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Soil structure degradation in greenhouse vegetable fields reduces vegetable production. Increasing aeration porosity is the key to ameliorating soil structure degradation. Thus, we tested the effect of a porous material, porous clay ceramic (PLC), on the amelioration of soil structure degradation under greenhouse vegetable production. A 6-month pot experiment was conducted with four PLC application levels based on volume, i.e., 0% (control), 5% (1P), 10% (2P), and 15% (3P) using Brassica chinensis as the test plant. At the end of the experiment, soil columns were sampled, and the aeration pore network was reconstructed using X-ray computed tomography (CT). The degree of anisotropy (DA), fractal dimension (FD), connectivity, aeration porosity, pores distribution, and shape of soil aeration pores and plant biomass were determined. The DA, FD, and connectivity did not significantly differ as the PLC application rate increased. Nonetheless, aeration porosity significantly linearly increased. The efficiency of PLC at enhancing soil aeration porosity was 0.18% per Mg ha–1. The increase in aeration porosity was mainly due to the increase in pores > 2 000 μm, which was characterized by irregular pores. Changes in aeration porosity enhanced the production of B. chinensis. The efficiency of PLC at increasing the plant fresh weight was 0.60%, 3.06%, and 2.12% per 1% application rate of PLC for the 1P, 2P, and 3P treatments, respectively. These results indicated that PLC is a highly efficient soil amendment that improves soil structure degradation by improving soil aeration under greenhouse conditions. Based on vegetable biomass, a 10% application rate of PLC was recommended.

Detailed information on the spatio-temporal changes of cropland soil organic carbon (SOC) can significantly contribute to the improvement of soil fertility and mitigate climate change. Nonetheless, information and knowledge on the national scale spatio-temporal changes and the corresponding uncertainties of SOC in Chinese upland soils remain limited. The CENTURY model was used to estimate the SOC storages and their changes in Chinese uplands from 1980 to 2010. With the Monte Carlo method, the uncertainties of CENTURY-modelled SOC dynamics associated with the spatial heterogeneous model inputs were quantified. Results revealed that the SOC storage in Chinese uplands increased from 3.03 (1.59 to 4.78) Pg C in 1980 to 3.40 (2.39 to 4.62) Pg C in 2010. Increment of SOC storage during this period was 370 Tg C, with an uncertainty interval of −140 to 1110 Tg C. The regional disparities of SOC changes reached a significant level, with considerable SOC accumulation in the Huang-Huai-Hai Plain of China and SOC loss in the northeastern China. The SOC lost from Meadow soils, Black soils and Chernozems was most severe, whilst SOC accumulation in Fluvo-aquic soils, Cinnamon soils and Purplish soils was most significant. In modelling large-scale SOC dynamics, the initial soil properties were major sources of uncertainty. Hence, more detailed information concerning the soil properties must be collected. The SOC stock of Chinese uplands in 2010 was still relatively low, manifesting that recommended agricultural management practices in conjunction with effectively economic and policy incentives to farmers for soil fertility improvement were indispensable for future carbon sequestration in these regions.

Organic manure is beneficial for macro-aggregate formation and soil organic carbon (SOC), but how SOC change in aggregate fractions in time-series is still uncertain. Moreover, greenhouse systems converted from cereal fields quickly faced soil degradation. Thus, the role of organic manure here should be discussed. The main objectives of this study were to determine the change of SOC fractions in bulk soil and aggregation level affected by long-term organic manure application. Using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, we investigated the SOC and its fraction changes within bulk soil and aggregate fractions under 1-year, 9-year, and 14-year organic greenhouse vegetable cultivation, and we also analysed the soil properties of rice-wheat rotation (RWR) fields as the control. Soil aggregate samples were wet sieved into large macro-aggregates (> 2 mm), small macro-aggregates (2–0.25 mm), micro-aggregates (0.053–0.25 mm), and silt and clay particles (

The availability of soil nitrogen (N) decreases as the structure of agricultural soils degrades. Traditional methods focus on organic amendments that indirectly affect the porosity and N content of soil. Due to the low efficiency of such amendments, new materials, particularly highly porous materials, are needed to improve the quality of soil, which has opened new directions.The addition of 2 to 7 mm of porous clay ceramic (PLC) significantly increased the fresh weight of Brassica chinensis. The soil aeration porosity (50 μm) increased by 0.69% on average in response to 1% PLC application. Soil NOThe application of PLC increased soil aeration and enhanced the availability of soil N, which yielded large vegetable harvests in clayey soils in the short term. © 2022 Society of Chemical Industry.

Objective of investigation: Land use conversion strongly alters soil structure and substantially affects soil organic carbon (SOC) sequestration. Changing from an anaerobic paddy field (PF) to a dry land easily causes SOC loss due to stimulation of C decomposition. However, no evidence of SOC loss from PF to intensive vegetable cultivation has been certainly presented. Experimental material: This study was conducted on the long-term cultivated open-field vegetable (OFV) and greenhouse vegetable (GHV) planting area converted from old PF in China. Undisturbed soil cores, natural structured soil, and disturbed soil from top soil layers were using for further analyses. Methods of investigation: To comprehensively investigate SOC and soil structure change in the land use conversion of PF to OFV and PF to GHV, we used 13C-CPMAS NMR spectroscopy to classify the SOC fractions. The soil macropores (> 50 μm) was valued by X-ray computed tomography, and soil aggregates distribution was determined by wet sieving method. Data collection: Data were obtained from the above-mentioned measurements and statistically analyzed in R. Results: The result showed that the SOC stock increased 1-fold from PF to GHV. SOC stability increased with recalcitrant C (aromatic-C and carbonyl-C) raised by 21 %–27 % in GHV bulk soil. Both macropores and macroaggregates (> 250 μm) increased in GHV, accompanied by an accumulation of recalcitrant C in large macroaggregates. Conclusions: we confirmed the expanded GHV cultivation sequestered more belowground SOC than PF, associated with the amplified physical protection by enhancing soil aggregation and by redistributing of soil macropores.

Organic farming can potentially mitigate soil compaction, which commonly occurs in vegetable plantations, particularly in greenhouses when compared with open‐air systems. Although several studies have addressed the effect of planting patterns on soil pore characteristics, few studies have focused on changes in pore attributes under organic fertilization. We used adjacent fields during green manure planting as a control to compare the differences in soil physicochemical and macropore parameters between 14‐year‐old greenhouse plots and open‐air plots under organic fertilization. Pearson's correlation analysis was performed to analyse the drivers of soil macropore characteristics in vegetable plantations in Jiangsu Province, China. A significant increase in connectivity, fractal dimensions and total macroporosity and a decrease in bulk density after 14 years of organic farming, particularly in the surface layer in the greenhouse, were observed. However, the difference in pores in the plough pan layer was not significant between the treatments. The volume of small pores (50–500 μm) and medium pores (500–1,000 μm) increased significantly (p 1,000 μm) showed a clear decrease, especially in open‐air fields, possibly due to the disappearance of the original straw residues in the surface layer. Small and medium pores in the plough layer increased in greenhouse fields, whereas the opposite occurred in open‐air fields. Overall, compared with open‐air systems, long‐term organic greenhouse patterns had a significantly positive effect on soil pore attributes.

This study evaluates the use of visible and near-infrared spectroscopy for rapid prediction of total carbon, total nitrogen, and total phosphorus concentrations in field crop samples. Two multivari...

