Preparation of Microcapsules of Slow-Release NPK Compound Fertilizer and the Release Characteristics

In this study, a novel type of slow-release fertilizer (SRF) was synthesized through lignin-based microcapsules. K2HPO4 and urea were coated by lignin and formaldehyde to prepare microcapsules of NPK compound SRF. The slow-release performance was measured by determining the NPK contents in water solution and soil column leaching. The release amounts of N, P and K after 5 days were 95.39, 95.28 and 96.75% in water, and 83.35, 96.62 and 90.75% in soil, respectively. The properties of SRF were analyzed by Fourier transform infrared spectroscopy, thermogravimetry and scanning electron microscopy. NPK release from the SRF was promoted by higher temperature and acid environment, but inhibited by alkaline environment. The first order kinetics equation provides the best correlation to describe nutrient release characteristics. The results indicated that SRF have good slow-release properties and are cost-saving and environment-friendly, and thus can efficiently improve the utilization efficiency of fertilizers in agricultural production.

本研究以木质素基微胶囊为载体，合成了一种新型缓释肥料（slow-release fertilizer, SRF）。以木质素与甲醛为包覆壁材，对磷酸氢二钾（K₂HPO₄）和尿素进行包埋，制备得到氮磷钾（NPK）复合型缓释肥料微胶囊。通过测定水溶液与土柱淋溶体系中的氮磷钾含量，表征该缓释肥料的缓释性能。该肥料在水溶液中5天的氮、磷、钾累积释放量分别为95.39%、95.28%和96.75%，在土壤体系中则分别为83.35%、96.62%和90.75%。采用傅里叶变换红外光谱（Fourier transform infrared spectroscopy, FTIR）、热重分析法（thermogravimetry, TG）与扫描电子显微镜（scanning electron microscopy, SEM）对该缓释肥料的理化性质进行表征分析。环境温度升高与酸性环境可促进该缓释肥料的氮磷钾养分释放，而碱性环境则会抑制其养分释放行为。一级动力学方程（first order kinetics equation）对养分释放特征的拟合效果最优，可精准描述该缓释肥料的养分释放规律。研究结果表明，该缓释肥料具备优异的缓释性能，且兼具低成本与环境友好的优势，可有效提升农业生产中的肥料利用效率。