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Green roofs have the ability to mitigate stormwater runoff and to reintegrate wild-life and biodiversity in urban areas. However, they constitute complex ecosystems that still encompass grey areas. For instance, there has been only few research conducted on the accuracy of sensors such as capacitive EC-5 or thermic PlantCare, given the specific composition of green roofs substrates. In addition, green roofs often present spatial heterogeneity such as differences in substrate depths or partially shaded areas. This heterogeneity is expected to impact SWC and consequently plants development. Hence, the objectives of this thesis was to test both types of sensors in green roof substrate and to monitor - with abiotic parameters and vegetation coverage - two plots on an extensive green roofs with two different depth and shadowed areas. Firstly, PlantCare appeared as the most suitable sensor for green roofs application, given EC-5 dysfunctions due to poor contact between the sensors and the substrate. Secondly, the difference in depth has an influence in SWC, since the deepest plots presented a higher SWC during the entire experiment. As a consequence, a disparity in vegetation coverage was noticed, as the deepest plot presented more than 20 % of plant coverage while its neighbour had only 5 %. Finally, the shadowed area presented a higher coverage of plants than the rest of the plot. However, the behaviour of SWC was more complicated to seize at this scale due to the presence of plants and the small volume of influence of Plantcare.

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Thailand subsidies the development of the culture of Hevea brasiliensis in the northern and northeastern parts of the country, yet far away from the optimal growth conditions of the species. This MSc Thesis studied the hydric behavior of two 5 years old rubber trees of the clone RRIM600 in the province of Phitsanulok in Thailand, known to be prone to drought. The "Tcrit_Tclim" model developed by Ayutthaya (2010) was selected for its ability to predict the hydric behavior of a mature rubberstand. The model was run from the 24th of March to the 29th of May 2015. The calibration showed a higher whole tree water conductance for young rubber trees than mature ones at a REW = 0. It also showed a threshold of -1.99 MPa for the midday leaf water potential under sunny conditions, similar to the -1.95 of Ayutthaya. The validation showed an estimation of the mean transpiration of the two trees with a difference of 2%, and a RMSE of 0.032 mm day-1, but the short calibration of the model didn't permit to follow daily differences in the transpiration of the trees. This study is encouraging as to the possibility of using the "Tcrit_Tclim" model on a wider age range than the one initially thought by Ayutthaya. However it has to be applied on a longer period in order to confirm the isohydric behavior of young rubber trees, establish complete calibration curves and further test its performances.

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The replacement of native vegetation by annual crops and pasture, by European settlers, involved dryland salinity, a major problem in Western Australia leading to land degradation. The idea of rehabilitating the salt-affected area to agriculture has emerged recently. One solution recently developed consists in planting some salt tolerant bushes to increase the evapotranspiration and consequently decrease the level of the saline groundwater. The specific hydrologic and pedologic properties and processes in combination with such remediation strategies are nearly unknown. This study carried out on a paddock at the University of Western Australia (UWA) farm at Ridgefield sets the first background information on the spatial and temporal variability of the hydrology, geology, pedology and salt content in the ground. The spatial distribution of the salinity at the paddock-scale is analysed by an electrical conductivity 1:5 soil:water extract (EC1:5) mapping for the surface and an electromagnetic induction (EMI) mapping for the subsurface. While the most saline area is described in more detail thanks to a 2D electrical resistivity tomography (ERT) survey and ground truth information such as texture, EC1:5 and water content data. The first methods both identified the same most saline area. Then the 2D inversed model section allows the assessment of the bedrock boundary as well as the horizontal and vertical distribution of the saline zone. However, the conclusions are based on qualitative results and not quantitative. Moreover, to analyse the water content more precisely the relation between bulk electrical conductivity (ECb) and water content (WC) should take the salinity into account.

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In temperate areas, irrigation in sandy soil is most of the time essential. Literature on the efficiencies of irrigation has highlighted different infiltration patterns. The purpose of this study was therefore to measure infiltration pattern with new non-invasive technique such as ERT after an irrigation event to measure irrigation efficiency. To address this question, we firstly designed the best ERT protocol with the specific microtopography of a potato field using virtual ERT measurements. The best array was the Wenner-alpha + Dipole-dipole. This latter was also resilient to a micro-topography change even though WC underestimation in ridges and WC overestimation in furrows on the first 5cm were observed. After this, we used ERT on the field to follow up and explain the different infiltration patterns caused by the potato canopy and the micro-topography. After an irrigation of 25mm, we observed that water was more likely to infiltrate in furrows (+20% of VWC) rather than in ridges (+2% of VWC). This pattern was explained by the canopy effect. We also determined the root density by counting the number of roots on a framework composed of 5cm by 5cm cell. Roots were mostly present in ridges on the first 50cm with 8 roots/cell causing important RWU bulb. In furrows, less than 2 roots by cell were counted.

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A better understanding of the processes governing soil-plant-water interactions is of paramount importance to come to a sustainable management of agricultural and forest ecosystems. New methods are needed to be able to study these invisible processes in time and space. In this master thesis, electrical resistivity tomography (ERT), a technique coming from the field of geophysics, is used to monitor root water uptake by barley (Hordeum vulgare L.) in repacked loamy soil columns. The experiment reveals the sensitivity of ERT to soil structure and moisture but also all the influence of the experimental setup. No clear link between resistivity and roots could be established because of effects linked to the experimental setup. Next to ERT, we explored the potential of induced polarization (IP), since it is assumed that the IP signal might be well correlated with the root density present in the soil. Nevertheless, our preliminary column tests with IP revealed important methodological issues to solve first. We therefore setup a simple experiment allowing to understand better the IP effect and spot elements that will help to improve IP setup and data collection such as an appropriate frequency, the electrode polarization due to successive measurements and the self-potential effect. Even though our results of highresolution ERT and IP experiments were somewhat disappointing, ERT and IP remain hot areas of research that could lead to interesting applications in soil sciences and agriculture.