Train the youth! Effect of water stress and intercropping on peach tree growth after plantation

info:eu-repo/semantics/publishedVersio

Vergers plurispécifiques: piloter l’enracinement des arbres en profondeur par l’association d’herbacées dès la plantation

UMR SYSTEM : équipe AMPLUSAgroforestry consists of associating trees and crop in the same plot and requires that complementarity relationships be established between the two species in order to reduce competition, especially at the root level. The aim of this work was to test and evaluate the possibility of driving young peach tree roots under the roots of the associated crop (grass) in order to establish complementarity in resources uptake using two levers: (i) a moderate water deficit to change the carbon allocation pattern between shoots and roots in favour of roots and (ii) interspecific water competition to exclude tree roots from the first soil horizons and force them to grow at depth. To do so, we planted in January 2014 a peach tree orchard composed of three treatments (well-watered control, moderate water deficit and moderate water deficit + grass groundcover) which was monitored for two years. Shoot growth was dynamically monitored over the growing season and root excavations were performed each year at the end of the growing season. Our results show that all components of aerial growth were significantly reduced by the very moderate water deficit applied. The combination of a moderate water deficit and a grass groundcover led to a fourfold reduction in tree size after two years due to (i) grass competition for space, which reduced soil volume for the tree roots and consequently reduced shoot size and (ii) grass competition for water which by drying the soil led the tree to send root to shoot signals in order to reduce transpiration by stomatal closure. Our results on roots show that peach tree roots in the first two years of growth are mainly plagiotropic in the conditions of our study. The root/shoot ratio was not significantly modified in favour of roots under a moderate water deficit but combination of water deficit with grass competition led to a threefold reduction in root biomass et excluded tree roots from the topsoil horizon (0-10 cm) after two years. However, root growth mainly concentrated in the first 30 cm of soil in all treatments, but a small fraction of the root system (5%) in the control treatment was growing below the first 70 cm of soil (maximal excavation depth in our study) and was able to take up water up to 2 m depth. Thus, our results suggest that root system separation between trees and crop is a manageable emerging property, given that tree root architecture is characterized, and especially its plasticity in young trees. Innovating practices such as sowing trees and grafting them in the field could alleviate root injuries inherent to nursery practices. It is also possible to adjust the effect of the associated crop by selecting species and cultivars whose competitive ability is adapted to the tree age, by associating species with low competitive ability at the beginning of the tree development and with gradually more important competitive ability as the tree ages.L'agroforesterie consiste à mélanger sur la même surface des arbres et des cultures et nécessite que des relations de complémentarité s'établissent entre les deux espèces pour diminuer la compétition pour les ressources, notamment au niveau des interactions racinaires. L'objectif du travail de cette thèse était