Soil organic carbon and its labile fractions in paddy soil as influenced by water regimes and straw management

Agricultural Water Management 224 (2019) 105752

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Soil organic carbon and its labile fractions in paddy soil as influenced by water regimes and straw management ⁎

Wenhai Mia,b,1, Yan Sunc,1, Cai Zhaoa, , Lianghuan Wud,

T

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a

Gansu Provincial Key Laboratory of Aridland Crop Science, Gansu Agricultural University, Lanzhou 730070, China College of Environmental Science and Engineering, Yangzhou University, Yangzhou 225127, China c Institute of Water Resources and Hydro-Electric Engineering, Xi’an University of Technology, Xi’an 710048, China d Zhejiang Provincial Key Laboratory of Agricultural Resources and Environment, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Soil organic C Particulate organic C Potassium permanganate-oxidizable C Water regimes Straw management

Understanding the effects of water regimes and straw management on soil organic carbon (SOC) pools is necessary to improve soil C sequestration and soil quality. Based on a long-term field experiment (15 years), we examined impacts of water regimes and straw management methods on total soil organic C (TOC), particulate organic C (POC) and potassium permanganate-oxidizable C (KMnO4–C) at two soil depths. Water regimes consisted of flooding cultivation and non-flooded cultivation. In non-flooded cultivation, limited irrigation was employed to keep the soil moist condition without standing water covering the field during the rice-growing season. It is substantially different from conventional flooded rice cultivation. The two straw management methods were straw mulching and straw removal. The results showed that water management had greater effects on TOC and KMnO4–C than did straw management at 0–10 cm soil layer. Compared to the non-flooded treatment, flooding cultivation resulted in 17.4% higher TOC and 31.4% higher KMnO4–C contents. Correspondingly, straw management showed dominant effects on POC. Straw mulching significantly increased POC content by 13.0% as compared to the straw removal treatment. However, at deeper soil depth (10–20 cm), labile SOC fractions were only affected by water regimes. The higher carbon management index (CMI) values at 0–20 cm were recorded in the flooding condition with straw mulching treatment. This was attributed to the increased carbon pool index (CPI), which contributed to the formation of more stable organic compounds that collectively act as a soil reservoir. The combined non-flooded cultivation and straw mulching method (NFC–SM) produced a similar 15–year average rice grain yield and TOC content in 2016 compared to the traditional flooding cultivation with straw removal treatment (FC–SR). Our data indicated that NFC–SM could be an ideal strategy not only to save water but also to maintain soil fertility.

1. Introduction Rice is one of the most important food crops in Asia, and it consumed about 90% of total irrigation water for crops (Li et al., 2007). Conventional flooded rice cultivation is very popular and requires a standing water depth of 5–10 cm in the fields, consuming about 0.5–3 m3 m−2 during the entire rice growth season (Qin et al., 2006). Diminishing water resources in seasonal drought areas present a challenge for this method. Thus, water saving techniques has been employed since the 1980s. These included alternate wetting and drying irrigation (Cabangon et al., 2011), non-flooded mulching (Li et al., 2017), and aerobic rice systems (Bouman et al., 2006). Previous studies have

reported the effects of different water regimes on rice grain yield, water use efficiency, and soil nutrient balance (Liu et al., 2003; Kudo et al., 2014). Recently, there has been considerable interest regarding soil organic C (SOC) storage under different water management practices. SOC plays a key role in the long-term soil productivity because it is linked to the physical, chemical, and biological properties of soil (Haynes, 2005; Tian et al., 2013a). In addition, it is important in mitigating atmospheric CO2 levels (Lal, 2004). Hence, the maintenance of satisfactory SOC levels is essential to the sustainability of agroecosystems. The storage of SOC depends on the balance between the C input derived from crop residues and the C output from soil organic matter (SOM) decomposition (Yan et al., 2013). Tian et al. (2013b) showed

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Corresponding authors. E-mail addresses: [email protected] (C. Zhao), fi[email protected] (L. Wu). 1 The authors equally contributed. https://doi.org/10.1016/j.agwat.2019.105752 Received 12 December 2018; Received in revised form 18 June 2019; Accepted 14 August 2019 Available online 22 August 2019 0378-3774/ © 2019 Elsevier B.V. All rights reserved.

