Nutrient release characteristics of water soluble resin coated controlled release fertilizers and their influential factors

In order to discuss the nutrient release characteristics from coated controlled release fertilizers(CRFs) of different N-P-K ratios, with the same coated technology, two kinds of CRFs coated by water soluble resin were made for involving the different N-P-K ratios of kernel fertilizers with the same thickness and the same N-P-K ratio of kernel fertilizer with different thickness. The CRFs were incubated in pure water with normal and high temperatures, which aimed to study the effects of kernel fertilizers, coating thickness and culture temperature on the nutrient release characteristics. Results showed that under (25±0.5)℃ or (40±0.5)℃, CRFs with a high nitrogen content kernel (HNCRF) had cumulative release sigmoid curve while amount of coating material was 50 g/m2 or 70 g/m2. Increasing coating thickness or reducing incubation temperature could prolong its nutrient lag period in the prophase of incubation. Under (25±0.5)℃, CRFs of high potassium compound (HKCRF) and the balanced N-P-K ratios of kernel fertilizer (TCCRF) had cumulative release parabolic curve with coating material content of 50 g/m2. The curve was translated to double parabolic pattern with the coating material of 70 g/m2, but under (40±0.5)℃,all were parabolic curves. The three factors affected not only nutrient release curves, but also the longevity of nutrients. Increasing coating thickness or reducing temperature could prolong the longevity of fertilizer. Longevity of nitrogen or phosphorus fertilizer had an order as HNCRF＞HKCRF＞TCCRF, and longevity of potassium fertilizer had anther order as HKCRF＞HNCRF＞TCCRF. In short, the nutrient release characteristics of coated NPK fertilizers were influenced by coating thickness, kernel fertilizers and incubation temperature simultaneously. The form of curve tended to a parabola with quick nutrient release, contrarily, the form of curve tended to a sigmoid. The high nitrogen content kernel fertilizer could work best controlled release performance of water soluble resin among three types of the kernel fertilizers.