Nitrogen pollution from paddy fields is a main contributor to global non-point source (NPS) pollution and greatly increases the risks of surface water eutrophication and groundwater contamination. This study assesses the comprehensive transport and transformation of water and nitrogen (TTWN) for a 4-year irrigation and urea application in the paddy field using 6 water balance components and 12 nitrogen inputs and outputs. The results show that alternate wetting and drying (AWD) irrigation reduces water and nitrogen for irrigation, drainage, and leaching, but has a minor effect on rice evapotranspiration (ETc). Urea application and mineralization are the most important nitrogen inputs to the paddy field, accounting for 58.7–68.2% and 23.7–35.0% of nitrogen input, respectively. Rice plant uptake, ammonia volatilization (AV), and nitrification-denitrification account for 68.0–75.0%, 11.9–17.1%, and 5.1–9.3% of nitrogen output, respectively. Nitrogen leaching (3.5–11.5 kg·ha⁻¹) is also large while the observed depth of leaching needs to be further investigated. Meanwhile, nitrogen drainage (0.72–1.11 kg·ha⁻¹) is not as large as conventionally accepted. AWD affects the nitrogen accumulation and release of duckweed, which is one of the potential reasons for the increase in rice yields. In the course of four continuous rice seasons, the soil nitrogen content (SNC) of the 0–20 cm and 20–40 cm soil layers continued to decrease and increase, respectively, and the overall nitrogen content did not change significantly. Irrigation modes and fertilization splits may promote or inhibit AV, and it depended on the time when urea was applied. In addition, AWD and three fertilization splits significantly promote nitrification-denitrification and nitrogen uptake by rice. This study presents a theoretical basis for NPS pollution reduction and provides an important framework for establishing an accurate model of TTWN for paddy fields.

来自稻田的氮污染是全球非点源（NPS）污染的主要贡献者，大大增加了地表水富营养化和地下水污染的风险。本研究使用 6 个水平衡分量和 12 个氮输入和输出评估了 4 年灌溉和尿素应用在稻田中的水和氮的综合运输和转化 (TTWN)。结果表明，干湿交替 (AWD) 灌溉减少了灌溉、排水和淋洗所需的水和氮，但对水稻蒸散量 (ETc) 的影响较小。尿素施用和矿化是稻田最重要的氮输入，分别占氮输入的 58.7-68.2% 和 23.7-35.0%。水稻植株吸收、氨挥发（AV）、硝化-反硝化分别占氮产量的68.0-75.0%、11.9-17.1%和5.1-9.3%。氮浸出（3.5-11.5 kg·ha^-1 ) 也很大，而观察到的浸出深度需要进一步研究。同时，氮排放（0.72-1.11 kg·ha ^-1) 没有传统上接受的那么大。AWD影响浮萍的氮积累和释放，是水稻增产的潜在原因之一。在连续4个稻季过程中，0~20 cm和20~40 cm土层土壤氮含量（SNC）分别持续减少和增加，总体氮含量变化不显着。灌溉模式和施肥分裂可能会促进或抑制 AV，这取决于施用尿素的时间。此外，AWD和三个施肥分裂显着促进了水稻的硝化反硝化和氮吸收。本研究为减少 NPS 污染提供了理论基础，并为建立精确的稻田 TTWN 模型提供了重要框架。