Soil improvers or soil additives contain hardly any nutrients such as N (nitrogen), P (phosphorus), K (potassium). They serve to process the biotic, chemical and/or physical properties of the soil.
Lime, for example, is a soil conditioner that increases the pH of the soil. Perlite loosens the soil and keeps moisture and oxygen in the soil.
Humus and soil enrich the soil with organic matter, which additionally loosens the soil and retains moisture.
Of course, all these substances offer much more, hardly any nutrients, but rather substances that promote the hormonal properties and the development of the plant's own defenses.
In addition, soil additives revitalize the soil by supporting the development of microorganisms.