The Determination of Macro‐Organic Matter in Soils 1

THE DETERMINATION OF MACROORGANIC MATTER IN SOILS THE term macro-organic matter is introduced to denote coherent particles of organic matter separated from the soil by screening and decantation procedures. Such separates have been variously termed "underground yields" by Shively and Weaver (6), "roots and other pknt residues" by Saharina (4), "root fibre" by Stevenson and White (7), and "underground plant materials" by Troughton (8). Washing and screening methods have been described by Goedewaagen (2) and Jacques (3). Soil cores were thoroughly wetted by soaking, then washed on top of a wire or horsehair screen of ca. 0.5 mm. aperture. Macro-organic matter was separated from the sand residue by washing in and pouring from shallow dishes onto a screen or baffle. Large clumps of organic debris were usually removed with tweezers. Salonen (5) ashed the separate obtained by washing and screening, and determined the weight of ash-free material. These methods were tedious, five to ten samples being determined per man day, and were liable to personal error. Barley (1) used a flotation method, in which macro-organic matter was separated by centrifugation of crushed samples suspended in salt solutions of density 1.2 gm. per ml. The separate was decanted onto a filter, washed with water and oven dried. This method was relatively rapid (20 determinations per man day), but it exposed expensive centrifuge equipment to corrosion, and efficiency of recovery was variable (80 to 100%).