When applying liquid fertilizers, the "ring of responsibility" should be at least 3 feet from the edge of the water. The same is true for applying granular fertilizers with a fertilizer spreader that features a deflector shield. A deflector shield only allows fertilizer to be distributed on one side. This half-circle application (instead of the typical full-circle application of most fertilizer spreaders) allows for more accurate fertilizer application. If you are applying fertilizer without a deflector shield, the "ring of responsibility" should extend at least 10 feet from the edge of the water.