A NEW APPROACH TO CALCULATE THE PARTICLE DENSITY OF SOILS CONSIDERING PROPERTIES OF THE SOIL ORGANIC MATTER AND THE MINERAL MATRIX

Abstract The particle density of soil ( ρ S ) represents one of the soil's basic physical properties and it depends on the composition of both the mineral and the organic soil components. It therefore varies for different soils, e.g. within the group of mineral soils, and ranges from 2.4–2.9 g cm −3 . Hence, awareness of this variability is important for properties estimated by a calculation involving particle density. Because ρ S depends on both the soil's solid mineral particles and soil organic matter composition, we derived a function based on the mixture ratio of these two soil components. This approach represents a further development of earlier investigations dealing with the influence of organic carbon ( C org ) on ρ S . To parameterise this function, two data sets were used: (1) data from soils with C org contents between 0% and 54.88% and corresponding values of ρ S between 1.49 and 2.72 g cm −3 ; and (2) data from soils of 17 German long-term experiments contrasting in soil texture and in soil mineral inventory. Data set 1 was used to quantify the influence of soil organic matter on ρ S , and data set 2 was used to calculate the influence of mineral matrix on ρ S . The soil organic matter has two major influences on ρ S : (1) via a mass effect (expressed as a mixture ratio between organic and mineral soil components); and (2) via a quality effect (expressed as calculated changes in particle density of organic soil components). Here, we calculated that with increasing content of soil organic matter (0–100%), the particle density of organic soil components rose from about 1.10 to 1.50 g cm −3 , and present possible reasons for this phenomenon. Additionally, we demonstrate that the mineral matrix of the soil affects ρ S especially via variations in the mineral inventory, but conclude that differences in particle size distribution of soils were to a lesser extent suitable for describing the influence of the mineral matrix on ρ S . Overall, using our approach should generate more realistic values of ρ S , and consequently of all calculated parameters which are sensitive to ρ S .