ZHAO Bohua, WANG Xiuru, YAN Shiyu, ZHANG Yufei, ZHANG Ting
Application of object-oriented classification method in the extraction of soil and water conservation measures
[Background] The combination of UAV remote sensing images and object-oriented classification methods is more and more widely used in soil and water conservation monitoring. This method can improve the efficiency and accuracy of the calculation after classification of the ground features in the project area. However, different object-oriented classification methods have different extraction accuracy for different ground features. Based on the water and soil conservation monitoring project of the Snowmobile Sled Center in the Yanqing Competition Area of the Beijing 2022 Winter Olympics, this study analyzed the accuracy difference of measure extraction in two areas within the monitoring range of soil and water conservation.[Methods] Based on UAV remote sensing image data and object-oriented classification methods, 5 classification methods, including membership function, the nearest neighbor classification, support vector machine (SVM), classification and regression tree (Cart) and random forest (RF) were adapted to extract the parameters of soil and water conservation measures. Three indicators, namely overall accuracy, Kappa coefficient, and producer accuracy (PA) were adapted to quantitatively evaluate the classification results by the five classification methods. Among them, the overall accuracy and Kappa coefficient were used to compare the overall classification accuracy, and PA was used to evaluate the classification accuracy of the specific land class.[Results] 1) The Kappa coefficients by 5 classification methods were all above 0.69, indicating that the classification effect was good. Among them, the overall classification accuracy of the two sections was better by SVM classification method. 2) The retaining wall was applicable to the nearest neighbor classification method with an accuracy of 71.42%. 3) The classification accuracy of SVM for vegetation and temporary coverage measures (bare soil) in the first area was better, and the PA was 93.25% and 80.0%. The better classification accuracy of weaving bags of surface soil and drainage ditch was also SVM classification method, the classification accuracy was 81.51% and 70.34%. The accuracy of the nearest neighbor classification method for the temporary coverage measures (bare soil) in the second area, temporary coverage measures (plants) and frame models of slope protection was better, with the accuracy of 73.94%, 76.23% and 66.37%, respectively.[Conculsions] The data comparison shows that SVM method has the best classification effect, and the results are higher than those by the other four classification methods. Therefore, the SVM method is more suitable for the extraction of measures in the soil and water conservation monitoring of UAV remote sensing images in this study. In addition, the Kappa coefficients by the 5 classification methods are all above 0.69, and all 5 classification methods have achieved good classification results. On the whole, the combination of UAV remote sensing image and object-oriented classification methods has a broad application prospect in soil and water conservation monitoring.
GUO Huan, CHEN Long, TANG Lixia, PAN Lu, RUAN Shihang
Experimental study on the pull-out friction of two kinds of slope protection shrubs in karst area
[Background] The root system is the organ that directly contacts with the soil and has the function of supporting the plant and fixing the soil. In karst area, the soil layer is shallow, the soil erosion is serious, and the ecological environment is poor. With the development of economy, climate change, debris flow, landslides and other natural disasters occur frequently, the stability of slope soil has aroused widespread concern.[Methods] In order to study the mechanical characteristics of slope greening shrubs in karst area,taking 4-year-old Cassia bicapsularis and Indigofera amblyantha as the research objects, the root diameters were divided into four grades. Under the loading rate of 100 mm/min, the friction test between the root and soil was carried out by using a single root vertical pull-out method. The effects of root length, root surface interaction and root length on the soil were investigated. The soil bulk density and water content were 1.43 g/cm3 and 17.15%.[Results] 1) The root bark surface of C. bicapsularis had dense longitudinal cracks and formed notches, while the root bark surface of I. amblyantha was scaly. The root-soil friction coefficient of C. bicapsularis was higher than that of I. amblyantha, the root system of C. bicapsularis had better ability of strengthening soil strength and resisting deformation and failure than that of I. amblyantha. 2) In the process of friction between single drawing and soil interface, the characteristic curve of force displacement relationship experienced three stages:viscous friction stage, debonding friction stage and bonding friction stage.3) The friction force between the roots and soil of C. bicapsularis and I. amblyantha increased with the increase of burial depth. The longer the extension of vegetation roots in soil, the greater the role of force. 4) The root diameter of C. bicapsularis and I. amblyantha showed a significant positive correlation with their maximum friction, while with the change of diameter, there was no significant difference in the friction per unit area.[Conculsions] That is to say, the force released by a single root of C. bicapsularis in the pull-out friction test was greater than that of the latter, and it was better to enhance the soil strength and resist the deformation and failure. Therefore, it is suggested that C. bicapsularis should be used as vegetation slope protection. The results provide a theoretical basis for the selection of greening tree species, soil consolidation mechanism and prevention of shallow landslide in the study area.
