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Differences in Chemical Composition of Plant Sample Fractions Resulting from Grinding and Screening¹

Alfalfa, barley straw, corn leaves, peas, red clover, and wheat straw samples were ground in a Wiley mill and screened to separate particle sizes. Particle size samples were analyzed for N, P, K, Ca, Mg, Zn, Se, and SiO₂ The percentage composition of N, P, Ca, Mg, and Si0₂ generally increased with decreasing particle sizes of three wheat straw varieties, one baled and one hand-cut sample each of barley straw and alfalfa, corn leaves, red clover, and peas. The K concentrations were unpredictable. Selenium tended to be more concentrated in the smaller than in larger particles. The variability in chemical composition because of particle sizes points out the necessity for adequate sample grinding and mixing for obtaining representative subsamples for chemical analyses and bilogical experiments.

Key Words: nitrogen • phosphoris • potassium • calcium • magnesium • silica • selenium • zinc • particle size

² Research Soil Scientists and Soil Scientists, respectively, Snake River Conservation Research Center, Kimberly, Idaho.

Received for publication July 26, 1967.