Nitrogen Release from Coated Urea

To estimate the nitrogen release from the coated urea, firstly the total available nitrogen content of the coated urea was evaluated using Kjeldahl. The detail of this method can be found elsewhere.^{27 (link)} Diacetyl monoxime (DAM) calorimetry method was used to estimate the amount of nitrogen leached out from the coated urea. This method involves the usage of color reagent, which was prepared by mixing the 25 ml of DAM solution (prepared by dissolving 2.5 g of diacetyl monoxime in 100 ml of distilled water), 15 ml of TSC solution (prepared by dissolving 0.25 g of thiosemicarbazide in 100 ml of distilled water) and 460 ml of acid reagent (prepared by mixing 10 ml of sulfuric acid, 240 ml of distilled water and 250 ml of phosphoric acid).^{20,21,28 (link)} 2 g of coated urea was placed in a conical flask containing 200 ml of distilled water. To estimate the amount of the nitrogen released in distilled water from coated urea, after every 24 h 2.5 ml of the aliquot was taken and mixed with 7.5 ml of the color reagent and heated to a temperature of 85 °C for 30 min in a water bath followed by cooling at room temperature. The obtained red color solutions were then analysed using Shimadzu UV-1800 UV-Vis spectrophotometer at 526 nm wavelength.^{13,20,21 (link)}