Influence of sedum plant on sediment yield from an acid soil under simulated rainfall

Managing soil erosion by water from marginal acidic soil employing traditional methods is difficult, if not impossible. The ability of Sedum sediforme (Rupestria group) to germinate, grow, and establish good ground cover under harsh environmental conditions induced us to assess its effectiveness as surface cover on an acid soil taken from mountain cuts (non-agricultural field) in Yamaguchi prefecture, Japan. This soil is widely used for road embankments in this prefecture. Two rainfall intensities, 30 and 60 mm h(-1), were tested for 2 h and 1 h, respectively, on sedum grown in soil plots measuring 50 x 30 x 5 cm at three levels of vegetation cover: bare soil, 25% cover, and 75% cover. Under both simulated rainfall intensities, the sediment concentration, total soil loss, and total splashed soil decreased significantly with increasing vegetation cover. The dissipation of the raindrop impact energy by sedum cover was among the main factors contributing to the improvement of aggregate size distribution of the sediment and the total splashed soil and consequently a decrease in the seal formation on the soil surface. Compared with the bare soil, cumulative soil loss decreased by 77% and 73% under 30 and 60 mm h-1 rainfall intensities, respectively. The total splashed soil under sedum cover decreased by 30% as compared to that from the bare soil. The mean weight diameter of the surface soil aggregate increased significantly with increasing sedum cover. This is attributed to its ability to effectively protect the soil surface, thereby reducing soil aggregate breakdown and detachment, and consequently soil erosion.