Abstract:In order to improve the water/nitrogen utilization efficiency and reduce the agricultural non-point source pollution, field investigation and lab analysis have been conducted to quantify the characteristics of water/nitrogen distribution and to explore the optimal irrigation and fertilizer schedules in paddy fields with different cultivation years (2 a, 18 a and >100 a) in the Jianghan Plain. The results showed that significant differences in soil properties were observed among the paddy fields. With the increase of paddy cultivation year, the thickness of plough layer and plow pan, bulk density of plow pan, and clay content of subsoil layer and plow pan were all increased, whereas bulk density of the plough layer was decreased. Significant differences in saturated hydraulic conductivity (Ks) were observed in soil profiles between the paddy fields, especially for the plow pan. The highest average Ks of the plow pan was observed in the 2 a field (37.02 cm/d), followed by the 18 a field (8.45 cm/d) and the >100 a field (3.11 cm/d). The profile distribution of water/nitrogen were affected by soil properties significantly. With the increase of paddy cultivation year, water/nitrate nitrogen (NO3--N) content increased gradually, the average soil water content was 0.39, 0.46 and 0.54 cm3/cm3, while the average soil NO3--N content was 3.75, 6.27 and 9.85 mg/kg for the 2 a, 18 a and >100 a paddy fields, respectively. However, little difference was observed in ammonium nitrogen (NH4+-N) in the paddy fields. The ratios of NO3--N and NH4+-N in 2 a, 18 a and >100 a fields were 0.61, 0.39 and 0.30, respectively. In order to reduce water/nitrogen percolation for the short-year paddy field, the strategies of more times but less amount in irrigation and fertilization could be applied, but for the longer-year paddy field, fewer times but high amount in irrigation and fertilization could be applied to cut the labor costs.