PROBLEM TO BE SOLVED: To provide an acid soil conditioner which does not supply excessive alkali and can supply alkali autonomously according to change of a quality of soil and can hold a pH of the soil within a certain width steadily for a long term.SOLUTION: A powder, granular or aggregated alkali material has chitosan coating on a surface thereof. Because the chitosan coating is solid and kept stably in alkali environment, and is not solidified in acidic environment when contacting soil is acidity, alkali is supplied to neighboring by losing the solid chitosan coating and exposing the alkali material to the environment, and the acidity of the soil can be improved.
