Nitrogen Balance and Loss in a Greenhouse Vegetable System in Southeastern China

High rates of fertilizer nitrogen （N） are applied in greenhouse vegetable fields in southeastern China to maximize production; however, the N budgets of such intensive vegetable production remain to be explored. The goal of this study was to determine the annual N balance and loss in a greenhouse vegetable system of annual rotation of tomato, cucumber, and celery at five N （urea） application rates （0, 348, 522, 696, and 870 kg N ha^-1 year^-1）. Total N input to the 0-50 cm soil layer ranged from 531 to 1 053 kg ha^-1, and N fertilizer was the main N source, accounting for 66%-83% of the total annual N input. In comparison, irrigation water, wet deposition, and seeds in total accounted for less than 1% of the total N input. The fertilizer N use efficiency was only 18% under the conventional application rate of 870 kg N ha^-1 and decreased as the application rate increased from 522 to 870 kg N ha^-1. Apparent N losses were 196-201 kg N ha^-1, of which 71%-86% was lost by leaching at the application rates of 522-870 kg N ha^-1. Thus, leaching was the primary N loss pathway at high N application rates and the amount of N leached was proportional to the N applied during the cucumber season. Moreover, dissolved organic N accounted for 10% of the leached N, whereas NH3 volatilization only contributed 0.1%-0.6% of the apparent N losses under the five N application rates in this greenhouse vegetable system.