Search

National audience

Beninese smallholders associate food or cash crops with young oil palm stands to reduce field maintenance costs and gain income before the oil palm comes into production. However, little is known about the effects of these agroforestry systems on nutritional and growth status of the tree at end of its juvenile phase although it is well known that the tree production could be affected by the management in juvenile phase. We selected 15 plantations where the crop succession associated with the trees was mostly based on maize, cassava, tomato and pineapple respectively. Nutrient contents in soil and tree leaves, and the vegetative growth of the tree were examined at end of juvenile phase. We found that N and P nutrition of young palms was satisfactory but K nutrition was deficient in all systems especially in tomato and pineapple ones. There was a significant correlation between K contents in soil and palm tree leaves. In the pineapple- and tomato-based systems, the amount of K fertilizer did not compensate the exportations by the crop. We concluded that competition for K are particularly important in pineapple- and tomato-based systems although fertilizer inputs were the highest. Trade-offs between profitability of these associated crops and the productive performance of the tree could be sought. A better adaptation of mineral fertilization could help in satisfying these compromises.

Huit ans de travaux de recherche sur les services écosystémiques dans une grande ferme caféière du Costa Rica (observatoire collaboratif Coffee-Flux, en système agroforestier à base de caféiers sous de grands arbres d'Erythrina poeppigiana, surface projetée de couronne de l'ordre de 16 %) ont suggéré plusieurs applications pour les agriculteurs et les décideurs. Il est apparu que de nombreux services écosystémiques dépendaient des propriétés du sol (ici des Andisols), en particulier de l'érosion, de l'infiltration, de la capacité de stockage de l'eau et des éléments nutritifs. Nous confirmons qu'il est essentiel de lier les services hydrologiques et de conservation au type de sol en présence. Une densité adéquate d'arbres d'ombrage (plutôt faible ici) permet de réduire la sévérité des maladies foliaires avec, en perspective, une réduction de l'usage de pesticides-fongicides. Un simple inventaire de la surface basale au collet des caféiers permet d'estimer la biomasse souterraine et la moyenne d'âge d'une plantation de caféiers, ce qui permet d'évaluer sa valeur marchande ou de planifier son remplacement. Le protocole de calcul actuel pour la neutralité carbone des systèmes agroforestiers ne prend en compte que les arbres d'ombrage, pas la culture intercalaire. Dans la réalité, si on inclut les caféiers, on se rapproche très probablement de la neutralité. Des évaluations plus complètes, incluant les arbres, les caféiers, la litière, le sol et les racines dans le bilan en carbone du système agroforestier sont proposées. Les arbres d'ombrage offrent de nombreux servies écosystémiques s'ils sont gérés de manière adéquate dans le contexte local. Par rapport aux parcelles en plein soleil, nous montrons qu'ils réduisent l'érosion laminaire d'un facteur 2, augmentent la fixation de l'azote (N2) atmosphérique et le pourcentage d'azote recyclé dans le système, réduisant ainsi les besoins en engrais. Ils réduisent aussi la sévérité des maladies foliaires, augmentent la séquestration de carbone, améliorent le microclimat et atténuent substantiellement les effets des changements climatiques. Dans notre étude de cas, aucun effet négatif sur le rendement n'a été enregistré.

La matière organique du sol conditionne la productivité et la durabilité des systèmes de culture, mais maintenir son niveau est problématique dans les régions agricoles densément peuplées. Les travaux présentés avaient pour objectif d’évaluer l’effet de la légumineuse de couverture Mucuna pruriens var. utilis sur la fertilité et la conservation des sols dans un système à base de maïs au Sud-Bénin. L’étude a été conduite en parcelles d’érosion (240 m², pente 4 %) de 1988 à 1999 sur sol ferrallitique sableux devenant argilo-sableux en profondeur, sous climat tropical subhumide. Trois traitements étaient comparés, tous avec travail du sol à la houe : culture pure de maïs sans apport (notée Trad) ou avec fertilisation minérale (notée NPK) ; association maïs-mucuna (notée Muc), le mucuna étant semé un mois après le maïs. Le rendement en grain du maïs était équivalent pour les trois traitements en 1988 (500 kg.ha-1) ; en fin d’essai il avait diminué sur Trad (200 kg.ha-1), et augmenté sur NPK (2,5 Mg.ha-1) et surtout Muc (3,5 Mg.ha-1). De même, le stock de carbone du sol à 0-40 cm de profondeur ne différait pas entre traitements en 1988 ; en 1999, il avait varié de - 2, + 2 et + 15 MgC.ha-1 sur Trad, NPK et Muc, respectivement. En moyenne, le taux de ruissellement annuel était de 28, 12 et 8 % sur Trad, NPK et Muc, et l’érosion annuelle de 34, 9 et 3 Mg.ha-1.an-1, respectivement. Le mulch épais de mucuna enrichit le sol en matière organique et en azote, et permet d’améliorer le rendement et de diminuer le ruissellement et l’érosion. Soil organic matter determines the productivity and sustainability of cropping systems, but its maintaining is challenging in densely populated rural areas. The experiment presented here aimed at assessing the effects of the legume cover crop Mucuna pruriens var. utilis on soil fertility and conservation in a maize-based cropping system in southern Benin. The study was carried out in runoff plots (240 m², 4 % slope) from 1988 to 1999 on a sandy Ultisol becoming more clayey with depth, under subhumid tropical climate. Three cropping systems were compared, all hand-hoe tilled: pure maize without any input (denoted Trad) or with mineral fertilizers (denoted NPK); maize-mucuna association (denoted Muc), mucuna being sown one month after maize. Maize grain yield was similar for the three treatments in 1988 (500 kg ha-1); by the end of the trial it had decreased on Trad (200 kg ha-1), but had increased in NPK (2.5 Mg ha-1) and Muc (3.5 Mg ha-1). Similarly, carbon stock at 0-40 cm depth did not differ between treatments in 1988; in 1999 it had varied by - 2, + 2 and + 15 MgC ha-1 on Trad, NPK and Muc, respectively. Mean runoff rate and soil losses were 28, 12 and 8 %, and 34, 9 and 3 Mg ha-1 yr-1 in Trad, NPK and Muc, respectively. The thick mulch of mucuna enriched the soil in organic matter and nitrogen, and resulted in yield increase and runoff and erosion decrease.

