Abstract: In traditional irrigation and fertilization practices, excessive water and fertilizers often cause soil salinity accumulation in greenhouse vegetable production. Drip irrigation is one of methods to accurately supply water and nutrient in root zone to meet crop needs. To determine effects of N application rate on soil NO3--N, soil electrical conductivity (EC), yield and root dry matter in greenhouse cucumber and tomato rotation, six-season experiments were conducted with drip irrigation under plastic film in greenhouse from 2008 to 2010. The experiment site was Mazhuang Experiment Station (37°18′ N, 115°28′ E) in Xinji city, Hebei province, China. Five treatments of no N fertilizer (NN), manure N (MN), optimal N (RN), high N (HN) and traditional N (CN) with 3 replicates each were designed. Chicken manure application rate (30 t/hm2) was applied only before cucumber season in 2008. The chemical N application rate was 0, 300, 600, 900 kg/hm2 in winter-spring cucumber season and 0, 225, 450, 675 kg/hm2 in fall-winter tomato season for NN, RN, HN, and CN, respectively. The yield, root dry matter, soil NO3--N, and EC were measured. The results showed that soil NO3--N and EC were significantly increased with the increase of N rate. The CN treatment accelerated and increased the soil NO3--N accumulation and soil salinity. During the 3 cucumber and tomato rotations, the average soil NO3--N content of RN, HN, and CN treatments was 176.9, 346.6, and 500.8 kg/hm2, respectively. The content of CN treatment was 2.83 times as high as RN (P<0.05). In cucumber season, soil NO3--N accumulation of RN, HN and CN treatments were -1.87, -49.61, and -3.52 kg/hm2, respectively, but 74.89, 225.23, 343.15 kg/hm2 in tomato season, respectively. The CN treatment was 4.58 times as high as RN (P<0.05). After 3 rotations, soil NO3--N residual of RN, HN, and CN treatment was 219.1, 526.9, 1028.9 kg/hm2 higher than before experiment, and increased by 73.0, 175.6, 339.6 kg·hm-2 in each rotation. The CN treatment was 4.65 times as high as RN (P<0.05). After 3 rotations, soil EC of NN, MN, RN, HN, and CN treatment were 433.8, 681.5, 824.5, 927.5, 1120 μS/cm, respectively. Soil EC of RN, HN, and CN treatment was significantly higher than MN and NN treatment (P<0.05). Soil EC of CN treatment was 1.15, 1.29, 1.40, 1.36 (P<0.05) times as that of RN after season of tomato in 2008, cucumber in 2009, tomato in 2009 and 2010, respectively. Soil EC was decreased significantly in RN treatment compared to CN treatment, indicating optimal N management decreased the risks of soil secondary salinizaton. During each rotation, there were 2 key periods for soil NO3--N and soil EC rapid accumulation: 1) in the summer from early July to early August, and 2) early September to middle November in fruiting period of Fall-winter tomato. In sum, the optimal N rate reduced N application rate by 66.7%, decreased soil nitrate residue and soil electrical conductivity significantly, but kept the tomato and cucumber yields as high as the other high and traditional N application rate treatments. These results provide valuble information for fertigation regime in cucumber and tomato rotation of greenhouse.