AbstractRooting patterns, biomass production, tillering, and yield formation of four winter wheat cultivars in a low external input systemGrowth conditions of winter wheat in agricultural low external input systems, e.g. ecological agriculture differ from those in conventional agriculture with regard to nutrient flow, impact of diseases, and weed competition. Knowledge of the dynamics of yield formation of winter wheat cultivars is very important for further development of such systems. During two growing seasons root growth, above ground biomass production, tillering, and yield formation were studied with four winter wheat cultivars of different periods of release at two ecologically managed farms in Northern Hessia. The results can be summarized as follows:– In general, plant breeding did not lead to a reduced development of root systems or above ground biomass production in winter wheat (Stöppleret al. 1989 a). Modern wheat varieties develop an extensive root system in greater depth, which means better drought resistance.– Not only root length densities, total root length, characteristics of tillering, and yield formation showed clear genotypic differences between the winter wheat cultivars, but also the development of root systems and above ground biomass production.– Winter wheat cultivars with a high plant density seem to have a retarded root growth after tillering due to intra‐plant‐competition and late root growth during grain filling, whereas cultivars with a high ear weight develop an extensive root system before the grain filling period. At the beginning of this period, a great root length per culm seems to be most important to achieve a high ear weight. The results indicate that those cultivars with poor to medium tillering and high ear weight are very well adapted to the reduced nutrient flow in low external input systems of farming.–In low external input systems, a satisfactory wheat crop need be established befo