| The availability of traditional chemical fertilizers is high, and can be readily uptake by crops. However, high application of the fertilizers may damage the growth of plants, and the duration of nutrient supply is also limited. When the nutrients added to soil are not absorbed by crops, they may lose from the soil through leaching, volatilization, and fixation, inducing low recovery of fertilizer and polluting the environment. Controlled-release fertilizers (CRFs), manufactured from traditional chemical fertilizers by physical or chemical methods, have been defined as a kind of fertilizer whose nutrient release could match the crop need, and are considered as an effective way to increase the nutrient efficiency. The high cost and the poor nutrient match are two problems for most of CRFs. In this study we used different incubation methods and pot experiments to evaluate the nutrient release characteristics from different CRFs, and determine the effects of temperature and water in soil on the release of CRFs. The mixture design was also used to determine the nutrient release characteristics from normal fertilizer (urea) and different CRFs. The main goals are to decrease the cost of fertilization with CRFs and to produce fertilizer-plant-well-matched CRFs. The main results are as follows:1. The initial solubility of seven kinds of CRFs was lower than 12.0%, and their differential solubility was in the range of 0.26% - 2.49%, which match the international standards.2. There were interactions between temperature and water content on nitrogen released from both urea and polymer-coated urea. The effect of temperature on nutrient release of CRFs varied with the water content in soil; yet for urea the effect of temperature was not obvious. As the increase of temperature, the NH 4+ in soil with CRFs increased; on the contrary, the NH4+ in soil with urea decreased. When water content in soils was high, the high level of NH4+ in soil remained a long time during incubation; when water content in soil was low, the NH4+ remained in soil for all treatments even at the end of incubation. The nitrate concentration in soil was related with temperature and fertilizers. The concentration of soil mineral nitrogen decreased significantly during the 5th to 20th days in the incubation.3. The NH4+ in soil of all treatments designed with the simplex centroid designmethod decreased in the incubation period, and soil nitrate and mineral nitrogen increased. The contents of ammonium, nitrate and mineral nitrogen in soil added with urea were highest among all treatments, and lowest contents of their kinds of N were found in the treatments when only two kinds of CRFs were added separately or together. When urea was added with CRFs the contents of ammonium, nitrate and mineral nitrogen in soil were between with urea and CRFs during the whole incubation. Soil ammonium mainly came from urea during the first 20 days, and during the 30th to 50th days the NH4+ was considered from CRFs (D60). And soil nitrate and mineral nitrogen mostly came from urea during the whole incubation; and their contents decreased while the proportion of urea in the fertilizer mixture was decreased.4. The first-order kinetic equation could be used to fit the nutrient release characteristics of different treatments. Both the nitrogen release rate and their combinational effectiveness can be reflected by velocity coefficient (k). In comparison with only application of CRFs, applying urea combined with CRF significantly increased the rate of nitrogen release, with an increase from 96.0% to 180.0%, and shortened the nitrogen release period from 20 to 79 days.5. Compared to the single application of readily available fertilizers or CRFs, the application of the combination of readily available fertilizers and CRFs significantly increased the crop biomass in the early growth period. In the late growth period, the application of CRFs or the combination of readily available fertilizers and CRFs increas...
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