A mechanism of nutrient release from resin-coated fertilizers and its estimation by kinetic methods. 4. Relation between release of nitrogen from resin-coated urea and water vapor pressure in saturated salt solutions

摘要

The release of nitrogen from two types of resin-coated urea was studied in two saturated salt solutions at a constant temperature. From the water vapour pressure of the saturated salt solutions, the temperature of corresponding vapour pressure of pure water was calculated and this converted temperature was used in the simulation with a release model. The results showed that: (1) the release rates in the saturated solution were proportional to the differences in water vapour pressure between insideand outside of the coatings. The rates of release were simulated satisfactorily with the proposed model by converting the temperature; (2) the cumulative nitrogen release did not reach 100%. This suggests that osmotic pressure affected the saturated saltsolutions; and (3) the coated urea swelled differently with different coatings and temperatures, and by correcting the gain in volume of the swollen fertilizer granules, the simulation of nitrogen release in saturated salt solutions agreed with the actual release data.