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    Chinese Cropland Quality and Its Temporal and Spatial Changes due to Urbanization in 2000-2015
    WANG Chunyu,SUN Xiaofang,WANG Meng,WANG Junbang,DING Qingfu
    Journal of Resources and Ecology    2019, 10 (2): 174-183.   DOI: 10.5814/j.issn.1674-764X.2019.02.008
    Abstract355)   HTML16)    PDF (1511KB)(270)      

    The acceleration of urbanization has led to the occupation of more cropland, especially higher quality cropland, which could pose a huge threat to food security and have other implications for the inadequate cropland resource supply in China. Though the spatial status of Chinese cropland quality has been assessed, its temporal changes since 2000 to 2015 are still not clear. An accumulated probability distribution method was used to determine the criteria of cropland quality using the net primary production data product (MOD17) from Moderate Resolution Imaging Spectroradiometer (MODIS). Then the cropland quality of higher, median and lower production was spatially mapped and its changes due to occupation by urbanization were analyzed through the land use changes (LUCC) data primarily from Landsat TM images in the three periods of 2000-2005, 2005-2010, and 2010-2015. The results showed that of the total cropland reduction area the proportion taken by urbanization increased from 47.29% in the early stage to 77.46% in the recent period. The quality of Chinese cropland was dominated by low- and medium-yield fields, accounting for 40.81% and 48.74%, respectively, with high-yield fields accounting for only 10.44% of the total cropland in the country in 2000. The high-yield areas have been seriously threatened by the expansion of construction land fields, with the ratio of high-yield area to total area occupied by urbanization increasing from 9.71% in 2000-2005 to 15.63% in 2010-2015. Spatially, this phenomenon has been moving from eastern and southern China to central and western China, especially in Northwest China where the ratio has arrived at the highest proportion, with 52.97% of high-yield cropland in the total land taken by the expansion by 2015. This study not only provides a method to assess cropland quality but also reveals the threatening trend from the expansion of urbanization on high-quality cropland. More attention should be paid to the latter in land use planning and policies made to prevent threats to food security from declines in both cropland quantity and quality.

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    Spatial Analysis of the Soil Carbon Sequestration Potential of Crop-residue Return in China Based on Model Simulation
    CHEN Jinghua,WANG Shaoqiang,Florian KRAXNER,Juraj BALKOVIC,XU Xiyan,SUN Leigang
    Journal of Resources and Ecology    2019, 10 (2): 184-195.   DOI: 10.5814/j.issn.1674-764X.2019.02.009
    Abstract338)   HTML7)    PDF (1242KB)(139)      

    Crop-residue return is a recommended practice for soil and nutrient management and is important in soil organic carbon (SOC) sequestration and CO2 mitigation. We applied a process-based Environmental Policy Integrated Climate (EPIC) model to simulate the spatial pattern of topsoil organic carbon changes from 2001 to 2010 under 4 crop-residue return scenarios in China. The carbon loss (28.89 Tg yr-1) with all crop-residue removal (CR0%) was partly reduced by 22.38 Tg C yr-1 under the status quo CR30% (30% of crop-residue return). The topsoil in cropland of China would become a net carbon sink if the crop-residue return rate was increased from 30% to 50%, or even 75%. The national SOC sequestration potential of cropland was estimated to be 25.53 Tg C yr-1 in CR50% and 52.85 Tg C yr-1 in CR75%, but with high spatial variability across regions. The highest rate of SOC sequestration potential in density occurred in Northwest and North China while the lowest was in East China. Croplands in North China tended to have stronger regional SOC sequestration potential in storage. During the decade, the reduced CO2 emissions from enhanced topsoil carbon in CR50% and CR75% were equivalent to 1.4% and 2.9% of the total CO2 emissions from fossil fuels and cement production in China, respectively. In conclusion, we recommend encouraging farmers to return crop-residue instead of burning in order to improve soil properties and alleviate atmospheric CO2 rises, especially in North China.

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