Soil Moisture Extraction by Vegetation in a Mediterranean/Maritime Climatic Regime

Timing and extent of soil moisture extraction are critical when evaluating perennial grasses for their adaptability to the climate and soils. We hypothesized that in the southwest Oregon foothills perennial grasses able to extract moisture early in the growing season should be more competitive with resident annual plants than those that utilize soil moisture later. Our objective was to assess the potential for competition of selected native and introduced perennial grasses with annual plants. The experiment consisted of growing perennial grasses with and without competition from the resident annual community and evaluating soil moisture throughout the growing season with a neutron probe. ‘Berber’ and ‘Palestine’ orchardgrasses ( Dactylis glomerata L.) extracted moisture earlier than later growing ‘Oahe’ intermediate and ‘Alkar’ tall wheatgrasses ( Agropyron intermedium [Host.] Beauv. and A. elongatum [Host.] Beauv., respectively). Soil moisture contents in plots of Idaho fescue ( Festuca idahoensis Elmer), a native and the earliest growing and maturing perennial grass in the study, were not consistently lower than soil moisture contents in plots of later growing perennial grasses. End‐of‐season soil moisture contents were similar ( P < 0.10) in perennial grass plots and plots dominated by yellow starthistle ( Centaurea solstitialis L.). Resident annual grasses left approximately 50% more soil moisture than perennial grasses or annual forbs. In years with an early summer drought, earlier growing perennial grasses should be able to satisfy their growth requirements.