WASHINGTON — Cranking up the lawn mower on a Saturday afternoon
may be a child’s most dreaded chore. But little does he or she know that
it also affects how much carbon and nitrogen are present in the soil
below the grass.

Quincy Law of Purdue University studies many aspects of lawn care and
their effects on the soil. Does the type of turf grass make a
difference? Does it matter if grass clippings are left on the lawn or
picked up? How frequently should people mow their lawns?

“My research demonstrates one of the many environmental benefits of
natural grass lawns, golf courses, athletic fields, cemeteries, and
similar areas,” he explains. “Grasses are able to remove carbon dioxide,
a greenhouse gas, from the atmosphere and deposit it into the soil as
organic matter.”

Law and his team found that the amount of carbon deposited into the
soil was affected by the species of grass and how it was mown.
Specifically, tall fescue resulted in more soil carbon than Kentucky
bluegrass. However, tall fescue required more frequent mowing. Both are
common grasses used in lawns in the United States.

“Soil is a nonrenewable resource that must be protected, which soil
carbon helps to do,” he says. “Soil carbon helps to bind soil particles
and build soil structure. It also decreases the risk of runoff and
erosion, and improves soil-water relations.”

In addition, returning grass clippings increased both soil carbon and
nitrogen compared to when clippings were collected. Grass clippings
contain these elements and if the clippings are returned to the soil,
they break down and are released into the soil.

In the soil they affect the carbon and nitrogen levels in two ways:
directly by simply being present but also indirectly by serving as
fertilizer for the grass.

However, Law notes it is difficult to make specific species
recommendations in this area. To get more grass clippings, the grass has
to be mowed more often, which can cause problems.

Lawn mowers, like cars and trucks, produce their own carbon emissions
and can offset some of the benefits of increased grass clippings.
Improvements in mower efficiency and alternative fuel sources may help
offset the mower emissions in the future, he says.

“By carefully selecting a grass and properly managing grass
clippings, homeowners can increase the carbon sequestered in the soil,”
he says. “While this will not single-handedly significantly reduce
carbon dioxide levels in the atmosphere, it is still helpful.”

For example, Law’s research shows that the carbon deposited by the
grass more than offsets the carbon emitted from managing the lawn and
helps to justify those emissions. It can be beneficial in that it allows
a way for an individual to reduce his or her net carbon footprint.

Lawns do more than look good, Law adds. They provide recreational
areas as well as environmental and societal benefits. For those looking
for more information about the best way to manage their turf, he says a
local university extension service is a great source of help.

“I grew up playing golf and immediately fell in love with working on a
golf course, so I have always enjoyed working closely with nature,” Law
says. “Additionally, I have a family history of farming. My brother
currently farms land that has been in our family for over 150 years, and
soil conservation has always been a priority. As my grandfather said,
‘Harvest the crop, not the land.’ ”

–American Society of Agronomy
via EurekAlert!