Effect Of Intermittent Drought On Alfalfa Rhizobia Symbiotic And Soil Nutrient

Biological nitrogen fixation is a biochemical process attracting almost the same attention as photosynthesis. Alfalfa is one of the main cultivated forage legumes in China, the acreage is more than 1.3×106hm2. The field environment of alfalfa is'Drying-wetting'or'levity and low water'in arid or semi arid regions. So it is vital to do some researches on the rule of alfalfa rhizobia and soil nutrient. In this study, a pot experiment was carried out to explore the effect of intermittent drought on inoculation, growth of alfalfa, nitrogenase, and soil nutrient of rhizobia inoculated alfalfa grassland in cold and drought regions, by simulating the drying-wetting process and intensity of soil in field. The results showed that:1) Soil moisture played a vital role on nodule number of alfalfa rhizobia. The drying-wetting affected the normal upgrowth of nodule, and the number of total nodules and effective nodules, the weight of effective nodules and the ratio of nodule on taproot decreased with the increase of the times and cycle of drought.2) The variation of the number of effective nodules depended on the variation of the number of total nodules. The weight of effective nodules changed little in different growth-phase of alfalfa under the steady water content of soil. The number of total nodules and effective nodules, weight of effective nodules were direct ratio to water content, but the ratio of nodule on taproot is reverse to water content and the nodules would transfer from taproot to side-root.3) The numbers of total nodules and effective nodules, and the weight of effective nodules were high under the treatment of drying-wetting 20d, 30d with 80% field moisture capacity and drying-wetting 20d with 50% field moisture capacity (i.e. the activity and validity of rhizobia is high with above irrigation policy). Considering the ecology and economy, it is better to take the treatment of drying-wetting 30d with...