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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.

【Objective】 Gravel mulching combined with drip irrigation is an improved agronomic technique for crop production in northwestern China. The purpose of this study is to investigate the impact of dripping rate of the emitters on soil water and salt redistribution, as well as the growth and yield of watermelon. 【Method】 The field experiment had three treatments with the dripping rate controlled at 2 L/h (Q1), 3 L/h (Q2), or 4 L/h (Q3), respectively. In each treatment, we measured the spatiotemporal variation in soil water and salt, water use efficiency, as well as growth, yield and fruit quality of the watermelon. 【Result】 Horizontal advancement of the wetting front in the soil increased with dripping rate. After harvest, soil salt content in the 0~100 cm soil layer decreased, with the decreasing rate increasing as the dripping rate increased. Also, with the increase in dripping rate, the soluble sugar content in the fruits increased first followed by a decline. Of the three dripping rates we compared, Q2 increased the soluble sugar content in the fruit the most, up by 54.3% and 22.3%, respectively, compared to Q1 and Q3. With the increase in dripping rate, the vitamin C content in the fruits decreased first and then ramped up. Q3 gave the highest vitamin C content, increasing by 53.7% compared to Q2. Increasing dripping rate boosted both fruit yield and water use efficiency. Compared to Q1 and Q2, Q3 increased fruit yield by 6.20% and 3.56%, and water use efficiency by 6.49% and 3.72%, respectively. 【Conclusion】 Taking soil water and salt redistribution, as well as watermelon yield and quality into account, the optimal dripping rate for watermelon growth in the gravel-mulched soil was 4 L/h when using the local saline water for irrigation.