Competition and yield advantage in barley varietal mixtures and in barley-oats mixtures were investigated. The trials were based on replacement series, but in a few cases the overall density of the stand was varied on the basis of an addition series. Both models of competition, one based on the de Wit model and the other upon a linear regression model, agreed as to which component was the dominant and which was the subordinate in the mixture. The competition coefficients from regression analyses depicted competition between components better in a dense than in a sparse stand. The competitive ability of a genotype did not depend directly upon individual characters of the genotype, such as rate of initial development, earliness, culm height, tillering capacity or grain yield in monoculture (adaptation), A good combination of characters from the viewpoint of competition was provided by the barley cv. Arra with its rapid initial development and rapid culm growth (earliness), the variety being dominant irrespective of number of components in the mixture, stand density, level of nitrogen fertilization or growing season. This suggests that competitive relations and distribution of resources within a mixture are determined at an early stage in the growing period. In other cases the competitive ability of a genotype varied from one environment to another with the competitive relations between components being inconsistent. The dominance of an aggressor usually increased with increasing nitrogen fertilization especially when the total density of the stand was high. As a rule, competition affected all the components of yield with the kernel weight being least affected. The grain yield of varietal mixtures did not differ from the yield of the highest yielding component grown alone, i.e., mixtures did not over yield. The relative yield total of varietal mixtures was higher at low (RYT > 1) than at optimal densities (RYT =1). Also the relative yield total was higher under conditions where the nitrogen fertilization was not optimal. The results of a varietal trial repeated during three successive years indicated that the relative yield total of a given mixture varied from one growing season to another, fluctuating around unity. Thus highly adapted barley varieties appear to compete for the same resources, and the grain yield advantage of such mixtures is marginal. The results of the barley-oats mixture trials revealed that the mixture may over yield. The relative yield totals of barley-oats mixtures were usually equal to or greater than unity the latter suggesting that the mixtures of barley and oats may use resources more efficiently than monocultures, and some grain yield advantage could be achieved with such mixtures. The protein yield of the barley-oats mixtures did not differ from the yield of the highest yielding component grown alone. The ratio of actual and expected protein yield and the relative protein yield total were usually slightly greater than one. The grain yields of mixtures were not consistently more stable than monocultures as determined by the coefficient of variation.
Assessment of competition and yield advantage in addition series of barley variety mixtures