Susceptibility to Compression of a Clay Loam Haplaquoll

The objective of this study was to determine the compressibility of a poorly drained clay loam soil cropped to corn ( Zea mays L.) with moldboard plowing as primary tillage (CN) or with no tillage (NT). Undisturbed cylindrical cores (100 cm 3 )obtained from planter‐tracked (WT) and untracked (NWT) interrows just prior to harvest, were subjected to uniaxial compression after being equilibrated at soil moisture potentials (ψ) of −5, −10, −20, and −40 kPa. The precompression (over‐consolidated) and virgin compression regions were isolated by plotting bulk weight volume ( v ) against the logarithm of applied pressure. The breakpoint or precompression pressures (σ p ), which separated the over‐ and virgin compression regions, were determined using a statistical procedure. There was no apparent σ p for cores from CN‐NWT interrows with ψ at or above −10 kPa. Tracking of tilled interrows resulted in the presence of over‐consolidated regions at all moisture potentials. Virgin compression indices (slopes) decreased in the order CN‐NWT > CN‐WT > NT‐NWT > NT‐WT. A highly significant correlation ( p < 0.01) was obtained between σ p and the undrained strength as measured by the fall‐cone device.