Effect of cultivar mixture on the competitive ability of barley against weeds

Abstract: While it is known that mixtures of cultivars generally stabilise crop yields and reduce losses caused by diseases, their influence on weeds has not yet been thoroughly investigated. Competitive effects against weeds are dependent on specific plant characteristics, which can vary between cultivars. The aim of this study was to investigate whether mixtures of barley cultivars with different characteristics could suppress weeds better than barley grown in pure stands, and whether the weed suppressive effect differed between the mixtures. A greenhouse trial was performed with three two-rowed spring barley (Hordeum vulgare L. spp. vulgare) cultivars grown in pure stands, all possible two-cultivar mixtures and the three-cultivar mixture. The barley cultivars Hydrogen, Henni and Troon were chosen because they differ in the three characteristics allelopathic activity, root length development and shoot length in the first growth stages. Turnip rape (Brassica rapa cv. Agat) and perennial ryegrass ( Lolium perenne cv. Helmer) were chosen as model weed flora. The results indicate that cultivar mixtures can improve the competitive ability of barley, reducing biomass production by weeds and diminishing barley biomass losses. Contrasting allelopathic activity and shoot development characteristics in the mixture increased the competitive effect. The weed suppressive effect differed between mixtures and was lowest in the mixture with differing root development but low shoot development and high allelopathic activity. Mixtures did not express the sum of characteristics of each individual barley cultivar. In fact, on some occasions the mixture that showed the best competitive ability did not contain the cultivar that demonstrated the best competitive ability when grown in pure stand. The mixtures that included cv. Hydrogen, which has high allelopathic activity, improved the competitive response in terms of barley biomass. Mixture design is needed to get cultivar mixtures that can control weeds. More research is needed on this aspect to devise a formula that allows us to design correct mixtures, and therefore to use cultivar mixing as a method for controlling weeds.