A negative pressure irrigation system (NPIS) was tested in 2016 and 2018 to determine the optimum soil water control conditions to improve water productivity (WP) and fruit quality for greenhouse-grown watermelon. Four levels of negative water pressure (-5, -10, -15 and -20 kPa) were imposed continuously to a clay-made emitter buried 5 cm under the soil surface during three major stages of greenhouse-grown watermelon (I-VE: vine extension, 32 days; II-FF: flowering and fruit setting, 16 days; III-FM: fruit expansion to maturity, 28 days), which created soil water conditions around the emitter being 96%, 80%, 72% and 63% of field capacity, respectively. Except for the testing stages with the four levels of water treatments, the water supply during other stages was all set with a constant -10 kPa water pressure. A traditional furrow irrigation treatment was included to assess the water-saving effects of the NPIS. The irrigation timing used for the furrow irrigation treatment was decided based on the soil water contents corresponding to the -15 kPa treatment under NPIS. The results indicated that with an increase in the negative pressure imposed on the emitters, the average daily evapotranspiration linearly decreased for all three stages, with the largest decrease occurring during III-FM, but the watermelon yield decreased more with the decline in the water supply during vine extension due to the after-effects of the reduced vine growth. Water stress improved watermelon quality by increasing sugar contents during II-FF and reduced acid contents during III-FM. Moderate water stress resulted in the highest water productivity (WP) as well as protein and total soluble solid contents in the melon during all three stages. Comparing the NPIS with furrow irrigation, the water use of the former was 18.3–31.2% less, the yield was 6.2–12.0% higher, and the WP was improved by 36.6–53.8%. The results indicated that NPIS is a water-saving irrigation system, and the water pressure of NPIS can be set at -5 to -10 kPa for vine extension and fruit expansion to maturity stages; and -10 to -15 kPa for flowering and fruit setting stage to achieve good quality, high WP and relatively stable yield for greenhouse-grown melon.

2016 年和 2018 年测试了负压灌溉系统 (NPIS)，以确定最佳土壤水分控制条件，以提高温室种植西瓜的水分生产力 (WP) 和果实品质。在温室种植西瓜的三个主要阶段（I-VE：藤蔓延伸，32 天；II-FF：开花坐果，16 天；III-FM：果实膨大至成熟，28 天），这创造了发射器周围的土壤水分条件，分别为 96%、80%、72% 和 63分别占场容量的百分比。除试验阶段采用四级水处理外，其他阶段的供水均设定为-10kPa恒定水压。包括传统的沟灌处理以评估 NPIS 的节水效果。沟灌处理的灌溉时间根据NPIS下-15 kPa处理对应的土壤含水量决定。结果表明，随着排放源负压的增加，三个阶段的平均日蒸散量均呈线性下降，其中III-FM期间下降幅度最大，但随着供水量的减少，西瓜产量下降幅度更大。由于藤蔓生长减少的后遗症，在藤蔓伸展期间。水分胁迫通过在 II-FF 期间增加糖含量和在 III-FM 期间降低酸含量来改善西瓜品质。在所有三个阶段中，适度的水分胁迫导致甜瓜中最高的水分生产率 (WP) 以及蛋白质和总可溶性固形物含量。NPIS与沟灌相比，前者用水量减少18.3-31.2%，产量提高6.2-12.0%，WP提高36.6-53.8%。结果表明，NPIS是一种节水灌溉系统，NPIS的水压可设置为-5～-10 kPa，用于蔓生和果实膨大至成熟阶段；-10 至-15 kPa 用于开花和坐果期，以实现温室种植甜瓜的优质、高WP和相对稳定的产量。WP 提高了 36.6-53.8%。结果表明，NPIS是一种节水灌溉系统，NPIS的水压可设置为-5～-10 kPa，用于蔓生和果实膨大至成熟阶段；-10 至-15 kPa 用于开花和坐果期，以实现温室种植甜瓜的优质、高WP和相对稳定的产量。WP 提高了 36.6-53.8%。结果表明，NPIS是一种节水灌溉系统，NPIS的水压可设置为-5～-10 kPa，用于蔓生和果实膨大至成熟阶段；-10 至-15 kPa 用于开花和坐果期，以实现温室种植甜瓜的优质、高WP和相对稳定的产量。