Temperature and precipitation simultaneously influence the soil organic carbon (SOC) in agroecosystems. While these parameters' individual impacts have been extensively studied, their combined effects remain poorly understood at a regional scale. Thus we conducted this study to quantify the combined influence of temperature and precipitation on the SOC in upland-crop fields of the northern Jiangsu Province in eastern China. This quantification was achieved by using the DeNitrification-DeComposition (DNDC, version 9.5) model with the most detailed upland soil database in China. The model simulations indicated that under a scenario where the air temperature (T) increased by 2 °C (T2) and the precipitation (Prec) simultaneously decreased by 20%, the upland soils in the study region were estimated to a sequestered 39.10 Tg C from 2010 to 2039. Meanwhile, a scenario with T2 and a simultaneous increase in Prec by 20% led to a lower C sequestration of 37.39 Tg C. We found that the respective C sequestration from the combined effects of T and Prec in the above two scenarios was 1.24 (or 2.12) Tg C less compared to the sum of their individual effects. Moreover, if the increase of T changed from 2 °C to 4 °C, and the Prec continued to decrease (or increase) by 20%, the C sequestration was 34.69 (or 33.64) Tg C, which was 3.60 (or 3.82) Tg C lower than the sum of the individual effects. Our analysis of the combined effects of T and Prec on the SOC changes suggested that future warming and Prec changes in this region may cause a decrease in the SOC sequestration, but the upland agroecosystems will still serve as a long-term sink for atmospheric CO2 due to the high application rates of chemical fertilizer and farmyard manure. Furthermore, the separate and combined effects of temperature and precipitation on the SOC changes in the different upland soil groups varied widely due to the heterogeneity of soil properties, physicochemical conditions and fertilizer practices. This result emphasized the importance of using fine scale soil datasets and the need to understand the intricacies in the soil carbon sequestration potential at a regional scale in a changing climate.

The impacts of rapid industrialization on spatio-temporal changes in soil pH have drawn major attention from the scientific community and decision-makers. A total of 1185 topsoil samples (0–20 cm) were collected from southern Jiangsu Province of China in 1980, 2000, and 2015, and the geostatistical sequential Gaussian simulation (SGS) was used to quantify the spatio-temporal patterns of changes in soil pH and identify the areas with significantly-declined pH. A significant topsoil acidification occurred in major croplands of the study area, with mean decrements of 0.56 and 0.52 units over the periods of 1980–2000 and 2000–2015, respectively. A significant decrease in pH occurred in the areas surrounding Taihu Lake during 1980–2000, and a further decrease was evident predominantly in the northeast during 2000–2015. Over the entire 35-year period, the soil pH for approximately 79% of the study area declined significantly. The decline over the first two decades (1980–2000) was largely attributed to increased chemical fertilizer inputs and the development of industries, while the further enhanced industrial emissions resulting from the significant expansion of factories were the primary reason for the accelerated soil acidification in the subsequent 15 years (2000–2015). Results from this study may serve as a basis for developing management strategies to achieve better soil quality in similar areas moving toward industrialization.

Process-based models have been successfully applied to predict long-term changes in soil organic carbon (SOC) at plot scales, but considerable uncertainties are still introduced into regional or national extrapolations due to the lack of spatially explicit information on the model input parameters. Using the CENTURY model we predicted SOC changes in the uplands of Northeast China during the period from 1980 to 2050 and provided 95% confidence intervals regarding the uncertainties associated with variability in the key input parameters. Regional SOC estimation predicted by CENTURY was reliable for the uplands of Northeast China when considering the uncertainty associated with heterogeneous key input parameters. SOC stocks were estimated to be 0.99, 0.88 and 0.87 Pg C in 1980, 2010 and 2050, with 95% confidence intervals ranging from 0.69 to 1.31, 0.66 to 1.11, and 0.69 to 1.07 Pg C, respectively. Overall, the upland soils of Northeast China functioned as a carbon source from 1980 to 2010, with a net decrease of 106 (9–207) Tg C. The SOC losses mainly occurred where SOC contents were high (Heilongjiang Province and eastern Jilin Province). However, assuming unchanged management, whether the uplands of Northeast China will serve as a carbon sink/source over the next 40 years remains uncertain. Information collection on the most influential input parameters (the initial SOC content and clay content) is critical to reduce uncertainty and to provide meaningful information for decision makers.

The use of three discrete soil organic carbon (SOC) pools proposed by the CENTURY model to study the SOC dynamics helps to understand the changes in cropland SOC pool and its stability. This study focuses on a typical black soil (mollisol) region in Northeast China. Based on historical soil data from samples that were collected in the 1980s, we selected 44 sampling points and collected 88 soil samples from the surface (0–20 cm) and subsurface (20–40 cm) layers in 2010. A 100-day laboratory incubation for each sample was conducted to measure the decomposition rates of SOC at different times, and data from the incubation experiment were fitted to a three-pool first-order model that divided the total SOC into active (Ca), slow (Cs) and resistant (Cr) SOC fractions. A method for predicting the concentrations of the three SOC fractions was developed and used to obtain the concentrations of SOC fractions in the 1980s at each sampling point. The results showed that a power function model (Dsoct = a × tb) could be used as the universal SOC decomposition curve model. Using the universal model, the predictive method accurately estimated the concentrations of Ca, Cs and Cr of upland soils in this black soil region, which effectively solved the problem of a lack of soil samples and SOC fractions data in previous studies of the spatial-temporal variations of SOC fractions in regional soils. From 1980 to 2010, the estimated variations of the Ca, Cs and Cr in the surface upland soil were +0.37, −5.53 and −6.32 g kg−1, and the corresponding contributions to the loss of the total SOC were -3.2%, +48.2% and +55.1%, respectively, while the variations of the Ca, Cs and Cr in the subsurface soil were +0.19, −0.43 and −2.45 g kg−1, and the corresponding contributions to the loss of the total SOC were −7.1%, +16.0% and +91.1%, respectively. The decrease in the total SOC is primarily attributed to the decrease of the Cs and Cr fractions in the region, although the Ca fraction has significantly increased. The overall variations in the SOC fractions suggest a declining stability of the SOC pool in the black soil region of Northeast China.

The shift from rice-wheat rotation (RWR) to greenhouse vegetable soils has been widely practiced in China. Several studies have discussed the changes in soil properties with land-use changes, but few studies have sought to address the differences in soil pore properties, especially for fields based on long-term organic fertilization under greenhouse vegetable system from RWR fields. This study uses the X-ray computed tomography (CT) scanning and statistical analysis to compare the long-term effects of the conversion of organic greenhouse vegetable fields (over one year, nine years, and fourteen years) from RWR fields on the soil macropore structure as well as the influencing factors from samples obtained in Nanjing, Jiangsu, China, using the surface soil layer and triplicate samples. The results demonstrated that the macropore structure became more complex and stable, with a higher connectivity, fractal dimension (FD) and a lower degree of anisotropy (DA), as the greenhouse vegetable planting time increased. The total topsoil macroporosity increased considerably, but the rate of increase gradually decelerated with time. The transmission pores (round pores ranging from 50 to 500μm) increased with time, but the biopores (>2000μm) clearly decreased after nine years of use as greenhouse vegetable fields. Soil organic matter (OM) has a significant relationship with the soil pore structure characteristics, especially for the transmission pores. In addition, organic fertilization on the topsoil had a short-term effect on the pores, but the effect stabilized and had a weak influence on the pores over longer periods. These results suggested that organic fertilization was conducive for controlling soil degradation regarding it physical quality for water and oxygen availability in the short term.

Digital soil maps with different scales have been widely used to quantify soil organic carbon (SOC) dynamics in the upland-crop fields. However, most of the regional SOC modeling often uses soil maps with a fixed scale, thus how varying map scales influence modeled SOC dynamics has rarely been quantified. Different map scales have different levels of details in describing the soil properties (e.g., soil texture, SOC content, bulk density, and pH) for a specific area, with the high resolution map having finer spatial representation. In this study, six digital upland soil databases of the northern Jiangsu Province in Eastern China at scales of 1:50,000 (P5), 1:250,000 (P25), 1:500,000 (P50), 1:1,000,000 (P100), 1:4,000,000 (P400), and 1:10,000,000 (P1000) have been used to drive the DeNitrification-DeComposition (DNDC, version 9.5) model to quantify SOC changes for the period of 1980–2009. This suite of scales selections covers all basic soil map scales in China. Our simulations indicate that the regional total SOC changes from 1980 to 2009 in the top layer (0–50 cm) for upland soils using P5, P25, P50, P100, P400, and P1000 soil maps were 37.89, 34.91, 36.04, 37.05, 39.28 and 38.46 Tg C, respectively. Taking the regional total SOC changes based on the most detailed soil map, P5, as a reference, the relative deviation of those derived from the P25, P50, P100, P400, and P1000 were 7.86%, 4.86%, 2.21%, 3.67%, and 1.51%, respectively. Although the relative deviation of regional total SOC changes for most soil maps are low, disparities exist among SOC changes for different soil groups (i.e. 4.8 to 981%) and for administrative areas level (i.e. 0.32 to 151%). The results indicate that SOC estimates are significantly influenced by soil map scale. Lack of detailed soil information, like representation of many soil types and spatial variations in soil types, in coarse-scale maps result in the large uncertainties in the estimates of SOC changes. This study stresses the needs of detailed soil digital maps for accurate quantification of regional SOC changes.

