Prevention of pea lodging by intercropping barley with peas at different nitrogen fertilization levels

Field pea (Pisum sativum L) that is grown in pure stands tends to lodge, which may lead to decreased grain yields. Barley (Hordeum vulgare L.) intercropped With peas prevents lodging, but this facilitative effect of the cereal on the pea has rarely been examined. Two two-factorial experiments (Experiment 1 and Experiment 2) were conducted in 2005, 2006, and 2007 to study interactions between barley and a medium-tall, leafy field pea (Wiato cultivar) and between barley and a tall, leafy field pea (Fidelia cultivar). In both experiments, mineral N fertilizer was used at rates of 0,30, and 60 kg of N ha(-1). Experiment 1 was conducted to evaluate plant lodging, grain yield, the intercrop yield advantage over pure stands and competition between the intercropped species. Experiment 2 was designed to separate the facilitative effect of the mechanical support provided to the peas by the barley in the intercrop from the effects of competition. In the experiment, groups of four pea plants were grown supported by an iron wire frame to prevent their lodging. The frames were kept in the plots until the peas flowered fully or reached full maturity. Similar groups of legumes were also grown in mixtures with nine barley plants. These treatments permitted the determination of the net benefits to the peas of the mechanical support provided by the added barley between pea flowering and maturity. In Experiment 1, there was little lodging of the pea cultivars in the intercrops, whereas the pure stands lodged severely. In all years, the barley-pea intercrops were more productive than the sole crops (LER > 1). The barley-Wiato mixture yielded more grain than the barley-Fidelia mixture in 2005 and 2006. Both mixtures transgressively overyielded in 2006 at the nitrogen fertilizer rate of 30 kg of N ha(-1), and the barley-Wiato mixture did so at 0 kg of N ha(-1). Experiment 2 showed that mechanical plant support (facilitation) was more important for the tall cultivar Fidelia than for the medium-tall cultivar Wiato, but Fidelia was the weaker competitor of the two with barley. Increasing the N fertilizer rates decreased the pea tolerance to competition from barley in the intercrop. (C) 2013 Elsevier B.V. All rights reserved.