Nitrogen Loss from Coffee Agroecosystems in Costa Rica: Leaching and Denitrification in the Presence and Absence of Shade Trees
- Liana I. Babbar and
- Donald R. Zak *
Coffee (Coffea arabica L.) management in Costa Rica is changing from traditional agroecosystems, where coffee is grown beneath a tree overstory, to management systems where shade trees are removed and N fertilizer is applied at high rates (ca. 300 kg N ha−1 yr−1). Although fertilization increases coffee bean production, it also increases the potential for substantial loss of N to groundwater and the atmosphere. We investigated NO−3 leaching and the factors controlling denitrification in shaded and unshaded coffee plantations in the Central Valley of Costa Rica; both plantation types were fertilized with 300 kg N ha−1 yr−1. Nitrate leaching was quantified using porous ceramic cup lysimeters placed 60 cm below the soil surface. Losses were estimated by multiplying the soil water NO−3 concentration by the monthly soil water excess, determined as the difference between precipitation and actual evapotranspiration. In addition, a laboratory experiment was conducted to investigate the influence of NO−3, C, and O2 availability on N2O production and total denitrification (N2O-N + N2-N). Annual leaching losses of NO−3 were almost three times greater in unshaded plantations (24 kg NO−3-N ha−1 yr−1) than those in shaded plantations (9 kg ha−1 yr−1). In contrast, mean total denitrification rates in control soil samples from shaded plantations were 60% higher (732 µg N2O-N kg−1 d−1) than in unshaded plantations (455 µg N2O-N kg−1 d−1). Carbon additions elicited the largest increase in denitrification, generating nearly a threefold increase (+ C = 8396 µg N2O-N kg−1 d−1; −C = 2985 µg N2O-N kg−1 d−1) in both plantation types. Anaerobic conditions also significantly increased denitriflcation (+ O2 = 4331 µg N2O-N kg−1 d−1; µO2 = 6656 µg N2O-N kg−1 d−1). In both plantation types, the potential for N loss via NO−3 leaching was small compared with that for gaseous N loss.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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