Introduction: Available water and its efficient use are the main determinants of yield in agricultural ecosystems specially in dryland farming. This study was conducted in order to evaluate the efficiency of precipitation use of dryland wheat and barley varieties and the factors affecting it.
Material and Methods: Evaluation of the efficiency of precipitation use (efficiency) was done based on two-year experiments (2015-2017) on wheat and barley genotypes in dryland conditions of Mashhad. In these experiments, planting dates (main plots) and genotypes of wheat and barley (subplots) were compared in split plots based on a randomized complete block design with three replications. The results of these experiments were used to calculate the efficiency of rainfall use based on kilograms of production per millimeter of rainfall, after deducting 110 millimeters for evaporation contribution. The resulting data were statistically analyzed using SAS_(8.2) software and the means were compared using Duncan's test.
Results and Discussion: The results showed that under the same environmental conditions, the efficiency of rainfall use (efficiency) of wheat and barley genotypes had a significant difference, and the highest and lowest efficiency in wheat genotypes was allocated to Karim and Line 14, with the rate of 9.6 and 4.3 kg of grain for each mm of rainfall, respectively. The highest and lowest efficiency in barley genotypes was recorded for Mahoor and Ansar cultivars, at the rate of 17.7 and 7.9 kg of grain per mm of rainfall, respectively. The difference between the two crops in terms of efficiency was considerable, so that the superiority of the highest efficiency of barley genotypes compared to the wheat cultivar of Karim (the highest efficiency for wheat cultivars) was 84.3%. The results showed that temperature is one of the most effective factors in improving efficiency, and on average, for each ˚C increase in temperature, the mean efficiency of wheat and barley genotypes decreased by 0.83 and 1.06 kg/ha per millimeter of rainfall, respectively. Among wheat genotypes, the Karim wheat cultivar, and among barley genotypes Mahoor barley cultivar started spring growth faster. The biomass growth rate of wheat genotypes was in the range of 84-106 kg/ha per day, and the biomass growth rate of barley genotypes was in the range of 136-166 kg/ha per day, but the difference between genotypes was not significant. The highest grain growth rate of wheat and barley genotypes was recorded for the Aftab wheat cultivar and the Khorram barley cultivar at the rate of 78.6 and 122 kg/ha per day, respectively. The time of pollination and the harvest index also played an important role in improving the efficiency of wheat and barley genotypes. So, every day of delay in pollination according to the average rate of seed production in wheat and barley genotypes, results in a reduction of 52.9 and 90.8 kg of grain per hectare, respectively. The highest harvest index was recorded for Karim wheat and Mahur barley cultivars, at 36.3 and 43.6, respectively, and the harvest index of barley varieties was greater than that of wheat varieties. Despite the effective role of each of the traits, superiority in one trait did not play a significant role in reaching efficiency, and the Mahoor cultivar with highest efficiency had a favorable status in terms of all traits.
Conclusion: It seems that by improving the effective traits, the efficiency of spring and winter wheat cultivars as well as winter and spring barley, can be improved according to a pattern similar to the Mahoor cultivar and even more than that. This situation only for wheat will mean an increase in grain yield potential by about 61.5% compared to the current situation of the best wheat variety in this condition.