Soluble Carbon Improves Macroaggregate Persistence to Wetting Disturbance

Macroaggregates that dissipate external forces by resisting to disintegration and deformation should persist when subjected to slaking forces when wetted. Accordingly, soil with persistent macroaggregates should maintain its integrity following wetting disturbance. This study determined how repeated wetting affects two pre-sieved macroaggregate size fractions (2–4 mm and 0.6–2 mm) of clay and organic soils pretreated with organic carbon substrates. Soil size fractions were unamended or treated with organic carbon (soluble glucose or insoluble wheat straw) before being exposed, during three months, to nine sequential wettings at three wetting intensities (no wetting, slow wetting of 1 g·s -1 or fast wetting of 2 g·s -1 water). The glucose-treated macroaggregate size fractions from the clay soil were minimally disturbed by repeated wetting, maintained their shape (shown by high aggregate circularity and low major/minor axis ratio) and were more cohesive, possibly because of a higher microbial activity provided by the glucose treatment. In contrast, the macroaggregate size fractions mixed with wheat straw, which had the same carbon content as glucose, did not persist when exposed to repeated wetting. The distinct persistence of macroaggregates treated with glucose suggests that microbial processes could produce persistent macroaggregates and deserve more in-depth evidence.