Because Compost:

1. Improves the soils structure, porosity and density, creating a better plant root environment.
2. Increases permeability of heavy soil, reducing erosion @ runoff.
3. Improves significant amount of organic matter.
4. Supplies a variety of macro @ micronutrients.
5. Can control or suppress certain soil-borne plant pathogens.
6. Supplies significant amount of organic matter.
7. Improves cation exchange capacity of soils, improving their ability  to hold nutrients for plant use.
8. Supplies beneficial microorganisms to soils and growing media.
9. Improves and stabilizes soil PH.
10. Can bind and degrade specific pollutants.