**4. Discussion and conclusion**

Du et al. [30] found that vinegar residue compost amendment could promote the growth of cucumber and could be applied as a method for biological control of cucumber Fusarium wilt. Our results showed that vinegar residue could promote the growth of blueberry and increase the biomass accumulation of shoot and root, and root dry weight of blueberry under VR2 increased by 83.94% compared with CK. Previous studies have found that the application of organic materials could increase the reducing sugar content and reduce the titratable acidity content of fragrant pear fruit [31] and increase the content of Vitamin C (VC) and soluble solids in tomato fruit [32]. This research showed that the application of vinegar residue could significantly increase the soluble solid content of blueberry fruits. In addition, the total phenol and flavonoid content of the fruits of VR2 increased by 71.42 and 100.00%, respectively, compared with CK, indicating that the application of 50% vinegar residue had the best effect on promoting the quality of blueberry fruits.

Blueberry is suitable to grow in soil with abundant organic matter and pH under 5 (below 5.5) [1]. Soil pH of VR2 is 4.62, which is quite suitable for the growth of rabbiteye blueberry. Soil conductivity reflects the water soluble salt content. And soil conductivity of VR2 was 224.80 μS·cm<sup>−</sup><sup>1</sup> , which was 102.71% higher than CK, but did not exceed the suitable range of soil conductivity for blueberry growth [33]. The exchangeability of soil salt ions and nutrient separators was higher with the increase of soil conductivity at a certain range, which is more conducive to nutrient absorption of blueberry. In addition, soil bulk density was decreased in VR2, which indicated that the application of vinegar residue could increase soil porosity. And soil pH, electrical conductivity, and bulk density were the key factors to promote the growth of blueberries by applying vinegar residue. The results showed that VR2 treatment significantly increased root-shoot rate by 72.00% and root nitrogen by 23.89% compared with the control, suggesting that vinegar residue could significantly promote root growth.

Previous studies reported that adding organic materials can significantly increase soil nutrient content and enhance soil biological activity [34]. Our results showed that the application of vinegar residue could significantly increase the content of total nitrogen, total phosphorus, and organic matter in soil. Soil nitrogen content of VR2 increased by 239.01% compared with CK, and soil organic matter content increased by 43.6 g/kg with the application of 50% vinegar residue. Improvement of soil organic matter could ameliorate soil structure and serve as resource of organic nitrogen and phosphorus. What is more, it could also enhance the activity of soil microbial. Soil urease and acid phosphatase are important enzymes for the transformation of soil nitrogen and phosphorus. Goyal et al. [35] found that the application of exogenous organic materials could improve the activity of soil urease and phosphatase and thus improve soil fertility. This study found that activities of urease and acid phosphatase were highest in VR2, with 26.60 and 22.87 g·kg<sup>−</sup><sup>1</sup> h<sup>−</sup><sup>1</sup> , respectively, 533.33 and 95.47% more than the control. The results showed that the application of vinegar residue increased the activity of soil urease and acid phosphatase, thus increased the transformation of soil nitrogen and phosphorus, and then promoted the growth of blueberry [36, 37].

In conclusion, the application of vinegar residue could improve soil structure and increase soil nutrient and organic matter content, thus promoting the growth and fruit quality of blueberry. In the meantime, the application of 50% vinegar residue appeared to have the best effect on promoting blueberry growth.

### **Author details**

Jiang Jiafeng, Wei Jiguang, Yu Hong\* and He Shan'an Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing, China

\*Address all correspondence to: njyuhong@vip.sina.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**99**

*The Developing Blueberry Industry in China DOI: http://dx.doi.org/10.5772/intechopen.88225*

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