Search

The effects of soil type and organic material quality on the microbial biomass and functional diversity of cropland soils were studied in a transplant experiment in the same climate during a 1-year field experiment. Six organic materials (WS: wheat straw, CS: corn straw, WR: wheat root, CR: corn root, PM: pig manure, CM: cattle manure), and three contrasting soils (Ferralic Cambisol, Calcaric Cambisol and Luvic Phaeozem) were chosen. At two time points (at the end of the 1st and 12th months), soil microbial biomass carbon (C) and nitrogen (N) (MBC and MBN) and Biolog Ecoplate substrate use patterns were determined, and the average well color development and the microbial functional diversity indices (Shannon, Simpson and McIntosh indices) were calculated. Organic material quality explained 29.5-50.9% of the variance in MBC and MBN when compared with the minor role of soil type (1.4-9.3%) at the end of the 1st and 12th months, and C/N ratio and total N of organic material were the main parameters. Soil properties, e.g., organic C and clay content were the predominant influence on microbial functional diversity in particular at the end of the 12th month (61.8-82.8% of the variance explained). The treatments of WS and CS significantly improved the MBC and microbial functional diversity indices over the control in the three soils in both sampling periods (P < 0.05). These results suggest that the application of crop straw is a long-term effective measure to increase microbial biomass, and can further induce the changes of soil properties to regulate soil microbial community., Competing Interests: The authors have declared that no competing interests exist.

Purpose: Fe-modified biochar could promote soil organic phosphorus (Po) mineralization and phosphorus (P) bioavailability; however, the role of biochar and Fe-modified biochar in driving the mineralization of Po by phoD-harboring bacteria in soil aggregates was less known, especially in saline-alkali paddy soil. Methods: A 5-year paddy field experiment was conducted in Yellow River Delta, in which four fertilization treatments were designed: no fertilization (Control), inorganic fertilizer (NPK), NPK + biochar (BC), and NPK + Fe-modified biochar (FeBC). Results: Compared with NPK treatment, the proportion of macroaggregates in BC and FeBC treatments was significantly increased by 10.42% and 24.67%, respectively. And the mean weight diameter was also increased under biochar treatments. Redundancy analysis (RDA) indicated that oxalate-extractable Fe was a main factor in the stability of soil aggregates, which was significantly increased in FeBC treatment. Meanwhile, the relative abundance of phoD-harboring bacteria was increased in both BC and FeBC treatments, which was driven by the content of soil organic carbon. And the diversity of phoD-harboring bacteria was positively correlated with Po mineralization. Meanwhile, compared with NPK treatment, the activity of alkaline phosphatase in macroaggregate was increased by 39.1% in FeBC treatments, which also promoted the mineralization of soil Po. Conclusions: Therefore, biochar addition, especially Fe-modified biochar combined with mineral fertilization, was a better strategy in improving soil aggregate structure and promoting Po mineralization in saline-alkaline paddy soil. [ABSTRACT FROM AUTHOR]

Aims: Soil organic carbon (SOC) plays an important role in improving soil quality, however, how long-term fertilization influences SOC and contrasting active C (AC) and passive C (PC) pools at large scale remains unclear. The aim of this study was to examine the effect of long-term fertilization on SOC, including AC and PC, across four typical croplands in China and to explore the potential relationships and mechanisms. Methods: We assessed the effect of chemical fertilizer and manure amendment (standard rate and 1.5 × standard rate of inorganic fertilizer (NPK) with or without manure (M), with a Control for comparison) at three soil depths (0–20 cm, 20–40 cm, 40–60 cm) on SOC, AC and PC. Results: We found that SOC, AC and PC increased in the order NPK < NPKM < 1.5NPKM. 1.5NPKM resulting in a significant increase in SOC, AC and PC, of 76.3%, 53.0% and 108.5% respectively across the soil profile (0–60 cm) compared with Control. The response ratio of PC to long-term fertilization was 2.1 times greater than that of AC across four sites on average. In addition, clay was identified as the most important factor in explaining the response of AC and PC to different fertilization application. Conclusions: Long-term fertilization enhanced both AC and PC, but the greater response of PC suggests that fertilization application could enhance the stability of C and thus the potential of cropland for SOC accumulation. [ABSTRACT FROM AUTHOR]

