Avilés-Vázquez, Ixia I.

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    Fijación biológica de nitrógeno y almacenamiento de carbon en agrosistemas de producción de carbono en agrosistemas de producción de café (Coffea arábica L.) en Puerto Rico
    (2009) Avilés-Vázquez, Ixia I.; Schröder, Eduardo C.; College of Agricultural Sciences; Van Bloem, Skip; González Muniz, Wigmar; O'Farril, Hipólito; Department of Crops and Agro-Environmental Sciences; Bellido, Canny
    Coffee agroforestry systems have been promoted because they have smaller environmental impact than sun grown coffee. The majority of shade grown coffee systems use leguminous trees capable of fixing N2 from the atmosphere, which can reduce the use of chemical fertilizer. In this study, biological nitrogen fixation was evaluated in leaf litter, lichens, epiphylls and in soil of three ecosystems, sun grown coffee, shade coffee and secondary forest at Jayuya, Lares and Las Marías. The acetylene reduction assay (ARA) was used to measure biological nitrogen fixation for a period of six months. N2 fixation in leaf litter at the three sites was significantly higher in the forest ecosystem, 71.8 mg N ha-1 period-1 , than in the coffee agrosystems (34.3 mg N ha-1 period-1 ). At Jayuya there was significantly higher N2 fixation in August and September in the forest ecosystem. Coffee phyllosphere N2 fixation was similar throughout the six month period and through the agrosystems at the three sites. Average N2 fixation by lichens was 2.75 µg N g dry weight-1 period-1 , similar throughout the six month period and throughout the ecosystems at all sites. N2 fixation in soil 0.5 m from Inga vera tree at Jayuya and Las Marías was 1.3 times higher than N2 fixation in soil 1.2 m from I. vera. Soil N2 fixation at shade coffee system was two times higher than sun grown coffee soil. At Lares, no significant differences were found between ecosystems. N2 fixation in all components studied was lower than other studies. These results suggest that agricultural systems have less capacity of asymbiotic N2 fixation than other natural ecosystems. Carbon pools of the different coffee agrosystems were evaluated. Aboveground biomass was calculated with regression equations for these life zones and C stored in biomass was determined. Coffee plants can store nearly 3.74 ton C ha-1 , while shade trees can store approximately 21.20 ton C ha-1 . Soil can store the largest amount of C in an ecosystem. Soil Carbon pools in sun grown coffee and shade grown coffee were 32.1 and 35.2 ton C ha-1 respectively; in the forest ecosystem C pool in soil was 50.8 ton C ha-1 . These results suggest that shade coffee agroforestry systems (59.65 ton C ha-1 ) are capable of storing more C on their biomass than sun grown coffee (36.42 ton C ha-1 ).