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St. Pierre, France

Toure A.,Africa Rice Center | Rodenburg J.,Africa Rice Center | Marnotte P.,Upr Sca | Dieng I.,Africa Rice Center | And 2 more authors.
Weed Biology and Management | Year: 2014

While weeds generally are considered as the most important overarching production constraints in inland-valley cropping systems in West Africa, little is known about species' associations with environmental and crop management factors. Weed species' associations with seasonal and environmental factors, such as their position on the catena, soils and cropping systems, were studied during two seasons (dry and wet) in 45 arable fields of three inland valleys in south-western Benin, Africa. The three most dominant weed species were Dactyloctenium aegyptium, Commelina benghalensis and Digitaria horizontalis on the inland-valley crests (uplands), Ludwigia hyssopifolia, Corchorus aestuans and Ludwigia octovalvis on the sloping hydromorphic fringes and Leersia hexandra, Ipomoea aquatica and Fimbristylis ferruginea in the valley bottoms (lowlands). Echinochloa colona, Cleome viscosa and Talinum triangulare were the three most dominant species in the dry-season crops (maize or vegetables) and Leer.hexandra, I.aquatica and Sphenoclea zeylanica were the three most dominant species in the wet-season crop (rice). Ageratum conyzoides, Synedrella nodiflora and D.horizontalis were observed throughout the catena. Problem weeds in inland-valley agro-ecosystems are those that combine a high frequency with a high submergence tolerance and ecological plasticity, C4 grasses, perennial C3 species with persistent root structures and broad-leaved species with high propagation rates. Weed management strategies that are aimed at increasing the resilience of rice-based cropping systems in the inland valleys of the southern Guinea Savanna of Africa should address the categories of problem species that were identified in this study. This can be done best by following an integrated approach, including the use of more weed-competitive cultivars and rotation crops. © 2014 Weed Science Society of Japan.


Lebourgeois V.,Upr Sca | Chopart J.-L.,CIRAD UPR SCA | Begue A.,CIRAD - Agricultural Research for Development | Le Mezo L.,CIRAD UPR SCA
Agricultural Water Management | Year: 2010

In humid regions, the timing and quantity of a complementary irrigation regime is challenging because of the irregularity of rainfalls events. In this study, we tested the use of a thermal infrared derived empirical crop water stress index (CWSIe) as an in situ measurement of the water status of sugarcane, to better monitor the irrigation scheduling. To do this, we set up a 2-year experiment in Reunion Island, on a trial with plots under different water conditions (rainfed and irrigated). Crop surface temperature was measured daily with infrared radiometers (Apogee Instruments) installed above the canopy, and soil moisture and drainage measurements were used to derive the ratio between actual and maximum evapotranspiration (AET/MET) values that were then averaged on "hydrically homogeneous" time periods (between 7 and 25 days). Only the thermal data acquired on clear days and 1 h after noon in 2007 were used to define the empirical lower and upper baselines required for the calculation of empirical CWSI. The data set acquired in 2008 was used to test the robustness of the method as we used the upper and lower baselines defined in 2007 to calculate CWSIe. The linear regression between AET/MET and (1 - CWSIe) averaged on the same periods (values ranging between 0.4 and 1) showed a significant correlation for both experimental years (global R2 = 0.75 and RMSE = 0.12). This result indicates the effectiveness of the CWSIe to measure the water status of the sugarcane crop, even in humid conditions with a vapor pressure deficit (VPD) between 0.5 and 2.1. We conclude the study by discussing the complementarity of this remote water stress index (CWSIe) with OSIRI water balance modelling tool currently used in Reunion Island for monitoring sugarcane crop irrigation. © 2009 Elsevier B.V. All rights reserved.


