Changes in carbon stock and greenhouse gas balance in a coffee (Coffea arabica) monoculture versus an agroforestry system with Inga densiflora, in Costa Rica

Abstract

Agroforestry represents an opportunity to reduce CO 2 concentrations in the atmosphere by increasing carbon (C) stocks in agricultural lands. Agroforestry practices may also promote mineral N fertilization and the use of N 2-fixing legumes that favor the emission of non-CO 2 greenhouse gases (GHG) (N 2O and CH 4). The present study evaluates the net GHG balance in two adjacent coffee plantations, both highly fertilized (250kgNha -1year -1): a monoculture (CM) and a culture shaded by the N 2-fixing legume tree species Inga densiflora (CIn). C stocks, soil N 2O emissions and CH 4 uptakes were measured during the first cycle of both plantations. During a 3-year period (6-9 years after the establishment of the systems), soil C in the upper 10cm remained constant in the CIn plantation (+0.09±0.58MgCha -1year -1) and decreased slightly but not significantly in the CM plantation (-0.43±0.53MgCha -1year -1). Aboveground carbon stocks in the coffee monoculture and the agroforestry system amounted to 9.8±0.4 and 25.2±0.6MgCha -1, respectively, at 7 years after establishment. C storage rate in the phytomass was more than twice as large in the CIn compared to the CM system (4.6±0.1 and 2.0±0.1MgCha -1year -1, respectively). Annual soil N 2O emissions were 1.3 times larger in the CIn than in the CM plantation (5.8±0.5 and 4.3±0.3kgN-N 2Oha -1year -1, respectively). The net GHG balance at the soil scale calculated from the changes in soil C stocks and N 2O emissions, expressed in CO 2 equivalent, was negative in both coffee plantations indicating that the soil was a net source of GHG. Nevertheless this balance was in favor of the agroforestry system. The net GHG balance at the plantation scale, which includes additionally C storage in the phytomass, was positive and about 4 times larger in the CIn (14.59±2.20MgCO 2eqha -1year -1) than in the CM plantation (3.83±1.98MgCO 2eqha -1year -1). Thus converting the coffee monoculture to the coffee agroforestry plantation shaded by the N 2-fixing tree species I. densiflora would increase net atmospheric GHG removals by 10.76±2.96MgCO 2eqha -1year -1 during the first cycle of 8-9 years. © 2011 Elsevier B.V.