Fertilizer nitrogen (N) is a main pollutant in the agricultural ecosystem, while the fate of fertilizer N influenced by different irrigation modes is not well comparatively investigated. In this study, the distribution of fertilizer N in soil layers and tomato organs as well as its loss under drip, spray and flood irrigation with different quotas of 140, 180 and 220 m3 ha-1 were evaluated quantitatively by using nitrogen-15 (15N) labeled urea (abundance of 19.6%) as fertilizer source. The results showed that the plant 15N, soil 15N and 15N loss accounted for 27.9-47.8%, 38.8-54.0% and 10.3-21.9% of the total applied 15N, respectively. The amount of 15N absorbed by plants was significantly (p < 0.05) higher under drip and spray irrigation in comparison to flood irrigation with the same irrigation quota. The maximum 15N use efficiency and the minimum 15N residual were detected under drip irrigation with quota of 180 m3 ha-1, indicating that the supply and demand of urea-15N was more synchronized under such an irrigation mode. The 15N loss increased obviously as irrigation quota increased. Moreover, the correlation analysis between 15N loss and the possible impact factors indicated that the soil mineral 15N content after irrigation was one important factor influencing the 15N loss. Among the three irrigation modes, spray irrigation caused the lowest 15N loss of 10.3-13.1% when using the same irrigation quota. It was concluded that the irrigation modes have profound impacts on the fate of urea-15N. Irrigation could be used as a regulation pathway of plant N absorption and agricultural N output.
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