【Objective】The Yangtze River Delta is one of the areas, where the input of nitrogen(N) fertilizer is very high, in China, but it is not quite clear whether nitrate (NO₃^--N) has accumulated in the soil profile in the region as in the North China Plain.【Method】In the present study, two-year field observation combined with indoor incubation experiments were carried out to investigate distribution of NO₃^--N and denitri?cation capacity in subsoil and groundwater as affected by arable land systems.【Result】The groundwater NO₃^--N concentration in 1～4 m depth was varied significantly with type of the cultivation system. In the paddy field, groundwater NO₃^--N was always low (<1 mg·L^-1), and did not vary much with depth. While in the vegetable field and vineyard, the average NO₃^--N concentration reached 5.6 and 17.5 mg·L^-1 in 1 m depth, but the NO₃^--N concentration dropped sharply with the depth and to a very low concentration (<1 mg·L^-1) in 4 m depth which was comparable to that in the paddy field. High groundwater NO₃^--N were only observed in vegetable field and vineyard during the fertilization period and NO₃^--N was low in non-fertilization period. The findings indicated that no apparent NO₃^--N accumulation in the farmland soil profile occurs in the Yangtze River Delta. The indoor incubation experiment using undisturbed soil columns shows that denitrification activity was high through the 0～4 m soil profile. The removal efficiency (RE) of NO₃^--N by denitrification was estimated by direct determination of N₂ and N₂O, products of denifrifiction, in groundwater. The RE increased with depth and removed 86%, 93% and 89% of the groundwater NO₃^--N in 4meter depth in paddy field, vegetable field and vineyard, respectively. 【Conclusion】All the findings in this experiment demonstrated that denitrification can effectively remove groundwater NO₃^--N, which explains why NO₃^--N does not accumulate in farmland soil profiles in Yangtze River Delta. Highly dissolved N₂ produced by denitrification accumulate in groundwater, and flow into nearby water bodies mainly via groundwater. In the case of vegetable field and vineyard, soil N loss in the form of dissolved gaseous N is nearly equal to that of NO₃^--N and hence an important fate of soil N, which deserves close attention.