Abstract: Closing a high-temperature plastic greenhouse after flood irrigation is widely used as an effective method of soil sterilization during summer fallow, and it may affect the nitrogen (N) cycle in the soil. The goal of this study was to reveal the effects of soil sterilization measures on soil mineral N and soluble organic N (SON) after different long-term applications of organic materials, based on drip and flood irrigation modes. The results showed that the mineral N content during summer fallow was 103.9 and 68.6 mg/kg under drip and flood irrigation modes, respectively. The flood irrigation before closing the plastic greenhouse significantly decreased the mineral nitrogen content of the soil by 30% under drip irrigation mode, but had no effect on mineral nitrogen under flood irrigation mode. The soluble organic N content of the soil during summer fallow ranged from 16.3-69.1 mg/kg and accounted for 15%-48% of the total soluble nitrogen. Flood irrigation increased the soluble organic N by factors of 2.9 and 2.5 under drip and flood irrigation modes, respectively. After the high-temperature plastic greenhouse was closed, soluble organic N significantly declined by 107.1 kg/hm² (41%) and 72.4 kg/hm² (34%), mineral N increased by 117.9 and 126.7 kg/hm², and the net mineralization rate of soil nitrogen was 1.7 and 1.8 mg/(kg·d) under the drip and flood irrigation fertilization modes, respectively. Compared with a single application of chicken manure, the combined application of chicken manure with maize or wheat straw significantly increased the mineral N under the drip fertilization mode; however, the method had no effect on mineral N under the flood fertilizer mode. In general, flood irrigation before closing the plastic greenhouse led to considerable mineral N loss under the drip irrigation mode, and closing the high-temperature greenhouse accelerated the mineralization of SON.