Mediation of gaseous emissions and improving plant productivity by DCD and DMPP nitrification inhibitors: Meta-analysis of last three decades

Abstract

Nitrification inhibitors (NIs), especially dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP), have been extensively investigated to mitigate nitrogen (N) losses from the soil and thus improve crop productivity by enhancing N use efficiency. However, to provide crop and soil-specific guidelines about using these NIs, a quantitative assessment of their efficacy in mitigating gaseous emissions, worth for nitrate leaching, and improving crop productivity under different crops and soils is yet required. Therefore, based upon 146 peer-reviewed research studies, we conducted a meta-analysis to quantify the effect of DCD and DMPP on gaseous emissions, nitrate leaching, soil inorganic N, and crop productivity under different variates. The efficacy of the NIs in reducing the emissions of CO2, CH4, NO, and N2O highly depends on the crop, soil, and experiment types. The comparative efficacy of DCD in reducing N2O emission was higher than the DMPP under maize, grasses, and fallow soils in both organic and chemical fertilizer amended soils. The use of DCD was linked to increased NH3 emission in vegetables, rice, and grasses. Depending upon the crop, soil, and fertilizer type, both the NIs decreased nitrate leaching from soils; however, DMPP was more effective. Nevertheless, the effect of DCD on crop productivity indicators, including N uptake, N use efficiency, and biomass/yield was higher than DMPP due to certain factors. Moreover, among soils, crops, and fertilizer types, the response by plant productivity indicators to the application of NIs ranged between 35 and 43%. Overall, the finding of this meta-analysis strongly suggests the use of DCD and DMPP while considering the crop, fertilizer, and soil types.

Graphical Abstract

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Environmental Science and Pollution Research (2023) 30:64719–64735
https://doi.org/10.1007/s11356-023-26318-5
RESEARCH ARTICLE
Mediation ofgaseous emissions andimproving plant productivity
byDCD andDMPP nitrification inhibitors: Meta‑analysis oflast three
decades
MuhammadAammarTufail1 · MuhammadIrfan2· WajidUmar3· AbdulWakeel4· RuthA.Schmitz1
Received: 14 December 2022 / Accepted: 3 March 2023 / Published online: 16 March 2023
© The Author(s) 2023
Abstract
Nitrification inhibitors (NIs), especially dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP), have been exten-
sively investigated to mitigate nitrogen (N) losses from the soil and thus improve crop productivity by enhancing N use effi-
ciency. However, to provide crop and soil-specific guidelines about using these NIs, a quantitative assessment of their efficacy
in mitigating gaseous emissions, worth for nitrate leaching, and improving crop productivity under different crops and soils is
yet required. Therefore, based upon 146 peer-reviewed research studies, we conducted a meta-analysis to quantify the effect of
DCD and DMPP on gaseous emissions, nitrate leaching, soil inorganic N, and crop productivity under different variates. The
efficacy of the NIs in reducing the emissions of CO2, CH4, NO, and N2O highly depends on the crop, soil, and experiment types.
The comparative efficacy of DCD in reducing N2O emission was higher than the DMPP under maize, grasses, and fallow soils
in both organic and chemical fertilizer amended soils. The use of DCD was linked to increased NH3 emission in vegetables,
rice, and grasses. Depending upon the crop, soil, and fertilizer type, both the NIs decreased nitrate leaching from soils; how-
ever, DMPP was more effective. Nevertheless, the effect of DCD on crop productivity indicators, including N uptake, N use
efficiency, and biomass/yield was higher than DMPP due to certain factors. Moreover, among soils, crops, and fertilizer types,
the response by plant productivity indicators to the application of NIs ranged between 35 and 43%. Overall, the finding of this
meta-analysis strongly suggests the use of DCD and DMPP while considering the crop, fertilizer, and soil types.
Keywords GHG emission· Nitrification inhibitors· DCD· DMPP· Nitrogenous gasses· Precision agriculture
Introduction
Modern agriculture largely depends on synthetic nitrogen
(N) fertilizer for sustaining crop productivity and ensuring
global food security. However, mitigating climate change
and improving food security are two of the world’s most
challenging issues (Shakoor etal. 2021). Since the inven-
tion of the Haber–Bosch process, N use in agriculture has
increased substantially to feed the rapidly expanding popu-
lation (Billen etal. 2013; Erisman etal. 2008; Smith etal.
2020). By 2050, the world’s population is expected to touch
Responsible Editor: V.V.S.S. Sarma
* Muhammad Aammar Tufail
mtufail@ifam.uni-kiel.de
* Ruth A. Schmitz
rschmitz@ifam.uni-kiel.de
Muhammad Irfan
irfan1513_uaf@yahoo.com
Wajid Umar
wajid.umar@phd.uni-mate.hu
Abdul Wakeel
abdulwakeel77@gmail.com
1 Institute forMicrobiology, Christian-Albrechts-University
Kiel, Kiel, Germany
2 Soil andEnvironmental Sciences Division, Nuclear Institute
ofAgriculture (NIA), Tandojam, Pakistan
3 Institute ofEnvironmental Science, Hungarian University
ofAgriculture andLife Sciences, Gödöllő2100, Hungary
4 Institute ofSoil andEnvironmental Sciences, University
ofAgriculture Faisalabad, Faisalabad, Pakistan
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64720 Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
10 billion (Shakoor etal. 2020), and global N consumption
has been projected to escalate from 142 to 169% by 2050
to achieve a 100–110% increase in crop yields (IFA, 2013).
Excessive use of N fertilizers causes severe N losses into
the environment, thereby reducing applied N’s efficiency
to 20–50% (Ahmed etal. 2017). Overuse of N fertilizers
accompanied by low N use efficiency (NUE) results in sub-
stantial monetary and environmental costs. For instance, Sut-
ton etal. (2013) estimated about 800 billion $US as global
damage because of N pollution annually. The amount of
reactive N (Nr) released into the biosphere through anthro-
pogenic means is prodigious and is estimated to be 120 Tg
per year, which is twice the N fixed by all-natural terrestrial
processes, i.e., 63 Tg per year (Fowler etal. 2013; Sánchez-
Vicente etal. 2019). Higher Nr in atmosphere, aquatic and
terrestrial systems are creating serious environmental con-
sequences such as global warming, greenhouse gas-driven
climate change, nitrate contamination, eutrophication of
freshwater resources, soil acidification, and loss of biodi-
versity (Liu etal. 2013; Tilman and Isbell 2015; Zhu etal.
2016) and negative impacts on human health by deteriorat-
ing air quality (Xu etal. 2017).
Globally, N recovery by major cereal crops, i.e., rice,
wheat, and maize, is notoriously low and often remains
below 50% during the first season of N application (Coskun
etal. 2017; Herrera etal. 2016; Shahzad etal. 2019), while
only < 10% of residual N is recovered during subsequent
years (Congreves etal. 2021). Gaseous emissions, including
ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), and
dinitrogen (N2), are the primary routes of N losses (Fowler
etal. 2013; Xia etal. 2017), causing colossal loss of resource
investment in addition to environmental pollution. Nitrous
oxide has become the leading stratospheric ozone-depleting
gas during the twenty-first century, and its concentration
in the atmosphere is continuously increasing at the rate of
0.2–0.3% per annum (IPCC, 2014). About 60–80% of global
anthropogenic N2O emissions and 10–12% of total green-
house gas emissions are attributed to agriculture (Turner
etal. 2015; Zhang etal. 2020). Hence, eco-friendly and cost-
effective strategies to reduce Nr and improve N resource
efficiency are urgently required to address environmental
problems without yield penalties.
