Preparation of an Attapulgite-Modified Composite Hydrogel and Application in an Environmentally Responsive Green Fertilizer

Conventional fertilizers suffer from uncontrollable nutrient release rates and low utilization efficiency, which lead to environmental issues. An environmentally responsive fertilizer that can regulate nutrient release in response to environmental fluctuation is considered an essential component of sustainable agriculture. In this study, composite hydrogels with temperature/pH responsiveness were prepared by using modified attapulgite (ATP) as the inorganic filler and N-isopropylacrylamide (NIPAm) and sodium alginate (SA) as the temperature/pH-responsive monomer, and it was used as a carrier of urea to construct the hydrogel fertilizer. The results show that the addition of ATP modified by humic acid and hydrochloric acid to the hydrogel can significantly improve the hydrogel performance, and the hydrogel fertilizers prepared by using these two hydrogels as carriers have excellent environmental responsiveness and slow-release performances. The nutrient release behavior study showed that the hydrogel structure was more easily disrupted, and urea was released more rapidly under acidic and alkaline conditions. The network of the hydrogel collapses and shrinks at 30 °C, while urea was easily released from the hydrogel network. Compared to ordinary urea, the hydrogel fertilizer has an excellent slow-release performance. The environmentally responsive fertilizer would improve nutrient availability and avoid plant root damage and environmental pollution.