Abstract：Nitrogen (N) is necessary element for crop growth, as well as an important factor of water eutrophication. In this paper, the Jiefangzha Irrigation District of Hetao Irrigation Zone of Inner Mongolia was chose as the study area to highlight the soil N circle during the irrigation periods. The distributions of total nitrogen (TN) and nitrate nitrogen (NN) in soil, shallow ground water and soil leachate during summer irrigation and autumn irrigation were analyzed. The results indicated that summer irrigation obliviously diluted the N, and denitrification in the groundwater lowered the concentration of NN, the corn field N loss relatively obviously after summer irrigation. Autumn irrigation was the main phase of nitrate loss in farmland. On the one side, the NN was leaching down under the watering; on the other side, the NN was released as the shape of N2O, N2 and O2 after denitrification. The peak value of TN in the groundwater lagged behind that of NN during both summer and autumn irrigation. It was conclude that included the loss of NN, partial NH4-N, organic N and some other forms of N had a certain extent lengthways leaching under the irrigations.
