Claude Hammecker

Processes driving soil solution chemistry in a flooded rice-cropped vertisol: analysis of long-time monitoring data

Abstract Senegal river water has positive alkalinity (0.55 meq l −1 ) and positive calcite-residual alkalinity (0.30 meq l −1 ). Without leaching, this water presents a possible alkalinization and sodication hazard for the soil. The effect of flooding on soil solution chemistry in an irrigated nondrained vertisol under rice was monitored during 3 years in northern Senegal. During flooding, soil solution redox potential dropped to about −0.15 V, and alkalinity increased to 15 meq l −1 . Mg content increased as well, from about 1 to 5 meq l −1 , whereas Cl and SO 4 contents decreased to very low levels at the end of the growing season (0.05 meq l −1 ). After the fallow, nonflooded period between two crop cycles, the soil solution composition returned to its initial neutral sulfate and chloride composition. The observed cycle in soil solution chemistry could not be explained by water and solute transfer because infiltration rates were very low, due to air entrapment in the soil profile. Geochemical control by calcite and gypsum was excluded during irrigation. Mossbauer spectroscopy showed that iron oxides were both well- and poorly crystallized goethite. Goethite dissolution was assessed by pH–Eh stability diagrams. We explained the increase in alkalinity and Mg concentration in the soil solution partly by the composition of the irrigation water, and partly by the reduction and dissolution of Fe oxides, and Fe 2+ fixation on exchange sites of the clay minerals. These processes were reversed as soon as the soil oxidized. The decline in Cl concentration was attributed to geochemical control through the formation of a GR-Cl − mineral around the porous cups. In that case, Cl should not be used as a natural tracer. Carbonates accumulate in soil solution not only due to iron reduction, but also because of the positive residual alkalinity of the irrigation water. When the soil dries at the end of crop cycle, the carbonate concentration of topsoil will increase and calcite will precipitate. This ongoing process may result in calcium control and ultimately soil alkalinization over the years.

Salt distribution in the Senegal middle valley : analysis of a saline structure on planned irrigation schemes from N'Galenka creek

In the middle Senegal valley, the saline soil distribution is not related to the present faint topography. The absence of a relationship is one of the major constraints in establishing new irrigation schemes. The salt distribution was studied to understand its variability, and to describe its structure and spatial arrangement. Saline areas were delineated by measuring the electromagnetic soil conductivity (ECm), a rapid technique with a portable instrument (EM38). The results indicate that the saline soils are distributed as strips. A detailed examination revealed that the major strip is actually composed of two parallel minor strips, and a comparison with aerial photographs showed that one lies in a former creek bed, and the other fringes it on the southern bank. The strip is intersected by an actual creek bed, indicating that the salt distribution is ancient, related to previous geo-morphology, and does not result from a recent remobilisation of the marine salt deposits incorporated in the soil. The identification of this relationship between the present saline soil distribution and previous geo-morphology allowed us to survey the whole N’Galenka region (about 6000 ha) using ECm measurements on selected transects. # 2001 Elsevier Science B.V. All rights reserved.

A Geometrical Pore Model for Estimating the Microscopical Pore Geometry of Soil with Infiltration Measurements

This paper presents a simple geometrical pore model designed to relate characteristic pore radii of the porous network of soils with macroscopic infiltration parameters. The model composed of a stack of spherical hollow elements is described with two radii values: the pore access radius and the actual pore radius. The model was compared to cylindrical pore models and its mathematical consistency was assessed. Soil sorptivity S and the second parameter A of the Philip infiltration equation (1957), have been determined by numerically simulated infiltration. A diagram and an empirical relation have been set in order to relate the pore access and pore radii to the infiltration parameters S and A. The consistency of the model was validated by comparing the predicted sorptivity and hydraulic conductivity values, with the widely used unsaturated soil hydraulic functions (van Genuchten, 1980). The model showed good agreement with experimental infiltration data, and it is therefore concluded that the use of a model with two radii improves the relation between microscopic pore size and macroscopic infiltration parameters.

DEPURATION OF HIGHWAY RUNOFF WATER INTO GRASS‐COVERED EMBANKMENTS

Abstract The management of polluted road runoff water is an important issue in environmental protection. A strategy could be to perform local depuration by infiltration into the soils of the embankment, but knowledge for designing such systems is lacking. This study aims at discussing the relevant soil properties, by estimating the long‐term depuration of road runoff water infiltrating into the sandy soil embankment of the A9 highway in Wallis, Switzerland. This was done by estimating the heavy metals (HM) mass balance of two sites 23 and 12 years old, respectively. The accumulated HM were estimated by soil and GB analyses. The HM input was estimated by average water quality and traffic. The results were discussed using two‐dimensional simulation of infiltration and a 14 months in situ monitoring of the runoff from the pavement to the embankment and at the bottom of the embankment. The soil properties were appropriate for both small particle adsorption and filtration. A good match between input and stored pollutant charges was found, and the HM profiles accorded well with infiltration simulation and monitoring results, which showed that 80–100% of the runoff water infiltrated into the embankment. Replacement of the cracked concrete gutters by an infiltration channel made of similar soil is recommended. These results oppose the Swiss guidelines for road‐polluted water infiltration, as much more clayey soils are recommended. These later soils are difficult to find in Switzerland, and may allow for preferential flow through macro pores, in contrast to the studied site.

