It has been considered that, in an artificial forest typified by a cedar forest or a Japanese cypress forest, forest functions can be restored by reducing the stand density therein through forest maintenance operations such as thinning and pruning so as to assure an adequate light intensity in the forest. However, an artificial forest with an excessive planting density is kept at a low light intensity over a long period of time and, therefore, has a number of sites where vegetation cannot be restored due to the marked progress of soil acidification. In a strongly acidic site having special soil such as acidic sulfate soil where the soil pH significantly decreases, the soil environment cannot be improved merely by leaving untreated. An acidity alleviation method using converter slag, comprising, in a strongly acidic soil site, where the soil pH has markedly decreased, to be treated, spraying a soil dressing, which is prepared by blending converter slag that is obtained in the course of producing steel with an organic material or the like, to the soil surface to be treated using a vegetation matrix-spraying machine to thereby improve the structure of the soil that has been dysfunctional because of the marked decrease in the soil pH.
