Long-term organic amendments enhanced soil organic carbon storage and stability in a typical paddy soil of Southern China

doi:10.21203/rs.3.rs-3123946/v1

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Long-term organic amendments enhanced soil organic carbon storage and stability in a typical paddy soil of Southern China

https://doi.org/10.21203/rs.3.rs-3123946/v1

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Background

The contribution of long-term fertilization to soil organic carbon (SOC) storage in arable soils is well acknowledged. The present study soil samples were collected from a 29 years long field trial in a red paddy soil of Jiangxi province, southern China to assess the effects of long-term fertilization on SOC storage and stability in top and sub-soil layers. The SOC storage of whole soil and SOC fractions were quantified at three soil depths (0–20, 20–40, 40–60 cm) under four treatments: no fertilization (Control), a combination of nitrogen, phosphorus and potassium (NPK), double the rates of NPK (2NPK), NPK plus manure (NPKM).

Results

The results showed that the effect of inorganic fertilizer application on SOC storage across the soil profile (0–60 cm) was negligible except for the 2NPK treatment. The larger SOC storage of the Non-labile C fraction was observed in the 2NPK (25.0 t C·ha^− 1) and NPKM (23.8 t C·ha^− 1) treatments compared to other treatments, and the NPKM treatment significantly (p < 0.05) accreted the SOC storage of less-labile C fraction by 46.7% averagely compared to other treatments. Besides, the SOC storage of passive pool (less-labile C + non-labile C) under NPKM was 30.7% higher than that in the Control. This was further supported by the higher proportion of passive than active pool indicating that fertilization, especially organic combined with inorganic fertilization, improved soil C stability. Additionally, the effect of different fertilization on SOC storage was mainly reflected in the surface soil, while very weak in the deeper soil as revealed by the stratification ratio and C sequestration rate.

Conclusion

Inorganic fertilizer combined with organic fertilizer have the ability to increase the storage and stability of SOC which further depend on annual C input and differences in soil depths. Taken together, in red paddy soil, the current fertilization had a significant effect on changing the dynamics of SOC in the topsoil, but a weak effect on the subsoil.

Soil organic carbon

Carbon fractions

SOC stability

Manure application

Sub-soil C

Soil is a complex system with characteristic physical, chemical and biological properties vital for nutrient cycling, biodiversity conservation and climate change regulation [1] particularly through carbon sequestration. Being the largest C pool in terrestrial ecosystem, the soil organic carbon (SOC) is a key parameter of soil quality and its ecosystem functioning [2]. Enrichment of carbon storage in soil is therefore important for maintaining soil quality and mitigating climate change. Long-term fertilization is one of the most efficient approaches for promoting carbon sequestration and sustaining soil fertility. The regular and sustained application of mineral fertilizers or manure have the potential to enhance SOC accumulation [3, 4, 5]. Studies conducted on paddy soils in China have demonstrated that combining manure application with mineral fertilizers enhances soil organic carbon (SOC) levels to a greater degree than solely using mineral fertilization [6, 7, 8], suggesting that manure has a significantly positive effect on soil fertility. However, the majority of studies on this topic have primarily focused on the dynamics of bulk soil SOC and have been limited to the topsoil layer. Additionally, the actual disparities in SOC increase could be determined by analyzing the dynamics of SOC fractions in both topsoil and subsoil layers, which have been overlooked in previous research.

Since different SOC fractions do not make equal contributions to soil C accumulation [9, 10], a better understanding of C distribution among SOC fractions and how this distribution is affected by long-term fertilization are essential in order to carry out a valid assessment of total organic carbon sequestration. In this regard, wet oxidation, a chemical fractionation method which is widely used in describing SOC lability and stability, can separate SOC into fractions with a gradient of oxidizability (very-labile C [C_frac1], labile C [C_frac2], less-labile C [C_frac3] and non-labile C [C_frac4]) [9, 11, 12]. The C_frac1 + C_frac2 represent the active C pool and serves as an early indicator of how management influences SOC, while C_frac3 + C_frac4 represent the passive C pool which is used as an indicator for describing the long-term effect of field management on SOC sequestration. However, there has been inconsistent results regarding the long-term fertilization effects on SOC enhancement in subtropical climate region [9, 12, 13, 14], which prompted a need for further studies in order to clarify how C storage occurs in SOC fractions in the long run.

