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−1yr−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−1yr−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.