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The storage of soil organic carbon (SOC) in cropland soils is an essential strategy that serves the dual purpose of enhancing soil fertility and mitigating climate change. However, how the stability of stored carbon is altered under long-term fertilization has not been well understood, especially in the double rice cropping system in Chinese paddy soils. In this study, we explored the SOC storage and consequent stability of SOC under long-term fertilization. The soil samples were fractionated chemically to isolate various fractions and constituent pools of SOC (i.e., very labile C/VLC, labile C/LC, less labile C/LLC, and non-labile C/NLC). The following treatments were tested: control (CK), recommended rate of inorganic fertilizer (NPK), double the amount of recommended rate of inorganic fertilizer (2NPK), and NPK combined with manure (NPKM). The results showed that, relative to the initial level, the application of NPKM significantly improved the SOC storage as compared to the control. The long-term NPKM increased the total SOC in the paddy soil and this increased SOC was mainly stored in LLC, as revealed by the highest increase (142%) over the control. Furthermore, the highest proportion of labile pool was associated with unfertilized CK, while the reverse was true for the recalcitrant pool, which was highest under NPKM. This supports the role of combining manure with NPK to improve the stability of SOC, further verified by the high recalcitrance index under NPKM (56.75% for 0–20 cm and 57.69% for 20–40 cm) as compared to the control. [ABSTRACT FROM AUTHOR]

Subsoils contain half of the total soil organic carbon (SOC) that is supposed to be relatively more persistent than that present in the topsoil. Improving SOC and total nitrogen (TN) stocks in croplands is crucial to mitigate climate change and ensuring food security. However, our insight into how the management practices and climatic variables influence stocks of SOC and TN, and crop grain yields in the soil profile is limited. In this study, we assessed the long‐term impacts of mineral and manure fertilizers on SOC and TN stocks at soil profile levels (up to 100 cm), and cropping system (wheat–maize–soybean) grain yields. Results indicated that in the top 0–40‐cm layers SOC and TN stocks were the highest in manure plus mineral fertilizers (MNPK) compared with control, that is, non‐fertilized control (CK). Conversely, compared with NPK, sole application of manure (M) clearly increased SOC stocks by 19%, 40%, and 39% and TN stocks by 51%, 105%, and 116% in 40–60, 60–80, and 80–100 cm, respectively (p < 0.05). Moreover, Pearson correlation revealed that climate variables, that is, mean annual temperature (MAT) affected both SOC and TN stocks in 0–40‐cm layers only of the soil profile. Our findings implicated that the sole application of manure (M) is vital to augment SOC and TN sequestration, particularly in the subsurface layers. However, trade‐offs between SOC and TN sequestration and crop yields should also need to be considered while making recommendations for SOC and TN stocks maintenance and increasing crop productivity in terms of management strategies. [ABSTRACT FROM AUTHOR]

Long-term manure application is recognized as an efficient management practice to enhance soil organic carbon (SOC) accumulation and nitrogen (N) mineralization capacity. A field study was established in 1979 to understand the impact of long-term manure and/or chemical fertilizer application on soil fertility in a continuous maize cropping system. Soil samples were collected from field plots in 2012 from 9 fertilization treatments (M0CK, M0N, M0NPK, M30CK, M30N, M30NPK, M60CK, M60N, and M60NPK) where M0, M30, and M60 refer to manure applied at rates of 0, 30, and 60 t ha−1 yr−1, respectively; CK indicates no fertilizer; N and NPK refer to chemical fertilizer in the forms of either N or N plus phosphorus (P) and potassium (K). Soils were separated into three particle-size fractions (2000–250, 250–53, and <53 μm) by dry- and wet-sieving. A laboratory incubation study of these separated particle-size fractions was used to evaluate the effect of long-term manure, in combination with/without chemical fertilization application, on the accumulation and mineralization of SOC and total N in each fraction. Results showed that long-term manure application significantly increased SOC and total N content and enhanced C and N mineralization in the three particle-size fractions. The content of SOC and total N followed the order 2000–250 μm > 250–53μm > 53 μm fraction, whereas the amount of C and N mineralization followed the reverse order. In the <53 μm fraction, the M60NPK treatment significantly increased the amount of C and N mineralized (7.0 and 10.1 times, respectively) compared to the M0CK treatment. Long-term manure application, especially when combined with chemical fertilizers, resulted in increased soil microbial biomass C and N, and a decreased microbial metabolic quotient. Consequently, long-term manure fertilization was beneficial to both soil C and N turnover and microbial activity, and had significant effect on the microbial metabolic quotient. [ABSTRACT FROM AUTHOR]

