Urea fertilizer coated with biodegradable polymers and diatomite for slow release and water retention

Slow release fertilizers (SRFs) are of vital importance to improve agricultural efficiency. However, their use is still limited due to their relatively high costs. Additionally, most of coating materials used to produce SRFs are nonbiodegradable and toxic to the soil. In this context, we utilized various biopolymers such as tamarind, xanthan, and guar gums together with diatomite to coat urea fertilizer granules. In this study, tamarind-urea-diatomite (TUD), guar-urea-diatomite (GUD), and xanthan-urea-diatomite (XUD) SRF granules were prepared in the presence of epichlorohydrin as crosslinker. The nutrients slow release behavior and the water retention capacity of these SRFs in soil were determined. The water absorbency of the product was 89% TUD, 93% GUD, and 142% XUD of its own weight when it was allowed to swell in tap water at room temperature for 2 h. Poly(methacrylic acid) was applied as the outermost layer of XUD to improve the nitrogen slow release efficiency of XUD SRFs. The results showed that the product had an excellent nutrients slow release property of 79.5% and good water retention capacity of 62.9% after 28 days. This suggested that XUDM could effectively improve the utilization of fertilizer. Furthermore, being biodegradable and low cost could be beneficial in agricultural and horticultural applications.