How much they are lowered is dependant on several factors including the clay and organic matter content of the soil, soil percolation rates, type of nitrogen fertilizer used and the timing of nitrogen applications. Sandy soils leach more heavily than clay or high organic matter soils. Slow release forms of nitrogen leach more slowly than water soluble forms of nitrogen. Lawns fertilized in the fall will have less nitrogen available this spring than lawns fertilized normally in the spring. Less mowing is one possibility.
Poor color is another possibility.
Increased incidence in disease is yet another possibility. Yes, with some turf diseases, but not all. In fact, there are two rather common turf diseases we frequently encounter in Maryland that are more likely to be found on lawns low in nitrogen. If above normal rainfall continues into the early to mid spring, keep your eyes open for the potential increase in the incidence of both dollar spot and red thread turf diseases. It may cause severe damage to fescues, ryegrasses, and bluegrasses.