An effective N management could match N availability with crop demand to maximize nitrogen use efficiency (NUE) and to optimize N application rate. Using polyolefin-coated urea (POCU) to replace regular or non-coated urea (NCU) might be an option to achieve such objectives. A 2-year field study with five fertilization treatments was conducted in a rice-rice cropping system, in Qiyang, Hunan, southern China. The treatments include a control, both NCU and POCU at 150 and 300 kg N ha-1 yr-1. The results showed that average annual NUE and grain yield over 2-years were significantly greater under POCU (50% and 11.4 t ha-1 yr-1, respectively) than under NCU (36% and 10.6 t ha-1 yr-1, respectively). Based on their price of both rice grains and fertilizers in 2014 with a quadratic model, an optimal N rate was calculated as 178-203 kg N ha-1 yr-1 under POCU but 364-374 kg N ha-1 yr1 under NCU. A decrease of 46-50% N inputs could be thus achieved under POCU than under NCU. The use of slow release urea fertilizer such as POCU could maintain high grain yield and grower's income, increase NUE and decrease N losses in such rice-rice cropping systems in southern China. Application of POCU was hence agronomically practical and cost-effective over NCU in rice plantation. © 2015 Friends Science Publishers [ABSTRACT FROM AUTHOR]

Fertilizer application can potentially change soil organic C (SOC) sequestration of croplands. However, how fertilization affects SOC sequestration and soil C fractions has not been sufficiently investigated. Here, we studied this issue in a rice-barley system of eastern China after 23-year repeated organic and chemical fertilizer amendments. The fertilization treatments were as follows: unfertilized control (CK), pig manure (M), chemical fertilizer NPK (NPK), and pig manure combined with NPK (MNPK). Our results showed that M, NPK, and MNPK significantly increased 25, 13, and 30 % of SOC content as compared with CK. Compared with CK, the three fertilizations, especially manure addition, significantly increased the content of SOC fractions such as microbial biomass C, dissolved organic C, labile organic C, and particulate organic C. Compared with the initial SOC stock at 0-20-cm depth (41.2 Mg C ha), M, NPK, and MNPK increased 11, 1, and 16 % of SOC storage, respectively, whereas CK decreased 9 % of SOC pool. The SOC sequestration was positively correlated with the cumulative C input (root residue-C + manure-C) (SOC sequestration = 0.21 × C input − 5.67, R = 0.88, P < 0.001). This linear relationship suggested that (i) the soil had not reached a SOC saturation, (ii) the conversion rate from input-C to SOC was 21 %, and (iii) a C input threshold of 1.17 Mg C ha year was needed for maintaining the initial SOC level. Therefore, manure application is recommended for promoting SOC sequestration in the rice-barley cropping system of eastern China. [ABSTRACT FROM AUTHOR]

Soil organic matter models are widely used to study soil organic carbon (SOC) dynamics. Here, we used the CENTURY model to simulate SOC in wheat-corn cropping systems at three long-term fertilization trials. Our study indicates that CENTURY can simulate fertilization effects on SOC dynamics under different climate and soil conditions. The normalized root mean square error is less than 15% for all the treatments. Soil carbon presents various changes under different fertilization management. Treatment with straw return would enhance SOC to a relatively stable level whereas chemical fertilization affects SOC differently across the three sites. After running CENTURY over the period of 1990–2050, the SOC levels are predicted to increase from 31.8 to 52.1 Mg ha−1 across the three sites. We estimate that the carbon sequestration potential between 1990 and 2050 would be 9.4–35.7 Mg ha−1 under the current high manure application at the three sites. Analysis of SOC in each carbon pool indicates that long-term fertilization enhances the slow pool proportion but decreases the passive pool proportion. Model results suggest that change in the slow carbon pool is the major driver of the overall trends in SOC stocks under long-term fertilization. [ABSTRACT FROM AUTHOR]

