Influence of rainfall interception by endemic plants versus short cycle crops on water infiltration in high altitude ecosystems of Ecuador

International audienceOwing to their high water retention, the volcanic ash-soils of the Northern Andean highlands (páramos) can be considered as natural 'water storage tanks' for drinking water and for irrigation. Vegetation plays an important role in transferring rain to the soil and in controlling the soil water content. To assess this role, we quantified the stemflow process under rainfall simulations for seve

Characteristics of non-allophanic andisols with hydric properties from the Ecuadorian paramos

So far, the occurrence of hydric properties (i.e. water retention values at 1500 kPa matrix potential larger than 1000 g kg(-1)) has generally been reported in Andisols characterised by advanced stages of weathering. Moreover, as these properties are due to the presence of short-range-ordered (SRO) minerals, they are frequently better expressed in the subsurface than in the surface horizons of these Andisols. The present paper describes the characteristics of three Hydric Melanudands whose properties distinctly depart from those briefly summarised above. These soils have been found in some of high-altitude (3200-4000 m a.s.l.) paramos of Ecuador where they are likely to cover several thousands of km(2). They either derived from or have been rejuvenated by volcanic ash deposited more recently than 3000 years BP and they develop under climatic and vegetation conditions favouring exceptionally large accumulations of organic matter. As a consequence, the deep (50-80 cm) epipedons of these Melanudands exhibit an unusual combination of properties. Though rich in primary weatherable minerals and virtually devoid of allophane, these epipedons have nevertheless 1500 kPa water contents either close to or even much larger than 1000 g kg(-1). In these Hydric Melanudands, organic colloids are the constituents responsible for their large porosity. Hydric Andisols are known to experience important irreversible physical changes on drying and this behaviour, in turn, makes them very fragile. As the hydric properties occur here in surface horizons, these paramos soils are thus expected to be especially susceptible to any land use change. (C) 2003 Elsevier Science B.V. All rights reserved

Why is the influence of soil macrofauna on soil structure only considered by soil ecologists?

These last twenty years have seen the development of an abundant literature on the influence of soil macrofauna on soil structure. Amongst these organisms, earthworms, termites and ants are considered to play a key role in regulating the physical, chemical and microbiological properties of soils. Due to these influential impacts, soil ecologists consider these soil macro-invertebrates as `soil engineers' and their diversity and abundance are nowadays considered as relevant bioindicators of soil quality by many scientists and policy makers. Despite this abundant literature, the soil engineering concept remains a `preach to the choir' and bioturbation only perceived as important for soil ecologists. We discussed in this article the main mechanisms by which soil engineers impact soil structure and proposed to classify soil engineers with respect to their capacity to produce biostructures and modify them. We underlined the lack of studies considering biostructure dynamics and presented recent techniques in this purpose. We discussed why soil engineering concept is mainly considered by soil ecologists and call for a better collaboration between soil ecologists and soil physicists. Finally, we summarized main challenges and questions that need to be answered to integrate soil engineers activities in soil structure studies. (C) 2014 Elsevier B.V. All rights reserved

Impact du changement d'usage des sols sur la biodiversite: consequences sur l'erosion des sols

Gestion integree des eaux et des sols': ressources, amenagements et risques en milieux ruraux et urbains, Editions AUF et IRD, Hanoi, Actes des Premieres Journees Scientifiques Inter- Reseaux de l'AUF, Hanoi, 6-9 novembre 2007Paper presented at Conference, Integrated Management of Waters and Soils: Resources, infrastructures and risks in rural and urban areas, Hanoi, Vietnam, 6-9 November 2007This study deals with the influence of land use change on earthworm diversity on the one hand and the consequences of these modifications on soil erosion on the other hand. This work has been realized in the Northern Vietnam, in the Dong Cao experimental watershed (average slope ~40%). Our work shows that endogeic earthworms are associated to agrosystems with low vegetation cover (or low litter content) while agrosystems with high vegetation cover are characterized by anecic earthworms that create casts on the soil surface. The quantity of soil accumulated on the soil surface by earthworms can be very important (10-20kg m-?). A simulation of water runoff associated to the annual measurement of soil erosion from 1m? plots shows that casts deposited on the soil surface lead to a better infiltration of water but do not increase soil erosion. This study highlights that other biological factors than the vegetation must be considered for a sustainable management of steep slope agro-ecosystems in the Northern Vietnam

The use of Slingram EM38 data for topsoil and subsoil geoelectrical characterization with a Bayesian inversion

International audienceWe use the Bayesian method to invert a simple two-layer pedological horizon (1-D with a topsoil and a subsoil) of a surveyed site to be assessed. We show how the Bayesian method is well suited to the determination of topsoil/subsoil features, and can be used in particular as a tool for the analysis of parameters to be retrieved in terms of information content. Our approach is devoted mainly to the assessment of topsoil thickness, and of topsoil and subsoil conductivities, which are provided in terms of probability density functions. We first summarize the methodology implemented with the Geonics EM38-MK2 conductivity meter, and discuss the adaptation of field procedures and post-processing methods to mitigate the effects of drift and bias. We briefly review some non-Bayesian approaches, and then develop the Bayesian approach for the context of our geophysical survey, highlighting its merits. Positivity constraints (on thickness and conductivity) are included in the form of log parameters. A priori knowledge, based on an objective choice made by the geophysicist, is naturally included in the Bayesian scheme. We discuss the equivalence problem associated with the application of the Slingram method to soil structure analysis. The survey of a luvisol at the Kwazulu-Natal (South Africa) site of Potshini is used to illustrate an ecological application of the Slingram and Bayesian methods, used to define the geo-electrical structure of the near-surface soil. These algorithms have demonstrated their usefulness in mapping the clay content of the Bt horizon associated with the control of encroaching trees. (C) 2013 Elsevier B.V. All rights reserved