Mechanism And Evaluation Of Nutrient Release Of Slow And Controlled-Release Fertilizers

The problem of population-resource-environment becomes more and more prominented. It should been pay more attention to the using of fertilizer in order to enhance the output of soil. The problems such as how to enhance the efficiency of fertilizer,how to reduce the waste of resources,how to lessen the environment pollution ,how to ensure soils and so on are the targets for fertilizer research.The efficiency of fertilizer have been improved evidently, loss and volatilization of nutrition elements hav been reduced, waste of resources have been lightened,product quality and crop output have been enhanced markedly by applied slow and controlled-release fertilizers,so many experts think highly of them. The production and use of slow and controlled-release fertilizers are one of the main trends for the development of chemical fertilizers at present, and are necessary need for the development of modern agriculture and sustainable development stratagem."Water extraction method""vapor pressure method in saturated salt""soil incubation method"and"fertilizer embedding method"were used to discuss mechanism of slow and controlled-release fertilizers. Nutrient release characteristics of fifteen different kind of slow and controlled-release fertilizers were evaluated according to the chemical industry standard of slow/controlled-release fertilizer (HG/T 3931-2007), the chemical industry standard of sulfur coated urea (HG/T 3997-2008)and the standard recommended by the Committee of European Normalization (CEN) using water extraction method and soil incubation method. The membrane microstructures of slow and controlled-release fertilizers were studied by scanning electron microscopy and infrared spectra. Meanwhile, the relationship between fertilizer release rates and nutrient requirements of plant were tested in a pot experiment and a field experiment. The main results were summarized as follows:1. Temperature was the main factor which affected the nutrient release of slow and controlled-release fertilizers. These slow and controlled-release fertilizers could include ploymer coated urea, risen coated compound fertilizers, polymer coated compound fertilizers, sulfur coated urea and Isobutylidene diurea, and the higher the temperature was , the quickly the release rate of them was. In water, the nutrient release curves in water were"S"pattern for CRF1 and CRF2, burst release for SCU, and reverse"L"pattern for IBDU. The dynamics of nitrogen release rate could be quantitatively described by three equations: the first-order kinetics equation (Nt=No(1-e-kt)), Elovich equation (Nt=a+blnt) and parabola equation (Nt=a+bt0.5). However, the imitation of the first-order kinetics equation was the best at 25℃and 40℃. So, the imitation of the first-order kinetics equation was the most practical for the release of nitrogen release. Besides, the nitrogen release of coated compound fertilizers was the fast, next was potassium, and phosphorus release was the slowest.2. The differences of inside and outside water vapor pressures arose to the nutrient release of coated controlled-release fertilizers. The constant k increased with the water vapor differential pressure increased. The bigger the water vapor differential pressure, the higher the nutrient release rate. Under the same water vapor pressure, the nutrient release rate would grow bigger when the time was extended, and at the same time, 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.3. Soil water content would influence the nutrient release rate of slow and controlled-release fertilizers. When the soil water content was under the field moisture capacity, the nutrient release would be speedy with the increase of soil water content. For coater urea, the correlation coefficient of fittingcurve was between 0.9740 and 0.9972, and the standard error would be between 0.0015 and 0.0022, so the fitting curve would reach best conspicuous level. For coated compound fertilizers, the nitrogen release of CRF1 and CRF2 would increase with the increase of soil water content at different time. For SCU1, the release rate in soil was higher than that in water, but opposite phenomenon occurred for IBDU.4. Scanning electron microscope test indicated that when the material of coat was different, the structure of membrane was different. The surface of thermoplast had minim pore which was the channel of the nutrient release. The surface of polymer was relatively collapse, and there was different solid particle, so minim pore could not see clearly. The surface of SCU was very smoothing, so arrange and deposit of material were relatively compactness. It could be seen that from fracture the film thickness of PCU1 CRF1 CRF2 Nutricote Osmocote and SCU1 were 59.5μm 58.6μm 41.4μm 107μm 46.3μm and 55.1μm. Besides, the film thickness of six fertilizers was uniformity, and the quality of coat was preferably.5. Infrared spectra test indicated, the infrared spectra of different coated material had distinct variance. For CRF1 and Nutricote, they had infrared absorption at 3447 cm-1 2919 cm-1 2850 cm-1 and 670 cm-1, so the material of the two fertilizers had some similarity. For CRF2 and Osmocote, the spectra of them also had prodigious similarity, but Osmocote had functional group of aliphatic hydrocarbons. The infrared spectra of SCU1 showed that there were ont only lots of inorganic sulfur but also addition such as ethylene epoxide and polyethylene wax.6. Nutrition release was accelerated when temperature of the solution in the water extraction method was raised from 25℃to 100℃. The regression equation for prediction and forecast of the 100℃fast extraction method fit a quadric equation in one variable with a correlative coefficient being < 0.98, and could be used to quickly and precisely predict release duration of slow/controlled fertilizers. The difference between the measured value and predicted one was only one to three days. Besides, electric conductivity measurement could also be used to quickly and precisely predict nutrient release rate and duration. By using the electric conductivity measurement at 100℃, the release duration of CRF2 and CRF3 was predicted to be 65days and 81days, less than 3.5% in difference from their measured duration of 66 days and 84. Parameters, like initial nutrient release rate, mean release rate, and release duration, could be used for integrative evaluation of slow- and controlled- release fertilizers.7. The nutrient release characteristics of the four fertilizers in"water extraction"and"soil incubation"all fit binomial equations, suggesting there was some correlation between the two methods. Therefore, when the agriculture evaluation of slow and controlled-release fertilizers was carried out,"soil incubation"test should be take on the base of"water extraction"test, and also the nutrient absorptivity of plant should be measured, and then the plant growth and output should be analysis. This study indicated that the release rate in soil could be predicted by the releasee rate in water at the same temperature.8. Slow and controlled-release fertilizers are fertilizers containing a plant nutrient in a form which either delays its availability for plant uptake and use after application, or which is available to the plant significantly longer than a reference"rapidly available nutrient fertilizer". The nutrient uptakes and biomass of plants treated with CRF1 and CRF2 were significantly higher than other treatments, among which CRF2 the greatest. Nutrient release curves of CRF1 and CRF2 accorded with nutrient requirements of canola more closely. Meanwhile, special purposes controlled-release fertilizers which suit the growth and development of plants could produce by evalution and predict of fertilizer kind and plant matching.