Measurements
- Several soil, vegetation and atmospheric parameters are monitored at the three
sites.
They include:
- Above Ground Biomass and Leaf Area Index: Above ground biomass and leaf area index
are determined from destructive samples taken from each study site.
- CO2, Water and Energy Fluxes: Landscape-level fluxes of CO2, water vapor and
energy are measured with the eddy covariance flux tower systems at the three study sites.
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- Intensive Management Zones: Within each site, six small (20m x 20m) measurement areas
(intensive management zones or
IMZs) were established for detailed process-level studies of soil carbon dynamics, crop growth and
partitioning, soil moisture, canopy and gas exchange, and crop residue decomposition. The locations were
selected using fuzzy k-means clustering applied to six data layers resolved to 4m x 4m cells. The data
includes elevation, soil type, electrical conductivity, soil organic matter content, digital aerial
photographs and near infrared remotely-sensed imagery. The IMZs represent all major occurrences of soil
type and crop production zones in the sites and allow accurate upscaling of ground measurements to the
whole field level.
- Litter Decomposition: Above and below ground litter decomposition are measured in each IMZ
with standard litterbags. Litter amounts are quantified, and litter composition (carbon and nitrogen) is determined in
each IMZ.
- N2O and CH4 Fluxes: Fluxes of N2O and CH4 are
being measured at the three sites using a chamber method.
- Plant Carbon Assimilation: Responses of net CO2 assimilation rate and stomatal conductance
with respect to relevant biophysical controlling factors (i.e. light intensity, leaf temperature, vapor pressure deficit,
and ambient CO2 concentration) are monitored using leaf photosynthesis chambers.
- Plant Root Carbon Dynamics: Standing root biomass (to a depth of 0.6 m) is quantified by replicate
transect sampling within each IMZ
twice during the growing season. In addition, below ground carbon deposition is monitored through analysis of
δ13C from implanted soil cores that have a δ13C signature vastly different
than the growing crop.
- Remote Sensing of CO2 Exchange: Upwelling and downwelling canopy spectral radiance are
measured using two separate systems: a) two hyperspectral radiometers mounted on an all-terrain sensor platform and
b) a set of upwelling broadband instruments, each mounted on the centrally located radiation tower at each site with a
complementary downwelling radiometer located nearby. The hyperspectral system provides a spatial sampling strategy
at each of six, randomly selected sampling plots. The fixed-mount, broadband system complements the spatial sampling
by providing temporal coverage of upwelling and downwelling radiance through daylight hours of the growing season.
In addition, leaf optical properties and the absorbed fraction of photosynthetically active radiation (PAR) are measured
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- Soil Carbon Stocks: Soil samples for determination of initial soil
carbon and nitrogen stocks were collected at 236 - 264 sampling locations per field in April 2001. Sampling
included a triangular sampling grid, transects and random locations which included the
IMZ areas.
Soil carbon and nitrogen concentrations and bulk density were measured in 0-5, 5-15 and 15-30 cm depths. In
addition, detailed soil characterization up to 150 cm depth was done in each IMZ. Soil sampling is repeated
annually in all IMZs to track changes in carbon, nitrogen and bulk density over time.
- Soil Surface CO2 Flux: Soil surface CO2 fluxes are measured with a portable gas
exchange system connected to a stainless steel sampling chamber. Permanent collars are placed at select locations
within each IMZ
in each study site. Surface fluxes are determined for each study site at approximately one week intervals.
- Soil Water: Soil water conditions in the root zone are monitored continuously at four
depths (0.10, 0.25, 0.5 and 1.0 m) in four IMZs
at each site.
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