Vu la dégradation de la productivité des sols labourés, il fallait tester l’effet du semis direct sous litière végétale pour contrôler l’érosion hydrique et améliorer le rendement des cultures pluviales sur les Hautes-Terres centrales malgaches. L’essai a été entrepris sur un dispositif de parcelles d’érosion à Andranomanelatra, sous pluies naturelles. Le dispositif compare plusieurs traitements en semis direct au labour conventionnel (bêchage à l’angady). Des mesures du ruissellement, de l’érosion et du rendement des cultures principales ont été effectuées durant quatre campagnes culturales. Les résultats ont confirmé l’effet positif des systèmes de semis direct pour contrôler le ruissellement et l’érosion. Par contre, les systèmes en semis direct n’améliorent pas automatiquement les productions. En effet, les rendements en grain de haricot sont significativement plus élevés sur les parcelles en semis direct que labourées. Alors que pour les rendements en maïs et en riz pluvial, d’une manière générale, ils sont significativement plus faibles en semis direct avec couverture vivante à base de Brachiaria ruziziensis que pour les parcelles labourées. Au fil du temps, il y a une nette augmentation des rendements en grain de riz et de maïs pour l’ensemble des traitements étudiés, avec une hausse encore plus visible sous systèmes en semis direct. The purpose of this study was to test the potential of no-tillage management to control erosion and improve crop yields in the Central Highlands of Madagascar. This study was carried out in Andranomanelatra under natural rainfall conditions. Conventional tillage and direct seeding system were imposed and compared in the experimental design. Runoff, erosion rates and crop yield were measured during four cropping periods. The results showed that direct seeding systems were significantly better to control erosion rates as compared to conventional tillage system. But direct seeding system does not systematically improve crop yield after 4 years. Indeed, common bean grain yields were greatest on direct seeding system than conventional tillage system. On the other hand, maize and rainfed rice yield were significantly lower in direct seeding mulch-based systems using living mulches (Brachiaria ruziziensis) than conventional tillage system. Over time, there is a real increase in rice and maize grain yields for all treatments studied with a larger increase in direct seeding system than conventional tillage system.

Depuis le milieu du xxe siècle, du fait de la forte croissance démographique, les sols et la végétation des zones tropicales et méditerranéennes subissent d'importantes dégradations. Actuellement, plus de 20 % des terres cultivées sont dégradées chimiquement, physiquement et biologiquement. En effet, malgré la mise en œuvre de grands projets tels la conservation de l'eau et des sols (CES), la production agricole ne peut être maintenue à un niveau suffisant pour nourrir une population qui double tous les vingt ans dans les pays du Sud. Cet ouvrage a ainsi pour objectif de présenter les principaux résultats de la recherche dans le domaine de la restauration de la productivité des sols. Les causes de la dégradation des sols des régions chaudes sont présentées dans un premier temps. On évalue ensuite les divers modes de gestion de la biomasse et des nutriments, puis les techniques culturales et les systèmes de gestion de l'eau. Les nombreuses données expérimentales présentées montrent que la restauration durable des systèmes agroécologiques est possible, moyennant le respect de six règles : une bonne maîtrise de l'eau, l'apport de matières organiques, l'utilisation de compléments minéraux, la revitalisation du sol (fumier / compost), la correction du pH du sol et le choix judicieux de cultures à fort développement de biomasse. L'ouvrage, qui présente de nombreuses études de terrain originales, s'adresse tant aux chercheurs qu'aux enseignants, aux étudiants, aux décideurs et aux différents acteurs en charge du développement rural.

