Grain yield of barley (Hordeum vulgare L.) in northern Syria is limited by water stress and extremes of temperature. The present study compared the grain yield of two barley cultivars, Harmal (spring type, cold-sensitive, early heading) and Arabi Aswad (winter type, cold-tolerant, medium early heading), under varying rainfall and temperature. Grain yield was obtained from three sites in northern Syria for seven seasons (1984/85 to 1990/91), resulting in 18 site × season combinations, here called environments. Multiple regression models, containing one rainfall and one temperature variable, were used to quantify yield responses to environmental fluctuations.
Total seasonal rainfall was the variable most strongly correlated with the grain yield of Harmal, accounting for 62·8% of the variance. For Arabi Aswad, rainfall from November to January gave the best fit, accounting for 61·8% of the variance. December and January rainfall had the highest contribution to the yield of both cultivars; the contribution of March rainfall tended to be negative. The overall yield response to seasonal rainfall was 11·89 kg/ha/mm for Harmal and 8·57 kg/ha/mm for Arabi Aswad; the expected grain yield at the driest site was c. 1270 kg/ha for both cultivars. The addition of a temperature variable gave a better fit, accounting for c. 80% of the variance in grain yield for both cultivars if winter rainfall was combined with number of night frosts in spring. It reduced the expected yields at the driest site to c. 986 kg/ha. Arabi Aswad had a lesser response to both rainfall and frost than Harmal.
In environments where low yields are due to both water and temperature stress, farmers are advised to grow Arabi Aswad because its lesser sensitivity to environmental fluctuations will ensure a better yield stability.