Conversion of rice-wheat rotation (RWR) to conventional vegetable cultivation, especially vegetable cultivation in plastic sheds, readily causes soil structure degradation, and organic manure is commonly applied to mitigate such degradation. Although many studies have focused on changes in SOC properties or structural soil parameters, additional details about the changes, such as the relationships between SOC fractions and soil aggregates during unique land-use changes, are unknown. Here, we studied the changes in soil aggregation, and SOC parameters in 14-year-old plastic-shed vegetable fields (PVFs) and open-air vegetable fields (OVFs) covered with organic manure, with adjacent RWR fields serving as a control. The vegetable fields were converted from RWR fields. SOC fractions were analyzed by using 13C solid-state NMR spectroscopy, and the aggregate classes were divided as follows: large macro-aggregates (>2 mm), small macro-aggregates (2–0.25 mm), micro-aggregates (0.25–0.053 mm), and silt and clay particles ( PVF (43.21%) > OVF (35.37%), in contrast to the trends in the carbonyl C and aromatic C fractions. The aggregate-associated C, especially that associated with large macro-aggregates and micro-aggregates, in the PVFs was highest among the treatments. The O-alkyl C fraction in large macro-aggregates decreased in the order RWR (44.67%) > OVF (35.76%) > PVF (32.40%), consistent with the results for micro-aggregates. Furthermore, there was a significant (P ≤ 0.05) positive relationship between macro-aggregates (>0.25 mm) and the active C fractions, in contrast to the relationships with stable fractions. It suggested that plastic-shed cultivation might have a more positive effect than open-air cultivation on soil structure and the carbon stock when large amounts of organic manure are applied; moreover, the SOC quantity and quality affect soil aggregation differently.

The successful determination of soil properties by visible and near-infrared (Vis–NIR) reflectance spectroscopy (350–2500 nm) depends on the selection of an appropriate multivariate calibration technique. In this study, four multivariate techniques (principal components regression, PCR; partial least squares regression, PLSR; back-propagation neural network, BPNN; and support vector machine regression, SVMR) were compared with the aim of rapidly and accurately predicting soil properties, including soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and total potassium (TK). A total of 148 intact soil cores (8.4 cm internal diameter and 40 cm long) collected from paddy fields in Yujiang, China were used as the dataset for the calibration-validation procedure. The Vis–NIR spectra were measured on flat, horizontal surfaces of soil core sections at four depths (i.e., 5, 10, 15, and 20 cm) in the laboratory. The coefficient of determination (R2), root mean square error (RMSE), and residual prediction deviation (RPD) were used to evaluate the accuracy of the calibration models. Both the cross-validation and independent validation data sets showed that the SVMR models outperformed the BPNN, PCR, and PLSR models for SOM, TN, and TP predictions, whereas BPNN outperformed the other models for TK. Furthermore, BPNN and SVMR provided better performance than PCR and PLSR. The best predictions were obtained by the SVMR model for SOM (R2P = 0.88; RMSEP = 4.87; RPDP = 2.84) and TN (R2P = 0.86; RMSEP = 0.31; RPDP = 2.69), which were classified as good model predictions. The predictions of TP (R2P = 0.76; RMSEP = 0.080; RPDP = 2.03) by SVMR were approximately quantitative predictions, whereas the TK (R2P = 0.65; RMSEP = 3.54; RPDP = 1.65) prediction with BPNN was unsuccessful. Vis–NIR spectroscopy combined with SVMR has great potential to accurately determine the selected soil properties of intact soil cores of paddy fields.

In order to implement optimal farming practices for increasing soil organic carbon (SOC) in agro-ecosystems, there is a need for understanding how management practices and climate change alter SOC levels. This study quantified the influence of agricultural management practices and climatic factors on SOC changes in Eastern China’s upland-crop fields in northern Jiangsu Province for the period of 2010–2039, by using the DeNitrification-DeComposition (DNDC, version 9.5) model. We utilized the currently most detailed soil database, which is at a scale of 1:50,000, containing 17,024 soil polygons derived from 983 upland soil profiles. Across all the examined scenarios of agricultural management practices, our results show that the carbon sequestration potential in the upper layer soil (0–50 cm) of the study area varied from 6.93 to 155.11 Tg C during 2010–2039, with an average rate of 59 to 1317 kg C ha −1 year −1 . As a promising alternative, the combined scenario of crop residue return rate of 50% and farmyard manure incorporation rate of 50% is recommended for agricultural management practice in this region. Meanwhile, climate conditions play a significant role in the annual SOC changes as well. Air temperature increase of 2–4 °C leads to 3.41–7.51 Tg C decrease in SOC under conventional management for the entire study region. Decreasing or increasing precipitation by 20% would increase 0.57 Tg C or decrease 1.09 Tg C under the conventional management scenario, respectively. Additionally, among all the soil groups, the fluvo-aquic soils have the highest C sequestration rate in most scenarios. Our findings could be used to inform optimal agricultural management toward climate mitigation.

The aim of this study was to reveal the regional patterns and the primary controls of three pools of SOC in Chinese croplands in 2010. The samples were analysed based on a combination method of acid hydrolysis and CO2-C release during a 100-day incubation. The data from acid hydrolysis-incubation experiments were fitted to a three-pool first-order kinetics model that divided SOC into active (Ca), slow (Cs) and passive (Cp) pools. The results showed that soils in the eastern and southern China contained larger proportions of Ca and Cs but a smaller proportion of Cp in total SOC (P

Reporting modeling results with uncertainty information can benefit decision making by decreasing the extent that variability exerts a disproportionate influence on the options selected. For making decisions with more confidence, the uncertainty interval should be as narrow as possible. Here, the soil organic carbon (SOC) dynamics of the major paddy soil subgroup from 4 different paddy field regions of China (located in 4 counties under different climate-soil-management combinations) were modeled using the DeNitrification-DeComposition (DNDC) model for the period from 1980 to 2008. Uncertainty intervals associated with the SOC dynamics for these 4 subgroups were estimated by a long-term global sensitivity and uncertainty analysis (i.e., the Sobol? method), and their sensitivities to 7 influential factors were quantified using the total effect sensitivity index. The results, modeled with high confidence, indicated that in the past 29 years, the studied paddy soils in Xinxing, Yixing, and Zhongjiang counties were carbon (C) sinks, while the paddy soil in Helong County was a C source. The 3 C sinks sequestered 12.2 (5.4, 19.6), 17.1 (8.9, 25.0), and 16.9 (−1.2, 33.6) t C ha −1 (values in the parentheses are the 5th and 95th percentiles, respectively). Conversely, the C source had a loss of −5.4 (−14.2, 0.06) t C ha −1 in the past 29 years. The 7 factors, which changed with the climate-soil-management context, exhibited variable influences on modeled SOC. Measures with potential to conserve or sequestrate more C into paddy soils, such as incorporating more crop residues into soils and reducing chemical fertilizer application rates, were recommended for specific soils based on the sensitivity analysis results.

