Effects of Seasonal Variations in Soil Moisture and Temperature on Earthworm Communities.

Earthworms are commonly known as ecosystem engineers because of the dramatic effects their activity can have on soil properties and above ground plant communities. Earthworm activity can affect nutrient cycling, soil structure, soil organic matter, soil pH and infiltration. However, the impact of earthworms is dependent on many factors including population density, species composition,  soil type and climatic variables, all of which display significant spatial variability.  Furthermore, earthworms become inactive or die when soil moisture levels become too low or soil temperatures rise too high, indicating that earthworms may be inactive for a large portion of the year in some regions. This study investigated changes in soil moisture, soil temperature and earthworm density, biomass and population structure over one growing season in winter wheat production systems within the Palouse region of northern ID and eastern WA. Beginning in April of 2014 fields at 6 locations, in two rainfall zones (460-490 mm and 590-640 mm) were sampled biweekly for earthworm density and biomass. Sites were also equipped with continuous soil moisture and temperature monitoring stations and characterized for bulk density, pH, SOM, and texture. Initial results include earthworm densities ranging from 19 to 240 individuals m^-2 for April and May with similar average densities of 43.17 and 45.7 individuals m^-2 in the low and high rainfall zones, respectively. Mean biomass was also not significantly different between zones with 29.7 g m^-2 in the low rainfall zone and 32.8 g m^-2 in the high. These numbers reflect warmer, drier soils (means of 17.2% volumetric soil moisture, 11.8 °C) at the lower rainfall sites and cooler wetter soils (means of 27.9% and 10.3 °C) at the higher rainfall sites. Additional results from the first 7 months of this study will be presented.