de tester et d'évaluer la possibilité de piloter l'enracinement de jeunes pêchers sous les racines de la culture associée (enherbement) afin d'établir une complémentarité dans l'utilisation des ressources du sol et en utilisant deux leviers: (i) un déficit hydrique modéré pour changer le patron d'allocation du carbone entre les compartiments aériens et souterrains en faveur des racines et (ii) la compétition interspécifique pour l'eau pour exclure les racines de l'arbre des horizons de sol superficiels et le contraindre à pousser en profondeur. Pour cela, un verger de pêchers composé de trois traitements (témoin bien irrigué, déficit modéré, déficit modéré + enherbement) a été installé en janvier 2014 et suivi pendant deux ans. La croissance du compartiment aérien a été suivie de manière dynamique sur la saison de croissance et des excavations racinaires ont été effectuées chaque année à la fin de la saison de croissance. Nos résultats montrent que tous les composants de la croissance ont été significativement réduits par le déficit hydrique très modéré. La combinaison d'un déficit hydrique modéré et d'un enherbement total ont réduit par quatre la taille des arbres au bout de deux années de croissance, réduction causée par deux mécanismes probablement additifs: (i) la compétition de l'herbe pour l'espace, réduisant le volume de sol prospectable par les racines de l'arbre et par répercussion le volume de l'appareil aérien et (ii) la compétition de l'herbe pour l'eau, qui en créant un dessèchement du sol, amène probablement le pêcher à générer des signaux racinaires à destination des parties aériennes pour réduire la transpiration par fermeture des stomates. Nos résultats sur les racines montrent que le développement du système racinaire du pêcher dans les conditions de notre étude pendant les deux premières années après la plantation est essentiellement plagiotrope. Le rapport racines/branches n'a pas été significativement modifié en faveur des racines sous l'effet du déficit hydrique mais la combinaison du déficit hydrique et de la compétition avec l'enherbement a diminué par trois la biomasse racinaire des arbres et exclu totalement les racines de l'horizon de surface (0-10 cm) au bout de deux ans. Cependant, la croissance racinaire se concentre majoritairement dans les 30 premiers cm de sol pour tous les traitements, mais une faible proportion du système racinaire totale (5%) des pêchers en condition hydrique non limitante dépasse les 70 premiers cm de sol (profondeur d'excavation maximale de l'étude) et est capable de prélever de l'eau jusqu'à 2 m de profondeur. Ainsi, nos résultats amènent à penser que la séparation des systèmes racinaires entre l'arbre et la culture est très certainement une propriété émergente pilotable, à condition de caractériser l'architecture racinaire de l'arbre et notamment sa plasticité chez des arbres jeunes. Des pratiques innovantes telles que l'installation des arbres par semis puis greffage au champ de la variété de production pourraient permettre de s'affranchir des traumatismes racinaires inhérents au mode de production des plants en pépinière. Il est également possible de moduler l'effet de la culture associée en sélectionnant des espèces et variétés dont la capacité compétitive souterraine est adaptée au stade de développement de l'arbre, en associant par exemple des espèces à faible capacité compétitive au début de son développement et à capacité compétitive graduellement plus importante au fur et à mesure qu'il grandit