Changes in soil organic matter (SOM) can affect food security, soil and water conservation, and climate change. However, the drivers of changes in SOM in paddy soils of China are not fully understood because the effects of agricultural management and environmental factors are studied separately. Soil, climate, terrain, and agricultural management data from 6 counties selected based on representative soil types and cropping systems in China were used in correlation analysis, analysis of variance, and cforest modeling to analyze the drivers of changes in SOM in paddy soils in the Middle and Lower Yangtze River Plain from 1980 to 2011. The aims of this study were to identify the main factors driving the changes in SOM and to quantitatively evaluate their individual impacts. Results showed that the paddy SOM stock in the study area increased by 12.5% at an average rate of 0.023 kg m−2 year−1 over the 31-year study period. As a result of long-term rice planting, agricultural management practices had a greater influence than soil properties, climate, and terrain. Among the major drivers, straw incorporation, the most influential driver, together with fertilization and tillage practices, significantly increased the accumulation of SOM, while an increase in temperature significantly influenced SOM decomposition. Therefore, to confront the challenge of rising temperatures, it is important to strengthen the positive effects of agricultural management. Rational fertilizer use for stabilizing grain production and crop straw incorporation are promising measures for potential carbon sequestration in this region.

Spectral variable selection is widely accepted as an important step in the quantitative analysis of visible and near-infrared (Vis–NIR) reflectance spectroscopy (350–2500 nm), as it tends to have parsimonious data representation and can result in multivariate models with greater predictive ability. In this study, a total of 123 intact soil cores (8.4 cm internal diameter and 40 cm long) were collected from paddy fields in Yujiang, China. The Vis–NIR spectra, measured in the laboratory for flat, horizontal surfaces of soil core sections at two depths (5 cm and 10 cm), were used to estimate the rice root density by support vector machine regression (SVMR). In addition to full-spectrum SVMR (FS-SVMR), four spectral feature selection techniques (competitive adaptive reweighted sampling, CARS; genetic algorithm, GA; successive projections algorithm, SPA; and uninformative variable elimination, UVE) were applied with SVMR (i.e., CARS-SVMR, GA-SVMR, SPA-SVMR, and UVE-SVMR) to determine the technique with the most accurate predictions. The coefficient of determination ( R 2 ), root mean square error (RMSE), and residual prediction deviation (RPD) were used to evaluate the accuracy of the optimized calibration models. Based on the independent validation data set ( n = 73), the order of the prediction accuracy was CARS-SVMR ( R 2 P = 0.92; RMSE P = 2.56; RPD P = 3.42) > GA-SVMR ( R 2 P = 0.91; RMSE P = 2.92; RPD P = 2.99) > FS-SVMR ( R 2 P = 0.88; RMSE P = 4.28; RPD P = 2.83) > SPA-SVMR ( R 2 P = 0.87; RMSE P = 4.43; RPD P = 2.55) > UVE-SVMR ( R 2 P = 0.86; RMSE P = 4.49; RPD P = 2.51). The proposed method of CARS-SVMR had a relatively strong ability for spectral variable selection, with the fewest variables ( n = 60) and the shortest computation time (0.12 min), while retaining excellent prediction accuracy. In conclusion, SVMR combined with CARS has great potential to accurately determine the rice root density of intact soil cores of paddy fields using Vis–NIR spectroscopy.

Matching soil grid unit resolutions with polygon unit map scales is important to minimize the uncertainty of regional soil organic carbon (SOC) pool simulation due to their strong influences on the modeling. A series of soil grid units at varying cell sizes was derived from soil polygon units at six map scales, namely, 1:50 000 (C5), 1:200 000 (D2), 1:500 000 (P5), 1:1 000 000 (N1), 1: 4 000 000 (N4) and 1:14 000 000 (N14), in the Taihu Region of China. Both soil unit formats were used for regional SOC pool simulation with a DeNitrification-DeComposition (DNDC) process-based model, which spans the time period from 1982 to 2000 at the six map scales. Four indices, namely, soil type number (STN), area (AREA), average SOC density (ASOCD) and total SOC stocks (SOCS) of surface paddy soils that were simulated by the DNDC, were distinguished from all these soil polygon and grid units. Subjecting to the four index values (IV) from the parent polygon units, the variations in an index value (VIV, %) from the grid units were used to assess its dataset accuracy and redundancy, which reflects the uncertainty in the simulation of SOC pools. Optimal soil grid unit resolutions were generated and suggested for the DNDC simulation of regional SOC pools, matching their respective soil polygon unit map scales. With these optimal raster resolutions, the soil grid units datasets can have the same accuracy as their parent polygon units datasets without any redundancy, when VIV < 1% was assumed to be a criterion for all four indices. A quadratic curve regression model, namely, y =–0.80 × 10–6 x 2 + 0.0228x + 0.0211 (R 2 = 0.9994, P < 0.05), and a power function model R = 10.394Ŝ 0.2153 (R 2 = 0.9759, P < 0.05) were revealed, which describe the relationship between the optimal soil grid unit resolution (y, km) and soil polygon unit map scale (1:10 000x), the ratio (R, %) of the optimal soil grid size to average polygon patch size (Ŝ, km2) and the Ŝ, with the highest R 2 among different mathematical regressions, respectively. This knowledge may facilitate the grid partitioning of regions during the investigation and simulation of SOC pool dynamics at a certain map scale, and be referenced to other landscape polygon patches’ mesh partition.

Background The predictive value of adiposity indices and the newly developed index for cardiometabolic risk factors and cardiovascular diseases ( CVD s) remains unclear in the Chinese population. This study aimed to compare the predictive value of A Body Shape Index with other 5 conventional obesity‐related anthropometric indices (body mass index, waist circumference, hip circumference, waist‐to‐hip ratio, waist‐to‐height ratio) in Chinese population. Methods and Results A total of 44 048 participants in the study were derived from the baseline data of the PURE ‐China (Prospective Urban and Rural Epidemiology) study in China. All participants’ anthropometric parameters, CVD s, and risk factors (dyslipidemia, abnormal blood pressure, and hyperglycemia) were collected by standard procedures. Multivariable logistic regression models and receiver operator characteristic curve analysis were used to evaluate the predictive values of obesity‐related anthropometric indices to the cardiometabolic risk factors and CVD s. A positive association was observed between each anthropometric index and cardiometabolic risk factors and CVD s in all models ( P AUC s) for predicting dyslipidemia ( AUC s: 0.646, sensitivity: 65%, specificity: 44%), hyperglycemia ( AUC s: 0.595, sensitivity: 60%, specificity: 45%), and CVD s ( AUC s: 0.619, sensitivity: 59%, specificity: 41%). Waist circumference showed the best prediction for abnormal blood pressure ( AUC s: 0.671, sensitivity: 66%, specificity: 40%) compared with other anthropometric indices. However, the new body shape index did not show a better prediction to either cardiometabolic risk factors or CVD s than that of any other traditional obesity‐related indices. Conclusions Waist‐to‐height ratio appeared to be the best indicator for dyslipidemia, hyperglycemia, and CVD s, while waist circumference had a better prediction for abnormal blood pressure.

Soil nitrogen (N) plays a central role in soil quality and biogeochemical cycles. However, little is known about the distribution and spatial variability of the different fractions of soil N within entire soil profiles. This study aimed to investigate the potential of laboratory-based hyperspectral imaging (HSI) spectroscopy to retrieve and map total N (TN), available N (AvailN), ammonium N (NH4-N), nitrate N (NO3-N), and microbial biomass N (MBN) in soil profiles at a high resolution. HSI images of eleven intact soil profiles of 100 ± 5 cm depth from three typical soil types were recorded. A variety of nonlinear machine learning techniques, such as artificial neural networks (ANN), cubist regression tree (Cubist), k-nearest neighbour (KNN), support vector machine regression (SVMR) and extreme gradient boosting (XGBoost), were compared with a partial least squares regression (PLSR) to determine the most suitable model for the prediction of the various soil N fractions. Overall, the results showed that nonlinear techniques performed better than PLSR in most cases, with a high coefficient of determination (R2) and low root mean square error (RMSE). Among the models, SVMR was found to be superior to the other tested models for TN (R2P = 0.94, RMSEP = 0.17 g kg−1), AvailN (R2P = 0.94, RMSEP = 13.35 mg kg−1), NO3-N (R2P = 0.82, RMSEP = 7.31 mg kg−1), and NH4-N (R2P = 0.70, RMSEP = 1.51 mg kg−1) based on independent validation, whereas MBN (R2P = 0.63, RMSEP = 6.62 mg kg−1) was predicted best by KNN. In addition, SVMR required less computational time and was less sensitive to spectral noise. It can therefore be concluded that HSI spectroscopy combined with SVMR is suitable for the high-resolution mapping of various soil N fractions in soil profiles.

