Abstract: The pot experiment was conducted to investigate the effect of water supply rate (field capacity 45%, 60% and 75%) and Phenol, 2-methoxy-4-(4-propenyl) on the soil microbial population under sole wheat, sole faba bean, and wheat-faba bean intercropping. The results showed that the number of bacteria, fungi and actinomycetes under intercropping were lowered than the weighted mean value of two sole cropping systems. Whereas, the allelopathic promotion effect and soil microbial diversity index under intercropping were greater than the weighted mean of the two sole cropping systems. Besides, this study revealed an obvious allelopathic promotion effect of Phenol, 2-methoxy-4-(4-propenyl) on the number of soil microbes under sole wheat and wheat-faba bean intercropping. Compared to the weighted mean of two sole cropping systems, the number of three soil microbes under intercropping was increased by 95.9%, 8.8% and 99.6% in the action of Phenol, 2-methoxy-4-(4-propenyl). Nevertheless, under sole faba bean, an obvious allelopathic inhibition effect was revealed. As increasing of the irrigation level, the allelopathic promotion effect of sole wheat was consistently improved, whereas the allelopathic inhibition effect of sole faba bean was consistently decreased. For wheat-faba bean intercropping, increasing irrigation level to 60% promoted the allelopathic promotion effect;however, exceed by 60%, continuously increasing of irrigation level decreased the allelopathic promotion effect. In terms of soil biodiversity index, it was improved by 74.3%, 96.1% and 134.0% at wheat jointing, grain filling and maturity under intercropping compared to the weighted mean of two sole cropping systems in the action of Phenol, 2-methoxy-4-(4-propenyl). In addition, the soil biodiversity index of sole wheat and wheat-faba bean intercropping both had threshold value of irrigation level at 60%, and increasing irrigation level to 60% increased the soil biodiversity index;while exceed by 60%, increasing irrigation level decreased the soil biodiversity index. For sole faba bean, increasing irrigation level consistently decreased the soil biodiversity index. Consequently, adopting intercropping and optimum irrigation level could facilitate the promotion effect of root exudates on the optimization of soil microbes quantities and biodiversity.

Key words: water supply levels, intercropping, allelopathy, soil microbial, diversity index