Water repellence and soil aggregate dynamics in a loamy grassland soil as affected by texture
Gryze, S De | Jassogne, L. | Bossuyt, H. | Six, J. | Merckx, R.
It has been hypothesized that aggregate stability is partly caused by subcritical (i.e. mild) water repellence. We conducted both a field study at a pasture site and an incubation experiment in the laboratory to characterize the relationship between aggregate dynamics and water repellence. In the field study, we investigated 53 samples from a natural texture gradient for water repellence and aggregation. In the 3-week incubation experiment, we added wheat straw to crushed soil material from five of the 53 soils representative of the texture gradient (a sandy loam, two loams, a silt loam and a clay loam), and followed changes in aggregate formation and water repellence. Although there was a dramatic increase (P < 0.0001) in aggregation in all the soils during incubation (the mean weight diameter increased from about 300 [mu]m to at least 900 [mu]m), we observed a concomitant increase in water repellence only in the clay loam soil (P = 0.0003). We found no significant correlations between water repellence and aggregation (n = 53, P > 0.05) in the field. Whereas correlation between aggregate formation and texture was weak in the incubation experiment, we found a significant correlation between aggregation and textural parameters in the field. The amount of large macro-aggregates (> 2000 [mu]m) was positively correlated with clay content (n = 53, r = 0.53, P < 0.001), and negatively with sand content (n = 53, r = [-]0.46, P < 0.001). These results indicate that (i) microbially induced water repellence might only become apparent when enough easily decomposable substrate is available, (ii) soil texture affects aggregate stabilization rather than aggregate formation, and (iii) aggregate formation is not necessarily associated with an increase in water repellence.
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