Enhancing Turfgrass Carbon Sequestration to Improve Sustainability and Market Access

Dr. Ruying Wang, Dr. Clint Mattox, Dr. Claire Phillips, and Dr. Alec Kowalewski
Oregon State University Horticulture and the United States Department of Agriculture

Criticisms of the environmental impacts of lawns, including a high climate footprint, pose challenges to the market acceptance of natural turfgrass domestically and internationally. However, turfgrass systems have been shown to accumulate soil organic carbon (SOC) at high rates, comparable to regenerating forests and fallowed cropland.

The greenhouse gas emissions associated with turfgrass come primarily from maintenance practices, including fuel emissions from mowing and soil N2O emissions following nitrogen fertilizer application. But what happens when turf is managed with low-intensity management? Is low-input turf still good at accumulating soil carbon? 

What is good for turf growth—fertilization and irrigation—should also be good for soil carbon accumulation, even though these practices also increase maintenance emissions. It is not known how a low-maintenance lawn—with infrequent fertilization, irrigation, and mowing—will compare to a lawn managed for aesthetic characteristics. While a number of studies have tried to make these comparisons with simulation models, there are few on-the-ground studies directly measuring turfgrass emissions. The turf team at Oregon State University has initiated a series of field trials to address this issue, evaluating trade-offs between maintenance intensity, soil carbon storage, and turf aesthetic characteristics. 

In one study, we are constructing a complete annual carbon budget for a newly-seeded perennial ryegrass lawn under optimum management practices (Fig. 1). We are using automatic chambers to continuously measure CO2 uptake (through photosynthesis) and release (through respiration) throughout the day and night. We hypothesize that cool-season turfgrass, which is able to grow during the winter in the northwestern U.S. and western Canada, can therefore provide a winter carbon sink in this region.

In a related experiment, we are comparing turfgrass plots that have been receiving different levels of maintenance intensity for the last four years. These plots are part of the Oregon School IPM trials, which were established in 2016 to make recommendations to Oregon schools on how to make best use of limited resources to care for school grounds. In these plots, we measured CO2 fluxes once every two weeks, and compare plots with high and low levels of N fertilization and irrigation, as well as mowing frequency and height of cut (Fig. 2). We will continue to measure these plots for two years, along with quantifying gasoline and fertilizer consumption needed to maintain the plots in order to complete carbon budgets for each treatment.

Our initial observations from January to March 2021 for both projects suggest that cool-season turfgrass lawns are actively assimilating atmosphere CO2 during the day in winter months. We will continue to collect data to calculate the annual carbon balance, which will provide a better understanding of the cool-season turfgrass system in our local environment. This effort will provide information on the climate footprint of turfgrass, which will allow turfgrass professionals to explain their environmental impacts to a concerned public and address regulatory constraints imposed by cap-and-trade programs. It is also our intent to identify best management practices for enhancing carbon sequestration and to deliver these results to turfgrass seed producers, turfgrass managers (golf course superintendents, commercial turf managers, school, and park employees), and other users (homeowners and master gardener programs). 

Figure 1: CO2 and CH4 fluxes are recorded every hour with two automatic chambers on a new stand of perennial ryegrass at the Lewis-Brown Horticulture Farm in Corvallis, Oregon.

Figure 2: Potential carbon assimilation is measured every two weeks on a subset of treatments focusing on mowing, irrigation, and fertility trials on a mixed stand of cool-season turfgrasses.