Chitosan microspheres-based controlled release nitrogen fertilizers enhance the growth, antioxidant, and metabolite contents of Chinese cabbage

Abstract

Agriculture lands have low fertilizer retention owing to porosity and irrigation, whereas a significant portion of fertilizer is lost through denitrification, volatilization, surface run-off, and leaching, causing losses of nutrients to air and ground/surface water. Urea fertilizer readily enhances the agricultural yield but also deteriorates the quality of fertile soils. To combat such problems, researchers are seeking to formulate controlled-release or slow-release fertilizers. We used chitosan microspheres as a carrier to encapsulate urea through emulsification and cross-linking techniques to reduce the wastage of urea fertilizer due to evaporation and water flow. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were used to characterize chitosan microspheres and urea-loaded microspheres. Chitosan microspheres and urea-loaded microspheres were authenticated by FT-IR, showing 89% of urea successfully incorporated with chitosan microspheres. Then an experiment was run to compare the effects on plant growth, antioxidant and metabolite contents with and without added nitrogen fertilizer. Various amounts of urea per pot were applied to Chinese cabbage, including T1 0.5433 g, T2 0.6033 g, T3 0.8033 g, CK 0.00, while the same content of urea in chitosan microspheres as T4, T5, T6, and T0 (no urea), respectively. The results indicated that chitosan microspheres-based controlled release nitrogen fertilizers (Cm-CRNFs) had higher seed germination (96%), plant height (17.04 cm), number of leaves (11.00), and leaf length (110.19 mm) as compared to urea and control treatments. In addition, Cm-CRNFs treatment enhanced net photosynthetic rate, stomatal conductance, transpiration rate, fluorescence, dark respiration rate, total sugar, proteins, flavonoids, and polyphenols. Overall, Cm-CRNFs showed promising results in all treatments for all tested physiochemical and growth parameters. It is concluded that controlled release urea fertilizers based on chitosan microspheres can be developed with a simple process. The fertilizers are biocompatible, economically viable, and environment-friendly, and have the potential to prolong the release of macronutrients and micronutrients for plant growth.