In this investigation, a novel water-insoluble slow-release fertilizer, biuret polyphosphoramide (BPAM),
was formulated and synthesized from urea, phosphoric acid (H3PO4), and ferric oxide (Fe2O3).The
structure of BPAM was characterized by Fourier transform infrared (FTIR) spectroscopy. Subsequently, a
coated slow-release BPAM fertilizer with superabsorbent was prepared by ionic cross-linked carboxy-
methylchitosan (the core), acrylic acid, acrylamide, and active carbon (the coating). The variable
influences on the water absorbency were investigated and optimized. Component analysis results
showed that the coated slow-release BPAM contained 5.66% nitrogen and 11.7% phosphorus. The
property of water retention, the behavior of slow release of phosphorus, and the capacity of adsorption of
cations were evaluated, and the results revealed that the product not only had good slow-release property and excellent water retention capacity but also higher adsorption capacities of cations in saline soil.