(Reçu le 15 février 1999 ; accepté le 3 mai 1999)Résumé -Afin d'estimer la pérennité de l'alimentation minérale de plantations forestières de Pinus pinaster et Eucalyptus globulus de forte productivité en Galice, nous avons calculé des bilans (entrées-sorties) d'éléments minéraux dans trois petits bassins versants. Dans chacun de ces trois bassins, les sorties par drainage de Ca, Mg et K sont inférieures aux entrées par les pluies. Cette particularité est attribuée à la relative pauvreté en cations alcalino-terreux des roches mères, au très faible drainage de sulfate et nitrate lié à l'absence de pollution atmosphérique, et surtout à la forte immobilisation forestière qui tire directement profit des apports par les pluies. L'exploitation forestière actuelle des peuplements de pins et d'eucalyptus conduit à des bilans fortement négatifs de Ca, Mg et K, mais qui diffèrent peu entre ces peuplements. La différence majeure provient du mode d'exploitation, selon que les arbres sont ou non écorcés en forêt, et que la litière est exportée. La libération par altération minérale d'un flux relativement important de Ca et K est nécessaire pour compenser ces pertes. Les estimations du flux d'altération conduisent à penser que ce flux est suffisant dans le bassin versant sur granodiorite. Dans les bassins versants sur granite, ce flux est vraisemblablement insuffisant en ce qui concerne le Ca, mais des mesures complémentaires sont nécessaires pour pouvoir l'affirmer. Les bilans d'azote montrent qu'une forte fixation symbiotique est indispensable pour assurer la pérennité de la production forestière. bassin versant / Eucalyptus globulus / Pinus pinaster / altération / GaliceAbstract -Budgets of mineral elements in small forested catchments in Galicia (NW Spain). In order to assess the sustainability of mineral supply to fast growing Eucalyptus globulus and Pinus pinaster stands in Galice (NW Spain), we calculated (input-output) nutrient budgets in three small catchments: the Castrove and Jabali catchments with eucalyptus on a base poor granite and the Arcos catchment with pine on granodiorite. In each catchment, the annual drainage output was lower than the rainwater input for Ca, Mg and K. This particularity is attributed to (a) the relative low content of Ca and Mg of the parent material, (b) the very low concentrations of NO 3 and SO 4 of drainage water in an area with very low level of atmospheric pollution, and (c) to the strong mineral uptake of fast growing stands. The present management of forests leads to negative budgets, both in the eucalyptus and pine catchments. But the traditional management of pine stands including the harvest of needles and branches was much more impoverishing than the present management of eucalyptus stands, where timber is the only harvested product. Various estimates of the weathering rate suggest that this flux is sufficient to compensate for the losses in the catchment on granodiorite but probably insufficient on granite. Since nitrogen deposition is extremely low, and forest fires are qui...

Analysis of energy flows and economic dynamics allows the diversity of variables involved in the agroecosystem production to be observed in the same dimension. In this way, efficiency and performance can be analysed integrally to identify critical points to be improved. The objective of this study was to analyse the energy-economic efficiency within three management strategies (Management I, Management II and Management III) of the maize agroecosystem in the Frailesca region of Chiapas (Mexico). The hypothesis was that systemic typologies, defined by modes of production, can lead to different efficiencies for the system performance. The study was descriptive; case studies were selected as representative based on their technological variants. The efficiency analysis was conducted using a balance of inputs and outputs expressed in energy and economic terms. Management III resulted in better energy use efficiency, with 6.47, while Management I and Management II were more economically feasible, with a benefit/cost ratio of 1.56 pesos.

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The establishment of new coffee plantations requires vigorous and healthy seedlings that guarantee good growth and high yields; hence the importance of studying the effect of bio-stimulant substances in the early stages of the crop's ontogeny. In this sense, the combined effect of five concentrations of salicylic acid (0; 0.0125; 0.025; 0.05; 0.1 and 1 mM) and different times of imbibition of the seeds (1, 2, 3 and 4 h), on the germination and initial growth of coffee plants (Coffea arabica L.) variety Costa Rica 95 was studied. The experimental design was completely randomized with a bifactorial arrangement, with 24 treatments and 20 repetitions. The percentage and germination rate, height and diameter of the hypocotyl were evaluated. The results showed that the concentrations (0.0125; 0.025 and 0.05 mM) and imbibition times of the seeds of 3 and 4 h in salicylic acid promoted an early germination and a positive effect on the height and diameter of the hypocotyl. The findings show that salicylic acid applied in low concentrations can be used to accelerate the germination of coffee seeds and induce the initial growth of coffee plantlets, while it could be considered as a viable option for coffee producers, both for its easy application and the safety of the product.

The identification and characterization of farmers types in the maize agroecosystem is an essential element for the development of effective and sustainable socio-productive strategies. In four municipalities of the Frailesca region in Chiapas, Mexico; maize farmers were typified and their agroecosystem was characterized regarding the criteria: socioeconomic, productive and energy efficiency. Besides, farmers relation to conventional, agro-ecological and mixed production strategies was determined. It was an exploratory socio-agronomic and descriptive research focused on a system approach and energy flows. The sample used was 300 farmers. For data management, descriptive statistics and exploratory multivariate analysis of principal components and clusters were used to construct the typologies. Five types of farmers-groups were identified based on six components that explained 83 % of the total variance. Among these components, the following stood out: "Yield and Efficiency", "Maize profile" (refers to the type of maize and its importance within the system) and "Energy Consumption". The typified groups of farmers were labeled as: "Small farmers", "Major farmers", "Mixed livestock-maize farmers", "Subsistence farmers" and "Maize-stubble producers". All groups are characterized by having small maize areas, but they are considered to have an acceptable energy efficiency, greater than 10 MJ and yields between 2.8 and 4.0 t.ha-1, higher than the average for the state of Chiapas. All groups were efficient in the use of energy, as result of the high productive and economic capacity of the agroecosystem. The maize yield is between 2.8 and 4.0 t.ha-1 and the energy efficiency is higher than 10 MJ. Conventional agriculture management predominates in the region in 86 % of the studied systems.