Soil nitrate distribution, N 2O emission and crop performance after the application of N fertilizers to greenhouse vegetables

The impacts of nitrogen (N) application rates on soil nitrate, electrical conductivity (EC), pH, soil N 2O emission, tomato yield and fruit quality were investigated in a 20-yr vegetable field experiment under greenhouse cultivation in Northeast China. The treatments included no N control (N0), the recommended N rate (N1; mean annual 300kg/ha) and the commonly used N rate by farmers (N2; mean annual 600kg/ha). Soil nitrate content and EC increased significantly to 120cm depth with increasing rates of applied N. An opposite trend was found for soil pH within the upper 20cm. Cumulative N 2O emission and maximum N 2O emission rates both increased significantly with increasing N rates. Tomato yield increased significantly from the N0 to N1 rate, but remained constant from the N1 to N2 one. Nitrate concentration in tomatoes also increased significantly with N rates. A contrasting trend was found for soluble sugar and organic acid concentrations. The results indicate that the commonly used N2 rate is excessive and causes adverse effects on tomato quality and on the environment. The recommended N1 rate is optimal for sustainable greenhouse vegetable production. In greenhouses, daily soil N 2O emission rates are strongly influenced by N application and fluctuate with irrigation frequency and the incidence of wetting/drying cycles