葡聚糖改性尿素对冬小麦产量和肥料氮去向的影响

【目的】糖类物质具有调控氮素转化和作物生长的作用,目前尚不明确不同聚合度糖类物质与尿素反应对尿素氮肥利用、作物生长的影响及机理。通过将不同聚合度葡萄糖（葡聚糖）与¹⁵N尿素熔融制备葡聚糖改性尿素,分析葡聚糖改性尿素的结构变化与小麦产量和氮素吸收利用的关系,以期为葡聚糖在提高尿素氮肥利用效率中的应用提供科学依据。【方法】采用¹⁵N示踪技术,供试作物为冬小麦（济麦22）,将葡萄糖（单体）、麦芽糖（2聚）、低聚麦芽糖（≈5聚）和聚葡萄糖（≈20聚）按1%添加量加入到熔融¹⁵N尿素（丰度为10.19%）中,制得葡聚糖改性尿素（葡萄糖、麦芽糖、低聚麦芽糖、聚葡萄糖改性尿素分别由GU、MU、OU和PU表示）,以不同聚合度葡萄糖改性尿素和普通尿素（U）为供试肥料,运用田间土柱栽培试验研究葡聚糖改性尿素对小麦生长及肥料氮去向的影响。利用傅里叶红外变换（FTIR）光谱和¹³C核磁共振（¹³C NMR）波谱特征探究葡萄糖聚合度及其改性尿素的结构变化,并揭示其与小麦产量、氮肥利用的关系。【结果】（1）与U相比,葡聚糖改性尿素的FTIR谱图在3 343和1 601 cm^-1处的伯酰胺振动强度减弱,¹³C NMR波谱在158—171 ppm处检测到一个新的化学位移峰,是葡聚糖的醛基与尿素的胺基发生席夫碱反应,生成含C=N物质的标志。（2）与U相比,不同聚合度葡萄糖改性尿素（GU、MU、OU、PU）增加了小麦产量,分别较U提高了1.9%、9.2%、10.3%和12.3%,主要通过增加小麦穗数和穗粒数实现增产。（3）与U相比,不同聚合度葡萄糖改性尿素的小麦籽粒总氮吸收量和肥料氮吸收量分别提高了8.7%—20.0%和6.1%—13.9%;MU、OU和PU处理的氮素吸收量均高于GU。（4）与U相比,不同聚合度葡萄糖改性尿素的¹⁵N利用率提高了2.0—6.1个百分点,肥料氮残留率提高了1.3—4.9个百分点,肥料氮损失率显著降低6.9—7.4个百分点。（5）相关性分析结果表明,小麦产量与葡萄糖聚合度呈显著正相关关系,而与席夫碱含量呈显著负相关;利用一元二次方程可显著拟合席夫碱含量与小麦产量和¹⁵N利用率的关系,葡萄糖聚合度5—8时,小麦产量和肥料氮利用率最高。【结论】与普通尿素相比,不同聚合度葡萄糖改性尿素可以增加小麦产量,促进氮素的吸收利用,提高肥料氮残留量,减少尿素氮肥损失。一定范围内,随着葡聚糖聚合度的增加,小麦产量和肥料氮吸收量逐渐增加,土壤中肥料氮残留量逐渐降低。葡萄糖聚合度为5—8,其对尿素改性增效的效果最佳。

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

【Objective】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. 【Method】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. 【Result】 (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. 【Conclusion】 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.