A pot experiment was carried out to investigate the effect of 3-methyl-phenol and phosphorous on soil microbes and enzyme activity in three cropping ystems: wheat faba-bean intercropping, wheat sole cropping and faba-bean sole cropping. Results show that at wheat flowering stage, treatments with 3-methy-phenol at a concentration of 300×10-6mol/kg of soil had significantly higher numbers of bacteria and total microbes, but had lower numbers of fungi.
Application of phosphorous fertilizer weakened the allelopathic effect of 3-methy-phenol on bacterial and total microbes. The average number of bacteria, fungi and actinomyces in the three treatments with 100mg/kg of soil phosphorous was 57.27%, 21.35%, 60.89%. This was higher than that of the treatments with no phosphorous application at wheat flowering stage. As the phosphorous rate was increased to 200mg/kg of soil, the numbers of microbes decreased. At crop maturity, the average numbers of bacteria, fungi and actinomyces were highest in treatments with 200mg/kg of soil phosphorous, 59.93%, 9.05% and 20.8% respectively.
The numbers of bacteria, fungi and actinomyces in the wheat faba-bean intercropping system were higher than those of sole cropping systems (calculated as half the sum of the two sole cropping systems’ microbe counts). At wheat flowering stage the intercropping system had 18.46%～150.02% of bacteria, -22.41%～5.44% of fungi and -17.06%～16.64% of actinomyces, and at maturity had -6.94%～145.81% of bacteria, 0.76%～25.36% of fungi and -17.31%～32.79% of actinomyces.
With higher phosphorous application rates, the difference in microbe numbers between intercropping and sole cropping systems increased. Application of 3-methy-phenol decreased the soil microbial diversity in all treatments at wheat flowering stage. The diversity in sole cropping systems was higher than that of intercropping systems at the same phosphorous application rate. Intercropping weakened the negative allelopathic effect of 3-methy-phenol on soil catalase activity, while phosphorous application increased the activity of soil catalase and urase. The 3-methy-phenol enhanced the urase activity of sole cropping faba-bean and wheat faba-bean intercropping systems, but it weakened the effect of phosphorous on urase. The allelopathic effect of 3-methy-phenol reduced soil acid phosphatase activity in sole faba-bean and intercropping treatments. As the phosphorous application rate was increased, this negative effect was weakened. However, the effects of 3-methy-phenol and phosphorous on acid phosphatase activity were different in the sole wheat system.At crop maturity of all treatments, the effect of 3-methy-phenol on soil microbes and enzyme activity decreased significantly, indicating that the effect of 3-methy-phenol on all treatments weakened continuously through crop growth stages.