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that aerobic environments have higher decomposition rates of SOM than anaerobic environments. Therefore, different water management practices may affect SOC level. Li et al. (2007) reported that continuous plastic film mulching with no flooding decreased SOC content by 8.3–24.5% at five sites compared to traditional flooding management. However, Fan et al. (2012) found that non-flooded plastic film or nonflooded wheat straw mulching resulted in similar or higher SOC content compared to traditional flooded cultivation in a 10–year field experiment. Soil organic C consists of various fractions varying in degree of recalcitrance, decomposition, and turnover rate (Wang et al., 2014). Most of SOC (60–70%) is found in the passive pool with turnover times extending to thousands of years. Approximately 20 to 40% of SOC is in the slow pool with decadal turnover times, while the active fractions comprise less than 5% of the SOC. The particulate organic C (POC) and potassium permanganate-oxidizable C (KMnO4–C) comprised the slow turnover pool (Sherrod et al., 2005). The influence of different management practices on the contents of SOC fractions can provide valuable information about mechanisms of C sequestration (Six et al., 2002). Mi et al. (2016) measured increases in POC and KMnO4-C after the addition of crop residues and manures that were greater than those in total soil organic C (TOC). Further, active SOC fractions are also a major source for C loss (Tian et al., 2013a). The oxidation of SOC drives the flux of CO2 from soils to the atmosphere. Therefore, measurements of POC and KMnO4–C are essential to the identification of changes in SOC and, ultimately, environmental sustainability. In addition, the carbon management index (CMI) is derived from the total SOC pool and C lability and is recommended as an early indicator of the effects of management practices on soil quality (Chaudhary et al., 2017). To the best of our knowledge, information is limited on the long-term effects of different water regimes and straw managements on soil total organic carbon and its labile fractions. Therefore, based on a 15–year field experiment, we evaluated the impacts of different water regimes (flooding cultivation and nonflooded cultivation) and residue management methods (straw mulching and straw removal) on TOC, its labile fractions including POC, KMnO4–C, and CMI at different soil depths. This information will be useful to develop reasonable management strategies to optimize sustainability of agroecosystems.

Fig. 1. Precipitation during the rice/fallow season and temperature during the rice/fallow season (2001–2015).

soil surface after rice harvest each year. One week before transplanting of rice of next year, all plots were artificially leveled and then soaked. Then rice seedlings were generally transplanted at a spacing of 20 cm × 28 cm with two seedlings per hill in late–June. For the traditional flooding management, the plots were flood-irrigated every 3–5 days to maintain 2–3 cm layer of water until the grainfilling stage of rice. For the non-flooded treatment, soil remained moist without standing water covering the field during the rice-growing season. Limited irrigation (30–50 mm per irrigation) was applied when soil water content was less than 80% of field water-holding capacity. During the whole rice growth period, the irrigation amount of flooded and non-flooded irrigation methods were 800–1000 mm and 300–500 mm, respectively. The rice crop was manually harvested in late–October. The plot size was 30 m2 isolated by ridges and plastic film cover to prevent water and fertilizer flow to adjacent plots. All treatments were applied at the same rate of 135 kg N ha–1 as urea, 47 kg P2O5 ha–1 as calcium superphosphate, and 67.5 kg K2O ha–1 as potassium chloride. The amount of organic C that was annually going to soils was calculated based on the sum of C input from paddy straw, stubble, roots and rhizosphere depositions (Table 1). Paddy straw, stubble or root C inputs into the soils were calculated by multiplying the biomass amount of paddy straw, stubble or roots by their respective C concentration. Rice rhizodeposition C input was computed as 28% of root biomass (Liu et al., 2019).

