a 3x5 factorial design with four repetitions. The first treatment factor in both experiments was: soil without hydrogel (SH), soil + 2 g kg-1 of alternative hydrogel (HA) and soil + 2 g kg-1 of commercial hydrogel (HC). The second treatment factor was composed of five electrical conductivities (EC) of the irrigation water (0; 0.5; 1.0; 2.0 and 4.0 dS/m). In the first experiment the soil water retention curve was evaluated with the treatments at low (0 -2 -6 and -10 kPa) and high (-33 -700 -and -1500 kPa) stress points, water availability and pore distribution were calculated. In the second experiment, in which lettuce was grown in soil with the previously mentioned treatments, measurements of plant development, physiological attributes, biomass, quality, and nutrient accumulation were made. Analysis of normality was performed and data that did not present a normal distribution were transformed. Analysis of variance was performed, followed by Tukey's test (p < 0.05) for qualitative factors and regression analysis for quantitative factors. In the HA treatment, soil water retention and availability were superior to those observed in the HC and SH treatments. The pore distribution in HA was similar to that observed in SH, with higher pore frequency and number up to an EC of 2 dS/m. HA was superior to HC in terms of fresh (22.89 and 1.07 g plant-1, respectively) and dry (16.39 and 1.02 g plant-1, respectively) mass of lettuce plants. Proline and nitrate contents were higher in HC (0.114 and 2.15 µmol g-1) than in HA (0.0915 and 1.345 µmol g-1). While chloride in HC (108.14 µmol kg-1) was quantitatively higher than in HA (103.01 µmol kg-1). The HA treatment favored greater uptake of macronutrients and attenuation of the effects of excess soil sodium at increasing electrical conductivities of irrigation water.