The research results of a large number of high-quality professional research teams have also made great progress in land reclamation research in China in the past 20 years. Hu (1996) believes that the land reclamation model has a guiding and exemplary role and has strong technical characteristics. It should be named according to the task of land reclamation, and the land reclamation mode should be divided into two categories: land management mode and reclamation technology mode. The specific system structure is shown in figure 1- 1.
Figure 1- 1 Block diagram of land reclamation mode classification (according to Hu 1996)
Land management modes include resource destruction management mode and reclamation process management mode.
(1) Broken resource management mode. Including damaged or degraded land resources management mode and ecological environment management mode, refers to the effective management mode of damaged or degraded land and environment by using the land and environmental resources management methods in land science and environmental science, that is, resource management before and after reclamation. Land resources in coal mining subsidence areas can adopt "temporary land use mode", "land for land mode" and "fund-raising reclamation mode"
(2) Management mode of reclamation process. It includes the macro management mode of reclamation work and the whole process management mode of a single reclamation project, and refers to the comprehensive and systematic reclamation management mode of the land or environmental administrative department from both macro and single projects. Macro management is to standardize and guide the reclamation work as a whole, while individual project management focuses more on project implementation management and quality control.
Reclamation technology modes include engineering reclamation mode, biological reclamation mode and ecological reclamation mode.
(1) Engineering reclamation mode refers to various restoration projects (mainly civil engineering) for damaged or degraded land and environment, including "deep excavation and shallow cushion", "filling reclamation" and "stripping mining and reclamation integrated process".
(2) Biological reclamation mode refers to various measures to quickly and efficiently restore biological activity on damaged, degraded or reclaimed land. It mainly refers to various biological and agricultural technologies (including agricultural, forestry, animal husbandry, sideline and fishery production technologies), such as various rapid vegetation technologies, soil improvement technologies, crop production technologies and biological treatment technologies of polluted land.
(3) Ecological reclamation mode refers to the floorboard of various measures to restore the ecosystem. Ecology, especially ecological engineering, is often used to restore and rebuild the damaged or degraded ecological environment.
In the research of land reclamation mode, engineering reclamation mode has been studied to a certain extent, but the research on biological reclamation and ecological reclamation is not deep enough, and the terms and concepts are not clear enough, which is often confused. Biology is a science that studies biology, mainly studying the structure, function, development, distribution and life process of biological organisms; Ecology is a science that studies the relationship between organisms and their environment, and pays more attention to the relationship between organisms and their environment. Therefore, the difference between biological reclamation and ecological reclamation is well understood. Biological reclamation focuses on biological recovery, while ecological reclamation focuses on the recovery and reconstruction of system environment. However, it is often inseparable from certain engineering reclamation and biological reclamation measures, so these three types of reclamation technology models are cross-compatible in some cases. With people's increasing attention to environmental problems, ecological reclamation will become more and more important.
Sun (2004) put forward three standards of land reclamation: ① Return to the standard of land use before destruction. In the process of land requisition before construction, the degree of land use before destruction is calculated by using the topographic map measured by project design. After the land is destroyed, the land reclamation work is still based on the degree of land use before the destruction, so that the land suitability, productivity and production potential can be restored to the level before the construction. ② Transforming cultivated land under new environmental conditions. Because the land in different areas has obvious regional differences, it is necessary to analyze the land with multiple suitability in land reclamation. Generally speaking, the land before destruction is more suitable, and after non-agricultural construction, the more suitable land has changed. Land reclamation planning should be based on the premise of the highest economic benefits. For example, a mining area is suitable for planting trees, planting grass and breeding. In the absence of water conservancy, it can be restored to dry land and planted with cash crops or Chinese herbal medicines; Irrigation can be carried out under water conservancy conditions, and dry land can be turned into paddy fields. In the specific decision-making, according to the local social and economic conditions, the farmland with the highest economic benefit is drawn up as the land reclamation standard. (3) enclosure, let nature take its course. In natural grassland areas, soil vegetation has its natural development law, and it is the most wise decision to conform to nature. Before the destruction, the land often has more suitability, and after the destruction, it decreases. It costs a lot to improve the utilization level of a certain type of land, so the regional differences of reclamation objects should be considered when formulating specific standards. When planning reclamation, the reclamation fee will be moved to the land that is easy to develop, and the destroyed land will be enclosed as wasteland. In the case of developing modern animal husbandry, it can also be planned as a modern pasture. In a word, vegetation reconstruction is the premise to test the success of reclamation, and soil reconstruction is the basis to achieve this goal.
Li Shuhui et al. (2008) studied the influence of topography on land reclamation in mining areas, and put forward that topography, geomorphological characteristics, ground slope, geology, soil and the relative distance from the city determine the suitability of land use, and topography directly determines the distribution and change characteristics of other factors. According to the topography, the land reclamation in the mining area needs slope cutting, soil covering and vegetation restoration. According to the topography, geomorphology and destruction characteristics of the mining area, the control measures of reclamation projects can be determined. The leveling parameters of different landform sites determine the excavation and filling amount in the project implementation stage.
Fan Wenhua (20 1 1) studied the effects of different reclamation years and reclaimed vegetation on soil fertility after reclamation. He believes that the total number of microorganisms increases with the increase of reclamation years; The selection of reclaimed vegetation not only affects the soil and water conservation and soil fertility in the reclaimed area, but also has a great influence on the number of soil microorganisms. The number of microorganisms is not only related to soil moisture and temperature, but also closely related to different land use patterns, and soil fertility is positively correlated with the number of microorganisms.
At present, land reclamation mainly solves the contradiction between eating and construction land. Land reclamation standard is not only a scientific problem in land reclamation, but also a problem in production practice. Although there is still a certain gap between China's land reclamation technology and foreign countries, "dredging", "digging deep and shallow" and landfill with mine solid waste are still the most important engineering methods in China's land reclamation. However, after decades of continuous exploration, it has moved from single reclamation to multi-technology reclamation; From unorganized sporadic spontaneous reclamation to organized conscious planned reclamation; From the traditional simple engineering reclamation, biological reclamation and ecological restoration to the current comprehensive reclamation, advanced reclamation and dynamic reclamation; Great changes from no evidence to evidence to continuous improvement. Whether it is agricultural land reclamation, construction land reclamation or industrial and mining wasteland reclamation, great progress has been made in technology and means. In recent years, more and more attention has been paid to land reclamation damaged by natural disasters.