NEON collects a variety of soil measurements and samples at all terrestrial field sites for physical and biogeochemical analyses, and one-time soil characterization. At aquatic sites, physical data of sediments are also collected.
Soil Core Sampling Methods
Every five years, field technicians collect soil cores from plots at terrestrial sites. Each plot is split into quadrants: three soil cores 30 cm deep and 0.5 m apart are collected from each quadrant and combined as a single soil composite representative of that quadrant.
Initial Soil Characterization
During site construction of all terrestrial field sites, NEON collects soil from each horizon at a single, temporary soil pit at terrestrial field sites, called the "megapit". Megapit soil samples characterize the soil conditions at the time of site construction. The pit is located in the locally dominant soil type, near the instrumented meteorological tower (or flux tower), and is selected to be representative of the soil sensor locations. In addition to the megapit, NEON collects soil pit samples from a number of 1 meter deep pits distributed throughout the site for a one-time characterization of soil properties. NEON works with the U.S. Department of Agriculture (USDA), Natural Resources Conservation Service Kellogg Soil Survey Laboratory to perform a suite of chemical and physical analyses on each soil sample. Results of these analyses and other relevant information are documented in the sample data. The list of laboratory analyses performed and associated data are available upon request.
Megapit Soil Sample Archiving Methods
Before NEON deposits samples in the Soil Archive, soil are air-dried, mineral soil are sieved (2 mm) and organic soil are broken up and mixed by hand in the laboratory. NEON archives a total of 1.2 to 3.6 kilograms of soil from each horizon. The total sample is split between at least four amber glass jars that are stored in locked, water-resistant and fire-resistant cabinets at ambient room temperature. After collection, megapit soil samples are stored in the NEON Soil Archive and available upon request to support community research. Surface soil samples are also available.
Megapit Soil Sample Analysis Methods
NEON works with the U.S. Department of Agriculture, Natural Resources Conservation Service Kellogg Soil Survey Laboratory, to perform a suite of chemical and physical analyses on each soil sample. Results of these analyses and other relevant information are documented in the soil sampling data. The list of laboratory analyses performed and associated data are available upon request. NEON also uses information collected from pits to calibrate soil and carbon dioxide (CO2) and moisture sensors installed in plots across NEON terrestrial sites.
An Integrated Sampling Design
Soil sampling at NEON terrestrial field sites occurs in close proximity to organismal sampling and within the airshed of the instrumented towers to establish connectivity with atmospheric and aboveground organismal measurements. Biotic and abiotic elements of soil affect the movement and availability of water and elements across ecosystems, determine the availability of nutrients to vegetation and organisms, and play a central role in the global carbon cycle.
Automated soil sensors measure physical, chemical and biological properties at the soil surface and in the underground environment. The following measurements are collected at multiple depths:
- Soil moisture
- Soil temperature
- CO2 concentration
The following measurements are collected at the soil surface
- Photosynthetically Active Radiation (PAR) at soil surface
- Soil heat flux
- Solar radiation
Key Soil Sampling within Distributed Sampling Plots
Soil samples and associated analyses characterize the following:
- Soil microbial communities, metagenomes
- Soil texture, bulk density and organic horizon mass for initial characterization; repeated measurements of soil temperature and moisture
- Biogeochemical analyses including pH, cations, anions, total carbon (C), nitrogen (N), phosphorous (P) and sulfur (S), fractions C and P, select soil N transformations (i.e., net N mineralization and net nitrification)
- Coarse and fine root biomass and total carbon (C) and nitrogen (N) concentrations in fine root biomass
Sampling Sediments for Physical Properties
At aquatic sites, sediment samples are collected from 2 stations at each site: at wadeable streams and non-wadeable river sites, the aquatic sampling reach is divided in half longitudinally and sediment is collected throughout each half. In lakes, there are also 2 stations, the first near the buoy (the deep center point in the basin), and the second near the inlet infrastructure (about 1-2 m deep). Within each station, sediment samples are collected and homogenized from 5-10 deposition zones from both stations two times per year during the spring and fall aquatic biological sampling bouts. Samples are distributed into separate containers (one per analysis type: inorganic, organic, metals and sediment size) and shipped to an external lab for a suite of analyses that also include biogeochemical properties.
- Sediment physical properties (NEON.DP1.20197)