Abstract
Earthworms are believed to be beneficial to the quality of the soil structure. An important aspect of quality of soil structure is the stability of aggregates. The influence of earthworms on soil structure stability was investigated in a silt loam soil under “conventional” (high-input) and “integrated” (reduced-input) management. Aggregates from the top 5 cm of soil were sampled, air dried and analysed for their size distribution and water stability. Dry-sieved aggregate size distribution did not differ appreciably among fields and between years, so aggregates of a certain size represented a similar fraction of the soil for all fields. The wet-sieving procedure, used to measure aggregate stability, yielded highly reproducible results. Within-field variability of the stability was lower than between-field variability, so in further sampling only one mixed sample per field was analysed for soil structure stability. Analysing only a large and a small aggregate fraction was enough to evaluate aggregate stability in this study, as there was a gradual increase in stability from large to smaller aggregates. A 2 year time series of samples was analysed for earthworm population density and aggregate stability. Aggregate stability showed a seasonal pattern and was correlated significantly with earthworm density. Other factors influencing aggregate stability were management history in the conventional and integrated fields and, for a wider range of fields, organic matter content of the soil. The lower plastic limit, another stability parameter, was influenced mainly by organic matter and clay content, and not by any of the seasonally changing factors.
Published Version
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