The field experiment with large-typed profile-undisturbed monolith lysimeters was carried out to study the nitrogen transformation at different soil depths (30cm, 65cm and 80cm) in WuShan soil in Taihu Region under a rice-wheat rotation system with different types and rates of urea fertilizers applied in rice season. The results showed that the NO3--N concentration in percolation in all treatments were lower than the criteria of NO3--N concentration for drink water. Under normal application of urea, the N l...