Release Kinetics of Urea from Polymer Coated Urea and Its Relationship with Coating Penetrability

Four kinds of polymer coated urea(PCU)were put in distilled water at 30℃ to determine the variation of coating penetrability and give a precise description of the urea release kinetics. The urea release from PCU could be divided into four stages: lag stage, swell stage, steady stage and decay stage. The release rate coefficient K, a measure of coating penetrability, was linearly increased at swell stage, but almost not variable at steady stage. At decay stage, the relation of X to time t could be described by the equation K= mtn-1where m and n are the coefficients). When n>1, the coating penetrability was gradually increased, and the urea release from PCU was accelerated; when n=1, the coating penetrability was steady, and the urea release from PCU obeyed the first-order kinetics; and when n<1.the coating penetrability was gradually decreased, and the urea release from PCU was delayed, resulting in a significant 'tailing effect'.

Study on Release Properties of Slow Release Urea Coated by Industrial Lignin

This study aimed to investigate the release properties of slow release ure- a coated by industrial lignin and the influences of temperature, pH and post-ripening period on the release of nutrients in coated urea. According to the experimental results, the release of nutrients in coated fertilizers showed an S-shaped curve; on the 28th d, the nutrient release rate reached 73.77%; the differential solubility was 1.83%, and the theoretical release period was 50.25 d. The release of nutrients was significantly influenced by temperature. As the incubation temperature rose from 25 to 40 ℃, preliminary solubility increased from 8.03% to 16.24%; differential solubility increased from 1.83% to 1.88%; theoretical release period was reduced from 51.25 d to 45.55 d. The release of nutrients was promoted by H＋ and OH-. After they were placed at room temperature within 30 d, coated fertilizers exhibited the optimal release properties.

A Comparative Study of Nitrogen Loss after Application of Biochar Coated Urea and Common Urea in Vegetable Soil at Chaihe Catchment of Dianchi Lake

[Objective] This study aimed to provide the basis for scientific and rea- sonable application of nitrogen fertilizer and control Of agricultural non-point source pollution in vegetable-growing area at Chaihe catchment of Dianchi Lake. [Method] A pot experiment was carried out to compare the loss of nitrogen via ammonia volatilization and nitrogen leaching after application of biochar coated urea （BCU） and common urea （Urea） with different nitrogen rates （0 mg N/kg soil, 400 mg N/kg soil, 320 mg N/kg soil and 280 mg N/kg soil）. [Result] The results indicated that the amount of nitrogen loss was proportional to nitrogen applied rate. Leaching nitrogen was higher than ammonia volatilization. Compare with Urea treatments, ammonia volatilization and nitrogen leaching losses were significantly lower in BCU treatments at the same nitrogen application rate. At the nitrogen application rate of 320 and 280 mg N/kg soil, nitrogen loss, ammonia volatilization and leaching nitrogen was 43.5%-45.5%, 3.7%-21.7% and 49.8%-52.1% lower in BCU treatments than in Ure- a treatments, respectively. [Conclusion] The application of BCU could minimize nitro- gen loss by reducing nitrate leaching loss. It can be concluded that the low nitrogen application rate combined with BCU have a practical influence on controlling the risk of nitrogen pollution in Dianchi Lake.

Study on the Nitrogen Release Law of Bamboo Charcoal-coated Urea and Its Biological Utilization Effects

[Objective] The study about the nitrogen releasing law of bamboo-charcoal coated urea and the biologic utilization effect was to find the coated urea with high efficiency,low price and simple production technology.[Method]Two kinds of bamboo-charcoal coated urea(BCCU)with different coating thickness were made by using bamboo-charcoal and macromolecule polymer as coating material.The experiments of soil eluviate,ammonia volatilization in corn field and potted plant of corn were conducted to study the nitrogen releasing law and the biologic utilization effect of self-made BCCU.[Result]The BCCU showed some slow-release capability and their accumulated nitrogen releasing rates in 29 d were 9.93%-16.27% lower than that of normal urea.Compared with the normal urea,the volatilization rate of ammonia in BCCU reduced to 16.66%-31.8%,the biomass of corn and nitrogen utilization rate increased by 12.8%-24.1% and 10.5%-16.99%,respectively.[Conclusion]Bamboo-charcoal in coated urea not only had some slow-release capability,but also had some adsorbability,which would reduce the eluviation and volatilization of nitrogen and protect environment from N pollution.

