Effect of Slow/Controlled Release Nitrogen Fertilizers on Soil Biological Activities

Using pot experiment, the effects of different slow/controlled release nitrogen fertilizers on soil urease and nitrate reductase activities and microbial C and N were researched at the seedling stage of maize. The coated granular urea amended with N-(n-butyl)thiophosphoric triamide(NBPT) or with NBPT and dicyandiamide (DCD) significantly inhibited the activity of soil urease, being 48~50 mg NH3-N·kg-1· 24 h-1, but coated granular urea amended with NBPT and DCD gave the highest activity of soil nitrate reductase, being 1.43 μg N·g-1·24h-1. Coated granular urea amended with NBPT had no significant effect on the activity of soil nitrate reductase, but gave the highest soil microbial C and N, being 241 mg·kg-1 and 57 mg·kg-1. Soil microbial C and N had the same variation trend under applying different kinds of slow/controlled release nitrogen fertilizers, but soil microbial N under the application of coated granular urea amended with NBPT and DCD had no significant difference with CK, being 50 mg·kg-1. Coated granular urea amended with NBPT and DCD had little effect on the N immobilization by soil microbes. Compared with the coated granular urea without any amendments, the effects of that with NBPT and/or DCD on soil biological activities were significantly higher. Methyl methacrylate was more effective than starch acetate as coating materials.