关键词: 水盐分布, 冬小麦, 养分利用, 包气带, 盐分阈值

Abstract:

【Objective】This study aimed to explore the combined effects of groundwater depth (GWD) and nitrogen application on soil water and salt distribution, stratified residues of nitrogen and phosphorus, and nutrient absorption and utilization of winter wheat, and to determine the nitrogen (N) application threshold for shallow groundwater depth based on the salt balance of cultivated soil and stable crop yield. 【Method】A soil column simulation experiment was conducted with four GWD gradients (60, 90, 120, and 150 cm, labeled as G1, G2, G3, and G4) and four N application rates (0, 150, 240, and 300 kg·hm^-2, labeled as NF0, NF150, NF240, and NF300), resulting in 16 treatments. The experiment was carried out during the 2020-2021 and 2021-2022 winter wheat growing seasons to monitor and analyze the distribution of soil water and salt, the nitrogen and phosphorus content in different soil layers, and the nitrogen uptake and utilization of winter wheat under different GWD and N application combinations. 【Result】 Two years of data showed that increased application of N fertilizer exacerbated soil drought in the main root zone (0-60 cm soil layer, MRZ), especially, when the GWD was greater than G3, the soil moisture in the MRZ of the NF300 treatment was significantly reduced. Under N application of NF0-NF150, the electrical conductivity of the 0-20 cm and 20-60 cm soil layers showed a decreasing trend with increasing GWD, whereas under treatment of NF240-NF300, the electrical conductivity of the 20-60 cm soil layer in 2021-2022 and two-year salt accumulation significantly enlarged with increasing GWD. The N application of NF240-NF300 significantly augmented the salt content in the 0-20 cm soil layer at the depth of G3-G4, especially in the NF300 treatment where the soil conductivity of 0-20 cm soil layer exceeded the threshold (360.19-362.89 μs·cm^-1) and showed an obvious trend of alkalization. At the NF0-NF240 treatment, the average soil total nitrogen content under the MRZ of G3 and G4 treatments was the highest, while the total nitrogen and total phosphorus content were significantly reduced with increasing GWD under NF300 treatment. Among them, the average soil total nitrogen content under G1-G3 treatment was significantly higher than that under G4 treatment by 11.90% (P<0.05). Growing N fertilizer under G1-G2 depth was beneficial for increasing soil total nitrogen content, while soil total nitrogen content under NF150-NF240 treatment was the highest at the G4 depth. The soil total phosphorus content was the highest under the NF0-NF150 treatment with the G1-G4 depth. Increasing the GWD could promote the absorption of nitrogen by grains and the aboveground parts of plants under the NF0-NF240 treatment. However, with the continuous increase in N application rate and the superimposition of N application for groundwater control between years, the increase in the GWD was not conducive to the absorption of nitrogen by grains and the aboveground parts. Increased application of N fertilizer significantly promoted the N accumulation in grains and aboveground parts at the GWD of G1-G2. However, for the GWD of G3-G4, the N accumulation in grains and aboveground parts was the highest under the N application condition of NF150-NF240. Moreover, after continuous N application and groundwater control in 2021-2022, increased N fertilizer significantly reduced the nitrogen harvest index of winter wheat. 【Conclusion】 In conclusion, under the GWD of 120-150 cm, N application rate of 150-240 kg·hm^-2 was conducive to maintaining soil water-salt balance in the MRZ, enhancing N accumulation in aboveground parts and grains, and achieving both reduced N fertilizer input and improved efficiency while ensuring scientific management of the main root zone salinity.

Key words: distribution of water and salt, winter wheat, nutrient utilization, vadose zone, salt threshold