Classing the soil skeleton (greater than two millimeters): proposed approach and procedure

In soil science analytical procedures apply almost exclusively to the fine earth (2 mm). Rock fragments or skeleton (2 mm) are regarded as inert and discarded during sieving; however we have found that the clasts display physical and chemical properties that can equal or surpass those of the fine earth. These properties depend largely on the degree of alteration of the clasts. In light of these findings we developed a method to separate the rock fragments into weathering classes. This method has been applied to five European skeleton-rich soils derived from different parent materials. Color intensity roughness and irregularities of the surfaces, cracks and surface features of the exposed minerals were considered reliable criteria for the separation or the clasts. We notice also that the degree of alteration of the clasts corresponds to size: as size decreased weathering increased. Consequently sieving could be used for separating the weathering classes. On the basis or these criteria, clasts were differentiated into highly moderately and slightly altered. There are statistically significant differences among the weathering classes in terms of bulk density porosity organic C, total N, and cation-exchange capacity. There are no statistically significant differences in pH. The results confirm that the procedure separates relatively homogeneous and different classes of rock fragments. We also compared the characteristics of the soil skeleton to those of the fine earth and fresh rock. We concluded that not characterizing the skeleton of the soils may provide distorted information on the capability of these substrata