Plurispecific orchards : shape in depth trees root system by association herbaceous crops at plantation

L'agroforesterie consiste à mélanger sur la même surface des arbres et des cultures et nécessite que des relations de complémentarité s'établissent entre les deux espèces pour diminuer la compétition pour les ressources, notamment au niveau des interactions racinaires. L'objectif du travail de cette thèse était de tester et d'évaluer la possibilité de piloter l'enracinement de jeunes pêchers sous les racines de la culture associée (enherbement) afin d'établir une complémentarité dans l'utilisation des ressources du sol et en utilisant deux leviers: (i) un déficit hydrique modéré pour changer le patron d'allocation du carbone entre les compartiments aérien et souterrain en faveur des racines et (ii) la compétition interspécifique pour l'eau pour exclure les racines de l'arbre des horizons de sol superficiels et le contraindre à pousser en profondeur. Pour cela, un verger de pêchers composé de trois traitements (témoin bien irrigué, déficit modéré, déficit modéré + enherbement) a été installé en janvier 2013 et suivi pendant deux ans. La croissance du compartiment aérien a été suivie de manière dynamique sur la saison de croissance et des excavations racinaires ont été effectuées chaque année à la fin de la saison de croissance. Nos résultats montrent que tous les composants de la croissance ont été significativement réduit par le déficit hydrique très modéré. La combinaison d'un déficit hydrique modéré et d'un enherbement total ont réduit par quatre la taille des arbres au bout de deux années de croissance, réduction causée par deux mécanismes probablement additifs: (i) la compétition de l'herbe pour l'espace, réduisant le volume de sol prospectable par les racines de l'arbre et par répercussion le volume de l'appareil aérien et (ii) la compétition de l'herbe pour l'eau, qui en créant un dessèchement du sol, amène probablement le pêcher à générer des signaux racinaires à destination des parties aériennes pour réduire la transpiration par fermeture des stomates. Nos résultats sur les racines montrent que le développement du système racinaire du pêcher dans les conditions de notre étude pendant les deux premières années après la plantation est essentiellement plagiotrope. Le rapport racines/branches n'a pas été significativement modifié en faveur des racines sous l'effet du déficit hydrique mais la combinaison du déficit hydrique et de la compétition avec l'enherbement a diminué par trois la biomasse racinaire des arbres et exclu totalement les racines de l'horizon de surface (0-10 cm) au bout de deux ans. Cependant, la croissance racinaire se concentre majoritairement dans les 30 premiers cm de sol pour tous les traitements, mais une faible proportion du système racinaire totale (5%) des pêchers en condition hydrique non limitante dépasse les 70 premiers cm de sol (profondeur d'excavation maximale de l'étude) et est capable de prélever de l'eau jusqu'à 2 m de profondeur. Ainsi, nos résultats amène à penser que la séparation des systèmes racinaires entre l'arbre et la culture est très certainement une propriété émergente pilotable, à conditions de caractériser l'architecture racinaire de l'arbre et notamment sa plasticité chez des arbres jeunes. Des pratiques innovantes telles que l'installation des arbres par semis puis greffage au champ de la variété de production pourraient permettre de s'affranchir des traumatismes racinaires inhérents au mode de production des plants en pépinière. Il est également possible de moduler l'effet de la culture associée en sélectionnant des espèces et variétés dont la capacité compétitive souterraine est adaptée au stade de développement de l'arbre, en associant par exemple des espèces à faible capacité compétitive au début de son développement et à capacité compétitive graduellement plus importante au fur et à mesure qu'il grandit.Agroforestry consists of association trees and crop in the same plot and requires that complementarity relationships be established between the two species in order to reduce competition, especially at the root level. The aim of this work was to test and evaluate the possibility of driving young peach tree roots under the roots of the associated crop (grass) in order to establish complementarity in resources uptake using two levers: (i) e moderate water deficit to change the carbon allocation pattern between shoots and roots in favour of roots and (ii) interspecific water competition to exclude tree roots from the first soil horizons and force them to grow at depth. To do so, we planted in January 2013 a peach tree orchard composed of three treatments (well-watered control, moderate water deficit and moderate water deficit + grass groundcover) which was monitored for two years. Shoot growth was dynamically monitored over the growing season and root excavations were performed each year at the end of the growing season. Our results show that all components of aerial growth were significantly reduced by the very moderate water deficit applied. The combination of a moderate water deficit and a grass groundcover led to a fourfold reduction in tree size after two years due to (i) grass competition for space, which reduced soil volume for the tree roots and consequently reduced shoot size and (ii) grass competition for water which by drying the soil led the tree to send root to shoot signals in order to reduce transpiration by stomatal closure. Our results on roots show that peach tree roots in the first two years of growth are mainly plagiotropic in the conditions of our study. The root/shoot ratio was not significantly modified in favour of roots under a moderate water deficit but combination of water deficit with grass competition led to a threefold reduction in root biomass et excluded tree roots from the topsoil horizon (0-10 cm) after two years. However, root growth mainly concentrated in the first 30 cm of soil in all treatments, but a small fraction of the root system (5%) in the control treatment was growing below the first 70 cm of soil (maximal excavation depth in our study) and was able to take up water up to 2 m depth. Thus, our results suggest that root system separation between trees and crop is a manageable emerging property, given that tree root architecture is characterized, and especially its plasticity in young trees. Innovating practices such as sowing trees and grafting them in the field could alleviate root injuries inherent to nursery practices. It is also possible to adjust the effect of the associated crop by selecting species and cultivars whose competitive ability is adapted to the tree age, by associating species with low competitive ability at the beginning of the tree development and with gradually more important competitive ability as the tree ages

Two years old peach trees intercropped with a grass mixture can grow through a lithic discontinuity to access water the grass cannot

