We grind plant and soil material using glass jars with teflon lined caps
(Qorpak), stainless steel rods, and a tumbler. The rods are 3, 5, and 6 mm in
diameter and 2.5 cm long. The rods are added to the jars in a ratio of 3:2:1
(small:medium:large diameter); the total number of rods to use depends on the
size of the jar and amount of sample. We tumble the samples at a rate of about
40 rpm for 20 min to an hour or more. Our tumbler comes from U.S. Stoneware.
Reference: Kelley, 1994. Conveyor-belt apparatus for fine grinding of soil and
plant materials, Soil Science Society of America Journal, v. 58, p. 144-146.