The contribution of rock fragments to the available water content of stony soils: Proposition of new pedotransfer functions

The contribution of rock fragments to the soil available water content (SAWC) of stony soil has been quantified by measurements of bulk density and gravimetric water content at different water potentials on rock fragments of different lithologies: flints, cherts, chalks, gaizes and limestones. More than 1000 pebbles (2 cm < equivalent diameter of the rock fragment < 5 cm) have been sampled in stony soils developed from each of the five lithologies. We demonstrated that the water content at saturation of the studied pebbles was equal to the water content at −100 hPa and to the water content at field capacity. A linear relationship between the water content at −100 hPa and at −15,840 hPa enabled to derive a simple pedotransfer function to determine the available water content of the rock fragments. We also proposed a second simple pedotransfer function, which expresses the available water content from the dry bulk density of the rock fragments only. A simulation at the horizon scale for a loamy-clay stony horizon showed that the SAWC could be strongly misjudged when the rock fragments were not taken into account: for a stony horizon containing 30% of pebbles, the SAWC is underestimated by 5% for chert pebbles and by 33% for chalk pebbles

Validation du module mais de GOA. Aspects genotypiques. Aspects geographiques

National audienc

The effect of soil stoniness on the estimation of water retention properties of soils: A case study from central France

International audienceEstimation of the water retention capacity of a heterogeneous soil requires knowledge of the hydric properties of each soil phase. Nevertheless, for stony soils, the rock fragments have often been neglected. The objective of this work was then to propose a methodology to improve the calculation of the available water content (AWC) of stony soils at a regional scale. On a 36,200 ha surface area in Beauce located in the Region Centre of France, the AWC was calculated by coupling pedotransfer classes developed for fine earth and rock fragments. When calculating the AWC for the first 120 cm of the soil and considering the rock fragments to be inert, the AWC was underestimated by 15% and showed a high spatial variability. When both the volume and the hydric properties of the rock fragments were ignored, the AWC was underestimated by 20%. This work is then the first proposal to estimate soil water properties at a regional scale by using the water storage capacity of the main part of the stony phase, say from gravels to stones. Results of this study will improve the calculation of water deficit on a regional scale and will aid both in regional water balance modelling and in regional assessment of irrigation needs

Predicting in situ soil N2O emission using NOE algorithm and soil database

International audienc

Outils d'estimation de production

*INRA, Documentation, Orleans Diffusion du document : INRA, Documentation, OrleansNational audienc

Using the electrical resistivity for describing the temporal variability of the soil water content at the field scale

International audienceWater transport in the vadose zone greatly depends on the hydric properties of soils which exhibit high variability whatever the spatial scale analysed. The determination of those properties in the field or in the laboratory involves considerable uncertainty. Recently, inverse modelling has been introduced to obtain hydric properties in situ by deducing from a measured time series of soil water content. Anyhow, the soil water content is commonly obtained by gravimetric measurements on soil samples, TDR measurements or neutron probes measurements. At the field scale, these methods give only punctual information on soil water content, with a low spatial resolution. Financial and time constraints limit the numbers of measurements locations and thus the description of the soil water content. Since recently, geophysical methods enable the monitoring of some soil characteristics on a continuous space with a high resolution. One of them, the electrical resistivity (ohm.m) -or DC method- is well adapted to characterise the soil subsurface and to describe soil properties, even if they are time-dependent. However the electrical resistivity depends on several chemical and physical soil variables that can interact. The influence of one soil parameter like the soil water content on the electrical resistivity is then hard to estimate. Our objective was then to use spatial measurements of electrical resistivity, to define zones of homogeneous electrical resistivity with time, to interpret them in terms of evolution of water content, and to compare them with a soil map. Our assumption was then that the time variation of electrical resistivity at the field scale was only due to the evolution of the soil moisture in our studied field. A time monitoring of the soil electrical resistivity and the soil moisture was realized during the year 2006, at four dates, both by the MUCEP device (MultiContinous Electrical Profiling), that gives measurements on a whole field area, and by local gravimetric measurements of the soil water content. Homogeneous zones were defined directly from measurements for the electrical resistivity, and after ordinary kriging for the water content. Our analysis of the spatial and temporal variability has permitted to discriminate three temporal homogeneous zones, both for electrical resistivity and the water content, that were mainly related to the soil map. We show that the use of electrical measurements enables (1) to directly describe the spatial and temporal evolution of soil water content at the field scale and (2) to extrapolate the temporal evolution of the water content in unknown zones. We could then describe some hydric processes, like lateral flows or upward capillary flows that would be difficult to derive from soil maps

L’estimation du Réservoir Utilisable (RU) dans les sols : une analyse bibliographique.

Ce travail s’inscrit dans le cadre du Projet Aquateam (www.projet-aquateam.org)