A National Soil Monitoring Network for Evaluating Long-Term Soil Quality Dynamics in the US.

Monitoring soil properties is imperative for understanding how soils change in response to land management and shifting climate patterns.  Improved management practices can increase soil quality and soil function, especially in agricultural lands.  Our objective is to establish a long-term soil monitoring network across the continental US that reflects the variability of soils, with respect to physical characteristics and environmental drivers, and utilizes the existing structure of the Natural Resources Inventory (NRI) program.  The primary focus is to detect relatively slow changing soil variables, such as soil organic carbon, by re-sampling survey locations every 5-10 years.  A subset of NRI sample sites were selected using a stratified random design that has been optimized with the Neyman allocation method.  The sample includes 5000 base sites and an additional 25,000 sites in a supplemental sample so that the network can expand to meet future monitoring needs. Sampling locations are centered on NRI survey points, and the sample plot is designed to capture local site variability for tracking trends through time.  Soil cores are taken to a 75 cm depth.  Additional site data collection includes standard soil profile descriptions and surface residue/biomass samples.  Soil samples are analyzed for a suite of physical and chemical properties, with a focus on soil quality and carbon stocks.  Data from the NRI soil monitoring network will provide critical information to quantify the response of soil properties to management and changing climate across the US at the century time scale, supporting climate change policy, food security, and overall ecosystem health.