It has been well established that, the SOC storage between soil layers is influenced primarily by crop root distribution and cultivation practices, and usually decreases with soil depth. To unveil these differences, stratification ratio (SR), defined as the ratio of a measurable property of the surface soil to that of deeper soil, can be used as an indicator of soil quality dynamics under various management practices [15, 16, 17]. Previous studies mainly focused on stratification of total SOC as affected by cropping systems or tillage practices [17, 18]. However, the heterogeneity of SOC in different soil layers and its response to long term fertilization are still not clear, and no explicit conclusions have been drawn on the SR of soil active and passive C pools which constitutes the further novelty of this work.

As one of the most important rice-producing soils, red paddy soils have attracted much attention with respect to SOC dynamics in China, whereas our knowledge about SOC storage and carbon stability at different soil depths under long-term fertilization managements has been still limited. This study was an attempt to investigate (i) the effects of long-term inorganic/organic fertilization on the SOC storage in different soil depths, (ii) assess the stability of SOC, and (iii) assess the rate of change of SOC accumulation or sequestration under applied treatments. The findings obtained would be beneficial to the management of farmland fertilization and the sustainable use of soil.

Site description

The experiment was introduced at the Jiangxi Research Institute of Red Soil, Jinxian, in the southern province of Jiangxi, China. The experimental site is located in a subtropical climate region at coordinates 28°35′24″N and 116°17′60″E, with an altitude of 26 m above sea level. The mean annual rainfall and temperature of the region are 1537 mm and 18.1°C, respectively. The soil at the site is red paddy soil, derived from quaternary red clay parent material. Soil samples collected from a depth of 0–20 cm at the beginning of the experiment indicated the presence of 16.3 g·kg^− 1 soil organic carbon, 1.49 g·kg^− 1 total nitrogen, 0.49 g·kg^− 1 total phosphorus, 144 mg·kg^− 1 available nitrogen, 9.50 mg·kg^− 1 available phosphorus, and 81.2 mg·kg^− 1 available potassium, with an initial pH of 6.9 [19].

Experimental design

The experiment conducted was a long-term study of a rice-rice cropping system that included a winter fallow period. The early rice was cultivated from April-July, while the latter rice was grown from the middle of July to late October. Crops were harvested manually close to the ground and all harvested biomass was removed from the plots. The size of each plot was 46.67 m². There were four treatments: (1) Control: no fertilization, (2) NPK: the application rates for N (urea), P (calcium superphosphate), K (potassium chloride) fertilizer were 90 kg·ha^− 1, 20 kg·ha^− 1, 62 kg·ha^− 1, respectively, during both growing seasons. (3) 2NPK: double the fertilization rates of NPK treatment, and (4) NPKM: NPK plus organic fertilizers, Chinese milk vetch (Astragalus sinicus L.) for the early rice and pig manure for the latter rice, the application rates of organic fertilizers were both 22.5 t·ha^− 1. The experiment followed a completely randomized block design, with three replicates for each treatment. In both the early and late rice crops, all phosphorus and potassium fertilizers, organic fertilizers, and 60% of the nitrogen fertilizer were applied as basal fertilizers prior to the transplantation of rice seedlings. The remaining 20% of the nitrogen fertilizer was split into two applications, with 20% being applied at the panicle initiation stage and the remaining 20% applied 10 days prior to the flowering stage.

