Competition and Productivity in Mixture of Oats and Wheat

The research assesses the productivity of mixture of oats (Avena saliva) and wheat (Triticum aestivum), and compares two different approaches used in plant competition studies: replacement (substitutive) designs and additive designs. The experiment was carried out on sandy loam soil at the Experimental Station of Agricultural University of Wroclaw (Poland). Oats and wheat were grown for grain as sole crops and in 1: 1 replacement mixtures at three rates of seeding: 150, 300 and 600 viable seeds m -2 . These designs allowed mixtures seeded at a rate of 300 and 600 seeds m -2 to be analysed according to either a replacement or an additive approach. In 1999, pure stand wheat and oats-wheat mixture yielded significantly more grain than oats grown alone but in 2000 there was no difference in yield. Wheat outcompeted oats in mixture but the relative competitive ability of the two species changed little with increasing seeding density. Relative yield total (RYT) for grain was significantly > 1.0 (RYT = 1.07) in 1999 for the lowest seeding density, showing partial complementarity in use of limiting resources by the species in mixture. Based on grain yields, the results obtained from substitutive and additive mixtures were similar with respect to the relative yields and relative competitive ability of the two species concerned.