Impact of agronomy practices on the effects of reduced tillage systems on CH4 and N2O emissions from agricultural fields: A global meta-analysis
Impact of agronomy practices on the effects of reduced tillage systems on CH4 and N2O emissions from agricultural fields: A global meta-analysis
Jinfei Feng☯ 0
Fengbo Li☯ 0
Xiyue Zhou 0
Chunchun Xu 0
Long Ji 0
Zhongdu Chen 0
Fuping Fang 0
China National Rice Research Institution 0
☯ These authors contributed equally to this work. 0
0 Editor: Dafeng Hui, Tennessee State University , UNITED STATES
The effect of no- and reduced tillage (NT/RT) on greenhouse gas (GHG) emission was highly variable and may depend on other agronomy practices. However, how the other practices affect the effect of NT/RT on GHG emission remains elusive. Therefore, we conducted a global meta-analysis (including 49 papers with 196 comparisons) to assess the effect of five options (i.e. cropping system, crop residue management, split application of N fertilizer, irrigation, and tillage duration) on the effect of NT/RT on CH4 and N2O emissions from agricultural fields. The results showed that NT/RT significantly mitigated the overall global warming potential (GWP) of CH4 and N2O emissions by 6.6% as compared with conventional tillage (CT). Rotation cropping systems and crop straw remove facilitated no-tillage (NT) to reduce the CH4, N2O, or overall GWP both in upland and paddy field. NT significantly mitigated the overall GWP when the percentage of basal N fertilizer (PBN) >50%, when tillage duration > 10 years or rainfed in upland, while when PBN <50%, when duration between 5 and 10 years, or with continuous flooding in paddy field. RT significantly reduced the overall GWP under single crop monoculture system in upland. These results suggested that assessing the effectiveness of NT/RT on the mitigation of GHG emission should consider the interaction of NT/RT with other agronomy practices and land use type.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: This work was supported by the State
Key Program of China (2016YFD0300906 to JF)
and the Innovation Program of Chinese Academy
of Agricultural Sciences.
Competing interests: The authors have declared
that no competing interests exist.
Agriculture is a main source of anthropogenic greenhouse gas (GHG) emissions [
contributing 47% and 76% of CH4 and N2O emissions, respectively. Agricultural practices (e. g. soil
tillage, fertilizer, and irrigation) play an important role in regulating the microbial process of
CH4 and N2O production in agricultural soil [
]. Detailed knowledge of the effects of
agronomical options on GHG emissions is imperative for the recommendation of low emission
Reduced (RT) and no tillage (NT) are widely recommended in world crop production to
improve soil structure, reduce soil erosion, and enhance soil organic matter as compared with
conventional tillage (CT). However, the effect of NT/RT on climate change mitigation has
been intensively debated because of the substantial inconsistency in individual field
experiments [3±5]. Previous studies have demonstrated that NT significantly reduced [
] or did not affect [
] CH4 emission from soil, compared with that of CT. Similarly, a
], increase [
], or insignificant change [
] of N2O emission was observed in
response to NT. In addition, the effects of NT on CH4 and N2O emissions were usually
inconsistency. For instance, a previous study reported that NT significantly reduced CH4 emission
in paddy field compared with CT, but increased N2O emission [
]. Similarly in the uplands,
NT significantly reduced not only N2O emission but also CH4 uptake [
]. The trade-off
relationship may offset the effect of NT on GHG mitigation. The highly diverse results from
individual studies are unlikely to reveal a general pattern of soil tillage on GHG mitigation.
Although some studies have been conducted to evaluate the effect of NT or RT on GHG
mitigation, they focused only on CH4 or N2O emissions [14±15]. The integrated effects of RT or
NT on the total GWP of CH4 and N2O emissions has not been well documented.
