Saturday, 15 July 2006

NIitogen and Phosphorus Contributions from Litterfall in Shade Gown Coffee (Coffea arabica) Plantations in the Venezuelan Andes.

Arellano Rosalva1, Jorge Paolini2, Miguel Robles1, and Elda Villegas1. (1) Univ de Los Andes Núcleo Univ Rafael Rangel, Av. Medina Angarita, Sector Carmona, Grupo de Investigaciones de Suelos y Aguas (GISA), Trujillo, Venezuela, (2) Instituto de Investigaciones Científicas (IVIC), Centro de Ecología, Caracas, Venezuela

The litterfall represents the main source of entrance of nutrients in many agroecosystems in Venezuela, especially in the coffee agroecosystems where shade trees are used to provide mulch, humus and nutrients, to protect the coffee bush from harsh wind, excessive light and soil erosion and to regulate temperature and humidity. However, it is usual for some farmers the application of chemical fertilizers without the previous knowledge of the nutritional contribution of the litterfall of the shade trees. The objective of the present study was to evaluate, during one year, the contributions of nitrogen and phosphorus through the litterfall in two agroecosystems of coffee (Coffea arabica) under shade in the venezuelan Andes. The Vitú Sector (Trujillo state) is located to an altitude of 1100 masl, slopes varied between 36 and 45%; with an average rainfall of 1200 mm characterized by bimodal distribution with maxima in the periods around May and October, being January the driest month. The agroecosystem A consists of Coffea arabica var. red and yellow caturra, 10 years old, with a density of 6000 plants / ha, with shade trees of Inga spp and Ficus spp. The agroecosystem B is compound for Coffea arabica var. red caturra 14 years old, with a density of 5500 plants / ha, with shade trees of Inga spp, Bixa oreana and Persea americana among other. The litterfall was collected monthly in traps distributed at random in three selected plots of 100 m2 (6 traps/plot, 18 traps/agroecosystem); the litter samples were taken to the laboratory and dried in oven at 60°C for two days to constant weight. The litter was separated into compartments divided by species and vegetative part: leaves of coffee, leaves of shade trees, branches, flowers and fruits and weighted. The chemical analysis was carried out to combined samples made up of the fraction of leaves of coffee and shade trees per plot and per month. Total nitrogen was determined by Kjeldahl method and total phosphor after ashing by the molybdenum blue colorimetric method. The total annual production of litterfall in the agroecosystem A was of 5.5 Mg/ha with a maximum in January (0,95 kg/ha) and in the agroecosystem B was of 5.7 Mg/ha with a maximum in February (0,79 kg/ ha). The litterfall in both agroecosystems, reaches maxima values in the dry season, because during this period the vegetation is subjected to hydrical shortage (water stress) which affects the physiological functions of the plants causing the fall of the leaves. The contribution to the annual litter fall of its different fractions was the following: Agroecosystem A: leaves of shade trees (52%) > leaves of coffee (24%) > flowers and fruits (16%) > branches (8%). Agroecosystem B: leaves of shade trees (64%) > leaves of coffee (21%) > branches (9%) > flowers and fruits (6%). The concentration of nitrogen and phosphorus in both agroecosystems was the following: Agroecosystem A: leaves of coffee: 2.10-3.00% N and 0.07-0.12% P; leaves of shade trees: 1.30-2.07% N and 0.05-0.09% P Agroecosystem B: leaves of coffee: 2.02-2.38% N and 0.11-0.16% P; leaves of shade trees: 1.90-2.16% N and 0.07-0.15% P In the agroecosystem A, the concentrations of N in the leaves of coffee overcome that of the shade trees in every month; in contrast to the agroecosystem B, where the concentrations are similar for both types of leaves. From a nutritional point of view, the observed range of total N concentration in both agroecosystems is considered appropriate for the cultivation of coffee, with suggests that the supply of N from the litterfall is appropriate. The concentrations of P are similar for both types of leaves and for both agroecosystems. Key words: nitrogen, phosphorus, Coffea arabica, litterfall, Andes, Venezuela.

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