Mixed cropping systems with oil crops are of growing interest in organic farming. They can offer agricultural advances like competition against weeds, support against lodg¬ing and buffering of yield fluctuations. The aim of the cultivation method is to gain additional oil yields for energy or feed purposes. The reported higher land-efficiency-ratios of those mixed cropping systems should lead to higher nutrient requirements. But it is unknown if the different crops just compete for rare soil nutrients or if comple¬mentary effects in mixed cropping systems lead to higher nutrient efficiency. In a field study N-contents in plants and N uptake of diverse mixed cropping systems were compared to sole cropping systems. In linseed (Linum usitatissivum) or false flax (Camelina sativa) in combination with spring wheat (Triticum aestivum) the oil crops showed lower N contents during stem elongation. The N concentrations in wheat tissue were not affected by competition. Wheat was dominating the mixtures. In mix-tures of peas (Pisum sativum) with false flax elevated N concentra¬tions in plant tissue of both component crops were determined. In non-leguminous mixtures with RYT >1 (spring wheat x false flax), N uptake exceeded the N-require¬ment of the sole crops. In mixtures of legumes with oil crops with RYT >1 (peas x false flax), the N-uptake of the mixtures was equivalent to or exceeded the N uptake of sole-cropped oil crops
