Compression characteristics of a clay soil as influenced by crops and sampling dates

This study was undertaken to determine the influence of previous crop sequences on soil compression behaviour. Soil compression tests were performed on undisturbed soil samples of a Kamouraska clay which had been cropped continuously for 4 years to barley, corn, alfalfa, or timothy. Samples were taken from the surface soil in the non-trafficked zone, five times during the season. Cropping treatments had small but significant effects on soil compression characteristics. Soils on which crops were grown presented lower bulk density under standard compression (300 kPa) and higher pre-compression pressure values than the soil left unplanted (fallow). These effects were attributed to water content at time of sampling which was lower in the cropped than in the bare soils. Seasonal variations of these two virgin compression parameters were important and were related to soil moisture. Conversely, the soil compression index (slope of the virgin compression line) was not affected by crops or water content and seems to be a characteristic dependent on soil constituents.