Highlights: [•] Long-term field research proved that manure application with chemical fertilizer improved the nitrogen use efficiency (NUE) of wheat–corn rotation system the most especially in acid soil. [•] Phosphorus is found to be another important factor to improve NUE up to 40–60% if soil is P deficient. [•] Between the rotation crops, both grain yield and NUE of wheat were determined more responsive to P fertilization, and that for corn were more responsive to manure application. [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]

A long-term double cropping wheat (Triticum aestivum L.) and corn (Zea mays L.) experiment was conducted at Qiyang, Hunan, China, to study the effects of inorganic fertilizers on grain yields and soil properties and to identify the possible causes of yield trends. Six treatments of unfertilized control, N, NP, NK, PK, and NPK were included. The treatments (N, NP, NK, and NPK) where inorganic nitrogen (N) was added showed significant (P<0.05) yield declines of 76 to 114 kg ha-1 yr-1 for wheat and 94 to 260 kg ha-1 yr-1 for corn, respectively, except for corn yield in the NPK treatment in which the decline was not significant during a 15-yr (1990-2005) period. Comparatively, the decline amounts in corn were much higher than in wheat. The yields of wheat and corn remained unchanged in the PK treatment. The total organic carbon (C), total N, phosphorus (P), and available P, potassium (K), copper (Cu), and zinc (Zn) contents of soil were either increased or decreased during the study period. Both the decreases of exchangeable calcium (Ca2+) and magnesium (Mg2+) and increases of exchangeable hydrogen (H+) and Al3+ contents of soil in the treatments where inorganic N was applied were significant (P<0.05). The same four treatments showed significant pH declines ranging from 0.07 to 0.12 yr-1. Several lines of evidence point to decline of soil pH due to inorganic N fertilizer added as leading to the overall yield decline of wheat and corn. However, the yields of both crops increased significantly after lime application. In the long term, the farmers should be encouraged to use adequate lime based on a balanced approach to ensure sustainable productivity. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) dynamics in agro-ecosystem is largely influenced by cropping. However, quantifying the contributions of various crops has been lacking. Here we employed a stable isotopic approach to evaluate the contributions of wheat and maize residues to SOC at three long-term experimental sites in north China. Soil samples were collected from 0-20, 20-40, 40-60, 60-80 and 80-100 cm after 13 and 20 years of wheat-maize rotation, and SOC and its stable 13C composition were determined. Our data showed that the δ13C value of SOC varied, on average, from −22.1‰ in the 0-20 cm to −21.5‰ in the 80-100 cm. Carbon input through maize residues ranged from 35% to 68% whereas the contribution of maize residues to SOC (0-40 cm) ranged from 28% to 40%. Our analyses suggested that the retention coefficient was in the range of 8.0-13.6% for maize residues and 16.5-28.5% for wheat residues. The two-fold higher retention coefficient of wheat versus maize residues was due to the differences in the quality of residues and probably also in the temperature during the growing season. Our study highlighted the importance of crop management on carbon sequestration in agricultural lands. [ABSTRACT FROM AUTHOR]

