To provide a humus precursor-ferrihydrite precursor complex containing humic acid, fulvic acid and physiologically active substances, growth promoters, antibiotic substances, etc., giving activity to plants and soil bacteria and capturing heavy metals, etc.

Humus raw material produced by crushing and mixing dry lumber and raw lumber is sprayed with a mixed culture liquid composed of a fermentation assistant and ionic water. When the temperature of the humus raw material reaches 65-70°C, the ionic water is sprayed on the raw material, the material is turned, the ionic water is sprayed on the material when the temperature of the material reaches 65-70°C, the material is turned and the product is left to stand for 1 week while introducing air into the material.