Nitrate nitrogen contents and quality of greenhouse soil applied with different N rates under drip irrigation

【Objectives】 Drip irrigation could effectively inhibit nutrient leakage as water and nutrients can be accurately sent to close the crop root zone. In this paper, the soil mineral N contents and environmental qualities were detected under different N rates and drip irrigation, to provide a base for efficient N management in vegetable production. 【Methods】 A three-years' feild experiment was conducted with winter-spring cucumber and autumn-winter tomato double cropping system in a greenhouse. Four N rates were applied as 0, 300, 600, 900 kg/hm2 for cucumber and 0, 225, 450, 675 kg/hm2 for tomato under drip irrigation (correspondingly recorded as N0, N1, N2, N3). The mineral nitrogen contents, salinity (EC5∶1) and acidity (pH) of 0-100 cm soil depth were investigated, and the economic and environmental efficiencies of N were calculated.【Results】 As the elongation of the cropping year, the NO3--N contents under N2 and N3 treatments in 0-100 cm soil profile were significantly increased from 14.4-31.1 and 14.9-41.0 mg/kg in cucumber season in 2008, respectively, to 76.4-119.8 and 129.0-184.5 mg/kg in tomato season in 2010, respectively, increased by 0.3-1.8 and 0.5-2.0 times respectively. The electrical conductivity (EC5∶1) of 0-100 cm soil profile under N2 and N3 was significantly increased from 379.6-514.3 and 407.0-476.7 S/cm, respectively, to 663.0-1212.4 and 710.0-1359.6 S/cm of tomato season in 2010, respectively, increased by 0.3-1.8 and 0.5-2.0 times. The N rates in N1 was 33.3%-50% of N2 and N3. Compared with N2 and N3, the NO3--N content and EC5∶1 of N1 decreased by 35.5%-67.4% and 6.0%-25.2% after three years cultivation, and the pH and NUE increased by 0.06-0.18 unit and 9.0-13.8 percentage points.【Conclusions】 Under this condition, the proper N rate for winter-spring cucumber and autumn-winter tomato was recommend as N 300 and 225 kg/hm2. In most crop seasons (5 seasons), the NO3--N contents in 0-60 cm depth were in the proper range for cucumber and tomato growth, and no significant accumulation of NO3--N was observed below 60 cm in the soil under this recommended N rate.