Cette étude vise à tester l’effet de systèmes de culture en semis direct sous couverture végétale permanente (SCV) pour contrôler l’érosion hydrique et améliorer le rendement de cultures pluviales sur versant des Hautes-Terres de Madagascar. L’essai a été entrepris sur un dispositif expérimental d’érosion à Andranomanelatra, sous pluies naturelles. Le dispositif comporte plusieurs traitements en SCV et en labour conventionnel (bêchage à l’angady) ainsi qu’un témoin avec sol nu et un autre en jachère herbacée spontanée. Pendant quatre campagnes, des mesures du ruissellement, des pertes en terre, de la hauteur de la pluie et de son intensité maximale ont été effectuées à chaque événement pluvial érosif. Des mesures de rendements ont également été réalisées à la fin de chaque campagne culturale.Dans le contexte étudié, les résultats obtenus ont confirmé l’effet positif du système SCV sur la réduction du ruissellement et de l’érosion. Les ruissellements sur les parcelles labourées et sur la parcelle nue sont respectivement huit et quatorze fois plus élevés que sur les parcelles SCV. Les pertes en terre sur les parcelles labourées et la parcelle nue sont respectivement de7,6 et 22,1 t/ha/an alors que sur les parcelles SCV, elles sont d’environ 0,13 t/ha/ an.En général, les rendements en maïs et en riz pluvial obtenus sur les parcelles labourées et en SCV sous couverture morte ne diffèrent pas significativement. Mais les rendements en maïs et riz pluvial sont significativement plus faibles en SCV avec couverture vivante de Brachiaria ruziziensis que pour les parcelles labourées. En revanche, le rendement moyen en haricot est nettement et significativement plus élevé sur les parcelles SCV que sur les parcelles labourées.

Face à la pression démographique et foncière dans les pays en développement, la productivité des terres connaît actuellement une forte baisse dans de nombreuses régions tropicales. Par ailleurs, la succession rapprochée des tempêtes cycloniques entraîne l'appauvrissement extrême de certaines populations du fait de la dégradation des terres et des inondations des plaines où se développent les principales agglomérations. Telles sont les problématiques étudiées par l'IRD et le réseau Érosion de l'AUF dont ce CD présente les derniers travaux. Initialement réunies dans la perspective d'un colloque à Haïti (annulé suite au séisme de 2010), les contributions publiées ici portent sur des études de cas à Haïti, mais aussi à Madagascar, au Maghreb ou au Vietnam, soit au total une soixantaine de communications et une série de documents récents issus des réflexions des experts. Structuré en six thèmes, ce CD constitue ainsi une source bibliographique précieuse pour les décideurs, les experts, les ONG, les acteurs de la société civile et les chercheurs concernés par la gestion durable de l'eau et la restauration de la productivité des sols (GCES).

L'application de la connaissance des services écosystémiques rendus par les sols passe par leur meilleure connaissance dans des contextes divers. La Guyane cherche à allier un développement local à un maintien des services environnementaux rendus par les écosystèmes. La déforestation, lorsque pratiquée hors de cahiers de charges bien établis, conduit à la destruction partielle ou totale de l'horizon de surface des sols, donc au principal réservoir de carbone (C) des sols. La connaissance actuelle du carbone des sols de Guyane est limitée. Les données collectées ici permettent d'approcher la spatialisation des contenus de C même si la variabilité des stocks reste forte. Les modélisations du devenir des stocks de C suite à la déforestation ont été réalisées à partir des données collectées dans le projet CarSGuy et le site expérimental de Terres Inovia ; s'ajoutent à ces valeurs la compilation de données issus de campagnes précédentes : Réseau de Mesures de la Qualité des Sols (RMQS) et ValSol. Ces modélisations indiquent l'importance de la prise en compte du stock initial (T0) pour le devenir des stocks. Enfin ce travail a testé une méthodologie de mesures spectrales (visible et proche infra-rouge) de terrain des sols pour l'évaluation du stock. Les données collectées à partir de 236 sites permettent de quantifier et spatialiser les stocks (0-0,3/0-0,5/0-1 m). La modélisation permet de constater que la mise en culture induit de fortes baisses des stocks, 16 % du stock initial à court terme (~ année) après défriche. L'essai expérimental du site de Combi, montre que les stocks ont tendance à croître avec la mise en place d'une prairie de fauche intensive (Urochloa ruziziensis). Enfin, l'étude méthodologique de mesure du stock par spectroscopie-spectrométrie sur le terrain n'a pas été concluante, car testée sur un échantillon à forte diversité pédologique.

