Cover crops as a management strategy to modify penetration resistance in the topsoil of coarse-textured soils

Soil penetration resistance (PR) is strongly influenced by soil water conditions and may restrict root growth in coarse-textured soils. This study evaluated cover crop effects on soil mechanical behavior by integrating soil water retention and PR models in a sandy loam Oxisol under six years of no-till management in Presidente Bernardes, São Paulo, Brazil. A randomized complete block design included five replicates and five treatments: fallow (FA), ruzi-grass ( Urochloa ruziziensis ) (BR), millet ( Pennisetum glaucum ) + crotalaria ( Crotalaria spectabilis ) (MI+CR), millet + ruzi-grass (MI+BR), and a mix of millet, ruzi-grass, crotalaria, and forage radish ( Raphanus sativus ). Undisturbed soil cores (5 ×5 cm) were collected from the 0–10 cm layer to determine soil water retention and PR curves. Water contents estimated at selected matric potentials were entered into the PR model together with soil bulk density (Bd) to predict PR and critical bulk density (Bd C ). Effective stress (σ e ) was calculated from matric potential, degree of saturation, and total porosity. Model R 2 values ranged from 0.87 to 0.91 for water retention and from 0.66 to 0.79 for PR. Results showed that PR remained below 2.0 MPa at −60 and −100 hPa, with restrictive values appearing at −300 hPa and becoming more frequent at −800 and −1000 hPa. Bd C decreased with drying, while σe increased, closely tracking the rise in PR. BR showed the lowest susceptibility to drying-induced PR increases, whereas FA and MI + BR were the most sensitive, and Mix showed an intermediate response, highlighting ruzi-grass as the most effective cover crop for mitigating mechanical impedance in sandy loam soils.