The Nr losses from agroecosystems originate from the
deprotonation of ammonium (NH4+) to ammonia (NH3).
This process is governed by soil pH, soil organic matter,
soil texture, temperature, moisture, N application rate, and
several microbial-mediated nitrification and denitrification
reactions (Chen etal. 2015). Nitrification, oxidation of NH3
to nitrate (NO3−), is catalyzed by the ammonia-oxidizing
bacteria (AOB), ammonia-oxidizing archaea (AOA), and
nitrite-oxidizing bacteria (NOB). The nitrification pro-
cess is initiated by AOB (Nitrosomonas and Nitrosococcus
spp.) which oxidizes NH3 to NH2OH (hydroxylamine) via
ammonia monooxygenase enzyme, and then NH2OH is oxi-
dized to NO2− by the enzyme hydroxylamine oxidoreduc-
tase. Finally, the NO3− is produced by NOB (Nitrobacter
spp.) through the enzyme nitrite oxidoreductase (Daims
etal. 2016). The denitrification process is also catalyzed by
a diverse set of bacteria, archaea, and fungi (Nitrosospira,
Chaetomium, and Fusarium) which reduced NO3− to NO2−,
NO, N2O, and N2 (Hayatsu etal. 2008; Rex etal. 2019).
Nitrification inhibitors (NIs) have been recognized as
promising tools to mitigate Nr pollution associated with
increased N inputs in cropping systems worldwide (Sha etal.
2020). NIs can provide substantial agronomic, economic,
and environmental benefits. They potentially minimize the
gaseous N losses and improve NUE through deactivating
ammonia monooxygenase (AMO), thus limiting the conver-
sion rate of NH3 to NO3− (Fu etal. 2020). NIs are products
that inhibit the bacterial oxidation of NH4+ to NO2− in soil,
so maintaining N as NH4+-N (Benckiser etal. 2013) can
reduce leaching, denitrification, and emission of N2O (Hu
etal. 2015), as NIs retain soil N in a less mobile form NH4+,
hence providing a better opportunity to plants for more N
uptake (Kim etal. 2012; Wang etal. 2021).
Dicyandiamide (DCD) and 3,4-dimethylpyrazole phos-
phate (DMPP) are the most widely used NIs in agriculture
globally. Both compounds have different chemical character-
istics and mechanisms for restricting nitrification (Barth etal.
2001). Diverse climate zones, ecosystems, soil types, and
planting systems are the critical influential factors resulting
in large disparities in the performance of these compounds.
Likewise, inhibitor type, soil pH, organic matter content,
and N rate are the key factors for retarding the nitrification
process (Sha etal. 2020). The advantages and effectiveness
of NIs in improving crop yields and NUE, minimizing N
losses via NO3− leaching, greenhouse gas emissions, and
NH3 volatilization (Afshar etal. 2018; Sun etal. 2015), have
been widely reported. Akiyama etal. (2010) reported that
N2O emissions from N fertilizer could be reduced by 38% by
using NIs, while Gilsanz etal. (2016) found that DCD and
DMPP are effective in reducing N2O emissions by 42 and
40%, respectively. Furthermore, NIs enhance the activity of
methane monooxygenase and influence soil carbonate hydro-
lyzation thereby reducing carbon dioxide (CO2) and methane
(CH4) emissions due to soil acidification (Fan etal. 2019).
Integrated assessments (using a meta-analysis approach)
could provide an opportunity to summarize the findings
from available studies to formulate a tangible estimate
regarding the impact of NIs on the environment and crop
yields. Several meta-analyses on the use and efficacy of NIs
in agriculture on an individual basis, for example, crop yield
and productivity (Hu etal. 2014; Yang etal. 2016b), NUE
(Abalos etal. 2014), emission factor (Gilsanz etal. 2016),
and NH3 volatilization (Pan etal. 2016), have previously
been conducted. Nevertheless, still little is known on how
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64721Environmental Science and Pollution Research (2023) 30:64719–64735
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NIs simultaneously affect greenhouse gas emissions, Nr
emissions, NO3− leaching, plant productivity, and soil
inorganic N contents in agricultural soils. Therefore, we
performed the first comprehensive global meta-analysis study
to fulfill this knowledge gap. This study was aimed primarily
at investigating the efficacy of NIs particularly DCD and
DMPP on greenhouse gas emissions (CO2, CH4, and N2O), Nr
emissions (NH3 and NO), NO3− leaching, plant productivity
(NUE, plant biomass, grain-N content, and plant-N update),
and soil inorganic N content, simultaneously.
Materials andmethods
Database search andselection criteria
Metadata was obtained following the PRISMA reporting
guidelines (Liberati etal. 2009). A literature search was
conducted in March 2021 using the SCOPUS® database
(http:// www. scopus. com) and the Web of Science® database
(https:// webof knowl edge. com/). Articles published in
scientific journals in only the English language were retrieved
using the following keyword combination: “nitrification
inhibitor” AND (“DCD” OR “DMPP”). The Boolean
truncation “*” character is included in combination to ensure
variations of the words, such as inhibitor or inhibitors. The
logical operator “AND” was used to refine the articles that
contain words written on both sides of the operator. Articles
found through the cross-reference citations from review and
research papers were also retrieved.
Study selection
Metadata searches from both databases yielded 1366 arti-
cles, 714 of which were left after duplicate removal. The
following eligibility criteria for the study selection were
predefined to eliminate publication bias:
1. The study should have demonstrated the effects of at
least one nitrification inhibitor (DCD or DMPP).
2. Studies investigating any parameters from gaseous emis-
sion, N leaching, plant productivity, and/or soil inor-
ganic-N were selected.
3. Studies investigating the combined effect of NIs were
excluded.
The studies not fulfilling the above criteria were excluded
from this analysis. If any of the traits were measured over
time, the data only for the final measurements were included.
Out of the 235 articles assessed for eligibility, 146 articles
fulfilling our criteria were selected (Fig.1, TableS1). The
selected papers spanned almost three decades, from 1993
to 2021.
Data extraction
Data including treatment means, sample size (number of
replications, n), and standard deviation were extracted
from each study. The standard errors (SE) reported in
some studies were converted into standard deviations (SD)
using the following equation: SE = SD (n−1/2). The data
from the graphs were digitized using Web Plot Digitizer
(Ankit, 2020). Since multiple experiments from one study
do not increase the dependence of meta-analysis on that
study (Gurevitch and Hedges 1999), therefore, different
treatments such as fertilizers or nitrification inhibitors in
a given study were regarded as independent experiments
and described in the study as separate data units. This tech-
nique increases the power of meta-analysis (Lajeunesse and
Forbes 2003) and has been used in several meta-analyses
(Dastogeer 2018; Mayerhofer etal. 2013; Mcgrath and
Lobell 2013). Parameters related to gaseous emission
(CO2, CH4, N2O, NH3, and NO), NO3− leaching, crop
productivity (grain N content, N uptake, N use efficiency
(NUE), and biomass/yield), and soil inorganic N (NH4+
and NO3−) were collected from each study for different
crop types, experiment types, fertilizer types, and soil tex-
ture and pH types.
Meta‑analysis
To estimate the effect size of DCD or DMPP treatment on
gaseous emissions, NO3− leaching, plant productivity, and
soil inorganic-N as compared to control (without DCD and
DMPP), log response ratio (lnRR) was calculated using the
following formula: lnRR = ln (Vni/Vc), where Vni is the mean
of nitrification inhibitor treatment and Vc is the mean of con-
trol treatment without nitrification inhibitor (Hedges etal.
