Nitrogen Loss from Coffee Agroecosystems in Costa Rica: Leaching and Denitrification in the Presence and Absence of Shade Trees

Abstract 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 O 2 availability on N 2 O production and total denitrification (N 2 O‐N + N 2 ‐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 N 2 O‐N kg −1 d −1 ) than in unshaded plantations (455 µg N 2 O‐N kg −1 d −1 ). Carbon additions elicited the largest increase in denitrification, generating nearly a threefold increase (+ C = 8396 µg N 2 O‐N kg −1 d −1 ; −C = 2985 µg N 2 O‐N kg −1 d −1 ) in both plantation types. Anaerobic conditions also significantly increased denitriflcation (+ O 2 = 4331 µg N 2 O‐N kg −1 d −1 ; µO 2 = 6656 µg N 2 O‐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.