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【Objective】 Brackish water has been used as a supplementary irrigation resource in some arid and semi-arid regions in northwestern China, but the impact of its long-term application on soil environment and crop growth and quality is not well understood. The objective of this paper is to fill this knowledge gap using watermelon as an example. 【Method】 The experiment was conducted in fields with sand mulch, where brackish water has been used as a supplementary irrigation resource for varying periods ranging from 2 to 14 years. During the experiment, we measured the distribution of soil water and salt in the 0~60 cm soil layer, soil bulk density, as well as the yield and quality of watermelon. An uncultivated piece of land nearby was used as the control. 【Result】 Soil salt content increased with the increase in duration of brackish water irrigation in both tendril elongation and harvest stage. The highest soil salt content was in the 20~40 cm soil layer for the control, and in the 40~60 cm soil layer for the sand-mulched field. The supplementary brackish water irrigation increased the soil moisture content in flowering and fruit-setting stages, but the increase varied in that with the increase in the duration of the brackish water irrigation, the soil water content increased first and then declined. The highest soil moisture content in the sand-mulched field was in the surface layer (0~10 cm), while for the control it was in the 10~20 cm soil layer. Sand mulch increased soil bulk density in the 0~40 cm soil layer and soil compaction in the 0~8 cm soil layer. It was also found that with the increase in length of brackish water irrigation, the yield and soluble solids content in the watermelon decreased, while the fruit quality improved first followed by a decline. 【Conclusion】 Long-term use of brackish water for supplementary irrigation in the sand-mulched fields increased soil bulk density and compaction in the upper soil layers, as well as soil moisture and salt content. As the years of brackish water irrigation increased, the yield of watermelon decreased while the quality of its fruits showed an initial improvement before deteriorating. |