International audienceThe hypothesis of niche complementarity for the use of soil resources is crucial for the performance of agroforestry systems. Our aim was to test the hypothesis that roots of 2 years old peach trees intercropped with grass can extract deep soil water below a shallow lithic discontinuity, composed of a layer of pebbles in a powdery calcareous matrix and that hardens in dry conditions. A peach tree orchard was planted on a soil with an average 0.5 m deep lithic discontinuity. Soil water content was measured every fortnight on the row and the inter-row with a neutron probe every 0.2 m up to 3 m depth. The contribution of each soil layer to trees and grass transpiration was simulated with a dynamic water balance model. Results show that tree roots grew through the lithic discontinuity and accessed a water refilled soil layer beneath it only 2 years after plantation, whereas grass roots did not grow below 0.5 m. Soil water content decrease up to 2 m depth after the cessation of irrigation was analysed as the result of tree water uptake. Tree water uptake simulations showed that soil layers below 1 m can contribute up to 17% of the total water uptake of the 2 years old trees. Our results suggest that a lithic discontinuity such as the one in our study may not be an impediment to the perennial trees root growth allowing them to access deep soil water. This suggests that soils with such a lithic discontinuity may be suitable for dryland agroforestry in which deep soil water available to the trees may help in reducing competition for water

Train the youth! Effect of water stress and intercropping on peach tree growth after plantation

The successful performance and stability of agroforestry systems relies on reduced competitionfor light and soil resources between trees and the intercrop. One management strategy couldtherefore be to ensure that the crop roots are well distributed in the upper soil horizons, whiletree roots are encouraged to forage in deeper horizons. In order for the latter to happen, thetree roots must have optimal growing conditions and at the same time be excluded by intensecompetition with crop roots from the upper soil horizons. One way of favouring optimal rootgrowth is to diminish the shoot carbon demand so that carbon is diverted towards roots insteadof shoots. Then combining shoot growth reduction with cover crop competition in the upper soilshould force tree roots to grow deeper.Shoot growth can be diminished through water stress, but net photosynthesis must remain at itsmaximum in order to maintain carbon fixation and allocation to roots. Our hypothesis is thatthere is a level of moderate water stress at which photosynthesis is not diminished while shootgrowth is (Pellegrino et al, 2006). This study aims to investigate the effects of moderate waterstress and grass intercrop competition on early shoot growth and net photosynthesis of peachtrees during the first two growing seasons after plantation

“Cropping the roots” of agroforestry systems: applying moderate water stress and water competition at plantation to increase tree root biomass

“Cropping the roots” of agroforestry systems: applying moderate water stress and water competition at plantation to increase tree root biomass. 5. International Symposium for Farming Systems Design (AGRO2015

Differential effect of regulated deficit irrigation on growth and photosynthesis in young peach trees intercropped with grass

The effects of a moderate soil water deficit on several shoot growth variables (1st and 2nd order shoot growth and final leaves number, final height and final number of 2nd order shoots) and on net photo- synthesis were studied in young peach trees during the two years following plantation (January 2014). Trees were either fully irrigated (C), subjected to moderate water deficit (RDI) or subjected to moderate water deficit and associated with a grass-legume mixture on the entire orchard floor (RDI +G). Irrigationwas scheduled according to soil water potential target ranges in order to keep C trees above −0.02 MPa, i.e. at field capacity, and RDI and RDI + G trees between −0.04 MPa and −0.06 MPa. The level of water deficit obtained was moderate but yet significantly reduced by 50% overall tree growth in 2014 in RDI.This reduction was enhanced when water deficit lasted longer and when it was associated with grass in RDI + G. No reduction in growth variables occurred in RDI in 2015 due to the shorter duration of water deficit. Overall reduction was observed in 2015 in RDI + G mostly due to a carry-over effect of the pre- vious year. Net photosynthesis was reduced by the longer and more intense water deficit in 2014, but was not reduced during the soil water deficit in 2015. An indicator of plant process sensitivity to water deficit, taking into account the variable reduction with regards to the control, the water deficit intensity and its duration was used to classify shoot growth variables and net photosynthesis according to their sensitivity to water deficit. Variables could be classified according to the following order of ascending sensitivity: net photosynthesis <1st order final leaf number < final tree height <1st order final shoot length <2nd order final leaf number <2nd order final shoot number <2nd order final shoot length. Applying a moderate water deficit combined with full grass cover drastically reduces overall tree size due to grass competitio

