Assessment of soil strength variability in a havested loblolly pine plantation in the Piedmont region of Alabama, United States

Abstract

hilechanised forest harvest operations are a significant source of soil corrlpacrlon for which intensive rillage is prescribed to a!leviate soil compaction and ensure successful regerreration of planted pine trzes. Soil strength is a poiential indicaror of comi;zction status of a harvest tract due tc its sensitivity and the ease of data collection with a cone penetrometer, but estimates may vary widely throughout a harvest tract. A IoSlolIy pine (Pinus raeda L.) plantation that had been harvested in winter 1998 was studied to assess soil strength and its spatial qualities through the measurement of soil strengrh on tw.o sampling scales, and to identify areas ofthe harvest tract where tillage operations would be beneficial. Cone index measurements indicated a high degree of variability in soil strength regardless of the scale of measurement, and high soil strength !evels throughout the soil profile. Spatial dependence was high in thesurface and immediate sabsurface soil layers ofeach point grid system and was attributed to the impact oftraffic or topographic position on soil strength. Spatial dependence was not detectable for the lowest subsoil layers of the large-scale sampling scheme. The -short ranges of spatial correlation associated with cone index estimations and the presence of compacted subsoil layers throughout the study area suggested the need to perform tillage throughout the harvest tract to ensure alleviation of subsoil compaction for adequate regeneration.