Responses of soil physicochemical properties and biological activity to continuous application of slow/controlled releasing urea

The effects of six-year continuous applications of different types of slow /controlled release urea on biological activity and physicochemical properties of aquic brown soil were investigated. The results showed that soil organic matter,total nitrogen,total phosphorus,available phosphorus and available potassium were significantly increased by continuous application of slow /controlled release urea,while total potassium,available nitrogen and pH were significantly decreased. The descent of pH was slowed down by continuous application of slow /controlled release urea compared to the use of normal urea,and the soil pH was higher after application with slow-release urea than with coated urea. Soil urease activity of slow /controlled release fertilizer treatments was higher than CK. Applications of nitrification inhibitors incorporated and coated urea resulted in the highest nitrate reductase activity and accelerated the nitrification potential activity. Application of nitrification inhibitors incorporated urea significantly increased soil microbial biomass carbon. In conclusion,continuous six-year applications of NBPT + DMPP + U and PCU significantly increased biological activity in contrast to the other treatments. Considering the cost and economic effects of the different fertilizers,the urea supplemented with NBPT and DMPP is suitable for continuous application in aquic brown soil.