Urea transformation and nitrification under different urea combined fertilization in the brown soils of Tea Garden

Using solo application of urea as contrast, the effects of different application methods, combining application urea with DCD ( Dicyanodiamide, short for UD), microbial agent (UJ), mixed fertilizer(UY), microbial agent plus with mixed fertilizer(UYJ) , and covering the tea dust on soil surface (UF), on urea transformation and nitrification were studied under the condition of aerobic incubation. The content of ammonium nitrogen, nitrate nitrogen, soil urease activity and the amount of ammonia-oxidizing bacteria (short for AOB) in the soil was measured and the rate of apparent nitrification was calculated. The results showed that, compared to the contrast, the content of ammonium nitrogen in the all treatment soils was increased, but the content of nitrate nitrogen reduced, the peak period of urease activity was delayed, the rate of apparent nitrification was decreased, and the amount of AOB were reduced. Among the five treatments, the treatment effect of UF is the best because it had the highest content of ammonium nitrogen, and the lowest content of nitrate nitrogen and the rate of apparent nitrification in the soil. The second is UD treatment because the DCD could delay the peak period of urease activity, reduce urease activity in the early days and it also could inhibit the amount of AOB significantly. In addition, by comparing the effect of UYJ to that of UJ, it could be speculated that the microbial agent inhibited nitrification insignificantly in tea garden soil with rich organic matter.