PATH COEFFICIENT ANALYSIS OF SOIL PHYSICAL PROPERTIES AND ORGANIC MATTER EFFECTS ON COMPRESSIBILITY AND PENETRATION RESISTANCE OF AN ULTISOL UNDER SUGARCANE

One of the ways to evaluate the soil structural status is by means of the pre-compaction pressure and soil penetration resistance. In view of the importance of associations between two variables in soil science, the objective of this study was the decomposition of the direct and indirect effects ("path coefficient analysis") of soil physical properties and organic matter on pre-compaction pressure (sigma p) and laboratory-determined soil penetration resistance (LPS) of a cohesive Yellow Ultisol under sugarcane in the coastal tablelands of the state of Alagoas. The study was conducted on the Fazenda Progresso, of the Usina Coruripe, where five sugarcane areas were selected representing a range of cropping periods and systems: four years under winter cropping (4 year W), 14 years under winter cropping (14 year W), 14 years under summer cropping (14 year S), 30 years under winter cropping (30 year W), and 30 years under summer cropping (30 year S), A native subperennial forest fragment (Forest) was also included in this study as reference area. Path coefficient analyses were performed for the layers 0-0.20, 0.20-0.40, and 0.40-0.60 in to assess the degree of association of soil physical properties and soil organic matter with sigma p and LPS. In all layers, the cause/effect relationship of the compaction degree and soil bulk density with sigma p and LPS of the studied Ultisol was highest. In the A or Ap horizons, soil organic matter and water aggregate stability had a direct effect on the shifts in sigma p and LPS; organic matter, percentage of water stable aggregates and compressibility were higher under native forest than in the agricultural areas.