Purpose: Soil microbial biomass (SMB), as the source and sink of soil nutrients, and its stoichiometry play a key role in soil organic carbon (SOC) and nitrogen (N) mineralization. The objective of this study was to investigate the responses of SOC and N mineralization to changes in microbial biomass and SOC, N, and phosphorus (P) stoichiometry resulted from long-term fertilization regimes. Materials and methods: Soil was sampled from a rice-wheat rotation system subjected to 37 years of nine fertilization treatments with different nutrient input amounts: control (CK), N alone, N combined with mineral phosphorus (NP), NP plus potassium (NPK), manure alone (M), and M combined with N (MN), NP (MNP), NPK (MNPK), and a higher rate of M with NPK (hMNPK). The sampled soil was incubated for the determination of SOC and N mineralization, C, N, and P stoichiometry of soil and SMB, and associated soil enzymes related to C and N cycling. Results and discussion: Relative to the CK and treatments with mineral fertilizers, treatments with manure (M, MN, MNP, MNPK, and hMNPK) significantly increased SOC and N mineralization by 48–78% and 54–97%, respectively. Microbial metabolic quotient (qCO2) decreased by 32–55% in treatments with manure compared to the N and NP treatments, but showed no effect on the qCO2 when compared to the NPK treatment. The leucine amino peptidase (LAP) enzyme showed significant positive correlation with SOC and N mineralization, and negatively related to the qCO2. Significantly negative correlations were also observed between SOC and N mineralization and soil C:P and N:P ratio, as well as microbial biomass SMBC:SMBP and SMBN:SMBP stoichiometry, respectively. However, the availability of N and P had limited effects on the qCO2 after reaching a certain value (0.69–0.72 mg CO2-C g−1 MBC h−1). Conclusions: Lower soil elemental (C:P and N:P) and microbial biomass stoichiometry (SMBC:SMBP and SMBN:SMBP) and increase of LAP resulted from combined application of manure and mineral fertilizers, accelerated SOC, and N mineralization. Mineral nutrient input with manure amendments could be an optimal strategy to meet the microbial stoichiometric demands and enhance nutrient availability for crops in agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Purpose: Understanding the underlying mechanism of soil carbon (C) and nitrogen (N) accumulation is of great significance for soil C sequestration and climate change mitigation, as well as soil fertility improvement. The objective of this study was to evaluate the response of C and N accumulation in aggregates and fine soil particles to long-term mineral fertilizer and manure application. Materials and methods: Five treatments from a long-term experiment with double maize cropping were examined in this study, i.e., (1) no fertilizer (control); (2) mineral nitrogen, phosphorus, and potassium application (NPK); (3) doubled application rate of the NPK (2NPK); (4) pig manure alone (M); and (5) mineral NPK fertilizers and manure combination (NPKM). By using physical particle-sized fractionation, we analyzed soil organic carbon (OC) and total nitrogen (N), and δ13C of OC in bulk soil and aggregates (53–2000 μm) and, coarse silt-sized fraction (5–53 μm), fine silt-sized fraction (2–5 μm), and clay-sized fraction (< 2 μm) under those five treatments. Results and discussion: Fertilizer application for 24 years, particularly M and NPKM treatments, significantly increased the concentration and proportion of OC and total N associated with aggregates and clay-sized fraction as compared with control. Manure application significantly increased the proportion of OC by 6.6–7.8 points in aggregates, whereas it was by 22.6–25.0 points in clay-sized fraction. Clay-sized fraction-associated C and N showed a non-linear response to C and N accumulation in bulk soil, contributing approximately 47% and 69% to soil OC and total N, respectively. Moreover, the mass proportion of aggregates and the mass ratio of aggregates to fine soil particles increased significantly with C accumulation in fine silt-sized and clay-sized fraction. Conclusions: Organic carbon and total nitrogen accumulation in soil clay-sized particles play important role in soil C and N sequestration in red soil. Our results also suggested that C accumulation in fine soil particles might benefit soil aggregation in intensive cropping system of South China. [ABSTRACT FROM AUTHOR]

