Permanganate Oxidizable Carbon in Humus Horizons of Soils in the European Russia

The method for assaying permanganate oxidizable carbon (POxC), a characteristic recommended for assessing soil quality, is analyzed in detail. The goal is to describe the range of POxC values in humus horizons of soils of different land uses in the European Russia and to assess its applicability as an indicator of the state of soil organic matter. The particular tasks comprise: (a) selection of the soil sample weight suitable for analysis and (b) determination of the POxC range in soddy-podzolic soils (Retisols), gray soils (Greyzemic Phaeozems), and chernozems (Haplic Chernozems) of different land use types in the European Russia. The soils with a carbon content of 1.6–4.7% display a negative nonlinear correlation between the POxC value and sample weight: in both natural and arable soils, the mean POxC value decreases 1.5–3.0-fold with an increase in the sample weight in the range of 0.5–7.0 g. The most suitable weight for determining POxC is 2.5 g because it allows POxC to be determined in the widest range of total carbon content. The absolute POxC content in three soil types in the European Russia varies from 358 to 1040 mg/kg and the relative content, from 1.2 to 4.4%. The considered method for determining POxC makes it possible to assess the pool of soil organic matter most easily metabolizable by soil microbiota. Low analytical variation and the sensitivity of observed POxC values to soil and land use types suggest that this parameter is promising for assessing the state of soil organic matter.