In this study, a novel double-layer slow-release fertilizer (SRF) was developed utilizing stearic acid (SA) as a hydrophobic inner coating and a blend of starch phosphate carbamate (abbreviated as SPC) and polyvinyl alcohol (PVA) as a hydrophilic outer coating (designated as SPCP). The mass ratios of SPC and PVA in the SPCP matrices were systematically optimized by comprehensively checking the water absorbency, water contact angle (WCA), water retention property (WR), and mechanical properties such as percentage elongation at break and tensile strength with FTIR, XRD, EDS, and XPS techniques, etc. Moreover, the optimal SPCP/5:5 demonstrated superior water absorbency with an 80.2 % increase for the total mass compared to natural starch/PVA(NSP), along with desirable water retention capacity in the soil, exhibiting a weight loss of only 48 % over 13 d. Relative to pure urea and SA/NSPU/5:5, SA/SPCPU/5:5 released 50.3 % of its nutrient within 15 h, leading to nearly complete release over 25 h in the aqueous phase, while only 46.6 % of urea was released within 20 d in soil, extending to approximately 30 d. The slow release performance of urea reveals that the diffusion rate of urea release shows a significant decrease with an increase in coating layers. Consequently, this work demonstrated a prospective technology for the exploration of environmentally friendly SRF by integrating biodegradable starch derivatives with other polymers.

A humic acid -gelatin (HA -Gel) hydrogel, a gallic acid-xanthan gum (GA-XG) hydrogel, a HA-Gel/GA-XG hydrogel, and superabsorbent polymer (SAP) of HA-Gel/GA-XG/polyacrylamide (PAM) hydrogel were synthesized using electron beam irradiation method. The capability of synthesized hydrogels in loading and controlled release of fulvic acid (FA) was studied. The chemical and physical structure of sorbents was confirmed by various analyses. The effect of irradiation dose on mechanical properties, gel percentage, swelling, and absorbency under load (AUL) of the sorbents was investigated. By changing the hydrogel structures into the SAP form, its swelling capacity was increased from 37 to 320 g/g. Both hybrid hydrogel and SAP were reusable for up to 7 cycles. The maximum fertilizer loading capacities for SAP and hybrid hydrogel were 402.1 and, 175.5 mg g -1 , respectively. In comparison to hydrogels, the SAP showed a slower FA -release performance. Thus, in soil media, 86 % of FA was released in 15 - 20 days from the hybrid hydrogel while with the SAP, 81 % of FA was released in 30 - 35 days. The significant improvement in the growth of fodder corn treated with FA -loaded SAP in the greenhouse media in comparison to the control groups showed the effective performance of the designed SAP, favoring its practical applications.

In order to attenuate the pollution problem caused by low fertilizer utilization, a biodegradable urea slow-release capsule was prepared in this study using gelatin as the main material. Glycerol was added to the gelatin solution as a plasticizer, and the mechanical properties and water resistance of the gelatin film were enhanced by crosslinking with glutaraldehyde. The addition of nano-SiO2 (nSiO2) and calcium magnesium phosphate fertilizer power (CaMgP) enhanced the hydrophobicity and tensile strength of the gelatin film. X-ray diffractometer confirmed that the nSiO2 could make the gelatin molecular chains more tightly entangled. Scanning electron microscope indicated that the addition contents of nSiO2 and CaMgP was optimal at 2 wt% and 40 wt%, respectively. The gelatin capsules were loaded with urea particles for slow-release experiments, the results of soil column drenching showed that the release rates of urea from nSiO2-modified and CaMgP-modified cross-linked gelatin capsules were 4.1 % and 5 % after 24 h, respectively, and 78.8 % and 75.2 % after 28 d, respectively.