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The agricultural sector in the Mediterranean basin faces many challenges related to the use of water and mineral resources for crop production and food security for an exponentially growing population. Most countries in arid and semi-arid areas suffer from water scarcity and soil nutrient depletion which severely impact the productivity of different cropping systems currently challenged by climate change and the high pressure on natural resources. Given its role in several plant biophysiological processes, such as plant photosynthesis, carbon fixation, energy transfer and allocation, and plant growth and development, phosphorus (P) nutrition take increasing attention in the last decades. The limited resources of rock phosphate as well as the low use efficiency of phosphorus fertilizers push the scientific community to urgently rethink the strategies of P fertilizer management at different scales. In this dissertation, we focus on the study of the impact of P agricultural management practices on P availability and mobility under drip fertigation systems and the consequent effects on plant photosynthesis, nutrient uptake, plant growth and productivity, and nutrient use efficiency. A series of agronomic pot experiments were conducted under controlled conditions to investigate the impact of various P drip fertigation practices on phosphorus availability in Moroccan alkaline soils, on chickpea physiology, productivity, and nutrient uptake. The objective of the first trials was to study the potential use of inorganic soluble polyphosphates (Poly-P) as slow-release fertilizer under drip fertigation. The impact of the chemical properties of polyphosphate and orthophosphate (Ortho-P) fertilizers (polymerization degree, solubility, and interactions with other nutrients), as well as P application frequency on the availability of phosphorus in soil (Olsen-P) and its relocation into deeper soil layers, were investigated. The second pot trials were conducted in controlled conditions to evaluate the interactive effect of P fertilizer form (Ortho-P vs Poly-P) and soil moisture conditions on chickpea photosynthetic activity, water and nutrient uptake, and their consequent effects on biomass accumulation and nutrient use efficiency. The mechanisms underlying phosphorus nutrition impacts on chickpea photosynthesis efficiency, grain yield, and nutrient uptake and use efficiency were explored using different plant sensors and analytical methods like chlorophyll fluorescence, plant phenotyping, and plant nutrient analysis. Based on the results of pot trials, two-years field experiments were conducted in a 2.5 ha plot. The objective of these field experiments was to evaluate the potential use of electromagnetic induction as a fast and reliable technique to characterize soil properties. Soil electrical conductivity (ECa), crop yield data, and soil chemical properties were used as input data to delineate chickpea fertigation management zones using unsupervised clustering analysis. The variable rate P application strategy was evaluated as an efficient agricultural practice to increase the chickpea grain yield and quality and to improve phosphorus use efficiency at the field scale in Moroccan semi-arid conditions. The results from pot experiments showed that soil phosphorus availability varied significantly between fertilizer forms and fertigation frequencies. As compared to the Ortho-P fertilizer, P becomes less mobile in soils fertigated with Poly-P forms (Poly-100 and Poly-53) and its availability is maintained until harvest. The analysis of Olsen-P at the harvest stage showed that the higher P availability in soil was obtained with Poly-P forms with higher values in the 0-5 and 5-10 cm soil layers than in the 10-20 cm. Moreover, weekly fertigation (Fweek) revealed the best results in terms of P availability compared to fertigation at sowing (Fsow) or 3-day frequency (F3days) and all P fertilizers significantly improved chickpea grain yield, seed quality, and water productivity, compared to the unfertilized control. In addition, our findings showed that the photosynthesis efficiency was significantly improved in fertigated chickpea plants compared to the control treatment as revealed by the electron transport chain between photosystem II and I, which was significantly enhanced. The polyphosphate fertilizer (Poly-A: Poly-53) increased the number of electron acceptors of the photosynthetic linear electron transport chain compared to the other P fertilizer forms. Furthermore, the interactive effect between P fertilizer forms and soil moisture conditions resulted in several significant changes in chickpea phenotypic and physiological traits. The stomata density and conductance, chlorophyll content, photosynthesis efficiency, biomass accumulation, and plant nutrient uptake were significantly improved under P drip fertigation with varied values depending on P fertilizer form and irrigation regime. Our results suggested that the P fertilizer form and irrigation regime providing chickpea plants with enough P and water, at the early growth stage, increased the stomatal density and conductance, which significantly improved the photosynthetic performance index (PIABS) and P use efficiency (PUE), and consequently biomass accumulation and nutrient uptake. The significant correlations established between leaf stomatal density, PIABS, and PUE supported the above hypothesis. Based on these results from the pots experiments we can conclude that Poly-P fertilizers can be recommended as an effective source of phosphorus for plants, due to their slow-release properties and the frequency of P application through the drip fertigation system which can be reduced while ensuring high crop yields. However, the effectiveness of Poly-P fertilizers was greatly reduced under water stress conditions, unlike the Ortho-P form which kept stable positive effects on the chickpea's physiological traits. On other hand, the field experiment showed that the soil spatial variability can be properly assessed by the electromagnetic induction sensor (CMD MiniExplorer), which represents basic information to conduct an oriented soil sampling design. Moreover, the statistical correlation analysis as well as the multiple regression model used for the prediction of chickpea yield greatly contributed to identifying the main soil properties influencing chickpea grain yield in the studied site. The combination of soil and plant sensing data (ECa, Ca, P, and GY) and their processing by geostatistical tools (semi-variograms, interpolation by ordinary kriging and IDW methods, and fuzzy c-means clustering algorithm) were very useful to delineate chickpea drip fertigation management zones (MZs). The application of variable rate P fertilizers through a drip fertigation system in the identified MZs increased the chickpea grain yield, seed size, and phosphorus use efficiency by 12%, 9%, and 18% respectively. Based on these results, we can conclude that the optimization of P fertigation practices, especially the choice of adequate P fertilizer form and application frequency, considering the availability of irrigation water and soil properties, can greatly contribute to improving crop yield and phosphorus use efficiency at field scale. Moreover, the integration of precision agricultural practices like variable rate application could be of great interest to farmers in semi-arid regions like Morocco to enhance water and mineral resource use efficiency which in return contributes to improving farmers' income, preserving the ecosystem, and ensuring sustainable agricultural production systems.

