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Quantifying soil organic carbon (SOC) decomposition under warming is critical to predict carbon-climate feedbacks. According to the substrate regulating principle, SOC decomposition would decrease as labile SOC declines under field warming, but observations of SOC decomposition under warming do not always support this prediction. This discrepancy could result from varying changes in SOC components and soil microbial communities under warming. This study aimed to determine the decomposition of SOC components with different turnover times after subjected to long-term field warming and/or root exclusion to limit C input, and to test whether SOC decomposition is driven by substrate lability under warming. Taking advantage of a 12-year field warming experiment in a prairie, we assessed the decomposition of SOC components by incubating soils from control and warmed plots, with and without root exclusion for 3 years. We assayed SOC decomposition from these incubations by combining inverse modeling and microbial functional genes during decomposition with a metagenomic technique (GeoChip). The decomposition of SOC components with turnover times of years and decades, which contributed to 95% of total cumulative CO2 respiration, was greater in soils from warmed plots. But the decomposition of labile SOC was similar in warmed plots compared to the control. The diversity of C-degradation microbial genes generally declined with time during the incubation in all treatments, suggesting shifts of microbial functional groups as substrate composition was changing. Compared to the control, soils from warmed plots showed significant increase in the signal intensities of microbial genes involved in degrading complex organic compounds, implying enhanced potential abilities of microbial catabolism. These are likely responsible for accelerated decomposition of SOC components with slow turnover rates. Overall, the shifted microbial community induced by long-term warming accelerates the decomposition of SOC components with slow turnover rates and thus amplify the positive feedback to climate change.

In agro‐ecosystems, fertilization practices must accomplish high and stable crop productivity, with maximum soil organic carbon (SOC) sequestration to address climate change and food security challenges. However, the impacts of these practices on SOC and crop yields are variable over the long‐term duration, and an improved understanding of the factors influencing SOC sequestration and sustainable productivity is still needed to provide evidence‐based management decisions. Therefore, we conducted a meta‐analysis to evaluate the impact of long‐term (≥10 years) application of different fertilizer management practices adapted across China on crop productivity, yield sustainability, and SOC sequestration. Results indicated that unbalanced mineral fertilizer (UMF), balanced mineral fertilizer (BMF), organic fertilizers (OF), combined unbalanced mineral and OF, and combined balanced mineral and organic fertilizers (BMOF) significantly enhanced the grain yield, and SOC sequestration compared with control (p <.05). For UMF, the increases in SOC and grain yields were least among fertilization practices. Comparing OF, BMF mostly produced more grain yields, but with a slight increase in C sequestration. Highest SOC sequestration rate of 0.43 Mg C ha−1 yr−1 was recorded in BMOF, among all the treatments. The data obtained indicated that SOC sequestration is highly time‐dependent. Irrespective of fertilization mode, SOC gradually increased and attained the peak of sequestration rate in the initial two decades rather than at later stages of fertilizer addition. The linear fitted model indicated that an increase in SOC sequestration benefits sustainable productivity. The available data indicate that crop yields can be improved by 143 kg ha−1 for rice (Oryza sativa), 255 kg ha−1 for maize (Zea mays), and 202 kg ha−1 for wheat (Triticum aestivum) with every 1 Mg ha−1 increase in SOC stock by fertilization in the root zone. In crux, BMOF can maintain and improve soil quality while producing high and stable crop yields. [ABSTRACT FROM AUTHOR]