Soil sampling and measurement

After 29 years of setting up the field experiment, soil samples were collected in November, 7 days after the late rice harvest. The samples were collected from three different soil layers, namely 0–20 cm, 20–40 cm, and 40–60 cm depths. To create each sample per layer per plot, 10 soil cores were pooled together. Soil samples were air-dried and sieved through a 2 mm sieve for analyses. Soil bulk density in the layers of 0–20, 20–40 and 40–60 cm was determined by taking three soil cores from the middle of each depth in each plot using the ring-knife with a diameter of 5 cm and volume of 100 cm³. Gravel and residue larger than 2 mm were removed from the sample. The bulk density samples were weighted after overnight drying at 105℃. The data of soil bulk density were shown in Table 1.

Table 1

Soil bulk density in three soil depths in different treatments
Treatment	Depth
Treatment	0–20 cm	20–40 cm	40–60 cm
CK	1.20 ± 0.01	1.55 ± 0.02	1.54 ± 0.01
NPK	1.21 ± 0.02	1.54 ± 0.03	1.51 ± 0.04
2NPK	1.21 ± 0.02	1.57 ± 0.02	1.55 ± 0.03
NPKM	1.06 ± 0.03	1.56 ± 0.02	1.50 ± 0.02

The SOC fractions were separated by a modified Walkley-Black method as described by Chan et al. (2001) [11]. Specifically, 0.5 g soil samples were added into 10 mL 0.167 mol·L^− 1 K₂Cr₂O₇ solution, then added 5 mL concentrated H₂SO₄ (18 mol·L^− 1) to produce reaction heat; after 30 min reaction, 1.0 mol·L^− 1 FeSO₄ was titrated to determine the excess dichromate. The amount of dichromate consumed by the soil was used to calculate the amount of oxidizible carbon, this amount of oxidized carbon was defined as the 6 mol·L^− 1 H₂SO₄ oxidized SOC. To obtain the 9 mol·L^− 1 H₂SO₄ oxidized SOC and 12 mol·L^− 1 H₂SO₄ oxidized SOC, the amounts of concentrated H₂SO₄ added were changed to be 10 mL and 20 mL, respectively. Finally, this resulted in four fractions in decreasing order of oxidizability: (1) Frac1 (Very-labile C): (2) Frac2 (Labile C): (3) Frac3 (Less-labile C): (4) Frac4 (Non-labile C). These four fractions were grouped into the active C pool [Frac1 + Frac2] and the passive C pool [Frac3 + Frac4] according to Chan et al. (2001). Soil samples for total SOC measurement were pretreated using 36% HCl-fumigation method to remove carbonates, and then were determined with an elemental analyzer. Due to different testing methods, the SOC content at the beginning of the experiment was corrected for comparison [12].

Calculations

The SOC storage (t C·ha^− 1) and carbon input (t C·ha^− 1) were calculated from the following equations:

SOC storage (t C·ha^− 1) = C_conc×B_d×D×10 (1)

Where C_conc represents SOC concentration (g·kg^− 1) at each soil depth, B_d is bulk density (g·cm^− 3) at each soil depth, and D is soil depth (cm), 10 is unit conversion factor. Total SOC storage is the sum of SOC storages at three soil depths.

C_input−root=(YS + YR)×R_r×C_rice×10^− 6 (2)

C_{input−stubble}=YR×R_s×C_rice×10^− 6 (3)

C_{input−organic fert}=m×(1-W)×C_{organic fert}×10^− 3 (4)

Where C _input−root, C _{input−stubble}, C _{input−organic fert} are carbon inputs from root (assume that root-carbon all distributed within 0–60 cm soil depth), stubble, organic fertilizers, respectively, t C·ha^− 1; YS and YR are the yields of rice seed and residue respectively, kg·ha^− 1; R_r is the proportion of carbon entering into underground part by photosynthesis, %; C_rice is the C content of the aboveground part of rice, %; R_s is the proportion of rice residue left in the fields after harvest, 5.6% in this study; m is the application rate of organic fertilizer, 22.5 t·ha^− 1 for both milk vetch and pig manure; W is the water content of organic fertilizers, %; C_{organic fert} is the C content of organic fertilizers, %. Total external carbon input (C_{input−total}) is the sum of C_input−root, C_{input−stubble}, and C_{input−organic fert}. Data of carbon input presented are average of 29 years, t C·ha^− 1 yr^− 1.