Train the youth! Effect of water stress and intercropping on peach tree growth after plantation

Train the youth! Effect of water stress and intercropping on peach tree growth after plantation. 3. European Agroforestry Conference (EURAF 2016

Simulating plant water stress dynamics in a wide range of bi-specific agrosystems in a region using the BISWAT model

International audienceThe ability to simulate soil and crop processes in many bi-specific systems (vineyards, orchards, silvo-arable agroforestry, strip-intercropping of arable crops…) is one of the major challenge for crop modelling in order to contribute to the design of agro-ecological cropping systems. A typical question is how soil, climate and management would influence the soil water deficit experienced by a plant grown alone or intercropped with a cover crop, with another crop or a tree, in order to improve the resilience of a cropping system to climate change and limit the use of chemical input. This study introduces BISWAT – Bispecific Intercrop System WATer Stress dynamic model - a new water balance model designed to simulate the dynamic of Soil Water deficit Experienced (SWEP) by two Plants when grown together or separated. BISWAT has been built to simulate a large range of agrosystems (annual and perennial crops, mono- or bi-specific) cultivated in various conditions. The model is primarily based on three modelling concepts: i) a 2D generic pattern for the system’s spatial representation, ii) the use of the Radiation Interception Efficiency (RIE) to drive potential plant transpiration and soil evaporation, iii) the use of the Total Transpirable Soil Water (TTSW) concept coupled with a simple root dynamics representation. These concepts are not new but they allowed us to define a model able to simulate many crops and trees (including vineyards) using a limited number of inputs and without an explicit need for parameter calibration. The model was evaluated on five reference agrosystems (mono-specific salads, mono-specific vineyards, bispecific vineyards, mono-specific peach orchards and bi-specific peach orchards). The RMSE of the SWEP variable ranged from 0.049 to 0.123. A combined sensitivity and uncertainty analysis performed on typical farmer’s fields situations stressed the particular importance of model inputs related to the TTSW of the soil-crop system. We conclude that the genericity of the BISWAT model, its method of parameterization and its performance open the perspective to use the model in a wide range of conditions where the dynamic of water stress between two species grown together is a key variable to be accessed with limited data for parameterization and a large number of fields to simulate

Effect of combined deficit irrigation and grass competition at plantation on peach tree root distribution

Agroforestry systems success is predicated on the assumption of root spatial separation between the tree and the crop species. Such a feature, where tree roots prospect subsoil horizons whereas intercrop roots prospect top soil horizon is thought to eventually happen as the system ages and trees get older. However, since roots are very plastic, we can hypothesise that it is possible to shape the tree root system when trees are young, i.e. after plantation. In this experiment, we tested the hypothesis that combining a moderate water deficit to change the carbon allocation pattern in favour of root over shoot growth combined with the top soil competition brought about by the intercrop will force tree roots to grow deeper, thus leading to the vertical separation of the trees and the intercrop root systems. To test this hypothesis, a peach tree orchard was established in 2014 with three water regime treatments: (i) a fully irrigated control without intercrop (C), (ii) a moderate water deficit treatment without intercrop (RDI) and (iii) a moderate water deficit treatment intercropped with a grass + legume mixture (RDI + G). Roots were manually excavated at the end of the first and the second growing seasons and root length and biomass per soil horizon and distance to the tree trunk were measured. The juvenile tree root system in all treatments was mainly plagiotropic, reaching 1.5 m from the tree trunk (middle of the inter row) horizontally as opposed to 0.7 m vertically, without difference between treatments. The combination of water deficit and intercrop competition reduced tree root biomass fourfold in 2014 and by 3 in 2015. Tree roots in RDI + G were also excluded from the topsoil horizon (0–10 cm) due to grass + legume competition, but because of the strong reduction in their total biomass, they did not grow in deeper soil horizons than the control tree roots (C). Secondary vertical tap roots were only starting to grow by the end of the second year, suggesting that root growth at depth could not take place the year after plantation especially in grafted scions