Highlights • Manure and synthetic fertilizer accounted for 39% and 21% of crop yields. • Synthetic fertilizer affected yields by weakly increasing soil nutrients and decreasing SOC and pH. • Manure affected yields by strongly increasing soil nutrients, SOC and pH. Abstract Fertilization is an important management strategy for crop yields by mediating soil fertility. However, rare studies quantitatively assessed the interactions among fertilization, crop yields, and soil fertility. Here, data from a 25-year fertilization experiment in the humid subtropical region of Southern China were used to evaluate and quantify the effect of fertilization on crop yields via soil fertility. Seven treatments were chosen: CK (non-fertilizer); N (synthetic nitrogen); NP (synthetic N and phosphorus); NPK (synthetic N, P and potassium); NPKM 1 (synthetic NPK with manure); 1.5NPKM 1 (1.5 times of NPKM 1); and M 2 (manure alone). Overall, the crop yields of wheat and maize under manure (1.36–1.58 and 3.85-5.82 Mg ha−1) were higher than those under CK (0.34 and 0.25 Mg ha−1) and synthetic fertilized treatments (0.27–0.97 and 0.48–2.65 Mg ha−1), as the averaged of 1991–2015. Higher SOC stocks were found under the NPKM 1 , 1.5NPKM 1 , and M 2 treatments with a pronounced increase in SOC over the first 10 years and stable over the last 15 years. By the boosted regression trees, manure, synthetic fertilizer and soil properties (SOC storage, soil pH, and soil nutrients) accounted for 39%, 21%, and 40% of the variation of the relative yield, respectively. Path analysis identified a network of inter-relations of manure, synthetic fertilizer, and soil properties in the relative yields. Compared to synthetic fertilized treatments, manure application strongly and positively affected the relative yield by increasing SOC storage, soil nutrients, and soil pH (path coefficients: 0.90, 0.88, and 0.76). These factors explained 72% of the crop yields' variance. These results suggest that manure application is a viable strategy for regulating crop yields due to its improvement in soil fertility. [ABSTRACT FROM AUTHOR]

Abstract: Long-term fertilization has a significant impact on total soil organic carbon (SOC) stock. However, fertilization impact on physical fractions of SOC is still poorly understood for red soils in southern China. This study assessed the impact of 17years (1990–2007) of long-term fertilization on the changes in different SOC fractions under an intensive maize (Zea mays L)–wheat (Triticum Aestivium L) cropping system in a red soil of southern China through various treatments: the unfertilized control (CK), the recommended applied rates of N (N), NP (NP), NPK (NPK), NPK+manure (NPKM), NPK+straw (NPKS) and manure only (M), and a 150% recommended applied rate of NPK+manure (1.5NPKM). Soil samples from 0 to 20cm soil layer taken in September, 2007, were separated into free particulate organic C (fPOC), intra-microaggregate particulate organic C (iPOC), and mineral associated organic C (MOC) with physical fractionation. In comparison with CK, all the C fractions and maize and wheat yields were significantly increased, except for N and NP treatments. The treatments with manure (M, NPKM, and 1.5NPKM) showed higher C sequestration rates in MOC (323–515kgha−1 yr−1), fPOC (291–408kgha−1 yr−1) and iPOC (162–179kgha−1 yr−1). It was estimated that 8.0 to 35.7% of the gross C input from manure and crop residues over a period of seventeen years contributed to the increase of total SOC stock. Both MOC C sequestration efficiency (CES) and C sequestration distribution (CSD) were the highest among the C fractions for all the treatments. Significantly positive linear correlations were observed between accumulated C sequestrations in all fractions with gross C input and both maize and wheat yields. Our result indicated that MOC was the primary fraction of C sequestration in the red soils. The most efficient fertilization practice for sequestering C in each fraction in the red soils was continuous applications of either manure or manure plus mineral fertilizers. [Copyright &y& Elsevier]

