Once construction is complete, NEON will measure and sample soil at terrestrial field sites. Soil observations include sensor measurements within the tower airshed, broadly distributed collections of soil cores used for physical and biogeochemical analyses, and one-time soil characterization. NEON soil sensor measurements directly characterize soil properties, such as soil moisture and temperature. Soil samples undergo a suite of chemical and physical analyses to characterize soil properties, such as soil texture, bulk density, biogeochemistry and nutrient concentrations in fine root biomass. Request soil data through the Soil Archive. Learn more about NEON's soil collection and the availability of soil samples.
Sampling, sensor measurement, archiving and analysis methods
At terrestrial sites, NEON 1) installs arrays of sensors near the tower location; 2) collects soil cores; and 3) collects soil pit samples. Learn more about the protocols and science designs that inform soil sensor and measurement collection methods in the Data Portal Document Library.
Soil array sensor measurements
NEON installs arrays of sensors in five soil plots within the airshed of the tower at each terrestrial site. Soil sensors are installed two meters deep in the locally dominant soil type. At sites where permafrost is present, NEON installs sensors in boreholes extending three meters deep or to the bedrock. Once installed, sensors are automated, calibrated and collect continuous information at various time scales.
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. Surface soil samples are archived at external facilities, where archiving methods may differ from those below; additional archiving methods are in development.
Soil pit sampling and analysis methods
During site construction, 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 NEON tower, and is selected to be representative of the soil sensor locations. In addition to the megapit, the Observatory 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 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 archived at external facilities, where archiving methods may differ; additional archiving methods are in development.
Megapit sample analysis
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.
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.
Key soil sensor measurements
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 plots distributed across site
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
High-level data products derived from soil measurements and samples
- Soil carbon dioxide (CO2) flux
- Belowground biomass
- Soil microbial abundance and diversity