Nutrient Release Characteristics Of Controlled-Release Compound Fertilizers In Soils And Their Effects On Growth Of Crops

In order to illustrate nutrient use efficiency of controlled-release compound fertilizers (CRCFs) and the existent configuration. the variability of validity of CRCFs on soils were studied. The methods of soil and water incubation for nutrient release, and pot experiments were conducted by comparison with common compound fertilizers (CCFs) in the research. The findings provided a theoretic support basis for improving the processing techniques, and exploring the intensive utilization of CRCFs. The research results were as follows:1. The nutrient release of CRCFs in soil and water showed a shape of S or parabola. Three release stages were found in CRCFs release courses. Release rate increased with time in the first stage, decreased with time in the second stage and stagnated with time in the third stage. There was a fastigium of release rate among the three stages. Compared the N, P and K nutrient release of CRCFs in water, the N release rate was the fastest and the P release rate was the lowest among three nutrients.2. The studied soils performed a strong adsorptive ability for H2PO4- and most of adsorption action was specific adsorption or chemical fixation, which considerably decreased the availability of the phosphate in soils. This adsorption was different from the exchange adsorption of NH4+ or K+ in soils.3. The nutrient release of CRCFs could be characterized through the changes of available N, P, and K during the plant-growing season. In early stage, the release rate of CRCFs was tardily increased, after 40 days there was a fastigium of release rate, then the release rate was tardily declined. The N nutrient release rate was fastest and the accumulation of N nutrient in soils was greatest as compared to P and K, and P release rate was slowest and the accumulation of P in soils was minimum comparatively, the K release rate wasbetween the release rate of N and P.4. The nutrient release characteristics of CCFs in soils showed a descending curve. After fertilization, the N, P, and K in CCFs released rapidly. Within ten days, the accumulation of nutrient in soils was so excessive that the cabbage, salvia, tomato and corn were suffered by the high concentration of nutrient salts of higher application rates of CCFs in the seedling stage.5. All four-application rates of CRCFs were effective and safe for cabbage, tomato, and corn. Slightly saline damage for the salvia was found for the high application rate of CRCFs at the early seedling stage. However, the growth potential, the number and duration of the salvia flowers were significantly increased for all CRCFs treatments as compared to the CCFs treatments and control at the later stages.6. The growth of cabbage was inhibited by the high concentration of nutrient salts in the CCF4 treatment with the rate of 0.8 g N/kg soil, but the growth was normally for the CCF3 treatment with the rate of 0.4 g N/kg soil. However, the seedlings of tomato and corn were damaged in the CCF3 treatment, but growing normally in the CCF2 treatment with the rate of 0.4 g N/kg soil. The salvia seedling was most sensitive for the salt concentration and damaged in the CCF2 treatment with the rate of 0.2 g N/kg soil, only CCF1 treatment with the rate of 0.1 g N/kg soil was safe for the salvia at the early seedling stages. All the results proved the advantages of controlled-release compound fertilizers (CRCFs) on the growth and development of these four crops, especially for the plants of flowers.