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In a recent study on the NPK balance of land use systems in sub-Saharan Africa, it was found that scale-inherent simplifications were inevitable (Stoorvogel et al., 1993). This article reports on a similar exercise in a well-inventorized smaller area (Kisii District, Southwestern Kenya). Land use types and land/water classes (combinations of rainfall zones and soil units) were combined into geographically well-defined land use systems with NPK inputs by mineral fertilizers, manure, wet and dry deposition, and biological N fixation, and outputs by aboveground crop parts, leaching, denitrification, and erosion. Primary data were available on applied mineral fertilizers and manure, crop yields, nutrient contents, residue removal and erosion. Deposition, leaching and denitrification were estimated using rainfall, clay, N and K content, and fertilizer input. Erosion was estimated along the lines of the Universal Soil Loss …