Quantification of biological nitrogen fixation in shadow trees from two coffee plantation in Cuba

In coffee agroecosystems, it is of much importance to maintain appropriate levels of nitrogen to guarantee stable and sustainable productions. In this agriculture type, it is fundamental to consider the insert of shade species that carry out the Biological Fixation of the Nitrogen like natural form of incorporating this element to the soil. In that sense, it was carried out an experiment in two coffee areas (Coffea canephora var. Robusta) of the East of Cuba, in Sagua-Nipe-Baracoa and Sierra Maestra mountains, with the objective of quantifying the production of dry biomass and content of two leguminous used as shade trees (Samanea saman and Gliricidia sepium) and starting, from those determinations, to estimate the nitrogen biological fixation by the total N difference method. The dry mass and N content quantified in the shade trees were superior to the valued in the coffee, due to the different behavior among the species in study, coffee dry mass oscillated between 1.23 and 1.75 t [ha.sup.-1] and the shade trees between 2 and 3 t [ha.sup.-1]. The contents of foliate N of the shade species oscillated among 25-40 kg [ha.sup.-1] and the coffee presented foliar concentrations of the element in appropriate ranges. The arboreal species present BFN between 20 and 55 %, that which transforms them into an important source for the contribution and recycling of the nitrogen inside the coffee ecosystems. Key words: Coffea canephora, Gliricidia sepium, dry mass, Samanea saman