Feasibility of applying pAAm/CA/MMT hydrogels AS slow release fertilizers

Background: Due to population growth, new technologies are needed for the production of fertilizers that can assist in increasing agricultural yields, while at the same time reducing environmental impacts. This article describes the synthesis, characterization, and behavior of a new series of hydrogels composed of polyacrylamide (pAAm), cellulose acetate (CA), and montmorillonite (MMT), suitable for the controlled release of fertilizers. The synergistic effects of the components were evaluated in sorption and desorption studies of a nitrogen fertilizer. Results: Four hydrogels were obtained: A, B, C, and D, with 0%, 5%, 10%, and 20% of MMT, respectively, in all cases with 10% of CA. The nitrogen contents of hydrogels A-D were 21.9%, 26.7%, 29.4%, and 25.2%, respectively. Hydrogel C absorbed the greatest amount of solution. Increase of the MMT content from 5% to 10% (w/w) led to swelling increases of 45%, 60%, 27%, and 20.7% at pH 5.0, 6.0, 7.0, and 9.0, respectively. Soil water retention assays showed that the soil containing the synthesized hydrogels retained up to 39% more water, compared to soil without hydrogel, with release during up to 30 days. The hydrogels presented low recovery percentages for applied nitrogen (around 42% lower than for the treatment with urea alone), demonstrating the effectiveness of the materials in reducing losses of nitrogen by leaching. The release of urea in the soil from hydrogel C (pAAm/10% MMT/10% CA) was gradual (25%, 75%, and 89% at 5, 20, and 30 days), indicative of slow release behavior. Conclusions: The presence of montmorillonite in the hydrogel caused the system to release the nutrient in a more controlled manner than obtained with the pure hydrogel. Hydrogel C, containing 10% montmorillonite and 10% cellulose acetate, showed excellent rates of swelling and nitrogen release in soil. The total nutrient values showed that this new material is potentially viable for application in agriculture.