We compared predictions of the modified Rothamsted Carbon Model (RothC) for paddy soils (RothC-26.3_p), with decomposition rate constants set at 0.2 and 0.6 times the values in the original RothC-26.3 for submerged and drained periods, respectively, with the results of five long-term field studies in southern China. These field studies included two paddy-upland rotation sites (Chongqing and Wuchang) and three double rice cropping sites (Wangcheng, Nanchang, and Jinxian). Several treatments (no fertilizer, inorganic fertilizer, and inorganic fertilizer with organic amendments such as straw, green manure, and farmyard manure) were tested at each site. RothC-26.3_p satisfactorily simulated the observed changes in soil organic carbon (SOC) at all paddy-upland rotation sites and in all plots without organic matter application at the double rice cropping sites, but overestimated SOC in plots with organic matter application at double rice cropping sites. We conclude that RothC-26.3_p is suitable for use in China with paddy-upland rotation management and with the regime based on relatively low carbon input at double rice cropping sites. However, for systems with large carbon inputs, RothC needs further modification. [ABSTRACT FROM PUBLISHER]

Long-term use of artificial fertiliser has a significant impact on soil organic carbon (SOC). We used physical–chemical fractionation methods to assess the impact of long-term (26 years) fertilisation in a maize cropping system developed on Brown Earth in Northeast China. Plot treatments consisted of control (CK); nitrogen (N) fertiliser (N2); low-level organic manure combined with inorganic N and phosphorus (P) fertiliser (M1N1P1); medium-level organic manure combined with inorganic N fertiliser (M2N2); and high-level organic manure combined with inorganic N and P fertiliser (M4N2P1). Our objectives were to (1) determine the contents of and variations in the SOC fractions; (2) explore the relationship between total SOC and its fractions. In treatments involving organic manure (M1N1P1, M2N2, and M4N2P1), total SOC and physically protected microaggregate (μagg) and μagg occluded particulate organic carbon (iPOC) contents increased by 9.9–58.9%, 1.3–34.7%, 29.5–127.9% relative to control, respectively. But there no significant differences ( P > 0.05) were detected for the chemically, physically–chemically, and physically–biochemically protected fractions among the M1N1P1, M2N2, and M4N2P1 treatments. Regression analysis revealed that there was a linear positive correlation between SOC and the unprotected coarse particulate organic carbon (cPOC), physically protected μagg, and iPOC fractions ( P < 0.05). However, physically–chemically, and physically–biochemically protected fractions responded negatively to SOC content. The highest rate of C accumulation among the SOC fractions occurred in the cPOC fraction, which accounted for as much as 32% of C accumulation as total SOC increased, suggesting that cPOC may be the most sensitive fraction to fertiliser application. We found that treatments had no effect on C levels in H-μsilt and NH-μsilt, indicating that the microaggregated silt C-fractions may have reached a steady state in terms of C saturation in the Brown Earth of Northeast China. [ABSTRACT FROM AUTHOR]

The carbon sequestration efficiency of manure (CSE-manure) is critical for the accurate estimation of manuring-induced changes in soil organic carbon (SOC). However, the mechanisms of large-scale spatiotemporal changes in CSE-manure and their crucial drivers are unclear. To investigate these under various manure regimes, we performed field observation and collected relevant data using 1023 fields across China's main cropland, as well as collected data on high-resolution climate and soil properties. The experimental durations significantly (P < 0.001) affected CSE-manure. The CSE-manure values were 31.4% ± 13.4 (mean ± SD), 19.2% ± 10.3%, and 16.1% ± 9.4 at the experimental durations of < 10, 10–20, and > 20 years, respectively. In addition, the manure sources significantly affected CSE-manure. The CSE-manure values of the manures from horse (27.9% ± 19.0) and sheep (26.9% ± 11.0) and farmyard manure (25.7% ± 14.8) were higher than those of the manures from pig (19.8% ± 15.4), poultry (19.1% ± 10.58), and cattle (23.1% ± 13.1). The CSE-manure values varied as per the region; the values were higher in North China than in South China. Of all the investigated variables, carbon and nitrogen input from manure, soil bulk density, annual average air temperature and precipitation, and initial SOC and soil clay content were the most important drivers of CSE-manure. The results suggested that carbon sequestration potential was higher in the northeast region. The spatiotemporal CSE-manure values under various climate conditions were predicted using trained machine learning models. Simulation results suggested that by 2100, the rate of decrease in CSE-manure will be higher at RCP (Representative Concentration Pathways) 8.5, and climate change will have a great impact on CSE-manure due to high warming effects. • The CSE-manure was decreased with the increase of experimental durations. • The CSE-manure values varied in different regions, with higher values in North than in South China. • Manure-C and N, soil bulk density, climate were the important drivers of CSE-manure. [ABSTRACT FROM AUTHOR]

