Systematically recognizing spatial patterns and driving factors of cultivated land fragmentation is of great significance for the exploration of locally appropriate path to relieve cultivated land ...fragmentation. This study aims to estimate cultivated land density, mean patch size and area-weighted mean shape index to respectively indicate the characteristics of cultivated land fragmentation from three dimensions, namely, natural resource endowment, spatial partition, and convenience of utilization. The regional leading factors of cultivated land fragmentation are also analyzed. The results demonstrate that the distribution of cultivated land density is higher in Northern regions compared with those of southern regions. The significant positive correlation between cultivated land density and mean patch size is found to be universal across nearly all cities, exceeding differences in terrain, elevation, climate, soil, and social economic condition. For cities in the southern part of China, cultivated land of regular shape is partitioned to smaller blocks compared with irregular ones; alternatively, intensive and meticulous farming under small-scale agricultural operation leads to clusters with low mean patch size - low area-weighted mean shape index. Random forest model explains the impact of driving factors on cultivated land fragmentation, with an explanatory power ranging from 66% to 95%. The terrain factor emerges as the primary driver negatively affecting cultivated land density. Gross domestic product emerges as the dominant factor with a significant (p < 0.01) negative correlation to mean patch size for nearly all agricultural climatic zones. Terrain, gross domestic product and population is the most important factor affecting area-weighted mean shape index. Rural development degree influences correlation between dominant factors and cultivated land fragmentation. This study is greatly instructive for recognizing the spatial patterns of cultivated land fragmentation at the national scale and for exploring the barriers that impede regionally scaled cultivated land use.
•First reveal 1-km grid scale cultivated land fragmentation in mainland China.•Detect the polarizing differences of cultivated land fragmentation between peri-urban and out-of-urban areas.•Analyze China national spatial clustering characteristics of cultivated land fragmentation.•Recognize regional dominant factor to cultivated land fragmentation.•Generate China national 1-km grid-based cultivated land fragmentation maps.
As an extension of a previous work (Chen and Han, 2015a), this study explored the arable land use of the world economy from source of exploitation to sink of final consumption via the global supply ...chain, by means of embodiment accounting that includes the indirect feedbacks associated with both intermediate and primary inputs. In magnitude, the global transfer of arable land use is estimated to be around 40% of the total direct exploitation. The connections as well as imbalances of major economies in intermediate and final trades of arable land use are discussed. Canada, Australia, Argentina, Pakistan and African regions turn out to have a massive deficit of arable land use in both intermediate and final trades. In contrast, the United States, Japan, Mainland China, the United Kingdom, Germany and France obtain a surplus of arable land use in both intermediate and final trades by land displacement in those net exporters. Indices in terms of arable land use self-sufficiency rate by source and that by sink are devised. For India as the biggest source region, around 20% of the arable land resources exploited locally are for final consumption abroad. For the United States as the largest sink region, around 40% of its arable land use originates from foreign regions led by Canada. For Japan as the biggest net importer in both intermediate and final trades, over 90% of its arable land use comes from foreign economies led by African and Asian regions. For sustained development, regions are suggested to be more adapted to the global supply chain based on their behaviors in both intermediate and final trades of arable land use.
Accurate information on farmland soil heavy metal elements is needed for pollution management and strategic decision making at the national level. In this paper, we review the Chinese literature on ...soil heavy metal elements (i.e., arsenic, cadmium, chromium, copper, lead, mercury, and zinc) over the past 20 years using meta-analysis. The overall pollution status, spatiotemporal distribution patterns and driving factors of heavy metals in China's farmland soil are explored by using the geoaccumulation index, the standard deviation ellipse method and the PCA/APCS model, respectively. The results show that most heavy metals in farmland soil from the study cases are similar to the world average. Seven types of elements have increased compared with background values. Cd and Hg have become the top polluting elements in China and industrial and agricultural activities are the main sources of current heavy metal element enrichment. Regional natural-social-economic differences have led to significant spatial heterogeneity of heavy metal pollution, showing an intensity pattern unfavourable to national food security. In the time period, the overall distribution range gradually increased with the accelerated growth of regional industrial output, and there was a tendency for the gravity centre of the pollution studies to migrate inland to the northwest and southwest. Regionally differentiated environmental regulation and pollution remediation measures should be developed for pollution prevention and control in the future.