Soil tillage can affect several soil properties (e.g. soil bulk density, temperature, moisture,
and the vertical distribution of crop residue) that influence the production and emission
processes of CH4 and N2O [16±18]. Even more complicatedly, some effects of tillage on CH4 and
N2O emissions function in potentially contrasting ways, making it difficult to predict the effect
of a tillage practice on GHG mitigation [
]. For example, in paddy fields, NT can increase
CH4 oxidation by improving the soil structure and decreasing the disturbance on the niche of
the Methanogenic bacteria [20±21]; whereas, NT tended to increase the soil organic matter,
which facilitated the increase in CH4 emission . The integrated effect of NT on CH4 and
N2O emissions was highly dependent on the climatic conditions, soil properties, and
agricultural practices. Van Kessel et al. [
] reported that dry climatic conditions were conducive for
NT/RT to reduce N2O emission based on a global meta-analysis of NT/RT on N2O emission
in uplands. Zhao et al. [
] reported that the inhibition effects of NT on CH4 or N2O emissions
were negatively correlated with temperature, precipitation, and soil pH by synthesizing the
experimental results in China. Besides the climate and soil factors, the interaction of tillage
with other agronomy options on CH4 and N2O emissions was also observed in previous field
experiments [23±24]. Van Kessel et al. [
] assessed the interaction of fertilizer application
depth with tillage and reported that NT/RT performed better on the mitigation of N2O
emission when N fertilizer was placed 5cm rather than < 5cm. However, the interaction effect of
other options (e.g., cropping system and irrigation) with NT/RT is still unclear. A better
understanding of the interaction of agronomy practices with NT/RT will be beneficial to
determining the best management practices for NT/RT to mitigate CH4 and N2O emissions in
Therefore, the main objectives of this meta-analysis were: 1) to quantitatively summarize
the effects of NT/RT on the total GWP of CH4 and N2O emissions and 2) to investigate the
effects of cropping system, crop residue management, fertilizer split application, irrigation and
tillage duration on the effectiveness of NT/RT.
Materials and methods
We conducted a literature survey of peer-reviewed papers published before December 2016
that reported the effects of NT/RT on both CH4 and N2O emissions using Google Scholar and
ISI-Web of Science. The preferred reporting items for system review and Meta-analysis
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(PRISMA) guidelines (Fig 1) have been followed for data collection and analysis. The
keywords used in literature search were ªsoil tillageº, ªno-tillageº, ªreduced tillageº, ªCH4º,
ªN2Oº, and ªgreenhouse gas emissionº. The following 3 criteria were used to select appropriate
paired experiments: (1) the NT/RT and CT plots must be conducted at the same site with the
same crop, agronomic management options (e.g., fertilizer, irrigation,), and experiment
duration; (2) CH4 and N2O fluxes were both measured by using statistic chamber methods in field
conditions for an entire crop growing season; and (3) the N application rate, crop straw
returning methods, experimental duration, and water management practices were clearly recorded.
Forty-nine studies including 196 comparisons (Table 1) were collected according to these
criteria. The experiment sites covered 7 countries (USA, Brazil, China, Japan, Mexico, Philippines
and Spain). The land use types in selected studies were primarily paddy field and upland. The
crops included rice, wheat, maize, soybeans, barley, oats, and vetch. RT consisted of rotary
tillage, zone tillage, shallow plowing, precision tillage, and subsurface tillage. The detailed
information of selected studies and collected data is listed in the support information (Table A in S1
The results of CH4 and N2O emissions were converted into global warming potential
(GWP) by multiplying the 100-year radiative forcing potential coefficients to CO2 (25 and 298
used for CH4 and N2O, respectively). Considering that upland and paddy fields showed a great
difference in CH4 and N2O emissions, we examined the effect of NT/RT on GHG emissions
for these two land use types separately.
Five agronomic practices, including cropping system, residue management, N split,
irrigation, and tillage duration, were analyzed. Cropping system was categorized into single crop
Fig 1. The PRISMA (preferred reporting items for system review and meta-analysis) guidelines used for the
collection and meta-analysis of data.
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monoculture system and double crops rotation system for upland, and rice-upland crop
rotation and double rice for paddy field, referred to the crop sequences in a whole year. Residue
management practices were categorized as crop straw remove and return. We further analyzed
the effects of N split methods on the effect of NT/RT. N split methods were categorized into
four groups based on the percentage of basal N fertilizer (PBN = 100%, 50% < PBN < 100%,
PBN = 50%, and PBN < 50%; PBN = basal N rate / total N rate 100). Irrigation practices were
divided into rain-fed and irrigation for uplands, and continuous flooding and intermittent
irrigation for paddy fields. Tillage duration was divided into three levels: short-term 1±5 years;
medium-term 5±10 years; and long-term >10 years.
