Differential Responses of Barley and Legumes to Precipitation and Temperature in a Semi-Arid, High Elevation Mediterranean Area.

In semi-arid Mediterranean areas, annual precipitation usually is assumed to have dominant influence on yields of all crops, although few studies have been conducted to verify this relationship. Thus we examined the effects of precipitation and temperature on seed yields of  barley (Hordeum vulgare), lentil (Lens culinaris), common vetch (Vicia sativa) and bitter vetch (Vicia ervilia) from a 10-yr rotation trial in Lebanon’s Bekaa Valley. Precipitation and temperature for periods of the growing season, besides annual precipitation and mean temperature, were used as explanatory variables in multiple-regression analyses, in which data were standardized within each variable. Mean yields were 940, 660, 900, and 1060 kg ha^-1 for barley, lentil, common vetch, and bitter vetch, respectively. The mean annual temperature was 13.0°C (11.3-15.1°C), and the mean annual precipitation was 544 mm (365-966 mm). Barley yield was correlated with precipitation only in March to May and common vetch yield with mean temperature in May. Yields of lentil and bitter vetch were not correlated with any weather variable. Among the variables, precipitation in March to May had the largest regression coefficient for barley, i.e., having the strongest influence on barley yield. In contrast, mean temperature in May, in March and April, and in January and February had the largest regression coefficients (negative for the first two variables; positive for the last) for the three legumes. Annual precipitation had the lowest regression coefficient, indicating the least influence on yields of the four crops. Thus, while dryland crop yields may be generally related to precipitation in the Mediterranean region, this study from Lebanon showed that this relationship may deviate considerably from this norm, and temperature in May or rainfall in March to May can have a disproportionate influence on yields.