The annual change rate of SOC storage (ACR_soc, t C·ha^− 1 yr^− 1) was calculated using the equation below:

ACR_soc = (SOC_t-SOC₀)/T (5)

Where SOC₀ and SOC_t represent the SOC storage at the beginning and the end of the experiment, respectively; T is the duration of this experiment, 29 years. Calculations were made at 0–60 cm depth.

Moreover, the SOC accumulation and sequestration rates were calculated based on following equations;

SOC accumulation rate (t ha^− 1 yr^− 1) = (SOC_t-SOC_c)/T (6)

Where, SOCt is SOC stocks (t ha^− 1) in treatments, whereas, SOCc is SOC stocks in control and T is experimental time.

SOC sequestration rate (t ha^− 1 yr^− 1) = (Rec.SOC_t - Rec.SOC_c)/T (7)

Where, Rec.SOCt and Rec.SOCc are recalcitrant C stocks (t ha^− 1) of a given treatment and unfertilized control and T is the experimental time.

Statistical analysis

Primary calculations of data were performed in Excel 2010 and statistical analyses were performed using SAS 9.4. A two-way analysis of variance (ANOVA) model was used to determine the main effect of treatments and soil depth. Multiple comparisons were made by using the least significant difference (LSD) at p = 0.05. Figures were made using Excel 2010, Origin 8.0.

Carbon input and SOC storage

Table 2 showed that the total carbon inputs (C_{input−total}) were consistent with the soil organic carbon (SOC) storage levels in the 0–60 cm soil depth. The carbon input from both roots and stubble (C_input−root, C_{input−stubble}) was higher in the fertilized treatments compared to the Control (p < 0.05). When combined with the carbon input from organic fertilizer (C_{input−organic fert}), the C_{input−total} showed a ranking of NPKM > 2NPK > NPK > Control (p < 0.05). Increasing C_{input−total} led to a larger SOC storage, but not in the same proportion. The SOC storage in the NPKM treatment was on average 7.33% higher than Control.

Table 2

Carbon input and SOC storages of 0-60cm soil depth in different treatments
Treatment	C_input−root (t C·ha^− 1yr^− 1)	C_{input−stubble} (t C·ha^− 1yr^− 1)	C_{input−organic fert} (t C·ha^− 1yr^− 1)	C_{input−total} (t C·ha^− 1yr^− 1)	SOC storage (t C·ha^− 1)	ACR_soc (t C·ha^− 1yr^− 1)
CK	2.13 ± 0.47 c	0.15 ± 0.05 c	——	2.29 ± 0.52 d	69.9 ± 2.08 b	0.126 ± 0.072 b
NPK	2.44 ± 0.55 bc	0.24 ± 0.08 b	——	2.68 ± 0.63 c	70.2 ± 0.33 b	0.134 ± 0.012 b
2NPK	2.88 ± 0.68 a	0.29 ± 0.11 a	——	3.17 ± 0.78 b	72.4 ± 1.21 ab	0.212 ± 0.042 ab
NPKM	2.75 ± 0.71 ab	0.28 ± 0.12 ab	3.48	6.51 ± 0.82 a	75.2 ± 3.85 a	0.307 ± 0.133 a
Note: Different lowercase letters indicate significant differences among treatments, p < 0.05.

The SOC storage was 66.28 t C·ha^− 1 along the profile at the beginning of this experiment. After 29 years, the differences of annual changing rate of SOC storage (ACR_soc) among the four treatments showed the same pattern as the SOC storage (Table 2). The correlation coefficient between C_{input−total} and annual changing rate of SOC (ACR_soc) was 0.952.