2. Materials and methods 2.1. Experimental site description The experiment was conducted at Panzhai Country (29°19′N, 119°43′E), Zhejiang Province, China. This region has an intermediate subtropical monsoon climate with mean annual precipitation of 1483 mm and a mean temperature of 19.5 °C (Fig. 1). The frost-free period is 265 d and the annual sunshine hours are 1982 h from 2001 to 2015. Initially, the top soil (0–20 cm) at the experimental site contained 30.2 g kg–1 organic matter, 2.28 g kg–1 total nitrogen (N), 88.5 mg kg–1 available phosphorus (P), 212.9 mg kg–1 available potassium (K), and pH in this case was 5.1.

2.3. Sampling and measurement Rice grain yield was calculated on 14% moisture content basis after manually harvesting each plot. Five soil samples per plot were collected from the 0–10 cm and 10–20 cm layer in May, 2016. The samples were Table 1 Average annual rice residue C going to soil through paddy straw, stubble, root biomass and rhizodeposition.

2.2. Experimental design

Treatment

The experiment was established in 2001 with a single cropping rice system. Fields remained fallow during November–June of next year. Treatments were laid out in a split-plot randomized complete block design with three replicates. It included two water management systems as main plots and two straw management methods as subplots. The two water management systems were conventional flooding cultivation (FC) and non-flooded cultivation (NFC). The two straw management methods consisted of rice straw mulching (SM) and rice straw removal (SR). For the rice straw mulching treatment, rice straw (airdried, 3 Mg ha–1) were cut into 3–5 cm long segments and applied to the

FC–SM FC–SR NFC–SM NFC–SR

Paddy straw biomass C

Mg ha−1 1.2 0 1.2 0

Stubble biomass C

Root biomass C

Rhizodeposition C

Annual rice residue C return to soil

0.17 0.16 0.16 0.16

1.16 1.11 1.12 1.09

0.93 0.89 0.90 0.87

3.46 2.16 3.38 2.11

Note: FC–SM, flooding cultivation–straw mulching; FC–SR, flooding cultivation–straw removal; NFC–SM, non-flooded cultivation–straw mulching; NFC–SR, non-flooded cultivation–straw removal. 2

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mixed to form a composite soil sample. The air-dried samples were sieved (< 2 mm) and ground further to pass through a 0.25 mm sieve for determination of TOC and TN. TOC was determined by oxidation with K2Cr2O7 and by titration with ferrous ammonium sulphate (Walkley and Black, 1934). Soil TN was measured using the Kjeldahl method after H2SO4 digestion (Bremner, 1996). Particulate organic C was separated from 2 mm soil following the procedure of Cambardella and Elliott (1992). Ten grams of air-dried soil was dispersed in 30 ml of sodium hexametaphosphate (5 g L–1) by shaking on a reciprocating shaker (100 r min–1) for 18 h. The soil suspension was poured over a 53–μm sieve using a steady flow of distilled water to ensure separation. All materials remaining on the sieve were washed into a dry dish and then oven-dried at 60 °C for 48 h, weighed, and ground in order to measure the C content. Potassium permanganate-oxidizable C was determined as described by Blair et al. (1995). Soil samples containing approximately 15 mg C were oxidized with 25 ml of 333 mM KMnO4, which were shaken for 1 h. After shaking, the tubes were centrifuged for 5 min. The supernatants were diluted and the absorbance was measured at 565 nm. The change of KMnO4 concentration was used to estimate the amount of C oxidized. The Carbon Management Index (CMI) and its components were calculated based on the method of Blair et al. (1995), which is described below: CMI = CPI × LI × 100

Table 2 Contribution (%) of water regimes and straw management to variation of SOC and its labile fractions (two-way ANOVA). Soil depth

C/N

POC

KMnO4-C

CMI

0-10 cm

Water regimes (W) Straw management (S) W×S Unexplained

54 28 1 17

5 66 13 16

75 2 7 16

38 50 3 9

59 21 9 11

55 20 11 13

10-20 cm

Water regimes Straw management W×S Unexplained

13 5 10 73

8 45 19 27

14 19 18 49

84 2 7 7

60 11 6 23

67 20 5 8

Table 3 Effect of water regimes and straw management on total soil organic carbon (TOC), total nitrogen (TN), and C/N at different soil depths. Soil depth (cm)