Process-based models such as CENTURY have been extensively validated for simulating soil organic carbon (SOC) dynamics at the homogeneous plot scale. However, considerable uncertainty may exist when upscaling a simulation from the plot scale to a larger scale because of variation in the model inputs. The objectives of this study were to assess the uncertainty of CENTURY-modeled SOC and to identify the most influential model inputs in various upland regions of China. Global sensitivity analysis was used to explore the sensitivity of CENTURY-modeled SOC to seven key model inputs. The uncertainties of the SOC simulated using various model inputs and climate-soil-management conditions were evaluated at 21 long-term monitoring sites located across upland areas in China. The identified sensitive model inputs differed among regions and periods due to diverse climate-soil-management conditions; nevertheless, initial SOC content (SOCi), soil clay content, and crop residue removal rate (Residuerr) were the most influential inputs. The site-to-region upscaling uncertainties remained moderately large (±42.7, ±49.4, and ±69.3 % at the 90, 95, and 100 % confidence levels, respectively) when currently available observation data were used. Therefore, the collection of detailed information on soil properties and crop residue removal, particularly legacy soil data such as the SOCi and clay content, is important for reducing the uncertainties in SOC modeling. Data on SOCi, Residuerr, and clay content need to be collected prior to other input data to reduce input-related uncertainty and thus to provide more reliable SOC assessment at the regional or national scale in China.

Understanding the impacts of climate change and agricultural management practices on soil organic carbon (SOC) dynamics is critical for implementing optimal farming practices and maintaining agricultural productivity. This study examines the influence of climatic variables and agricultural management on carbon sequestration potentials in Tai-Lake Paddy soils of China using the DeNitrification-DeComposition (DNDC, version 9.1) model, with a high-resolution soil database (1:50,000). Model simulations considered the effects of no-tillage, the application rates of manure, N fertilization, and crop residue, water management, and changes in temperature and precipitation. We found that the carbon sequestration potential in the top soils (0–30 cm) for the 2.32 Mha paddy soils of the Tai-Lake region varied from 4.71 to 44.31 Tg C under the feasible management practices during the period of 2001–2019. The sequestration potential significantly increased with increasing application of N-fertilizer, manure, conservation tillage, and crop residues, with an annual average SOC changes ranged from 107 to 121 kg C ha− 1 yr− 1, 159 to 326 kg C ha− 1 yr− 1, 78 to 128 kg C ha− 1 yr− 1, and 489 to 1005 kg C ha− 1 yr− 1, respectively. Toward mitigating greenhouse emissions and N losses, no-tillage and increase of crop residue return to soils as well as manure application are recommended for agricultural practice in this region. Our analysis of climate impacts on SOC sequestration suggests that the rice paddies in this region will continue to be a carbon sink under future warming conditions. Specifically, with rising air temperature of 2.0 °C and 4 °C, the average annual SOC changes were 52 and 21 kg C ha− 1 yr− 1, respectively.

The use of three conceptual pools for soil organic carbon (SOC) proposed by the CENTURY model to study soil organic C (SOC) dynamics helps to more clearly understand the mechanism of C sequestration and the stability of SOC pool in farmlands. We studied a typical rice-growing area, Chengdu Plain in southwestern China. Based on historical soil data collected in the early 1980s, 48 sampling points that include four major types of paddy soils from the surface layer (0–20 cm) and the subsurface layer (20–40 cm) were selected to collect soil samples (n = 96) in 2010. A 100-d laboratory incubation was conducted to measure the SOC decomposition rates at different times, and data from the incubation experiment were fitted to a three-pool first-order model that divided SOC pool into active (Cₐ), slow (Cₛ), and resistant (Cᵣ) SOC fractions. Based on these data, a universal predictive method for the concentrations of SOC fractions was developed and used to obtain the 1980s’ concentrations of SOC fractions. The results showed that an exponential function model (Dₛₒcₜ = a - b × cᵗ) can be used as the optimal prediction model for the SOC decomposition process. The Cₐ, Cₛ, and Cᵣ concentrations increased in surface and subsurface soils in the study area from 1980 to 2010. The increases of Cₛ and Cᵣ contributed to more than 90% of the increase in the paddy SOC pool, whereas the contribution of the Cₐ increase was less than 10%. Thus, the increase in the paddy SOC pool mainly derived from the increases of Cₛ and Cᵣ.

Long-term global sensitivity analyses have been made for DNDC modeling SOC.Six different uncertainty methods are compared for their suitability.Morris produced similar sensitivity results with fewer DNDC runs compared with Sobol'.Morris combined a user defined MSF or MC is recommended for uncertainty analysis. Process-based modeling is a powerful tool for identifying predominant factors that influence soil organic carbon (SOC) so that rational management decisions can be made for improving soil fertility and increasing carbon sequestration in agricultural soils. To achieve these goals, a sensitivity and uncertainty analysis of modeling output is required. Based on the data collected at a long-term observation site with a 21-year rice-bean planting history, two global sensitivity analysis (SA) methods and six uncertainty analysis (UA) methods were applied and compared for the DeNitrification-DeComposition (DNDC) model to simulate inter-annual SOC changes (dSOC). Morris and Sobol' SA methods were used to identify the most influential parameters, and then the dSOC uncertainty intervals estimated by Morris, Sobol', Morris and a joint use of Monte Carlo (MC) with the five most sensitive parameters considered (Morris-MC-5Fac), Morris and a joint use of MC with the four most sensitive parameters considered (Morris-MC-4Fac), DNDC embedded Most Sensitive Factor method (DNDC-MSF), and the user-modified Most Sensitive Factor method with the five most sensitive parameters considered (MSF-user-5Fac) were compared. Sensitivity analysis results indicated that the Morris and Sobol' methods produced similar sensitivity indices for 11 DNDC model input parameters. The initial SOC, bulk density, amount of manure applied, ratio of crop residue incorporated into soils, and amount of chemical fertilizer applied are the five most influential parameters on dSOC uncertainty at the site. In our case, Morris is recommended for a pure sensitivity analysis due to its low model running cost compared to that of Sobol'. Among the six uncertainty analysis methods, the Sobol' estimated uncertainty result is considered the most reliable, followed by that estimated with Morris-MC-5Fac, MSF-user-5Fac, Morris-MC-4Fac, Morris, and DNDC-MSF. DNDC-MSF has the lowest model running cost, followed by Morris, MSF-user-5Fac, Sobol', Morris-MC-4Fac, and Morris-MC-5Fac. Considering both the reliability of the uncertainty analysis results and the model running costs, MSF-user-5Fac is the most efficient. However, it should be noted that MSF-user-5Fac is not suitable for models in which the input parameters and modeling outputs are not monotonically related. For the latter models, Sobol' is a better choice. The information in this paper benefits DNDC users by providing guidance in proper sensitivity and uncertainty analysis method selection.

Using the DeNitrification-DeComposition (DNDC, version 9.5) model, we investigated the soil organic carbon (SOC) changes from 1980 to 2009 in Eastern China's upland-crop fields in northern Jiangsu Province. A currently most detailed high-resolution soil database, containing 17,024 polygons at a scale of 1:50,000, derived from 983 unique upland soil profiles, was used. A coarser county-level soil database was also used for a pair-wise simulation for comparison. We found that SOC changes modeled with the county-level soil database differ significantly from those with high-resolution soil data, with the deviation ranging from −64% to 8.0% in different counties. This implies that coarse soil data may lead to large biases in SOC simulation. With the high-resolution database, the model estimates a SOC increase of 37.89 Tg C in the top soils (0–50 cm) over the study area of 3.93 Mha for the past three decades, with an average rate of 322 kg C ha −1 year −1 . The SOC accumulation in the study region accounts for 10.2% of annual national carbon sequestration of upland soils, compared with the fraction of 3.7% in the total upland area of China. This underscores its significance to national climate mitigation. The annual SOC change varied between 61 to 519 kg C ha −1 year −1 , mainly driven by the variations in N-fertilizer and manure applications. This study highlights the significance of high-resolution soil databases in quantifying SOC changes. Our high-resolution estimates of SOC will support farming and carbon management in this region.