1999). The lnRR was used as an effect size metric because
log transformation of the parameter(s) reported in different
units among studies maintains symmetry within the analy-
sis (Borenstein etal. 2011). Furthermore, percent change
(%Δ) in effect size was calculated from lnRR, i.e., %Δ = (exp.
(lnRR) − 1*100). We calculated pooled variances using the
“escalc” function in the metafor (version 2.4–0) package of
the R environment (Viechtbauer 2010).
Before constructing the meta-analysis model, the hetero-
geneity (Q) test was performed to determine the choice of
fixed or random/mixed effects model. Heterogeneity on the
full dataset, including 366 observations, was highly signifi-
cant (Cochran’s Q = 124,337.57, df = 649, p < 0.001), indi-
cating that a random/mixed effects approach was guaranteed
(Cochran 1954).
It is assumed that studies with low effect sizes are less
likely to be published than studies with high effect sizes
due to publication bias (Rothstein etal. 2006). On the
other hand, Head etal. (2015) stated that p-curve analysis
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64722 Environmental Science and Pollution Research (2023) 30:64719–64735
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for publication bias is not the cause of no or less publi-
cation rather; they “play” around their data (e.g., selec-
tively removing outliers, choosing different outcomes,
and controlling for different variables) until it becomes
significant. This bad practice is called p-hacking and is
very common among researchers. Therefore, a p-curve
analysis of selected studies was conducted to check the
publication bias.
The synthesis produced by this meta-analysis is balanced
based on the weight of each study, to maintain an equal
contribution to the results produced by meta-analysis. This
study used the inverse variance method to assign the weights
using meta and metafor packages in R. The estimated pooled
effect sizes produced by the meta-analysis with their 95%
confidence intervals (95% CI) were presented in forest plots.
The effect of DCD or DMPP was considered significant if
95% CIs did not coincide with the zero line (Augé etal. 2014).
A positive value indicates an increase, whereas a negative
value indicates a decrease in the nitrogenous gasses’ emission
following the application of DCD or DMPP. Statistical
analyses were performed in R environment (https://r- proje
ct. org/) using metafor (Viechtbauer 2010), meta (Schwarzer
2007), and ggplot (Wickham 2011) packages.
Metadata
Metadata was collected from 146 published scientific articles
from 28 countries spanning between 1993 and 2021 (Fig.2).
A total of 650 observations (k) were obtained, including
treatments without and using nitrification inhibitors.
Publication bias
Out of 650 total observations, only 361 (55.54%) observations
showed significant effect sizes at p < 0.05, and 328 (50.46%)
observations showed significant effect sizes at p < 0.025. Stud-
ies showing nonsignificant results (p > 0.05) were excluded
from the p-curve analysis. The p-curve plot shows that our data
is significantly right-skewed and not flat, indicating an effect
behind our data (Fig. S1). The estimated power of our studies
in the meta-analysis is 99%, and the evident value is present,
which shows the true effect size is present in the analysis.
Fig. 1 Preferred reporting items
for systematic reviews and
meta-analyses (PRISMA) flow
diagram for the meta-analysis
Records idenfied through
SCOUPUS database
searching
(n = 674)
Screening
Included Eligibility noitacifitnedI
Records aer duplicates removed
(n = 714)
Records screened
(n = 714)
Records excluded
(n = 479)
Full-text arcles assessed
for eligibility
(n = 235)
Full-text arcles excluded,
-Plant producvity
parameters were not
tested (n = 58)
Studies included in
qualitave synthesis
(n = 177)
Studies included in
quantave synthesis
(meta-analysis)
(n = 146)
Full-text arcles excluded,
-without a measure of
variance (n = 31)
Records idenfied through
WEB of Science database
searching
(n =639)
Records idenfied through
cross-referencecitaons
(n = 53)
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64723Environmental Science and Pollution Research (2023) 30:64719–64735
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Results
Overall effect ofNIs
The overall effects of NIs on the gaseous emissions, N
leaching, plant productivity, and soil inorganic-N are pre-
sented in Fig.3a. In general, the NIs remained ineffective in
reducing CO2, CH4, and NH3 emissions from agricultural
soils. However, they mitigated N2O and NO emissions by
20 and 14%, respectively. Plant productivity indicators (i.e.,
plant N-uptake, grain yield, and NUE) improved slightly,
while grain N-content increased significantly (40%). On
the other hand, no significant reduction in NO3− leaching
was observed with the use of the NIs. Nevertheless, the NIs
effectively reduced the nitrification process, as indicated by
the decline in NO3−-N content in soils by 30%, with a sub-
sequent increase in soil NH4+-N.
The comparisons between the relative efficacy of the two
NIs (DCD and DMPP) in minimizing N losses and improv-
ing crop productivity are presented in Fig.3b. The DCD
and DMPP, with reductions of 20 and 19%, respectively,
remained equally effective in reducing N2O emissions from
agricultural soils. However, DCD reduced NO emission by
16%, whereas the effect of DMPP was nonsignificant. The
NIs showed a significantly (p = 0.034) different effect on
NH3 emission: for instance, DCD slightly increased, while
DMPP reduced NH3 emissions to some extent. Regarding
plant productivity attributes, DCD increased grain N-content
(42%), plant N-uptake (39%), grain yield (39%), and NUE
(42%), whereas nonsignificant effects were observed when
DMPP was applied. In the current study, both the NIs
reduced soil NO3−-N content, but their effects remained non-
significant. On the other hand, DMPP significantly increased
soil NH4+-N (59%), while DCD did not exhibit any signifi-
cant effect.
Effect ofNIs andcrop type
The effect of the NIs on CO2, CH4, NH3, and NO emission
was highly crop-type specific (Fig.4). DCD significantly
reduced the CO2 emission from the wheat field by 25%,
CH4 emission from maize and rice fields by 30 and 21%,
respectively, NH3 emission from wheat fields by 20%, and
NO emission from rice and maize fields by 14 and 10%,
respectively. On the other hand, DCD elevated NH3 emis-
sions from vegetables and rice fields and grasslands by 39,
40, and 44%, respectively. DMPP reduced CO2 emission
from vegetable fields by 31%, CH4 emission from rice fields
by 22%, NH3 emission from wheat fields by 20%, and NO
emission from vegetable fields by13%. DMPP application
enhanced CH4 emission by 88% and NH3 emission by 41%
from vegetable fields. Both the NIs proved highly effective
in mitigating N2O emissions from all crop fields and crop
types. DMPP curtailed N2O emission from wheat, rice,
maize, vegetable fields, and grasslands by 21, 16, 11, 19,
Fig. 2 Location of the experiments obtained from the selected studies (146) used in this meta-analysis
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64724 Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
and 13%, respectively, while the corresponding decreases
for DCD were 18, 16, 19, 20, and 18%, respectively (Fig.4).
However, DCD and DMPP increased the biomass yield of
rice by 39 and 41%, respectively, and the increase in yield in
the former case was concomitant with a 46% increase in grain
N-content. Grain N-content in maize was increased by both
DCD (41%) and DMPP (38%), but N uptake and yield were
improved (40 and 38%, respectively) by DCD only. DCD and
DMPP remained equally effective in enhancing yield in grass-
lands (38 and 37%, respectively); however, DCD significantly
increased plant N-uptake and grass biomass by 39 and 38%,
respectively, while DMPP had shown a nonsignificant effect.
The use of DMPP in vegetables increased biomass by 37%.
