Loading Glyphosate in Attapulgite and Sodium Alginate Hydrogels to Construct pH-Responsive Controlled Release Microsphere for Enhanced Soil Sustained Release

Herein, we constructed the microsphere SAH-Gly by loading glyphosate (Gly) with dopamine-modified attapulgite (DA-Gly) and capsuling in sodium alginate hydrogels. The Gly releasing rate and the hydrogel swelling rate were manifestly increased to the highest of 60 and 26% within 70 and 24 h in alkaline solution (pH = 8.5), respectively, while only 20% Gly releasing rate and less than 15% hydrogel swelling rate were observed in both acidic (pH = 5.5) and neutral solutions (pH = 7.0). The abundant carboxyl groups in SAH-Gly provided the swelling characters through H+ ionization. Both DA-Gly and SAH-Gly enhanced the stability of Gly to ultraviolet rays and temperature variability. The sustained release of Gly from SAH-Gly resulted in its partial absorption in soils. DA-Gly and SAH-Gly released maximum Gly molecular concentrations after 28 and 32 h, respectively, and then degraded completely in 200 h in soil. First-order kinetics showed that the half-life (DT50) of the Gly residue in soil was 65.89 h, while the DT50 values of DA-Gly and SAH-Gly were 31.18 and 66.27 h, respectively, with the following order: DA-Gly < Gly < SAH-Gly. In addition, leaching experiments depicted that SAH-Gly displayed a weaker elution behavior and longer elution time in the upper soil ring of the column. The sustained release behavior of Gly from SAH-Gly in soil could decelerate the degradation, adsorption, and leaching characters of Gly molecular, helping reduce the loss of active Gly and enhancing its sustainable agricultural practice in response to environmental factors.