sentences:  Because grass consists largely of water (80% or more), contains little lignin, and has high nitrogen content, grass clippings easily break down during an aerobic process  (comparable to composting) and returns the decomposed clippings to the soil within one to two weeks, acting primarily as a fertilizer supplement and, to a much smaller degree, a mulch.Grasscycling can provide 15 to 20% or more of a lawn's yearly nitrogen requirements.Proponents also note that grasscycling reduces the use of plastic bags for collecting yard waste and reduces trips to the curb or landfill to haul waste.