Agro-ecosystem models have been widely used to quantify soil organic carbon (SOC) dynamics based on digital soil maps. However, most of the studies use soil data of single or limited choices of map scales, thus the influence of map scales on SOC dynamics has rarely been quantified. In this study, six digital paddy soils databases of the Tai-Lake region in China at scales of 1:50,000 (P005), 1:200,000 (P02), 1:500,000 (P05), 1:1,000,000 (P1), 1:4,000,000 (P4), and 1:14,000,000 (P14) were used to drive the DNDC (DeNitrification & DeComposition) model to quantify SOC dynamics for the period of 2001⿿2019. Model simulations show that the total SOC changes from 2001 to 2019 in the top layer (0⿿30 cm) of paddy soils using P005, P02, P05, P1, P4, and P14 soil maps would be 3.44, 3.71, 1.41, 2.01, 3.57 and 0.10 Tg C, respectively. The simulated SOC dynamics are significantly influenced by map scales. Taking the total SOC changes based on the most detailed soil map, P005, as a reference, the relative deviation of P02, P05, P1, P4, and P14 were 7.9%, 58.9%, 41.6%, 3.9%, and 97.0%, respectively. Such differences are primarily attributed to missing soil types and spatial variations in soil types in coarse-scale maps. Although the relative deviation of P4 soil map for the entire Tai-Lake region is the lowest, substantial differences (i.e., 22⿿1010%) exist at soil subgroups level. Overall, soil map scale of P02 provides best accuracy for quantifying SOC dynamics of paddy soils in the study region. Considering the soil data availability of entire China, P1 soil map is also recommended. This study suggested how to select an appropriate scale of input soil data for modeling the carbon cycle of agro-ecosystems.

To improve our understanding of biomass allocation and soil carbon cycling in paddy fields, information on the root biomass of rice is fundamental. The commonly used conventional methods to study root biomass are difficult and time-consuming. In this study, visible and near-infrared (Vis–NIR) reflectance spectroscopy (350–2500 nm) was evaluated for the rapid analysis of rice root density from the flat, horizontal surface of a soil core section. A total of 123 intact soil cores (0–40 cm depth, with a 8.4 cm diameter) were collected from paddy fields in Yujiang, China, and the Vis–NIR reflectance was measured in the laboratory at two depths (5 and 10 cm). Three multivariate regression methods (principal component regression, PCR; partial least square regression, PLSR; and support vector machine regression, SVMR) were used to develop models to predict root density, and these models were compared to determine the one with the most accurate predictions. Based on the comparisons with both cross-validation and independent validation data sets, the SVMR model outperformed the PCR and PLSR models. The predictions of root density with the SVMR model were more accurate (coefficient of determination [R2] = 0.88; root mean square error [RMSE] = 4.28; ratio of standard deviation to RMSE [RPD] = 2.83; ratio of performance to inter-quartile distance [RPIQ] = 3.23; Slope = 0.80) than those with the PCR model (R2 = 0.81; RMSE = 5.58; RPD = 2.17; RPIQ = 2.47; Slope = 0.74) or the PLSR model (R2 = 0.82; RMSE = 5.22; RPD = 2.32; RPIQ = 2.65; Slope = 0.76), based on 73 independent validation samples. In conclusion, the Vis–NIR spectra acquired from the intact soil cores were used to accurately predict rice root density. Therefore, Vis–NIR spectroscopy combined with SVMR calibrations has the potential to detect root densities in paddy soils under field conditions.

Understanding the spatiotemporal distribution of soil organic carbon (SOC) and its controlling factors is extremely important for improving soil quality and developing sustainable management practices. We quantified spatiotemporal variations in SOC in three typical regions (Shuyang, Rugao, and Shanghai) in southeastern China during 1981–2011, by using geographically weighted regression (GWR), and explored the drivers with a geographical detector method. A total of 219 topsoil samples were collected in the three regions to measure the SOC in 2011, and a total of 109 SOC data for 1981 were obtained from the soil survey reports of Shuyang, Rugao, and Shanghai, which involved in the database of the second national soil survey of China. The results showed that the mean SOC contents in 2011 were 14.68 g kg−1, 9.55 g kg−1, and 18.00 g kg−1 in Shuyang, Rugao, and Shanghai, respectively. The topography (q = 0.60) and the sand content of the soil (q = 0.70) were the main drivers of the spatial variability in the SOC in Shuyang and Rugao, while the carbon inputs (q = 0.68) predominantly explained the spatial heterogeneity of the SOC in Shanghai. Significant increases in SOC storage occurred in Shuyang and Rugao from 1981 to 2011, with increase rates of 0.55 t ha−1 yr−1 and 0.26 t ha−1 yr−1, respectively. Land use change (dryland farming to rice cultivation) was identified as the largest driver of the SOC increases in Shuyang and Rugao (q values of 0.16 and 0.09, respectively), followed by increasing carbon inputs (0.14 and 0.07). However, the SOC storage in Shanghai rapidly decreased at a rate of −0.38 t ha−1 yr−1 during 1981–2011. The land use change from wetlands to rice cultivation was the primary reason for the decreasing SOC (q = 0.24), and a net decrease in carbon inputs between 1981 and 2011 was another main driver of the reduction in the SOC in Shanghai (q = 0.14). Our results from this study provide important information on the spatiotemporal changes in SOC and its drivers to the scientific community and decision-makers, for the development of management strategies to sustain soil fertility in many areas with rapid economic development and increasing populations.

Soil organic carbon (SOC) and its labile C fractions play a central role in soil quality and C cycles. This study aimed to investigate the potential of laboratory-based hyperspectral imaging (HSI) spectroscopy to predict and map SOC and its labile C fractions (e.g., dissolved organic C, DOC; readily oxidizable organic C, ROC; and microbial biomass C, MBC) in soil profiles with a high resolution. The HSI images were captured from 16 intact paddy soil profiles to a depth of 100 ± 5 cm from four typical parent materials. The linear (i.e., partial least squares regression, PLSR) and nonlinear (i.e., artificial neural networks, ANN; cubist regression tree, Cubist; Gaussian process regression, GPR; and support vector machine regression, SVMR) multivariate techniques were compared to assess their ability to map the soil C fractions in the profiles. A spectral variable selection technique (i.e., competitive adaptive reweighted sampling, CARS) was applied to these multivariate models (i.e., CARS-PLSR, CARS-ANN, CARS-Cubist, CARS-GPR, and CARS-SVMR). Overall, the results showed that the nonlinear models performed better than the PLSR models in most cases. All optimized multivariate models with CARS achieved prediction performances similar to the full spectrum models, with high Lin's concordance correlation coefficient (LCC) and low root mean square error (RMSE). CARS-SVMR used only 37–70 spectral variables and took less time-consuming on computations (

The impacts of rapid industrialization on agricultural soil cadmium (Cd) accumulation and their potential risks have drawn major attention from the scientific community and decision-makers, due to the high toxicity of Cd to animals and humans. A total of 812 topsoil samples (0&ndash, 20 cm) was collected from the southern parts of Jiangsu Province, China, in 2000 and 2015, respectively. Geostatistical ordinary kriging and conditional sequential Gaussian simulation were used to quantify the changes in spatial distributions and the potential risk of Cd pollution between the two sampling dates. Results showed that across the study area, the mean Cd concentrations increased from 0.110 mg/kg in 2000 to 0.196 mg/kg in 2015, representing an annual average increase of 5.73 &mu, g/kg. Given a confidence level of 95%, areas with significantly-increased Cd covered approximately 12% of the study area. Areas with a potential risk of Cd pollution in 2000 only covered 0.009% of the study area, while this figure increased to 0.75% in 2015. In addition, the locally concentrating trend of soil Cd pollution risk was evident after 15 years. Although multiple factors contributed to this elevated Cd pollution risk, the primary reason can be attributed to the enhanced atmospheric deposition and industrial waste discharge resulting from rapid industrialization, and the quick increase of traffic and transportation associated with rapid urbanization.