The response ratio (R) was used to compare the CH4, N2O and overall GWP under NT/RT
and CT. The natural log of R was used as the effect size, which was calculated by following
Where, XNT/RT and XCT are the amounts of CH4, N2O and overall GWP under NT/RT and
This meta-analysis was performed by using a nonparametric weighting function and the
confidence intervals (CIs) were generated by using bootstrapping [
]; because only 22.4% of
selected studies reported the standard deviation or error of CH4, N2O and GWP. Effect size
was weighted by the number of experiment replicates and the number of CH4 and N2O flux
measurements per month.
Where, W is the weight factor, n is the number of experiment replicates; and f is the number of
CH4 and N2O flux measurements per month. This weighting approach assigned more weight
to field experiments that were well replicated.
The mean effect size was calculated from lnR of individual studies by:
Where, w(i) is the weighting factor estimated by formula (2). To ease interpretation, the mean
effect size was back-transformed and reported as the percent change of NT/RT relative to that
The Mean effect size, 95% confidence intervals (CIs), group heterogeneity and publication
bias were calculated by MetaWin 2.1[
]. The random-effects model was used in the calculation
of mean effect sizes, based on the assumption that random variation in GHG emissions occurred
between observations. The 95% CIs around mean effect sizes were calculated by using
bootstrapping with 4999 iterations [
]. The mean effect sizes were considered to be significantly different
if their 95% CIs did not overlap. P-values for differences between categories of studies (Table 2)
were calculated using resampling tests [
]. The publication bias was checked using Rank
Correlation Test method (Kendall's tau and Spearman rank-order correlation). For the categories existing
publication bias, a bias corrected CI was used instead of bootstrap CI.
Results and discussion
Overall, reduced tillage system (NT/RT) did not exhibit significant effects on CH4 and N2O
emissions as compared with CT (Fig 2). However, their effects on the overall GWP of CH4 and
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Fig 2. The overall effects of reduced tillage system on CH4, N2O and overall GWP.
N2O emissions was marginally significant. The overall GWP was mitigated by 6.6% by NT/RT
as compared with CT. The performance of NT/RT depended on land use type and tillage
methods. In rice paddies, a trade-off relationship existed in the effects of NT/RT on CH4 and
N2O emissions (Fig 3(A)). NT tended to mitigate the CH4 emission, whereas it increased the
N2O emission, resulting in no significant impact on the overall GWP in rice paddies (Fig 2).
However, RT significantly increased the CH4 emission and overall GWP compared with CT.
The poor performance of RT in the inhibition of CH4 emission was possibly attributed to its
weaker effect on reducing CH4 production than that of CT and weaker effect on increasing
CH4 oxidation than that of NT. CT incorporated crop residue into deeper soil than RT,
reducing the decomposition of these residues through the protection of the soil matrix [
Fig 3. The relationship of the LnR of NT/RT on CH4 and N2O emissions in paddy and upland fields.
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Fig 4. Impact of cropping system on the effects of NT and RT on CH4, N2O and overall GWP.
soil disturbance and a shallower CH4 oxidation zone for NT than RT were conducive to
improving CH4 oxidation [
Unlike that of rice paddies, upland soil usually absorbed CH4 from the atmosphere through
the microbial process of CH4 oxidation by methanotrophs [
]. The effect of NT/RT on CH4
uptake did not show an obvious relationship with its impact on N2O emission (Fig 3(B)). The
overall GWP was reduced 11.6% by NT as compared with CT (Fig 2). Whereas the effects of
RT on CH4 uptake, N2O emission and overall GWP were not significant.