DCD reduced soil NO3−-N content by 14% in rice fields but
remained ineffective in influencing NO3−-N in soils under
other crops included in this meta-analysis. DMPP lowered soil
NO3−-N in fields of wheat (27%) and vegetables (30%). DCD
reduced NH4+-N in rice fields by 31%, but its effect on soil
NH4+-N content in all other crop fields was nonsignificant.
DMPP decreased soil NH4+-N by 27 and 32% in vegetable
fields and grasslands, respectively. Conversely, it enhanced
NH4+-N content in soil by 56% under maize crop (Fig.4).
20%
NS
NS
14%
NS
NS
NS
NS
NS
NS
40%
NS
30%
Soil inorganic−N
Plant productivity
N leaching
Gaseous emission
−2.0 −1.5−1.0 −0.50.0 0.5
−2.0 −1.5−1.0 −0.50.0 0.5
−2.0 −1.5−1.0 −0.50.0 0.5
−2.0 −1.5−1.0 −0.50.0 0.5
CO2 emission
CH4 emission
NH3 emission
NO emission
N2O emission
NO3 leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR )
Number of studies
50
100
150
200
(a)
NS
NS
20%
NS
16%
NS
NS
19%
NS
NS
)430.0=P()430.0=P(
NS
NS
NS
42%
42%
39%
39%
43%
NS
NS
NS
NS
(P<0.001)
(P=0.005)
(P=0.015)
(P<0.001)
(P=0.005)
(P=0.015)
NS
NS
59%
NS
Soil inorganic−N
Plant productivity
N leaching
Gaseous emission
−1 0 1
CO2 emission
CH4 emission
NH3emission
NO emission
N2O emission
NO3 leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR )
Ty pe of NI
a
a
DCD
DMPP
Number of studies
30
60
90
120
150
(b)
Fig. 3 Overall effect of DCD and DMPP on gaseous emissions, N
leaching, plant productivity, and soil inorganic-N. Error bars repre-
sent 95% CI. Variables are significant if error bars do not overlap with
zero and are denoted in percent change (%) in effect size. Otherwise,
NS shows a nonsignificant difference. Blue color represents the DCD,
and red color represents DMPP treatments. The p-value inside each
box denotes a significant difference between DCD and DMPP treat-
ments, while nonsignificant differences show no p-values
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64725Environmental Science and Pollution Research (2023) 30:64719–64735
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Effect ofNIs andfertilizer type
The efficacy of the NIs significantly depended on the ferti-
lizer type (organic, chemical, and no fertilizer) for reducing
N losses, increasing plant productivity, and soil inorganic N
status (Fig.5). DCD application did not affect CO2 emission
under all fertilizer types. However, it decreased CH4 emis-
sion by 27% in soils receiving chemical fertilizers, NO emis-
sion from both the chemical and organic fertilizers applied
soils (9 and 12%, respectively), and N2O emission from
unfertilized soil (28%), organic fertilizers (17%) and chemi-
cal fertilizers (18%) applied soils. However, DCD increased
NH3 emission (44%) from soils receiving organic fertiliz-
ers. DMPP remained ineffective in reducing CO2, CH4, and
NH3 emissions from chemical fertilizers applied to soils
and NH3 and N2O from unfertilized soils. However, DMPP
reduced N2O emissions by 12 and 16%, respectively, from
the soils receiving organic and chemical fertilizers. Overall,
DCD and DMPP had no significant effect on NO3− leach-
ing. However, individually NO3− leaching was decreased
by 19 and 24%, respectively, with DCD and DMPP applica-
tion to soils receiving organic fertilizers. However, the NIs
remained ineffective in reducing NO3− leaching from soils
receiving chemical fertilizers (Fig.5).
The application of DCD along with organic fertilizers
improved plant N-uptake by 39% and crop yield by 38% but
remained ineffective in increasing NUE (Fig.5). DMPP had
nonsignificant effects on plant-N-uptake and crop yield in
soils without any fertilizer. In chemical fertilizer-amended
soils, DCD increased grain N-content, plant N-uptake, NUE,
and yield by 38, 37, 41, and 38%, respectively; however,
DMPP remained ineffective. The difference between the
NIs was significant regarding their effect on plant N-uptake
(p = 0.023), NUE (p < 0.001), and grain yield (p = 0.018).
Soil inorganic-N (NO3−-N, NH4+-N) contents were not
affected by DCD application in organic fertilizers amended
soils. In soils receiving chemical fertilizers, DCD reduced
soil NO3−-N content by 25% but showed a nonsignificant
effect on soil NH4+-N content. On the other hand, DMPP
had a nonsignificant effect on soil NO3−-N but escalated soil
NH4+-N by 40% (Fig.5).
Effect ofNIs andexperiment type
The effect of NIs as a function of experiment type (field, pot,
and incubation) on gaseous emissions, N leaching, plant pro-
ductivity, and soil inorganic-N status is presented in Fig.6.
Under field conditions, neither of NIs had a significant
NS
12%
NS
NS
(P<0.001)
NS
NS
NS
18%
44%
13%
NS
(P=0.002)
10%
NS
38%
39%
38%
NS
NS
NS
37%
NS
NS
32%
NS
(P=0.046)
30%
19%
10%
NS
NS
11%
NS
(P=0.004)
39%
30%
(P=0.001)
NS
41%
NS
40%
38%
NS
38%
NS
NS
NS
NS
NS
56%
NS
NS
NS
10%
NS
NS
NS
9%
NS
44%
NS
NS
39%
NS
NS
NS
NS
NS
NS
(P<0.001)
(P=0.008)
NS
NS
21%
NS
16%
40%
14%
22%
16%
46%
39%
NS
NS
NS
41%
31%
14%
NS
20%
39%
NS
88%
31%
19%
41%
13%
(P=0.021)
30%
NS
37%
NS
NS
NS
NS
NS
27%
30%
(P=0.001)
NS
25%
18%
20%
NS
NS
NS
22%
(P<0.001)
49%
NS
NS
NS
NS
NS
NS
NS
NS
NS
NS
(P=0.012)
NS
NS
N
S
27%
Fallow Grasses Maize Other crops Rice Vegetables Wheat
Gaseous emission N leaching Plant productivity Soil inorganic−N
−2 −1 012 −2 −1 012 −2 −1 012 −2 −1 012 −2 −1 012 −2 −1 012 −2 −1 012
CO2 emission
CH4 emission
NH3 emission
NO emission
N2O emission
NO3 leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR)
Type of NI
a
a
DCD
DMPP
Number of studies
30
60
Fig. 4 Effect of crop type on DCD and DMPP efficacy in gaseous
emissions, NO3− leaching, plant productivity, and soil inorganic-N.
Variables are considered significant if error bars do not overlap with
zero. Error bars represent 95% CI. Variables are significant if error
bars do not overlap with zero and are denoted in percent change (%)
in effect size. Otherwise, NS shows a nonsignificant difference. Blue
color represents the DCD, and red color represents DMPP treatments.
The p-value inside each box denotes a significant difference between
DCD and DMPP treatments, while nonsignificant differences show
no p-values
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64726 Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
effect on CO2, CH4, and NH3 emissions from soils. How-
ever, under incubation and pot experiments, DCD increased
NH3 emissions by 83 and 41%, respectively. Among the
three experiment types, under field conditions, only the
DCD application reduced NO emission (10%) and DCD
caused a higher reduction in N2O emission than DMPP in
all types of experiments. These differences were significant
between both NIs under the pot as well as field conditions.