We aimed to quantify the relative contributions of plant residue and organic manure to soil carbon sequestration. Using a 27-year-long inorganic fertilizer and manure amendment experiment in a maize (Zea mays L.) double-cropping system, we quantified changes in harvestable maize biomass and soil organic carbon stocks (0-20 cm depth) between 1986-2012. By employing natural 13C tracing techniques, we derived the proportional contributions of below-ground crop biomass return (maize-derived carbon) and external manure amendment (manure-derived carbon) to the total soil organic carbon stock. The average retention of maize-derived carbon plus manure-derived carbon during the early period of the trial (up to 11 years) was relatively high (10%) compared to the later period (22 to 27 years, 5.1-6.3%). About 11% of maize-derived carbon was converted to soil organic carbon, which was double the retention of manure-derived carbon (4.4-5.1%). This result emphasized that organic amendments were necessary to a win-win strategy for both SOC sequestration and maize production. [ABSTRACT FROM AUTHOR]

The application of nitrogen (N) fertilizer is key to realize high crop yields and ensure food security. Excessive N application and relatively low N use efficiency (NUE), however, have led to substantial N losses to air and water with related impacts on biodiversity and health. We used historical data from 13 long-term experiments to unravel how the NUE depends on fertilizer strategy and site conditions such as crop rotation, soil properties and climate. During nearly 40 years of fertilization, NUE decreased when crops were fertilized with N and potassium fertilizers only, while the NUE increased when multi-nutrient or organic fertilizers were used. The highest NUE was found when 25–30% of the total N input was supplied in organic form. Among the site conditions analysed, soil pH was the most important factor controlling NUE with an optimum pH around 6. In addition to soil acidity, phosphorus availability increased NUE. Crop rotation, soil properties and fertilizer management together explained 46–85% of the variation in NUE, allowing site specific fertilizer strategies to be developed boosting NUE. Current NUE equalled on average 30% in paddy soils, 39% in upland soils and 42% in paddy upland soils. Optimizing all fertilizer inputs and soil nutrient levels might increase the NUE up to 40–47% in paddy soils, up to 40–77% in upland soils and even up to 40–87% in a paddy upland soils. [Display omitted] • Data from 13 experimental sites were used to assess nitrogen use efficiency (NUE). • Site conditions and fertilizer management explained 46–85% of the NUE variation. • Soil pH was a very important factor controlling NUE, with an optimum around 6. • Phosphorus and potassium availability had a substantial impact on the NUE. • The highest NUE was found when 25–30% of the N input was supplied in organic form. [ABSTRACT FROM AUTHOR]

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]

Understanding dynamics of soil organic carbon (SOC) stock in agroecosystems under climate change is imperative for maintaining soil productivity and offsetting greenhouse gas emissions. Simulations with the SPACSYS model were conducted to assess the effects of future climate scenarios (RCP2.6, RCP4.5 and RCP8.5) and fertilisation practices on crop yield and SOC stock by 2100 for a continuous winter wheat cropping system in southeast England. Weather data between 1921 and 2000 was considered as the baseline. SPACSYS was first calibrated and validated with the data of the Broadbalk continuous winter wheat experiment for over a century. Six treatments were used: no fertiliser, a combination of chemical nitrogen, phosphorus and potassium with three nitrogen application rates (N1PK, N3PK and N5PK), manure only (FYM, close N application rate to N5PK) and a combination of manure and chemical nitrogen application (FYMN, the same chemical N application rate as N3PK). Compared with the observations, SPACSYS was able to simulate grain yields and dynamics of SOC and TN stocks. Our predications showed that wheat yield would increase by 5.8–13.5% for all the fertiliser application treatments under future climate scenarios compared to that under the baseline because of a gradual increase in atmospheric CO 2 concentration. Meanwhile, the SOC stock can increase for the practices under the scenarios except the NPK fertiliser practices under RCP2.6. Increased C input through "CO 2 -fertilisation effects" can compensate C losses by soil respiration under the RCP scenarios. We concluded that manure application practices can be considered as a sustainable strategy for enhancing wheat yield and soil C sequestration under the future climate scenarios. [Display omitted] • SPACSYS was able to simulate wheat yield of different varieties, SOC and TN stocks. • Future climate change positively impacts wheat yield. • Climate change effects on SOC varied among RCP scenarios and fertiliser practices. • Manuring acts as a sustainable strategy for soil productivity and C sequestration. [ABSTRACT FROM AUTHOR]

