Characteristics of Filtrates From Soil Treated by Ozone

Ozone soil treatment is very effective not only in exterminating soil-born worms but also in enhancing plant growth. According to the authors' previous works, vegetables cultivated in ozone-treated soil showed enhanced plant growth. In order to understand the mechanism behind the effectiveness of ozone-treated soil in boosting plant growth, in this study filtrates were extracted from ozone-treated soil and were examined by ultraviolet-visible spectrophotometry. Two types of soil-commercial soil and natural andosol-were treated by ozone in both infrared-transparent and infrared-absorbing chambers. The increased nitrogen content was notably higher in the andosol in comparison to the commercial soil. In addition, the filtrates extracted from the ozone-treated soils showed brown coloration, corresponding to absorbance at approx. 300 to 600 nm and indicating the generation of fulvic acid, which is a biostimulant. Therefore, it can be considered that biostimulants such as fulvic acid are generated after ozone treatment of soil and activate microorganisms around the plant's roots, which leads to enhanced plant growth. Moreover, the filtering of ozone-treated soil can be a unique method to produce a biostimulant in a very short time.