Nutrient cycling in agroecosystems: nitrogen cycling in southern Sweden in the 1850s and two Tanzanian villages in the 1990s

This study presents a general model for analysing nutrient cycling in agroecosystems. The focus is on food production intensity, human carrying capacity, sustainability and efficiency. The model can be used on systems including different kinds of land uses, which makes it applicable for studies on different scales. Comparisons of all kinds of agroecosystems, independent of time and place, are made possible. Different kinds of nutrients can be studied with the model. Here, nitrogen cycling is used as an example. A region in Scania, southern Sweden, 1858, and two Tanzanian villages, 1989-91, are analysed. The book includes a discussion of ecological principles of how humans can increase their food production, based on nutrient cycling and with concrete examples. Main conclusions in the thesis are: - There exists a conflict between increase of food production and sustainability. - Crop-dominated agroecosystems have higher human carrying capacities and are more efficient, concerning nitrogen losses per unit of nitrogen in the food produced, than livestock-dominated agroecosystems. - Neither the Tanzanian nor the Scanian agroecosystems can be judged as being sustainable. - There were high losses of nitrogen from livestock manure/excreta, especially in the Scanian agroecosystems. - Biological nitrogen fixation on cultivated land was the most important input in the Scanian agroecosystems and has a large potential for improving the negative nitrogen budgets of cultivated land in the Tanzanian systems.