Makroaggregater

Makroaggregater are soil aggregates larger than about 0.25 millimeters in diameter. They form the larger, interconnected units of soil structure and create pore networks that influence water movement, aeration, and root penetration. The aggregates consist of mineral particles bound together by organic matter, clay minerals, roots, and microbial products such as extracellular polysaccharides and hyphae.

Formation and stability of makroaggregater are driven by biological and chemical processes. Soil fauna like earthworms and termites, plant roots, and microbial communities contribute to binding through mucilages, glomalin-related compounds, and root exudates. Organic matter content and the presence of cementing minerals (such as calcium or iron oxides) contribute to aggregate stability. Disturbances such as tillage disrupt macroaggregates, while practices that preserve or increase organic matter and biotic activity, such as reduced tillage or cover cropping, tend to promote their formation and persistence.

Functions and importance of makroaggregater include improving soil porosity and drainage, enhancing infiltration, reducing surface crusting, and increasing resistance to erosion. They also play a role in carbon storage by protecting organic matter within larger aggregates from rapid decomposition and helping create diverse microhabitats for soil organisms. Changes in land use, management, or climate that affect organic matter, moisture, or biological activity can shift the balance between macro- and microaggregates, altering soil structure and function.

Measurement and assessment of makroaggregater often involve wet-sieving or dry-sieving methods to separate the macroaggregate fraction, typically using a threshold around 0.25 millimeters. This helps evaluate soil structure, health, and the impact of management practices.

See also: soil structure, macroaggregate stability, soil organic carbon.