Nutrient flows and balances at the field and farm scale: Exploring effects of land-use strategies and access to resources

Nutrient flux and balance studies are valuable tools to assess the sustainability of agro-ecosystems and potential consequences for agricultural productivity. This paper presents results from a study at the field/farm scale representing mixed farming systems typical for the East African Highlands. We selected catchments in the Dega (cool highlands and Woina Dega (warm-to-cool mid-highlands) of the Central Highlands of Ethiopia, to get more insight on how individual land use strategies and access to resources affect the magnitude of nutrient flows and resulting balances and to explore some of reasons of the variability within and between farming systems at different altitudes. Our results show that environmental condition, farming system (e.g. choice of crop), access to resources (e.g. land, livestock and fertilizer) and smallholders' source of off farm income influence the magnitude of nutrient fluxes and the degree to which nutrient fluxes may be imbalanced. In some respects our results differ from studies carried out at larger (i.e. more aggregated) spatial scales, which consistently show that homestead fields are zones of accumulation and distant fields as zone of depletion. Our results indicate that this is not always the case, and highlight the need for studies at the field and farm scales to include detailed biophysical and socioeconomic information to help explain major nutrient fluxes and to evaluate the system with respect to sustainable production. (C) 2006 Elsevier Ltd. All rights reserved.