Fusion of glucose into urea affects the urea hydrolyzation and enzyme activities in fluvo-aquic soil

Objectives The influence of glucose on the hydrolyzation of urea and the related enzyme activities was studied in fluvo-aquic soil, in order to provide a theoretical basis for utilizing low molecular organic compounds to improve nitrogen fertilizer use efficiency.

Methods Glucose was added into urea through fusion method in rates of 0.5%, 1%, 5% and 10%, and four urea-glucose products were prepared as GU0.5, GU1, GU5, and GU10. An indoor constant-incubation experiment was conducted using the four products and common urea (U), taking no urea addition as control (CK). The N adding amount of each treatment was the 0.3 g/kg dry soil, except CK. The soil samples were collected on the half, 1st, 3rd, 5th, 7th, 14th, and 21st day since the start of incubation. The contents of urea-N were determined in the soil samples of the half, 1st, 3rd and 5th day. The soil pH, contents of NH₄⁺-N and NO₃^–-N, and urease activities were determined in all the collected samples. And the activities of β-glucosidase, N-acetyl-glucosaminidase and L-leucine aminopeptidase were analyzed in soil samples of the 3rd, 5th, 14th day.

Results 1) On the half day, the contents of urea-N under GU treatments were increased by 1.9%–12.2%, compared with that under ordinary urea treatment. On the 3rd day, the GU treatments accelerated the hydrolyzation of urea compared with common urea treatment, and the urea hydrolysis under GU10 treatment was significantly faster than under the others. 2) Compared with common urea treatment, the GU treatments significantly increased the NH₄⁺-N contents by 19.0%–26.2%, and NO₃^–-N contents by 16.5%–30.9% on the days of 3–7; increased the soil urease activities by 6.9%–8.5% in average on the days of 3–14; increased β-glucosidase activity by 6.3%–9.0%, and GU10 treatment increased L-leucine aminopeptidase activity by 21.3% on the 3rd day; GU5 and GU10 treatments enhanced the activity of N-acetyl-glucosaminidase by 47.8% and 52.4% respectively on the 5th day. 3) The contents of ammonium N and mineral N in soil were significantly or very significantly positively correlated with the activities of urease, β-glucosidase and N-acetylglucosaminidase on the 3rd day. Nitrate N was very significantly and positively correlated with the activity of β-glucosidase. soil pH was very significantly and negatively correlated with the activity of β-glucosidase and L-leucine aminopeptidase.

Conclusions Fusion of glucose into urea can first slow down and then promote the hydrolyzation and transformation of urea in fluvo-aquic soil, and increase soil mineral N contents. Compared with common urea, four urea-glucose products can influence the activities of soil urease, β-glucosidase, N-acetylglucosaminidase and L-leucine aminopeptidase in different extents during the incubation, especially on the days of 3–5. Mineral N is significantly and positively correlated with the related soil enzyme activities, while soil pH is significantly and negatively correlated with them.