WANG Weiwei, ZHANG Lixin, LIANG Zhishui, ZHAO Yanbing, ZHANG Jishu, WANG Zhong, YUAN Qin, YE Lina
Physical and nutrient characteristics of sand soil improved by Pisha sandstone via field experiment
[Background] Pisha sandstone is a kind of interbedding generated in Mesozoic rock that is mainly distributed in Shanxi, Shaanxi and Inner Mongolia. Due to its special properties of collapsing easily encountering water, it is eroded seriously. Additionally, Aeolian sandy soil and Pisha sandstone are complementary in structure, and the both can be transformed into useful composite soil and be effectively utilized for planting through effective combination. However, the related research on improvement of soil structure and nutrients is mainly carried out in laboratory conditions and the systematic research of field test is rare, especially in the Kubuqi Desert.[Methods] The research was conducted by the field test method (each is 6 667 m2) to study the improving effect by adding different proportions of Pisha sandstone on the physical structure and nutrient characteristics of the Aeolian sand soil from the hinterland of Kubuqi Desert in the northwest of Ordos Plateau. In the experimental test field, the different volume ratios (0%, 30%, 50%, 80% and 100%) of Pisha sandstone were added and mixed evenly. Additionally, the Haloxylon ammodendron and Glycyrrhiza uralensis were inter-planted. One month later, the evaluation indexes include mainly soil capillary porosity, field water holding capacity, organic matter, available nitrogen and available phosphorus were tested.[Results] With the increase of the adding proportion of Pisha sandstone, the contents of clay, silt, capillary porosity, field water-holding capacity, soil aggregate, organic matter, available nitrogen and available phosphorus increase gradually and the sandy soil is improved significantly. Under the condition of the same proportion of Pisha sandstone, with the increasing soil depth (0-30 cm) of the improved soil, the contents of clay, silt, soil organic matter, available nitrogen and available phosphorus decrease, but the vertical variation characteristics of soil bulk density, capillary porosity and field water-holding capacity are small. And the variation is smaller with the increase of mixing proportion, showing the phenomenon of obvious surface aggregation. According to multiple indexes, the mixing ratio of 50% has the best improvement effect, which can be used as the boundary value for improving the Aeolian sand soil. Additionally, the structure of soil particle and aggregate is positively correlated with soil capillary porosity, field water-holding capacity, organic matter, available nitrogen and available phosphorus content, which shows that the particle size of Pisha sandstone and Aeolian sand soil is complementary.[Conculsions] This is the first time to study the composite soil by the field test in Kubuqi Desert. The physical and nutrient characteristics of sand soil are improved by Pisha sandstone. It can provide a reference for the large-scale popularization and application of Pisha sandstone to improve the Aeolian sandy soil in Kubuqi Desert and promote the desertification control.
GAO Guanglei, YIN Xiaolin, DING Guodong, ZHAO Yuanyuan, SUN Guili, WANG Long
Soil erodibility for wind erosion: A critical review
[Background] Wind erodibility, which symbolizes the resistance of soil to the erosion by wind, is an important foundation for a variety of erosion models. It is well acknowledged that studies on it could effectively help deepen the understanding about erosion prevention and desertification combating. Globally plenty of empirical models have been put forward to evaluate soil wind erodibility, which have doubtlessly provided great conveniences. However, there are still some critical issues remaining unclear with respect to its mechanical properties, quantitative evaluation, dynamic characteristics, etc. In order to systematically discuss the limitations above, here we summarized relevant results and conclusions to knit the framework, aiming at promoting the developments in exploring the mechanisms of wind erodibility.[Methods] All selected references were from CNKI, ScienceDirect, Springer and other domestic and international databases with the keywords of "wind erosion" and "wind erodibility". Based on the high-frequency vocabulary of references, combined with the focus of current research, this paper mainly reviewed the research progress of wind erodibility from three aspects:Concept and connotation, quantitative evaluation, and dynamic characteristics.[Results] 1) Essence and connotation of wind erodibility. Wind erodibility now is generally defined as the sensitivity of soil to wind erosion, which is insufficiently precise to describe its essence. And from the perspective of erosion dynamics, mechanics property of wind erodibility is of great importance. Thus, it is highly recommended that mechanics property should be considered to accurately depict the resistant capacity of soil to wind erosion, so that providing the guide for its quantitative evaluation further. 2) Key indices and quantitative assessment. Wind erodibility is dominated by soil intrinsic features. Thus, many different soil indices including soil organic matter (SOM), calcium carbonate (CaCO3), particle size distribution (PSD), etc are proposed to evaluate wind erodibility quantitatively. However, the assembly of these indices tend to be intricate, in which each one of them could only represent a partial appraisal system, but not an integrated one. Therefore, it is an urgent and imperative task to figure out how to distinguish and combine the function of different soil indices, to establish a comprehensive equation in assessing wind erodibility, which could be more reasonable, convenient, and ubiquitous. 3) Modeling in consideration of dynamic characteristics. Wind erodibility could vary followed the change of climate and anthropogenic activities. However, the influencing factors, driving mechanism and key processes of wind erodibility are still unclear, and the dynamic characteristics of wind erodibility are not included in the basic framework of the model. Therefore, the quantitative model of wind erodibility should be modified to improve the calculation accuracy of wind erodibility and wind erosion.[Conclusions] This improved information will be essential to make a better understanding on technical know-how of the limitations and disadvantages in wind erodibility, providing new references for relative researchers and guiding consecutive developments and progresses.
