There has been some exciting new research that proves that NOT fertilizing your lawn (or improperly fertilizing) actually is contributing to sediment and phosphorus runoff. The research proves that a well fertilized home lawn reduces runoff substantially and is much better for the environment. Those that believe that fertilizers are contributing to runoff, pollution and environmental degradation are strongly mistaken. The reasoning behind this is that a well fertilized lawn is thick and healthy and traps most moisture and anchors sediment. A lawn that has not been fertilized and has been maligned causes significant compaction and open soil in which is prone to runoff during large water events. See the short video in the link below, great insight and really easy to follow.