Carbon storage in SOC fractions at the whole soil profile

The data of carbon storage in the SOC fractions (Very-labile C, Labile C, Less-labile C and Non-labile C) at the soil profile of 0–60 cm were shown in Fig. 1A. The SOC storage of Very-labile C fraction showed no significant difference among four treatments. Organic fertilization lowered the SOC storage of the Labile C fraction by 19.1% and 15.3% comparing with the Control and 2NPK treatments respectively (p < 0.05), but accreted the SOC storage of Less-labile C fraction by 46.7% compared to other treatments on average. The larger SOC storage of the Non-labile C fraction was observed in the 2NPK (25.0 t C·ha^− 1) and NPKM (23.8 t C·ha^− 1) treatments compared to other treatments.

Total SOC storage at different soil depths

The SOC storage was much higher at 0–20 cm depth (45.3 t C·ha^− 1, average of the four treatments) than those at depths of 20–40 cm (13.1 t C·ha^− 1) and 40–60 cm (13.6 t C·ha^− 1) (p < 0.001). The NPKM treatment showed the larger SOC storage than the Control and NPK treatments at 0–20 cm depth (p < 0.05), no significant difference among the four treatments was observed for both 20–40 cm and 40–60 cm layers (Fig. 1B). Moreover, in line with the SOC storage results, the SOC accumulation as well as sequestration rates were higher in at 0–20 cm depth as compared to other depth intervals (Fig. 2). The highest SOC accumulation and sequestration rates were associated with NPKM treatment and patterned as NPKM > 2NPK > NPK.

Carbon storage in SOC fractions at different depths

In terms of different soil layers, the amounts of C stored in the four SOC fractions at 0–20 cm depth were all significantly higher than those at deeper layers (Fig. 1C, D, E and F). Irrespective of the soil layers, the SOC storage of Very-labile C fraction showed no significant difference among four treatments (Fig. 1C). The influences of fertilization on SOC storage of LC, LLC and NLC fractions were mainly reflected in the topsoil (Fig. 1D, E and F). Compared to other SOC fractions, the Less-labile C fraction was most affected by organic fertilization, especially in topsoil. The SOC storage of Less-labile C fraction at 0–20 cm depth increased by 113%, 49.5% and 72.8% under NPKM compared to that in the Control, NPK and 2NPK treatments, respectively (p < 0.05). The SOC increment in Non-labile C fraction after long-term organic fertilization was not only in the surface soil but also in the sub-soil (20–40 cm) (Fig. 1F).

Carbon storage in SOC pools at different depths

By analyzing the proportion of active and passive pools of SOC under different fertilization treatments (Fig. 3) and redundancy analysis (Fig. 4), it can be seen that the labile, less-labile and non-labile C stocks were related to whole depth interval as well as surface soil layer. On the other hand, deeper soil layers were linked to lower soil carbon fraction and pools. Axis two (F2) is also related to surface soil depth (0–20 cm) as well as to the fertilization treatment category, characterized by SOC sequestration rate. Which implies that NPKM treatment led to increased SOC sequestration rate in the top layer (0–20 cm) of the soil.

From the perspective of carbon pools with different stability, the storage of active carbon pool was higher in the Control (39.6 t C·ha^− 1) than in other treatment (36.2 t C·ha^− 1 on average), and the passive pool showed the opposite scenario (Fig. 5). Fertilization increased the SOC storage of passive pool (p < 0.05), and the value in the NPKM treatment was 30.7%, 16.1%, 11.8% higher than in the Control, NPK, 2NPK treatments, respectively. The difference of SOC storage among treatments for passive pool was mainly resulted from the difference at surface soil, and for active pool were the deeper layers.

