Pyroligneous acids can be used in herbicides, but the dosage used often more than 1000 kg ha-1. Five treatments including the application of bamboo, wood, straw vinegar, acetic acid and sulphuric acid at high dosages sprayed once every 6 days, for a total of 3 times. We then continuously monitored the changes in soil pH, moisture content and the activities of three soil hydrolase enzymes involving in urease, protease and sucrase. We found that after 1~3 days of spraying with all 5 kinds of acid, the soil pH was not immediately reduced, but from 3 days after application onward it was reduced by a maximum of 1.54~1.75, which showed that the soil had some buffering capacity. Over time, the pH began to return to the water control pH value, which showed that the soil also had good restorative capacity. After the second and third times of spraying, the pH change measured showed no cumulative effect, which demonstrated that the soil had adaptive capacity. We accidentally found that bamboo vinegar could improve the soil pH by a maximum of 0.65~1.02, while the other four acids reduced its pH. Bamboo vinegar was found to contain the 6 compounds while wood and straw vinegar contained none of these compounds. These compounds may be a new potential reagent(s) for improving the pH. Three soil sample processing methods tested for determining pH, including the moist soil test, oven-dry soil test and air-dried soil test, all produced extremely and significantly different pH values. Five acids were unable to significantly improve the water holding capacity of the soil; they had adverse effects on the activity of the urease enzymes while beneficial effects on the protease and sucrase enzymes. Therefore, pyroligneous acid and acetic acid have no effects on soil health as herbicides.
Keywords: Bamboo wood straw vinegar; Biochar byproduct; Biomass energy and biochar; Enzyme activities; Natural herbicide; Soil acidification and health.