Enhancing Turfgrass Carbon Sequestration - 2023 Results from OSU

by Wrennie Wang, PhD, and Alec Kowalewski, PhD

Criticisms of the environmental impacts of lawns, including a high climate footprint and high irrigation requirement, pose challenges to the market acceptance of natural turfgrass.

There are limited assessments of how irrigation rate and frequency affect turfgrass carbon sequestration potential and compare irrigation treatments to non-irrigated turf and bare soil. Considering this a trial was initiated on tall fescue plots in Corvallis, OR in the spring of 2023. The goal of this study is to identify the minimum irrigation required to maintain turfgrass for the benefit of sequestering atmospheric CO2. Factors in this experiment included two irrigation frequencies (once or 4 times a week) and two reference evapotranspiration (ET) replacement rates (45% and 80%) compared to non-irrigated with and without turf. Response variables included CO2 flux measured with a potable clear chamber connecting to a CO2 gas analyzer (PP systems), NDVI, turf quality, volumetric water content and surface temperature.

Results: 

Irrigating tall fescue turf at 80% ET generally produced higher CO2 assimilation rate compared to 45% ET, such effect was only statistically significant on 12 and 26 July (table 1). Irrigation applied once a week produced higher CO2 assimilation rate compared to irrigation applied four times a week only on 26 July. Tall fescue without irrigation produced similar CO2 assimilation rate only for the first two dates and contributed to the release of CO2 to the atmosphere for rest of the dates, whereas tall fescue plots subjected to irrigation treatments were shown to assimilate atmospheric CO2. As expected, tall fescue turf has been shown to have carbon sequestration benefits. In contrast, soil without turfgrass was demonstrated to constantly release significant amount of CO2 into the atmosphere. 

Table 1: Effects of irrigation rate and frequency, non-irrigated turf and no turfgrass cover on CO2 flux in Corvallis, OR in 2023. 

Irrigation applied at 45 and 80% ET replacement resulted in greater NDVI values and turfgrass quality compared to non-irrigated turfgrass.  The 80% ET replacement rate was able to keep summer turfgrass quality at values greater than 6, or acceptable. Evapotranspiration replacement rates were inversely correlated with August atmospheric temperatures, with the non-irrigated turf resulted in 114.5° F, followed by 45% ET replacement which resulted in 102.5° F, and finally 80% ER replacement which resulted in the lowest surface temperature (93.3° F).  It is important to note that areas without irrigation or turfgrass cover were the hottest at this time, reaching temperatures of 126° F. 

More research is needed to evaluate the effects of irrigation rates on turfgrass carbon sequestration and temperature, as well as other eco-system services. 

Table 2: Contrasts comparing the control (no irrigation) to reference evapotranspiration (ETref) replacement rates, and irrigation frequency, data collected in Corvallis, OR and pooled across Aug 14, 16 and 18, 2023 (average atmospheric temperature at the time of data collection 97°F, and no turf 126°F).