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Summary The influence of root growth and activities on soil aggregate stability was investigated using five crop species and two soils. Single plants were grown in pots for 6 weeks or less to minimise any possibility of changes in aggregate stability caused by decomposition of dead roots. Planted soils were compared with fallow controls. Aggregate stability was estimated by a turbidimetric technique (used for fresh and air‐dried samples) and by wet sieving (used for air‐dried samples only). Root growth of perennial ryegrass and of lucerne for 42 days was generally associated with increases in aggregate stability whether the soil was tested in a fresh or an air‐dried condition. These beneficial effects were associated with periodate‐sensitive (probably polysaccharide) materials produced in the rhizosphere. Growth of maize, tomato and wheat roots for 25 days decreased the stability of fresh soil aggregates, although the effects of tomato and of wheat were not consistent. However, the deleterious effects of these three species on aggregate stability were not apparent after air‐drying. The restabilization of maize soils (relative to fallow controls) on air‐drying appeared to be caused by increased stabilization by periodate‐sensitive materials. The results suggest that the growth and activities of living roots may be a major factor controlling the overall direction and magnitude of changes in aggregate stability under arable or ley crops.
Reid et al. (1981) studied this question.