(a) Distributions of mean stocks of soil organic carbon (SOC), peodgenic carbonate (PIC) and lithogenic carbonates (LIC) over 0–100 cm in the north China, and spatial distributions of (b) SOC and (c) PIC over 0–100 cm in cropland of the North China Plain, and (d) the relationship between PIC and SOC stocks. • PIC stock was significantly larger than SOC stock over 0−100 cm in the cropland of the North China Plain. • There was a significant positive correlation between PIC and SOC stocks. • Intensive cropping resulted in an increase in both SOC and PIC stocks in the semi-humid region. There is evidence of higher levels of pedogenic carbonate (PIC) than soil organic carbon (SOC) in cropland, and a positive relationship between PIC and SOC in salt-affected soils of arid and semi-arid regions. This study is designed to test the hypothesis that PIC is influenced by intensive cropping and salinization in semi-humid regions, in which soil carbonate (SIC) often exceeds SOC. We select a typical cropland with a maize-wheat rotation in the North China Plain, which covers two distinct regions, i.e. the Hebei Plain (HBP) under intensive cropping and the Yellow River Delta (YRD) under soil salinization. Our data show large variations in soil carbon stocks, with slightly higher values for PIC (3.9–14.5 kg C m−2) relative to those of SOC (2.2–9.2 kg C m−2) in the top 1 m. On average, SOC stock is 5.65 kg C m−2 in the YRD, which is slightly lower than in the HBP (6.21 kg C m−2); SIC is significantly higher in the YRD (16.9 kg C m−2) relative to the HBP (13.7 kg C m−2). However, PIC stock is smaller in the YRD (8.67 kg C m−2) relative to the HBP (9.41 kg C m−2). Despite no clear SIC-SOC relationship, there exists a significant positive correlation (P < 0.01) between PIC and SOC stocks in the study area. The PIC:SOC ratio is generally greater than one over a 0–100 cm layer in the majority of croplands in the north China, with larger ratios in the salt-affected soils. Our analyses suggest that the formation and storage of PIC are regulated by levels of SOC and Ca2+/Mg2+ in soil profiles, and there is large potential for enhancing carbon sequestration as carbonate under intensive cropping through sound management in the cropland of arid, semi-arid and semi-humid regions. [ABSTRACT FROM AUTHOR]

Abstract Application of livestock manure has been recognized as an important strategy for enhancing soil organic carbon (SOC) stocks. However, the magnitude of manure application impacts on SOC changes as compared with conventional mineral fertilizers still needs to be better assessed. In this study, we conducted a meta-analysis to address the effects of various fertilization practices on SOC changes in China's arable topsoil. The analysis was based on 148 peer reviewed articles reporting 69 sites and 729 observations with an average experimental duration of 18 years across China. We compared the response of SOC content to application of manure alone (M) or manure plus mineral fertilizers (NPKM) with the SOC response to NPK or no fertilizers (Control). We systematically analyzed how SOC responses were influenced by different environmental and management factors (land use, climate and soil properties, etc.). First, the retention coefficient of manure was used to present the percentage of C input from manure "converted" to SOC. Compared to Control, on average, manure had C-retention coefficients of 31% ± 12% (95% Confidence Interval, CI) and 18% ± 2% for the experimental duration of ≤10 years and >10 years, respectively. When compared to NPK, manure had C-retention coefficients of 29% ± 13% and 9% ± 3% for the experimental duration of ≤10 years and >10 years, respectively. In addition, compared to Control and NPK, application of manure increased SOC content by 0.23–0.26 and 0.18–0.19 g kg−1 yr−1, respectively. The results also indicated that the mean differences of SOC change between the treatments with or without manure application were mainly controlled by soil properties (28–43%) and anthropogenic farming practices (21–27%). Our results highlight the significance of improving or maintaining SOC stocks by manure applications, and provide insights for making manure application recommendations or guidelines to improve SOC stocks of China's cropland based on soil properties, climatic conditions and management practices. Graphical abstract Soil factors and anthropogenic practices explained 49–70% of SOC changes induced by manure. REF-zero (a): manure vs. no fertilizer; REF-min (b): manure vs. mineral fertilizer. S: soil factors; P: anthropogenic farming practices; C: climate. Unlabelled Image Highlights • Manure increased SOC content by 0.23–0.26 g kg−1 yr−1 compared to unfertilized soils. • Manure increased SOC content by 0.18–0.19 g kg−1 yr−1 compared to mineral fertilizers. • Manure-C retention coefficient of 9–31% could be estimated across China's arable land. • Soil factors and anthropogenic practices explained 49–70% of SOC changes induced by manure. [ABSTRACT FROM AUTHOR]

