Effects of Dextran Modified Urea on Winter Wheat Yield and Fate of Nitrogen Fertilizer

Saccharides could regulate nitrogen transformation and promote crop growth. However, the effect and mechanism of carbohydrate reaction with urea with different degrees of polymerization on urea nitrogen utilization and crop growth are still unclear. In this paper, the dextran modified urea were prepared by incorporated of glucose (dextran) with different polymerization degrees into ¹⁵N labelled urea. The relationship between structure of dextran modified urea and wheat yield and nitrogen utilization was analyzed, in order to provide scientific basis for the application of dextran in improving nitrogen utilization efficiency.

In the current study, the dextran modified ¹⁵N labelled-urea (glucose, maltose, oligomeric maltose, and polydextrose modified urea are represented by GU, MU, OU, and PU, respectively) and ordinary ¹⁵N labelled-urea (U) was prepared, and the effects of dextran modified urea on winter wheat (Jimai 22) growth and the fate of fertilizer nitrogen were studied by using soil column cultivation experiments. The relationship between the dextran polymerization degree and the winter wheat yield or fertilizer nitrogen fate was explored by structure investigation of the dextran modified urea using Fourier Transform Infrared (FTIR) and ¹³C nuclear magnetic resonance (¹³C NMR) spectroscopy.

(1) Compared with U, the dextran modified urea showed a weaker vibration intensity of primary amide at 3 343 cm^-1 and 1 601 cm^-1 in FTIR spectra, and a new chemical shift peak was detected at 158-171 ppm in ¹³C NMR spectra, which was a sign that the aldehyde group of dextran and the amine group of urea reacted and that a C=N structure attributed to Schiff base was formed. (2) The wheat yield treated with GU, MU, OU and PU was higher than that of U by 1.9%, 9.2%, 10.3% and 12.3%, respectively. The yield increase was mainly attributed to the improvement of the ears number and grains per ear. (3) The total nitrogen uptake and fertilizer nitrogen uptake of grain of the dextran modified urea treatments were also higher than that under the U treatment by 8.7%-20.0% and 6.1%-13.9%, respectively. MU, OU and PU treatments had a higher nitrogen uptake than GU. (4) Compared with U, the ¹⁵N utilization rate and the fertilizer residue rate of dextran modified urea was enhanced by 2.0-6.1 and 1.3-4.9 percentage points, respectively, while the nitrogen loss rate of dextran modified urea was reduced by 6.9-7.4 percentage points. The ¹⁵N utilization rate of MU, OU and PU treatments was significantly higher than that of U. (5) Correlation analysis showed that the yield of wheat was significantly positively correlated with the polymerization degree of dextran, while the content of Schiff base was significantly negatively correlated. Among them, the relationship between Schiff base content and wheat yield and ¹⁵N utilization rate could be significantly fitted by using one quadratic equation. When the polymerization degree of dextran was 5-8, wheat yield and fertilizer nitrogen utilization rate were the highest.

Compared with common urea, the dextran modified urea could increase wheat yield, promote nitrogen absorption and utilization, increase fertilizer nitrogen residue and reduce urea loss. Within a certain range, the wheat yield and nitrogen absorption gradually increased, while the residual fertilizer nitrogen in soil decreased along with the increase of the polymerization degree of dextran. When the polymerization degree of dextran was 5-8, the corresponding modified urea would have the best performance.