Abstract: 【Objective】It is of great importance to study the distributions of water, sanility and nitrogen in soil and cotton root for optimizing soil salinity, irrigation and fertilization strategies with drip irrigation. 【Method】Spatial distributions of water, salinity and nitrogen in cotton root zone were investigated in a pot experiment with different irrigation and fertilization methods under greenhouse conditions. According to the application order of nitrogen (N) fertilizer solution and water (W) involved in an irrigation cycle, four fertigation treatments were designed, nitrogen applied 1) in the beginning of the irrigation cycle (N-W), 2) at the end (W-N), 3) in the middle (W-N-W), and 4) throughout the irrigation cycle (NW). Conventional nitrogen fertilizer broadcasted in soil following surface irrigation was the control (SN-W). 【Result】Distributions of water and salinity in soil were significantly influenced by irrigation methods, but no differences were found between the four nitrogen fertigation strategies. 15N in the soil profile was concentrated at depth 0-20 cm 24 h after fertigation, and the distribution of %15N atoms in soil was significantly influenced by the different fertigation strategies. In strategy NW, 15N in the soil moved deeper and there was less lateral movement 24 h after fertigation than in the other treatments, and significant amounts of residual soil nitrate were found in deeper soil layers after harvest. In contrast, nitrogen was more evenly distributed at 0-20 cm depth 24 h after a fertigation cycle and fewer nitrates were left at the end of experiment after N-W treatment, and furthermore, the distribution of roots with N-W treatment was also better. 【Conclusion】These results suggest that the N-W strategy would work better in increasing nutrient-use efficiency, and reducing the risk of chemical leaching from the root zone.

Key words: drip irrigation under film, soil salinity, fertigation, 15N, root distribution