Pascal Clouvel

Seed exchange networks for agrobiodiversity conservation. A review.

The circulation of seed among farmers is central to agrobiodiversity conservation and dynamics. Agrobiodiversity, the diversity of agricultural systems from genes to varieties and crop species, from farming methods to landscape composition, is part of humanity’s cultural heritage. Whereas agrobiodiversity conservation has received much attention from researchers and policy makers over the last decades, the methods available to study the role of seed exchange networks in preserving crop biodiversity have only recently begun to be considered. In this overview, we present key concepts, methods, and challenges to better understand seed exchange networks so as to improve the chances that traditional crop varieties (landraces) will be preserved and used sustainably around the world. The available literature suggests that there is insufficient knowledge about the social, cultural, and methodological dimensions of environmental change, including how seed exchange networks will cope with changes in climates, socio-economic factors, and family structures that have supported seed exchange systems to date. Methods available to study the role of seed exchange networks in the preservation and adaptation of crop specific and genetic diversity range from meta-analysis to modelling, from participatory approaches to the development of bio-indicators, from genetic to biogeographical studies, from anthropological and ethnographic research to the use of network theory. We advocate a diversity of approaches, so as to foster the creation of robust and policy-relevant knowledge. Open challenges in the study of the role of seed exchange networks in biodiversity conservation include the development of methods to (i) enhance farmers’ participation to decision-making in agro-ecosystems, (ii) integrate ex situ and in situ approaches, (iii) achieve interdisciplinary research collaboration between social and natural scientists, and (iv) use network analysis as a conceptual framework to bridge boundaries among researchers, farmers and policy makers, as well as other stakeholders.

Using multidirectional thermography to characterize water status of cotton

Abstract A pertinent interpretation of thermal infrared (TIR) information to characterize crop water status requires at least to consider the fraction of crop cover. Even if the crop cover is known, such an interpretation remains difficult and the current issues to be overcome in the field of TIR remote sensing applications stands on bare soil effects. An experiment was conducted during summer 1999 in Montpellier (France) on a row-cotton crop in order to acquire a data set relating thermal and optical multidirectional measurements to crop structure and water status. The crop was monitored all along its development. Three plots were delimited: a reference plot with no water limitation and two plots without water supply respectively at flowering and cutout stage. On three dates, directional TIR and optical images were acquired both on the reference plot and on the one with limited water supply. Directional averaged temperatures (Ts) and Normalized Difference Vegetation Index (NDVI) values showed a strong dependence on canopy gap fraction. Ts appeared particularly influenced by directional sunlit soil fraction variability, depending on both sun/sensor angle configuration, crop structure and water status. Leaves at different levels in the canopy (with different ages and spectral properties) could be observed by the sensor, but the impact of the sunlit/shaded leaves ratio on directional temperature measurements was weak in comparison to soil effects. The different directional influence of sunlit soil fractions on Ts and NDVI values explains in a large part the limits encountered by water stress indices approaches, aiming at relating linearly such variables, when applied to partially covering crops. Such results provide an exhaustive experiment-based biophysical analysis of very high resolution multidirectional TIR signal. They point out further ways of investigations to be explored in the field of water stress indices improvement or performing. This comes as a preamble of an experiment-based analysis of the limits and opportunities of water stress indices methods, complemented with a 3D model-based analysis that allows confirmation and extrapolation of the results to larger ranges of crop characteristics and directional configurations.

Wine contamination by ochratoxin A in relation to vine environment

Since 2006, a new EC regulation has imposed 2.0 microg/l as the upper limit for OTA concentration in wines (CR 1881/2006). OTA production results from a harmful combination of skin lesions and favourable conditions for A. carbonarius growth, namely the air temperature and humidity, and the berry sugar content. The aim of our research was to highlight in vivo interaction between the number of damaged berries and the conditions for fungus development in relation to OTA concentration in wine. A survey carried out on the 2005 production from 156 vineyards bordering on the French Mediterranean enabled a link to be made between information on crop management, vineyard characteristics, meteorological data and the OTA concentration in wine. With humid air conditions during the susceptible berry period of 20 days before harvest, combined with a large number of damaged berries and a temperature conducive to both fungus growth and OTA production, critical levels of OTA concentration in wine were observed. Within the range of average daily air temperatures investigated, from 17.2 to 22.8 degrees C, during the susceptible berry period, 21 degrees C appeared to be the lower limit below which fungus growth and OTA production were not sufficient to result in critical levels of OTA concentration in wine. In our experiment, an average daily air temperature under 21 degrees C corresponded to an average minimum daily air temperature under 15 degrees C, below which fungus growth stopped under in vitro conditions. The importance of the berry sugar content before harvest was also demonstrated and our results suggest that the risk of wine contamination by OTA might be predicted from the number of damaged berries and the berry sugar content, along with climate monitoring.

