Study On The Spatial Allocation About Topsoil Stripping And Reusing In The Hilly Region

Topsoil is the essence of farmland and a non-renewable resource for agricultural production. In recent years, with the rapid social and economic development in China, a large number of fertile farmlands are occupied by the non-agricultural construction, and the fertile topsoil of these farmlands have not been stripped and reused. This waste phenomenon is in sharp contrast with the request of farmland protection in China. Now the quantity of farmland keeps decreasing, but what makes things worse is that the quality of the supplementary farmland is not as good as the farmland occupied. Presently, the Chinese government has realized the importance of topsoil stripping and reusing, and issued the policy to carry out the job in nationwide. However, so far, there has been little research concentrated on optimizing spatial allocation of topsoil, leading to a lack of systematic theory and research methods in this area. The work of topsoil stripping and reusing was extremely difficult and demands high input especially in hilly areas, due to the small amount of farmland area, the steep slope and the scattered distribution. Henceforth, the problem about how to choose the suitable topsoil to strip cost-efficiently is a scientific question which has to be solved urgently.Firstly, this thesis summarizes the main research progress at home and abroad on the relevant aspects of the space allocation about topsoil stripping and reusing, and defines the connotation about space allocation. Then, it elaborates the principles, content and process of spatial allocation, and analyzes the structure of the spatial allocation system, and studies its mechanism from the motivations, conditions, influencing factors and effecting process, and built its mathematical theory model. Finally, it proposes four models to evaluate the topsoil stripping suitability, the priority to cover topsoil, the stripping potential and the total demand of soil-covering, and presents the spatial allocating method based on the supply-demand balance, and takes the Guangze County in the hilly area of Fujian province as a case study to verify the scientificalness and practicability about the presented models and methods. The main conclusions of the study are as follows:Ⅰ、 Utilizing Analytic Hierarchy Process (AHP) method, delving from the three aspects of earthwork, unit implementation cost and soil quality, this paper chose the five indicators as earthwork, distance to the lanes, topography, soil texture and organic matter to establish a synthetic evaluation index system for the topsoil-stripping suitability in hilly regions, and then evaluated the study area to find out the plots which was suitable for topsoil stripping. The results showed that, the level I of suitable stripping region was 105.06 hm2 accounting for 60.2% in the total stripping region. The level I had the priority to be stripped because there was a fertile soil, a good soil texture, a deep topsoil thickness, a gentle slope, a large scale in the region, and it was close to the road, and had a lower unit cost and a large benefit to strip and reuse the topsoil. The level II and III of suitable stripping region was 28.44 hm2 and 35.73 hm2, accounting for 16.3% and 20.5% in the total stripping region. In the above two regions, there was medium soil quality, good texture and medium topsoil thickness, but the plots scale was smaller, and the distance to the lanes was more far away than the plots in Level I. It had a moderate unit cost and benefit to strip and reuse the topsoil in the above two regions. The level IV region area was 5.26 hm2, accounting for 3% in the total stripping region. The region was far from the road, and had the smallest size. The unit stripping cost was higher and the benefit was lower. Based on the cost-benefit principle, the level Ⅰ、Ⅱ and Ⅲ region can be identified as the suitable stripping plots, whose total area was 169.23 hm2 and earth volume to strip was 300,500 m3.2、 Utilizing AHP method and examining from the four aspects of soil configuration, traffic convenient conditions, plots site conditions and plots physicochcmical conditions, this thesis then chose topsoil thickness, soil thickness, distance to the lanes, topography, plots sizes, irrigation and drainage conditions, soil texture and organic matter to establish a synthetic evaluation index system for the priority of farmland cultivated horizon soil-covering demand in hilly regions. It then utilized the established model to evaluate and classify the farmland which needed covering cultivated horizon soil. The results were as follows:The 5.2% of the whole region was grade Ⅰ region which had the most priority region of soil-covered demand. 54% of the grade Ⅰ region was the planning and development farmland which had low quality and the other was the low-yield paddy field which had good basic conditions but low quality. In the region, covering the cultivated horizon soil would have the lower cost and higher comprehensive benefit. The priority region in the grade Ⅱ approximately accounted for 49.1%. which was inferior to the grade Ⅰ, and was the alternative region to cover the cultivated horizon soil. The priority region in the grade Ⅲ and Ⅳ level accounted for 45.7%, where it was unnecessary to arrange soil-covering projects. The evaluation results were good, consistent with the reality in Guangze County, which would provide a scientific basis for the special plan formulation of the cultivated horizon soil stripping and re-utilization and the practice of cultivated land protection.3、 According to the above base evaluation results, this paper established a thinking method to allocate the stripping topsoil in the space based on the supply-demand balance circle to do the research of space allocation in the study area. There were 33 supply-demand balance circles identified in the study area, with the total stripped area of 172.7 hm2, the total soil-covering area of 547.13 hm2, the total earthwork of 306000 m3, and the average transport distance of 4.65 km, which is lower than the default boundary value. And 80% of the township in the study area could realize a balance of supply-demand by itself. The result scheme had a lower unit cost, better comprehensive benefits and stronger operability. which would provide a scientific basis for the study area to carry out the special planning and practice about topsoil stripping and reusing. The space allocation method proposed in this paper had a better generalization.4、 Based on the space allocation schemes, utilizing AHP method from farmland protection, promoting social stability, increasing the income of farmers and improving ecological environment, this paper chose 13 indicators such as the ratio of stripping, the area of added farmland, the area of amelioration, increased level of soil quality, productive capacity increasing, the straight-line distance of the road, slope, soil quality and organic content and so on to establish the expected benefit evaluation model about the allocation schemes. Then this paper proposed countermeasures and suggestion for the result scheme’s implementation from the legal policy matching, the management system establishing, the implementation mechanism innovation and the technology specification formulate. The results were as follows:the stripped area accounted for 97%, the area of added farmlands was 57.79 hm2 and the existing low yield cropland improvement area was 501.25 hm2. With the scheme, the average of soil quality was expected to increase 1-2 level and it could increase 670,000 kg of grain productive capacity every year and reduce the number of abandoned land up to an area of 100 hm2, which would benefit 2,600 people and directly increased 700RMB income every year per person, and the petition rate for farmland lose would be reduced by 17% and also saved the cost a lot. Therefore, the result scheme had the extremely remarkable comprehensive effects to protect farmland, improve farmland quality, increase grain output, promote social stability and raise the farmer’s income.Through this research, this thesis had built the theoretical framework, models and methods about the topsoil spatial allocation, which made up for the gap in previous research and laid a solid scientific foundation for the work of topsoil stripping and reusing.