KBS004: Composite Soil Sampling - MCSE

Active

Replaces MCSE: Baseline Soil Sampling

In use from 1989-04-01

Abstract

Composite soil samples are made by physically mixing individual soil cores taken within a specific area into one homogenous sample. Compositing reduces the number of analyses to be performed and is designed to provide a representative sample of the area or treatment.


Soils of the Main Cropping System Experiment (MCSE) are sampled throughout the growing season by taking soil cores at each of 5 sampling stations per plot. Samples are then composited by plot. Composite samples are sieved and then subsampled for soil moisture and inorganic N analysis, and annually subsampled for determination of N mineralization potential. Samples may also be subsampled for other analyses as requested by various investigators.


Sampling frequency: minimum of once per month throughout the growing season (March–November), typically biweekly from April–September.

Protocol

Soil cores are taken at each of the 5 established sampling stations per plot (see plot maps with sampling station locations). Soil cores are taken within a 2 m radius of each station flag by sampling (push) probes (2 cm dia., 25 cm depth) or by bucket auger (5 cm dia., 25 cm depth) when the soil is too dry to use push probes. A standard sampling consists of 2 cores at each station. All cores from one plot are composited in the field into one sampling bag. For row crop plots, an equal number of cores are taken within rows and between rows, avoiding wheel tracks between rows. For poplar plots, an equal number of cores are taken within the tree row and between tree rows. Every effort is made to sample all plots on the same day. Forested sites may be sampled by one person at the same time the main site is being sampled or, if necessary, they may be sampled in the afternoon while soil from the main site is being sieved.


Composited soil samples are brought to the lab and sieved through a 4 mm screen to remove debris and homogenize the soil sample. Each treatment has a permanently designated screen to reduce contamination between treatments. Latex gloves are worn for sieving and mixing the soil.


Field moist soils are stored in closed plastic bags at 4 C until Gravimetric Soil Moisture and Soil Inorganic N determinations are completed. All samples, except the April sample, are disposed of at the end of the year. The April sample is air-dried and archived. Once per year, typically in July, composite samples are subsampled for N Mineralization Potential.

Materials

    • Printed bag labels
    • 8×4×18 Plastic sampling bags
    • Sharpies
    • Butter knives
    • Site and sampling station maps
    • Soil sampling probes (bucket augers when soil is too dry for push probes)
    • Buckets
    • Latex gloves
    • Tote Trays
    • Brush
    • 4 mm mesh soil sieves (one for each treatment)

Procedure

  1. Label plastic bags with appropriate information about the sample (e.g. project, date, plot, variate). Cover labels with clear mailing tape to secure label to bag and protect it against moisture.
  2. Prepare 5-gallon sampling buckets. Each bucket should have the following: site map, sharpie marker, butter knife, sampling bags, and soil probe.
  3. Take samples to 25 cm depth (as marked on the soil sampling probe or auger) at each of the 5 sampling stations. A butter knife is helpful in removing soil from the probe. In row-cropped systems, take two cores per station: one in the row and one between rows, avoiding wheel tracks. Take the same number of cores from non-cropped systems. Composite all samples for one plot in one plastic bag.
  4. When soil conditions are too dry to allow for sampling with a push probe then a bucket auger can be used.
  5. Tie the sample bag and place near the edge of the plot to be picked up when the sampling is completed.
  6. Take a core at the edge of the next plot to clean the soil probe and reduce contamination between plots.
  7. Continue sampling each plot in the same manner until all have been sampled. Sampling should be completed within one day.
  8. Pick up soil samples and return to field lab.
  9. Separate soils by treatment.
  10. Find the 4-mm mesh soil sieve that corresponds to the treatment being sieved. Each treatment has its own sieve. Sieves are stored in the field lab.
  11. Wear latex gloves while sieving and mixing. Sieve soil into a plastic tote tray and return sieved soil to the original plastic sample bag. Discard rocks and large organic matter debris that remains on the screen.
  12. Brush sieve and tote tray clean.
  13. Change latex gloves after each treatment.
  14. Store soil samples in a 4 degrees C refrigerator until soil moisture and inorganic N analysis are complete.
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