Mapping Cropping Practices of a Sugarcane-Based Cropping System in Kenya Using Remote Sensing

Over the recent past, there has been a growing concern on the need for mapping cropping practices in order to improve decision-making in the agricultural sector. We developed an original method for mapping cropping practices: crop type and harvest mode, in a sugarcane landscape of western Kenya using remote sensing data. At local scale, a temporal series of 15-m resolution Landsat 8 images was obtained for Kibos sugar management zone over 20 dates (April 2013 to March 2014) to characterize cropping practices. To map the crop type and harvest mode we used ground survey and factory data over 1280 fields, digitized field boundaries, and spectral indices (the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI)) were computed for all Landsat images. The results showed NDVI classified crop type at 83.3% accuracy, while NDWI classified harvest mode at 90% accuracy. The crop map will inform better planning decisions for the sugar industry operations, while the harvest mode map will be used to plan for sensitizations forums on best management and environmental practices.

3D Simulation of directional temperature variability within a row-cotton crop : Toward an improvement of experimental crop water status monitoring using thermal infrared

Existing experimental methods based on the measurement of crop temperature to estimate water stress have been applied for 20 years. However, the application of such techniques is limited because they are not able to totally overcome either soil interference on the measured signal or directional effects involved in temperature measurements according to sun/sensor angles configuration and crop structure. An energy balance model, based on the 3D description of plants at leaf level, is used to simulate directional cotton crop temperature variability according to crop structure and water status. The model is implemented with a bare soil compartment so that soil temperature, water balance as well heat exchanges with the crop can be computed. Once validated, this approach provides an accurate interpretation of thermal infrared information considering the directional effects involved in surface temperature measurements. This offers the opportunity of analyzing the limits of using temperature-based crop water status indices when dealing with partially covering crops. This study underlines the knowledge and tools to be further investigated in order to improve or perform such experimental techniques.

Estimating potential soil erosion for environmental services in a sugarcane growing area using multisource remote sensing data

Characterization of landscapes is crucial in modelling potential soil erosion to ascertain environmental services that are provided by the main land use in the ecosystem. Remote sensing techniques have proved successful in characterization of landscapes. In this study area of a rain-fed Kibos-Miwani sugar zone of Kenya, we used Normalized difference vegetation index (NDVI) data extracted from satellite imagery to characterize the spatial and temporal heterogeneity of the vegetation conditions, and to model potential soil erosion. Data used included Moderate Resolution Imaging Spectroradiometer (MODIS) 250 m NDVI acquired in the period 2000 to 2013; 30 m Landsat5 time series images acquired between November 2010 and June 2011; a 30 m digital elevation model (DEM); and ground observations (land cover and soil characteristics). Temporal NDVI was extracted directly from MODIS 250 m images to study the changes in seasonal vegetation conditions with time, and spatial NDVI was extracted by analysing Landsat5 images at the field scale. NDVI extracted from Landsat images for a specific date, represented vegetation conditions for that simulation period. To compute potential soil erosion, we used Landsat 5 NDVI, the slope, aspect, curvature and soil physical properties as input data sets in the spatially explicit Fuzzy-based dynamic soil erosion model (FuDSEM). Land cover data collected revealed that sugarcane was the main land use, occupying 76% of the land cover. Results were consistent with crop management practices, illustrating a spatially heterogeneous land scape with varied vegetation conditions throughout the year. Out of simulations, we noted a homogeneous low erosion risk in areas with natural land cover with a global mean of 0.42. Medium to intense erosion risk in cropped areas was evident, with erosion risk varying from one pixel to the other. Simulation results suggest that crop management practices (planting and harvesting processes) are the drivers of erosion in sugar cane cultivated areas.

Architectural and Geometrical Representations of Cotton Plants to Simulate Their Light Interception at Low Density

The purpose of this investigation was to develop a method for building simplified geometrical representations (GM) of cotton plants that could be used to simulate plant light interception at low planting densities. Individual plants were observed infield trials throughout their growing period and their 3D architecture (AM) was reproduced at all growth stages. The crown envelope of the GM was represented by an ellipsoid. The ellipsoid content consisted of foliage elements randomly dispersed in a planophile distribution. The radiative transfers of both plant representations were simulated in the PAR range using the ARCHIMED simulation platform. Different ellipsoid envelope and foliage element sizes were investigated. With an appropriate set of sizes, light interception calculated using GMs tallied well with that obtained using AMs. It can be concluded that a simple turbid medium model is sufficient for modelling GM content without needing to introduce a clumping factor.