TOC TNg g kg−1 kg−1 0-10 cm

C/N

TOCg TNg kg−1 kg−1 10-20 cm

C/N

Flooding cultivation

21.2aa

1.8a

11.6a

15.2a

1.4a

11.1a

19.3a

1.6b

11.9a

14.8a

1.3a

11.1a

18.5a

1.8a

10.2a

12.7a

1.5a

8.2a

1.7a

9.2a

14.7a

1.3b

11.3a

1.7A 1.8A 1.8A 1.7B

11.7A 9.7B 10.9A 10.6A

15.0A 13.7A 13.9A 14.7A

1.4A 1.4A 1.5A 1.3B

11.1A 9.8A 9.6A 11.2A

Straw mulching Straw removal Non-flooded Straw cultivation mulching Straw removal Flooding cultivation mean Non-flooded cultivation mean Straw mulching mean Straw removal mean

(1)

CPI= (TOC content in sample soil) / (TOC content in reference soil) (2) (3)

Where L refers to the C lability, which is determined as follows: L= (KMnO4–C content) / (TOC content – KMnO4–C content)

TN

Note: TOC, total soil organic carbon; TN, soil total nitrogen; POC, particulate organic carbon; KMnO4–C, Potassium Permanganate oxidized organic carbon; CMI, carbon management index.

Where CPI is the carbon pool index and LI is the lability index. The CPI and LI are determined as follows:

LI= (L in sample soil) / (L in reference soil)

TOC

(4)

16.0a 20.3A 17.3B 19.8A 17.7B

b

a Means (n = 3) followed by lower-case letters in the same column are significant (p < 0.05) different between different straw management within each water regime. b Means (n = 6) followed by upper-case letters in the same column are significant (p < 0.05) different between water regimes or straw management.

In this study, the flooding cultivation method without rice straw mulching was used as a reference for the calculation of CMI. 2.4. Statistical analysis

methods (Table 2). Compared to the straw removal treatment, rice straw mulching exhibited 12.5% higher TN content at 0–10 cm under flooding conditions, and 15.4% higher TN content at 10–20 cm under non-flooded conditions after 15 years.

Data collected were analyzed using a two-way analysis of variance (ANOVA) with STATISTICA software Version 5.5. The contribution of each variation source is calculated based on the ratio of the sum of squares of deviations (SS) of each factor to the total SS. Differences were considered significant at p < 0.05 using Duncan multiple range test.

3.2. POC Significant POC content responses to water regimes and straw management methods were recorded at 0–10 cm, accounting for 38% and 50% variations, respectively (Table 2). Compared to the straw management methods, water regimes showed a higher contribution (84%) to the POC content at 10–20 cm (Table 2). The POC content was 11.1% higher at 0–10 cm and 15.8% higher at 10–20 cm under flooding condition than under non-flooded condition when averaged across two straw management methods (Fig. 2). POC contents were significantly higher in the rice straw mulching treatment than without rice straw mulching at 0–10 cm. However, no differences were recorded between the two straw management methods at 10–20 cm.

3. Results 3.1. TOC and TN The water and straw management methods respectively accounted for 54% and 28% of the variation in TOC content at a depth of 0–10 cm. However, no significant differences were recorded at 10–20 cm soil depth (Table 2). The mean TOC content (across both straw management treatments) at 0–10 cm was 17.4% higher in the flooding cultivation than that in the non-flooded treatment (Table 3). Between the two straw management methods, rice straw mulching resulted in 11.9% higher TOC content than rice straw removal at 0–10 cm soil depth (Table 3). Overall, the combined flooding cultivation and straw mulching (FC–SM) method showed the highest TOC content (21.2 g kg–1). The combined non-flooded cultivation and straw mulching (NFC–SM) treatment produced a similar TOC content compared to the flooding cultivation with straw removal (FC–SR) treatment after 15 years. Soil TN content was significantly affected by straw management

3.3. KMnO4–C Both water regimes and straw management methods influenced KMnO4–C content at 0–10 cm soil layer. At deeper soil depth (10–20 cm), water regimes showed dominant effect on KMnO4–C content, accounting for 60% of the variation (Table 2). 3

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Fig. 2. Effect of water regimes and straw management on particulate organic carbon at different soil depths. Different lower-case letters at each water regime present significant difference between straw management methods at the 5% level. Different upper-case letters present significant difference between water regimes at the 5% level. Vertical bar indicates the standard error of the mean.

