Microwave-assisted one-step synthesis and characterization of a slow release nitrogen fertilizer with inorganic and organic composites

A slow-release fertilizer (SRF) was synthesized in one step based on urea incorporated in a polymer matrix composed of sodium alginate (NaAlg), acrylic acid (AA), acrylamide (AM) and bentonite (Bent) via microwave irradiation. The proposed microwave-assisted method yielded high reaction rates with less reaction time of 5 minutes at 300 W. The raw materials and final products were characterized in terms of the structure and properties through Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and uniaxial compression measurements. The application potential was verified on the basis of swelling in different environments, largest water-holding ratio and water-retention capacity of soil, release study in soil, and the effect of the proposed SRF product on the germination rate of cotton seed. Results indicated that the addition of Bent not only contributed to the increase in water absorbency, largest water-holding ratio and water-retention capacity of soil, but also caused the system to liberate the nutrient in a more prolonged manner based on a Case II release mechanism with skeleton erosion. Thus, microwave irradiation would be a possible method to produce SRFs for potential agricultural and horticultural applications.