Critical Limits for Soybean and Black Bean Root Growth, Based on Macroporosity and Penetrability, for Soils with Distinct Texture and Management Systems

Abstract

Soil compaction is a worldwide problem in agricultural areas, and it is important to define soil properties and reference values that allow knowledge of the compaction level for decision making. The objective of this study was to define the critical values of physical properties associated with the compaction of soils. Three Ultisols and two Oxisols, under different management systems, were collected at different depths for an evaluation of particle size, volumetric moisture, bulk density, and porosity. In the field, soil resistance to penetration and the root length of the soybean and edible black bean crop were measured. The soil profiles presented horizontal layers with similar resistance, but in some cases, there is discontinuity of these layers, which allows the roots to use the zones of lower resistance to deepen in the profile. The values of bulk density and resistance to penetration critical to soybean and edible black bean (only in sandy loam soil) root growth, according to soil textural class, are: sandy loam = 1.66 Mg m−3 and 1.5 to 2 MPa; loam and clay loam = 1.52 Mg m−3 and 1 to 1.5 MPa; silty clay loam and silty clay = 1.32 Mg m−3 and 1.5 to 2 MPa; and clay = 1.33 to 1.36 Mg m−3 and 2 to 3.5 MPa.