Nitrogen availability and soil N2O emissions following conversion of forests to coffee in southern Sumatra

Abstract

Changes in land use impact on the N cycle with both local and global consequences. We examined how conversion of forest to agriculture in one catchment in southern Sumatra altered N availability and soil N2O emission. Measurements were made along a chronosequence of forest land converted to coffee gardens. A number of different management practices were also examined. Inorganic N stocks and N cycling rates were highest in the forest and lower in the coffee gardens. The forest and young conversion sites appeared to be N limited, whereas the older agricultural sites and the more intensively managed sites were not as strongly N limited. N2O emissions were low in the forest (<2 kgN ha-1 yr-1) and increased sharply following deforestation. Emissions on recently cleared land were 4.6 kgN ha-1yr-1 and 8.4 kgN ha-1yr-1 in a 1-year-old coffee garden. Emissions in the older coffee gardens were lower with the lowest flux observed in a 10 year old site (1.8 kgN ha-1yr-1). We explored the effects of different types of management approaches that farmers are using in this landscape. Emissions in an 18-year-old multistrata coffee garden with a significant overstory of N fixing trees were 5 times greater (15.5 kg ha-1 yr-1) than emissions from forests. We also found that intensive organic matter management produced high emissions. To understand the spatial and temporal variability of the N2O emissions we used the hole-in-the-pipe conceptual model. N2O fluxes were lowest on N limited sites. Soil water content also played an important role and emissions were highest when water filled pore space (WFPS) was between 85 and 95%. A number of formulations of this model have been applied in different ways over the years to explain spatial and temporal variation in the soil N-oxide flux, and in this study we found the mechanistic explanation useful. Our study suggests that land use change and intensification of agriculture in N limited highland landscapes may significantly increase the biosphere to atmosphere flux of N gases. Copyright 2006 by the American Geophysical Union.