Soil greenhouse gas fluxes (N2O, CH4, CO2) and nitrogen (N) leaching in the humid tropics are expected to increase substantially in the near future due to increased deforestation, atmospheric N deposition, and agricultural intensification. However, only relatively few studies have investigated the biogeochemical implications of these anthropogenic and natural changes on soil greenhouse gas fluxes and N leaching in the tropical ecosystems. This PhD project is focused on the role of soil nutrients for soil biogeochemical processes in two contrasting ecosystems; tropical rain forest and sugarcane plantations in Uganda. More specifically, the study aims to investigate (1) how nutrient limitations affect soil greenhouse gas fluxes in the tropical rain forest; and (2) how conversion from natural forest to sugarcane production affects trace greenhouse gas fluxes and N leaching along a fertilizer intensification gradient. The research plans to explore soil factors controlling trace gas fluxes, net soil N cycling rates, and N leaching rates under nutrient elevated tropical forest ecosystems and large scale fertilizer-intensive sugarcane plantation. Our findings will contribute to (1) the scientific discourse about the likely effects of increased nutrient additions (through N deposition) to soil gas fluxes and N leaching in the humid tropics, (2) permit assessment and comparison of land use specific greenhouse gas fluxes budgets in order to inform policy makers about the likely impacts of converting forest land to sugarcane production; and (3) provide insights on fertilizer use efficiency and optimum fertilizer use in large scale intensive sugarcane production.

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