Crop attributes explaining current grain yield dominance of maize over sorghum

Yield genetic gains have been significantly higher for maize (Zea mays L.) than for sorghum (Sorghum bicolor L. Moench). Today there is questioning under which environments sorghum is a better option than maize, since maize has increased its tolerance to water and N limitations. For this we conducted eleven rainfed experiments at different sites around the central region of Argentina, using representative commercial genotypes of each crop. Experiments involved different sowing dates and N fertilization treatments, generating a total of 21 growing conditions where both crops were simultaneously compared. Measured traits included yield, phenology, leaf area development, light interception, and biomass accumulation. Explored growing conditions yielded from 1.8 to 11.7 Mg ha(-1) for maize, and from 1.4 to 9.9 Mg ha(-1) for sorghum. Crops yield difference (maize minus sorghum) ranged from -0.3 to 4.8 Mg ha(-1), and this difference significantly favoured maize in all growing conditions except one. As expected, the yield difference in favor to maize increased in magnitude in the environments with more positive water balance (r: 0.54; p < 0.01) and higher N levels (r: 0.43; p < 0.05). When compared to maize, sorghum always showed a longer time to anthesis and a shorter grain-filling duration, higher LAI, lower post-anthesis biomass accumulation, and similar total biomass at physiological maturity. Maize harvest index was higher and less variable than the sorghum one (0.44 to 0.56 and 0.28 to 0.45, for maize and sorghum, respectively). A comparison with previous literature showed that the cut-off yield (i.e., maize yield below which sorghum has better yield performance) is significantly lower than expected. Results reinforce previous evidences highlighting that the differential research investment in the two crops is limiting the capacity of sorghum to out-yield maize across environments.