Shuqin He

Fractal dimensions of soil structure and soil anti- erodibility under different land use patterns

Soil structure fractal features and soil anti-erodibility were studied by the combinative means of field investigation and laboratory analysis under different land use patterns. The results showed that fractal dimensions of mechanical composition were greater than that of micro-aggregates, and fractal dimensions of water-stable aggregates were greater than that of dry aggregates. Five land use patterns had a high proportion of aggregates measuring >2 mm after dry sieving and <0.5 mm after wet sieving. Soil dispersion was mainly reflected in aggregates that measure between 0.05 to 0.001 mm. Soil antierodibility in the Chinese fir plantation and Eucalyptus plantation were higher than those of the tea plantation, loquat orchard and abandoned farmland. Stability of water-stable aggregate was highest in the Chinese fir plantation, followed by the eucalyptus and tea plantations, and it was lowest in the loquat orchards and abandoned farmland. With the exception of coarse dust, changes in the composition of other soil particles of the same size varied according to different land use patterns. Changes in the status of aggregates and the degree of aggregation were inversely related to changes in the dispersive coefficient. Water stability indices and contents of soil organic matter in the Chinese fir plantation, the eucalyptus plantation and loquat orchard were higher than those of the abandoned farmland and tea plantation. From the results, it can be concluded that land use patterns of the Chinese fir and eucalyptus plantations are a reasonable manner for the increases in soil anti-erodibility and improvements in soil structure in the study area.

Dynamics of soil organic carbon mineralization in tea plantations converted from farmland at Western Sichuan, China

Climate warming and land use change are some of the drivers affecting soil organic carbon (SOC) dynamics. The Grain for Green Project, local natural resources, and geographical conditions have resulted in farmland conversion into tea plantations in the hilly region of Western Sichuan. However, the effect of such land conversion on SOC mineralization remains unknown. In order to understand the temperature sensitivity of SOC decomposition in tea plantations converted from farmland, this study considered the different years (i.e., 2–3, 9–10, and 16–17 years) of tea plantations converted from farmland as the study site, and soil was incubated for 28 days at 15°C, 25°C, and 35°C to measure the soil respiration rate, amount, and temperature coefficient (Q10). Temperature and land use type interactively affected the SOC mineralization rate, and the cumulative amount of SOC mineralization in all the plots was the largest at 35°C. SOC mineralization was greater and more sensitive to temperature changes in the farmland than in the tea plantations. Compared with the control, tea plantation soils showed lower SOC mineralization rate and cumulative mineralization amount. The 16–17-year-old tea plantation with a low SOC mineralization amount and high SOC content revealed the benefits of carbon sequestration enhancement obtained by converting farmland into tea plantations. The first-order kinetic equation described SOC mineralization dynamics well. Farmland conversion into tea plantations appeared to reduce the potentially mineralizable carbon pool, and the age of tea plantations also had an effect on the SOC mineralization and sequestration. The relatively weak SOC mineralization temperature sensitivity of the tea plantation soils suggested that the SOC pool of the tea plantation soils was less vulnerable to warming than that of the control soils.

Changes in micro-relief during different water erosive stages of purple soil under simulated rainfall

This study investigated the variation characteristics of micro-topography during successive erosive stages of water erosion: splash erosion (SpE), sheet erosion (ShE), and rill erosion (RE). Micro-topography was quantified using surface elevation change, soil roughness (SR) and multifractal model. Results showed that the area of soil surface elevation decay increased gradually with the development of water erosion. With rainfall, the combined effects of the detachment by raindrop impact and the transport of runoff decreased SR, whereas rill erosion contributed to increase SR. With the increase in slope gradient, soil erosion area gradually decreased at the splash erosion stage. By contrast, soil erosion area initially decreased and then increased at the sheet and rill erosion stages. The width of the Dq spectra (ΔD) values increased at the splash erosion stage and then decreased at the sheet and rill erosion stages on the 10° slope, opposite to that on the 15° slope. The ΔD values decreased with the evolution of water erosive stages on the 20° slope. The slope had an enhancing effect on the evolution of water erosion. In this study, we clarified the essence of micro-topography and laid a theoretical foundation for further understanding diverse hydrological processes.

Assessing the impacts of microtopography on soil erosion under simulated rainfall, using a multifractal approach

Hydrological Processes. 2018;32:2543–2556. Abstract This study aimed to investigate the changing characteristics of microrelief of purple soil and its erosional response during successive stages of water erosion, including splash erosion, sheet erosion, and rill erosion. Methods employed included a rainfall simulator and the use of a laser scanner to generate a digital elevation model. Three artificial tillage practices, including conventional tillage (CT), artificial digging (AD), and ridge tillage (RT), were used to simulate different microrelief patterns. Eighteen artificial rainfall experiments were conducted using three 2 × 1 m boxes with a rainfall intensity of 1.5 mm min on a 15° slope. The results showed that the soil roughness (SR) index values for the tillage slopes were RT > AD > CT. The combined effects of detachment by raindrop impact and transport by run‐off decreased the SR index, whereas rill erosion increased the SR index during rainfall event. Microtopography and drainage networks have strong multifractal behaviours. The multifractal parameters of microtopography reflect the overall characteristics as well as the characteristics of the local soil surface. Within a certain range of threshold values, higher microrelief causes less soil erosion. However, when the parameters of spatial heterogeneity of microtopography exceed the threshold values, a higher degree of microrelief can increase soil erosion. These results help clarify the effect of microtopography on soil erosion and provide a theoretical foundation to guide future tillage practices on sloping farmland of purple soil.