Both NIs remained ineffective in reducing NO3− leach-
ing under field conditions. While in pot experiments, the
NIs showed a contrasting effect on NO3− leaching: DCD
increased NO3− leaching by 44%, whereas DMPP reduced
NO3− leaching by 12% (Fig.6).
Only DCD improved grain N-content (38%), plant
N-uptake (39%), NUE (40%), and yield (38%) under field
experiments (Fig.6). DMPP remained ineffective except
for biomass which increased by 38%. In pot studies, DCD
improved yield and biomass by 37 and 46%, respectively
but showed a nonsignificant effect on plant N-uptake. On
the other hand, DMPP increased grain yield by 32% but
remained ineffective for plant N-uptake, NUE, and biomass
in pot experiments. Similarly, the positive effect of DMPP
was not found on plant N-uptake, yield, and biomass. The
use of DCD reduced soil NO3−-N by 20% in pot experiments
but remained ineffective in field and incubation experiments.
Conversely, DMPP reduced soil NO3−-N by 33% in field
27%
NS
NS
NS
17%
16%
NS
NS
12%
NS
NS
NS
NS
43%
38%
NS
41%
NS
37%
NS
38%
NS
(P<0.001)
(P=0.023)
(P=0.018)
NS
40%
25%
NS
28%
NS
NS
NS
NS
NS
NS
18%
12%
44%
9%
19%
24%
39%
NS
39%
38%
NS
NS
Chemical fertilizer No fertilizer Organic ferilizer
Gaseous emission N leaching Plant productivity Soil inorganic−N
−2 −1 012 −2 −1 012 −2 −1 012
N2O emission
NO emission
NH3 emission
CH4 emission
CO2 emission
NO3leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR)
Ty pe of NI
a
a
DCD
DMPP
Number of studies
30
60
90
Fig. 5 Effect of fertilizer type on DCD and DMPP efficacy in gase-
ous emissions, N leaching, plant productivity, and soil inorganic-N.
Variables are considered significant if error bars do not overlap with
zero. Error bars represent 95% CI. Variables are considered to be sig-
nificant if error bars do not overlap with zero and are denoted in per-
cent change (%) in effect size. Otherwise, NS shows a nonsignificant
difference. Blue color represents the DCD, and red color represents
DMPP treatments. The p-value inside each box denotes a significant
difference between DCD and DMPP treatments, while nonsignificant
differences show no p-values
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64727Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
experiments but had shown nonsignificant effects in incuba-
tion and pot experiments. DCD did not exhibit any signifi-
cant effect on NH4+-N content in the soil, whereas DMPP
increased soil NH4+-N in the following decreasing order:
field experiment (47%) > incubation experiment (37%) > pot
experiment (27%) (Fig.6).
Effect ofNIs andsoil texture
Gaseous N emissions from different textured agricultural soils,
i.e., coarse, medium, and fine, differed greatly in response to
the NIs application (Fig.7). Both the NIs exhibited nonsignifi-
cant effects on CO2, CH4, and NH3 emissions in fine-textured
soils, and DMPP did so in medium texture soils as well. In
medium-textured soils, DCD mitigated the emission of both
CO2 and CH4 by 28%, while its effect on NH3 was nonsignifi-
cant. In all the soil textures, DCD and DMPP were equally
effective in reducing N2O emissions, ranging from 14 to 19%.
The application of DCD in medium and fine-textured soils
minimized NO emissions by 10 and 6%, respectively. This
study finds a nonsignificant effect of DCD on NO3− leaching
in fine and medium-textured soils. However, DMPP reduced
NO3− leaching by 30 and 19% in coarse and fine-textured
soils but proved ineffective in medium-textured soils (Fig.7).
Wide variations were observed regarding plant produc-
tivity indices in response to NIs application in different soil
NS
8%
NS
83%
NS
NS
NS
NS
37%
NS
NS
(P=0.031)
NS
16%
7%
41%
NS
(P=0.001)
44%
12%
(P<0.001)
46%
NS
NS
NS
NS
37%
32%
(P<0.001)
(P<0.001)
NS
27%
20%
NS
(P=0.001)
NS
NS
NS
NS
20%
17%
NS
NS
10%
NS
NS
NS
NS
38%
38%
NS
40%
NS
39%
NS
38%
NS
(P<0.001)
(P=0.004)
(P=0.019)
NS
47%
NS
33%
Incubation Pot Field
Gaseous emission N leaching Plant productivity Soil inorganic−N
−2 −1 012 −2 −1 012−2 −1 012
N2O emission
NO emission
NH3 emission
CH4 emission
CO2 emission
NO3 leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR )
Ty pe of NI
a
a
DCD
DMPP
Number of studies
30
60
90
120
Fig. 6 Effect of experiment type on DCD and DMPP efficacy in gase-
ous emissions, N leaching, plant productivity, and soil inorganic-N.
Variables are considered significantly different if error bars did not
overlap with zero. Error bars represent 95% CI. Variables are con-
sidered significantly different if error bars did not overlap with zero
and are denoted in percent change (%) in effect size. Otherwise, NS
shows a nonsignificant different. Blue color represents the DCD, and
red color represents DMPP treatments. The p-value inside each box
denotes a significant difference between DCD and DMPP treatments,
while nonsignificant differences show no p-values
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64728 Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
textures. Both plant N-uptake and yield were improved by
38% with the use of DCD in coarse-textured soils; however,
DMPP remained ineffective. In fine-textured soils, DCD
significantly increased NUE by 41%, while all other plant
productivity indicators included in the meta-analysis were
not influenced significantly by either of the NIs. In medium-
textured soils, DCD improved grain yield by 38%, whereas
DMPP improved biomass yield by 38%, however, all other
effects remained nonsignificant (Fig.7). Application of DCD
exhibited nonsignificant effects on soil NO3−-N content in all
soil textures. On the other hand, DMPP reduced NO3−-N in
soil by 28 and 30% in fine and medium-textured soils, respec-
tively, but had a nonsignificant effect in coarse-textured soils.
DCD decreased soil NH4+-N by 13% in fine-textured soils
and showed nonsignificant effects in coarse and medium-tex-
tured soils. On the other hand, DMPP increased soil NH4+-N
by 81% in fine-textured soils. Nonetheless, it reduced soil
NH4+-N by 27% in medium-textured soils (Fig.7).
Effect ofNIs andsoil pH
Results pertinent to the effect of NIs on gaseous emissions
and N leaching in croplands with different soil pH types,
i.e. acidic (pH ≤ 6), neutral (pH 6–8), and alkaline (pH ≥ 8),
are presented in Fig.8. DCD did not affect CO2 and CH4
emissions from acidic soils, while decreasing CH4 emission
NS
NS
NS
19%
14%
NS
NS
6%
NS
19%
NS
NS
NS
NS
41%
NS
NS
NS
NS
NS
(P<0.001)
13%
81%
NS
28%
(P=0.001)
28%
NS
28%
NS
17%
16%
NS
NS
10%
NS
NS
NS
NS
38%
NS
NS
NS
NS
NS
38%
NS
(P=0.02)
NS
27%
NS
30%
16%
18%
30%
NS
NS
NS
38%
NS
38%
NS
NS
NS
NS
Fine Medium Coarse
Gaseous emission N leaching Plant productivity Soil inorganic−N
−2 −1 012 −2 −1 012 −2 −1 012
N2O emission
NO emission
NH3 emission
CH4 emission
CO2 emission
NO3 leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR)
Type of NI
a
a
DCD
DMPP
Number of studies
30
60
90
Fig. 7 Effect of soil texture on DCD and DMPP efficacy in gase-
ous emissions, N leaching, plant productivity, and soil inorganic-N.
