The presence of air in soil ensures that aerobic soil organisms have the oxygen required for metabolism. Many soil organisms require oxygen, including plant roots, insects and microorganisms. When soil is not aerated, the decomposition of organic matter can slow or even stop.
Healthy soils are composed of a mixture of solid soil particles, water and air. Within this matrix, plant roots can access water and nutrients while maintaining access to oxygen.
Most of the microorganisms responsible for decomposition are aerobic in nature. In poorly aerated soils, these organisms can not break down organic matter or transform nutrients into bio-available forms.