Effect of a sowing regime and water conditions on nitrogen content and accumulation in the aerial biomass of spring barley (Hordeum vulgare L.) and Italian ryegrass (Lolium multiflorum Lam.)

Competitive interactions are common in plant communities, but the underlying mechanisms and effects of competition have not been fully elucidated to date. A pot experiment (3 series in 2009-2011) was conducted to evaluate the effect of a sowing method of spring barley and Italian ryegrass, and different water condition on the nitrogen (N) content and accumulation in the aerial biomass of plants at different stages. The experimental factors were as follows: 1) sowing regime – pure sowing and mixed sowing – spring barley undersown with Italian ryegrass, 2) water supply – plants supplied with water to meet their full requirements and 50% water supply reduction. The N content of the aerial biomass of plants was determined at five phenological development stages of spring barley grown in a pure stand under optimal soil moisture conditions: leaf development, tillering, stem elongation, heading and ripening. Nitrogen uptake was determined based on the N content and dry matter accumulation in plants. Nitrogen concentrations in the aerial biomass of barley and ryegrass varied throughout the growing season. Nitrogen content was particularly high in leaves, and it decreased steadily during plant development. Neither the sowing regime nor the water supply exerted significant effects on the N content of the aerial biomass of spring barley. In Italian ryegrass, under optimal water supply, mixed sowing with spring barley decreased N concentrations in shoots only during tillering. In spring barley, mixed sowing reduced N uptake by biomass, and the observed decrease was exacerbated under water deficit. In Italian ryegrass, reduced water supply decreased N uptake, but the effect of competitive interactions between the analyzed species was usually stronger than the influence of water deficit. Differences in N accumulation in aerial biomass were determined by the amount of biomass produced in mixed stands and the responses of barley and ryegrass to water deficit.