The biogeochemical cycle of Si has become a subject of increasing interest in recent yearsbecause of its interconnection with the C cycle and global change. Recent studies have suggestedthat land use and particularly agriculture can modify the Si cycle. However, the consequences ofsuch a modification for the global Si cycle and for the growth of crops which are Si accumulators(most of the cereals) are still not well constrained. The bioavailable Si fraction is govern by severalfactors, among which the amount in total Si (Si-tot) that represent the long term weatherable pool.This amount has thus to be quantified at the territory scale. However, its determination is timeconsuming and costly. It is performed by ICP-AES after mineralization by sodium peroxide andsodium carbonate fusion. We thus propose an alternative estimation of the Si-tot at the Frenchterritory scale, within the project BIOSISOL (ANR-14-CE01-002), based on the samples of theFrench soil monitoring network (RMQS). This network consist in 2130 sites sampled in a regular 16× 16-km grid. We measured topsoil Si-tot at 630 sites of the RMQS network consisting in one pointout of four from this network (that is 450 points) and a set of 150 points selected randomly amongthe remaining sites. Mid-infrared reflectance and a large set of soil properties were measured at allsites of the RMQS. These soil properties are particle-size distribution, pH water, organic carbon,Total N, soluble and total P contents, calcareous, CEC and exchangeable cations (K, Ca, Mg, Na),Bo and 8 trace elements (Cd, Cr, Cu, Co, Ni, Pb, Tl, Zn). The dataset was then divided in 3 sets:Calibration, validation and test sets. The two formers were defined using a repeated folding stepwithin the 650 sites and the latest corresponded to the 1500 remaining sites. Using a regressionrule algorithm called CUBIST, we found that Si-tot was very well predicted by the mid-infraredspectroscopy (validation R ~ 0.98 and test R ~ 0.97) and by conventional pedotransfer functionsusing soil properties (validation R ~ 0.98). This last model was used to evaluate the MIR model.Based on the MIR predictions, we then mapped the concentration of Sitot across France usingdigital soil mapping techniques.

Eight years of monitoring ecophysiology and ecosystem services (ES) in a large coffee farm of Costa Rica yields a range of practical applications for the farmer and stakeholders, thanks to numerous scientific actors and disciplines contributing to our collaborative observatory (Coffee-Flux). • A lot of ecosystem services depend on the soil properties, such as runoff/infiltration, water and nutrient storage capacity. It is essential to relate hydrological and soil conservation services to the soil type, since this might have even more importance than the crop itself for ES. Regarding the use of fertilizer, we show that some soils may have a large storage capacity, allowing producing coffee at normal yields with just a reduced, or even a minimum amount of fertilizers, for instance when the economic conditions are unfavorable. Also, due to the soil variability within the farm, it is possible to adjust fertilization to micro-local conditions and reduce the total expenses and risks of leaching of N to the environment. VNIRS and MIR are promising broadband tools for screening the variability in soils. Adjusting N fertilizer to the optimum will also considerably reduce the N2O emissions and improve the GHG balance of the farm. • Pesticides-fongicides: we show that an adequate amount of shade trees allows reducing the severity of the whole complex of leaf diseases. This also should reduce expenses and impacts on the ecosystem. • Roots: a simple survey of basal area at collar allows estimating the belowground biomass and the average age of a plantation, to judge of its market value and to decide when to replace it. • Also starch plays a key role in the trophic equilibrium between the perennial parts of the coffee plant (aerial stump, belowground stump, coarse roots) and its ephemeral parts (resprout, leaves, fruits, fine roots). Coffee plants accumulate starch in the stumps by the end of the life of their resprout, as a strategy for survival. Breeding plants with less starch build-up capacity would probably allow increasing the fraction of productive years during the lifespan of the resprouts. • Coffee farms are probably much closer to C neutrality than currently admitted using the C-Neutrality protocol. We stress the prevailing role of coffee plants + litter + soil in the ecosystem C balance. If those are excluded from the calculations as done so far, coffee farms are GHG sources, by definition. We argue that either full assessments (as proposed here, at the ecosystem level, including trees, coffee, litter, soil and roots) or consensus on “sequestration factors” (the counterpart of emission factors) would allow performing a more realistic assessment of the GHG balance. • Finally, we bring new data confirming that shade trees offer numerous ecosystem services, when adequately managed for the local context. As compared to full sun conditions, they may (i) reduce laminar erosion by a factor of ca. 2, (ii) increase the atmospheric N2 fixation and the % of N recycled into the system, thus reducing the fertilizer requirements, (iii) reduce the severity of the leaf disease complex, (iv) increase C sequestration, (v) improve the microclimate, and (vi) be a large part of the solution to face climate changes. All this is possibly without negative effects on profitability or yield, if managed properly. In our particular case-study, we encount.

