Abstract Field infiltration tests using portable rainfall infiltrometers were conducted in the Wangjiagou experimental basin in the hilly loess region of north China. Based on data collected at 27 sites, a topographic zonation of infiltration characteristics was observed. The average steady infiltration rate and the average ponding time decreased from the hilltop to the hillslope and further decreased to the gully wall. Such a zonation is closely related to the variations of topography, soil and land use conditions in the study area. A general infiltration model is proposed. Collected field data are used to establish the applicability of the proposed model in the study area.
Aggregate disintegration and crust formation at soil surfaces exposed to rain are caused by rapid wetting of the dry aggregates and by raindrop impact. The relative importance of these two mechanisms was evaluated by studying the effects of the wetting rate (WR) and raindrop impact on crust strength and crust micromorphology. Two soils, a loess (Typic Haplustalf) and a black soil (Pachic Udic Argiboroll), varying in their organic matter content (15.2 and 42.6 g kg −1 , respectively) and aggregate stabilities, were packed in splash cups, prewetted at WRs of 2 or 50 mm h −1 , and exposed to 5 to 60 mm of simulated rainfall. For the unstable loess soil, crust strength increased and crust microfabric deteriorated with increases in cumulative rainfall but were unaffected by the WR. Conversely, in the black soil with high aggregate stability, changes in crust strength and crust microfabric were affected by the WR; for the slow WR, both phenomena were largely unaffected by increases in cumulative rainfall but, for the faster WR, the phenomena were greatly affected by rain depth and crust formation proceeded rapidly. Both WR and raindrop impacts affect surface aggregate breakdown and crust formation. The energy released by slaking while wetting dry aggregates is, however, considerably higher than that of raindrop impact. Thus, the relative importance of WR and rain depth depends on the stability of the soil aggregates. For soils with stable aggregates, raindrop impact alone is not sufficient to destroy aggregates and form crusts. Rapid wetting of the dry soil is essential for aggregate breakdown and crust formation. For soils with unstable aggregates, the energy of raindrop impact is sufficient for seal formation.
Soil particle size is one of the key parameters determining splash erosion and soil crust development. Based on simulated rainfalls with a high intensity of 1.2 mm min-1, the rain splash erosion and soil crust development of Loess soil separates with different diameters are studied and the key factors predicting soil crust formation are discussed. The results indicated that: (1) as the diameter of soil separates increases, the amount of detached particles increases from < 0.038 mm to a maximum amount of 0.15-0.22 mm, and subsequently decreases; (2) the smaller the soil separates, the easier the development of soil crust and the higher the degree of soil crust development; (3) the susceptibility of soil crust formation can be predicted by integrating three indices of soil texture, aggregate stability, and rainfall energy together.
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