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Soil aggregate stability is an important measure for assessing soil structural quality. Here we compare stable and unstable soil aggregates from organically and conventionally managed soils that have similar organic matter contents to determine the role of management in aggregate stability. Aggregate stability was determined by slaking, which proved to be an accurate estimator of the rate of aggregate turnover. The results indicate that, in soil aggregates released by slaking, the organic matter is held in aggregates > 0.3 mm diameter. A relatively short aggregate turnover rate will prohibit the production of stable micro-aggregates within macro-aggregates and thus gradually reduce aggregate stability, as was observed in soils under conventional management. Data obtained by X-ray mCT suggested that intra-aggregate porosity did not significantly affect stability. We observed cracks and elongated pores connected to the surface of stable soil aggregates that can provide an escape route for entrapped air, thus reducing pressure build-up and potentially reducing slaking. Our results show that organic management has the potential to develop more stable aggregates compared with conventionally managed soils for the soil type studied. Thus, conventional soils require particular attention to management practices that increase the rate of aggregate turnover in order to reduce the production of unstable aggregates that can contribute to crusting, erosion and runoff.

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