Detachment and transport characteristics of sandy loam soil by raindrop action in the northern Loess Plateau, China

Abstract

The detachment and transport of soil aggregates, which result from raindrop splash, is the initial stage and an important step for water erosion. To study the detachment and transport characteristics of loamy sand soil in the surface layer (0 to 5 cm) in the northern Loess Plateau, the experiment determined the splash effects of five raindrop diameters (2.67 mm, 3.05 mm, 3.39 mm, 3.79 mm, and 4.05 mm) on soil aggregates by simulating rainfall. Splash plates were used to collect the aggregate fragments at five distance intervals (0 to 10 cm, 10 to 20 cm, 20 to 30 cm, 30 to 40 cm, and 40 to 50 cm), and seven aggregate fractions were sieved. Then, we analyzed the relationships between raindrop diameters, splash distances, splash amounts, and the size distribution of the aggregate fragments. The results indicated that the splash erosion was distributed at a splash distance of 0 to 20 cm. In addition, the splash amount decreased exponentially with increasing splash distance and increased exponentially with raindrop diameter (p < 0.05). The aggregate fragments larger than 1 mm were broken down, so almost none were transported with the increase in raindrop diameter and splash distance. The splash aggregates were mainly concentrated in three fragment sizes smaller than 0.25 mm, accounting for 97% to 100% of the total splash amount; the splash amounts of the 0.106 to 0.053 mm aggregate fragment were the highest among the seven fragments, accounting for 56% to 72% of the total splash amount, and were most likely to detach and transport. There was no significant difference between the fractal dimensions (D) of different splash distances for the same raindrop diameter (p < 0.05). The breakdown of the soil aggregate was the largest when the raindrop diameter was 3.79 mm. The splash enrichment ratio (ER) of the larger than 1 mm aggregate fragment was almost close to zero with the increase of raindrop diameter and splash distance. In addition, the ER of the 1 to 0.106 mm aggregate fragment changed with the increase in raindrop diameter and splash distance. The results indicated that the aggregate fragments of sandy loam are easily broken and transported, and massive breakdown and transport of the microaggregates are an important index of soil erosion in the northern Loess Plateau.