Slowly-available nitrogen is released over a longer period of time. From a groundwater quality standpoint, quickly-available nitrogen is more prone to leaching and should be applied very carefully. Nitrogen in this form is more slowly available and releases over a longer period of time, and would be less likely to leach through the soil to the water table. Amount, Frequency, and Timing of Fertilizer Application - The proper amount and scheduling of fertilizer application depends on a variety of factors including the source of nitrogen, soil type, type of turf grass, and whether or not clippings are collected. If the nitrogen in the fertilizer is slowly available, higher rates can be applied with less frequency than otherwise.
Sandy soils are more prone to leaching than silt loam or clay loam soils.
Higher levels or more frequent nitrogen applications may be required for sandy soils. However, great care should be exercised when applying fertilizers to sandy soils to reduce the chance of groundwater contamination. A slowly available nitrogen source may provide the best insurance against leaching in sandy soils while providing the proper nutrients as well. The timing of application is also important. Excessive spring application of nitrogen to cool-season grasses can be detrimental because it leads to excessive leaf growth at the expense of root development.