Drying and Grinding
Drying
Most samples that are received fresh or are suspected moist will be put into paper bags with adequate room for air movement within the bag and dried at 55-60°C for approximately 12 hours or until the material snaps or breaks easily.
Exceptions:
- Range samples take 24 hours or more to dry.
- Power plant ash samples take 3 days to dry.
- Solid pieces of wood take 24 hours to dry.
- Rice soils takes 2 days to dry.
- Any material larger than gallon size will take 1 or more days to dry.
- Fruits, vegetables, and manure material go through the freeze drying process, pureed if needed, and weighed before and after the freeze drying process.
- All samples are turned every 24 hours except freeze drying material.
Grinding
Most samples are ground to pass through a 40 mesh screen on the Intermediate Wiley Mill or a 1 mm screen on a model 4 Wiley Mill and soil is crushed in a Bico-Braun soil pulverizer to pass through a 2 mm sieve.
Exceptions:
- 20 mesh screen used on grape blades due to tricomb separation from leaf.
- 20 mesh screen used on sugar beet petioles due to high sugar content.
- 20 mesh screen used on walnut leaf due to fibers in veins.
- 10 mesh screen used on corn stalks due to high sugar content.
- Freeze dried samples are easily crushed manually.
- Soil for carbon analysis is ground to a powder fine enough to pass a 50 mesh sieve.
- Timing:
- Most samples that are smaller than the size of a fist are sent through the Intermediate Wiley Mill. On the average, 1 minute per sample if less than 15 grams or 3-4 minutes for samples of 100-150 grams.
- Samples larger than two fists are sent through the model 4 Wiley Mill.
- Average time is 4-5 minutes per sample.
- Samples between the size of one and two fists are ground through either grinder depending upon the type of material.
- All residual material held in either grinder is put with the ground material and thoroughly incorporated.
- Soil grinding time is from 1-4 minutes per sample.
- Fine soils vs. large hard soils that need to be pounded smaller first.
- Clean soils without debris vs. with debris that needs to be sieved out.
- Material size runs from 100 grams to 2 kg.
- Any material smaller than 100 grams is ground by mortar and pestle.
- All other samples that are not dried and ground are refrigerated until analysis.