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.

Forage production and water use efficiency (WUE) of Lucerne were investigated in three varieties at different water availabilities. Forage production decreased with the severity of soil water availability. At 50% field water capacity (FWC), forage production dropped but in two varieties, Algonquin and Longdong, was still high and from 75%FWC to 50%FWC, forage production in Longdong decreased at the least rate. The greatest leaf WUE was observed in Longdong at all soil water availabilities. From 75%FWC to 50%FWC, it increased in Longdong and Xinjiangdaye, but decreased in Algonquin. With the severity of water deficit, δ¹³C value increased in all three varieties. At the same water availability, the greatest value was observed in Longdong. It suggested that moderate water stress can improve WUE in Lucerne. Longdong is to some extent more efficient in water use and may be more drought-tolerant with more steady production at moderate water deficit.