Most plant samples are ground to pass through a 40 mesh screen on the Wiley Mini-Mill or a 1 mm screen on a model 4 Wiley Mill. Soil is crushed in a Bico-Braun soil pulverizer to pass through a 2 mm sieve. For this kind of soil grinding, the ordinary crusher or hand
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 processed through the Wiley Mini-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.