Abstract
Hydrogels have potential as soil conditioners due to their high capacity to retain water and mitigate soil salinity. However, investigations under saline conditions are necessary because there are losses in both water absorption and salinity mitigation depending on the composition of hydrogel and ions involved in salinity. In this work, we studied a commercial hydrogel in two experiments. The first experiment was conducted in the laboratory to evaluate the absorption by the hydrogel of water with electrical conductivity (EC) of 0.5, 1.5, 3.0, and 4.5 dS m–1, promoted by NaCl. The second experiment was conducted in a greenhouse in a 2 × 4 factorial scheme (with and without hydrogel × EC of the first experiment). Although salinity reduced water absorption by hydrogel by 84 %, the polymer applied in a sandy soil under saline conditions reduced water losses by 58 %. However, hydrogel did not increase the final soil moisture (~ 0.10 g g–1). The polymer reduced Na+ concentration in leachate from 1,499 to 1,219 mg L–1 at the highest salinity level (4.5 dS m–1), but it increased Na+ soil availability by 0.1 mg kg–1 in comparison with polymer absence. Hydrogel application increased Na+ content in plants from 9 to 13 mg kg–1 at the highest salinity, while K+ content was 10 to 16 mg kg–1 lower than that observed without a polymer. Hydrogel 0.07 % (w/w) reduced maize biomass, indicating damage by monovalent ions, compromising the polymer potential under salinity.
Highlights
Superabsorbent hydrogels (SAHs) are composed of cross– linked and tridimensional polymers that absorb hundred folds of their weight in water (Essawy et al, 2016; Saha et al, 2020; Ai et al, 2020)
Hydrogel composed of K+ acrylate, acrylamide, and mineral is expected to improve soil conditions and plant growth even when subjected to increasing salinity in which monovalent ions prevail
To characterize the polymer used, we carried out analyses at room temperature (25 ± 1 °C), as described below: The organic composition of the superabsorbent polymer was obtained by Fourier Transform Infrared Spectroscopy (FTIR) using a spectrometer within the range from 4,000 to 400 cm–1
Summary
Superabsorbent hydrogels (SAHs) are composed of cross– linked and tridimensional polymers that absorb hundred folds of their weight in water (Essawy et al, 2016; Saha et al, 2020; Ai et al, 2020). Agricultural SAHs are commonly synthesized from K+ acrylate and acrylamide as monomers, exhibiting water absorption capacity (WAC) according to cross–linking, as well as the presence of hydrophilic groups (Saha et al, 2020). Minerals added in the polymer synthesis may improve WAC under saline conditions by the increase of cross–linking points bonded with monomers, improving polymeric network structure (Qin et al, 2012; Magalhães et al, 2013; Banedjschafie and Durner, 2015). Hydrogel composed of K+ acrylate, acrylamide, and mineral is expected to improve soil conditions and plant growth even when subjected to increasing salinity in which monovalent ions prevail
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