Effects of drying on Amazonian ferralsols and podzols. Determination of water desorption curves from mercury porosimetry

Abstract

We established pedotransfer functions to define the water desorption curve from MIP, organic carbon content, and bulk density (table I and II). These functions can be used for soils with the following characteristics, thus for most tropical soils: - negligible fine clay (< 0.2 [nu]m) content, in order to enable the extrapolation of nanopore volume from MIP, without needing nitrogen desorption [Bruand and Prost, 1987]; - soils mainly composed of kaolinite and quartz. The organic carbon content has little influence on the humic podzol studied here, so the equations established here are pertinent for other podzols. These pedotransfer functions give information on the structure of these soils : - residual and micro- porosities modify between MIP and water desorption, according to the organic carbon content and the texture of clay (given by the average textural pore size), with the same law for all soils; - mesoporosity changes according to two different types of structure : (1) clay microaggregates for clayey soils, (2) sandy fabric for podzol, loose at depth due to eluviation of parent clay, consolidated near the surface by pedoturbation; - total porosity follows, with an attenuation, the changes in the MO-linked porosity and in the porosity linked to soil structuring particles, that is the residual porosity for clayey soils, and the mesoporosity for podzols; - macroporosity, in reality as in the equations, compensates for the difference. This method could be tested on soils with other granulometry, mineralogy, or higher OM content. This work was supported by IRD and the PEGI and PROSE programs, we thank Max Sarrazin for his technical collaboration and the reviewers for their critical reading.