Abstract: Soil nitrogen migrates into deeper soil layer even into groundwater in the conditions of rainfall, which results in not only the degradation of soil fertility, but also the pollution of groundwater. In this study, soil samples of 0-20 cm and 0-40 cm depths were collected from Puer Tea plantations with different cultivation ages of 0 (i.e. forest), 5, 20, 33, and 56 years old respectively in Dadugang Town, Xishuangbanna. Undisturbed soil columns were used to study the migration characteristics of TN, NO₃^--N, NH₄⁺-N, DON and the influence of soil pH on nitrogen migration by simulating local heavy rainfalls indoors. The results showed that TN migration fluxes increased with the increase of tea planting age in the soil layers of 0-20 cm and 0-40 cm (P<0.05). The migration increased by 235.13 mg·m^-2 through 20 cm soil layer, and 151.24 mg·m^-2 through 40 cm soil layer for each additional year of tea cultivation. A significant positive correlation between NO₃^--N migration flux and cultivation age of tea plantation was observed in the layer of 20-40 cm (P<0.05), and the same pattern was found between DON migration flux and tea planting age in the layer of 0-20 cm (P<0.05). However, NH₄⁺-N loss fluxes did not change with tea planting age (P>0.05). While the migration of TN, NH₄⁺-N, DON in tea plantations occurred mainly in the layer of 0-20 cm, most of NO₃^--N migration existed in the 20-40 cm layer. The soil nitrogen mainly migrated in the form of DON through 40 cm soil layer, followed by NO₃^--N, and NH₄⁺-N the least. No evident effects of soil pH on nitrogen migration was observed in our study (P>0.05).

Key words: Se uptake, selenium, Se metabolism, Se biofortification, phytoremediation