Appropriate dissolved oxygen concentration and application stage of micro-nano bubble water oxygation in greenhouse crop plantation

•DO concentration and MNBO application period affected tomato and cucumber yield, IWUE and fruit quality.•MNBO application improved soil quality by increasing rhizosphere soil enzyme contents and soil microbial species.•15 mg/L and the fruiting stage were the optimal DO concentration and application period of MNBO for tomato and cucumber. Micro-nano bubble water oxygation (MNBO) has been recognized an effective way to increase crop yield and quality, but the effects and potential mechanism of dissolved oxygen (DO) concentration and application period on crops are unknown yet. Consequently, experiments within two consecutive growing seasons were conducted to determine the effects of two MNBO application period (SF: seeding and flowering stage, FR: fruiting stage) and two DO concentration (15 mg/L and 25 mg/L) on the yield, IWUE, fruit quality of tomato and cucumber as well as the soil quality under two kinds of water source (RW: reclaimed water, GW: groundwater). The results indicated that application of MNBO resulted into higher yield and IWUE of tomato and cucumber compared to no-oxygation treatments (CK) and RW irrigation showed higher production than GW treatments. Significant differences on fruit quality (p