Title : Urea-loaded hydroxyapatite-carboxylated cellulose slow-release nitrogen fertilizer pellets for efficient delivery of nitrogen: nitrogen release and kinetics study
Nitrogen (N) is the most widely applied macronutrient to maintain soil fertility and plant growth; however, irrational and excessive use of N fertilizers causes significant loss to the surrounding environment and negative environmental impacts. Hence, it is important to develop technologies that allow efficient and targeted delivery of N. The purpose of this study was to elaborate on a slow-release N fertilizer using carboxylated cellulose nanocrystals (CNC) surface-modified hydroxyapatite (HAP-CNC) composites prepared by wet chemical precipitation as an N carrier to reduce urea loss and increase N use efficiency. Here, we provided a simple and scalable method for the elaboration of urea-impregnated HAP-CNC composites as fertilizer pellets having an N loading from 5.8 to 9%, a phosphorus content from 17.51 to 17.71% and a potassium content from 0.69 to 1,54%. Characterization tools (XRD, FTIR, SEM-EDS) of developed slow-release fertilizers (SRFs) demonstrated that urea molecules are strongly bounded to HAP and HAP-CNC composites through several mechanisms, including H-bonding, metal−ligand interactions, and physical storage within the existing micro-and nano-pores. The effectiveness of the produced N SRFs was investigated using a water release experiment. Results demonstrated that the developed SRFs displayed a slow-release N property and required 18 days for a complete N release in water compared to the pure urea, which dissolves rapidly within the first 3 hours. The release kinetics of urea in water was best described by Kormeye Peppas, suggesting urea release to be by diffusion via the pores and channels of the SRF. However, the release mechanism in water is best described by the first-order kinetic model, suggesting that the release rate in water is dependent on concentration and probably on diffusion rate via the pores and channels of the SRF.
KEYWORDS: cellulose-modified hydroxyapatite composite, Urea fertilizer, Slow-release nitrogen fertilizer, carboxylated cellulose nanocrystals, oxidized cellulose nanocrystals