Manure application to soil has declined globally due to increased availability of mineral fertilizers. However, mineral fertilizer overuse has caused serious consequences for soil quality and the environment. We analyzed the results of 20 long‐term field trials (22–32 years, start year [ranged from 1980 to 1990] to 2012) and combined this with a climate change model and soil organic carbon (SOC) model to quantify the importance of manure and mineral fertilizers for grain yield and SOC sequestration across croplands in China. During the past three decades mineral fertilizers have increased grain yield for 91–184% but had minor impact on SOC sequestration (4–16%). In contrast, manure applied with mineral fertilizer increased grain yield by only 6–19% but strongly raised the SOC content (9–39%) compared with mineral fertilizer. Modeling (to the year 2099) indicated that manure used in combination with mineral fertilizers will increase future C sequestration in soils across China by 2,086 Tg C and by 2,482 Tg C based on current net primary productivity with no climate change and on increased net primary productivity with climate change scenarios, respectively. This corresponds to an additional 43–58% increase in C sequestration compared to mineral fertilizers only. The manure efficiency for C sequestration in soil was about 9.6% of C input and decreased with increasing SOC content. To maintain the current SOC content (i.e., 2010), 11 t·ha−1·year−1 fresh manure or 4.8 t·ha−1·year−1 dry maize straw would be required. We conclude that the regular use of manure with mineral fertilizers is essential for the long‐term dual functions of soil for food production and SOC sequestration. Key Points: The increase of SOC by manure is much higher than that of crop yield; manure C efficiency is 9.6% of C input and decreased with SOC contentMineral fertilizers just maintained the SOC, while combined with manure they sequester more C under current climate and increase crop yieldWe modeled the minimal level of manure application to maintain SOC on the current management practices [ABSTRACT FROM AUTHOR]

Introduction: To generate information for the effective management of soil organic carbon (SOC) sequestration in Chinese croplands, we compared the additional organic carbon (C) that can be stabilized by fine soil particles (<20 µm) with typical fertilization practices across soil types and climate zones. Using data from 30 long-term experimental study sites across the major agricultural zones in China, we estimated stable SOC saturation deficit (SOCdeficit) under no fertilization (CK), chemical fertilization (CF), straw plus CF (S + CF), and manure plus CF (M + CF). Stable SOCdeficit was defined as the difference between potential and current SOC stabilized by fine soil particles. Outcomes: Stable SOCdeficit values varied from 51% to 82%. Soils dominated by 2:1 clay minerals showed larger stable SOCdeficit than soils dominated by 1:1 clay minerals under each treatment. For soils dominated by 2:1 clay minerals, stable SOCdeficit was significantly lower under M + CF (69%) than under CK, CF, and S + CF (78-82%) treatments, and it increased with increasing mean annual temperature (<10°C). In soils dominated by 1:1 clay minerals, stable SOCdeficit was considerably lower in paddy and paddy-upland than in upland soils, suggesting that paddies effectively stabilize C inputs. Discussion: Agricultural soils in China have considerable C sequestration potential, despite decades of fertilization practices. To manage soil C sequestration and model soil C dynamics effectively, factors such as soil mineral types, fertilization, and cropland use should be considered. Conclusion: Our results demonstrated that manure addition was the best fertilization method for improving soil fertility, whereas straw return in Chinese croplands should take into account climate mitigation in future. [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]

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]

We determined the historical change in soil organic carbon (SOC) stocks from long-term field trials that represent major soil types and climatic conditions of northern China. Soil carbon and general circulation models were validated using these field trial data sets. We then applied these models to predict future change in SOC stocks to 2100 using two net primary production (NPP) scenarios (i.e., current NPP or 1% year−1 NPP increase). The conversion rate of plant residues to SOC was higher in single-cropping sites than in double-cropping sites. The prediction of future SOC sequestration potential indicated that these soils will be a net source of carbon dioxide (CO2) under no fertilizer inputs. Even when inorganic nutrients were applied, the additional carbon input from increased plant residues could not meet the depletion of SOC in parts of northern China. Manure or straw application could however improve the SOC sequestration potential at all sites. The SOC sequestration potential in northern China was estimated to be −4.3 to 18.2 t C ha−1 by 2100. The effect of projected climate change on the annual rate of SOC change did not differ significantly between climate scenarios. The average annual rate of SOC change under current and increased NPP scenarios (at 850 ppm CO2) was approximately 0.136 t C ha−1 yr−1 in northern China. These findings highlight the need to maintain, and where possible increase, organic carbon inputs into these farming systems which are rapidly becoming inorganic fertilizer intensive. [ABSTRACT FROM AUTHOR]

