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Urea-based multi-coated slow release fertilizer was produced using water hyacinth, humic substances, and chitosan, with water rich in natural organic matter as a solvent. Elemental analysis showed that the nitrogen content of the fertilizer (FERT) was around 20%. Swelling tests demonstrated the effectiveness of the water hyacinth crosslinker, which reduced the water permeability of the material. Leaching tests showed that FERT released a very low concentration of ammonium (0.82 mg L−1), compared to the amount released from urea (43.1 mg L−1). No nitrate leaching was observed for FERT, while urea leached 13.1 mg L−1 of nitrate. In water and soil, FERT showed maximum releases after 30 and 40 days, respectively, while urea reached maxima in just 2 and 5 days, respectively. The results demonstrated the promising ability of FERT to reduce nitrogen losses, as well as to minimize environmental impacts in the soil–plant-atmosphere system and to improve the efficiency of nitrogen fertilization. Graphic abstract

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.