Calculating the Effect of Soil Organic Matter Concentration on Soil Bulk Density

Abstract

Soil bulk density (ρb) is required to estimate, evaluate, and calculate many physical soil properties and processes and is essential to convert data from weight‐based to volume‐ and area‐related data. One of the dominating factors changing ρb is the soil's organic matter (SOM) concentration that alters the soil's compressibility; ρb is an important soil structure attribute. Currently, no parameter for characterizing soil compactness giving directly comparable values for all soils is available. Therefore, our aim was to develop a general approach to calculate the effect of SOM concentration on ρb that would be universally valid for soils different in their genesis, compaction, and type of land use. To describe the effect of SOM on ρb mathematically, we used a nonlinear regression model that was parameterized and validated using published data from experiments where SOM concentration was the main ρb–affecting factor (long‐term fertilization and proctor experiments, wetlands, reclaimed soils, and volcanic soils). To obtain a standardized parameter describing the present compaction status of a site, we introduced the standardized bulk density sρb Mathematically, sρb is the intercept parameter of the used nonlinear regression model, and ranged between 0.7 and 2.1 Mg m−3 and was very simple to estimate. Another distinct advantage of this novel concept is that only one representative pair of ρb and SOM has to be known to calculate sρb as well as the bulk densities corresponding to other SOM concentrations measured on the site. This concept might also be helpful for identifying similar universal approaches to standardize the effect of other ρb affecting parameters (e.g., texture, soil depth, tillage regime), however, reassessed from the SOM effect.