A simple framework to analyze water constraints on seasonal transpiration in rubber tree (Hevea brasiliensis) plantations

Climate change and fast extension in climatically suboptimal areas threaten the sustainability of rubber tree cultivation. A simple framework based on reduction factors of potential transpiration was tested to evaluate the water constraints on seasonal transpiration in tropical sub-humid climates, according pedoclimatic conditions. We selected a representative, mature stand in a drought-prone area. Tree transpiration, evaporative demand and soil water availability were measured every day over 15 months. The results showed that basic relationships with evaporative demand, leaf area index and soil water availability were globally supported. However, the implementation of a regulation of transpiration at high evaporative demand whatever soil water availability was necessary to avoid large overestimates of transpiration. The details of regulation were confirmed by the analysis of canopy conductance response to vapor pressure deficit. The final objective of providing hierarchy between the main regulation factors of seasonal and annual transpiration was achieved. In the tested environmental conditions, the impact of atmospheric drought appeared larger importance than soil drought contrary to expectations. Our results support the interest in simple models to provide a first diagnosis of water constraints on transpiration with limited data, and to help decision making toward more sustainable rubber plantations.

TRANSPIRATION, GROWTH AND LATEX PRODUCTION OF A HEVEA BRASILIENSIS STAND FACING DROUGHT IN NORTHEAST THAILAND: THE USE OF THE WaNuLCAS MODEL AS AN EXPLORATORY TOOL

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Transpiration, growth and latex production of a Hevea brasiliensis stand facing drought in Northeast Thailand : the use of the WaNuLCAS model as an exploratory tool Laurie Boithias, Frederic Do, Supat Isarangkool Na Ayutthaya, Junyia Junjittakarn, S. Siltecho, Claude Hammecker

Land use changes the soil carbon stocks, microbial biomass and fatty acid methyl ester (FAME) in Brazilian semiarid area

ABSTRACT Land use affect soil C and microbial structure, especially in tropical dry areas. The objective of this study was to evaluate the effects of the land use on physical, chemical, and microbiological attributes of soils from Brazilian semiarid. We analyzed soil physical, chemical, total carbon stocks (TCS), water-soluble carbon (WSC), microbial biomass carbon (MBC) and microbial structure of soil from forest, no irrigation maize, succession areas (Anadenanthera falcate and Tabebuia alba) and secondary shrubby vegetation. The use of soil influences C stock. The forest soil showed higher TCS and MBC. The conversion in T. alba reduced in 9% soil total bacteria. The multivariate analysis showed that TCS, MBC and FAMEs contributed to separation of natural forest and other areas in the superficial layer. This study indicates that the conversion of forest into successional areas can decrease by up to 44% TCS and 68% MBC. The present study provided alarming data concerning the impact of land use on quality of soil in a tropical dry region in Northeastern Brazil. Our results provide an alternative tool for the management of deforested dry areas that could serve as guideline for management plan to sustainability for agricultural impacted dry areas.

Utilização do Método Inverso para a Caracterização Hidrodinâmica de um Neossolo Flúvico

The parameters of the soil-water retention curve and the hydraulic conductivity curve of the superficial layer (5-17 cm) of a Fluvent soil, with a loamy sand texture, were determined by using the inverse method. The hydraulic functions used were combined, thus forming the so-called VGBC(B) (van Genuchten-Burdine/ Brooks&Corey) and VGBC(M) (van Genuchten-Mualem /Brooks&Corey) models. On a surface plot, located in the Experimental Station of the Group of Soil Physics of DEN-UFPE, the water content data and the matric potential of the water in the soil were obtained automatically and stored in a datalogger every 30 minutes for 72 hours, at the depths of 5, 11 and 17 cm. The implementation of the inverse method was accomplished by combining the hydraulic model, which solves the equation of Richards, with the subroutine DBCONF that minimizes an objective function by using the quasi-Newton method. The parameters α and n of h(θ) and Ks, and c of K(θ) were obtained by minimizing the sum of the squares of the deviations between the measured and the calculated water content at the depth of 11 cm. The inverse method was shown to be effective in determining the parameters of h(θ) and K(θ). Both models showed the same ability to describe the experimental data.