| The field experiment was carried out at the center of Dingxi country in semi-Arid Area of Gansu bewteen May 2009 and November 2009. In this study, potatoes were selected as materials, limited irrigation volume and limited irrigation period were selected as factor. Using catchment rainfall facilities and natural precipitation. This experiment were studied in different supplementary irrigation treatments ,the growth characteristics of potato, dry matter accumulation and dealing, soil evapotranspiration, water effect, yield and the yield constituents of potato, The results indicated:1. The limited irrigation significantly increased the yield and economical coefficient of potato. The economical yield of the limited irrigation increased 1.22~14.48%, biomass increased 1.13~4.83% compared with the control. The increase production of T3 is 14.48%, T7 is 12.22%, the results were the T3 and T7 were better than others and significant effects on yield compensation. Limited irrigation decreased Small tuber rate and increased potato weight per plant. The Big tuber rate of the limited irrigation was higher than control, T7 is the best about 59.23%. But the limited irrigation of green tuber rate and blet tuber rate were higher than control, T5 was the worst.2. The evapotranspiration of Potato Field about 90mm in July, T5 was the best. As the strong sunlight, total evapotranspiration was increasing, the peak in August during the growing period, it is account for about 36.56% in totol evapotranspiration and decreasing in September. In July the ratio of transpiration and evaporation to evapotranspiration were the highest in different supplementary irrigation treatment, and the lowest in September. In July, abundant rainfall, suitable temperature, the evapotranspiration was lower than in August of the test year. In August , the evapotranspiration of potato was more than July, but in August many of rainfall, high temperature, but the evaporation was more than July, the ratio of transpiration to the evapotranspiration was decreased, most of the water was evaporated in invalid. In the period, supplemental irrigation was negatively effect for crop. In September, with the potato was mature, leaves was old, crop growing was slow, the transpiration was decreased comparison with the August. So, the ratio of transpiration to the evapotranspiration was decreased.3. The results of WUE in different supplementary irrigation treatments: Low fixed of limited irrigation and graded the same scale supplementary irrigation will help improve WUE. Limited irrigation in seeding stage is higher than tuber enlargement stage. WIUE in seeding stage high fixed of limited irrigation is significantly higher than others. Low fixed of limited irrigation better than the high fixed of limited irrigation and limited irrigation in seeding stage better than the limited irrigation in tuber stage will have significant effect on WSUE.4. When ripening stage, potato plant dry matter reached the peak of his life to "S" type curve, the limited supplementary irrigation treatment compared with the control, the dry matter had different degrees of growth. Including T3 and T7, the dry matter accumulation per plant was significantly more than other treatments. Meanwhile, it showed larger transportation amount and higher distribution rate of dry matter after anthesis, which would be benefit for the nutrient accumulation of tuber. T3 with amount of movement of potato plant was 44.76g, the conversion rate of 23.30%, T7 with the total amount of movement of potato plant was 36.15g, the conversion rate of 19.29%, compared with the control the conversion rate 6.60% and 2.59%. The limited supplementary irrigation treatment on plant high, number of leaf, leaf area were stabilized earlier than control, and when plant into mature, these are increased than control. Limited supplementary irrigation treatment was significantly higher than control, T3 and T7 which the best performance.5. In general, limit irrigation to improve the quality of the potato have some compensation effect. Limited irrigation treatments compared with the control, the starch content improve between 0.19% ~ 1.60%. Which deal with the differences between the T6 and the control were significant. The other limited irrigation treatment and control of the differences were not significant. Protein content of limited irrigation treatments was increased in varying degrees, but the limited irrigation treatment compared with control was not significant. Limited irrigation treatment of VC content was higher than the control, the limited irrigation treatment had significant compensation effect on improve the VC content of potato tubers. The VC content improve between 9.85% ~ 14.12%, including T6 compared with the control increased 14.12%.6. Through the yield, WUE and other important indicators, the result that limited irrigation 90mm in seeding stage is the best, limited irrigation 45mm in seeding stage and limited irrigation 45mm in tuber expanding stage is the backup plan.
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