The incorporation of crop straw with fertilization is beneficial for soil carbon sequestration and cropland fertility improvement. Yet, relatively little is known about how fertilization regulates the emissions of the greenhouse gas nitrous oxide (N 2 O) in response to straw incorporation, particularly in soils subjected to long-term fertilization regimes. Herein, the arable soil subjected to a 31-year history of five inorganic or organic fertilizer regimes (unfertilized; chemical fertilizer application, NPK; 200% NPK application, 2 × NPK; manure application, M; NPK plus manure application, NPKM) was incubated with and without rice straw to evaluate how historical fertilization influences the impact of straw addition on N 2 O emissions. The results showed that compared to the unfertilized treatment, historical fertilization strongly increased N 2 O emissions by 0.48- to 34-fold, resulting from increased contents of hot water-extracted organic carbon (HWEOC), NO 3 −, and available phosphorus (Olsen-P). Straw addition had little impact on N 2 O emission from the unfertilized and NPK treatments, primarily due to Olsen-P limitation. In contrast, straw addition increased N 2 O emissions by 102–316% from the 2 × NPK, M, and NPKM treatments as compared to the corresponding straw-unamended treatments. These results indicated that N 2 O emissions in response to straw addition were largely regulated by historical fertilization. The N 2 O emissions were closely associated with the depletion of NO 3 − and decoupled from change in NH 4 + content, suggesting that NO 3 − was the main substrate for N 2 O production upon straw addition. The stoichiometric ratios of HWEOC to mineral N and mineral N to Olsen-P were key factors affecting N 2 O emissions, underscoring the importance of resource stoichiometry in regulating N 2 O emissions. In conclusion, historical fertilization largely regulated the impacts of crop straw incorporation on N 2 O emissions via shifts in NO 3 − depletion and the stoichiometry of HWEOC, mineral N, and Olsen-P. Image 1 • Historical fertilization regulated the response of N 2 O emission to straw addition. • The magnitude of N 2 O emissions was closely linked to the depletion of soil nitrate. • The availability and stoichiometry of soil C, N and P were key factors affecting N 2 O emission. [ABSTRACT FROM AUTHOR]

Fertilization affects soil microbial community by altering soil organic carbon (C) and nutrients availability. However, it remains unclear how changes in stoichiometric C, N, and P ratios resulting from fertilization affect microbial community. We investigated a 26-year field experiment receiving inorganic fertilizers (N, NP, PK, and NPK), organic N combination (with manure and straw), natural recovery (fallow), and no fertilizer (control). The aim of this study was to explore the responses of microbial community to C: N:P stoichiometry in soil and microbial biomass of topsoil (0–20 cm) and subsoil (20–40 cm). Results showed that compared to control treatment, organic application increased the ratio of fungi to bacteria (F:B) in topsoil and gram-negative bacteria to gram-positive bacteria (G−:G+) in subsoil. However, application of inorganic decreased both the F: B and G−:G+ ratio in topsoil. Increasing soil C, N and P availability resulted from inorganic fertilizers and organic combination fertilization caused stoichiometric imbalance between soil and microbial biomass. As a result, the F:B and G−:G+ ratio were positively related to C:N imbalance but negatively associated with N:P imbalance in topsoil. Redundancy analysis (RDA) showed that main factors regulating microbial community were pH, C:P and N:P imbalances in topsoil, whereas TDN, N:P imbalance, DOC and soil C:N in subsoil. Furthermore, C:P and N:P imbalance explained 16.4% in topsoil, and N:P imbalance explained 22.0% in subsoil of microbial community variation. These results reveal the shifts of soil microbial community are driven by changes in soil pH and C, N and P stoichiometric imbalance from long-term fertilization. [Display omitted] • Long-term organic combination enhanced soil C, N, and P pool and availability. • Soil microbial community was linked to stoichiometric C, N, and P imbalances. • F:B and G−:G+ ratios were regulated by N limitation in topsoil but P limitation in subsoil. • Driving factors on microbial community differed from topsoil to subsoil. [ABSTRACT FROM AUTHOR]

