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To investigate the distribution and, possible sources of soil heavy metals and the effects of anthropogenic cultivation activities on the contents of these metals in purple hilly regions of China, samples of soils and parent materials in purple hilly regions of China were collected before and after land consolidation and after 7 and 19 months of intensive agricultural production, and contents of Pb, Cd, Cu, Zn, Cr, Ni, Hg, and As were analyzed. The results showed that, in the soil samples compared with the parent materials, the greatest accumulation of Cd, As, and Hg occurred in surface layer and a few other horizons. Furthermore, the Cd and Hg contents showed the largest differences among different soil horizons. Parent materials played an important role and anthropogenic cultivation activities greatly affected the soil heavy metals. Under traditional agriculture, Pb, Cd, and Hg had higher contents in surface paddy soils than in surface dry land soils. Land consolidation induced the homogenization of heavy metal elements and dramatically reduced Cd and Hg in the surface soils. The As and Hg contents in the surface soils increased after 19 months of intensive agricultural production. Multivariate statistical analysis (correlation analysis and principal component analysis (PCA)) showed that all eight metals were well represented by the first two principal components (PCs). PC1, which showed relatively high loadings for Cr, Zn, Cu, Ni, and As, was associated with parent materials and therefore represented natural sources. PC2 showed relatively high loadings for Pb, Cd, and Hg, reflecting the effect of air pollution under traditional agriculture, and showed relatively high loadings for Cd, Hg, As, and Pb, reflecting the effect of fertilization under intensive agriculture. This study provides guidelines for the prevention of soil heavy metal pollution and the remediation of polluted soils in purple hilly regions of Sichuan Basin, China.

Chinese farmers are traditionally family-centered in their thinking and behavior and are passionately attached to their land. In a market economy, farmers are the principal agents in agricultural land use, and are directly involved in the allocation of land resources. In the present study, we intended to acquire reasonable interpretations of land transfer under the household responsibility system (HRS) from the perspective of the farmers and identify the underlying driving forces affecting rural land transfer in China. Using a large data set gathered in household surveys conducted in Chongqing from December 2003 to April 2005, this paper examines some important aspects of agricultural land use under HRS, illustrates the present status of the development of land transfer market and describes the responses of the farm households to contract land transfer in the sampling villages. The total area of land transfer varies considerably across the sampling villages. The scope of land transfer shows a striking inter-regional heterogeneity. The general trend is that the rate of land transfer is higher in the Yuxi economic corridor than in the metropolitan area, which, in turn, has a higher transfer rate than the Three Gorges economic zone. The ratio of the area of transferred land to the total area of household contract land shows a similar trend. Gradually, the mode of subcontracting has been accepted and adopted by the local farmers, and the modes of land renting and alienation in exchange of cash are beginning to appeal to some of the households. Land renting, or leasing, which terminates the original contract relations of the household with the village, is the chief form of land transfer in the metropolitan area, while most farm households in the Yuxi economic corridor and the Three Gorges economic zone prefer the form of subcontracting, which does not terminate the original contract relations. The responses of land use patterns and land use environment to land transfer are noticeable in the sampling villages. Most of the transferred farmland in the metropolitan area is allotted to non-agricultural uses. In the Yuxi economic corridor and the Three Gorges economic zone, only a small portion of the transferred land is used for non-agricultural uses and the intensiveness of land use is enhanced for most of it without major changes in land cover. A household survey shows that the conditions of land tenure control the scope of land transfer without great inter-regional variation. The degree of development of the rural land market not only impacts the scope of land transfer in the region, but also constitutes the fundamental causes for the inter-regional variation in land transfer scope and in the evolution of transfer modes. Social security plays a decisive role in whether the farmers are willing to quit farming and in what way they will quit farming. Management of land transfer, which includes rights security management and land use management after the transfer, is essential for standardizing the behavior of the principal agents in land transfer, for reducing disputes in transfer and ensuring the smooth proceeding of land transfer according to law. Understanding the psychology of the farm households under the changing macroeconomic environment and their responses to the driving factors for land transfer is of tremendous significance to the establishment of a market law-abiding and human-oriented system for land transfer in China.

