Antecedent Water Content and Rainfall Energy Influence on Soil Aggregate Breakdown
- C. C. Truman ,
- J. M. Bradford and
- J. E. Ferris
Stability of soil aggregates under rainfall plays an important role in determining the magnitude of soil loss from cultivated fields. Soil and environmental factors controlling aggregate breakdown have yet to be fully defined. The objective of this study was to determine the influence of soil water condition, aggregate size, and rainfall intensity and duration on aggregate breakdown. Five soils ranging in texture from sandy loam to clay were studied. Using the wet-sieving method, median aggregate diameter values (D50) were determined on both whole-soil samples (0–19 mm) and aggregate samples (2–4, 4–8, and 8–19 mm in diam.) at three water conditions (−0.5 kPa, −1.0 kPa, and air dried). A companion set of whole-soil samples was subjected to 64 and 127 mm h−1 simulated rainfall for 5, 15, and 30 min, and a set of aggregate samples was exposed to 64 mm h−1 simulated rainfall for 15 min; all samples were then wet sieved. Prewetting from air dry to −1.0-kPa matric potential provided the greatest increase in D′50 values (D50 corrected for primary particle size) for the wet-sieved Broughton clay (0.49–1.91 mm). Prewetting the Broughton clay also decreased the difference (ΔD50) between Broughton D50 values obtained from whole-soil samples receiving rain plus wet sieving and D50 values of only wet-sieved samples by 1.4 mm for all rainfall energies. Changes in D′50 and ΔD50 values due to rainfall energy were greatest for the air-dried Heiden clay. Rainfall energy (0.26 J cm−2) decreased D′50 values from 0.87 to 0.33 mm and increased ΔD50 values from 0.32 to 0.54 mm. Results of this study indicate that an increase in initial water condition increases the resistance of an aggregate to the forces of raindrops and flowing water, thereby lessening particle detachment (if other hydraulic variables are held constant).
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