Des bilans de phosphore majoritairement négatifs pour les systèmes de grandes cultures biologiques sans élevage en Midi-Pyrénées. Quels impacts sur le phosphore biodisponible des sols et l’état de nutrition des cultures ?

Soil phosphorus (P) fertility management in organic cropping systems is a debated issue in the general context of decreasing resources in a near future. A survey showed that in Midi-Pyrenees a majority of stockless organic cropping systems present overdrawn P balances. We investigated the impacts of P balances on the soil plant available P and nutrition status on the long-term field experiment of La Hourre (CREAB, Auch, France), which is representative of rainfed systems set on clayey calcareous soils. The changes in soil plant available P were monitored between 2002 and 2012 using P Olsen soil test. The results specified the declining rate of P availability in time and according to the amplitude of the negative balance. The levels of soil available P did not still lead to degradation of the crop P nutrition status; in this context, N inputs are low, so consequently crop P needs remain limited. However the problems associated with long term management of soil P fertility remain. Beyond the desirable scientific perspectives, we propose a first analysis of the factors on which it would be relevant to act in order to allow the farmers to improve their practices

Stratégies d'acquisition des ressources des plantes prairiales sous contraintes hydrique et minérale - Rôle du système racinaire dans la réponse aux facteurs structurant les communautés

A l heure où l on cherche à optimiser les services éco-systémiques fournis par les prairies, une meilleure compréhension du fonctionnement des systèmes racinaires apparait comme nécessaire. Nous avons donc décidé de caractériser les stratégies d espèces issues des familles des Fabaceae et Poaceae prairiales par la mesure de traits fonctionnels racinaires. Le principal résultat de ce travail est la mise en évidence de plusieurs axes majeurs de différentiation des stratégies racinaires et de leurs relations avec les exigences écologiques des espèces. Le plus important est le compromis entre stratégies de capture et de conservation des ressources. Les espèces à stratégie de capture sont mieux adaptées aux milieux peu stressants notamment pour l eau, mais sont peu impactées par le manque de phosphore, ce sont aussi des compétitrices efficaces. Bien que les plantes à stratégie de conservation soient mieux à même de se développer dans des milieux continentaux, elles sont plus impactées que les autres par la présence de compétiteurs et le manque de phosphore. Le type de relations existant entre les stratégies aériennes et racinaires apparait aussi comme un marqueur de l adaptation des plantes aux stress. L étude du système racinaire est donc un moyen efficace de prédire le comportement des espèces de plantes prairiales face à des contraintes abiotiques et biotiques. Cela ouvre des perspectives particulièrement intéressantes notamment pour la construction de mélanges d espèces mieux adaptées à leurs environnements.In order to optimise grassland ecosystem services we need to improve our understanding of root system functioning. As a result, we decided to characterise strategies of species coming from grassland Fabaceae and Poaceae families, by root functional traits measurement. The main result of this work is the establishment of several axes of root strategies differentiation. The main axis is the trade-off between resources capture and conservation strategies. Species with capture strategies appear to be adapted to non-water stressful habitat and are barely impacted by phosphorus shortage; they also happen to be strong competitors. On the opposite, species with conservation strategies are adapted to water stressful continental climates, but are strongly impacted by phosphorus shortage and happen to be weak competitors. The kind of relation between above-ground and below-ground strategies also appears to be a marker of the plants adaptation to stress. We showed that the root system study is a good way to predict grassland species comportment to face abiotic and biotic constraints. The present work widens interesting perspectives for the sowing of mixed grassland species better adapted to their environments.TOULOUSE-INP (315552154) / SudocSudocFranceF

CONTRIBUTIONS DES PARTENARIATS POUR CONCEVOIR DES CONNAISSANCES AGRONOMIQUES SUR LA GESTION DE L'HERBE ET DEVELOPPER DES OUTILS ACTIONNABLES PAR DES CONSEILLERS FOURRAGERS