The biogeochemical cycle of Si has become a subject of increasing interest in recent years because of its interconnection with the C cycle and global change. Recent studies have suggested that land use and particularly agriculture can modify the Si cycle. However, the consequences of such a modification for the global Si cycle and for the growth of crops which are Si accumulators (most of the cereals) are still not well constrained. The bioavailable Si fraction is govern by several factors, among which the amount in total Si (Si-tot) that represent the long term weatherable pool. This amount has thus to be quantified at the territory scale. However, its determination is time consuming and costly. It is performed by ICP-AES after mineralization by sodium peroxide and sodium carbonate fusion. We thus propose an alternative estimation of the Si-tot at the French territory scale, within the project BIOSISOL (ANR-14-CE01-002), based on the samples of the French soil monitoring network (RMQS). This network consist in 2130 sites sampled in a regular 16 × 16-km grid. We measured topsoil Si-tot at 630 sites of the RMQS network consisting in one point out of four from this network (that is 450 points) and a set of 150 points selected randomly among the remaining sites. Mid-infrared reflectance and a large set of soil properties were measured at all sites of the RMQS. These soil properties are particle-size distribution, pH water, organic carbon, Total N, soluble and total P contents, calcareous, CEC and exchangeable cations (K, Ca, Mg, Na), Bo and 8 trace elements (Cd, Cr, Cu, Co, Ni, Pb, Tl, Zn). The dataset was then divided in 3 sets: Calibration, validation and test sets. The two formers were defined using a repeated folding step within the 650 sites and the latest corresponded to the 1500 remaining sites. Using a regression rule algorithm called CUBIST, we found that Si-tot was very well predicted by the mid-infrared spectroscopy (validation R ~ 0.98 and test R ~ 0.97) and by conventional pedotransfer functions using soil properties (validation R ~ 0.98). This last model was used to evaluate the MIR model. Based on the MIR predictions, we then mapped the concentration of Sitot across France using digital soil mapping techniques.

Vu la dégradation de la productivité des sols labourés, il fallait tester l'effet du semis direct sous litière végétale pour contrôler l'érosion hydrique et améliorer le rendement des cultures pluviales sur les Hautes-Terres centrales malgaches. L'essai a été entrepris sur un dispositif de parcelles d'érosion à Andranomanelatra, sous pluies naturelles. Le dispositif compare plusieurs traitements en semis direct au labour conventionnel (bêchage à l'angady). Des mesures du ruissellement, de l'érosion et du rendement des cultures principales ont été effectuées durant quatre campagnes culturales. Les résultats ont confirmé l'effet positif des systèmes de semis direct pour contrôler le ruissellement et l'érosion. Par contre, les systèmes en semis direct n'améliorent pas automatiquement les productions. En effet, les rendements en grain de haricot sont significativement plus élevés sur les parcelles en semis direct que labourées. Alors que pour les rendements en maïs et en riz pluvial, d'une manière générale, ils sont significativement plus faibles en semis direct avec couverture vivante à base de Brachiaria ruziziensis que pour les parcelles labourées. Au fil du temps, il y a une nette augmentation des rendements en grain de riz et de maïs pour l'ensemble des traitements étudiés, avec une hausse encore plus visible sous systèmes en semis direct.

Introduction: Agroforestry systems are land use management systems in which trees are grown in combinationwith crops or pasture in the same field. In silvoarable systems, trees are intercropped with arable crops, andin silvopastoral systems trees are combined with pasture for livestock. These systems may produce forage andtimber as well as providing ecosystem services such as climate change mitigation. Carbon (C) is stored in theaboveground and belowground biomass of the trees, and the transfer of organic matter from the trees to the soilcan increase soil organic carbon (SOC) stocks. Few studies have assessed the impact of agroforestry systems oncarbon storage in soils in temperate climates, as most have been undertaken in tropical regions

Introduction: Besides producing food (or fiber) and wood, agroforestry systems may provide a variety of ecosystem services including climate change mitigation. Carbon (C) is stored in both the tree aboveground and belowground biomass, and organic inputs from the trees could increase soil organic carbon (SOC) stocks. However, few studies have assessed the impact of agroforestry systems on carbon storage in soils under temperate climates, as most of them have been performed in tropical regions. Methods: This study was conducted in five silvoarable agroforestry systems and in one silvopastoral system in France. All sites included an agroforestry system and an adjacent agricultural control plot. In all cases, crop and soil management in the agroforestry inter-rows and in the control plot were strictly the same. The ages of the study sites ranged from 6 to 41 years since the tree planting. Sampling depth ranged from 20 to 100 cm and SOC stocks were measured on an equivalent soil mass basis. Tree aboveground biomass was also measured at all sites. Results: In silvoarable systems, the mean SOC accumulation rate was 0.24 (0.09-0.46) Mg C ha-1 yr-1 at 0-30 cm depth. Additional SOC storage was also found in deeper soil layers at the oldest sites (Cardinael et al. 2015). Young plantations also stored SOC but mainly in the tree rows, and we suggested that the herbaceous vegetation growing in the tree rows was a key factor. In the silvopastoral system, additional storage was only found below 40 cm depth. The mean carbon stocks in the aboveground biomass was about 16 (0.02-36.69) Mg C ha-1 for all sites. Additional SOC between the agroforestry and the control plot was related to the age since the tree planting and to soil clay content. Discussion: All together our study demonstrated the potential of agroforestry systems to store SOC in temperate regions. It also pleads for implementation of long-term and diachronic agroforestry trials in order to estimate more accurately SOC storage potentialities, especially in old plantations where data are lacking. (Texte intégral)