China's terrestrial ecosystems have functioned as important carbon sinks. However, previous estimates of carbon budgets have included large uncertainties owing to the limitations of sample size, multiple data sources, and inconsistent methodologies. In this study, we conducted an intensive field campaign involving 14,371 field plots to investigate all sectors of carbon stocks in China's forests, shrublands, grasslands, and croplands to better estimate the regional and national carbon pools and to explore the biogeographical patterns and potential drivers of these pools. The total carbon pool in these four ecosystems was 79.24 ± 2.42 Pg C, of which 82.9% was stored in soil (to a depth of 1 m), 16.5% in biomass, and 0.60% in litter. Forests, shrublands, grasslands, and croplands contained 30.83 ± 1.57 Pg C, 6.69 ± 0.32 Pg C, 25.40 ± 1.49 Pg C, and 16.32 ± 0.41 Pg C, respectively. When all terrestrial ecosystems are taken into account, the country's total carbon pool is 89.27 ± 1.05 Pg C. The carbon density of the forests, shrublands, and grasslands exhibited a strong correlation with climate: it decreased with increasing temperature but increased with increasing precipitation. Our analysis also suggests a significant sequestration potential of 1.9-3.4 Pg C in forest biomass in the next 10-20 years assuming no removals, mainly because of forest growth. Our results update the estimates of carbon pools in China's terrestrial ecosystems based on direct field measurements, and these estimates are essential to the validation and parameterization of carbon models in China and globally.

Rising temperatures and elevated atmospheric CO2 are two factors that simultaneously affect the dynamics of soil organic carbon (SOC). This study separately examines the effects arise from these two factors in Tai-Lake Paddy soils using DeNitrification–DeComposition (DNDC) model, with the currently most detailed soil database for the paddy region of China. The soil database is at a scale of 1:50,000, containing 52,034 paddy soil polygons derived from 1107 unique paddy soil profiles. Our simulations indicate that, the SOC in the top soils (0-30 cm) increases 0.83, 1.09, 1.32, and 1.51 Tg C under conventional management (3.44 Tg C) in the 2.32 Mha paddy soils of the Tai-Lake region from 2001 to 2019, respectively, with the atmospheric CO2 concentration increases at 1.5, 2.0, 2.5, and 3.0 times the normal rate (1.9 ppm year−1). By contrast, with rising air temperature of 0.5, 1.0, 1.5, 2.0, 3.0, and 4 °C, the SOC decreases 0.09, 0.54, 0.69, 1.13, 1.80, and 2.51 Tg C under conventional management, respectively. Thus, the effect of carbon sink induced from CO2 fertilization at the 2.0 times normal CO2 concentration increase rate could generally offset the effect of carbon source resulted from a 2.0 °C air temperature increase. In addition, the paddy soils in this region tend to persistently be a sink of atmospheric CO2 under warming and elevated CO2 scenarios, even if when the air temperature has increased by 4 °C. These results suggest that SOC storage in paddy soils of this region is prone to benefit from future global climate change and this carbon sequestration potential in the agro-ecosystems is likely to contribute to climate mitigation under current agricultural practices, despite any negative effects derived from warming. As a representative of paddy soils in eastern China, the insights gained from the Tai-Lake region may be potentially transferable to other paddy soils in eastern China where 95% of the total of China is located.

Large dam projects attract worldwide scientific attention due to their environmental impacts and socioeconomic consequences. One prominent example is the Three Gorges Dam (TGD) at the Yangtze River in China. Due to considerable resettlements, large-scale expansion of infrastructure and shifts in land use and management, the TGD project has irreversible impacts on the Upper Yangtze River Basin and strongly challenges the environmental conditions of this fast-developing region. Soil erosion and landslides are major geo-hazards. Knowing the extent and consequences of those geo-hazards for the landscape is essential to predict and evaluate their risk potential and allows for the development of strategies for a sustainable future land use in the Three Gorges Region (TGR). In this context, our research objectives are (1) to better understand the mechanisms of soil erosion, landslides, and diffuse matter fluxes in the TGR and their anthropogenic and environmental control factors, (2) to predict their hazard potential by combining spatial and temporal, scenario-driven high-resolution modeling in combination with multi-scale earth observation data, and (3) to develop a multi-component approach for the assessment and monitoring of geogene structures and processes. The paper describes the workflow of the project and introduces case studies, representing the current state of our research. It is shown that land-use changes as well as the water-level fluctuations of the reservoir are the crucial drivers for the soil erosion and landslide hazard. Furthermore, we present a framework aiming at the establishment of a monitoring and measuring network as well as an early warning system.

Given the positive effects of mediating the growth of greenhouse gases in the atmosphere, interest in soil carbon stock dynamics has greatly increased. Several questions still exist as to whether irrigation with sediment laden water benefits carbon sequestration in soil profiles. This case study documented how long-term irrigation with sediment laden water from the Yellow River affected soil carbon sequestration in the Ningxia Irrigation Zone, China. The study included eight durations of irrigation management (10, 20, 30, 50, 280, 1300, 2100, and 2200 years) and five soil types. Soil samples from 44 profiles were collected to a depth of 100 cm, divided into four layers (0–20, 20–30, 30–60, 60–100 cm), and analyzed for soil organic carbon (SOC). SOC stocks both of soil profiles (0–100 cm) and irrigation-silted soil (ISS) layer, were 28.2 Tg C and 24.1 Tg C, respectively. The ISS layer was formed by the overlapping actions of irrigation and tillage, manure addition, and sediment silting as a result of long-term irrigation from the sediment laden water of the Yellow River. Compared to non-irrigated and non-cultivated control soils of similar depths and thicknesses, SOC stocks of the ISS layer increased 16.9 Tg C, and accounted for 89.9% of a total increment of 18.8 Tg C in the 0–100 cm layer of irrigated cropland soils. A significant correlation was found between the SOC density increment of the ISS layer and the number of irrigation years. Long-term irrigation with sediment laden Yellow River water greatly influenced SOC stocks, especially in the ISS layer, which plays an important role in soil carbon sequestration.

Soil erosion is the most severe environmental problem in the red soil region of southern China. Erosion has been significantly reduced over the last 30 years through the deployment of a massive government re-forestation program. Nevertheless, soil erosion is still severe in some areas, and an efficient method for assessing soil erosion under secondary forest canopy is needed. Traditionally the vegetation indices derived from remotely sensed imagery have been used for identifying eroded areas. However, under high density forest canopy (HDFC) their applicability suffers due to biomass light absorption, which varies by canopy structure. A mapping method was developed by integrating remote sensing parameters to identify eroded areas. The remotely sensed vegetation indices, vegetation fractional canopy (VFC) and leaf area index (LAI) were calibrated based on soil erosion measurements from previous runoff plot experiments and extrapolated from USLE modeling to a regional scale. Using vegetation restoration degree (VRD), based on VFC (VRDVFC = VFC/VITVFC) and LAI (VRDLAI = LAI/VITLAI), soil erosion under HDFC was identified. Results indicate that the threshold value of VFC (VITVFC) and LAI (VITLAI) ranged from 0.45 to 0.60, and from 1.3 to 2.7, respectively. Secondary forest associated with VRDVFC > 100% or VRDLAI > 100% occupied 75.8% and 37.8% of the total study area, respectively. About 50% of the area distinguished as being eroded by LAI, was mapped as having no obvious erosion by VFC. LAI based mapping had a precision of 96.7% according to field validation. The eroded areas were primarily distributed in locations with elevation between 300 to 500 m and slope angles below 25°. The present method for distinguishing soil erosion under HDFC by combining VRDVFC and VRDLAI is effective and can be used for operational erosion monitoring in the red soil region of southern China.

