Effects Of Intercropping Sugarcane With Soybean On Physical And Chemical Properties, Diversity Of Bacteria And Nitrogen-fixing Bacteria In Rhizosphere Soil

Sugarcane is the most important sugar crop and one of the most promising bioenergy crops in China. Guangxi has the biggest sugar production in China, and sugar industry plays an important role in local economy. However, the sugarcane production cost is high in China, and excessive application of nitrogen fertilizer is one of the reasons for that. The amount of nitrogen fertilizer applied in Guangxi is500-700kg·ha, equivalent to6-8times of the average in Brazil. Improve of productivity and comprehensive benefits in commercial sugarcane production is the objective requirement for the sustainable development of the sugar industry in China, and sugarcane intercropping and sugarcane-associative nitrogen fixation resources are important for improving the efficiency of sugarcane production. The distance between rows is relatively big, the growth duration is long and the plants grow relatively slow for sugarcane, so reasonable intercropping with various fast-growing and short duration crops could increase the use of energy, nutrients and other agricultural resources, and improve crop production and farmers income. In the present study, we used three sugarcane varietis B8, ROC22and GT21intercropped with a soybean variety Guizao2. Physical and chemical properties of sugarcane rhizosphere soil were analyzed, the PCR-DGGE was used to detectl6S rRNA gene fragments of bacteria and nifH gene fragments of nitrogen-fixing bacteria, and the influence of sugarcane/soybean intercropping on the diversity of bacteria and nitrogen-fixing bacteria in sugarcane rhizosphere soil were analyzed. The main results were as follows.Intercropping sugarcane with soybean had significantly impact on the moisture, nutrients, pH, organic matter, enzyme activity in sugarcane rhizosphere soil. Under light alkaline condition, the pH was significantly lower in the intercropping soil than in the monoculture soil, and tend to be neutral that was more suitable for sugarcane growth. Intercropping sugarcane with soybean also reduced the contents of moisture, alkaline hydrolysis N and available K in sugarcane rhizosphere soil. The activities of urease, phosphatase and invertase in the sugarcane and soybean rhizosphere soils in intercropping system were higher than those in the sugarcane monoculture treatment and control. This indicated that intercropping soybean could enhance the utilization of moisture, alkaline hydrolysis N and available K, and improve nutrient levels and enzyme activity in sugarcane rhizosphere soil.Analysis of DGGE profiles showed that the intercropping with soybean significantly changed the original community structure and composition of the bacteria and nitrogen-fixing bacteria in sugarcane rhizosphere soil, and the evolutions between them had tremendous change. Analysis of Shannon index and Simpson index showed that intercropping with soybean significantly improved the diversity of bacteria and nitrogen-fixing bacteria in rhizosphere soil, which was significantly higher than that in sugarcane monoculture treatment and control. The diversity of nitrogen-fixing bacteria was affected greater by the intercropping treatment, but was varied between varieties as well as growth stages. The bacterial diversity in the rhizosphere soil of the sugarcane variety B8presented the most abundant in the plant and ratoon crops of sugarcane, while the of nitrogen-fixing bacteria showed the greatest in the intercropping treatment of the sugarcane variety ROC22.