21Development of technology to improve the mineralization of organic fertilizer and to enhance 22 crop production is essential to achieve the transition from traditional farming to eco-friendly 23 organic farming. Nanobubble oxygation (NB) was employed to compare with traditional pump 24 aerated oxygation (AW) and a control group through both soil incubation and soil column 25 experiments. Plant-available N and P contents in the NB treatment group were higher than 26 that in the AW and control groups. Enzymatic activities including β-1,4-N-acetyl-27 glucosaminidase, phosphatase, α-1,4-glucosidase, β-1,4-xylosidase, peroxidase, and phenol 28 oxidase were significantly higher in both oxygation groups compared with the control. The soil 29 microbial biomass, activity, and diversity were also significantly improved due to the oxygation 30 treatment. Additionally, the microbial metabolic functions were shifted in both oxygation 31 treatments compared with the control group. The final tomato yield increase from the NB 32 treatment group was 23%, and that from the AW treatment 17%, compared with the control. 33 4 36 52 the applied nutrients from the organic fertilizer can only be utilized by crops after 53 decomposition and mineralization of organic matter and release of plant-available nutrients, 54 such as nitrogen and phosphorous. It has been reported that only 35%, 39%, and 53% of the 55 plant-available nitrogen can be released from cow, pig and chicken manures on farmland over 56 6 months, respectively. 8 As a result, crop production in organic farming has been 57 demonstrated to be up to 25% lower than that in conventional agriculture using chemical Page 4 of 29 ACS Paragon Plus Environment Journal of Agricultural and Food Chemistry 5 58fertilizer. 9 This slow release of mineral nutrients from organic fertilizer has become the major 59 yield-limiting factor, 10 which indicates that further research could focus on the acceleration of 60 the mineralization of organic fertilizer in organic farming.
61The mineralization is driven by microbial biodegradation processes, where oxygen is 62 crucial in order to improve the bio-decomposition rate. The soil oxygen content in traditional 63 farmland originates mainly from air diffusion, which is always limited, especially in the deep 64 soil layer. Thus, an appropriate method to deliver sufficient oxygen into the soil is crucial to 65 improve microbial activity. The application of aerated water to the farmland through a drip 66 irrigation system has been used to deliver oxygen to the crop root zone. 11 Previous studies 67 demonstrated that these approaches could not only enhance crop yields, but could also 68 improve the nutrition quality of fruit. 12 To improve the soil oxygenation efficiency, the 69 aeration pump was upgraded from common air pumps, fine bubble diffusers and to venturi 70 injectors. 13 The main aim of the development of this technique was to deliver smaller-sized 71 air bubbles into irrigation water and to improve oxygen dissolution efficiency. Recen...