Mechanism Of Nutrient Diffusion And Micro-pore Structure Of Polymer Coated Fertilizer

Currently,the research of coated controlled release fertilizer focused on the technology and application in agriculture,research on controlled release mechanism is less.Therefore, in this paper, using the water immersion method, vapor pressure in saturated salt solution method and soil incubation method to explore the controlled release characteristics of controlled-release fertilizers.Analysis the microstructure and chemical composition of coating layer by use the SEM and FTIR spectra;Base on the bubble point method, establish the test apparatus for determination of maximum pore size of the film;Determination of film pore size distribution and the impact of nutrient release of pore structure with the mercury intrusion method, the research results are as follows:(1) Temperature was the main factor which affected the nutrient release of controlled-release fertilizers. The temperature increased, the nutrient release rate of speed,the release period is shorter.The polyolefin coated controlled release fertilizer in the water release is inverted "L" type, the release curve of the coated fertilizer was "S" type.It were caused the different pore structure of the film. the order of nutrient cumulative release rate was H2O>KH2PO4 saturted solution>KCl saturted solution.So the base factor of controlling the nutrient release rate was the differences of inside and outside water vapor pressures. Soil water content would influence the nutrient release rate of slow and controlled-release fertilizers.Determination of POCF4 and PCU1 fertilizers, the nutrient release rate increased with the soil moisture increased.(2) The controlled release fertilizer coating was observed by SEM,the result shows that,Different materials coated controlled release fertilizer has different film structures,Polyolefin coated controlled-release fertilizer local surface micro pore and particle projection, the other parts are very smooth, it is difficult to see the pore on thecoating.The polyurethane coated controlled-release fertilizer coating surface smooth,there is no particles and pore structure. It could be seen that from fracture the film fracture the film thickness of Polyolefin coated fertilizer were about 80 nm. Besides, the film thickness of the coated fertilizer was uniformity, and the membrane has no pore structure on it can be observed.(3) The maximum pores of the film is determined directly by the pressure bubble method with self-made apparatus at temperature of 25℃, Q-16 selected as wetting agents and being soaked for 5 min. The average pore sizes of the coated fertilizer with releasing periods of 46,105, 150 and 199 d are 1.93 μm, 0.58 μm, 0.45 μm and 0.41 μm, respectively. The maximum pore sizes are increased with the shortening of releasing period and increasing of nutrients.Therefore, the close relationship exists between the maximum pore size and the release performance.(4) The pore structure of the film were measured by mercury intrusion method.The POCF1, POCF2, POCF3, POCF4 four kinds of polyolefin coated fertilizer pore size distribution range is 2000nm~100nm,The pore volume accounted for 60%, 66%, 63%, 20%of the total porosity.The pore diameter that more than 2000 nm were21%, 24%, 19%, 55% of total porosity.The surface of polyurethane coated fertilizer has no micropores,it can be see from the SEM photos. The fertilizer release period and the relationship between membrane pore, and the properties of the coating.