Mineralogy and pore size distribution of clayey Oxisols with granular structure and the effect of management systems

Abstract

There is a general consensus in the tropical literature on the crucial role played by clay mineralogy in the formation of the very stable granular structure of Oxisols, which has been mainly attributed to gibbsite. Gibbsite hinders the face-to-face adjustment of kaolinite plates responsible for the very common block structure. While kaolinite predominates in the clay fraction of most Oxisols, gibbsite occurs in variable contents. Studies have reported that the granular structure is secondarily associated to goethite and hematite, soil organic matter and biological activity. However, the variation of clay mineralogy on the alteration of the pore size distribution of clayey Oxisols with granular structure remains unclear. So, the main aim of this work was to study several granular Oxisols from the Brazilian Cerrado biome, under native vegetation, with clayey texture and variable clay mineralogy, focusing on the influence of the latter on pore size distribution and related physical and hydric attributes, and to assess how these attributes are affected by management practices. Results showed that greater contents of gibbsite led to an increase in the micropores/total pores ratio and a higher frequency of smaller pores distribution. Low mesoporosity and water availability values were common in the studied Oxisols. A case study was conducted to evaluate the influence of management practices in physical and hydric attributes when such soils are incorporated to agricultural production systems. Overall, clayey Oxisols with similar granular structure can have distinguishing physical and hydric environments and soil management systems may constitute important strategies to overcome the intrinsic low water availability of these soils.