Compost Incorporation Increases Plant Available Water in a Drastically Disturbed Serpentine Soil

Construction activity typically results in the removal of existing topsoil, exposing unconsolidated parent material that is often difficult to revegetate. In areas with serpentine mineralogy, revegetation is even more difficult because of low nutrient concentrations, heavy metal toxicity, and a low Ca:Mg ratio. Because serpentine-tolerant plants typically display xeric morphology, we hypothesized that water stress was a main factor limiting revegetation on serpentine roadcuts and that compost incorporation would increase plant available water (PAW). Four treatments were evaluated for their ability to increase PAW on a large serpentine roadcut: nontilled (ambient), tilled, and two rates of incorporated compost (270 and 540 Mg/ha or 12 and 24% by volume). Soil water release curves and moisture depletion were measured in situ using time domain transmissometry and soil psychrometers from early spring through the dry summer months. Compost incorporation (24% by volume) resulted in greater than a 2-fold increase in PAW and generated more than 4 times more vegetative biomass compared with the nontilled control. In contrast to the in situ method, by the conventional pressure plate method showed significantly less PAW in the 24% compost treatment compared with the nontilled treatment. In situ measurements of PAW agreed well with biomass data, indicating that for this atypical soil, in situ measurements were more accurate. Compost incorporation into a drastically disturbed serpentine soil is a successful revegetation technique that will increase PAW as well as the ability of the plants to access this water resource through greater root proliferation.