Fig. 3. Effect of water regimes and straw management on potassium permanganate-oxidizable carbon contents at different soil depths. Different lower-case letters at each water regime present significant difference between straw management methods at the 5% level. Different uppercase letters present significant difference between water regimes at the 5% level. Vertical bar indicates the standard error of the mean.

The KMnO4–C content was significantly higher under flooding conditions than under non-flooded conditions across the two straw management methods. In flooding conditions, straw mulching resulted in 26.7% higher KMnO4–C content than in straw removal at 0–10 cm soil layer (Fig. 3). Correspondingly, straw mulching increased the KMnO4–C content at 0–10 cm by 6.8% compared to straw removal under non-flooded conditions (Fig. 3).

Table 4 Effect of water regimes and straw management on soil carbon management index. Soil depth (cm)

CPI LI 0-10 cm

CMI

CPI LI 10-20 cm

CMI

Flooding cultivation

1.1aa

1.2a

132a

1.0a

1.1a

113a

1.0b

1.0a

100a

1.0a

1.0a

100b

1.0a

0.9a

88a

0.9a

1.1a

93a

0.8a

1.0a

83a

1.0a

0.9a

88a

1.1Ab 0.9B 1.0A 0.9A

1.1A 1.0A 1.1A 1.0A

116A 86B 110A 92B

1.0A 0.9A 0.9A 1.0A

1.1 A 1.0A 1.1A 1.0A

107A 91B 103A 94B

Straw mulching Straw removal Non-flooded Straw cultivation mulching Straw removal Flooding cultivation mean Non-flooded cultivation mean Straw mulching mean Straw removal mean

3.4. CMI Both water regimes and straw management methods significantly influenced the CMI values, accounting for 55% and 20% variations, respectively, at 0–10 cm and 67% and 20% variations, respectively, at 10–20 cm soil layer (Table 2). Flooding cultivation increased the CMI value by 34.9% at 0–10 cm and 17.6% at 10–20 cm as compared to nonflooded cultivation when averaged across the two straw management methods (Table 4). Similarly, straw mulching resulted in comparable or higher CMI values than straw removal irrespective of irrigation regimes in both soil depths.

Note: CPI, carbon pool index; LI, lability index; CMI, carbon management index. a Means (n = 3) followed by lower-case letters in the same column are significant (p < 0.05) different between different straw management within each water regime. b Means (n = 6) followed by upper-case letters in the same column are significant (p < 0.05) different between water regimes or straw management.

3.5. Rice grain yield Rice grain yields varied greatly under different treatments during the first seven years, and then remained relatively stable in the subsequent eight years (Fig. 4). Over the total 15 years, the ranking of rice grain yields followed the sequence of FC–SM > NFC–SM > FC–SR > NFC–SR (Fig. 4). The FC–SM and NFC–SM treatments increased 15-year average rice grain yields by 6.9% and 3.4%, respectively, compared to the NFC–SR treatment (Fig. 4).

explanation is that waterlogged conditions kept the soil in a reduced state and led to a lower soil temperature, which in turn decreased SOC decomposition. Another possible reason is that larger inputs of stubble and root residues returned to the soil as a result of higher crop productivity under flooding conditions (Yang et al., 2012). However, Fan et al. (2005) found that non-flooded cultivation led to a similar TOC content compared to the traditional flooding in a five-year rice-wheat rotation system. This observation was probably due to the fact that nonflooded conditions increased the amount and transferred proportion of C remaining underground as rhizodeposition (Tian et al., 2013c). In this study, straw mulching increased both TOC and TN contents at 0–10 cm soil layer as compared to straw removal. This was mainly attributed to the increase in carbon and nitrogen inputs resulting from

