Fig. 1. Penetration resistance (kPa) with depth (cm) at Beltsville Agricultural Research Center (BARC) and Wye Research and Education Center (WREC). Average volumetric water content at time of penetration resistance measurement was 0.22 cm³ cm^–3 (WREC) and 0.27 cm³ cm^–3 (BARC) in the surface soil (0–20 cm) and 0.29 cm³ cm^–3 (WREC) and 0.39 cm³ cm^–3 (BARC) in the subsoil (20–40 cm).