A proper soil raster unit resolution for grid sampling design is important to estimate the soil organic carbon (SOC) pool at certain map scales, which is related to the soil sampling density and the accuracy of the estimation. A series of raster soil unit data sets at varying resolutions were derived from different vector soil unit data sets at six map scales of 1:50,000, 1:200,000, 1:500,000, 1:1,000,000, 1:4,000,000, and 1:14,000,000 in the Tai-Lake region of China. Four indices—soil type number (STN) and area (AREA), average SOC density (ASOCD), and total SOC stocks (SOCS) of surface paddy soils—were attributed from all these vector and raster units data sets. Subjected to the four index values (IV) from parent vector unit data set, the relative variability (VIV, %) from raster unit data set was used to assess its accuracy and redundancy, which reflects uncertainty and workload of SOC estimation, respectively. Optimal raster unit resolutions were generated and suggested for each map scale’s SOC estimation, in which the soil raster unit data set can hold the same accuracy as its parent vector unit data set without any redundancy when VIV < 1% of all the four indices was assumed as criteria to the assessment. A relationship between map scale (1:x) of soil vector unit and its optimal grid resolution (y, km) was found to be: y = −8.03 × 10⁻⁶x² + 0.0256x- 0.087 (R² = 0.998, p < 0.05). The results may serve for soil unit conversion from vector to raster and soil grid sampling design at a certain map scale in the investigation of regional SOC pool.

The conversion of cereal to vegetable represents a significant shift in land use in China, and it causes significant changes in soil properties. Most studies have only focused on chemical or biological properties; few have investigated soil structure. Soil structure, especially macropore space, is very important for plant growth because of its relation to important soil functions and processes, such as gas diffusion and water permeability. The objective of this study was to assess the effect of land use conversion from rice to vegetable on soil macropores (>50 μm) measured by computed tomography (CT) and to examine the relationships between CT-measured pore characteristics and soil chemical properties. By using space instead of time, we sampled three land uses – rice/wheat rotation (RWR), open-field vegetable (OFV) and plastic-greenhouse vegetable (PGV) – in a tilled and plow pan layer in a suburban area of Nanjing, China, and analyzed the basic physicochemical properties and CT-measured macropore characteristics. The results showed that the tilled layer soil had a significant response to the land use change. The macroporosity decreased from 11.5% under RWR to 8.0% under OFV and 5.8% under PGV, and the decreased portion consisted mainly of elongated large macropores (>1000 μm). In addition, the macropore morphology of vegetable fields also showed degradation, with a higher degree of anisotropy (DA) and lower fractal dimension (FD) and connectivity compared to those under RWR, but PGV experienced a higher degree of degradation than did OFV. This study also showed that soil structure degradation was significantly correlated with decreasing soil organic matter (SOM). Increasing the amount of organic fertilizer applied might improve the SOM content and therefore improve the soil structure. Based on the linear regression equation, adding 1 g of SOM per kilogram of soil can improve the macroporosity by 0.54 m3 m−3.

Land-use/land-cover changes (LUCCs) have links to both human and nature inter- actions. China's Land-Use/cover Datasets (CLUDs) were updated regularly at 5-year inter- vals from the late 1980s to 2010, with standard procedures based on Landsat TM\ETM+ im- ages. A land-use dynamic regionalization method was proposed to analyze major land-use conversions. The spatiotemporal characteristics, differences, and causes of land-use changes at a national scale were then examined. The main findings are summarized as fol- lows. Land-use changes (LUCs) across China indicated a significant variation in spatial and temporal characteristics in the last 20 years (1990-2010). The area of cropland change de- creased in the south and increased in the north, but the total area remained almost un- changed. The reclaimed cropland was shifted from the northeast to the northwest. The built-up lands expanded rapidly, were mainly distributed in the east, and gradually spread out to central and western China. Woodland decreased first, and then increased, but desert area was the opposite. Grassland continued decreasing. Different spatial patterns of LUC in China were found between the late 20th century and the early 21st century. The original 13 LUC zones were replaced by 15 units with changes of boundaries in some zones. The main spatial characteristics of these changes included (1) an accelerated expansion of built-up land in the

The 3-D spatial distributions of vegetation are of great significance for water and soil conservation but are rarely concerned in literatures. The live vegetation volume (LVV) was used to relate to water/soil loss under 144 natural erosive rainfall events from 2007 to 2010 in a typical water-eroded area of southern China. Quadratic polynomial regression models were established for five pure tree ( Pinus massoniana Lamb) plots between LVV and water (runoff)/soil conservation effects (RE/SE). RE/SE corresponds to the ratios of runoff depth/soil loss of the pure tree plots to that of the control plot under each rainfall event. Increasing LVV exhibits descending (DS), descending-ascending (DA), ascending-descending (AD), and ascending (AS) trends in the LVV–RE and LVV–SE curves. The effects of soil conservation on the plots were generally more noticeable than the effects of water conservation, and most of the RE and SE values reflected the positive effects of water and soil conservation. The effects were mainly positive under heavy rains (e.g., rainfall erosivity, R = 140 MJ mm ha −1 h, maximum 30 min intensity, I 30 = 16 mm h −1 ), whereas the effects were mainly negative under light rains (e.g., R = 45 MJ mm ha −1 h, I 30 = 8 mm h −1 ). The trees' water/soil conservation effects notably transformed when rainfall erosivity and intensity were lower than the positive or negative effects to a certain threshold. About 50% rainfall events led to obvious transform effects when LVVs were near 0.5 or 0.6. These results are able to aid in the decision making on the forest reconstruction in water-eroded areas.

The agricultural soil carbon pool plays an important role in mitigating greenhouse gas emission and understanding the soil organic carbon-climate-soil texture relationship is of great significance for estimating cropland soil carbon pool responses to climate change. Using data from 900 soil profiles, obtained from the Second National Soil Survey of China, we investigated the soil organic carbon (SOC) depth distribution in relation to climate and soil texture under various climate regimes of the cold northeast region (NER) and the warmer Huang-Huai-Hai region (HHHR) of China. The results demonstrated that the SOC content was higher in NER than in HHHR. For both regions, the SOC content at all soil depths had significant negative relationships with mean annual temperature (MAT), but was related to mean annual precipitation (MAP) just at the surface 0–20 cm. The climate effect on SOC content was more pronounced in NER than in HHHR. Regional differences in the effect of soil texture on SOC content were not found. However, the dominant texture factors were different. The effect of sand content on SOC was more pronounced than that of clay content in NER. Conversely, the effect of clay on SOC was more pronounced than sand in HHHR. Climate and soil texture jointly explained the greatest SOC variability of 49.0% (0–20 cm) and 33.5% (20–30 cm) in NER and HHHR, respectively. Moreover, regional differences occurred in the importance of climate vs. soil texture in explaining SOC variability. In NER, the SOC content of the shallow layers (0–30 cm) was mainly determined by climate factor, specifically MAT, but the SOC content of the deeper soil layers (30–100 cm) was more affected by texture factor, specifically sand content. In HHHR, all the SOC variability in all soil layers was predominantly best explained by clay content. Therefore, when temperature was colder, the climate effect became stronger and this trend was restricted by soil depth. The regional differences and soil depth influence underscored the importance of explicitly considering them in modeling long-term soil responses to climate change and predicting potential soil carbon sequestration.

Accumulation and potential health risk of cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn) in a plot-scale vegetable production peri-urban area near Nanjing city, China was investigated through element balance method, model simulation and dietary risk assessment. The heavy metals accumulated in the surface soils were due to long-term and heavy application of organic fertilizers, among which the accumulation of Cu and Zn were greater than those of Cd and Pb. The result of a mass balance model simulation indicated that intensive vegetable production would result in accumulation of Cd, Pb, Cu and Zn in soils exceeding the target values in 55, 36, 34 and 71 years, respectively. The estimated dietary intakes of Cd, Pb, Cu, and Zn were far below the tolerable limits and the hazard quotient values were below one for both children and adults. Although there is no imminent health risk from heavy metals through vegetable consumption, more attention should be paid to the long-term accumulation and risk, especially for children.