Turfgrasses, Carbon Dioxide and Global Warming: Part Two of Two
Samples, Thomas J., Landscape & Irrigation
Possible strategies to global C[O.sup.2] issues are being proposed, discussed and researched (1, 2, 3). One method being considered to maintain or reduce the level of C[O.sup.2] in the atmosphere is to remove and inject it into natural reservoirs not in contact with the atmosphere. These include deep geological formations or the oceans. Production from some oil and natural gas reservoirs can be enhanced by pumping C[O.sup.2] gas into the reservoir to push out the product. The United States leads the world in enhanced oil recovery technology (4). Approximately 32 million tons of C[O.sup.2] are used for this purpose each year (4). Liquid C[O.sup.2] could be pumped to an ocean depth of 3,200 feet or more, where the gas is denser than sea water (5). Estimates of the amount of C[O.sup.2] (Gigatons of C, where 1 Gigaton = 1 billion metric tons of C equivalent) that could be stored in reservoirs in order of magnitude are: oceans, 1,000s; deep saline formations, 100s to 1,000s; depleted oil and gas reserves, 100s; coal seams, 10s to 100s; and terrestrial, 10s (5).
More than 49 million acres of urban land in the United States are covered by turfgrasses (6). After absorbing C[O.sup.2] from the atmosphere, turfgrasses produce, or synthesize, a number of sugars that can be transported to, and eventually become a part of, plant roots. Sequestered C in turfgrass soils is often a combination of decomposing roots and shoots that have been mixed with soil.
Research indicates that turfgrasses may sequester up to 800 pounds of atmospheric C per acre per year (7). Based on this estimate, urban turfgrasses in the United States could remove about 20 million tons of C from the atmosphere annually (8).
Researchers Ronald F. Follett (USDA-ARS Soil-Plant-Nutrient Research Unit, Fort Collins, Colo.) and Yaling L. Qian (Dep. of Hortic. and Landscape Architecture, Colorado State University, Fort Collins, Colo.) are studying the impact of turfgrasses on C levels in soil. They report that, in Colorado, four years after turf establishment, about 14 to 16 percent of the soil organic C (SOC) at a depth from 0 to 4 inches, and 7 to 11 percent of the SOC at a depth of 4 to 8 inches, came from turfgrasses (7). Fine fescue and creeping bentgrass sequestered more C than Kentucky bluegrass (7). In a previous study of 15 golf courses near Denver and Fort Collins, Colo., and one golf course near Saratoga, Wyo., research results show that, after turfgrasses are established, C sequestration continues for up to 31 years in fairways and 45 years in putting greens (9). Most rapid SOC increases take place during the first 25 to 30 years (9).
Trade-in, greenhouse gas "offsets" paid by companies and individuals worldwide may total more than $100 million per year (10). The Outdoor Power Equipment Institute suggests that homeowners managing lawns may not need to look any further for a C offset than their own back yard (11). According to a research report by Ranajit Sahu, turfgrass in an average-managed lawn removes four times more C from the air, and a well-managed lawn five to seven times more C from the air, than is produced by today's typical lawn mower (12). …