Accurate information on farmland soil heavy metal elements is needed for pollution management and strategic decision making at the national level. However, large-scale soil heavy metal element studies face many difficulties in China, and most studies are characterized by small-scale, refined and stage-specific characteristics. In this paper, using meta-analysis, we review the Chinese literature on soil heavy metal elements over the past 20 years and attempt to analyse the overall pollution status, spatiotemporal patterns and drivers of heavy metals in farmland soil from the study cases. A total of 121 county-scale study cases from 112 Chinese studies published during 1998–2019 were collected, and statistical information of 7 soil heavy metal elements (i.e., arsenic, cadmium, chromium, copper, lead, mercury, and zinc) from each study was collected. The geoaccumulation index (Igeo) was calculated to characterize the extent of heavy metal contamination, considering the influence of the regional natural background. In addition, the standard deviation ellipse (SDE) method was used to characterize the temporal variation in pollution studies over the past 20 years. This study shows that most heavy metals in farmland soil from the study cases are similar to the world average. Seven types of elements have increased compared with background values. Cd and Hg have become the top polluting elements in China. Regional natural-social-economic differences have led to significant spatial heterogeneity of heavy metal pollution, showing an intensity pattern unfavourable to national food security. In the time period, farmland soil heavy metals from the study cases showed an improving trend, but the overall distribution range gradually increased, and there was a tendency for the gravity centre of the pollution studies to migrate inland to the northwest and southwest. Regionally differentiated environmental regulation and pollution remediation measures should be developed for pollution prevention and control in the future. Display omitted
•Overall heavy metal pollution status of China's farmland soil is analysed using meta-analysis and geoaccumulation index.•Spatiotemporal patterns and drivers of heavy metals are presented using GIS method.•Seven types of heavy metal elements have increased to different degrees.•Cd and Hg have become the top polluting elements in China.•A tendency for the gravity centre of the pollution studies to migrate inland to the northwest and southwest is discovered.
Heavy metals and metalloids (HMs) are environmental pollutants, most notably cadmium, lead, arsenic, mercury, and chromium. When HMs accumulate to toxic levels in agricultural soils, these ...non-biodegradable elements adversely affect crop health and productivity. The toxicity of HMs on crops depends upon factors including crop type, growth condition, and developmental stage; nature of toxicity of the specific elements involved; soil physical and chemical properties; occurrence and bioavailability of HM ions in the soil solution; and soil rhizosphere chemistry. HMs can disrupt the normal structure and function of cellular components and impede various metabolic and developmental processes. This review evaluates: (1) HM contamination in arable lands through agricultural practices, particularly due to chemical fertilizers, pesticides, livestock manures and compost, sewage-sludge-based biosolids, and irrigation; (2) factors affecting the bioavailability of HM elements in the soil solution, and their absorption, translocation, and bioaccumulation in crop plants; (3) mechanisms by which HM elements directly interfere with the physiological, biochemical, and molecular processes in plants, with particular emphasis on the generation of oxidative stress, the inhibition of photosynthetic phosphorylation, enzyme/protein inactivation, genetic modifications, and hormonal deregulation, and indirectly through the inhibition of soil microbial growth, proliferation, and diversity; and (4) visual symptoms of highly toxic non-essential HM elements in plants, with an emphasis on crop plants. Finally, suggestions and recommendations are made to minimize crop losses from suspected HM contamination in agricultural soils.