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Les conditions environnementales des toitures vertes peuvent gravement impacter la croissance des plantes ainsi que leur survie. Cependant, les études à l'échelle de communautés n'ont été menées que très rarement. Nous avons ainsi démarré une expérimentation dans laquelle des toitures se distinguaient par leur type et profondeur de substrat (variation dans le taux de matière organique, la rétention en eau et la capacité de drainage). Le même mélange a été utilisé afin d'assurer la comparaison. Ce mélange consiste en un ensemble de 22 espèces : 4 espèces généralistes (ou compagnes) complétées des 3 cortèges comprenant chacun 6 espèces spécialistes. Durant 2 mois, sans irrigation, l'abondance des individus (semis et adultes) a été calculée afin de différencier de potentielles communautés. Il s'est avéré que les variations de conditions environnementales sur toitures vertes se sont soldées par une distinction entre communautés tout comme sur l'habitat analogue correspondant. La profondeur du substrat et la météo ont toutes deux affecté la trajectoire évolutive de la communauté. Les dynamiques individuelles des plantes, et par extension leur taux de succès, peuvent peut-être aider à expliquer ces différences. Toutefois, l'expérimentation n'a pu souligner aucune influence des traits fonctionnels, spécifiquement la surface foliaire spécifique et la masse des graines, qui ont démontré un intérêt tant au niveau du retour rapide d'investissement foliaire que du succès de germination sur un sol pauvre en nutriments. Pour conclure, il est recommandé d'intégrer les conditions environnementales dans une sélection appropriée des plantes.

toiture verte, extensif, trait foctionnel --- specific leaf area --- Sciences du vivant > Sciences de l'environnement & écologie

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The management of irrigation districts is becoming laborious in some regions of Colombia. In the Tolima region, the bimodal climate is present in hot and semi-arid areas that are vulnerable due to the increasing impact of climatic phenomena that cause an intensification of droughts, but also of rainfall. The systems in place sometimes require more water than is needed, in a context of increasing producer density. Agricultural yields, particularly for rice, which is very present in the region, can sometimes decrease in an unprecedented way in the event of insufficient water supply. Moreover, the experiments to be carried out to put an end to these problems are sometimes costly in terms of time and money. In this study, trials of irrigation systems and scheduling were tried, and the use of a calibrated crop simulation model to assess the possibility of predicting the behaviour of these experiments on a variety of Oriza sativa L. from the region. The calibration shows simulations of the evolution of plant parameters, such as canopy cover with an average RMSE of about 2.60 % and correlated for the first cycle and a much poorer simulation for the second cycle, but also a simulated dry yield with an overall MBE of 0.621t/ha that is rather accurate and can differ from the observed evolution of the different treatments to some extent. Further simulations were carried out to assess the importance of the parameters on these outputs. The sensitivity analysis shows 7 parameters explaining 95 % of the total sensitivity of the evolution during a fictitious cycle of different soil water content, biomass, canopy cover and dry yield. These results will allow future evaluation of irrigation schedules in order to optimise yields according to local water consumption. Based on the results of the sensitivity analysis, further analyses can be done in the region to facilitate and plan future calibrations in a local environment. Thanks to the processed and modelled local climate data, it will also be possible to carry out irrigation schedules according to extreme weather events.