Impact of cropping system
NT significantly reduced CH4 uptake, N2O emission, and overall GWP by 18.4%, 21.0% and
20.8% under the double crops rotation system, respectively, whereas its effects was not
significant under the single crop monoculture system (Fig 4). The effects of cropping systems on
CH4 and N2O emissions after adopting NT may primarily attribute to the variability in the
quantity of aboveground crop residues and roots in soil profile. Increasing in cropping
frequency and crop diversity, such as double crops rotation, can produce more residues and
roots than that of single crop monoculture system. Most of the crops in the double crops
rotation system of this analysis were cereals crops (such as maize, wheat, and barley) with high C:
N ratio. The decomposition of crop residues with high C:N ratio could stimulated microbial N
immobilization in soil, thus reduce the available N for N2O production [
]. Additionally, the
decomposition of crop residues also consumed sizable O2 in soil pores, which may inhibit the
CH4 oxidation [
]. RT significantly reduced the overall GWP of CH4 and N2O by 20.8%
under the single crop monoculture system, as compared with CT (Fig 4). However, its effect
on the overall GWP was not significant under the double crops rotation system. The upland
field was usually tilled once in one year under the monoculture system; but usually two times
per year under the rotation system. Less tillage operation could reduce the disturbance to
methanotrophic microbes and enhance CH4 uptake [
]. Less tillage operation could also
prevent soil aggregates and inhibit organic N mineralization, which is beneficial to the mitigation
of N2O production [
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As in the paddy fields, NT significantly reduced the overall GWP by its cumulative
abatement on CH4 and N2O emissions (Fig 4) under the rice-upland crops rotation system; whereas
its effect was not significant on the overall GWP under double rice system. A previous study
has reported that soils with higher water contents during the annual crop growing season
produced more CH4 because of their higher methanogenic populations and activities [
annual flooding time was less for the rice-upland crop rotation system than the double rice
system. The rotation of upland crop could improve the soil permeability, aerobic condition and
methanogenic activities, which may enhance the inhibition effect of NT on the CH4 and N2O
]. NT significantly increased the N2O emission under the double rice system.
This was possibly because of the difference in temperature between late rice and winter upland
crops. Late rice was commonly planted in summer, whereas winter upland crops were planted
in fall. Higher temperature with surface applied N fertilizer may stimulate the N2O emission
. RT significantly increased the CH4 emission and the overall GWP under the double rice
system. But it should be noted that only three comparisons from two studies were included for
this category. The existence of publication bias was suggested by Spearman Rank-Order
Impact of crop straw management
NT significantly reduced the N2O emission and the overall GWP by 10.9% and 20.4% as
compared with CT, respectively, when crop straw was removed (Fig 5). However, when the crop
straw was returned, the effect sizes of NT on CH4 uptake, N2O emission, and overall GWP
were not significant. Crop straw has direct and indirect positive effects on N2O production.
The decomposition of crop straw directly provided substrate C and N for nitrifiers and
denitrifiers, which may stimulate the N2O production in soil [
]. Indirectly, the returned crop straw
was commonly mulched on the soil surface in the NT field, which could reduce soil water
evaporation and conserve rainwater in situ, resulting in enhanced soil moisture [
]. High soil
moisture promotes N2O production and inhibits CH4 oxidation by reducing gas diffusion
[73±74]. Therefore, crop straw return may weaken the effects of NT on the mitigation of N2O
and CH4 emissions.
Fig 5. Impact of crop straw management on the effects of NT and RT on CH4, N2O and overall GWP.
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As in paddy fields, NT significantly reduced the overall GWP by 20.4% when crop straw
was removed; but did not affect the overall GWP when crop straw was returned (Fig 5). RT
significantly increased the CH4 emission and overall GWP when crop straw was returned;
whereas it did not increase the overall GWP when crop straw was removed. The effect of soil
tillage on CH4 emission in paddy field was mostly determined by its influence on straw
decomposition, which provides abundant C substrate for CH4 production [
]. Soil tillage
determined the vertical distribution of crop straw in the soil profile. RT usually mixed straw into
the surface soil (5±10cm depth); whereas plowing in CT buried the crop straw into the deeper
soil layer (10±15cm), which could reduce access of these residues by microbes by the
protection of soil matrix [
]. Thus, RT with crop straw return might facilitate crop straw
decomposition into intermediate products that serves as substrates for methanogens [
], resulting in
producing higher CH4.
Impact of N split
Split application of N fertilizer is an important practice to synchronize nutrient supply with
crop demand and reduce N loss to the environment. Tillage directly affected the vertical
distribution and transformation of basal N fertilizer. The effectiveness of NT/RT on CH4 and N2O
emissions may influenced by the percentage of basal N fertilizer (PBN). As shown in Fig 6,
when the PBN = 100%, NT significantly reduced the overall GWP by 14.4% in upland, as
compared with CT. When 50% < PBN < 100%, the overall GWP was marginally significantly
mitigated by 13.6% by NT in upland. When PBN < or = 50%, NT did not significantly affect CH4
uptake, N2O emission, and the overall GWP. This can be explained by two possible reasons.
