Nitrogen and water use efficiencies of wheat and barley under a Mediterranean environment in Catalonia

In Southern Mediterranean regions, farmers usually grow barley monocultures in drought-prone areas while wheat is grown in better-watered regions. This is based on an assumption of better performance of barley than wheat in terms of productivity and resource capture. Information about the comparative performance of these species under scarce resource availability is rudimentary. The aim of the present work was to compare the performance of bread and durum wheat and barley in terms of water use, nitrogen uptake, water use efficiency and nitrogen use efficiency under Mediterranean environments. Four experiments were conducted on farmers’ fields at Agramunt, in the province of Lleida (Catalonia, north-eastern Spain) during 2004/05, 2005/06 and 2006/07. Treatments consisted of barley, bread wheat and durum wheat grown under different combinations of water (rainfed or irrigated) and nitrogen availabilities. Water and nitrogen availabilities resulted in a wide range of water use efficiency (from 6.3 to 23kggᵣₐᵢₙha⁻¹mm⁻¹) and nitrogen use efficiency (from 2.9 to 31.8kggᵣₐᵢₙkgₐᵥₐᵢₗₐbₗₑN ⁻¹ in soil). Nitrogen uptake was closely and positively related to grain yield and total biomass at maturity for the three species. Nitrogen fertilization modified yield of the three species, mainly through changes in water use efficiency (R²=0.75). Differences between the species were low but existed in relative terms; they were not always in favor of barley. In fact, barley did not consistently outperform bread or durum wheat in terms of resource use or resource use efficiency under poor-yielding conditions. The relative differences between wheat and barley in terms of grain yield (analyzed as wheat yield/barley yield) were explained by the relative differences between them in terms of nitrogen use efficiency and water use efficiency (analyzed as wheat resource use efficiency/barley resource use efficiency).