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Severe soil compaction often occurs with heavy traffic during mining, particularly for a large number of large-scale opencast mines in the Loess Plateau. An important indicator, the soil hydraulic property can be widely used to measure the soil pore conditions of compacted soils. Biochar can also be added to improve the land quality for higher crop yields in farmland in recent years. The environmental soil amendment has presented higher ecological and economic benefits, due to the specific properties from the special porous structure of biochar, including the large surface area, high porosity, low bulk density, and high organic carbon contents. As such, the soil bulk density can be reduced to increase the water holding capacity in the coarse texture soil. However, only a few studies focused on the biochar addition in the soil improvement in the mining areas, especially the hydraulic characteristics of compacted soil. The purpose of this study is to evaluate the impact of addition rates and particle sizes of biochar on the soil hydraulic conductivity under various compaction conditions in a mining dump. The soil sample was collected from Datong City in Shanxi Province of China. The experiment was then carried out under the four particle sizes of biochar (1-2, 0.25-1, 0.10-0.25, and <0.10 mm) with four addition rates (0, 4, 8, and 16 g/kg) and five compaction conditions (1.3, 1.4, 1.5, 1.6, and 1.7 g/cm3). A modified van Genuchten (VG) model was also established to determine the characteristic curve of soil water. The results show that all the correlation coefficients were above 0.960, and the standard deviations were below 0.015, indicating this model suitable for the characteristic curve of soil water after the biochar addition. Most macropores and mesopores with larger pore sizes were distributed to significantly improve the water holding capacity in the field. The specific values increased from the lowest 22.74% (1.3 g/cm3, 1-2 mm, 0 g/kg) to 37.56% (1.4 /cm3, 0.25-1 mm, 16 g/kg) with the amount of biochar addition. Furthermore, the initial soil water content increased from 0.135 cm3/cm3 (1.3 g/cm3, 1-2 mm, 0 g/kg) to 0.166 cm3/cm3 (1.3 g/cm3, 1-2 mm, 8 g/kg), where the maximum increase was 0.031 cm3/cm3 in an initial soil water content. Therefore, the biochar addition greatly contributed to the water holding capacity of compacted soil with less air entry for the better use of soil water. Correspondingly, the higher capacity of water holding was obtained at the lower bulk densities (1.3 and 1.4 g/cm3), and the larger particle sizes (0.25-2 mm). A combination of parameters was achieved for the optimal water holding at the high bulk density (1.5, 1.6, and 1.7 g/cm3), lower particle sizes (<0.25 mm), and higher addition (8, 16 g/kg). Consequently, the targeted application of biochar can be widely expected to effectively improve the water holding and water retention capacity of the soils with various compaction in the mining areas. This finding can also provide a promising basis for recovery the low-quality soil. [ABSTRACT FROM AUTHOR]

The land consolidation project is one of the most important approaches to ensure national food and ecological security. An academic journal “Transactions of the Chinese Society of Agricultural Engineering” launched a column of “Land Consolidation Project” in 2002, in order to promote the research of land consolidation project. This column was renamed the “Land Resource Guarantee and National Land Ecological Security” from the 9th issue of May 2020, with the continuous expansion of research fields in the modern land consolidation project. In this study, the bibliometrics was utilized to statistically analyze the papers published in the “Land Consolidation Project” column of “Transactions of the Chinese Society of Agricultural Engineering” from 2002 to 2020. Great research progress was highlighted in the different research directions, and then the future focus was proposed in the field of land resource and national ecological security, with emphasis on China's strategy of food and ecological security. The results showed that the research directions of land consolidation project mainly included land use, land evaluation, agricultural land consolidation, cultivated land quality and safety, 3S and land information technology, industrial and mining wasteland reclamation, rural residential area consolidation, land ecology, land restoration, basic farmland construction and protection, land saving, rural spatial pattern and development, cultivated land development, as well as urban land consolidation. Furthermore, land evaluation, agricultural land consolidation, and cultivated land quality and safety had become hot topics, where the publications accounted for 10.52%, 10.16%, and 8.51%, respectively. 5-keyword clustering was formed, such as the land evaluation, agricultural land consolidation, cultivated land quality and safety, 3S and land information technology, as well as industrial and mining wasteland reclamation. Additionally, 10 groups of cooperation networks were formed in the leading research fields using the cooperation network of research authors generated by VOSviewer. More importantly, the published papers in the “Land Consolidation Project Column” had covered all directions of the land consolidation project. Ecological land consolidation and land-use security pattern were established in recent years, where the ecological effect of land consolidation was analyzed using the theory of landscape ecology. Moreover, many efforts have been made on the ecological design and restoration technology of single land consolidation project, together with the pattern evolution and layout optimization of rural residential areas. In the future, much more attention can be paid to the land resource security and national land ecological security, particularly to the theories and mechanisms in the “systematization, ecologicalization, informationization and intelligence” for the protection and restoration of the regional ecosystem, to realize “overall protection, unified restoration and comprehensive management” of “mountain-water-forest-field-lake-grass”. Consequently, the ecological security pattern of national land can be built, once the research on the intelligent management of one map of natural resources was implemented using the state-of-the-art big data in intelligent agriculture [ABSTRACT FROM AUTHOR]

Opencast coal mining is an anthropogenic activity that changes the antecedent soil profile, and the physical, chemical and biological properties. The compaction activities of large machinery play a great effect on reconstructed soil pore structure in opencast coal-mine dump, so it is an important work to reconstruct a suitable soil pore structure for vegetation growth during the land reclamation for dump. In order to make a quantitative analysis on the pore number and porosity of reconstructed soils in dump, high precision and lossless computed tomography (CT) was used to study the effect of opencast coal-mining, land reclamation and dumping on soil pore number and porosity by scanning the soils in Antaibao opencast coal mine in Pingshuo mining area, Shanxi Province, China. The soils were taken from the dump platform covered by loess parent material, which were the ones with different reclamation time (0, 20 and 23 a) and the one of original landform. The softwares, including Photoshop 7.0, ArcGIS 10 and AutoCAD 2010, were used to process the scanned image and carry out statistical analysis for soil pore properties, and the image characteristics of soil pores and the changes in the number of soil pores and the porosity were analyzed. The changes in macropores, mesopores and micropores of reconstructed soils were also studied in this paper. The results indicated that: 1) Applying the combination method of high precision CT scan imaging technology and computer graphics software could accurately analyze the size, number and distribution of reconstructed soil in opencast coal-mine dump; 2) The number of soil pores and the porosity in original landform were the largest, followed by the soils reclaimed for 23 and 20 years, and the soils after dumping before reclamation were the lowest; 3) Opencast coal-mining and dumping activities reduced the number of soil pores and the porosity because of the effects of large mechanical compaction, especially for macrospores, and land reclamation had a certain function of increasing soil pore size and improving soil porosity; 4) The effect of mining, dumping and other activities on the number of soil pores and the soil porosity for surface soils was higher than that for the bottom soils. During the land reclamation process, subsoiling, planting green manure, applying organic fertilizer and other land reclamation measures should be used to increase the number of reclaimed soil pores and the porosity of macropore on surface soils. This research can provide theoretical reference for the quantitative expression of reconstructed soil pores' distribution, the selection of land reclamation measures, and the optimization of reconstructed soil structure in opencast coal-mine dumps in loess areas. [ABSTRACT FROM AUTHOR]