Implications of land use transitions on soil nitrogen in dynamic landscapes in Tanzania

Land use transitions are rated among the leading sources of greenhouse gas emissions in the tropics. They significantly challenge the functioning of ecosystems and affect multi-temporal stability of greenhouse gases such as N2O and soil properties. Studies on dynamics in nitrogen balances are essential in understanding greenhouse gas emissions such as N2O and to manage their impacts on productivity. In this study, multi-temporal Landsat images (1975, 1995 and 2012) were classified to determine land use transitions and potential drivers. The classified images were categorized into degraded and non-degraded lands and eighty sampling plots generated within the entire study area. Soil samples were then collected at 0-15, 15-30 and 30-60 cm depths on each plot and soil nitrogen determined. A regression analysis was developed to determine the influence of forest and grassland degradation on soil nitrogen. Results indicated a significant change in major land use and land cover types. Specifically, there was a decrease in areas covered by forests, woodland and grassland, however, area covered by less dense forest increased. Results also indicated variability in mean nitrogen content between degraded and non-degraded areas and depths. Furthermore, levels of degradation influence nitrogen content up to a soil depth of 30 cm. The present study is relevant in the detailed assessment of the extent of damage and threats posed to biodiversity hotspots in sub-Saharan Africa. These results are transferable to other parts of the world characterized by dynamic ecological transformation.