This study analyzes the influence of various fertilizer management practices on crop yield and soil organic carbon (SOC) based on the long-term field observations and modelling. Data covering 11 years from 8 long-term field trials were included, representing a range of typical soil, climate, and agro-ecosystems in China. The process-based model EPIC (Environmental Policy Integrated Climate model) was used to simulate the response of crop yield and SOC to various fertilization regimes. The results showed that the yield and SOC under additional manure application treatment were the highest while the yield under control treatment was the lowest (30%–50% of NPK yield) at all sites. The SOC in northern sites appeared more dynamic than that in southern sites. The variance partitioning analysis (VPA) showed more variance of crop yield could be explained by the fertilization factor (42%), including synthetic nitrogen (N), phosphorus (P), potassium (K) fertilizers, and fertilizer NPK combined with manure. The interactive influence of soil (total N, P, K, and available N, P, K) and climate factors (mean annual temperature and precipitation) determine the largest part of the SOC variance (32%). EPIC performs well in simulating both the dynamics of crop yield ( NRMSE  = 32% and 31% for yield calibration and validation) and SOC ( NRMSE  = 13% and 19% for SOC calibration and validation) under diverse fertilization practices in China. EPIC can assist in predicting the impacts of different fertilization regimes on crop growth and soil carbon dynamics, and contribute to the optimization of fertilizer management for different areas in China. [ABSTRACT FROM AUTHOR]

Although organic carbon sequestration in agricultural soils has been recommended as a ‘win-win strategy’ for mitigating climate change and ensuring food security, great uncertainty still remains in identifying the relationships between soil organic carbon (SOC) sequestration and crop productivity. Using data from 17 long-term experiments in China we determined the effects of fertilization strategies on SOC stocks at 0–20 cm depth in the North, North East, North West and South. The impacts of changes in topsoil SOC stocks on the yield and yield stability of winter wheat ( Triticum aestivum L.) and maize ( Zea mays L.) were determined. Results showed that application of inorganic fertilizers (NPK) plus animal manure over 20–30 years significantly increased SOC stocks to 20-cm depth by 32–87% whilst NPK plus wheat/maize straw application increased it by 26–38% compared to controls. The efficiency of SOC sequestration differed between regions with 7.4–13.1% of annual C input into the topsoil being retained as SOC over the study periods. In the northern regions, application of manure had little additional effect on yield compared to NPK over a wide range of topsoil SOC stocks (18–>50 Mg C ha − 1 ). In the South, average yield from manure applied treatments was 2.5 times greater than that from NPK treatments. Moreover, the yield with NPK plus manure increased until SOC stocks (20-cm depth) increased to ~ 35 Mg C ha − 1 . In the northern regions, yield stability was not increased by application of NPK plus manure compared to NPK, whereas in the South there was a significant improvement. We conclude that manure application and straw incorporation could potentially lead to SOC sequestration in topsoil in China, but beneficial effects of this increase in SOC stocks to 20-cm depth on crop yield and yield stability may only be achieved in the South. [ABSTRACT FROM AUTHOR]