This paper provides a broad review of the existing study on soil aggregate and its responses to land management practices. Soil aggregate is used for structural unit, which is a group of primary soil particles that cohere to each other more strongly than other surrounding particles. The mechanism of soil particle aggregation may be expressed by a hierarchical model, which is based upon the hypothesis that macroaggregates (>250 μm) are collections of smaller microaggregates (<250 μm) held together with organic binding agents. Primary particles form microaggregates and then macroaggregates. Carbon (C)-rich young plant residues form and stabilize macroaggregates, whereas old organic C is occluded in the microaggregates. The interaction of aggregate dynamics with soil organic carbon (SOC) is complex and embraces a range of spatial and temporal processes within macroaggregates and microaggregates. The nature and properties of aggregates are determined by the quantity and quality of coarse residues and humic compounds and by the degree of their interaction with soil particles. The mechanisms resulting in the binding of primary soil particles into stable aggregates vary with soil parent material, climate, vegetation, and land management practices. Land management practices, including tillage methods, residue management, amendments, and soil fertility management, enhance soil aggregation. However, there is still much uncertainty in the dynamics of organic matter in macroaggregation and microaggregation, and research is still needed to understand further the mechanisms of aggregate formation and its responses to human activities.

Open space of metropolitan suburbs in mountain region, has been increasingly becoming the coupling mosaic structure of industrial actions and landscape behaviors. However, the local governments, when making land use planning, often aim at economic development, and rarely refer to the coordination of compatibilities and conflicts between industrial actions and landscape behaviors in the mosaic structure. In this study land use in the Jinyun Mountain and its surrounding area, Chongqing is adjusted by gray multi-objective programming approach and local-level decision-making process to cope with conflicts between objectives for human welfare and objectives for landscape conservation. The results indicate that: 1) the compatibilities and conflicts among different behavior characters and different landscape types result in the compatibilities of landscape to human behavior; 2) a land use planning in the study area is produced based on the sustainable land use and social-eco development, which pays more attention to the resources and environment constraints and economic objectives, and follows the distribution law of rare resources; 3) in the study area, cultivated land of 1,207.27 ha can meet the demands for food and byproducts by the residents there, orchard land and forestland of 632.55 ha, 2,276.61 ha, respectively can provide enough space for the local people to improve their living structure and meet their demands for recreational activities, and urban residential land, rural residential land, mining land and transportation land of 1,107.60 ha, 120.27 ha, 162.48 ha, 100.91 ha, respectively can satisfy the resident’s economic development and infrastructures; 4) the equilibrium among industrial actions, landscape accessibility and ecological conservation can be obtained by analyzing the possible impacts of human activities on landscape ecological process in open space of metropolitan suburbs in mountain areas.

In order to evaluate the soil erosion rate for different land uses and make recommendations on land-use alternatives for erosion control in hilly and mountain areas on a Purplish soil (Regosols in FAO taxonomy), experimental data were obtained from three continuously monitored sites located at Yanting, Nanbu and Pengxi of Sichuan province. The data showed that the rank of erosion rate is farmland > unfenced grassland > fenced grassland > forestland. The erosion rate of farmland was more than 3 times higher than that of forestland and fenced grassland, indicating that restricting human activity is crucial for over-erosion. The erodibility was higher at the initial period of rainy season for all the three types of land use. The erosion rates of fenced grassland and mature afforestation land were not proportional to rainfall intensity because these land uses changed impact energy of the rainfall. This research showed that restricting human activity, intensifying the management of initial period of rainy season, and increasing the cover rate of land surface are the three major measures for soil erosion prevention. It is recommended that farmers should cease cultivation on farmland at the top of hills and steep slope land return those lands back to grassland or forestland.

Soil aggregate breakdown is the first key factor that causes soil erosion. At present, research on the mechanisms of soil aggregate breakdown during rainfall is common. However, the research to on quantifying the relative contributions of internal and external forces to aggregate breakdown remains limited. This paper was conducted to analyse the relative contribution of internal and external forces to aggregate disintegration and the factors affecting aggregate stability during rainfall. Soil aggregates with a series of textures were selected as test soil samples; deionized water was employed as the soaking solution and rainfall material in static disintegration experiments and rainfall simulation tests. The effect of internal force (soil hydrophilicity) on aggregate disintegration was analysed by the static disintegration method, and the combined effects of internal force (soil hydrophilicity) and external force (raindrop impact) on soil aggregate breakdown were analysed by rainfall simulation experiments. The results indicated that external force caused more severe soil aggregate breakdown than internal force, and the crushed aggregate was mainly distributed in the range of 2–0.25 mm. With increasing rainfall kinetic energy, the degree of aggregate breakdown increased gradually, and the degree of aggregation of the soil particles decreased gradually. Furthermore, soil aggregates with a high clay content (> 30%) were more stable than medium-clay (20–30%) and low-clay (< 20%) soil aggregates, and the correlation coefficient provided a good representation of the relationship between the clay content and soil aggregate stability index (ASI). Therefore, external force contributed more to soil aggregate breakdown than internal force during rainfall, and clay plays an important role in aggregate stability. The results of this study are of great significance for elaborating the mechanism and factors affecting aggregate breakdown.