Modelisation du bilan hydrique d'un sol cultivé : approches deterministes et stochastique

A capacity-based simulation model has been developed to predict components of the field water balance. The model requires daily information such as the atmospheric evaporative demand and rain events, maximum-available soil water storage (MAWS) and root growth characteristics as weil as crop and soil factors. Actual evapotranspiration is modelled using Eagleman's parameterization. The model was tested for upland rice grown on a 3500 m2 field plot and on an undisturbed Iysimeter, both located at Bouaké, Ivory Coast. Good agreement between calculations and observations of actual evapotranspiration (AET) and drainage (D) measured at 15 sites equipped with neutron access tubes and tensiometers demonstrates the reliability of the mode!. This is also independently confirmed against the Iysimeter data. The model was used to study the influence of the soil spatial variability on AET and D at the bottom of the soil profile. This was achieved by considering MAWS as a stochastic process defined by its probability density and covariance functions. Therefore, the model response for the entire field is expressed in terms of probability. It is shown that a deterministic simulation obtained with the mean value of MAWS may lead to unacceptable predictions of the field average AET and D values, the difference with the stochastic mean strongly depending on the degree of variability and on the water supply conditions. (Résumé d'auteur

REBECCA-DB.A: an opensource flexible database for managing data from energy cane

REBECCA is a research project on energy cane in Guadeloupe aiming at producing electricity from the burning of the whole sugarcane. This project has emphasised the importance to store, share and manipulate numerous field data and NIRS analyses collected. A relational database named REBECCA-DB.A has been created to manage agronomic and genotypic data from the project including biomass, fibre content, and low heating value of several above-ground biomass components (millable stalks, top of the stalks, green and dead leaves). The results of the analysis of fibre content and low heating value can be automatically imported into the database from the NIRS system. Data can be exported in an appropriate format to be used in other statistical and modelling tools; for example as input data in the tool REBECCA-LCA to carry out environmental studies on energy cane. From the results of biomass and biomass quality of 35 cultivars, it has been possible to easily select the best three cultivars for use as energy canes taking into account the main functional characteristics. REBECCA-DB.A, originally designed for a specific project, could be adapted for other applications on energy or fibre cane studies. This is a free tool within the scientific community. (Résumé d'auteur

Résultats du programme REBECCA phase 1 de septembre 2011 à mars 2012. Volet agro-variétal modèle d'estimation de la qualité de la biomasse par des mesures SPIR chlordécone dans le système sol-plante : Note pour le COPIL n° 4 du 17 avril 2012

Cette note est préparée en vue du COPIL du 17 avril. Elle fait état des principaux résultats obtenus depuis celui de septembre 2011, concernant les volets agro-variétal, qualité de la biomasse et chlordécone (CLD) dans la plante. Elle constituera, avec le rapport intermédiaire portant sur la première année, le matériau de base du rapport scientifique final de la phase 1 (2 ans, 2010-2012). (Résumé d'auteur

RACINE2: A software application for processing spatial distribution of root lenght density from intersections on trench profiles

A field method has been developed to quantify root length density (RLD) from root intersection density (RID) measured on a trench-profile, using modelling RID-RLD relationships. For 2D spatial distribution mapping of RID (at 5-cm scale for example), the large amount of data is processed and converted into RLD and root distances (ARD) through modeling. Calculations and RLD mapping can be performed quickly using a new freeware: RACINE2, tailored to this field method. The software also allows a simple modeling of potential root exploration ratio in the soil (PRER) taking ARD into account. The software contains published models calculating RLD from RID for several crops (maize, sorghum, sugarcane, rice), ARD from RLD and PRER from RD. Models may be changed or added into RACINE2. RLD, ARD and PRER are calculated for each spatial unit. They can be mapped. Data can be exported to a spreadsheet or a surface mapping software for further analysis. It is also possible to import data into RACINE2 from a spreadsheet. RACINE2 thus makes studies about root-soil interactions, root growth and root uptake easier. Some examples of field results calculated by RACINE2 are presented (RLD, ARD and RER profiles and maps). They point out differences of PRER when taking (or not taking) into account 2D spatial root distribution. Taking into account spatial variability of root system in relation with soil characteristics may be important for root water and nutrient uptake in field conditions. (Résumé d'auteur

Modelling the potential root water extraction ratio in soil: application to sugar cane on the Island of Reunion

While very little is yet known about the root system depth of sugar cane, the study set out to model the potential root extraction ratio in soil (PRER), by counting root intersections (RI) obtained using the trench?profile method (TPM), to infer the spatial distribution of sugar cane root length densities (RLD) and root distances (RD). The experiment was conducted in a deep clayey cambisol in Réunion. RI values were counted using a grid with a 5 x 5 cm mesh, down to a depth of 4 m over a 1.5 m wide soil profile. The results revealed: i) wide variability in root distribution between the soil surface and root front (4 m), with many competing roots and other rootless zones over distances of more than 5 cm, ii) the PRER, calculated as the ratio of the volume of soil available to a root for water uptake to the volume of soil assigned to that root, ranged from 80% near the surface to values between 30% and 1% between 1 and 3 m, iii) if RLD mean values were used to estimate usable water, as is often the case in crop models, the values were overestimated, with an even greater gap when only depth of the root front was accounted for. It is thought that the PRER approach may be an indicator of crop functioning under water stress and may facilitate the identification of genotypes able to withstand drought, as reported by Nidichao et al., (2011) for oil palm. (Résumé d'auteur