HAN Lei, ZHAO Zilin, YANG Meili, LIU Zhao, ZHAO Yonghua
Research progress and prospects of gully shoulder line in the Loess Plateau
[Background] The gully shoulder line is the topographic structure line that can best reflect the morphological characteristics of loess landform. The shape, level, and spatial distribution of the gully shoulder line show the regional differences of loess geomorphology and is also an important basis for measuring gully erosion and landform evolution. The research of the gully shoulder line has gradually matured and has widely used. This paper systematically summarizes the current research results and scientific theoretical progress of the gully shoulder line, deeply ponders over the current research status, aiming to explore future research emphases and promote the subsequent research. [Methods] In this study, using “gully shoulder line” and “positive and negative terrain” as the keywords, relevant references were selected from CNKI, Web of Science core database and other domestic and foreign databases. Starting from the definition, this paper reviewed and summarized the conceptual model and extraction method of the gully shoulder line, and used VOSviewer software to analyze it, so as to clearly grasp the research hotspots and application directions of gully shoulder line. [Results]1) The gully shoulder line can reflect the internal evolution process of loess landforms. At present, the cognition of the gully shoulder line is relatively perfect, but its classification system is shortage. 2) There are currently 4 commonly used extraction methods: Image hand-painted method, geomorphological morphology method, image segmentation, and point cloud data method, but the scope of application is not wide and the extraction accuracy is different, the traditional image hand drawing method has the highest accuracy, but it needs a lot of manpower and material resources. Compared with the traditional extraction method, the method based on geomorphic morphology is of higher efficiency, but the effect on extraction accuracy and continuity is poor. The method based on image segmentation is better in accuracy and extraction efficiency, but the algorithm of model method is more complex. The accuracy of point cloud data extraction method is second only to the traditional method. It can reflect the rich detailed information of the gully shoulder line, but it needs strong computer carrying capacity. 3) The application research of the gully shoulder line is relatively simple, and the wide range application is less. The most widely used research is based on the loess landform, followed by the research on soil erosion of the gully, while the research on land use and vegetation cover is less. [Conclusions] The study proposes that the future research on the gully shoulder line should focus on the following aspects: High-precision automatic extraction, global efficiency and local fidelity of the extraction algorithm of the gully shoulder line, the coupling relationship between the gully shoulder line and the gully of the Loess Plateau, providing theoretical reference and new thoughts for researchers.
ZHANG Dengxiao, JIE Hongbin, ZHANG Wenjing, GAO Ya, RAO Wei, LI Donghao, WANG Daichang
Effect of biochar amendment on soil water retention and crop drought resistance:A review
[Background] With the aggravation of global climate change, drought stress has become one of the main limiting factors affecting agricultural production. Reports showed that most crop yield reduction was related to drought, which would result in food shortages especially in arid and semi-arid areas. Therefore, it is critical to improve the drought resistance of crops, and the increase of soil water holding capacity may ensure agricultural production and food security. Biochar soil amendment shows the benefit in promoting crop growth and improving soil structure and fertilizer retaining, and have the function of increasing soil water holding capacity and alleviating crop drought stress. [Methods] We reviewed the literatures related to the effect of biochar amendment on soil water retention and on crop drought resistance ability. We conducted literature search via Web of Science, Wiley-Blackwell and CNKI, using the keywords of “biochar” “soil water” and “drought stress”. We discussed the effect of biochar soil amendment on soil water retention and crop resistance for drought stress, and the potential mechanisms, and gave a brief overview of the future research direction. [Results] Drought stress is the main environmental stress factor affecting agricultural production, which seriously affects crop growth, especially the continuous severe drought may cause the disorder of crop metabolism and even lead to crop death. Under drought stress, crops may adjust biomass allocation, especially promoting root growth to get more water, and crops may adapt to drought stress through a series of physiological and biochemical reactions. Researches demonstrated that biochar improved the drought resistance of crops, including mechanisms of improvement of root architecture, and increased the secretion of root exudate, increased the activity of soil microbe. And biochar may adjust crop osmotic potential and increase the water use efficiency of crops. In addition, biochar soil amendment may increase soil water holding capacity, and the key mechanisms including the large numbers of hydrophilic functional group of biochar, the improvement of soil porosity especially the decrease of soil bulk density increased the field water capacity. Due to the variability of biochar properties and soil conditions, it leads to the variability effect of biochar soil amendment on soil water retention and crop resistance for drought stress, and the mechanisms had insufficient understanding. [Conclusions] It is certainly that biochar soil amendment demonstrates the potential to increase soil water retention and increase the drought resistance of crops, and shows a long-term lasting effect. While the mechanisms of biochar on soil water holding capacity and on crop physiological response in different types and textures of soils, and it is urgent to identify the key influencing factors under different. Field experiments are necessary to explore the suitable biochar application method for different soil conditions, and determine the persistence effect, and develop the biochar-based water-retaining products.