Abstract:
Objectives Glucose-modified urea (GMurea) has high fertilizer use efficiency but low decomposition. We investigated the mechanism responsible for decreasing the conversion rate of glucose-modified urea from its structural perspective under various glucose addition rate.
Methods Glucose (10%) was added to molten urea to produce glucose-modified urea. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and liquid chromatography-mass spectrometry (LC-MS) were employed to characterize the chemical structure, material composition and relative molecular mass of the glucose-modified urea. Glucose-modified urea containing 0.2%, 0.5% and 1.0% of glucose were prepared, then urease solution (1 U/mg) was added and incubated at (25±2)℃ for 30 min. The remaining urea was tested using spectrophotometer.
Results 1) In the mixture of glucose and melted urea, the FTIR at 1599 cm–1, the primary amide NH2 variable angle vibration disappeared, and the primary amine NH2 at 3441 cm–1 weakened the asymmetric stretching vibration intensity. It was speculated that glucose reacted with the urea amine group. In addition, XPS C 1s and N 1s spectra showed unknown carbon structure (―CX) and nitrogen structure (―NX), and aldehyde-based carbon (―CHO) disappeared, and the O 1s spectrum showed that the C=O chemical bond of the aldehyde group was broken, indicating that the aldehyde group of glucose reacted with the amine group of urea to form a new product. The aldehyde group in glucose underwent a nucleophilic addition reaction with the amine group of urea to produce a substance containing a C=N structure through LC-MS analysis. 2) All the three ratios of glucose-modified urea reduced the decomposition rate of urea. The decomposition rate of urea and GMurea containing 0.2%, 0.5% and 1.0% glucose were significantly different vis – 20.16%, 15.5%, 3.3%, and 11.0%, respectively. Reduction in the rate of urea decomposition was markedly higher by 0.5% modification treatment, with 16.9 percentage points lower than that of ordinary urea.
Conclusions The formation of C=N bond between glucose and urea slowed down the decomposition of urea by urease. The glucose addition ratio has significant impact on the decomposition of glucose-modified urea, with an optimal glucose addition of 0.5%.