Nitrogen Cycling and Losses Under Rice-Wheat Rotations with Coated Urea and Urea in the Taihu Lake Region

A lysimeter experiment with undisturbed soil profiles was carried out to study nitrogen cycling and losses in a paddy soll with applications of coated urea and urea under a rice-wheat rotation system in the Taihu Lake region from 2001 to 2003. Treatments for rice and wheat included urea at conventional, 300 （rice） and 250 （wheat） kg N ha^-1, and reduced levels, 150 （rice） and 125 （wheat） kg N ha^-1, coated urea at two levels, 100 （rice） and 75 （wheat） kg N ha^-1, and 150 （rice） and 125 （wheat） kg N ha^-1, and a control with no nitrogen arranged in a completely randomized design. The results under two rice-wheat rotations showed that N losses through both NH3 volatilization and runoff in the coated urea treatments were much lower than those in the urea treatments. In the urea treatments N runoff losses were significantly （P 〈 0.001） positively correlated （r = 0.851） with applied N. N concentration in surface water increased rapidly to maximum two days after urea application and then decreased quickly. However, if there was no heavy rain within five days of fertilizer application, the likelihood of N loss by runoff was not high. As the treatments showed little difference in N loss via percolation, nitrate N in the groundwater of the paddy fields was not directly related to N leaching. The total yield of the two rice-wheat rotations in the treatment of coated urea at 50% conventional level was higher than that in the treatment of urea at the conventional level. Thus, coated urea was more favorable to rice production and environmental protection than urea.

Synthesis and Performance of Polyurethane Coated Urea as Slow/controlled Release Fertilizer

Polyurethane coated urea slow/controlled release fertilizer was prepared based on urea granules, isocyanate, polyols and paraffin. Isocyanate reacted with polyols to synthesize the polyurethane skin layer on urea granules surface. Paraffin serves as a lubricant during syntheses of polyurethane skin layers. The structure and nutrient release characteristics of the polyurethane skin layers were investigated by FTIR, SEM and TG. Urea nitrogen slow-release behavior of the polyurethane coated urea was tested. The experimental results indicated that compact and dense polyurethane skin layers with a thickness of 10-15 lam were formed on urea surface, the urea nitrogen slow-release time can reach 40-50 days. Paraffin proves to play a key role in inhibiting water to penetrate into urea, but excessive addition would decrease the polyurethane crosslinking density.

Study on Membrane Microstructures and Characteristics of Infrared Spectra and Nitrogen Release of Solid-Liquid Reaction Coated Urea

The membrane microstructures and the mechanism of two coated ureas formed through solid- liquid reaction were observed by scanning electron microscope and infrared spectra, the relation of the structural characteristics with the nitrogen release feature was also discussed by combining with nitrogen dissolution in water. The results showed that the membranes were made of solid particles tightly connected to each other and were piled up layer by layer through liquid glue. Porosity and aperture of membrane were determined by compactness of piled layers and the particles in a single layer and also related to the characteristics of coating materials. Research of the infrared spectra of membrane, made of a solid powder and a liquid glue, proved that O-H on the solid surface was bonded with the double bond of the liquid glue, thus forming membrane and keeping it stable. It was found that the two coated ureas showed obvious differences in nitrogen releasing due to their membrane structures, the porosity and aperture of membrane were the critical factors for nitrogen releasing.

Ammonia volatilization and availability of Cu,Zn induced by applications of urea with and without coating in soils

Ammonia volatilization and the distribution of Cu and Zn were investigated in two types of soil treated with coated and uncoated urea.The rate of ammonia volatilization in two weeks after fertilizing with coated urea was 8% in soil 1 （soil derived from river alluvial deposits in Dongting Lake Plain） and 5.15% in soil 2 （red soil derived from quaternary red clay）,about half the rates observed when fertilizing with common urea,implying that the hydrolysis speed of the coated urea was lower than for common urea,and that the coated urea can increase nitrogen use efficacy.As for the availability of Cu and Zn,their concentrations decreased in the first week after fertilization,and then increased,which was contrary to the effect of treatment on soil pH.For example,when the pH was 7.99,there was 0.79mg/kg exchangeable Cu and 0.85mg/kg exchangeable Zn in the soil derived from river alluvial deposits in Dongting Lake Plain.However,the concentrations of exchangeable Cu and Zn were generally lower for the common urea treatments than those with the coated urea because the peak pH for the common urea treatment was greater.The concentrations of these elements correlated well with pH in the range 4–8 in second order polynomial fits.

Swelling and diffusion model of a hydrophilic film coating on controlled-release urea particles

Controlled-release urea was fabricated by coating urea particles with a polymer latex in a fluidized bed. The latex film coated on the urea particle surface was hydrophilic and swelled in water. The film swelling in water and urea solution and properties of the swollen film were studied. The film swelling in urea solution followed the Lagergren＇s pseudo-first order kinetics with the swelling coefficient depending on the film material and experimental conditions. The effects of swelling on film structure and permeability were studied. The film permeability coefficient decreased with increasing swelling ratio with an approx- imately linear relationship. Based on the film formation process and structure of the swollen film. a film structure model consisting of dense and swollen phases was proposed. The permeability coefficient of the spherical film and cumulative release of urea from the coated particles were calculated from the swelling ratio of the spherical film. which was determined from the expansion curve of the coated particle during the release process, The calculated and measured release curves agreed well, This research indicates that the swelling of the hydrophilic film and the controlled-release mechanism are important factors in the development of controlled-release urea.