Title : Nitrogen release rates from controlled release fertilizers
Abstract:
Controlled-release urea (CRU) fertilizers are increasingly adopted in horticultural systems to improve nitrogen-use efficiency and minimize environmental losses. Nitrogen (N) release rates through the crop growth period dictates the uptake efficiency of applied CRF formulations. This study investigates the N release dynamics of two CRU formulations, CRU-60 and CRU-75, across three growing seasons. N release rates and patterns were quantified and compared using a field and a laboratory method. Through biweekly samplings of buried mesh bags with the mix of formulations in the field, rates of release were determined using the weight loss method all through the three seasons. The data were analyzed to evaluate seasonal trends and formulation differences. Results indicate that CRU-60 consistently demonstrated faster N release compared to CRU- 75, a trend that aligns with their respective design durations (60 vs. 75 days). By the end of each growing season, cumulative N release for CRU-60 ranged from approximately 55.8% to 86.7%, while CRU-75 ranged from 26.7% to 83.5%, depending on the season. These differences were statistically significant (p < 0.05) across all three seasons. In the laboratory method, the formulations were subjected to high-temperature (100°C) and incubated to determine the maximum potential release rates under accelerated conditions. Under these conditions, CRU-60 reached nearly 80% N release within 73 hours, while CRU-75 achieved approximately 40% over the same period. Notably, the cumulative release of CRU-60 reached nearly 80% in laboratory conditions and ranged from 55.8% to 86.7% in the field, indicating that both methods captured comparable total N release, with field variability primarily influenced by seasonal temperature differences across seasons. On the other hand, CRU-75 showed a slow and steady release pattern in both environments. Polynomial regression analysis was used to model the N release trends over time for each treatment. Despite environmental differences, both field and lab methods showed strong polynomial fits (R² > 0.94), highlighting consistency in formulation-dependent release behavior. The comparison between methods underscores the importance of both environmental factors and formulation design in determining nutrient availability. These findings support more informed selection of CRU formulations tailored to specific crop cycles and production systems, particularly in high-input vegetable systems where timing of nutrient release is critical.
