YIELD RESPONSE OF BARLEY TO RAINFALL AND TEMPERATURE IN MEDITERRANEANENVIRONMENTS

Grain yield of barley (Hordeum vulgare L.) in northern Syria is limite d by water stress and extremes of temperature. The present study compa red 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 seaso ns (1984/85 to 1990/91), resulting in 18 site x season combinations, h ere called environments. Multiple regression models, containing one ra infall and one temperature variable, were used to quantify yield respo nses to environmental fluctuations. Total seasonal rainfall was the va riable most strongly correlated with the grain yield of Harmal, accoun ting for 62.8% of the variance. For Arabi Aswad, rainfall from Novembe r to January gave the best fit, accounting for 61.8% of the variance. December and January rainfall had the highest contribution to the yiel d of both cultivars; the contribution of March rainfall tended to be n egative. 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 ad dition of a temperature variable gave a better fit, accounting for c. 80% of the variance in grain yield for both cultivars if winter rainfa ll 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 environment s where low yields are due to both water and temperature stress, farme rs are advised to grow Arabi Aswad because its lesser sensitivity to e nvironmental fluctuations will ensure a better yield stability.