N° ISBN - 978-2-7380-1284-5International audienceCo-design of artifacts usable by extension services can be a long-lasting task. It partly depends on the developments of scientific knowledge. In addition, as we will show in this testimony, training and partnership with practitioners play a key role in the design of an artifact, here a tool to diagnose the opportunity of grassland management practices in a farm. Discussions between researchers and practitioners during training sessions led to the design of prototypes of articfact. Partnership between researchers and practitioners on the long term contributed to adjust the artifact, to simplify its procedure, and overall to improve its diagnosis capacity by capitalizing on researchers' and practitioners' knowledge. This experience has required adaptive capacity of researchers, leading them to adopt different research postures according to the stages in the interactions with practitioners. Researchers considered practitioners as knowledge providers by associating them to articfact co-design, or as experts to be equipped by involving them in participatory research projects

Shared Research Questions On Soil Quality In Organic Farming Systems

"In 2018, a participatory national workshop was organized by ITAB (Organic Food and Farming Technical Institute) and INRA (National Institute for Agricultural Research) in order to highlight issues on soils in Organic Farming (OF) systems. The objectives were: i) to identify the key research questions to be addressed on soils in OF, ii) to make it possible to facilitate network and project building from interactions between academics and stakeholders.Over 150 participants from academic and professional origins attended the workshop which was designed according to The Town Hall Meeting (THM) methodology.High level discussions among participants and panel experts ended up with a list of 20 research questions which confirmed the important lack of knowledge on that topic and the needs for research on the following issues: soils functioning with a focus on biogeochemical cycling and biological interactions; long term effects of agricultural practices, more or less specific to OF; soils protection; tools for soils diagnosis and management.

Nutritive value and physical and chemical deterrents of forage grass litter explain feeding performances of two soil macrodetritivores

Millipedes (Diplopoda) and terrestrial isopods (Isopoda) may play a significant role in soil decomposition. The present study aimed to contribute to the general understanding of feeding performances of macrodetritivores consuming grass litter by answering two questions. Q1: Are grass litter traits indicating nutritive value (i.e. chemical) and traits indicating feeding deterrents (i.e. mainly physical but not necessarily) both necessary to explain individual feeding performances of soil invertebrates consuming grass litter? Q2: Do grass physical traits indicating physical deterrents (e.g. WHC for mechanical aspects) provide more than, less than or the same amount of information about invertebrate individual performances as grass chemical traits indicating mainly chemical but also physical deterrents (e.g. lignin content directly for digestibility and indirectly for mechanical aspects)? We thus designed a laboratory experiment to assess individual feeding performances of two common macrodetritivores (Armadillidium vulgare (Latreille, 1804) and Glomeris marginata (Villiers, 1789)) in four monospecific treatments of litter from perennial forage grasses (Brachypodium pinnatum P. Beauv., Bromus erectus Huds., Festuca rubra L. and Holcus lanatus L.). A. vulgare feeding performances were correlated with nutritive values (litter N and P contents) and plant mechanical aspects (LDMC: leaf dry matter content). G. marginata performances were correlated with chemical deterrents (cellulose and lignin contents). Thus, (Q1) for grass litters, both traits indicating nutritive value (e.g. N, P) and feeding deterrents (e.g. LDMC, lignin content) are necessary to explain macroinvertebrates feeding performances. We also demonstrated the results depend on the invertebrate species considered. Also, (Q2) chemical deterrents may influence feeding performances of G. marginata the most, while physical deterrents related to mechanical aspects may influence those of A. vulgare the most. Our study shows that using grass chemical and physical traits that indicate both nutritive value and feeding deterrents can help explain feeding performances of macrodetritivores

Surface energy of clay-synthetic humic acid complexes from contact angle measurement

