Nitrogen balance and optimized potential of integrated nitrogen management in greenhouse vegetable system

Greenhouse tomato experiments, including four growing seasons, were conducted in Shouguang from 2004 to 2006, in order to investigate effects of integrated N management (INM) on crop productivity, N surplus and apparent N loss based on the analysis of N balance and soil Nmin in the soil profile of 180 cm. The results showed that considering nitrate-N from irrigated water and soil initial nitrate-N content (0-30cm), INM treatment could maintain tomato yield as conventional N treatment, however, the 73% of fertilizer N was reduced through maintaining critical rootzone N level. Fertilizer N saving with INM treatment was in the late growing stage of Spring tomato season, and in the early growing stage of Autumn tomato season. High risk of N loss should not be ignored in the period from summer fallowing to the first event of N sidedressing because of high nitrate-N content accumulated in soil profile and high irrigated water in greenhouse system. Catch crop planting or crop straw with high C/N incorporation are expected to regulate N transformation, which is beneficial for reducing N loss in this system.