4. Discussion 4.1. TOC and TN Long-term flooding cultivation significantly improved the TOC content compared with non-flooded cultivation (Table 3). A possible 4

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stable organic compounds that collectively act as a soil reservoir (Sousa et al., 2012; Tian et al., 2013b). 5. Conclusion The TOC and labile SOC fractions in the surface soil were significantly influenced by water regimes and straw management. Water regimes had greater effects on TOC and KMnO4–C than did straw management. However, at deeper soil depth, labile SOC fractions were only affected by water regimes. Compared to the non-flooded conditions, flooding cultivation significantly improved total SOC content at 0–10 cm and labile SOC fractions at 0–20 cm. The higher CMI values in flooding condition and straw mulch were attributed to the increase in CPI, which contributed to the formation of more stable organic compounds that collectively act as a soil reservoir. The combined nonflooded cultivation and straw mulching method (NFC–SM) not only produced a similar 15-year average rice grain yield but also saved 50% amount of irrigation water compared to the traditional flooding cultivation with straw removal treatment (FC–SR). In addition, there was no significant difference in TOC content between the two management practices after 15 years. Our result suggested that a combination of nonflooded cultivation and straw mulching could be an ideal strategy to maintain agroecosystem productivity.

Fig. 4. Rice grain yield under various combined water regimes and straw management practices from 2001 to 2015. Vertical bar indicates the standard error of the mean.

straw return. However, Yang et al. (2012) found that straw incorporation did not enhance TOC content in a 20–year field experiment. The inconsistent findings are possibly due to the variations in straw return rate, soil types, and climate conditions. At deeper soil layer (10–20 cm), no difference was observed in TOC content, suggesting that straw residue mulch mainly improved total SOC in the surface soil. This observation was consistent with the results from Li et al. (2012) and Mi et al. (2016). Correspondingly, higher TN content in the deeper soil depth could be explained by the increased mineralization of crop biomass that caused more leaching of labile N from the soil profile.

Acknowledgements This research was financed by the National Key Research and Development Program of China (2016YFD0200102), the Jiangsu Natural Science Funding for Youth Scholars (BK20180905), the Natural Science Foundation of Gansu Province (17JR5RA157), and the Research Program Sponsored by Gansu Provincial Key Laboratory of Arid land Crop Science, Gansu Agricultural University (GSCS–2016–05).

4.2. Soil labile organic C fractions Labile SOC fractions including POC and KMnO4–C were significantly influenced by water regimes and straw management (Table 2). The trends in the labile SOC fractions reflect that of the total SOC in the surface soil, indicating that total SOM was a major determinant of the labile SOM fractions. Additionally, water regimes and straw managements influenced both quantity and quality of POC and KMnO4–C. In this study, straw management showed dominant effects on POC. The main reason was that POC was composed of decomposing plant and animal residues. The increase in POC may reflect higher C input from straw, stubble, and root residues. POC is regarded as the “slow” pool of SOC with an intermediate turnover time between the “active” and “passive” pools (Parton et al., 1987). Thus, POC may be of greater importance in defining SOC turnover (Yang et al., 2005). In a reservoir of nutrients, higher POC content may accelerate SOC turnover and influence soil nutrient cycling and biological productivity (Liebig et al., 2002). The KMnO4–C content reflects less recalcitrant and relatively younger organic compounds (Rudrappa et al., 2006). Higher KMnO4-C content under straw mulching indicated larger crop residue input. In addition, the result showed that flooding cultivation had greater KMnO4–C content than the non-flooded conditions. Tian et al. (2013c) found that non-flooded conditions showed higher roots and rhizomicrobial respiration than the flooded treatment. Labile SOC fractions are major energy sources for microorganisms. Thus, we speculated that non-flooded cultivation might increase the microbial activity and labile SOC fraction loss. However, in this study, we have not measured the microbial C and dissolved organic C contents. The related inferences need to be validated in future studies. CMI is a sensitive tool to evaluate soil quality in different management practices. We found greater CPI and CMI values in flooding and straw mulching treatments. However, no differences in LI were recorded between both water regimes and straw management method. This result indicated that CPI contributed to the formation of more