Variables are significantly different if error bars did not overlap with
zero. Error bars represent 95% CI. Variables are considered signifi-
cantly different if error bars did not overlap with zero and are denoted
in percent change (%) in effect size. Otherwise, NS shows a non-
significant different. Blue color represents the DCD, and red color
represents DMPP treatments. The p-value inside each box denotes
a significant difference between DCD and DMPP treatments, while
nonsignificant differences show no p-values
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64729Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
by 27% in neutral soils and similarly decreasing CO2 and
CH4 emissions by 26 and 31%, respectively, in alkaline soils.
DMPP did not affect CO2 and CH4 emissions under different
pH types. DCD affected NH3 emission only in acidic soil and
increased it by 36%, whereas DMPP had shown a nonsignifi-
cant effect on NH3 emission in soils of different pH. DCD
reduced NO emissions by 9% from neutral pH soils, while
DMPP showed a nonsignificant impact. In acidic and neutral
soils, DCD and DMPP were equally effective in mitigating
N2O emissions, and emission reductions ranged from 14 to
17%. However, DCD reduced N2O emission in alkaline soils
by 20%, whereas DMPP remained ineffective. Both NIs had
a nonsignificant effect on NO3− leaching from acidic soils.
In neutral soils, however, the NIs showed converse effects
on NO3− leaching: DMPP reduced NO3− leaching (by 19%),
whereas DCD increased NO3− leaching (by 48%) (Fig.8).
In acidic soils, the use of DCD enhanced grain N-content,
plant N-uptake, grain yield, and biomass by 41, 39, 38, and
37%, respectively (Fig.8). Similarly, DMPP increased grain
N-content by 41%, grain yield by 35%, and biomass yield
by 37% in acidic soils. However, both NIs remained inef-
fective in improving NUE in acidic soils. In alkaline soils,
except for plant N-uptake which increased by 37% with the
application of DCD, all the productivity indicators were not
affected by either of the NIs. Likewise, except for the 38%
increase in grain yield by DCD in neutral pH soils, all plant
NS
NS
NS
NS
17%
17%
38%
NS
NS
NS
NS
37%
37%
41%
37%
NS
NS
39%
NS
38%
35%
(P=0.001)
(P<0.001)
NS
NS
NS
NS
27%
NS
NS
NS
15%
14%
NS
NS
9%
NS
48%
19%
(P<0.001)
NS
NS
NS
NS
NS
NS
NS
38%
NS
NS
NS
23%
NS
(P=0.023)
31%
NS
25%
NS
20%
NS
NS
NS
(P=0.012)
NS
NS
NS
NS
NS
37%
NS
NS
NS
NS
pH ≤ 6 pH 6−8 pH ≤ 8
Gaseous emission N leaching Plant productivity Soil inorganic−N
−2 −1 012 −2 −1 012 −2 −1 012
N2O emission
NO emission
NH3 emission
CH4 emission
CO2 emission
NO3 leaching
Biomass
Yield
NUE
Plant N−uptake
Grain N−content
NH4−N in soil
NO3−N in soil
Effect Size (lnRR)
Type of NI
a
a
DCD
DMPP
Number of studies
30
60
90
Fig. 8 Effect of soil pH on DCD and DMPP efficacy in gaseous emis-
sions, N leaching, plant productivity, and soil inorganic-N. Variables
are significantly different if error bars did not overlap with zero. Error
bars represent 95% CI. Variables are considered significantly differ-
ent if error bars did not overlap with zero and are denoted in percent
change (%) in effect size. Otherwise, NS shows a nonsignificant dif-
ference. Blue color represents the DCD, and red color represents
DMPP treatments. The p-value inside each box denotes a significant
difference between DCD and DMPP treatments, while nonsignificant
differences show no p-values
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64730 Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
productivity parameters were not influenced by either of the
NIs. Both the NIs remained ineffective regarding the change
in soil inorganic-N (NO3−-N and NH4+-N) in acidic soils.
Concerning NH4+-N and NO3-N content in soils, only DCD
resulted in higher NH4+-N content (23%) in neutral soils
(Fig.8).
Discussion
Effect ofNIs ongaseous emissions
Mitigating gaseous emissions (i.e., CH4, CO2, NO, N2O,
and NH3) from agricultural soils using NIs and their conse-
quences on plant productivity have been extensively studied
worldwide (Li etal. 2018; Qiao etal. 2015; Scheer etal.
2014; Sha etal. 2020; Wu etal. 2021; Xia etal. 2017; Yang
etal. 2016b). There is still a debate on the efficacy of vari-
ous NIs in reducing these gaseous emissions in relation to
different soil and plant factors, particularly at the field level.
We conducted this comprehensive meta-analysis to evaluate
the effect of DCD and DMPP (the most commonly used NIs
in agriculture) on gaseous emissions, N-leaching, plant pro-
ductivity, and changes in soil inorganic-N status in relation
to different crop and soil factors (crop type, fertilizer type,
experiment type, soil texture type, and soil pH).
In general, NIs were ineffective in mitigating CO2, CH4,
and NH3 emissions from croplands; however, they decreased
NO and N2O emissions significantly. Among the NIs, in gen-
eral, DCD mitigated N2O and NO emissions more effectively
than DMPP (Figs.3 and 4). Akiyama etal. (2010) conducted
a meta-analysis and found that DCD was more effective than
DMPP in mitigating N2O emissions. Yang etal. (2016b) also
reported a significant reduction in N2O emissions amounting
to 44 and 47% by DCD and DMPP, respectively. Similarly,
Gao etal. (2021) reported an inhibition in N2O by 30 and 60%
using DCD and DMPP, respectively. As nitrification and sub-
sequent denitrification are the principal pathways for produc-
ing N2O and NO in agricultural systems, the NIs reduce N2O
production by suppressing these processes (Kim etal. 2012).
Application of inhibitors mainly lowers NO3−-N avail-
ability for soil denitrification, thereby reducing N2O emis-
sions (Benckiser etal. 2013). DCD effectively mitigated NO
and N2O emissions from organic fertilizer-amended soils.
In chemical fertilizer-amended soils, both NIs effectively
reduced N2O emissions under field conditions (Figs.5 and
6). Our findings further showed that texture type substan-
tially influences the efficacy of NIs for N-emissions from
soils. Both NIs effectively mitigated N2O emissions in
coarse-textured soils. They also reduced N2O in fine-tex-
tured soils but had nonsignificant effects on CO2, CH4, and
NH3 emissions. In medium-textured soils, DCD effectively
reduced CO2, CH4, NO, and N2O emissions (Fig.7). In
coarse-textured soils, NIs increased the NH4+-N by delay-
ing the process of denitrification (Cui etal. 2021). The rea-
son behind could be the low physicochemical interaction
in coarse texture soils due to low organic matter contents,
while in heavy-textured soils, the higher organic matter
and clay contents increased the activity of Nitrosomonas
sp. which reduced the effectiveness of the NIs (Barth etal.
2019). However, further research is warranted to explore the
mechanisms behind the varying effects of NIs on N emis-
sions in different texture types.
DCD was found to increase NH3 emissions in vegeta-
bles, rice, and grasses but reduced its emission from wheat-
cropped soils (Fig.4). Similarly, in pot and incubation stud-
ies, DCD significantly increased NH3 emissions (Fig.6).
