Compaction modeling of contrasting brazilian tropical soils: Implications of pseudosilt and reference values in proposing pedotransfer functions

• Brazilian tropical sandy and very clayey soils have contrasting physical behaviours. • The most clayey and highly weathered samples present high susceptibility to compaction. • Pedotransfer functions describe the structural changes in Brazilian soils well. • Standard particle size analysis has low efficiency for analysing highly weathered and clayey soils. • Pseudosilt in these soils is merely descriptive and not functional. Compaction is a serious driver of physical soil degradation worldwide. To address, it is necessary to define reference values in representative soils for structural interpretation. The hypothesis of this study is that, for the compaction modeling using transfer functions for Brazilian tropical soils, the proposition of reference values for soil physical attributes is intrinsic to soil texture and may be influenced by the analytical aspects of their determination The aim was to model soil compaction in contrasting Brazilian tropical soils by evaluating two soils with contrasting textures, defining beneficial or limiting/critical reference bulk density values for structural conditions associated with edaphic functions, and providing improvements to pedotransfer functions to assess soil structure by considering the analytical aspects of soil physical attributes. To achieve this aim, undisturbed soil samples were collected from sandy soil with 73 g kg −1 clay and very clayey soil with 823 g kg −1 clay. These samples were subjected to additional compaction by uniaxial compression testing, and structural changes were quantified through increases in bulk density (Bd), the least limiting water range, soil porosity, and the following pressures: preconsolidation (σp), beneficial (σb) and limiting (σl). The results indicated that the main physical limitations of sandy soil are related to its very low ability to supply water to plants, making crops very susceptible to water stress in these pedoenvironments, whereas for very clayey soil, susceptibility to compaction is of the greatest concern for management responses. The Bd reference values under all the structural conditions of the soil decreased with increasing clay content and quantifying them made it possible to update pedotransfer functions for the textural ranges of the two modelled soils. Thus, it is suggested to quantify the total clay in soil or, alternatively, establishing a boundary condition of the sum of textural fractions smaller than 0.05 mm (clay + silt), as these soils, especially very clayey soils, are pseudosilt, though this characteristic is merely descriptive and not functional.