ASRIS Technical Specifications V1.6

Layer-1 Texture and clay contentThe control section and convention for recording Layer-1 Texture and Layer-1 Clay content are as follows.• If there is a single A1 horizon without subdivisions (e.g. A11, A12), then Layer-1 Texture and Layer-1Clay content are the texture and clay content of the A1 horizon.• If there are subdivisions within the A1 horizon, the Layer-1 Texture and Layer-1 Clay content are takenfrom the thickest A1 horizon layer within the top 0.20 m of the soil profile (the upper layer is used ifthicknesses are equal).• If the surface layer is an O horizon, the texture of the underlying A1 horizon is used in accord with theabove criteria.• If the surface layer is an O horizon and there is no underlying A1 horizon, the Layer-1 Texture and Layer-1 Clay content are taken from the thickest layer in the 0.20 m directly beneath the O horizon.• If the surface layer is a peat, Layer-1 Texture and Layer-1 Clay content are recorded using the 7 classesof organic materials defined by NCST (2009) and shown in Table 23.Layer-2 Texture and clay content• The Layer-2 Texture and Layer-2 Clay content usually refer to the average texture and clay content ofthe lower portion of the A horizon. The A horizon at this depth may be an A1, A2, A3, AB, A/B orsubdivision thereof. Layer 2, if present, is always below Layer 1.• If the surface layer is not an A1 horizon (e.g. O horizon) and there is no underlying A horizon, theattribute is recorded as missing (NA for texture, –9999 for clay content –see page 66)• If the A horizon is thin and the profile only has a few layers, Layer-2 Texture and Layer-2 Clay contentmay be recorded as missing.• If the A horizon is thin and multiple contrasting layers occur deeper in the profile, Layer-2 Texture andLayer-2 Clay content can refer to layers below the A (e.g. B1, 2A, 2B, 2D).Layer-3 Texture and clay contentThe B-horizon definition below follows the Field Handbook with the modification suggested by Isbell (2002)(the criteria in part being “…an illuvial concentration of silicate clay, iron, aluminium, humus, carbonates,gypsum, or silica, alone or in combination”). The Layer-3 Texture and Layer-3 Clay content are defined inmost cases as follows.• If a B horizon is present, the Layer-3 Texture and Layer-3 Clay content are the texture encounteredin the upper B (usually B1 and B21).• If no B horizon is present and the sequence consists of an AC profile, the Layer-3 Texture and Layer-3Clay content generally refers to the materials directly below the A horizon (usually the upper 0.20m).• In more complex profiles, Layer-3 Texture and Layer-3 Clay content refer to the third functional layerin the profile.37