Characterizing soils at NEON sites to inform sensor-based sampling strategies

Background/Question/Methods

Soils are one of the most complex components of terrestrial ecosystems and play a key role in a range of ecological properties and processes, including carbon storage, ecohydrology, nutrient cycling, and supporting hyper-diverse biological communities. As a result soil measurements represent a major focus of the National Ecological Observatory Network (NEON) and soil-based sensors will monitor profiles of soil temperature, moisture, CO₂, and root activity, as well as soil heat flux. Soil pits are being used to characterize soil at NEON sites in order to maximize the accuracy of these measurements, to provide information on soil properties to NEON users, and to establish a soil archive as a community resource. Specifically, at each site a location was identified with the same soil type as the sensor measurement locations and 1) the soil profile was described to 2 m or bottom of C horizon if shallower, 2) soil physical and chemical properties were measured (bulk density, texture, pH, and elemental composition), 3) samples were collected to calibrate soil moisture sensors to the local soil type and measure CO₂diffusivity, and 4) samples were collected for the NEON Terrestrial Instrument System Soil Archive. Here we present results from the initial phase of soil characterization.

Results/Conclusions

To date, nine soil profiles have been described and sampled, with sampling at all 60 sites expected to be completed within 3-4 years. Two-thirds of the soil series identified in the soil pit differed from the dominant soil series reported in the USDA NRCS soil survey map. On average, 7 soil horizons were identified from each soil pit, however, this varied from 4 horizons at Klemme Range Research Station, OK and Ordway-Swisher Biological Station, FL to 10 horizons at Harvard Forest, MA and Dakota Coteau, ND. The average thickness of all 63 soil horizons was 26 cm (minimum-maximum: 2-97 cm). This horizon information is being used to ensure that NEON’s soil sensors are placed at depths that reflect the full range of soil properties in the soil profile at each site. In addition, soil from a total of 43 horizons, representing 6 sites, has been processed and placed in the Archive (soil from the remaining horizons is being processed). At the time of writing the method for requesting samples from the Archive is under development, but once it is in place NEON’s Terrestrial Instrument System Soil Archive aims to be a valuable resource for the scientific community.