Because nitrogen moves freely with water, water-soluble sources of nitrogen should be avoided when the lawn is not actively growing or when it is being grown on coarse sandy soils particularly near bodies of water. Slow-release sources of nitrogen reduce the leaching potential. Phosphorus fertilizers move very little in most soils but may leach through very sandy and organic soils. Most phosphorus movement is through sediment eroding from disturbed soils. The figure below shows an example of a nitrogen fertilizer label.
Urea nitrogen is a water-soluble source of nitrogen.
Tips Whenever possible, apply fertilizers that are composed of slow-release sources of nitrogen. These sources are made so that the nitrogen is metered out slowly to the grass plants. These fertilizers are best applied to cool-season grasses when they are green but not actively growing, in early spring or near the end of the growing season. They should also be applied where sandy soils are prevalent, near surface water, or where the water table is shallow. Water lightly immediately following application to wash the material into the soil where the nutrients can be used by the grass plants.