Abstract: With pot experiment and simulating field ecological environment, this paper studied the effects of different slow/controlled release N fertilizers on the soil nitrate-reductase and urease activities and microbial biomass C and N at maize seedling stage. The results showed that granular urea amended with dicyandiamide (DCD) and N-(n-bultyl) thiophosphoric triamide (NBPT) induced the highest soil nitratereductase activity, granular urea brought about the highest soil urease activity and microbial biomass C and N, while starch acetate (SA)-coated granular urea, SAcoated granular urea amended with DCD, methyl methacrylate (MMA)-coated granular urea amended with DCD, and no N fertilization gave a higher soil urease activity. Soil microbial C and N had a similar variation trend after applying various kinds of test slow/controlled release N fertilizers, and were the lowest after applying SAcoated granular urea amended with DCD and NBPT. Coated granular urea amended with inhibitors had a stronger effect on soil biological activities than coated granular urea, and MMA-coating had a better effect than SA-coating.

Key words: Semiarid region, Interaction between water and fertilizer, Regressive model