Biolog ECO plates (31 different carbon sources, Biolog Inc., Hayward, USA) were used to discriminate between rhizosphere soil samples from 4- and 9-year alfalfa stands each with three replication. The growth curves for different groups of carbon sources were nearly sigmoidal, but the maximum rate of utilization was faster for amino acids, carbohydrates and polymers t㏊n for amides, miscellaneous and carboxylic acids, and carbon sources utilization efficiency were all higher in 9-year t㏊n in 4-year alfalfa stand.

• Xianzhi Wang
• Yuying Shen