Introduction : Les systèmes agroforestiers sont des agro-écosystèmes où sont associés des arbres et des cultures ou des prairies au sein d’une même parcelle. Ces systèmes fournissent un ensemble de services écosystémiques, et pourraient contribuer à l’atténuation du changement climatique. Du carbone est stocké dans la biomasse aérienne et souterraine des arbres, et les apports en matières organiques provenant des arbres pourraient avoir un impact positif sur les stocks de carbone organique du sol. Cependant, en milieu tempéré très peu d’études se sont intéressées à l’impact des systèmes agroforestiers sur le stockage de carbone organique dans les sols, la majorité ayant été menées en zones tropicales. De plus, beaucoup de questions demeurent quant à l’impact sur les stocks de carbone profonds. Méthode : Cette étude a été réalisée sur cinq sites agro-sylvicoles (arbres et cultures) et sur un site sylvopastoral (arbres et prairie pâturée) en France. Chaque site comprenait une parcelle agroforestière et une parcelle agricole adjacente comme parcelle témoin. Les itinéraires techniques dans les inter-rangs agroforestiers cultivés et dans les parcelles agricoles sont strictement identiques depuis la plantation des arbres, âgés de 6 à 41 ans selon les sites. Les prélèvements au cylindre ont été réalisés entre 20 et 100 cm de profondeur selon un protocole d’échantillonnage prenant en compte la distance aux arbres, et les stocks de carbone organique du sol mesurés à masse de sol équivalente. La biomasse aérienne des arbres a également été mesurée sur les différents sites. Résultats et discussion : Dans les parcelles agro-sylvicoles, un taux d’accumulation moyen de 0,24 (0,09-0,46) t C ha-1 an-1 a été mesuré sur l’horizon 0-30 cm par apport aux parcelles agricoles. Un stockage de carbone additionnel a également été mesuré en profondeur sur les sites les plus anciens. Dans les jeunes plantations, le stockage de carbone était principalement localisé sur les lignes d’arbres, et pourrait être la conséquence du couvert herbacé permanent plutôt que des arbres. Dans le système sylvopastoral, un stockage de carbone additionnel a seulement été mesuré en dessous de 40 cm de profondeur, probablement car les stocks de carbone organique dans les horizons de surface sous prairie étaient déjà très importants. Le stock de carbone dans la biomasse aérienne des arbres était de 16 (0,02-36,69) t C ha-1 en moyenne. Conclusion : Cette étude démontre le potentiel des systèmes agroforestiers pour améliorer les stocks de carbone organique du sol sous climat tempéré. Elle met également en évidence un manque de données sur les systèmes agroforestiers âgés, et montre la nécessité de mettre en place des essais diachroniques de long-terme.

Soil provides ecosystem services, supports human health and habitation, stores carbon and regulates emissions of greenhouse gases. Unprecedented pressures on soil from degradation and urbanization are threatening agro-ecological balances and food security. It is important that we learn more about soil to sustainably manage and preserve it for future generations. To this end, we developed and analyzed a global soil visible-near infrared (vis-NIR) spectral library. It is currently the largest and most diverse database of its kind. We show that the information encoded in the spectra can describe soil composition and be associated to land cover and its global geographic distribution, which acts as a surrogate for global climate variability. We also show the usefulness of the global spectra for predicting soil attributes such as soil organic and inorganic carbon, clay, silt, sand and iron contents, cation exchange capacity, and pH. Using wavelets to treat the spectra, which were recorded in different laboratories using different spectrometers and methods, helped to improve the spectroscopic modelling. We found that modelling a diverse set of spectra with a machine learning algorithm can find the local relationships in the data to produce accurate predictions of soil properties. The spectroscopic models that we derived are parsimonious and robust, and using them we derived a harmonized global soil attribute dataset, which might serve to facilitate research on soil at the global scale. This spectroscopic approach should help to deal with the shortage of data on soil to better understand it and to meet the growing demand for information to assess and monitor soil at scales ranging from regional to global. New contributions to the library are encouraged so that this work and our collaboration might progress to develop a dynamic and easily updatable database with better global coverage. We hope that this work will reinvigorate our community's discussion towards larger, more coordinated collaborations. We also hope that use of the database will deepen our understanding of soil so that we might sustainably manage it and extend the research outcomes of the soil, earth and environmental sciences towards applications that we have not yet dreamed of.

De la mise en place d’indicateurs pour la planification urbaine à la mesure des stocks de carbone, en passant par les instruments juridiques et économiques pour la protection des sols, cet ouvrage, issu du programme Gessol, synthétise les dernières connaissances biotechniques et sociétales sur le sujet. Il souligne l’importance d’une gestion durable des sols dans les enjeux globaux et identifie les leviers d’actions possibles.

Additional storage of soil organic carbon in an agroforestry system under Mediterranean climate. 5. International Symposium on Soil Organic Matter

Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. Annual additional SOC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm), and were mainly due to particulate organic matter fractions (> 50 μm). Only 10 to 15% was associated to clay particles. When the biomass of the trees was taken into account, total organic carbon storage rate reached 1.2 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. Agroforestry systems provide higher amounts of carbon at depth than other agricultural practices, like no-till farming, and could therefore provide a more stable C storage in the long-term.

