Soil splash erosion:An overlooked issue for sustainable rubber plantation in the tropical region of China

Soil erosion by water is known to be a major driver of land degradation.Splash erosion is the initial stage of water erosion and directly contributes to the detachment of soil particles on sloping land.Splash erosion may be exacerbated or mitigated by ongoing land use/cover change.To estimate the effects of various land use and management systems on splash erosion in the humid tropics,we measured the actual splash erosion under natural rainfall conditions in a tropical rainforest(TR),rubber monoculture(RM),and four rubber agroforestry ecosystems in Xishuangbanna,Southwestern China.The average cumulative splash mass in the RM was 48.7 times higher compared to that in the TR,indicating that the replacement of TR by RM results in severe splash erosion.In the rubber agroforestry systems,the throughfall kinetic energy and splash mass were 34-76%and 86-97%lower,respectively,than that in the RM,indicating that intercropping crops with rubber trees can effectively alleviate erosive power of throughfall and thus splash erosion.Under all land use regimes,in the plots where the litter layer was removed,splash erosion was significantly(2.0-12.1 times)higher and more spatially heterogeneous than in those with litter cover.This highlighted the key role of the forest litter layer in protecting the soil from raindrop detachment.In the study area,the actual splash erosion was strongly correlated with the conditions of precipitation(amount and intensity(I10)of rainfall)and the vegetation structure(especially the crown base height,leaf area index,and canopy cover),but weakly correlated with the soil properties.Given the importance of near-ground intercrops(height<5 m)for improving the vegetation structure,surface cover,and soil conditions,the intercropping of Camellia sinensis and Theobroma cacao with rubber trees is a promising approach for controlling splash erosion and also has benefits on the sus-tainable development of rubber plantation.

Specific ion effects on soil aggregate stability and rainfall splash erosion

Soil interparticle forces can pose important effects on soil aggregate stability and rainfall splash erosion.Meanwhile,these interparticle forces are strongly influenced by specific ion effects.In this study,we applied three monovalent cations(Li^(+),Na^(+),and K^(+))with various concentrations to investigate the influence of specific ion effects on aggregate stability and splash erosion via pipette and rainfall simulation methods.The specific ion effects on soil interparticle forces were quantitatively evaluated by introducing cationic non-classical polarization.The results showed that aggregate stability and splash erosion had strong ion specificity.Aggregate breaking strength and splash erosion rate at the same salt concentration followed the sequence as Li^(+)>Na^(+)>K^(+).With decreasing salt concentration,the difference in aggregate breaking strength or splash erosion rate between different cation systems increased initially(1–10^(-2)mol L^(–1))and later was nearly invariable(10^(–2)–10^(–4)mol L^(–1)).The experimental results were well quantitatively explained by soil interparticle forces considering cationic non-classical polarization.Furthermore,both aggregate breaking strength and splash erosion rate of three cations revealed a strong positive linear relation with net force subjected to cationic non-classical polarization(R^(2)=0.81,R^(2)=0.81).These results demonstrated that different non-classical polarization of cations resulted in different soil interparticle forces,and thus led to differences in aggregate stability and splash erosion.Our study provides valuable information to deeply understand the mechanisms of rainfall splash erosion.

Landscape Effects on Decomposition

The average annual rainfall was close to the average for the Jornada Experimental Range basin (225 mm∙y−1). Decomposition of leaf litter bags on the soil surface was a function of the rainfall at the site and of soil texture. Sites with the highest splash erosion and infiltration (highest sand content) had the highest decomposition rates. There was no evidence that run-off, run-on processes had an effect on the decomposition of surface litter. Root decomposition was only different at one of the tarbush sites (p > 0.001) and that difference was primarily due to soil texture and spatial distribution of rainfall. High concentration of the clay-silt fraction resulted in differences in mass loss of surface litter at grassland, dry-lakes, and tarbush sites. One site at each of these was different from the other two sites because they are between 8 and 20 km from the other two sites.

黄土溅蚀过程中土壤有效粒径分布和富集/损耗的临界粒径

Effective soil particle size composition can more realistically reflect the particle size sorting process of erosion.To reveal the individual contributions of rainfall intensity and slope to splash erosion,and to distinguish the enrichment ratio of each size and the critical size in splash,loessial soil collected on the Loess Plateau in May 2019 was tested under different rainfall intensities(60,84,108,132,156 mm h^(-1))and slopes(0°,5°,10°,15°,20°).The results demonstrated that 99%of splash mass was concentrated in 0–0.4 m.Rainfall intensity was the major factor for splash according to the raindrop generation mode by rainfall simulator nozzles.The contributions of rainfall intensity to splash erosion were 82.72%and 93.24%,respectively in upslope and downslope direction.The mass percentages of effective clay and effective silt were positively correlated with rainfall intensity,while the mass percentages of effective very fine sand and effective fine sand were negatively correlated with rainfall intensity.Opposite to effective very fine sand,the mass percentages of effective clay significantly decreased with increasing distance.Rainfall intensity had significant effects on enrichment ratios,positively for effective clay and effective silt and negatively for effective very fine sand and effective fine sand.The critical effective particle size in splash for loessial soil was 50μm.