Evaluating Nitrogen Release Rates of Commercial Slow-Release Urea Products Using Brix Value Analysis: A Validation Study Comparing Two Methods

The stability of three slow-release urea products (SRU) and a non-protected granulated urea (U) product was assessed based on their Brix value and total Nitrogen (N) Kjeldahl concentration in water. Each SRU and U products (10 g) was mixed with 50 ml of distilled water at 23.5 °C for various durations: 1, 3, 6, 12, and 24 h. After each period of time, Brix values and total N concentrationswere measured in the aliquots. The N concentrations in all products exhibited time-dependent changes. A positive and linear correlation was observed between the total N in water and Brix values. The R2 between both methods was 0.97. Thus, the Brix value serves as a convenient and effective method to evaluate the relative rate of N release for different SRU products.