Soil Carbon Dynamics in Lawns Converted From Appalachian Mixed Oak Stands

Conversion of native forests to turfgrass-dominated residential landscapes under a wide range of management practices results in dramatic changes to vegetation and soils, which may affect soil carbon storage. To better understand the effects of landscape conversion and management on soil carbon, we conducted a study on residential properties in the Valley and Ridge physiographic province of southwest Virginia to compare soil carbon storage and dynamics between turfgrass landscapes and the surrounding mixed oak forests from which they were developed.

Sixty-four residential properties ranging from 5 to 52 years since site development were investigated. Soil samples were collected from lawns and adjacent forest stands to a depth of 30 cm and analyzed for carbon and nitrogen content. Additional measurements taken were soil bulk density, temperature, moisture, and total soil CO₂ efflux rate. Homeowners participating in the study completed a survey on their lawn management practices so that the effects of specific practices (e.g. fertilization) and intensity levels on carbon dynamics could be analyzed. Also included in the survey were 11 questions regarding the homeowners' commitment to the environment. Homeowners were assigned an environmental commitment score based on their responses which was compared with lawn management practices in order to identify any connection between environmental attitude and lawn management practices.

Total soil carbon content to 30 cm depth of lawn (6.5 kg C/m²) and forest (7.1 kg C/m²) marginally differed (P=0.08); however, lawn soil contained significantly greater C than forest soil at the 20-30 cm depth (0.010 vs. 0.007 g C/cm³, P=.0137). There was a weak negative relationship between carbon in the lawn and time since development at the 20-30 cm depth (P=0.08), but no significant relationship between time and C content at shallower depths. We found a positive relationship between time since development and percent C of lawn at the 0-5 cm depth (P=0.04), whereas there was a negative relationship with percent C and time at the 20-30 cm depth (P=0.03). Based on the homeowner survey, we found a positive correlation between lawn fertilization frequency and both lawn nitrogen content (P=.07) and lawn carbon content (P=.0005) in the top 0-5 cm of soil. Nitrogen content was greater in lawn than forest soil at the 0-5 cm depth (0.0025 vs. 0.0018 g/cm³³, P<.0001) and the 5-10 cm depth (0.0013 vs. 0.0009 g/cm³, P <.0001). There was a positive relationship (P=0.059) between overall environmental commitment score and level of management intensity. Higher environmental commitment (EC) score corresponded with a higher level of management intensity (fertilizer and pesticide use).

Our results indicate that converting unmanaged Appalachian hardwood forest into managed, turf-grass dominated residential homesites results in similar soil organic concentration and depth distribution as the previous forest within a short period of time following development. Although total soil carbon does not differ between lawn and forest, lawn may develop greater density at 20-30cm depth over time. Fertilization enhances carbon and nitrogen content in the upper 0-5cm in lawns. Homeowners who feel that they are more strongly committed to the environment are more likely to apply higher levels of fertilizer to their lawn.