As an effective field management practice for better crop productivity, fertilization showed profound impacts on soil health by altering soil chemical, physical, and biological processes. But, how soil health and related ecosystem multifunctionality (EMF) respond to long-term fertilization remains unclear. In this study, based on a 29-year field experiment, we evaluated soil health and EMF under chemical fertilization versus manure application. Long-term manure application maintained soil pH, significantly increased water-stable aggregate, total and available nutrients, microbial biomass and community (bacteria, fungi, and actinomycetes, etc.), and enzyme activities compared with treatments under chemical fertilizers. Edaphic factors of soil organic carbon (SOC), available phosphorous (AP), fungi, cation exchange capacity, and clay content were identified as key indicators of soil health evaluation by network analysis. The soil health indices (SHIs) of chemical fertilizer treatments were 39–52% lower than that of natural vegetation recovery, with carbon and nutrient cycling, soil biodiversity maintenance, and productivity at low ecosystem function levels. Manure application enhanced soil health by 150–196% compared to unfertilized control by improving SOC, P availability, and sustaining ecosystem functions with carbon and nutrient cycling, soil biodiversity maintenance, buffering and filtering capacity, and productivity at relatively high ecosystem function levels. The individual functions of carbon and nutrient cycling, physical structure stability, and productivity illustrated sensitive responses to the increase in soil health, while inherent soil functions of buffering and filtering capacity and soil biodiversity maintenance were only correlated with high soil health. Manuring improved soil functions and soil health simultaneously, indicating a synergistic relationship. Our findings highlight the significance of manure application to improve soil health and sustain functions in intensive agricultural systems. • SOC, AP, fungi, clay content, and CEC were identified as key indicators. • Natural vegetation recovery improved SHI compared with chemical fertilization. • Manuring improved soil health by sustaining soil multifunction at high levels. • Soil functions had diverse responses to soil health shifts. [ABSTRACT FROM AUTHOR]

Manure amendments have been generally considered to enhance soil nutrient supply, thus improving soil fertility and crop productivity, especially in subtropical area. However, the underlying mechanisms of manure application effects on soil nitrogen (N) supply capacity and N transformation processes remain uncertain. Here, 15N isotope pool dilution techniques were used to determine the gross rates of N mineralization, ammonium (NH 4 +) immobilization and nitrification in red soil subjected to three decades of long-term fertilization regimes. Results showed that compared to treatments without manure, manure application alone or combined with chemical fertilizers significantly increased gross N mineralization rates by 4.55−8.31 folds, resulting from increased N-acquiring enzyme activity and decreased microbial N use efficiency (NUE). The decreased microbial NUE in the manure application treatments was due to alleviated imbalance of C:N between soil and microbial biomass. Gross NH 4 + immobilization rates were 7.35−11.34 folds higher in the treatments amended with manure (1.51−2.23 mg N kg−1 d−1) relative to without manure, attributed to increased microbial biomass and bacterial abundance. Compared to chemical fertilizers application, manure application decreased gross nitrification rates by 38−55%, due to the decline in NH 4 + availability via enhanced NH 4 + immobilization. The significantly lower ratio of gross nitrification to NH 4 + immobilization in the treatments with manure suggested that manure amendments could potentially mitigate the risk of soil N losses. Overall, long-term manuring has the potential to improve soil N supply and retention capacities by enhancing gross N mineralization and NH 4 + immobilization accompanying with decreased gross nitrification. • Manuring increased gross N mineralization rate via decreased microbial NUE. • Manuring facilitated gross NH 4 + immobilization, due to increased microbial biomass. • Gross nitrification rate was positively related to NH 4 + content and AOA abundance. • Manuring decreased ratio of gross nitrification to NH 4 + immobilization rates. [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]

