Changeability of Content and Storage of Soil Organic Matter: an Analytical Review

Abstract

An aim of analytical review is to systematize information about quantitative characteristics of changeability in the content and storage of organic carbon (Corg) in soils. The review considers evaluations of validity and reproducibility of Corg determination, spatial variability and heterogeneity of Corg at different hierarchic levels of soil cover pattern and change them in time. The most powerful factor of Corg changeability in soils is spatial variability. Ascending trend of absolute standard deviation and coefficient of variation for Corg content and storage in soil with the increase in the logarithm of site area has been revealed. However, the values of the indicators of spatial variation of Corg have a wide spread in each narrow range of variation of the plot area, which leads to high uncertainty of the estimates as the area coverage increases. Direct dry combustion method is considered preferable among used methods for determination of Corg content. It allows obtaining valid (i.e. with the least systematic deviations) and well reproducible data. Indirect Turin’s and Walkley-Black’s methods systematically underestimate the Corg content and have reproducibility comparable with amplitude of seasonal dynamics and with minimal values of spatial variability indices within elementary soil area. Obtaining estimates of long-term trend of Corg content strict adherence to stringent monitoring conditions over time intervals of more than 15 years. Spatial variation of Corg storage is stronger than Corg content, which further increases the monitoring requirements.