Impact of Residential Prairie Gardens on the Physical Properties of Urban Soil in Madison, WI.

Prairie gardens have become a common addition to residential communities in the Midwestern United States, as prairie plants are native to the region and require fewer nutrient inputs and less irrigation than turfgrass. Although prairie systems have deeper and more diverse root systems than turfgrass, no one has tested the effect of prairie gardens on the physical properties of urban soil. We hypothesized that residential prairie gardens would yield lower soil bulk density and penetration resistance, and greater soil organic matter and soil saturated hydraulic conductivity compared to turfgrass. To test these hypotheses, twelve residential properties in Madison, Wisconsin, were examined in a field study where the property owner had adopted natural landscaping practices, and a comparison was made between prairie gardens and their adjacent turfgrass lawns. We found differences in soil properties beneath prairie gardens compared to the lawns, yet these differences depended on sampling depth. At a depth of 0-0.15 m, the soil beneath the prairie vegetation had a lower bulk density by 10%, a lower penetration resistance by 15%, a greater level of soil organic matter by 25%, and thus, increased saturated hydraulic conductivity compared to the adjacent lawns. These differences were not detected at the deeper sampling depths of 0.15-0.30 and 0.30-0.45 m. The observed changes in soil physical properties, and the consistent direction of these changes when viewed in aggregate, suggest that residential prairie gardens may help mitigate the effect of urbanization on the physical and functional properties of soil.