Current water quality models do not consider the time release rate of sulfur-coated ureas (SCUs). However, the use of these slow-release formulations is prevalent in urban agricultural management. Using documented slow-release fertilizer data, a first-order decay equation was fit with reasonable accuracy for both surface (Efficiency R{sup}2 = 0.63) and incorporated (Efficiency R{sup}2 = 0.70) applications. In both cases the decay coefficient was best represented using a two-parameter model. Temperature and seven-day dissolution amount were determined as best descriptive parameters for the surface model while soil moisture and temperature were used for the incorporated model. Temperature was the more sensitive parameter for the surface applied model while soil moisture was the more sensitive input for the incorporated model. Each model was validated with a limited amount of data. The surface applied model was validated with a prediction efficiency of 0.82 while the subsurface model was validated with a prediction efficiency of 0.63. Even though the models are based on a limited amount of data, incorporation of these results in water quality models will permit the initial simulation of SCUs and allow better simulations of real world situations.
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