To find a solution regarding sustainable arable land use pattern in the important grain-producing area during the rapid urbanization process, this study combined agricultural production, locational ...condition, and ecological protection to determine optimal arable land use. Dongting Lake basin, one of the major grain producing areas in China, was chosen as the study area. The analysis of land use transition, the calculation of arable land barycenter, the landscape indices of arable land patches, and the comprehensive evaluation of arable land quality(productivity, economic location, and ecological condition) were adopted in this study. The results showed that (1) in 1990–2000, the arable land increased by 11.77%, and the transformation between arable land and other land use types actively occurred; in 2000–2010, the arable land decreased by 0.71%, and more ecological area (forestland, grassland, and water area) were disturbed and transferred into arable land; (2) urban expansion of the Changsha-Zhuzhou-Xiangtan city cluster (the major economy center of this area) induced the northward movement of the arable land barycenter; (3) the landscape fragmentation and decentralization degree of arable land patches increased during 1990–2010; (4) potential high-quality arable land is located in the zonal area around Dongting Lake, which contains the Li County, Linli County, Jinshi County, Taoyuan County, Taojiang County, Ningxiang County, Xiangxiang County, Shaoshan County, Miluo County, and Zhuzhou County. The inferior low-quality arable land is located in the northwestern Wuling mountainous area, the southeastern hilly area, and the densely populated big cities and their surrounding area. In the optimized arable land use pattern, the high-quality land should be intensively used, and the low-quality arable land should be reduced used or prohibitively used. What is more, it is necessary to quit the arable land away from the surrounding area of cities appropriately, in order to allow more space for urban expansion. This study could provide guidance for sustainable arable land use by both satisfying the future agricultural production and the local economic development, which can be used for the other major grain-producing areas in this rapid developing country.
•There is aninverted N-shaped relationship between rural out-migration and arable land use intensity.•The underlying influence mechanism has been explained.•Labor scarcity resulted from the excessive ...emigration of rural labors has negative impacts onarable land use intensity.•The added fertilizer and pesticide inputs or changes in crop type can compensate for the negative effect of labor scarcity.•Over-intensive use of farmland has negative impacts on the ecological environment and national food security.
Since the late 1990s, massive rural out-migration has had a significant impact on the utilization of cultivated land. However, the links between rural out-migration and arable land use intensity remain ambiguous. This paper expands the current theories on the relationship between migration flows and land use intensification and explains the underlying mechanism that arable land use intensity is fluctuating upward with the increase of rural out-migration. Panel data of 5 mountain cities in Guangdong Province from 1996 to 2012 is used to empirically examine the impact of rural out-migration on arable land use intensity and analyze the influence of rural out-migration income, land scale, GDP per capita and multiple crop index on arable land use intensity. Our results show that there is an inverted N-shaped relationship between rural out-migration and arable land use intensity. The positive effect of the productivity increase caused by the Household Responsibility System (HRS) is the main reason for the increase of arable land use intensity. Labor scarcity that results from the excessive emigration of rural labors leads to a decline in arable land use intensity. The added fertilizer and pesticide inputs or changes in crop type can ultimately compensate for the negative effect of labor scarcity and promote the improvement of arable land use intensity. In addition, over-intensive use of farmland has negative impacts on the ecological environment and national food security. Based on the empirical results of this paper, some policy recommendations are suggested, such as the transformation of the agricultural development mode for a less demand in rural labor, increasing the inputs of agricultural technique and capital instead of labor, raising the comparative benefit of agriculture to attract young rural labor for farming, cultivation of professional farmers, establishment of an agricultural supporting system and developing circulative agriculture.
•Passive heat-storage greenhouse walls were designed for non-arable lands.•An unsteady model of the solar greenhouse’s thermal environment was established.•The thermal performances and energy ...efficiencies of these walls were analysed.•The effects of these walls on the greenhouses’ thermal environment were assessed.