Stratification characteristics

The SR values of total SOC storage (Fig. 6) for both surface and deep soil layers were significantly greater in the NPKM treatment (3.74 and 3.68) than in the Control (3.12 and 3.03) (p < 0.05). The SR of both the active pool and the passive pool for 0–20 cm: 20–40 cm showed no significant difference among the four treatments, while the SR of the passive pool for 0–20 cm: 40–60 cm was higher under NPKM (4.24) than that in other treatments (3.29 averagely) (p < 0.05).

Fertilization impacts on SOC storage and sequestration

Long-term fertilizer application is believed to affect crop yields and biomass [7, 20, 21], thus alter the amount of exogenous carbon input. This increase in carbon input is concomitantly linked to the soil carbon concentration [7, 22]. This long-term study showed that applying standard rate of inorganic fertilizer or double the standard amount of fertilizer can significantly increase crop biomass and carbon input, but their effects on SOC storage of the 0–60 cm soil profile were very limited (Table 2). The sole application of organic fertilizer can effectively improve the SOC storage. This was not completely consistent with previous works which was done in the surface soil [7], probably because the change of SOC storage in 0–60 cm soil layer was slower and more insensitive than in the surface layer. Besides, whether the fertilizer application rate doubled or not did affect the carbon input, but did not show significant impact on SOC storage, suggesting that the SOC concentration did not increase proportionally with increasing NPK fertilizer rate, which agrees with Li et al. (2020) [23]. However, there was a great difference observed for SOC storage for different soil depths, whereby, the top soil (0-20cm) showed significantly highest SOC storage as compared to other depths. This is consistent with Abrar et al. (2022) who observed the highest SOC storage in top soil layer under long-term fertilization in a Chinese Mollisol [24]. Moreover, the manure combined with NPK had the highest SOC storage along the soil profile (Fig. 1). This is due to the higher organic carbon input from manure and its stabilization in the soil as further revealed by higher C input (Table 2) and higher proportion of passive carbon observed in this study (Fig. 1). These findings were further substantiated by the observation that the accumulation rate of SOC storage during 29-year experimentation was significantly positively correlated with the amount of external carbon input, which suggested the potential of the red paddy soil in sequestrating exogenous carbon. The highest SOC accumulation and sequestration observed in topsoil under NPKM treatment (Fig. 2) further verify these findings. Taken together, these findings suggested that combining manure with balanced NPK could be an attractive strategy in improving SOC sequestration however which is further governed by annual C input and soil depths.

Fertilization impacts on SOC stratification characteristics

In red paddy soil, the distribution of carbon in SOC fractions showed variation with depth, with a higher level of SOC storage found in the surface soil compared to the deeper soils. This was mainly caused by C accumulation from stubble and root residue in the surface soil. Zhang et al. (2013) reported that, about 80–90% of the roots of rice crop are distributed in the 0–10 cm soil layer and little in deeper layers [25] which might be due to soil compaction in deeper layers limiting root growth [16]. This implies that there is a wide gap in external C input between the surface soil and the deeper soils (Table 2). Thus, the SOC would be stratified in surface soil layers with higher stratification ratios being regarded as good indicators of dynamic soil quality [15]. In this study, the enhancement of stratification ratio of total SOC under manure application was mainly reflected in the passive pool rather than active pool (Fig. 6), indicating that manure application could efficiently improve carbon stability in surface soil. This can be associated with the properties of manure resulting in higher recalcitrant compounds, which consequently enhanced SOC stability [26].

Fertilization treatments influenced total SOC storage in surface soil and showed no significant effect on deeper layers except for the non-labile C fraction at 20–40 cm soil depth. Green manure or animal manure can improve root biomass [27] and the external C input from roots would accumulate not only in the top soil but also in the subsoil due to leaching or the increased soil microbial activity [28]. However, the amounts of root biomass distributed in the 20–60 cm soil layers were usually very low, about 10–20% of the total [25]. Thus, the increase in root biomass in the deeper soil layers caused by fertilization was also limited, this result was consistent with previous studies [29] depicting a pattern similar to the one observed in the present study.

