**3. Effect of vinegar residue on soil properties and blueberry growth**

Blueberry grows in acidic soil with high organic content [25]. Generally it is necessary to add a large number of organic materials for soil amelioration [26] due to its low content of soil organic matter and other factors in commercial cultivation in China. Therefore, exploring suitable acidic organic materials has become one of the basic factors to ensure the sustainable development of blueberry cultivation in China.

Vinegar residue, a unique organic material, is a by-product of traditional vinegar-making industry in China. Resource of vinegar residue is abundant, as there is 2.6 million tons of vinegar residue produced annually by just one enterprise, Jiangsu Zhenjiang Hengshun Sauce and Vinegar Co., Ltd. [27]. Vinegar residue has high crude fiber content, strong acidity, and high moisture content, which makes it difficult to be disposed [28]. It is reported that vinegar residue could ameliorate soil structure and increase soil organic matter content by its large amount of grain husks [29]. Besides, it contains high organic matter, protein, as well as N, P, and K nutrients, making it to possess potential in agricultural resource business, especially in blueberry cultivation, that prefers acidic organic matter.

Therefore, the effect of vinegar residue on soil physical and chemical properties, enzymatic activities, growth of blueberry, nutrient uptake, and fruit quality should be studied. And the effect of vinegar residue on the composition and diversity of rhizosphere microbial community of blueberry should further be analyzed. By this research we would clarify the effect of vinegar residue on the growth of blueberry and the mechanism revealed from the perspective of soil amelioration, in order to provide scientific basis for the application of vinegar residue on blueberry cultivation.

### **3.1 Experiment setup**

The pot experiment was carried out in the blueberry nursery of the Institute of Botany, Chinese Academy of Sciences, Jiangsu province, in March 2016. And three treatments were set up as CK was pure soil; VR1 was V (vinegar residue),

V (soil) = 25:75; and VR2 was V (vinegar residue), V (soil) = 50:50. At harvest time in July 2017, soil and plant samples were collected, and soil physical and chemical properties (pH, conductivity, bulk density, total N content, total P content, and organic matter content), enzymatic activities (urease activity and acid phosphatase activity), growth of blueberry (plant height, basal diameter, average single fruit weight, fruit shape index, aboveground dry weight, root dry weight and rootshoot ratio), nutrient uptake (leaf N content, leaf P content and root N content, root P content) and fruit quality (total phenol and total ketone), and composition and diversity of rhizosphere microbial community of blueberry were examined.
