But, pores in clay soils can be so small and hold water so tightly that tiny feeder roots cannot extract the moisture. Organic matter in the soil affects both the physical and chemical properties of the soil. A fertile soil rich in organic matter is literally alive. Although insects and earthworms are the most obvious inhabitants, microorganisms, such as bacteria and fungi, constitute the largest population by weight in the soil community. Organic matter in the soil comes from decomposed plant and animal tissue as well as the micro-organisms themselves.
Organic matter enhances the aeration and water-holding capacity of the soil.
It also affects the soil's chemical properties by supplying necessary plant nutrients. Effective rooting depth may be limited by circumstances that restrict soil porosity or hinder plant growth. Four relatively common problems are surface crusting, high water tables, poor sub-surface drainage and claypans or hardpans. In extremely compacted soil, or soil without adequate aeration, roots are found growing on the surface of the soil where conditions are more favorable for growth. Soil Compaction Soil compaction is the major cause of death or decline of mature trees where efforts have been made to save them.