Firstly, basal N fertilizer is commonly applied with tillage operation; whereas topdressing N
fertilizer is usually applied with irrigation or precipitation in uplands. Soil tillage had a greater
Fig 6. Impact of N split application on the effects of NT and RT on CH4, N2O and overall GWP.
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effect on the microbial process of the basal N fertilizer than top dressing N fertilizer. Thus,
high PBN may intensify the inhibition effect of NT on N2O emission. Secondly, a large amount
of field studies has reported that reducing the ratio of basal N and increasing the ratio of
topdressing N enhanced plant N recovery and the N use efficiency [
]. Less PBN could improve
the synchronization of crop demand with N supply and inhibit N2O emission. Therefore, the
better synchronization of crop demand with N supply may weaken the inhibition effect of NT
on N2O emission. RT significantly reduced CH4 oxidation and enhanced N2O emission when
the percentage of PBN was between 50% and 100% in uplands (Fig 6). The overall GWP was
significantly enhanced by 5.1% by RT. However, the existence of publication bias was
suggested by Spearman Rank-Order Correlation. When PBN was decreased to less than 50%, RT
significantly mitigated the overall GWP because of the increase in CH4 uptake and the
reduction in N2O emission. These results indicated that high PBN (> 50%) with NT and low PBN
(< 50%) with RT benefited the GHG mitigation in upland fields.
As in paddy fields, NT significantly mitigated the overall GWP by 22.4% when PBN < 50%;
whereas increased the overall GWP by 14.9% when PBN = 50%, which was different from that
of uplands (Fig 6). The effectiveness of NT on overall GWP was largely determined by its
impact on CH4 emission in paddy fields. The surface application of basal N fertilizer under NT
could have either positive or negative effects on CH4 emission. On one hand, the production
of CH4 mostly occurred at the surface layer because of the surface application of basal N
fertilizer under NT, which benefited the diffusion of CH4 from the soil to the atmosphere . On
the other hand, a shallow CH4 production zone may also benefit CH4 oxidation, because the
interface between water and soil was a main CH4 oxidation zone [
]. The integrated effect
was possibly determined by the basal N application rate. The average basal N rate were 45 and
90 kg N ha-1 for the groups of PBN < 50% and PBN = 50%, respectively. We speculated that, at
low PBN, rice uptake might outcompete the microbial process of CH4 production because of
the limited N source [
]; and the capability of CH4 oxidation was possibly higher than CH4
production because of the insufficiency available N for Methanogenic bacteria. Thus, NT
inhibited CH4 emission. With the PBN increased to 50%, the N supply for Methanogenic
bacteria was less serve, and the abundant N supply stimulated CH4 production and inhibited CH4
oxidation by suppressing Methanotrophs and switching substrates from CH4 to ammonia
[78±79]. Additionally, the shallow CH4 production zone under NT may enhance the flux of
CH4 from soil to atmosphere. Thus, NT significantly increased the CH4 emission under high
basal N application rates.
Impact of irrigation
As shown in Fig 7, NT significantly reduced the overall GWP by 16.7% under rain-fed
condition as compared with CT. The effect of NT on the overall GWP was not significant under
irrigation option. NT improved soil structure, which increased the gas diffusivity and improved
the tendency of the formation of aerobic microsites, and therefore increased CH4 oxidation
and inhibited N2O emission [80±81]. The irrigation options in selected studies were all
flooding irrigation, which may weaken the effectiveness of NT by increasing soil water and
decreasing the aerobic condition in soil profile [
As in paddy fields, NT significantly mitigated CH4 emission and overall GWP in
continuously flooded paddy field as compared with CT (Fig 7); whereas it did not produce a significant
effect on CH4 and overall GWP in intermittently irrigated paddy fields as compared with CT.
