Genetic improvement of yield responsiveness to nitrogen fertilization and its physiological determinants in barley

Traditionally, barley in Argentina has been cultivated in low-yielding environments. A study was conducted to test whether breeding for improved performance under these conditions would have also improved the responsiveness to nitrogen availability. Four cultivars of two-rowed malting barley (released in 1944, 1960,1982 and 1998) were grown under 4 rates of nitrogen fertilizer at sowing (20, 50, 110and 160 kgN ha^-1). All cultivars increased their yield with the increase in soil nitrogen. But yield of modern cultivars responded more strongly than yield of old ones. For modern cultivars, increase in grain yield was of 12 ± 0.6 kgha^-1 for each 10 kg ha^-1 of increase in the mean yield (environmental index). Absolute values of genetic gain were related to nitrogen availability: 1.59, 2.58, 4.52 and 4.29 g m^-2 year^-1 for the N₂₀, N₅₀, N₁₁₀ and N₁₆₀ treatments, respectively. Grain yield was associated with grain number m^-2, which was dependent on spikes m^-2 and grains spike^-1. Total biomass at maturity also explained the changes in yield. It is concluded that selection under stress conditions was, in this case, beneficial to identify cultivars with high yields under a wide range of nitrogen availabilities. This revised version was published online in July 2006 with corrections to the Cover Date.