Inoculation of sterilized soil with diluted non-sterilized soil suspension (1, 10^-2, 10^-4, and 10^-6) was used to investigate the effects of a reduction in soil microbial diversity on canola (Brassica chinensis L.) growth, nutrient uptake, soil nutrient availability, and enzyme activity. The results indicated that:(1) Canola biomass decreased with increased dilution of the soil suspension. Canola biomass at 10^-4 fold dilution was significantly lower than at the 1- and 10^-2 fold dilution, and canola biomass at the 10^-6-fold dilution was 26% that of the 1-fold dilution. (2)Nitrogen, phosphorus, and potassium uptake of canola followed the same trend as biomass across the microbial diversity gradient. (3) Concentration of ammonium decreased with soil suspension dilution. Soil nitrate concentration was highest at the 10^-4 fold dilution, and there was no significant difference among other dilution treatments. Soil available phosphorus did not change significantly; however, available potassium exhibited an increasing trend. (4) Soil polyphenol oxidase (PhOX) activity gradually increased with increasing dilution of the inoculated soil solution. β-1,4-glucosidase (βG) activity at the 10⁶ fold dilution was the highest, whereas there was no significant difference in the rest dilution treatments. Soil leucine aminopeptidase (LAP) activity and acid phosphatase (AP) activity did not change significantly across the diversity gradient. (5) Correlation analysis indicated canola biomass was positively correlated with the logarithm of soil ammonium concentration, whereas it was negatively correlated with polyphenol oxidase, glucosidase, and leucine aminopeptidase activity. This study showed that reduction of microbial diversity suppresses crop growth by inhibiting soil nitrogen release.