Soil structure, an essential part of soil health, is the organization of soil particles and aggregates and the pores between them. Soil with a good structure is able to resist erosion and compaction, provide water and gas infiltration, hold a healthy amount of water, and enhance plants’ access to nutrients, creating an optimal foundation for crops. In a healthy soil structure, half of the soil is made up of particles, which group together to form aggregates. This leaves spaces between the clumps called pores, which make up the other half of the structure. Soil structures are made up of four key elements: mineral solids, like sand or clay; soil solution, made up of water and dissolved nutrients; air; and organic matter, which includes living organisms, fresh residues, and well-decomposed residues called humus. While the matter making up the soil particles are invaluable to soil health, pore space is also important. Water and air move through the pores, and soil organisms and plant roots also grow there.
Soil structure changes over time, depending on water, biological, and physical influences. As water enters and leaves the soil, soil structure shrinks and swells. Plants affect soil structure just as soil affects plants; roots stabilize the structure by creating aggregates. Physical influences like tillage and compaction also impact soil structure, both positively and negatively. As physical forces manipulate the structure of soil, they may force particles closer together, forming aggregates and strengthening bonds between chemicals. However, compaction and tillage primarily degrade soil by destabilizing the aggregates and disrupting the existing structure. Erosion can also negatively impact soil structure, as can changes in water levels. With too much water filling soil pores, no oxygen and carbon dioxide can be exchanged through the soil, and without water, the soil structure and plant life will suffer.
Research in soil health recommends many agricultural practices that can build and maintain good soil structure. Reducing tillage practices to conservative tillage can decrease the harm tillage does to the structure. Higher plant growth biomass and more surface residue can help the formation of healthy soil structure, as well as using fewer chemical fertilizers. Managing grazing practices can also influence the structure of the soil. Soil structure makes up the building blocks of soil and plant health, so keeping it healthy and stable is a key part of ensuring crop yield and productivity.