Disclosed are a soil diagnosis method for diagnosing soil using a cycle activity indicator which is calculated using the following factors (I) to (III): (I) the ammonia reduction rate in target soil (II) the activity of forming phosphoric acid from phytic acid in the target soil and (III) the activity of forming potassium from compost in the target soil, and (IV) the soil bacteria count in the soil and a soil quality control method and a soil improvement method.
