The effects of rotations and intercropping of sorghum, maize, yam and groundnuts on organic nitrogen content were examined by analyzing soil samples from a 5 year old field trial. Significantly higher soil N levels were observed under rotations that included groundnut. Cropping in sequence was apparently more effective than intercropping for maintaining soil N status. Yams also showed beneficial effects on soil organic N. Statistical analysis of results was greatly hindered by soil variability which could not be eliminated by the randomized block design. Relationships between variability, experimental design and sampling methods are discussed.