Macropores

Macropores are pores in soils and other porous media that exceed approximately 0.08 millimeters in diameter. They form a connected network that enables rapid movement of water and air, contrasting with smaller micropores that hold water more tightly and contribute to slower exchange with the soil matrix.

Most macropores arise from biological and physical processes. Biotic channels include earthworm burrows, root channels, and galleries created by soil fauna. Abiotic processes such as cracking from drying and swelling can also create larger pore spaces. Macropores can persist for varying lengths of time, but their size and connectivity are influenced by moisture, texture, organic matter, and soil disturbance, especially compaction and tillage.

Macropores play a crucial role in soil hydrology and biology. They enhance infiltration and drainage, promote gas exchange, and support deep root growth by providing preferential pathways that bypass the finer pore network. Because of their connectivity, macropores can control hydraulic conductivity and contribute to rapid transport of water and dissolved substances, including nutrients and contaminants, under certain conditions. This makes macroporosity a key factor in irrigation planning, drainage design, nutrient management, and considerations of groundwater protection.

Measurement and study of macropores involve observation of pore pathways and flow patterns. Tools include dye-tracing experiments to visualize flow, infiltration rate measurements, and imaging techniques such as X-ray computed tomography or soil cores analyzed for pore size distribution. Interpretation often focuses on the balance between macroporosity, soil structure, and management practices.

Management of macroporosity emphasizes preserving and enhancing pore networks. Practices that reduce compaction, promote biological activity, and maintain organic matter—such as reduced-till farming, cover cropping, and careful irrigation—support healthy macropores. Conversely, heavy machinery use and poor soil structure can diminish macroporosity and alter water and solute movement in soils.