• Long-term manure application and stover return increased macroaggregate by 10 %. • Manure incorporated soil reduced N retention from chemical fertilizer in all aggregates. • The cPOM, intra-MOM and inter-MOM were the main fractions to retain fertilizer N. • The cPOM in NPKM treatment produced higher biomass than that without manure. • The use efficiency of the retained N in cPOM and inter-MOM were higher than in intra-MOM. Long-term incorporation of manure has shown many benefits to improve soil productivity, but its effects on nitrogen (N) partitioning in soil aggregates and availability to plants is not well understood. The aim of this study was to examine the influence of different long-term field fertilization regimes on N partitioning and availability in soil aggregates. Soils from a field after 25-yr treatments of no fertilization (CK), mineral fertilizer (NPK), NPK with stover return (NPKS), and NPK with manure application (NPKM) were examined for N partitioning after adding 15N-labelled urea and incubating for 42 days. Using a wet sieving procedure, soil was separated into macroaggregates (> 250 μm, coarse particulate organic matter or cPOM), microaggregates (53–250 μm), and silt + clay (< 53 μm, inter mineral-associated OM or inter-MOM). The OM in microaggregates was further separated into fine free POM (ffPOM), physically protected intra-aggregate POM (iPOM), and intra mineral-associated OM (intra-MOM). Total N and 15N concentrations were determined. All fractions except ffPOM (limited mass) were used to cultivate ryegrass (Lolium perenne L.) and 15N uptake was determined. Mass of macroaggregate was 10 % higher from NPKM and NPKS with significantly higher use efficiency than that from NPK while the opposite was true for intra-MOM fraction with no differences in other fractions. The 15N retained in cPOM, intra-MOM, and inter-MOM ranged from 24 to 34%, 28–37 %, and 33–38 %, respectively, and that from ffPOM and iPOM was 1–4% of all retained in aggregates. Ryegrass N uptake was in the range of 14–19 %, 14–24 %, and 3–5% for the cPOM, inter-MOM, and the intra-MOM, respectively. However, the total amount of 15N fertilizer retained in aggregates from the NPKM treatment (14 %) was the lowest due to its higher amount (86 % of 15N) as in soluble phase compared to other treatments (78–83 %). This research concludes that long-term manure application resulted in increased formation of macroaggregates, higher plant-available N in the aggregates, and larger amount of soluble N that contributed to the high yield in the field illustrating the role of manure to improve soil productivity and sustain crop production. [ABSTRACT FROM AUTHOR]

• Mineral fertilizers combined with manure significantly increased MOC and MN concentrations. • TN and TSOC, crop rotation, and soil texture explained 72 % of the variations of MOC and MN. • Estimation models on attainable MOC and MN sequestration capacities was calibrated. • MOC and MN sequestration potentials were 528 and 37 Tg, respectively, across Chinese dry cropland. Mineral-associated organic carbon (MOC) and mineral-associated nitrogen (MN) are the major pools of total soil organic carbon (TSOC) and total nitrogen (TN) stocks. Thus, it is important to understand the impact of agricultural practices on MOC and MN stocks and capacities. The present study aimed to explore how the application of various fertilizers and crop rotation affect MOC and MN, and how improved management practices sequester carbon and nitrogen as MOC and MN to mitigate climate change. Twenty-one long-term experiments across China dry croplands with various soil types and crop rotations were involved to investigate the effects of the application of various fertilizers on MOC and MN. Results showed that mineral fertilizers combined with manure significantly increased TSOC (62 %) and TN (57 %), and MOC (33 %) and MN (32 %) concentrations, respectively, resulting in decreased ratios of MOC/TSOC (0.59) and MN/TN (0.47). Moreover, mineral fertilizers with straw significantly increased MOC/TSOC ratio, but had no effects on MN/TN ratio compared with mineral fertilizer application (0.72−0.77). Significantly positive linear correlations were observed between MOC (MN) concentrations and the mass proportion of fine soil particles (<20 μm). Further analysis suggested that TN, TSOC, crop rotation (e.g., wheat-maize, wheat-soybean, maize-soybean, maize-rape, and maize monoculture), and fine soil particle content were the key regulating factors, which accounted for about72 % of the variations of MOC and MN concentration. Boundary line analysis suggested that MOC and MN had the potential to increase by 48 % and 39 %, respectively. In conclusion, main dry croplands in China might sequester an additional 527 Tg for MOC and 37 Tg for MN with appropriate crop rotation and manure application. [ABSTRACT FROM AUTHOR]