Precision agriculture, irrigation, crop modeling, global warming, sensitivity analysis, --- Sciences du vivant > Agriculture & agronomie

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Biochar is a recalcitrant carbon rich product obtained through the pyrolysis of biomass and used in soils as an amendment. It is commonly known that tropical soils are highly weathered soils and thus where biochar influence on the fertility of agricultural systems can be the most substantial. Herein we aim at filling the missing data for the application of biochar in in situ experiments. To do so we study the effects of biochar, produced from cotton branch residues, on maize biomass production (Zea mays L.) in a field trial in Koumbia, province of Tuy, Burkina Faso. The effect of biochar application rate (0 t.ha-1, 10 t.ha-1, 30 t.ha-1) and its combination with conventional fertilizer quantities (0 kg.ha-1, 100 kg.ha-1, 150 kg.ha-1) have been investigated. Soil physico-chemical characteristics and plant tissue nutrient concentrations were analyzed. The content of bioavailable phosphorus (P) and potassium (K), pH values and organic carbon concentration increased with biochar application in soil. In parallel, we observed a significant growth of P content in plant tissue. Our results show an increase in total aboveground biomass but no significant variation of yield in response to biochar. We conclude that higher concentrations of bioavailable nutrients could lead to a reduced fertilizer use and reduced production costs for farmers. Le biochar est un produit riche en carbone obtenu lors de la pyrolyse de biomasse végétale et utilisé dans les sols comme amendement. Les sols tropicaux étant connus pour être hautement altérés, l’utilisation de biochar y a le plus haut potentiel d’amélioration de leur fertilité. Dans cette étude nous visons à combler le manque de données sur l'application du biochar in situ. Pour ce faire, nous mettons en œuvre des essais sur un champ de maïs (Zea mays L.) à Koumbia dans la province de Tuy, Burkina Faso et étudions les effets du biochar fait à partir de résidus de coton. La quantité de biochar appliquée (0 t.ha-1, 10 t.ha-1, 30 t.ha-1) et sa combinaison avec différentes quantités conventionnelles de fertilisants (0 kg.ha-1, 100 kg.ha-1, 150 kg.ha-1) ont été étudiées. On observe que, suite à l’application de biochar, la quantité de phosphore (P) et de potassium (K) biodisponibles, les valeurs de pH et la concentration en carbone organique du sol augmentent. En parallèle, on remarque un accroissement significatif de la concentration en P dans les tissus végétaux. Les résultats montrent également une augmentation en biomasse aérienne, mais aucune variation significative en termes de rendement en grains. On peut donc en conclure que le biochar pourrait permettre une diminution des besoins en fertilisants ce qui impliquerait alors des moindres coûts pour l'agriculteur.

Biochar --- Tropical soils --- Plant nutrient uptake --- Zea mays L. --- maize --- in situ field experiment --- Burkina Faso --- Biochar --- Sols tropicaux --- absorption de nutriments par la plante --- Zea mays L. --- expérimentation in situ --- Burkina Faso --- Sciences du vivant > Agriculture & agronomie --- Physique, chimie, mathématiques & sciences de la terre > Sciences de la terre & géographie physique --- Sciences du vivant > Sciences de l'environnement & écologie

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As the world population is increasing in a world threatened by global warming, the uncertainty on our abilities to provide enough resources is growing. Among these concerns, water is a major element. Therefore, new farming methods, more respectful of our primary resources and of the durability or our soils are emerging. This study focuses on the effects of the type of tillage, crop residue management and the date of plowing on the hydraulic properties of the soil. Therefore, the water content has been studied from 2014 to 2016 after eight different treatments split on three fields. The tests showed that incorporating the crop residues was the most important factor improving the water storage capacity thanks to an increase of the organic matter. To a lesser extent, a reduced tillage has also a positive effect on the water storage. However, it has a significant positive effect compared to other treatments on the water retention capacity after a rain event. That might be explained by the smaller size of the soil pores, often caused by such treatment. The timing of tillage has no significant impact on the storage capacity or on the water retention of the soil. Conclusions could thus be drawn for the three studied factors. However, to increase the understanding on the treatment’s impact, a similar study should be conducted in a few years, when the soil modifications will be more pronounced.

cover crop --- crop residue --- hydraulic properties --- Sciences du vivant > Agriculture & agronomie