International audience; Soil degradation and fertility loss pose severe threats to the livelihood of farmers in sub-saharan regions. Due to the need for land, continuous cultivation with staple food has gradually replaced previous shifting cultivation systems, so that fallow periods have considerably reduced and no longer fulfill their soil regeneration role. Here we explore the use and management of native woody resources for providing an in situ renewable organic amendment as a basis for increasing soil carbon and biological status, thus sustaining fertility, enhancing water capture and utilization and therefore buffering climatic stress.

Agroforestry is a land use type where crops and tree are grown together in the same place and at the same time. a groforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. i f they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate or Mediterranean conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize s OC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what s OC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. t he trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. s OC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. a nnual additional s OC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm). a dditional storage was mainly due to particulate organic matter fractions (> 50 μm) and 10 to 15% was associated to clay particles. When the aboveground biomass of the trees was taken into account, total organic carbon storage rate reached 1.11 ± 0.16 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. a groforestry systems provide higher amounts of carbon at depth than other agricultural practices, such as no-till farming, and could therefore provide a more stable C storage in the long-term. t his study was funded by a D e M e within the a gripsol project as part of the r eacctif program

Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. Annual additional SOC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm), and were mainly due to particulate organic matter fractions (> 50 μm). Only 10 to 15% was associated to clay particles. When the biomass of the trees was taken into account, total organic carbon storage rate reached 1.2 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. Agroforestry systems provide higher amounts of carbon at depth than other agricultural practices, like no-till farming, and could therefore provide a more stable C storage in the long-term.

Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate or Mediterranean conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m soil depth, and particle-size fractionation was performed on 64 soil samples. Carbon stocks of trees and of the herbaceous vegetation in the tree rows were also quantified. A trench was dug to 4 m soil depth to quantify tree fine root distribution and biomass. Minirhizotrons were installed at different depths to study tree fine root turnover. Annual additional SOC storage rates were estimated at 259 ± 59 kg C ha-1 yr-1 (0-30 cm) and at 350 ± 88 kg C ha-1 yr-1 (0-100 cm). Additional storage was mainly due to particulate organic matter fractions (> 50 μm) and 10 to 15% was associated to clay particles. When the aboveground biomass of the trees was taken into account, total organic carbon storage rate reached 1.11 ± 0.16 Mg C ha-1 yr-1. High tree root densities were observed at depth, but root turnover decreased with depth. Agroforestry systems provide higher amounts of carbon at depth than other agricultural practices, such as no-till farming, and could therefore provide a more stable C storage in the long-term.

In Sudano-Sahelian agriculture, organic amendments are often limited by resource availability. Small branches (ramial wood, RW) represent an organic resource found in many landscapes but little is known about their effects. This field trial (2007–2009) studied the effects of RW or straw at low application rate (0.69 Mg C ha−1 year−1) on topsoil carbon (C), nitrogen (N) and available phosphorus (P, Pav), termite cast abundance, and sorghum yield. Straw and RW were chopped and either buried (StBu, WoBu) or mulched (StMu, WoMu). Mineral fertilizers were added to straw so that RW- and straw-amended plots received similar applications of C, N, P, and potassium. Another treatment had RW buried with additional N (WoBuN), and there was a control (Ctrl). Branches came from Piliostigma reticulatum, very common in the area. The treatments had little significant effect on topsoil and crop, owing to the low application rate and spatial variability. However, Pav was significantly lower with buried than mulched amendments in 2009, and decreased significantly over time in Ctrl and with buried amendments. Topsoil C also decreased significantly with time in WoMu. Significantly more termite casts were observed with RW. The sorghum yield averaged 0.87 Mg DM ha−1 in 2007 and then decreased. The treatments affected yield significantly in 2008 only: it was higher in WoBuN and StBu than in Ctrl. In 2009, the yield was mainly affected by initial topsoil Pav. These results suggest that RW stimulated biological activity, leading to P immobilization and C mineralization, but had little effect on yields.

