Soil Organic Matter Fractions as Indices of Soil Quality Changes

Soil organic matter (SOM) is commonly used as an indicator of soil quality, with different fractions being used as indices to measure changes in SOM caused by management. The objective of this study was to compare whether selected SOM fractions exhibited sensitivity to short-term changes in management. The experiment was conducted for similar to 3 yr as a split-split-plot design with crop rotation as the whole-plot treatment factor, tillage as the subplot treatment factor, and cover crop management as the sub-subplot treatment factor. Soil samples were collected at the 0- to 15-cm depth. Soil organic C (SOC) and N, particulate organic matter (POM), free light fraction (FLF), Illinois soil N test (ISNT), and easily oxidizable C (EOC) were tested as possible sensitive indices to changes in management. The stable fraction SOC was only affected by cover crop management, while C and N contents and C/N ratio of the labile POM and FLF fractions were affected by additional management practices. Between POM and FLF, the latter was the most sensitive, with cover crop management having the greatest effect. Because FLF is chemically and structurally closer to plant residues than POM, the sensitivity rank position of these fractions would probably be at least more similar if only tillage management was considered. In addition, the lack of sensitivity of ISNT and EOC to any tested management practice is added to previous studies that have raised questions of the representation of the labile SOM pool through these fractions.