The surface free energy components of clay-organic complexes were determined to assess to what extent an organic adsorbate modified the surface properties of the mineral, insofar as the stability of soil aggregates is concerned. Adsorption isotherms for two synthetic, humic acid-like polymers were determined on a Ca-montmorillonite. From contact-angle measurements performed on dry surfaces, the surface free energy properties of the clay-organic complexes were determined using the two-liquid-phases method (water and hydrocarbons). This method allows both the dispersive and nondispersive components of the solid surface free energy, 3,Ds and 7 v, to be determined. The results show that a very small amount of polymer (1% by weight) adsorbed on the external surfaces of the montmorillonite decreased markedly the surface free energy components of the clay: 3,Ds decreased from 75 to 28 mJ /m ~ for polycondensate catechol (PC) and from 75 to 30 mJ /m 2 for polycondensate catechol triglycine (PCT), whereas 3,vs ranged from 35 to 16 rrd/m 2 (PC) and from 35 to 17 mJ/m 2 (PCT). Although their chemical compositions were different, both polymers similarly modified ~sD and -iPs . Increasing the amount of polymer adsorbed (from 1% to 3.5% by weight) affected mostly 3,vs , which became as low as 5 mJ/m:; meanwhile, 3'~ decreased from 30 to 23 mJ/m 2. Possibly, the molecular orientation of the adsorbate changed in the process of dehydration. Following adsorption of synthetic humic acid-like polymers, dry Ca-montmorillonite complexes displayed 3's values < 50 mJ/m 2, which were consistent with the solid-water contact angles measured in air.Les composantes de l'énergie libre de surface sont mesurées pour des complexes organo-minéraux. Cette étude est menée dans le but de vérifier de quelle manière un revêtement organique modifie les propriétés de surface du minéral et peut jouer sur la stabilité structurale. On a déterminé les isothermes d'adsorption sur une montmorillonite calcique pour deux polymères synthétiques modules d'acides humiques. L'énergie libre de surface des complexes organo-minéraux est calculée à partir de la mesure des angles de contact obtenus sur des surfaces déshydratées avec la méthode à deux phases liquides (eau et hydrocarbures). Cette méthode permet de déterminer à la fois "r~ et ~,~, qui sont respectivement la composante polaire et la composante dispersive de l'énergie de surface 3's. Les r6sultats montrent qu'une quantité très faible de polymère (1% en poids) adsorbé sur les surfaces externes de la montmorillonite diminue de manière importante les composantes de l'énergie libre de surface du minéral: 3,Ds diminue de 75 ~t 28 mJ/m 2 pour le polycondensat catéchol (PC) et de 75 h 30 mJ/m 2 pour le polycondensat catéchol triglycine (PCT), alors que 3,Ps varie de 35 ~ 16 mJ /m 2 (PC) et de 35 ~t 17 mJ /m 2 (PCT). Bien que leurs compositions chimiques soient différentes, les deux polymères modifient pareillement ~sP e t "y~'. Une augmentation sensible des quantités adsorbées (de 1% ~t 3,5% en poids) affecte principalement 3,vs qui diminue jusqu'à une valeur de 5 mJ/m 2, alors que "y~ passe de 30 h 23 mJ/m 2. Ces modifications importantes sont attribuées à un changement d'orientation des polymères adsorbés, susceptible de s'être produit au cours de la déshydratation. Après adsorption de polymères synthétiques modèles d'acides humiques, la montmorillonite calcique à l'état sec présente des valeurs de "Vs inférieures ~ 50 mJ/m 2 qui sont en accord avec les angles de contact solide-eau-vapeur qui sont mesurés

Wetting properties of Fe and Ca humates

Contact angle determinations were carried out on Ca, Fe and H-humates in order to assess their wettability. The two liquids method (ref. 7) was suitably employed to characterize polar and dispersive interactions. Fe and H-humates displayed large contact angle with water and behaved as low surface energy polymers, whereas Ca-humate was quite hydrophilic

The fertility status of two protected saline wetlands in NE Spain

1 copia .pdf (con Fots., Figs., Tabls.) del Póster original presentado por los autores en el Congreso.We studied the soil and vegetation fertility of two saline wetlands located in arid (Guallar) and semiarid (Gallocanta) environments, with a mean rainfall of 346 and 488 mm, respectively. Fertility data could be useful to apply agro-environmental measures in vulnerable areas under the Nitrates Directive (91/676/EEC), as is the case of saline wetlands in agricultural areas. Soil management in semiarid lands is key to preserve diversity and to reconcile agriculture with habitats conservation.The sampling was performed in April 2013, and the sampling sites followed a gradient in soil salinity and flooding conditions. The first 25 cm of the soil (5 cm in GA19, GA20 and GA21), the surface water, and the vegetation were sampled along a soil transect extending from the crop towards the wetlands shoreline.This study is a result of the research project AGL2012-40100 funded by the Spanish Government (MINECO). We acknowledge the data provided by the Spanish Meteorological Agency (AEMET). E. Luna was financed by a fellowship from the Government of Aragón, Spain.Peer reviewe