Paddy Water Environ
DOI 10.1007/s10333-016-0551-1
ARTICLE
Effect of organic, inorganic and slow-release urea fertilisers
on CH4 and N2O emissions from rice paddy fields
Mai Van Trinh1 • Mehreteab Tesfai2 • Andrew Borrell3
Udaya Sekhar Nagothu2 • Thi Phuong Loan Bui1 •
Vu Duong Quynh1 • Le Quoc Thanh1
•
Received: 3 May 2016 / Revised: 5 August 2016 / Accepted: 9 September 2016
Ó The International Society of Paddy and Water Environment Engineering and Springer Japan 2016
Abstract Vietnam is one of the world’s top two rice
exporting countries. However, rice cultivation is the primary
source of agriculture’s greenhouse gas (GHG) emissions in
Vietnam. In particular, strategies are required to reduce GHG
emissions associated with the application of organic and
inorganic fertilisers. The objective of this study was to assess
the effects of various combinations of biochar (BIOC),
compost (COMP) and slow-release urea (SRU) on methane
(CH4) and nitrous oxide (N2O) emissions. In total, 1170 gas
samples were collected from closed gas chambers in rice
paddies at Thinh Long commune and Rang Dong farm in
northern Vietnam between June and October 2014. The gas
samples were analysed for CH4-C and N2O-N fluxes using
gas chromatography. The application of BIOC alone resulted
in the lowest CH4 emissions (4.8–59 mg C m-2 h-1) and
lowest N2O emissions (0.15–0.26 lg N m-2 h-1). The
combined application of nitrogen–phosphorus–potassium
(NPK) ? COMP emitted the highest CH4 (14–72 mg C m-2
h-1), while ‘NPK ? BIOC emitted the highest N2O
(1.03 lg N m-2 h-1 in the TL commune), but it was the
second lowest (0.495 lg N m-2 h-1) in the RD farm. Green
urea and orange urea reduced N2O emissions significantly
(p \ 0.05) compared to white urea, but no significant differences were observed with respect to CH4 emissions. SRU
& Mehreteab Tesfai
[email protected]
1
Vietnam Academy of Agricultural Sciences (VAAS), Vinh
Quynh Commune, Thanh Tri District, Hanoi, Vietnam
2
Norwegian Institute of Bioeconomy Research, Frederik, A.
Dahls vei 20, 1430 Ås, Norway
3
Hermitage Research Facility, Queensland Alliance for
Agriculture and Food Innovation (QAAFI), The University of
Queensland, Warwick, QLD 4370, Australia
fertilisers and BIOC alone measured the lowest greenhouse
gas intensity, i.e. \2.5 and 3 kg CO2 eq. kg-1 rice grain,
respectively. Based on these results, application of fertilisers
in the form of BIOC and/or orange or green urea could be a
viable option to reduce both CH4 and N2O emissions from
rice paddy soils.
Keywords Biochar Compost Slow-release urea Greenhouse gas emissions Methane Nitrous oxide Rice Vietnam
Introduction
Rice cultivation is the largest source of agriculture’s greenhouse gas (GHG) emissions in Vietnam, with estimated
emissions of 37.4 Tg CO2 equivalents, accounting for 58 %
of the total agricultural GHGs (MONRE 2014). Vietnam is
one of the world’s top two rice exporting countries, with
more than seven million hectares of land under paddy rice
(FAO 2013). Application of nitrogen (N) fertiliser in rice
fields is a common farmers’ practice in the Red River Delta
of Vietnam, and likely contributes to increased global
warming via enhanced emission of N2O into the atmosphere.
Significant amounts of applied fertiliser N are not taken up by
the rice plant (Borrell et al. 1998) and lost as ammonia, which
can be a major contributor to N2O emissions from agricultural soils (Nash et al. 2012).
There are many factors contributing to increased GHG
emissions, including CH4 and CO2 from rice cultivation,
and management of inorganic fertilisers, animal manure
and crop residue inputs. Burning of organic residues such
as rice straw in the field after crop harvest results in the
emission of large amounts of smoke particles containing
CO2 and other GHGs into the atmosphere, contributing to
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Paddy Water Environ
global warming potential (GWP) and particle air pollution.
GWP compares the integrated radiative forcing over a
specified period (e.g., 100 years) from a unit mass pulse
emission and enables the potential climate change associated with emissions of different GHGs to be compared
(IPCC 2007).
More than 40 % of the rice straw produced in Vietnam is
burned in the field (Truc et al. 2012). Consequently, organic
C content in the straw is lost and a considerable amount of
CO2 is emitted into the atmosphere (Miura and Kanno 1997).
Such practices likely reduce organic carbon inputs into the
soil as well as deplete soil organic matter (OM) levels,
eventually leading to low rice yields. By 2020, Vietnam aims
to reduce CH4 and N2O emissions in rice production systems
by 20 % compared to the 2010 baseline (UN, Vietnam 2013).
Interventions in the form of improved slow-release N fertilisers (Akiyama et al. 2010; Soares et al. 2015), organic
fertiliser management of composted straw (Khosa et al.
2010) or biochar derived from rice straw may potentially
reduce N2O and CH4 emissions (Bruun et al. 2011; Wang
et al. 2012). Slow-release fertilisers contain plant nutrients in
a form that delays N availability for plant uptake and use after
application, or which extends its availability to the plant
significantly longer than a ‘rapidly available nutrient fertiliser’ such as ammonium nitrate, urea, ammonium phosphate or potassium chloride (Trenkel 2010; Liu et al. 2014).
