Oxisol toposequences developed from basaltic rocks in Parana State, Brazil. II - Relationship between clay fraction mineralogy and physical soil properties

Soil structure (type, size and development) defines the total soil porosity and macro and microporosity distribittion, and is considered to be one of the most important agricultural soil properties. The aim of this work was to study the effect of the clay, fraction mineralogy, including the crystallographic mineral characteristics, in the soil physical properties of two Oxisols developed from the basaltic rocks, in different landscape positions (toposequence) in Parana State, Brazil. With this objective, the soil profile was morphologically described and the Bw1 and Bw2 horizons samples were submitted to physical and micromorphological characterizations. The hematite (Hm), goethite (Gt) and gibbsite (Gb) were responsible for the increased macroporosity and total porosity (TP) and reduced bulk density (BD) in the Red-Yellow Latosol (LBw). The effect of haolinite (Ka) was opposite. The correlation between physical properties and Ka, Hm, Gt, Gb concentration in the clay fraction were not significant for the Dusky Red Latosol (LVdf). The amorphous Fe and Al oxides apparently were more important for the increased macroporosity and improved TP of the LVdf horizons. The only significant correlation in crystallographic characteristics of the clay fraction minerals was observed between Gb crystal size [MCD(110)] and TP (negative correlation) and BD (positive correlation) for the LVdf A similar behavior was observed for mean crystal diameter of Hm (104 direction) for the LBw.