The utilization efficiency of phosphate fertilizer in the whole life of plant is only 10%-25%. By analyzing the research progress in the literatures,it indicates that the phosphorus is easily fixed in soils,including adsorption fixation and chemical reaction fixation. The amount of phosphorus fixed is determined by the content of calcium carbonate,iron oxide,aluminum oxide,clay and the initial concentration of phosphorus in soils. Most of phosphorus is fixed in adsorption fixation in early period, which lasts several hours to tens of hours. In later period,chemical reaction fixation occurs mainly and lasts a few months to a few years,which results in phosphorus unavailable to plants. The dynamics of the entire fixation period can be described by Elovich equation. For reducing the amount of phosphorus fixed, an efficient way is to reduce the concentration of phosphorus in soils. By using the fixation data from the red soil in Shenxian (in Zhejiang province,China),together with the research data on the phosphorus uptake of cole,the release,the fixation and the plants uptake of phosphorus are quantitatively analyzed. The calculation result based on the established mathematical model indicates that the consumption amount of fertilizer can be greatly reduced and utilization efficiency can be increased by fertilizing the mixed DAP and controlled released DAP,compared with that by fertilizing DAP only.

An efficient method for the prediction of the release characteristics of film-coated urea from its film structure is proposed. A model spray-coating apparatus was built to prepare a plane film to directly measure the film permeability coefficients by simulating the characteristics of randomness, intermittence and multiple layers of the coating, and eliminating particle collision effects. From analysis, the spray-coated film structure can be modeled as comprising a dense structure and a defect structure. Both structures contributed to the penetration flux and the apparent permeability coefficients of the film for water and urea diffusion. The permeability coefficients of the plane films were calculated from the film structure model, and were shown to be close to the measured values.

Spherical 2–4mm granules of ammonium sulfate (NH4)2SO4 are promising fertilizer for practical use, though only much smaller grains are being produced in industry. This work used coating granulation to produce large spherical granules of (NH4)2SO4 in a fluidized bed by spraying its aqueous solution onto 0.9–1.6mm (NH4)2SO4 core particles. However, the overall coating efficiency was only 58% due to loss as dust by attrition of (NH4)2SO4 in the vent gas. By adding CaCO3 or SiO2 particles into the feed solution, the coating efficiency was increased to over 90%. This increase in coating efficiency was due to a change in the crystallization mechanism of (NH4)2SO4. The added CaCO3 or SiO2 particles provided a heterogeneous surface that induced (NH4)2SO4 to crystallize uniformly to form a more compact structure less susceptible to attrition.

Spray coating of polymer latex onto fertilizer particles in a fluidized bed for producing controlled-release urea is an environment friendly technology as it does not need any toxic organic solvent. Since the spray coating process in a fluidized bed occurs in the presence of particle collisions, the coating of the particles is random, intermittent and multiple, thus making it difficult to investigate the film formation process. In this paper, an experimental model apparatus was designed and used to investigate the effects of the key factors in the spray coating process. This apparatus reasonably simplified the complex process to avoid particle collisions and randomness in the coating. The intermittent coating in the fluidized bed was modeled by periodic coating and dewatering in the experimental apparatus. A large area film was obtained, and the film permeability was measured. The effects of atomizing gas flow rate, spray rate of latex, solid content of latex and gas temperature on film structure and film permeability were investigated. It was found that water transfer played a dominant role in the spray coating process. (C) 2011 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.