Soil structure is formed from rocks and decaying plants and animals. An average soil sample is 45 percent minerals, 25 percent water, 25 percent air and 5 percent organic matter. Different-sized mineral particles, such as sand, silt and clay, give soil its texture. Organic matter content gives soil its structure and provides necessary nutrients for plant growth.
What Plants Need
Plants need space in the soil to absorb oxygen, space to grow roots, suitable acidity or alkalinity and adequate sunlight, water and mineral nutrients. Soil structure determines the root space, water absorption and nutrient availability. These attributes are a function of the organic content in soil. Plants thrive in soil that is not too sandy and porous nor too heavy and claylike.
What Soil Gives
Aggregates are formed from clusters of mineral particles in soil. Aggregates also contain particles of organic matter. Plant roots cling to soil aggregates and are provided nutrients from the organic matter. Aggregates also provide the structure that holds water in the soil. Without soil structure from aggregate particles, water would quickly seep away from growing plants.
Organic Matter and Soil Structure
Organic matter improves plant growth. Nutrients are derived from organic matter. Healthy soil structure and plant growth are intertwined. The USDA Natural Resources Conservation Service says that “increasing levels of organic matter promote a higher water-holding capacity, which results in increased plant growth.”
Enhance Soil Structure
Roots are the primary source of organic matter in soil structure. As roots grow and decay they are decomposed by tiny organisms and converted to organic matter. The organic matter thus increases soil’s stability and adds nutrients necessary for further plant growth. The no-till method of organic farming and gardening allows decayed roots to remain in the soil without disturbance. Soil structure is enhanced by this practice.
Fungi, bacteria, worms, insects and other microorganisms digest and break down the organic matter content of soil. Nutrients are released by this activity. There are between 5 and 10 tons of animal life within one acre of soil, all contributing to the creation of nutrients that go into plants. Plants then decay and become part of the organic matter content of the soil.