Kim etal. (2012) observed a significant increase in NH3 in
urea-fertilized pastures and cropping soils by the application
of NIs. Pan etal. (2016) found in a meta-analysis that DCD
aggravates the release of NH3 by 22–220%, but DMPP had
nonsignificant effects. Wu etal. (2021) also found that NIs
increased NH3 volatilization by 35.7%, and volatilization
varied greatly with NI type, soil pH, experimental method,
and fertilizer type. The DCD and DMPP increased NH3
emissions by 27.4 and 43.2%, respectively (Gao etal. 2021).
Similarly, Qiao etal. (2015) reported a 33–67% increase in
NH3 emissions from agricultural systems by applying NIs.
As the main principle, NIs interfere with the nitrification
process, and NH4+ stays for a prolonged time in the soils.
Thus, the longer the exposure of NH4+ to the soil envi-
ronment, the higher chance of NH3 volatilization into the
atmosphere (Soares etal. 2012). The solution to reduce NH3
volatilization from soil is demonstrated by many researchers
including the use of slow release fertilizers, coated fertilizer,
and biofertilizers. In a recent study, Xue etal. (2021) used
the Bacillus amyloliquefaciens biofertilizer on alleviating
ammonia volatilization in alkaline farmland soil. Bioferti-
lizer treatment reduced ammonia volatilization by 68 per-
cent, increasing crop production and nitrogen recovery by
19% and 19%, respectively, when compared to conventional
fertilizer.
Converse to the finding of this study, the meta-analysis
by Yang etal. (2016b) revealed an 8.7% reduction in CO2
emission with the use of DMPP. Likewise, Weiske etal.
(2001) reported a significant reduction in mean CO2 emis-
sions over three years by DMPP application to soil. This
effect of DMPP is generally ascribed due to altered rates
of C-mineralization in soil. Weiske (2001) observed a 28%
reduction in CH4 emissions by DMPP, suggesting that it
might stimulate CH4 oxidation. There exist many similarities
between ammonium monooxygenase (AMO) and methane
monooxygenase (MMO). Suppressing the activity of AMO
by NIs might have improved the activity of MMO, thus facil-
itating the oxidation of CH4 (Wang etal. 2016). In contrast,
Ménendez etal. (2012) and Huérfano etal. (2022) reported
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

64731Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
that DMPP is ineffective in reducing CO2 and CH4 emissions
at different soil water and temperature regimes. However, the
underlying mechanism needs further investigation. Gao etal.
(2021) found a decrease in CH4 by 11% with DCD, and it is
in line with the findings of this study.
Both NIs remained equally effective in mitigating N2O
emissions from acidic soils. Likewise, DCD decreased CO2,
CH4, and N2O emissions from alkaline soils, while DMPP
remained ineffective. Both NIs reduced N2O emissions but
had no significant impact on the release of CO2 and NH3
from neutral pH soils (Fig.8). Kim etal. (2012) observed
more NH3 emissions from soils with high pH irrespective of
crop type and land use. Under alkaline conditions (pH ≥ 7.6),
NH4+ ions dissociate into NH3 and thus favor NH3 volatiliza-
tion (Francis etal. 2008). Unfortunately, there is still room
for more study in this field because the relative efficacy of
DCD and DMPP under various soil pH types has not been
properly examined (Tufail etal. 2022).
Effect ofNIs on NO3− leaching
NIs suppress nitrification and thus are expected to minimize
subsequent denitrification and NO3− leaching from soils
(Norton and Ouyang, 2019; Subbarao etal. 2006). Accord-
ing to this meta-analysis, the overall effects of NIs were
nonsignificant to NO3− leaching from croplands. The effect
of DCD and DMPP differed significantly among different
crop types because of the large variance associated with the
effect sizes. DCD reduced NO3− leaching in grasses, while
DMPP did so in maize crop. Conversely, NO3− leaching was
increased (39–49%) in wheat, maize, and other crops by
DCD (Fig.4). Both NIs significantly reduced NO3− leach-
ing from organic fertilizer-amended soils but remained inef-
fective in soils amended with chemical fertilizers (Fig.5).
However, Yang etal. (2016b) found in a meta-analysis that
DMPP could effectively reduce soil NO3−-N leaching when
applied with urea in neutral soils. This discrepancy between
the meta-analysis studies might have occurred due to varia-
tions in the number of observations. For instance, the num-
ber of observations in our meta-analysis was greater (k = 220
for DMPP, 430 for DCD) as compared to an earlier study
(k = 113 for DMPP, 185 for DCD) by Yang etal. (2016b).
In pot studies, contrasting effects of both NIs were
observed, i.e., DMPP reduced, whereas DCD increased
NO3− leaching. Both the NIs did not exhibit any effect on
NO3− leaching under field conditions (Fig.6). DCD had
a nonsignificant effect on NO3− leaching from fine and
medium-textured soils. Conversely, DMPP reduced N leach-
ing from fine and coarse-textured soils but had no effect
in medium-textured soils (Fig.7). Soil with coarse texture
are more prone to leaching than fine texture soils, but more
microbial biomass is present in fine-textured soils; therefore,
DMPP reduced the N leaching from fine-textured soils. Both
NIs had nonsignificant effects on N leaching from acidic
soils. Nevertheless, DMPP reduced while DCD increased
N leaching from neutral pH soils (Fig.8). Our results are
similar to Yang etal. (2016a, b), and they reported the higher
effectiveness of DMPP over DCD in reducing soil NO3−-N
leaching in neutral soils. However, future research is needed
to do for understanding the whole mechanism.
Effect ofNIs onplant productivity
The management and environmental factors significantly
influence the effectiveness of NIs. The findings of our
meta-analysis demonstrated that using NIs in combina-
tion with chemical N-fertilizer could be an effective strat-
egy to improve NUE and crop yields. This fact was fur-
ther supported by the highly consistent effects of the NIs
on a range of soil and crop management factors evaluated
in the present study. In our meta-analysis, DCD increased
grain-N andcropyield in rice and maize,and also increased
plant N-uptake and biomass in grasses. Neither of the NIs
improved wheat productivity but remained equally effective
to enhance grass yield. On the other hand, DMPP improved
rice yield, maize grain-N, and biomass yield in vegetables
but did not significantly influence N-uptake and biomass in
grasses (Fig.4). Inhibiting the process of nitrification until
the log phase of crop growth provides a better opportunity to
absorb NO3− thereby increasing NUE (Akiyama etal. 2010;
Saud etal., 2022). We found higher NUE with the use of
NIs, which agreed with the findings of Abalos etal. (2014),
Qiao etal. (2015), Xia etal. (2017), and Li etal. (2018).
Abalos etal. (2014) also found that the application of NIs
along with fertilizer resulted in improved productivity of
forages and cereal crops than fertilizer alone. They further
stated that NIs increased NUE in forages, cereal, and vegeta-
bles/industrial crops. However, the effect was significantly
higher for forages than cereals regarding productivity and
NUE. One possible reason might be the higher N application
in cereals compared to vegetables and forages, as DCD is
relatively more effective under medium to high N applica-
tion rates. Moreover, cereals are mainly harvested for grains,
but aboveground biomass is more responsive to NIs than
grain yield (Yang etal. 2016b).
Significant differences also existed among NIs regard-
ing their effect on plant productivity in different fertilizer
types. DCD improved plant N-uptake and crop yield but did
not influence NUE in organic fertilizer-amended soils. On
the other hand, DCD significantly increased grain-N, plant
N-uptake, NUE, and grain yield in soils with chemical fer-
tilizer, while DMPP showed no effect (Fig.5). Yang etal.
