Assessment of soil strength variability in a harvested loblolly pine plantation

Mechanised forest harvest operations are a significant source of soil compaction for which intensive tillage is prescribed to alleviate soil compaction and ensure successful regeneration of planted pine trees. Soil strength is a potential indicator of compaction status of a harvest tract due to its sensitivity and the ease of data collection with a cone penetrometer, but estimates may vary widely throughout a harvest tract. A loblolly pine (Pinus taeda L.) plantation that had been harvested in winter 1998 was studied to assess soil strength and its spatial qualities through the measurement of soil strength on two sampling scales, and to identify areas of the 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 levels throughout the soil profile. Spatial dependence was high in the surface and immediate subsurface soil layers of each point grid system and was attributed to the impact of traffic 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