Apparent field texture (Figure 11).
Apparent field texture.—A tactile evaluation of soil texture in the field, with no inference as to expected laboratory results for textural analysis. Some soil samples cannot be adequately dispersed in the laboratory for accurate texture analysis using standard procedures. Factors that hinder the effectiveness of standard procedures for particle-size analysis include high content of low-activity clays or iron oxides, andic or spodic materials in soils having an isotic mineralogy class, carbonates, and gypsiferous materials. These soils tend to have ratios of 1500 kPa water to clay outside the normally expected range of 0.25 to 0.6, and clay content is therefore estimated rather than measured for family particle-size class as indicated in Soil Taxonomy (see note preceding item C in the key to particle-size and substitute classes). The apparent field texture reported in the soil profile description commonly appears coarser than the calculated result for placement in a taxonomic family particle-size class (e.g., fine sandy loam apparent field texture vs. fine family particle-size class).
Figure 11.—An Oxisol from the Cerredo physiographic region of Brazil. Oxisols may have 75 percent or more clay; however, both the structure and “feel” of Oxisols are deceptive. Upon first examination, the soil may appear structureless and have the feel of a loamy texture. The clay particles are bound by iron oxides in a matrix with strong, very fine and fine granular structure. As demonstrated in this sample, the apparent field texture was clay loam; however, laboratory analysis indicated the true texture was clay. The gritty feel is attributed to the very firm, very fine structural aggregates referred to as “pseudo sand”.
Apparent field texture (Figure 11).
Apparent field texture.—A tactile evaluation of soil texture in the field, with no inference as to expected laboratory results for textural analysis. Some soil samples cannot be adequately dispersed in the laboratory for accurate texture analysis using standard procedures. Factors that hinder the effectiveness of standard procedures for particle-size analysis include high content of low-activity clays or iron oxides, andic or spodic materials in soils having an isotic mineralogy class, carbonates, and gypsiferous materials. These soils tend to have ratios of 1500 kPa water to clay outside the normally expected range of 0.25 to 0.6, and clay content is therefore estimated rather than measured for family particle-size class as indicated in Soil Taxonomy (see note preceding item C in the key to particle-size and substitute classes). The apparent field texture reported in the soil profile description commonly appears coarser than the calculated result for placement in a taxonomic family particle-size class (e.g., fine sandy loam apparent field texture vs. fine family particle-size class).
Figure 11.—An Oxisol from the Cerredo physiographic region of Brazil. Oxisols may have 75 percent or more clay; however, both the structure and “feel” of Oxisols are deceptive. Upon first examination, the soil may appear structureless and have the feel of a loamy texture. The clay particles are bound by iron oxides in a matrix with strong, very fine and fine granular structure. As demonstrated in this sample, the apparent field texture was clay loam; however, laboratory analysis indicated the true texture was clay. The gritty feel is attributed to the very firm, very fine structural aggregates referred to as “pseudo sand”.