| The arable land with K-deficiency in China exceeds 22,700,000 hm2, which accounts for 23% of the farmland. As a result, K deficiency in crops is a serious problem in agricultural production, and greatly limits the improvement of yield and quality of crops, which is getting more and more serious in the erea of barley production in China. The conventionally adopted approach to solve this problem was to apply K fertilizer. However, it has made the K fertilizer in China scarcity, which led to the imbalance between supply and demand of the Chinese K resourse. Therefore, screening of crop genotypes for high K-efficient barley genotype was studied in this reserch. Then, the experiments of soil culture with different K levels was carried out to study the difference in K use efficiency, K accumulation and distribution of K-efficient and K-inefficient barley genotypes, and to find the physiological and biochemical characteristics of K-efficient barley genotype. The main results were as the bellowing:1. The screening of crop genotypes with high K efficiency plays a fundamental role in understanding their physiological mechanisms. In this study, soil culture was conducted to reveal the differences in uptake and use of K among 56 barley varieties. The coefficient of variance (CV) of K accumulation (KA) and K dry matter production index (KDMPI) of these varieties were higher than those of other indices, and both differed significantly among the barley varieties. KA and KDMPI were positively correlated with dry matter weight (DMW) over the whole growth period; K use efficiency (KUE) and K harvesting index (KHI) were significantly related to grain weight (GW) in the maturing stage. Through cluster analysis by using these indices, (Sandrime) and (AC Westech) were found to be the most K-efficient and K-inefficient genotypes of barley. Significant differences were observed in uptake and use capacity of K between these two genotypes. KA, K dry matter production efficiency (KDMPE), KDMPI and DMW of K-efficient genotype were 1.5～1.8,1.4～2.3,2.1～3.9,1.7～2.1 times higher than those for the most K-inefficient genotype over the whole growth period, respectively, and the GW, KUE, KHI of efficent genotype were 2.83,2.60 and 2.56 times higher than those of the inefficient one in the maturing stage, respectively. The results show that Sandrime is the most efficient candidate among the tested varieties for K efficiency, and further studies should be conducted to investigate its physiological and biochemical characteristics.2. Due to K deficiency, K-inefficient barley genotype suffered more serious symptom, which indicated that K-efficient genotype had higher ability to tolerate K deficiency. The root-shoot ratio of K-efficient barley genotype were lower than that of K-inefficient barley genotype during the growth period, but its biomass were 107%,46% and 58% more than those of K-inefficient genotype in the tillering, jointing and maturing stages, respectively. The K content in the root, stem and leaf of K-efficient genotype was lower than that of K-inefficient genotype. But the biomass of K-efficient genotype was more than the inefficient one, which lead the K accumulation of K-efficient genotype was more. With every K treatment, the distribution ratio for K in shoot of K-efficient barley genotype was higher than that of K-inefficient genotype, and it indicated K-efficient genotype had higher transfer capability for K.3. K-efficient barley genotype had lower roots vigor, and the trend of K-efficient genotype changed less obviously than that of K-inefficient genotype. The chlorophyll contents of the two genotypes reached the maximums when the K was offered normally, and K-efficient genotype had more chlorophyll contents than K-inefficiency genotype. SOD activity of K-efficient genotype was higher than K-inefficient genotype, between which the biggest difference at seedling, tillering, jointing and maturing stages were 2.74 times,3.26 times,1.68 times and 1.29 times, respectively, which showed significantly in tillering stage. But K-efficient barley genotype had lower POD activity than that of K-inefficiency genotype, and the differences between them showed significantly under. every K level, which was 2.94～4.98 times in seedling stage,2.12～2.76 times in tillering stage,1.11～2.24 times in jointing stage and 1.55～2.38 times in maturing stage. MDA and soluble sugar contents of K-efficient genotype were less than K-inefficient genotype at these two stages, all of which were reduced gradually when the K level was increased.
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