References Blair, G.J., Lefroy, R.D.B., Lisle, L., 1995. Soil carbon fractions based on their degree of oxidation, and the development of a carbon management index for agriculture systems. Aust. J. Agric. Res. 46, 1459–1466. Bouman, B.A.M., Yang, X.G., Wang, H.Q., Wang, Z.M., Zhao, J.F., Chen, B., 2006. Performance of aerobic rice varieties under irrigated conditions in North China. Field Crops Res. 97, 53–65. Bremner, J.M., 1996. Total nitrogen. In: Sparks, D.L., Page, A.L., Helmke, P.A., Loeppert, R.H., Soltanpour, P.N., Tabatabai, M.A., Johnson, C.T., Sumner, M.E. (Eds.), Methods of Soil Analysis, Part 3. Chemical Methods, pp. 1085–1122 Madison, Wisconsin, USA. Cabangon, R.J., Castillo, E.G., Tuong, T.P., 2011. Chlorophyll meter-based nitrogen management of rice grown under alternate wetting and drying irrigation. Field Crops Res. 121 (1), 136–146. Cambardella, C.A., Elliott, E.T., 1992. Particulate soil organic-matter changes across a grassland cultivation sequence. Soil Sci. Soc. Am. J. 56, 777–783. Chaudhary, S., Dheri, G.S., Brar, B.S., 2017. Long-term effects of NPK fertilizers and organic manures on carbon stabilization and management index under rice-wheat cropping system. Soil Till. Res. 166, 59–66. Fan, M.S., Liu, X.J., Jiang, R.F., Zhang, F.S., Lu, S.H., Zeng, X.Z., Christie, P., 2005. Crop yields, internal nutrient efficiency, and changes in soil properties in rice-wheat rotations under non-flooded mulching cultivation. Plant Soil 277, 265–276. Fan, M.S., Lu, S.H., Jiang, R.F., Six, J., Zhang, F.S., 2012. Long-term non-flooded mulching cultivation influences rice productivity and soil organic carbon. Soil Use Manage. 28, 544–550. Haynes, R.J., 2005. Labile organic matter fractions as central components of the quality of agricultural soils: an overview. Adv. Agron. 85, 221–268. Kudo, Y., Noborio, K., Shimoozono, N., Kurihara, R., 2014. The effective water management practice for mitigation greenhouse gas emissions and maintaining rice yield in central Japan. Agric. Ecosyst. Environ. 186, 77–85. Lal, R., 2004. Soil carbon sequestration to mitigate climate change. Geoderma 123 (1–2), 1–22. Li, C.F., Yue, L.X., Kou, Z.K., Zhang, Z.S., Wang, J.P., Cao, C.G., 2012. Short-term effects of conservation management practices on soil labile organic carbon fractions under a rape-rice rotation in central China. Soil Till. Res. 119, 31–37. Li, Y.S., Wu, L.H., Zhao, L.M., Lu, X.H., Fan, Q.L., Zhang, F.S., 2007. Influence of continuous plastic film mulching on yield, water use efficiency and soil properties of rice fields under non-flooding condition. Soil Till. Res. 93, 370–378. Li, Y.T., Lam, S.K., Han, X., Feng, Y.X., Lin, E., Li, Y.C., Hao, X.Y., 2017. Effects of elevated CO2 on rice grain yield and yield components: Is non-flooded plastic film mulching better than traditional flooding? Eur. J. Agron. 85, 25–30.

