The stability of soil aggregates as affected by organic materials, microbial activity and physical disruption

On moist incubation the equivalent of 50 t ha-1 or more of ground, readily decomposable organic materials greatly increased the proportion of stable aggregates of Shepparton fine sandy loam within 1-4 weeks; the aggregates remained stable for up to 32 weeks if left undisturbed. Severe restriction of microbial activity in aggregates of Shepparton fine sandy loam by sterilization or dryness increased the effect of physical disruption associated with intermittent wetting and drying, and simulated cultivation. The results suggest that microorganisms in non-sterile moist soil can produce bonding substances which compensate partially for those bonds broken physically.