Abstract: [Objective] Nitrogen (N) is the greatest demand element for Moso bamboo (Phyllostachys edulis) growth. Improper fertilization could result in the decrease of nitrogen use efficiency (NUE) and the increase of nitrogen loss. Ammonia (NH₃) volatilization is one of the main pathways of nitrogen loss from soil. Improper depth of fertilizer application in the soil could accelerate the loss of NH₃ volatilization. However, very little information is available regarding NH₃ volatilization and its influence factors in Moso bamboo forests. Thus, in this study the NH₃ volatilization characteristics at different fertilization depths in a Moso bamboo forest were investigated by field experiment to provide the scientific guidance for the reasonable fertilization depth in terms of reducing the ammonia volatilization. [Method] In this paper, seven fertilization depths of 0, 5, 10, 15, 20, 25 and 30 cm and a control treatment without fertilizer were set in Huangshan, Anhui Province of China. The NH₃ volatilized from each plot was absorbed by 2% H₃BO₃ with the venting method. One-way ANOVA was conducted to test the significance of the indexes, and the least significant difference (LSD) was applied for multiple comparisons. [Result] The NH₄⁺ content after fertilization increased first and then declined with the extension of time, and finally stabilized. The NH₃ volatilization showed obvious regularity changes with time, and it was closely related to fertilization depth. NH₃ volatilization was detected on the second day after fertilization. The NH₃ volatilization rates of all fertilization treatments increased first and then decreased, showed a single peak curve. NH₃ volatilization rates at fertilization depths of 0, 5 and 10 cm peaked on the third day, while rates of NH₃ volatilization at fertilization depths of 15, 20, 25 and 30 cm reached a maximum in 6 days after fertilization. Then, the rates decreased gradually. About twelve days later, NH₃ volatilization rates dropped to a low level similar to the control. NH₃ volatilization of urea could be divided into 2 stages, namely, rapidly and slowly increasing stages. The first eight days were recognized as the rapidly increasing stage. The ratios of NH₃ volatilized within the first eight days to the total volatilization loss were ranged from 81.93% to 92.38%. Then it changed to the slowly increasing stage. The relationship between the cumulative NH₃ volatilization (y) and the corresponding time (t) accorded with the Elovich equation (y=a + b lnt). By the end of this experiment, the losses of NH₃ volatilization from the fertilization treatments were ranged from 10.12 to 27.17 kg·hm^-2. Results showed that NH₃ volatilization was influenced significantly by fertilization depth. The mean NH₃ volatilization flux and total loss decreased with the increase of fertilization depth. NH₃ volatilization losses of fertilization placed at 0 and 5 cm depths were larger than that at other depths, up to 27.17 and 25.66 kg·hm^-2, equivalent to 21.05% and 19.88% of the applied N, respectively. When fertilization depth exceeded 15 cm, the loss ratio was significantly reduced. [Conclusion] In this study, NH₃ volatilization was characterized by a high speed within the first eight days after fertilization in an intensive management bamboo forest. Thus, the regulation of environmental conditions was suggested to reduce N loss. The nitrogen losses through NH₃ volatilization of fertilization placed below 15 cm depth were lower, however deep fertilization application could result in leaching loss and also increased the production cost. Comprehensive consideration of the distribution of bamboo root and nitrogen loss and utilization, the reasonable fertilization depth should be 15-20 cm in P.edulis forests.

Key words: Phyllostachys edulis, nitrogen, ammonia volatilization, fertilization depth, ammonium nitrogen content