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Ocho años de estudio de la ecofisiología del café, a través de experimentación y de modelación y el monitoreo de los servicios del ecosistema (SE) en una gran finca cafetalera en Costa Rica, revelaron varias recomendaciones prácticas para los agricultores y los formuladores de políticas. El sistema de cultivo estudiado dentro de nuestro observatorio colaborativo (Coffee-Flux), corresponde a un sistema agroforestal (SAF) a base de café bajo la sombra de grandes árboles de Erythrina poeppigiana (16% de la cubierta del dosel). Una gran cantidad de SE y limitantes dependen de las propiedades locales del suelo (en este caso Andisoles), especialmente de la erosión/infiltración, el agua/carbono y la capacidad de almacenamiento de nutrientes. Por lo tanto, para la evaluación de SE, el tipo de suelo es crucial. Una densidad adecuada de árboles de sombra (bastante baja aquí por la condición de libre crecimiento), redujo la severidad de las enfermedades de las hojas con la posibilidad de reducir el uso de plaguicidas y fungicidas. Un inventario simple del área basal en el collar de las plantas de café permitió estimar la biomasa subterránea y la edad promedio de la plantación, para juzgar su valor de mercado y decidir cuándo reemplazarla. Las fincas de café probablemente estén mucho más cerca de la neutralidad de C que lo indicado en el protocolo actual de C-neutralidad, que solo considera árboles de sombra, no los cafetos ni el suelo. Se proponen evaluaciones más completas, que ncluyen árboles, café, hojarasca, suelo y raíces en el balance C del SAF. Los árboles de sombra ofrecen muchos SE si se gestionan adecuadamente en el contexto local. En comparación con las condiciones a pleno sol, los árboles de sombra pueden (i) reducir la erosión laminar en un factor de 2; (ii) aumentar la fijación de N y el % de N reciclado en el sistema, reduciendo así los requisitos de fertilizantes; (iii) reducir la severidad de enfermedades de las hojas; (iv) aumentar el secuestro de C; (v) mejorar el microclima y (vi) reducir sustancialmente los efectos del cambio climático. En nuestro estudio de caso, no se encontró ningún efecto negativo sobre el rendimiento del café.

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.

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.

In agroforestry systems, shade trees strongly affect the physiology of the undergrown crop. However, a major paradigm is that the reduction in absorbed photosynthetically active radiation is, to a certain extent, compensated by an increase in light-use efficiency, thereby reducing the difference in net primary productivity between shaded and non-shaded plants. Due to the large spatial heterogeneity in agroforestry systems and the lack of appropriate tools, the combined effects of such variables have seldom been analysed, even though they may help understand physiological processes underlying yield dynamics. In this study, we monitored net primary productivity, during two years, on scales ranging from individual coffee plants to the entire plot. Absorbed radiation was mapped with a 3D model (MAESPA). Light-use efficiency and net assimilation rate were derived for each coffee plant individually. We found that although irradiance was reduced by 60% below crowns of shade trees, coffee light-use efficiency increased by 50%, leaving net primary productivity fairly stable across all shade levels. Variability of aboveground net primary productivity of coffee plants was caused primarily by the age of the plants and by intraspecific competition among them (drivers usually overlooked in the agroforestry literature) rather than by the presence of shade trees.

Introduction: Net primary productivity (NPP) plays a key role in the knowledge of the functioning, production and C sequestration of ecosystems. The part of C allocated to belowground organs is non-negligible and amounts to 33% of total NPP for fine roots (Jackson et al. 1997). Fine root turnover is rather high, particularly in tropical ecosystems (Jourdan et al. 2008). Nevertheless, belowground NPP (bNPP) was usually estimated from shallow soil samplings whereas it is now well-known that fine roots can grow deep into the soil and reach several meters in depth (Maeght et al. 2013). Agroforestry systems are often said to exhibit root competition which leads to deep rooting ecosystems. Coffee trees associated to native shade trees don't escape to this assumption. They are pruned every 5th year and resprout biomass represents a relatively small contribution to overall plant biomass, due to accumulation in perennial parts only (stumps, coarse roots). Our objectives here were to assess coffee root biomass and bNPP along the whole rooting profile (0-4.5 m) in coffee tree plantations as a function of distance to shade tree, between coffee trees and soil depth. Method: In this study, root biomass by root category was assessed on ten coffee plants, distributed according to an inventory of diameter at collar via 10 Voronoi trenches down to 1.5 m and 2 deep trenches along the full rooting profiles, down to 4.5 m. Fine root NPP was assessed by sequential coring with 8-cm-diameter cylindrical auger during 16 consecutive months in Costa Rica within the 0-30 cm soil horizon. We then extrapolated to the complete rooting profile of coffee trees using the Voronoi and deep trenches. Fine root bNPP calculations were performed using “decision matrix” (including fine root decomposition rate; Fairley and Alexander 1985) and “Max-Min” (McClaugherty et al. 1982) methods. Coarse root bNPP calculations were performed by allometry with the diameter at collar and annual growth rate. Results and Discussion: The total root biomass within the entire coffee root profile (down to 4.5m deep) amounted to 22.4 t ha-1 which represented almost the same amount as the aboveground perennial organs (stumps - 25.7 t ha-1) excluding the aerial renewal organs (sprouts, leaves, flowers and fruits). When adding the non-perennial aboveground compartments, the total coffee tree biomass amounted to 64.7t ha-1 with 65% and 35% of above- and belowground parts, respectively and a root:shoot ratio of 0.53. Coffee root biomass was spread out preferentially in shallow soil layers with 30% and 55% within the first 10cm and 30cm soil depth, respectively. 87 % and 92% % of root biomass were found within the first 1.0m and 1.5m of soil respectively. No significant differences in function of distances to shade trees were found. By contrast, a significant effect of the sampling positions was shown with more than two times higher coffee fine root biomass within the rows than within the adjacent inter-rows, whatever the soil depth. Fine root production of coffee trees in the 0–30cm soil layer amounted to 1.2 t ha-1 y-1; while fine root contributed to only 5% of the total NPP, which is rather low as compared to previous studies. Fine root turnover rates ranged from 0.7 to 0.8 y-1 estimated by “Max-Min” and decision matrix calculation methods, respectively, rather low for tropical humid perennial plantations (Jourdan et al. 2008). Large monthly fluctuations of fine root standing biomass might indicate large necromass production through senescence and mortality processes each month, which was not shown in the necromass amounts. High observed fine root decomposition rates may explain such result. Conclusion: Our results exhibited the first coffee root biomass estimates which integrates the total root profile, here down to 4.5m. High values of root production associated to low estimates of fine root turnover rates indicated a high potential of C sequestration in the belowground of these agroforestry systems. (Texte intégral)