Climate change and excessive fertilization will threaten the crops yields and nitrogen utilization in coming decades. The aim of this study is to quantify the response of crop yields and nitrogen use efficiency (NUE) to different fertilization strategies and climate change scenarios in the northern China by 2100 using the process-based SPACSYS model. The model was calibrated and validated with the data from four long-term experiments with winter wheat ( Triticum Aestivium L.) and summer maize ( Zea mays L.) rotation in the northern China. Five fertilizer treatments based on the long-term experiments were chosen: non-fertilizer (CK), a combination of mineral nitrogen, phosphorus and potassium (NPK), NPK plus manure (NPKM), a high application rate of NPKM (hNPKM) and NPK plus maize straw (NPKS). The model simulations and projections were performed under four different climate change scenarios including baseline, RCP2.6, RCP4.5 and RCP8.5. Validation demonstrated that SPACSYS can adequately simulate crop yields, N uptake and annual NUE for the wheat–maize rotation. Without considering the impact of cultivar change, maize yield would increase by an average of 8.5% and wheat yield would decrease by 3.8%, and the annual NUE would decrease by an average of 15% for all fertilization treatments under RCP climate scenarios compared with the baseline. This might be the interactive effects among elevated CO 2 concentration, more concentrated and intensive rainfall events, and warming temperature. For each climate scenario, manure amendment could alleviate the negative influences of future climate change on crop growth and nitrogen utilization, given that manure applied treatments had higher soil organic matter and persistent supply of nutrients, which resulted in a more stable crop yield and N removal by wheat and maize than other treatments. In addition, the highest and most stable annual NUE (38.70–52.78%), crop yields and N removal were found in hNPKM treatment until 2100. The results could provide a reference for nitrogen fertilization in study regions to improve crop yield and nitrogen use efficiency and minimize environmental risks in the future. [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]

Fig. Relative importance of independent variables for controlling SMBC (a), SMBN (c) changes after manure application as determined using random forests (RF) models and the performance of random forests models for detecting controlling factors of SMBC (b), SMBN (d) change in the croplands in China. • Manure application increased SMBC (40%) and SMBN (55%) related to NPK. • Manure type was the predominant regulator of SMBC responses to manure application. • Local edaphic and climate condition constrain increase in SMBC by manure. Soil microbial biomass carbon (SMBC) and nitrogen (SMBN) are important indices of soil bio-fertility. While intensively managed cropping systems can reduce microbial biomass, application of manure is a potential way to rebuilt microbial biomass and improve soil functions. However, the responses of SMBC and SMBN to manure application relative to mineral fertilizers (NPK) in Chinese cropping systems remains unclear. We conducted a meta-analysis based on 103 peer-reviewed publications with 1448 paired observations to identify the degree to which climate types, soil properties and agricultural managements regulate the responses of microbial biomass to manure amendment relative to NPK. The results indicated that manure application increased SMBC, SMBN, SMBC/soil organic carbon (SOC) and SMBN/soil total nitrogen (TN) by 40%, 55%, 16% and 21%, respectively, across all the observations compared to NPK. SMBC/SMBN under manure amendment (6.58 in average) was lower than that in NPK (7.86 in average). Manure-related factors, e.g. manure types, duration of application, manure-C and N input rates, were the strongest regulators of the response of microbial biomass. Soil properties and climates also contributed to considerable degrees of variation in microbial biomass response based on variance partitioning analysis (VPA). Results of the random forest (RF) models showed that manure type, application rate (manure-C and N input) as well as soil initial properties (SOC, TN and clay contents) were likely the predominant factors controlling the response of microbial biomass to manure application. Our study indicates that manure application can be an effective way to restore the loss of microbial biomass due to intensive application of NPK, yet variations in response are determined by specific manure type, application rate, as well as local conditions of climate and inherent soil properties. [ABSTRACT FROM AUTHOR]