Characteristics of Surface Runoff for Four Vegetation Types in Small Watershed of Nver Zhai in West Hunan, China

Characteristics of the surface runoff of four vegetation types in the small watershed of Nver Zhai, Wuling Mountain Area, West Hunan were studied. Results indicated that, from June 10, 2015 to September 10, 2016 the precipitation recorded was up to 1971.80 mm, and there occurred 83 rainfalls during the period of investigation. With the increase in the rainfall, the surface runoff gradually increased, among which the Eucommia ulmoides Oliv. plantation showed significantly high runoff. When the rainfall gradually increased to 30 mm, the surface runoff was highest for the sloping farmland. Under an intense rainfall >50 mm, there was a significant augmentation in the surface runoff of the four types of forest lands, indicating that the soil water content began to reach to saturation. Furthermore, the total runoff of the different types of vegetation, the runoff depth and the runoff coefficient were in the order of: E. ulmoides plantation > Pinus massoniana Lamb. forest > Sloping farmland > maple- Cinnamomum camphora (L.) J. Presl. mixed plantation. Additionally, under the same rainfall, there was a reduction in the runoff with an increase in the evaporation, and the total runoff of maple- C. camphora mixed plantation was the lowest. Bangladesh J. Bot. 50(3): 603-611, 2021 (September)

Development of Rill Erosion On Bare Sloping Farmland Under Natural Rainfall Conditions

Rill erosion is an important type of soil erosion and provide a basis for preventing and controlling soil loss on sloping farmland. This study was conducted in a standard runoff plot of bare soil (20 m length, 5 m width with a slope of 10 degrees) to monitored runoff and sediment processes during two continuous and two intermittent natural rainfall events, and observed the rill morphological characteristics after multiple rainfall conditions. We observed the runoff and sediment processes presented a pattern of multi-peaks for continuous rainfall events, and a pattern of single or two peaks during two intermittent rainfall events. The sediment yield rate with instantaneous rainfall intensity and runoff rate exhibited a peak lag phenomenon with 1–6 min. After multiple rainfall events, rill were identified as strip-shaped, V-shaped, and tree-branched distribution, and rills were mainly distributed in 5–20 cm width and 0–10 cm depth, and the mean rill length, width and depth increased 2.27, 0.30 and 0.16 times compared to the initial slope (R0). The side-wall collapse erosion was mostly greater than downcutting erosion in the slope section I, II and III. In conclusion, this study help to understanding the slope runoff and erosion mechanisms, and provide a scientific basis for soil erosion model on sloping farmland.

Establishment of the minimum data set for cultivated-layer quality assessment and its verification: A case study of sloping farmland in a purple hilly area, China

Sloping farmland is an important cultivated land resource and erosion source. Cultivated-layer quality directly affects the soil productivity and erosion resistance of sloping farmland. We aim to select the most effective soil property index to construct a minimum data set (MDS) and use two methods (the weighted additive cultivated-layer quality index (CLQIW) and Nemoro cultivated-layer quality index (CLQIN)) to accurately evaluate the cultivated-layer quality of sloping farmland in purple hilly areas. The total data set (TDS) of 12 soil indexes was screened by principal component analysis (PCA) and correlation analysis, and a MDS was constructed to assess the CLQIW and CLQIN. The results showed that (1) the cultivated-layer soil quality of the MDS comprises cultivated-layer thickness, soil bulk density, saturated hydraulic conductivity, sand, clay, shear strength and soil organic matter. The MDS can accurately reflect the effective soil information (RW2=0.7524, RN2=0.8059) and can replace the TDS in cultivated-layer evaluation. (2) CLQIN-MDS has a higher Ef and lower ER than CLQIW-MDS does, so CLQIN-MDS is better for evaluating the cultivated-layer quality of purple soil of sloping farmland. (3) For the two evaluation methods, the quality classifications of the two small watersheds have similar trends, with most plots in grades II~III (approximately 90%). (4) The main obstacles of the two small watersheds are poor nutrients and low soil shear strength, which can be reasonably controlled by subsoiling combined with biochar. These results can facilitate the construction of reasonable cultivated-layers and improvements in the cultivated-layer soil quality of sloping farmland.

Experimental Study of Runoff and Sediment Yield Affected by Ridge Direction and Width of Sloping Farmland

Water and soil losses from sloping farmlands potentially contribute to water eutrophication and land degradation. However, few studies explored the combined effects of ridge direction and ridge width on surface runoff and soil losses of sloping farmlands. Twenty-seven experimental plots (8 m long and 4 m wide) with nine treatments (three ridge direction: cross ridge, longitudinal ridge, and oblique ridge; and three ridge width: 40, 60, and 80 cm) were adopted under natural rainfall conditions for two years in the Luanhe River Basin of China. Results indicated that ridge direction had significant effects on runoff and sediment yield (p < 0.05). The ridge width had no significant effect on runoff and sediment yield. No significant interaction effect was found between ridge direction and width on runoff and sediment yield of the sloping farmland based on statistical analyses. Compared with cross-ridge (CR) tillage and oblique-ridge (OR) tillage, longitudinal-ridge (LR) tillage significantly decreased runoff by 78.9% and 64.9% and soil losses by 88.2 and 83.5%, respectively (p < 0.05). The effects of ridge directions on runoff and sediment yield were related to rainfall grade. When the rainfall grade reached rainstorm, the runoff yield under CR, LR, and SR had significant differences (p < 0.05). The runoff under LR and OR treatment was 5.16 and 3.3 times, respectively, of that under CR. When the rainfall level was heavy rain or rainstorm, the sediment yield under LR was significantly greater than that under CR. The sediment yield was 13.45 times of that under CR. Cross-ridge tillage with a ridge width of 40 cm is an optimally effective measure of soil and water conservation on sloping farmland in arid and semiarid regions of China.