Continuous flooding provided a sufficient anaerobic environment for CH4 production in
paddy fields. Thus, the labile C availability and CH4 oxidation capacity were two important
factors controlling the total CH4 emission amount in flooded paddies. A previous field study
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Fig 7. Impact of irrigation on the effects of NT and RT on CH4, N2O and overall GWP.
showed that NT reduced the volume fraction of large soil pores, which was conducive to the
prevention of the decomposition of soil organic matter [
]. Additionally, most of the crop
residue and inorganic N fertilizer were placed on the soil surface in NT paddy fields, which
enhanced the CH4 oxidation and prevented the anaerobic decomposition of organic matter
because of the high O2 content in the soil-water interface [
]. Therefore, NT was conducive
to inhibition of CH4 emission under continuous flooded field conditions. As in intermittent
irrigated field, the water usually drained out and maintained the dry-wet alternation after the
rice tillering stage, which greatly increased the aerobic periods and mitigated the CH4 emission
as compared with that of continuous flooding . Thus, intermittent irrigation may weaken
the effect of NT on the inhibition of CH4 emission.
Impact of tillage duration
NT only significantly mitigated N2O emission and overall GWP under long-term duration
(>10 years) in uplands (Fig 8), which is consistent with previous studies [
adoption of NT can improve soil structure and therefore is conducive to the enhancement of
CH4 uptake and inhibition of N2O emission . The inhibition effect of RT on overall GWP
showed a trend that increase with tillage duration. However, its effectiveness was not
significant because of wide variance.
As in paddy field, NT did not exhibit significant effects on CH4 and overall GWP under
short-term duration (<5 years); whereas it significantly reduced CH4 and overall GWP under
medium-term duration (5±10 years) (Fig 8). The existence of publication bias for the category
of 5±10 years was suggested by Spearman Rank-Order Correlation. Based on a five-year field
experiment, Kim et al. [
] reported that NT effectively reduced the CH4 emission in the 1st
and 2nd years, but increased the CH4 emission in the 5th year, because of increased soil organic
carbon (SOC) content, as compared with CT. The contrasting results were possibly attributed
to the difference in the cropping practices. The cropping system in the study of Kim et al. [
was mono-rice with winter fallow; and the crop residue was placed in the field after rice harvest
and would have completely decomposed under aerobic conditions in winter [84±85]. The
SOC content was possibly the primary factor determining the CH4 production in the following
rice cropping season. Thus, NT increased the SOC resulting in enhanced CH4 emission. As in
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Fig 8. Impact of tillage duration on the effects of NT and RT on CH4, N2O and overall GWP.
the selected studies [86±87] in this analysis, the cropping systems were rice-upland crops
rotation and the upland crop residue applied preceding the rice cropping provided an abundant
substrate for CH4 production. The effect of NT on CH4 emission was possibly controlled by its
impact on CH4 oxidation. Thus, continuous adoption of NT may facilitate the CH4 oxidation
and significantly reduce the CH4 emission. These results indicated that the temporal effect of
NT in rice paddies might highly depend on the cropping system. However, the long-term
experiment of NT in paddy fields was still limited. The number of long-term experiments
conducted in paddy field was far less than that in upland. More field studies are needed to
investigate the temporal effect of NT on GHG emission in paddy field under different agricultural
NT/RT significantly reduced the overall GWP of CH4 and N2O emissions by 6.6% as
compared with CT. The effectiveness of NT/RT depended on tillage methods, land use type, and
agricultural practices. The suggested practices for NT to reduce the GHG emission were crop
rotation and straw remove both in upland and paddy field, PBN>50% and rainfed in upland,
while PBN<50% in paddy field. RT was less effective on the mitigation of GHG emission than
NT. RT significantly enhanced the CH4, N2O or overall GWP under several practices, such as
double rice system and crop straw returned in paddy field, and PBN>50% in upland. Only
single crop monoculture facilitated RT to reduce the overall GWP.
S1 Appendix. The detailed information of selected studies.
S2 Appendix. Literature search strategy.
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S3 Appendix. PRISMA checklist.
Conceptualization: Jinfei Feng, Fengbo Li, Fuping Fang.
Data curation: Jinfei Feng, Fengbo Li, Xiyue Zhou, Chunchun Xu.
Formal analysis: Xiyue Zhou.
Funding acquisition: Fuping Fang.
Investigation: Jinfei Feng, Long Ji, Zhongdu Chen.
Methodology: Jinfei Feng, Fengbo Li, Chunchun Xu, Long Ji, Zhongdu Chen.
Project administration: Fuping Fang.
Writing ± original draft: Jinfei Feng, Fengbo Li.
Writing ± review & editing: Fuping Fang.
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Wang B., 2013. The rules and regulation of farmland carbon cycle under conservational tillage.
Shandong Agricultural University.
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