Preparation Of Controlled Release Fertilizer Of Urea Microcapsules

In the agricultural application of nitrogen fertilizer, urea is widely used because of its high nitrogen content and low cost. However, due to the high water solubility, about 40% ~ 60% of applied urea had lost to environment and could’t be absorbed by crops, this not only cause low utilization rate which is a huge economic losses, but also caused serious environmental pollution. Microcapsule technology in the application of controlled release fertilizer had lots of advantages compared to traditional way of fertilizer formulation. This research carried out a way to form controlled release microcapsule, controlled release fertilizer can improve the utilization rate of fertilizer, reduce fertilizer damage to environment and improve human health.In this paper, using low-cost, non-toxic, biodegradable natural polymer materials as the wall material, and using urea as core material, microcapsules controlled release urea fertilizer was prepared of by emulsification and cross-linking method. First the research discussed how the main factor effect the results, then designed orthogonal experiment to study the way they effect the results in combination, and optimum prepared conditions of the urea microcapsule was obtained in the end.1. Single factor study was carried out in the preparation of urea/chitosan microcapsule. When the stirring speed, the amount of crosslinking agent glutaraldehyde and temperature increased, the fertilizer-loading rate of urea/chitosan microcapsule decreased. When the dosage of chitosan and urea, and emulsifier increased, the fertilizer-loading rate of urea/chitosan microcapsule increased first and decreased later. According to the results of single factor, designed a four factors three levels orthogonal experiment, the influence factors were in the order of urea/CS, temperature, speed and amount of glutaraldehyde. The optimal conditions was as follows: urea/CS was 6:2, the dosage of glutaraldehyde was 1.5%, the temperature was 30℃, and the speed rate was 600 r/min. The microcapsules prepared under this condition was almost round in morphology and had smooth surface, the size of microcapsules was around 100 um. And under this condition, the fertilizer-loading rate and the encapsulation efficiency were 11.26% and 15.01%. The release rate of urea in microcapsules was fast in the first 24 h, and the ralease rate of urea reached to 79.6%, and then the release rate slowed down, after 72 h of releasing in water, the release rate reached to 93.9%.2. In the preparation of urea/gelatin microcapsules, the effect of single factor like stirring speed, p H, curing time and dosage of curing agent on the morphology of microcapsule, the fertilizer-loading rate and the encapsulation efficiency was studied respectively. According to the results of single factor designed the orthogonal experiment, the influence factors were in the order of p H, stirring speed rate and the dosage of formaldehyde and curing time, the optimal conditions was as follows: stirring speed was 900 r/min, p H was 4.0, curing time was 60 min, the dosage of formaldehyde was 10 m L. Microcapsule preparation under this condition was round and uniform particle size distribution. And under this condition, the fertilizer-loading rate and the encapsulation efficiency were 69.41% and 76.35%.The release rate of urea in microcapsules was slow in the first 24 h, and the ralease rate of urea reached to 49.5%, and then the release rate speeded up between24~48 h of releasing in water, the release rate reached to 94.5%, in the end, the released of urea nearly finisded.