Makroaggregates

Makroaggregates, or macroaggregates, are the larger clumps of soil particles that remain intact when soil is dispersed in water. They are typically defined as soil aggregates larger than about 0.25 millimeters in diameter, with microaggregates being the finer fraction. The macroaggregate fraction is commonly determined by wet-sieving a dispersed soil sample, using the >0.25 mm size class to separate it from the smaller particles.

Formation of macroaggregates involves physical, chemical, and biological processes. Plant residues and living roots provide organic matter that binds mineral grains together. Fungal hyphae, bacteria, and extracellular polymers act as binding agents, while clay minerals and iron/aluminum oxides contribute to cementation. Glomalin, a glycoprotein produced by arbuscular mycorrhizal fungi, is often cited as an important cementing substance that helps stabilize macroaggregates.

Macroaggregates play a central role in soil function. They create a porous pore network that enhances water infiltration, storage, and drainage, while improving aeration and resistance to erosion. By occluding organic matter and protecting it from rapid decomposition, macroaggregates contribute to soil carbon sequestration and influence nutrient cycling.

Management and environmental factors strongly affect macroaggregates. Soils rich in organic matter, with balanced texture and stable moisture regimes, tend to form and sustain larger macroaggregates. Tillage disrupts these structures, reducing stability, whereas practices such as cover cropping, residue retention, and reduced tillage promote macroaggregate formation and persistence. Measuring the macroaggregate fraction provides insight into soil structure, health, and its capacity to support productive, sustainable soils.