Benefits of recycling lawn clippings
- It is most important to remember that proper mowing practices include not removing more than 1/3 of the above-ground growth in any one mowing, regardless of growth rate. Removing more than that can cause undue stress to the turf and stop root growth for as much as six days to two weeks.
- Returning clippings to turf can reduce nitrogen fertilizer requirements by as much as 75% or more.
- Recycling clippings can increase water infiltration rates by 12%.
- Recycling clippings increases net carbon sequestration by at least 11% and up to 59%.
Recycling turfgrass clippings to a lawn after mowing provides several advantages to the turfgrass and the people maintaining it. It is suggested that clippings always be recycled, except where:
- Returning clippings will interfere with the intended use of the turf;
- The clippings are unusually heavy or excessive clumping of the clippings will occur;
- There is significant chance of disease development due to the increased tissue present.
Some literature claims that recycling clippings can lead to excessive thatch accumulation or unsightly brown grass clippings on the surface of the lawn, which can shade the plants below. However, the scientific research has demonstrated significant time, energy, cost and environmental benefits from recycling clippings, when done properly.
Turfgrass growth rates
Turfgrass growth rates vary widely among species and are highly dependent on environmental characteristics, management practices and time of year. However, for many cool-season grasses under typical lawn management, total dry clippings production may be in the range of 1 to 3 grams per square meter per day or about 4700 kilograms per hectare per year. Regardless of growth rate, it is most important to remember that proper mowing practices include not removing more than 1/3 of the above-ground tissue in any one mowing. Removing more than the recommended amount can cause undue stress to the turf plant and stop root growth for as much as six days to two weeks.
Fertilizer requirement reductions
Allowing the removed tissue to return to the turf, rather than collecting it, has been shown to reduce nitrogen fertilizer requirements by approximately 98-294 kg nitrogen per hectare per year – that is, by as much as 75% or more. For example, on well-fertilized Kentucky bluegrass, between 68-274 kg nitrogen per hectare per year that is contained in the turf tissue may be removed from the turf system if clippings are not returned. When clippings are returned to the turf, that nitrogen is slowly released from the deteriorating plant tissue back into the soil. The result is an overall reduction in the total cost of fertilizer as well as the time and energy to apply it.
Ensuring maximum water infiltration into the soil is one important part of proper water management. Doing so minimizes the amount of water that would otherwise be wasted as runoff, and helps keep soil and nutrients from being lost from the lawn into surface waters. Recycling clippings has been shown to increase water infiltration rates by 12% over turf where clippings have been removed. This is likely due to improved soil structure resulting from increased soil organic matter.
Increasing soil organic matter has other benefits as well. Strong concern over global climate change, coupled with an increased awareness of the need for sustainable soil management, has driven the desire to sequester and retain substantial quantities of carbon in soils under managed turfgrass. The average carbon content of grass species is 42.7%. Returning clippings to the turf can eliminate the excessive removal of carbon from the turfgrass system. One study found that, not accounting for carbon expenditures associated with management practices, properly managed cool-season turfgrass sequestered between 0.32 and 0.78 mg of carbon per hectare per year when clippings were returned to the turf. In a subsequent study, it was estimated that recycling clippings increased net carbon sequestration by the turfgrass by 11 to 59% over removing clippings.
A study by Busey and Parker, estimates that disposal of lawn waste accounts for approximately 3% of the total energy expenditures associated with lawn maintenance. While this number is highly dependent on the choices of the turf manager, it demonstrates that significant energy savings may be achieved by simply returning clippings to the turf instead of bagging them for removal.
Taken together, studies indicate a strong environmental and economic benefit to returning clippings to the turf during mowing operations. Realization of those benefits is dependent on the turf manager adhering to proper mowing, irrigation and fertilization practices. A turf manager must determine if the required practices fit within his or her maintenance schedule and abilities, and compare the potential for increased time and maintenance against the significant benefits gained by recycling clippings.
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Revised October 2016