(2016b) found DCD to be more effective in improving crop
yields when applied with organic or chemical N sources as
compared to DMPP which had nonsignificant effects. DCD
increased plant productivity and NUE, but DMPP remained
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64732 Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
ineffective except for biomass under field conditions. Both
NIs improved grain yield but remained ineffective in influ-
encing plant N-uptake in pot studies (Fig.6). Application
of NIs may aggravate N losses via NH3 volatilization under
field and laboratory conditions, as indicated by a range of
field and laboratory investigations (Kim etal. 2012). On
the other hand, DCD improved plant N-uptake and grain
yield in coarse-textured soil, while DMPP showed no sig-
nificant effect. In fine-textured soils, DCD significantly
increased NUE, but other plant productivity indicators were
not influenced by both NIs. In medium-textured soils, DCD
and DMPP improved grain and biomass yield, respectively
(Fig.7). In a meta-analysis, Abalos etal. (2014) found an
average increase of 7.5% in crop yields and 12.9% in NUE
as a result of using DCD and DMPP with a higher response
on course-textured soils, as NIs prolong the detention of
N in the soil as NH4+ thus providing more time for plants
to uptake NH4+ (Kim etal. 2012). Abalos etal. (2014)
observed a significantly lower response of NIs toward crop
yield on fine-textured soils than medium or coarse-textured
soils, although the effect was insignificant.
The efficacy of DCD and DMPP differed with the changes
in soil pH: both NIs significantly improved plant productiv-
ity but remained ineffective to enhance NUE in acidic soils.
In contrast, in alkaline soils, except for an increase in plant
N-uptake by DCD, all productivity indices evaluated in the
meta-analysis were not improved by both the NIs. In neutral
pH soils, only DCD increased grain yield while other traits
were not affected by both NIs (Fig.8). Most probably, soil
pH regulates the efficiency of NIs by affecting NH3 volatili-
zation. The improved plant productivity on acidic and neu-
tral soils by NIs might be attributed to their nonsignificant
effects on N losses as NH3 emissions. However, Yang etal.
(2016b) observed in their meta-analysis that DMPP only
improved crop yields by 9.4% in alkaline soil, whereas DCD
was equally effective in acidic and alkaline soils. Abalos
etal. (2014) reported a positive response of NIs on crop
productivity and NUE in three soil pH groups (i.e., ≤ 6.0,
6–8, and ≥ 8.0). However, the effect was the most significant
when NIs were applied to acidic soils (pH ≤ 6.0). Linquist
etal. (2013) found a higher positive response of NIs on N
uptake and paddy yield in rice crop with high pH soils. In
contrast, Abalos etal. (2014) observed a low response of
NIs on NUE and crop yields on neutral and alkaline soils
because of more N losses via NH3 volatilization.
Effects ofNIs onsoil inorganic‑N
Our meta-analysis showed that, in general, NIs effectively
inhibit the process of nitrification as revealed by lower soil
NO3−-N with subsequent increase in soil NH4+-N content
(Fig.3). DCD effectively reduced NO3−-N and NH4+-N con-
tent in rice crop only. DMPP significantly lowered soil NO3−-N
in wheat and vegetables, whereas soil NH4+-N in grasses and
vegetables. Conversely, DMPP enhanced soil NH4+-N content
in maize crop (Fig.4). For soil NO3−-N, DCD was found to be
comparatively good NIs for chemical fertilizers applied soils
(Fig.5). Numerous investigations have documented that the
efficiency of DCD and DMPP differed when applied with both
organic and chemical fertilizers (Dai etal. 2013; Lei etal.,
2022; Yang etal. 2016a). This discrepancy could be attributed
to differential hydrolyzing rates of N sources to NH4+ form,
available for nitrification in soil. Yang etal. (2016b) revealed
that both DCD and DMPP, when combined with organic
fertilizer or urea, proved equally effective in increasing soil
NH4+-N content. NIs significantly limit the conversion rate
of NH4+ to NO3−, increase the NH4+ in the soil profile, and
ultimately increase soil NH4+-N contents. In case of organic
fertilizers the NIs significantly reduced the population of AOB
and amoA gene abundance (Tao etal. 2021). The organic fer-
tilizer provides suitable alkaline conditions for NIs to reduce
the population of AOBs (Lei etal., 2022).
NIs primarily hampers the microbial conversion of NH4+-N
to NO3−-N, thus minimizing N losses through leaching
(Benckiser etal. 2013; Meng et al. 2021). We found that
DCD effectively reduced soil NO3−-N in post studies, while
DMPP did so under field conditions (Fig.6). DMPP reduced
NO3−-N in fine and medium-textured soils. In contrast, DMPP
significantly increased soil NH4+-N in fine-textured soils but
reduced NH4-N in medium-textured soils (Fig.7). Both NIs
remained ineffective regarding the change in soil inorganic-N
in acidic soils. DCD slightly reduced NO3−-N in alkaline
soils while significantly reducing soil NO3−-N and NH4+-N
content in neutral pH soils (Fig.8). Gao etal. (2021) found
that DCD and DMPP increased NH4+-N by 90.7 and 81.6%
under incubation conditions whereas 46 and 44% under field
conditions, respectively. They further reported decrease in
NO3−-N by 45.5 and 70% under the laboratory and by 25.2 and
20.9% in the field with DCD and DMPP, respectively. Higher
microbial activities in the field than laboratory conditions
usually accelerate biodegradation rates of NIs, thereby
declining their efficiencies (Kelliher etal. 2014).
Conclusion
The meta-analysis undertaken here has extended our
knowledge and concluded that the overall effect of NIs was
insignificant in reducing CO2, CH4, and NH3 emissions.
It further concludes that (i) DCD and DMPP remained
equally effective in reducing N2O emissions; however, DCD
reduced NO emission by 16%, whereas the effect of DMPP
was nonsignificant. (ii) Although the effect of NIs was
highly crop-specific, but the DMPP and DCD were highly
effective in mitigating N2O emissions. (iii) DCD decreased
CH4 emission by 27% in soils receiving chemical fertilizers,
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64733Environmental Science and Pollution Research (2023) 30:64719–64735
1 3
while DMPP remained ineffective in reducing CO2, CH4,
and NH3 emissions from chemical fertilizers. (iv) The effect
of soil texture and soil pH on NIs suggested that DCD and
DMPP were equally effective in reducing N2O emissions in
all the soil textures and from acidic and neutral soil. Taken
together, these observations indicate our understanding of the
role of DMPP and DCD in various agroecological scenarios.
However, more research is needed to understand the role of
NIs other than DCD and DMPP.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s11356- 023- 26318-5.
Author contribution All authors contributed to the study conception
and design. Conceptualization, writing original draft, review, editing,
formal analysis, visualization, project administration, and supervision
were performed by Muhammad Aammar Tufail. Project administration
and writing original draft were done by Muhammad Irfan. Writing,
review, editing, formal analysis, and visualization were carried out by
Wajid Umar. Writing, review, and editing were performed by Abdul
Wakeel. Supervision and project administration were performed by
Ruth A. Schmitz. All authors commented on previous versions of the
manuscript. All authors read and approved the final manuscript.
Funding Open Access funding enabled and organized by Projekt
DEAL.
Data availability Not applicable.
Declarations
Ethics approval Not applicable.
Consent to participate Not applicable.
Consent for publication All authors agreed with the content to publish
and received consent from there institutes.
Competing interests The authors declare no competing interests.
Open Access This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
provide a link to the Creative Commons licence, and indicate if changes
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included in the article's Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not included in
the article's Creative Commons licence and your intended use is not
permitted by statutory regulation or exceeds the permitted use, you will
need to obtain permission directly from the copyright holder. To view a
copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.
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