Particle size and element concentration in ground plant material

Abstract

Abstract Two different mills were tested for their effect on grinding quality of stem and leaf of soybean (Glycine max. L.) and concentrations of several elements in the ground plant material. Particle size distribution in the ground powders was dependent on the kind of tissue and the mill used. In both leaf and stem powders, small (<90 μm) particles showed higher percent ash, absorbed more water vapor upon storage, and contained higher concentrations of several elements than the larger (90–250 or >250 μm) particles. Concentrations of P, K, Ca, Mg, Fe, Mn, Zn, and Cu were significantly higher (in cases, 6‐fold) in the smaller particles than in the larger ones. Nitrogen and Na concentrations (in most cases) were the same in particles of different size. The differences in percent ash and the element concentrations in powders with different particle size could not be solely attributed to contamination from atmospheric or soil dusts or to abrasion of elements from the mill parts coming in contact with the plant powder. Uneven distribution of elements in the original fresh plant tissue or some redistribution of elements during the drying or grinding processes are postulated to be possible causes of the differences observed in the concentrations of elements in ground powders with different particle size.