Fertilization impacts on SOC stability

The SOC storage of active pool was greater under no fertilization than in fertilized treatments, and fertilization increased the SOC storage of passive pool (Fig. 5). This was associated with the increased SOC storage of less-labile C fraction in the surface soil, hence the SOC storage of passive pool. This suggested that fertilization derived SOC accumulated in the passive pool and improved soil carbon stability, whereby the highest values were found under combined organic fertilization with inorganic fertilization. These findings corroborate with Yanardag et al. (2015) stating that pig manure increased the amount of recalcitrant C in Luvisol [30]. Contrarily, Mandal et al. (2008) found that the increase in SOC due to manure application was not limited to the less-labile C fraction, but also involved the very-labile C and non-labile C fractions [9]; and Sun et al. (2013) showed that manure application increased total SOC by increasing C accumulation only in very-labile C fraction [12]. These inconsistent results were probably due to variability in manure quality and quantity [30]. The differences in the findings of the studies by Mandal et al. (2008) [9], Sun et al. (2013) [12], and the current study could be attributed to variations in the types and quality of the organic amendments used. The manure used in Mandal et al. (2008) was highly decomposed and had high amounts of lignin and polyphenol [9], while the manure used in Sun et al. (2013) [12] and the current study were fresh pig manure and legume and fresh pig manure, respectively. These variations could lead to differences in the proportions of WSC, biodegradable organic compounds, and non-decomposable organic compounds, and thus affect the distribution of SOC fractions in response to different organic amendments [31, 32], and this could lead to differences in the C decomposition, immobilization and distribution characteristics of SOC fractions which ultimately affects OC stabilization. In nutshell, our results highlighted the positive influence exerted by organic amendments in intensive double-rice cropping in terms of increasing the stability of SOC.

In conclusion, this study has found that the impact of inorganic fertilizer application on SOC storage in the 0–60 cm soil profile of paddy soil is limited except for the 2NPK treatment. The larger SOC storage of the Non-labile C fraction was observed in the 2NPK and NPKM treatments compared to other treatments. Inorganic fertilizer combined with organic fertilizer could increase the storage and stability of SOC which further depend on annual C input and be revealed by higher SOC passive pool. Taken together, in red paddy soil, the current fertilization had a significant effect on changing the dynamics of SOC in the topsoil, but a weak effect on the subsoil. Therefore, it is imperative to appropriately increase the application of manure and reduce the chemical fertilizer use.

Acknowledgements

We thank the experimental station staff for managing the experimental fields.

Author contribution

X. Chen, M. Xu, Q. Huang, K. Liu: Design of the work, performed the research, data analysis; M. Xu: Supervision, project administration, conceptualization; X. Chen, H Xu, N Sun, A Mustafa: Wrote the manuscript; M. Xu, A Mustafa: Revised the manuscript.

Funding

The work was supported by National Natural Science Foundation of China (42177341).

Availability of data and materials

All data generated or analysed during this study are included in this article, and be available from the corresponding author on reasonable request.

Ethical approval and consent to participate

Not applicable.

Consent for publication

All authors listed have read the complete manuscript and have approved submission of the paper.

Competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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No competing interests reported.

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Editorial decision: Major revision
30 Jun, 2023
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30 Jun, 2023
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Long-term organic amendments enhanced soil organic carbon storage and stability in a typical paddy soil of Southern China

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Version 1

Abstract

Background

Results

Conclusion

Figures

Introduction

Materials and methods

Site description

Experimental design

Soil sampling and measurement

Calculations

Statistical analysis

Results

Carbon input and SOC storage

Carbon storage in SOC fractions at the whole soil profile

Total SOC storage at different soil depths

Carbon storage in SOC fractions at different depths

Carbon storage in SOC pools at different depths

Stratification characteristics

Discussion

Fertilization impacts on SOC storage and sequestration

Fertilization impacts on SOC stratification characteristics

Fertilization impacts on SOC stability

Conclusions

Declarations

References

Additional Declarations

Status:

Version 1