蛋白水解物改性脲甲醛缓释肥的结构及氮素释放特征

针对脲甲醛养分释放与作物生长曲线不匹配的问题,该研究采用蛋白水解物来改善脲甲醛的氮素释放率。土柱淋洗结果表明,蛋白水解物降低了脲甲醛初期的氮素释放率,加快了脲甲醛在后期的氮素释放率。在当量尿素与甲醛的摩尔比为1.2时,蛋白水解物水解度越小,氮素释放率越快。到第7周,蛋白水解物改性脲甲醛的氮素释放率和未改性的脲甲醛相比,氮素释放率提高了58.9%。采用傅里叶红外光谱、X射线衍射、热重和扫描电镜分析了蛋白水解物和蛋白水解物改性脲甲醛的结构,发现:蛋白水解物的活性基团能够与甲醛反应,并与尿素聚合,以嵌段的方式引入到脲甲醛的分子结构中;蛋白水解物水解度越低,改性脲甲醛结晶度降低的越多;和未改性的脲甲醛相比,改性的脲甲醛的最大分解温度有所降低,并且改性后的脲甲醛疏松多孔。因此,可以通过蛋白水解物的水解度来调控改性脲甲醛的氮素释放率,进而适应不同作物的生长周期,提高氮肥的利用率。

Structure of hydrolyzed soy protein modified urea formaldehyde and its nitrogen release characteristic

The production and consumption of nitrogen fertilizer in China rank first in the world, and the nitrogen utilization rate by crops is far below the world average. An effective way to improve the utilization rate of nitrogen fertilizer is to develop and use slow release nitrogen fertilizer, which can reduce the production cost, decline the usage of nitrogen fertilizer, and reduce the environmental pollution in the production process. For this reason, to develop and apply slow release nitrogen fertilizer have an important significance. Urea formaldehyde is one of the great potential slow release nitrogen fertilizers. However, low molecular weight of urea formaldehyde releases nitrogen faster in the early growing season, while high molecular weight of urea formaldehyde releases nitrogen slower during the late growing season. In recent years, blended urea formaldehyde of high and low molecular weight has been reported to improve its nutrient release rate. However, the nitrogen release rate of urea formaldehyde cannot be achieved by the physical blending. Therefore, it is necessary to change the molecular structure so that its nitrogen release rate can be changed. In the traditional modification method, the ratio of urea to formaldehyde, the pH value of reaction system, reaction temperature and reaction time are used. The methods can only adjust the molecular structure, the size of the molecular weight, and content of each component, but urea formaldehyde slow-release fertilizer chemical modification is relatively small. However, the small molecular weight of poly (methylene urea) that generated in the synthesis process appears promising. As such, we developed an effective method to optimize the nitrogen release rate in urea formaldehyde by copolymerizing with other materials. The nitrogen release rate was improved by the introduced hydrolyzed soy protein. The nitrogen release rate of modified urea formaldehyde was reduced in the earlier stage and faster in the later stage from soil column leaching experiments. The hydrolysis degree of soy protein was lower, the nitrogen release rate was faster. The nitrogen release rate of the modified urea formaldehyde was up to 74.4%, and the nitrogen release rate of unmodified urea formaldehyde was 46.8%, with the nitrogen release rate was improved 58.9%. Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscope were applied to characterize the hydrolyzed soy protein modified urea formaldehyde. The functional groups of soy protein were exposed after hydrolyzation. The hydrolysis degree of soy protein became higher, more formaldehyde was reacted. The reactive groups of hydrolyzed soy protein can react with formaldehyde and copolymerize into the urea formaldehyde molecular. The crystallinity of modified urea formaldehyde was lower because of the introduced hydrolyzed soy protein. The maximum mass loss rate of temperature of modified urea formaldehyde decreased as the decreasing of the hydrolysis degree of soy protein, which decreased 11.9℃ at most, compared with non-modified urea formaldehyde. Therefore, the nitrogen release rate can be regulated by the hydrolysis degree of soy protein to adapt to crop life cycles, which was an effective way to improve nitrogen use efficiency. The hydrolyzed soy protein modified urea formaldehyde shows a good application potential.