Chinese solar greenhouses rely entirely on solar energy to provide a suitable growing environment for crops. Moreover, they offer a remarkable opportunity for boosting ‘Gobi agriculture’ and promoting the economy and ecology of non-arable lands. Further, enhancing the thermal performance of the north wall has been considered an efficient way of improving the greenhouse’s thermal environment and thereby increasing agricultural productivity. To improve the solar energy efficiency and boost ‘Gobi agriculture’, five passive heat-storage north walls were designed for non-arable lands by using non-soil and locally available inexpensive materials. These included a flange-layered wall (FL), a concrete-layered wall (CL), a gravel-layered wall (GL), an aerocrete brick-layered wall (AL) and a concrete hollow block-layered wall (HL). A mathematical model of the thermal environment of a solar greenhouse in non-arable lands was established, and a comparative study was conducted to evaluate the designed walls’ effectiveness over conventional walls. Their thermal performances were quantitatively assessed using both theoretical and simulation methods. Moreover, the impacts of these walls on the greenhouse’s thermal environment were investigated using an unsteady-state simulation analysis. The results verified the larger contributions of FL, CL, and GL toward promoting the thermal environment of solar greenhouses. FL, CL, and GL enhanced the heat storage/release performance by 5.0%, 38.0%, and 37.3% and the energy efficiency by 9.2, 12.9, and 13.5 percentage points, respectively, resulting in average increases in the nocturnal interior temperature of 0.7, 2.5, and 2.5 °C, respectively.
The abandonment phenomenon is familiar in China. It threatens food security and seriously affects the sustainable development of society, the economy, and the natural environment. However, monitoring ...and mapping abandoned cropland on a large scale remains a challenge because of its complex land-use change process. According to the World Food and Agriculture Organization, cropland not used for agricultural production for more than 5 years is defined as abandoned cropland. This study uses the Landsat high-precision long-time series product to detect cropland nationwide from 1990 to 2019 by using the sliding window method on Google Earth Engine to profile the spatial distribution, intensity, trend, frequency, and recultivation of abandoned cropland. Between 1992 and 2015, the results illustrate that the total area of abandoned cropland in China was 559,170.26 km2, 18.59 % of the cropland area. Excluding the recultivated cropland area, China's abandoned cropland area amounted to 392,156.24 km2, 13.03 % of the total cropland. Cropland abandonment is mainly distributed in the second terrain gradient in midwestern and southwestern regions such as Inner Mongolia and Gansu. It rarely happens in western and eastern coastal areas. A high abandonment rate area usually has high elevation and slope. The light index is negatively correlated with the abandonment rate in suburban areas. This study is the first to map the spatiotemporal distribution of abandoned cropland in China with high precision at 30 m resolution. It provides an important basis for policies regarding the recultivation of abandoned cropland.
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•The spatial distribution, intensity, trend, frequency, and recultivation of abandoned cropland were profiled.•Excluding the recultivated, China's abandoned cropland amounted to 392,156.24 km2, 13.03% of the total from 1992 to 2015.•The abandoned cropland was mainly distributed in the second terrain gradient in China.•Abandonment rates were positively correlated with elevation and slope, and negatively correlated with suburban light index.
The factors that contribute to the composition of the root microbiome and, in turn, affect plant fitness are not well understood. Recent work has highlighted a major contribution of the soil inoculum ...in determining the composition of the root microbiome. However, plants are known to conditionally exude a diverse array of unique secondary metabolites, that vary among species and environmental conditions and can interact with the surrounding biota. Here, we explore the role of specialized metabolites in dictating which bacteria reside in the rhizosphere. We employed a reduced synthetic community (SynCom) of Arabidopsis thaliana root-isolated bacteria to detect community shifts that occur in the absence of the secreted small-molecule phytoalexins, flavonoids, and coumarins. We find that lack of coumarin biosynthesis in f6′h1 mutant plant lines causes a shift in the root microbial community specifically under iron deficiency. We demonstrate a potential role for iron-mobilizing coumarins in sculpting the A. thaliana root bacterial community by inhibiting the proliferation of a relatively abundant Pseudomonas species via a redox-mediated mechanism. This work establishes a systematic approach enabling elucidation of specific mechanisms by which plant-derived molecules mediate microbial community composition. Our findings expand on the function of conditionally exuded specialized metabolites and suggest avenues to effectively engineer the rhizosphere with the aim of improving crop growth in iron-limited alkaline soils, which make up a third of the world’s arable soils.
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