Active Carbon Kit for in-Field Assessment of Managment Impacts On Soil Health.

The active organic carbon pool is important for stabilization of soil aggregates, release of nutrient by mineralization and support of general microbial activity in soil.  The size this carbon pool is responsive to soil management over a year or two. Our active carbon field kit provides a simple means to demonstrate soil differences that result from management practices. The kit is based on a bleaching reaction between easily oxidized organic C and a 0.02 M solution of neutralized KMnO_{4 (}with CaCl₂ added eliminate the need for filtering)_. The highly visual bleaching of the purple color is proportional to the amount of active C in soil. We assume that 1 mol MnO₄ is reduced from Mn⁺⁷ to Mn⁺⁴ in the oxidation of 0.75 mol of C. The field kit active C correlates very well with laboratory determinations using more sophisticated bench top equipment. Contrasting soil managment treatments have consistently shown different active C levels when measured repeatedly during different seasons over several years. The active C measured by our kit correlates quite well with such biological properties of soil as short term respiration rates, stability of macroaggregates and nitrogen mineral potential. Across a large range of soils from many regions, the active C appears to account for about 85% of the variation in total organic C, making the kit a reasonably accurate and simple field measure for soil organic matter. The one non-toxic solution has proved to be quite robust (in a brown plastic) even under adverse conditions. The pocket colorimeter has proved to be so robust, trouble free and consistent that repeated calibration is not normally needed and the absorbance value can reasonably be converted directly to active C concentration using a standard equation or graph. We will demonstrate the kit using a range of air-dry soil samples.