High soil carbon sequestration rates persist several decades in turfgrass systems: A meta-analysis

Authors: Phillips, Claire; WANG, RUYING - Oregon State University; MATTOX, CLINT - Oregon State University; TRAMMELL, TARA - University Of Delaware; YOUNG, JOSEPH - Texas Tech University; KOWALEWSKI, ALEXANDER - Oregon State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2022
Publication Date: 11/5/2022
Citation: Phillips, C.L., Wang, R., Mattox, C., Trammell, T.L., Young, J., Kowalewski, A.R. 2022. High soil carbon sequestration rates persist several decades in turfgrass systems: A meta-analysis. Science of the Total Environment. 858(3). Article 159974. https://doi.org/10.1016/j.scitotenv.2022.159974.
DOI: https://doi.org/10.1016/j.scitotenv.2022.159974

Interpretive Summary: Turfgrass is common within urban landscapes and serves many functions, including potentially sequestering soil carbon. Turfgrass might be able to help reduce greenhouse gas emissions from urban and low-density residential areas. However, it is not known how variable soil carbon sequestration rates are in turfgrass or how they change through time. This study summarized rates of soil carbon sequestration in turfgrass across all known studies. We showed that average soil carbon sequestration rates are high compared to other soil conservation practices, including conversion of croplands to grasslands, cover crop adoption, and no-till adoption. However, average rates of soil carbon sequestration declined to zero by fifty years from turf establishment. This research showed that turfgrass cultivation may be useful for temporarily reducing emissions in urban landscapes, but that mowing and nitrogen fertilizer applications need to be minimized to realize the full sequestration benefits of turfgrass. These findings will be helpful for the turfgrass and lawncare industries to better understand opportunities and liabilities stemming from emerging carbon markets and climate legislation. It will also be useful for scientists and regulatory agencies who want to quantify the emissions impacts of urbanization in the United States.

Technical Abstract: Managed turfgrass is a common component of urban landscapes that will likely expand with population growth and urbanization. Several studies have previously reported high rates of soil carbon sequestration in turfgrass, but no systematic review has summarized these rates nor evaluated how they change as turfgrass ages. Here we conducted a meta-analysis of soil carbon sequestration rates from 62 studies globally, including 29 studies that evaluated carbon changes over 75 years or longer. We showed that turfgrass established within the last ten years had on average a positive soil C sequestration rate of 5.28 Mg CO2 ha-1 yr-1 (95% CI = 3.78 - 6.78). Areas converted to turf from forests were an exception, sometimes lost soil carbon, and had a cross-study mean sequestration rate did not differ from 0. In some locations soil C accumulated linearly with turf age over several decades, but the major trend was for soil C accumulation rates to decline through time, and 50-year-old turf had a cross-study mean sequestration rate that was not different from 0. We show that fitting soil C stock timeseries with a mechanistically derived function rather than purely empirical functions did not alter these conclusions, nor did employing equivalent soil mass versus fixed-depth carbon stock accounting. We conducted a partial greenhouse gas budget that estimated emissions from mowing, N-fertilizer production, and N2O emissions. At high N-fertilizer rates emissions largely offset soil C sequestration, even in recently established turfgrass. However, the potential carbon sink provided by turf can be maximized if mowing and N-fertilizer related emissions are abated through improved management. Management decisions that avoid losing accrued soil C—both when turfgrass is first established on productive soils and when it is eventually replaced with other land-uses—will also help maximize the C sequestration potential provided by turfgrass systems.