Effects of straw return and aeration on oxygen status and redox environment in flooded soil

To study the effects of straw return and aeration of the water layer on oxygen and redox status in the water column and at different depths in paddy field soil, a short-term incubation experiment was conducted with four treatments: (1) no straw return (NS); (2) straw return without aeration (S); (3) straw return and 30 minutes of aeration per day (SO30); and (4) straw return and 90 minutes of aeration per day (SO90). Compared to NS, S decreased dissolved oxygen (DO) and redox potential (ORP) by 23–58% and 47–53 mV, respectively, and increased active reducing substance (ARS) by 21–46% in the water and soil layers. The aeration treatments increased DO and ORP by 25–120% and 11–86 mV, respectively, and reduced ARS by 5–16% compared to S. The results indicated that straw return to paddy fields exacerbated hypoxia and reducing conditions in the soil. SO90 achieved better effects than SO30 in alleviating the negative impact of straw return by supplying more oxygen, but the effects weakened over time and with soil depth.