Mineral-associated organic carbon (MOC), that is stabilized by fine soil particles (i.e., silt plus clay, <53 μm), is important for soil organic carbon (SOC) persistence and sequestration, due to its large contribution to total SOC (TSOC) and long turnover time. Our objectives were to investigate how climate, soil type, soil texture, and agricultural managements affect MOC contributions to TSOC in China. We created a dataset from 103 published papers, including 1106 data points pairing MOC and TSOC across three major land use types: cropland, grassland, and forest. Overall, the MOC/TSOC ratio ranged from 0.27 to 0.80 and varied significantly among soil groups in cropland, grassland, and forest. Croplands and forest exhibited significantly higher median MOC/TSOC ratios than in grassland. Moreover, forest and grassland soils in temperate regions had higher MOC/TSOC ratios than in subtropical regions. Furthermore, the MOC/TSOC ratio was much higher in ultisol, compared with the other soil types. Both the MOC content and MOC/TSOC ratio were positively correlated with the amount of fine fraction (silt plus clay) in soil, highlighting the importance of soil texture in stabilizing organic carbon across various climate zones. In cropland, different fertilization practices and land uses (e.g., upland, paddy, and upland-paddy rotation) significantly altered MOC/TSOC ratios, but not in cropping systems (e.g., mono- and double-cropping) characterized by climatic differences. This study demonstrates that the MOC/TSOC ratio is mainly driven by soil texture, soil types, and related climate and land uses, and thus the variations in MOC/TSOC ratios should be taken into account when quantitatively estimating soil C sequestration potential of silt plus clay particles on a large scale. [ABSTRACT FROM AUTHOR]

The effect of different fertilization strategies on changes in soil organic carbon (SOC) largely depends on the current status of a given agricultural region. We analysed the results of 90 long-term field trials (20–37 years) in Chinese croplands to determine the effects of fertilization strategies [i.e., no fertilizer (CK), chemical fertilizer (NPK), manure only (M) and manure plus chemical fertilizers (NPKM)] on soil organic carbon stock (SOC s) at 0–20 cm depth in the North (NC), Northeast (NEC), Northwest (NWC) and South (SC) China. Compared with initial values, SOC s increased by 24–68% and 24–74% under NPKM and M applications, respectively, over the experimental periods. Furthermore, final SOC s under NPKM in NEC and NWC were significantly higher than those under other treatments, but there was no significant difference between NPKM and M in SC and no significant differences among fertilizer treatments in NC. Average SOC stock change rates (SOC r) were positive under all treatments for all regions except for CK and NPK in NEC, which were negative. There were regional differences in treatment effects: all treatments showed significantly different rates in NC and NWC, whereas there were no significant differences between the M and NPKM in NEC and SC. Random forest (RF) modeling showed that among the selected variables initial SOC s was the most important in accounting for differences in SOC r , followed by soil bulk density, mean annual temperature and precipitation for all treatments. Soil total nitrogen content was also an important explanatory variable for SOC r for CK and NPK, and soil pH for M. This study has highlighted the main driving variables of SOC change which can be of use in optimizing fertilization strategies, by taking account of the baseline SOC s status and environmental factors for different regions, to minimize soil carbon emissions while maximizing carbon sequestration in soils. Unlabelled Image • Compared with initial values, final SOC stock increased by 24–74% under manure. • SOC r was positive for all regions but were negative under CK and NPK in Northeast. • A decrease in SOC stock was reported in some trials in Northeast under manure. • SOC r has no significant differences between the M and NPKM in Northeast and South. • SOC r was main controlled by initial SOC, soil BD and climate. [ABSTRACT FROM AUTHOR]