5

Agricultural Water Management 224 (2019) 105752

W. Mi, et al.

and nitrogen in degraded Brazilian semi-arid soils undergoing desertification. Agric. Ecosyst. Environ. 148, 11–21. Tian, J., Lu, S.H., Fan, M.S., Li, X.L., Kuzyakov, Y., 2013a. Labile soil organic matter fractions as influenced by non-flooded mulching cultivation and cropping season in rice-wheat rotation. Eur. J. Soil Biol. 56, 19–25. Tian, J., Lu, S.H., Fan, M.S., Li, X.L., Kuzyakov, Y., 2013b. Integrated management systems and N fertilization: effect on soil organic matter in rice-rapeseed rotation. Plant Soil 372, 53–63. Tian, J., Pausch, J., Fan, M.S., Li, X.L., Tang, Q.Y., Kuzyakov, Y., 2013c. Allocation and dynamics of assimilated carbon in rice-soil system depending on water management. Plant Soil 363, 273–285. Walkley, A.E., Black, C.A., 1934. An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci. 37, 29–38. Wang, Q.Y., Wang, Y., Wang, Q.C., Liu, J.S., 2014. Impacts of 9 years of a new conservational agricultural management on soil organic carbon fractions. Soil Till. Res. 143, 1–6. Yan, X., Zhou, H., Zhu, Q.H., Wang, X.F., Zhang, Y.Z., Yu, X.C., Peng, X., 2013. Carbon sequestration efficiency in paddy soil and upland soil under long-term fertilization in southern China. Soil Till. Res. 130, 42–51. Yang, C.M., Yang, L.Z., Ouyang, Z., 2005. Organic carbon and its fractions in paddy soil as affected by different nutrient and water regimes. Geoderma 124, 133–142. Yang, X.Y., Ren, W.D., Sun, B.H., Zhang, S.L., 2012. Effects of contrasting soil management regimes on total and labile soil organic carbon fractions in a loess soil in China. Geoderma 177, 49–56.

Liebig, M.A., Varvel, G.E., Doran, J.W., Wienhold, B.J., 2002. Crop sequence and nitrogen fertilization effects on soil properties in the western Corn Belt. Soil Sci. Soc. Am. J. 66, 596–601. Liu, X.J., Wang, J.C., Lu, S.H., Zhang, F.S., Zeng, X.Z., Ai, Y.W., Peng, S.B., Christie, P., 2003. Effects of non-flooded mulching cultivation on crop yield, nutrient uptake and nutrient balance in rice-wheat cropping systems. Field Crops Res. 83 (3), 297–311. Liu, Y.L., Ge, T.D., Zhu, Z.K., Liu, S.L., Luo, Y., Li, Y., Wang, P., Gavrichkova, O., Xu, X.L., Wang, J.K., Wu, J.S., Guggenberger, G., Kuzyakov, Y., 2019. Carbon input and allocation by rice into paddy soils: a review. Soil Biol. Biochem. 133, 97–107. Mi, W.H., Wu, L.H., Brookes, P.C., Liu, Y.L., Zhang, X., Yang, X., 2016. Changes in soil organic carbon fractions under integrated management systems in a low-productivity paddy soil given different organic amendments and chemical fertilizers. Soil Till. Res. 163, 64–70. Parton, W.J., Schimel, D.S., Cole, C.V., 1987. Analysis of factors controlling soil organic matter levels in Great Plains grassland. Soil Sci. Soc. Am. J. 51, 1173–1179. Qin, J.T., Hu, F., Zhang, B., Wei, Z.G., Li, H.X., 2006. Role of straw mulching in noncontinuously flooded rice cultivation. Paddy Water Manage. 83, 252–260. Rudrappa, L., Purakayastha, T.J., Singh, D., Bhadraray, S., 2006. Long-term manuring and fertilization effects on soil organic carbon pools in a Typic Haplustept of semi-arid sub-tropical India. Soil Till. Res. 88 (1–2), 180–192. Sherrod, L.A., Peterson, G.A., Westfall, D.G., Ahuja, L.R., 2005. Soil organic carbon pools after 12 years in no-till dryland agroecosystems. Soil Sci. Am. J. 69, 1600–1608. Six, J., Feller, C., Denef, K., Ogle, S.M., Moraes, S.C.J., Albrecht, A., 2002. Soil organic matter, biota and aggregation in temperate and tropical soils-effects of no-tillage. Agronomie 22, 755–775. Sousa, F.P., Ferreira, T.O., Mendonca, E.S., Romero, R.E., Oliveira, J.G.B., 2012. Carbon

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