Maurice J.,Agro ParisTech | Laclau J.-P.,CIRAD - Agricultural Research for Development | Laclau J.-P.,University of Sao Paulo | Re D.S.,Sao Paulo State University | And 9 more authors.
Plant and Soil | Year: 2010

The objectives of the study were to assess changes in fine root anisotropy and specific root lengths throughout the development of Eucalyptus grandis (W. Hill ex Maiden) plantations and to establish a predictive model of root length density (RLD) from root intercept counts on trench walls. Fine root densities (<1 mm in diameter) were studied in 6-, 12-, 22-, 28-, 54-, 68- and 72-month-old E. grandis plantations established on deep Ferralsols in southern Brazil. Fine root intercepts were counted on 3 faces of 90-198 soil cubes (1 dm3 in volume) in each stand and fine root lengths (L) were measured inside 576 soil cubes, sampled between the depths of 10 cm and 290 cm. The number of fine root intercepts was counted on one vertical face perpendicular to the planting row (Nt), one vertical face parallel to the planting row (Nl) and one horizontal face (Nh), for each soil cube sampled. An overall isotropy of fine roots was shown by paired Student's t-tests between the numbers of fine roots intersecting each face of soil cubes at most stand ages and soil depths. Specific root lengths decreased with stand age in the upper soil layers and tended to increase in deep soil layers at the end of the rotation. A linear regression established between Nt and L for all the soil cubes sampled accounted for 36% of the variability of L. Such a regression computed for mean Nt and L values at each sampling depth and stand age explained only 55% of the variability, as a result of large differences in the relationship between L and Nt depending on stand productivity. The equation RLD = 1.89*LAI*Nt, where LAI was the stand leaf area index (m2 m-2) and Nt was expressed as the number of root intercepts per cm2, made it possible to predict accurately (R2 = 0.84) and without bias the mean RLDs (cm cm-3) per depth in each stand, for the whole data set of 576 soil cubes sampled between 2 years of age and the end of the rotation. © 2010 Springer Science+Business Media B.V.


Sabatier D.,Upr Sca | Dardenneb P.,CRA W | Thuries L.,CIRAD
Journal of Near Infrared Spectroscopy | Year: 2011

Frequent variations in spectral intensity due to particle size and/or of particle size distribution are observed in plant products processed in powder form and scanned with near infrared reflectance (NIR). In this study, two grinders, with differences in time consumption, practicality and providing homogenates with different particle size range and distribution, were tested to evaluate their effects on NIR spectra. Optimisation of NIR calibration was necessary before predicting lignocellulosic compounds in sugarcane (Saccharum spp.) samples with coarse particle size to supply a pre-existing ecophysiological growth model. Sixty samples from three varieties, grown in four contrasting pedoclimatic areas and from five anatomical parts were scanned and then analysed by biochemical fractionation. Different calibration methods, resulting in a combination of multiple linear regressions (MLR) applied to three calibration sets (fine, coarse and mixed particle sizes) treated with six data pretreatments-first derivative (D), second derivative (D2), multiplicative scatter correction (MSC), standard normal variate and detrend (SNVD), standard normal variate and detrend successively followed by first derivative (SNVD-D) or second derivative (SNVD-(D2)-were investigated. The best NIR model statistical values were obtained by calibration developed on a mixed calibration set treated by SNVD-(D2. Results confirmed that NIR spectroscopy could be an accurate and efficient method to predict lignocellulosic compounds in different botanical parts of sugarcane samples when used as input to an ecophysiological growth model. © 2011 IM Publications LLP. All right reserved.


Audebert A.,French National Institute for Agricultural Research | Mouret J.C.,French National Institute for Agricultural Research | Roques S.,French National Institute for Agricultural Research | Carrara A.,French National Institute for Agricultural Research | And 4 more authors.
Weed Biology and Management | Year: 2013

Bolboschoenus maritimus is one of the major weed constraints for irrigated rice-cropping systems in the Camargue, France. This perennial plant propagates mainly through the production of numerous tubers. Observations in both controlled conditions and on-field studies were used to enhance the level of knowledge of the biology, functioning and infestation dynamics of B.maritimus, with a view to rationalize weed control practices. It was found that B.maritimus displayed a great potential to produce a large number of shoots, rhizomes and tubers. Its propagation in the field plots depended on the initial weed density and its spatial colonization did not show any preferred direction (isotropic). Further observations that were made in the paddy fields showed an interaction between the different cultural practices that were tested and the infestation dynamics of B.maritimus. Efficient control of B.maritimus infestation in the field should make use of the data reported here, based on three levels: (i) prevention of weed stem proliferation during the cropping season with specific herbicides; (ii) elimination of the tubers after the rice crop; and (iii) reduction of the tuber-germinating ability. © 2013 Weed Science Society of Japan.

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