The Earth's soils are a large reservoir of carbon (C), containing about 1500 Pg C, which represents two to three times the C contained in the atmosphere. This reservoir is extremely sensitive to land use and can act as a source or as a sink of atmospheric CO 2. Agroforestry systems are expected to sequester C into both above and belowground biomass. Such systems could also increase soil organic carbon (SOC) stocks due to higher organic inputs including leaf litter, pruning residues, tree fine root s' turnover and root exudates. However, although tropical agroforestry systems have been thoroughly investigated, there are very few estimates of C sequestration in soils from temperate conditions. The objectives of this study were (i) to quantify the SOC stocks down to 2m soil depth in an 18 - year-old agroforestry system and in an adjacent agricultural plot , and (ii) to assess which SOC fractions are responsible for this additional storage. The experimental field was established in 1995 in Restinclières, South of France, on an alluvial carbonated Fluvisol. In the agroforestry system, hybrid walnuts (13x4 - 8m spacing, 85 trees ha-1 ) are intercropped with durum wheat, wh ereas in the adjacent agricultural plot, only durum wheat is cultivated. Spontaneous vegetation also gr ows on the tree row. About 200 soil cores were sampled from ten soil layers from 0 to 2m into the two plots of 625 m2 each. Bulk densities , texture and SOC contents were determined for each soil samples at each soil depth, using field spectroscopy. Carbon stocks were spatialized at the field scale. To determine which SOC fractions were affected by the agroforestry system, soil particle size fractionation was performed on 64 soil samples from 0-10, 10-30, 70-100 and 160 - 180 cm soil depth. C stocks were characterized by a high, but organized spatial variability. Spatial analysis showed doubled SOC contents on the tree row compared to the inter-row in surface soil layers, probably due to high inputs from the natural vegetation. Thanks to our extensive sampling scheme, we are able to provide the first quantification of soil C sequestration in these very representative agroforestry systems. After 18 years, this agroforestry system stored 4.9 ± 1.2 MgC ha - 1 down to 30 cm, and 6.3 ± 1. 8 MgC ha-1 down to 1 m. Annual additional soil carbon storage rates were estimated to be 272 ± 68 kgC ha-1 year-1 (0 - 30 cm) and 352 ± 98 kgC ha - 1 year - 1 (0 - 100 cm). This additional SOC storage was mainly due to the particulate organic matter fraction (50 - 200 and >200 μm), whereas only 10 to 15% was associated to clay particles. The total annual carbon storage rate would be about 1 MgC ha -1 year-1 when trees' biomass is taken into account, which is a lot compared to other techniques used to improve carbon storage in agriculture, like no-till farming or conservation agriculture. (Texte integral)

absent

Le stock de carbone (C) des sols est extrêmement sensible au changement d’usage des terres, et peut à la fois être une source ou un puits de CO2 atmosphérique. Les systèmes agroforestiers, associations d’arbres et de cultures sur une même parcelle, permettent de stocker du C dans la biomasse ligneuse aérienne et souterraine des arbres. De tels systèmes pourraient également améliorer les stocks de C organique du sol, de part des entrées de C plus importantes, comme les litières aériennes des arbres, les résidus de tailles, le renouvellement des racines fines et les exsudations racinaires des arbres et de la strate herbacée des allées d'arbres. Cependant, bien que les systèmes agroforestiers aient été largement étudiés en milieu tropical, très peu d’estimations du potentiel de stockage de C de ces systèmes sont disponibles pour les milieux tempérés et méditerranéens et les estimations ne concernent que les horizons superficiels du sol (Lorenz et Lal 2014). De plus l’estimation du potentiel de stockage est rendue plus difficile en raison de la variabilité spatiale importante dans ces systèmes.

La validation des méthodes et l’évaluation de l’incertitude sont deux exigences de la norme ISO 17025. L’utilisation de la spectroscopie proche infrarouge à des fins d’analyse quantitative nécessite par conséquent l’estimation de la justesse, de la répétabilité et de la reproductibilité de la méthode utilisée. L’hétérogénéité de l’échantillon est une composante des sources d’incertitude liées à une mesure analytique, au même titre que l’équipement utilisé, l’opérateur, les conditions ambiantes, etc.Dans cette étude, la justesse et la fidélité d’une méthode de prédiction des teneurs en carbone total et azote du sol par spectroscopie visible et proche infrarouge (VisNIR) sont estimées. Pour ce faire, 45 échantillons de sol de surface (0-30 cm) provenant du Réseau français de mesures de la qualité des sols (RMQS, INRA Orléans) ont été sélectionnés pour former des classes de teneur croissante en carbone total (de 5 à 130 gC/kg de sol ; sur ces échantillons, la teneur en azote varie de 0.7 à 13 gN/kg). Ces échantillons ont été analysés par la méthode de référence (combustion Dumas) avec un analyseur élémentaire CHN (FISONS - Thermo). Les spectres de réflectance de ces échantillons ont été acquis dans le VisNIR avec un spectromètre ASD LabSpec 2500 (350-2500 nm).Les modèles de prédiction ont été réalisés par régression des moindres carrés partiels (PLS) avec validation croisée « leave-one-out ». La fidélité intermédiaire ainsi que l’intervalle de tolérance pour les différentes classes de teneurs en carbone et azote ont été estimés pour la méthode de référence et pour la méthode spectroscopique en répétant les mesures, avec différents opérateurs, et à différentes dates. Les résultats de validation de méthode et d’évaluation de l’incertitude ont été représentés graphiquement en se basant sur les profils d’exactitudes développés par Feinberg et al (2004). En fixant une limite d’acceptabilité de ± 20% autour de la mesure de référence, le domaine de validité des modèles de prédiction étaient de 40 à 130 gC/kg pour les teneurs en carbone total du sol, et de 5 à 13 gN/kg pour les teneurs en azote du sol.