GROWTH AND YIELD RESPONSES OF 2 CONTRASTING BARLEY CULTIVARS IN A MEDITERRANEAN ENVIRONMENT

The central area of the Ebro valley in northern Spain has a continenta l Mediterranean climate with variable rainfall, ranging from 250 to 50 0 mm. Water is the main factor limiting yield of rainfed agriculture. During four seasons (1985-86 to 1988-89), the performance of two barle y cultivars of contrasting phenology (cvs. Dobla and Tina) was studied at El Canos (north-eastern Spain). Growth, yield and yield components , water use and root development were evaluated. Yields ranged from 1. 2 to 3.0 t ha(-1) for the four experimental years which were all below average in rainfall. Total water use by the crop and ET during the pr e-anthesis period were main determinants of grain yield (r = 0.75, p < 0.001). The most variable yield component across genotypes and years was the number of ears per square meter, which determined final grain yield. Dobla, a modern cultivar, had greater plasticity and responded by having greater growth rates during pre-anthesis when the number of grains per ear was determined. Dobla avoided the terminal water stress , and its grain filling period was less adversedly affected than that of Tina, a late-flowering and older cultivar. Dobla produced less leaf area but had a greater extintiction coefficient and intercepted more radiation per unit leaf area. In the very dry years, yields of both cu ltivars were similar; however, Dobla outyielded Tina (3.0 vs. 2.3 t ha (-1)) in 1987-88 when the rainfall approached normal. It is concluded that Dobla is a cultivar better suited for the area despite the greate r stability and higher biomass production of Tina.