For instance, ‘orange’ urea is coated with agrotain, which
inhibits the urease enzyme responsible for driving the conversion of urea to ammonia during volatilisation (Turner
et al. 2008).
Aerobically composted straw has also been suggested as
a potential soil amendment strategy to mitigate CH4
emissions from rice paddies, since it contains a more stabilised form of C (Corton et al. 2000; Khosa et al. 2010). In
addition, anaerobically composted straw has a potential to
maintain N2O emissions at a low level (Yao et al. 2010).
Another alternative is straw biochar (a product after the
pyrolysis of straw), which has also been recommended as a
potential soil amendment to reduce CH4 emissions from
rice paddies due to its recalcitrant C component (Liu et al.
2011; Feng et al. 2012). Biochar (BIOC) derived from crop
straw can also suppress N2O emissions by enhancing
complete denitrification of NO3- to N2 due to its alkaline
properties (Yanai et al. 2007). BIOC can also improve soil
water holding capacity in sandy soils (Briggs et al. 2005),
increase soil pH (Laird et al. 2010; Peng et al. 2011),
increase soil cation exchange capacity (Yamato et al. 2006;
van Zwieten et al. 2010; Peng et al. 2011), potentially
reduce nutrient leaching (Lehmann et al. 2003; Major et al.
2009) and lower N2O and CH4 emissions by improving soil
aggregation (van Zwieten et al. 2009). More specifically,
BIOC-amended paddy soils increase rice yield while concurrently contributing more to soil carbon storage (Cuong
123
et al. 2012). Application of BIOC derived from rice straw
to field soils is therefore a promising alternative for organic
matter management in rice farming systems, combining the
positive long-term effects on soil quality with GHG
reduction through carbon sequestration in soils (Zhang
et al. 2010).
One of the explanations for the reduction in N2O
emissions from BIOC-amended soils includes reductions in
the amounts of N that are available for denitrification, as
adsorption and retention of ammonium (NH4) is much
enhanced in soils amended with BIOC (Singh et al. 2010;
Steiner et al. 2010). However, the degree to which N2O
emissions can be reduced has been a controversial issue
which varies depending on the feedstock used to produce
BIOC (van Zwieten et al. 2009), as well as by the type of
soil, BIOC application rate and soil moisture conditions.
Counterintuitively, BIOC additions to soils may also
decrease crop yield (van Zwieten et al. 2010; Rajkovich
et al. 2011) and increase decomposition rates (Hamer et al.
2004; Zimmerman et al. 2011), N2O efflux (Yanai et al.
2007) and CH4 emissions (Zhang et al. 2010).
In general, organic fertilisers and slow-release urea
fertilisers may differ greatly in composition and, as a result,
there may be differences in the mitigation potential of N2O
and CH4 emissions following their application to soils
(Meijide et al. 2007). There is still a shortage of studies
investigating both CH4 and N2O emissions and overall
GWP of rice soils amended with BIOC and/or compost and
slow-release fertilisers with urea alone, or in combination,
with other inorganic fertilisers. We conducted two field
experiments in rice paddy soils at two locations. The
objective of Experiment 1 was to assess the effects of
compost and BIOC on CH4 and N2O emissions when
applied alone, or in combination, with inorganic fertilisers.
We hypothesised that the application of COMP and/or
BIOC derived from rice straw would mitigate CH4 and
N2O emissions. The objective of Experiment 2 was to
evaluate the mitigation potential of two SRU fertilisers,
namely ‘green urea’ and ‘orange urea’ on N2O emissions.
We hypothesised that N2O emissions from rice soils may
be reduced by applying slow-release urea fertilisers, since
nitrification and consequently denitrification is curtailed.
This study is expected to provide baseline information
from which to explore appropriate mitigation measures that
can reduce CH4 and N2O emissions from rice paddy fields.
Materials and methods
Experiment site
Field experiments were conducted during summer 2014 in
Thinh Long (TL) commune (106°80 500 E and 19°590 1100 N)
Paddy Water Environ
and Rang Dong (RD) farm (106°130 100 E and 20°30 2800 N) in
northern Vietnam. At the study sites, the summer is characterised as hot with high rainfall. The mean summer air
temperature is between 26 and 28 °C, and the hottest
months of the year are July and August. The annual mean
air temperature is 23–24 °C and the annual mean air
humidity is about 80–85 %. The highest air humidity (i.e.
90 %) is often recorded in March. The cumulative annual
rainfall ranges from 1700 to 1800 mm, with the main rains
falling between May and October, accounting for about
80 % of the annual rainfall.
Experiment 1: BIOC, compost and NPK fertilisers
In Experiment 1, the field trial consisted of ten treatments
that were randomly allocated within four replicates, i.e.
completely randomised design (Table 1). The total number
of subplots was 40 and the plot size was 20 m2 (5 9 4 m)
separated by soil embankments. The first top-dressing
fertiliser was applied 7 days after transplanting (DAT) at
the beginning of the tillering stage. The second top-dressing fertiliser was applied between 53 and 56 DAT (after the
panicle initiation stage). The fertiliser doses per ha matched the farmers’ application rate in the spring cropping
season (i.e. 110 kg N, 60 kg P2O5 and 80 kg K2O) and in
the summer season (i.e. 100 kg N).
Table 1 Description of the
treatments applied in
Experiment 1 at the RD farm
and the TL commune
Treatment
Experiment 2: slow-release urea fertilisers
In Experiment 2, the field trial consisted of three treatments
that were randomly allocated within four replicates, i.e.
completely randomised design. The total number of subplots was 12. The plot size was 20 m2 (5 9 4 m) separated
by soil embankments. In this experiment, three types of
urea were used: conventional white urea (WU: CO(NH2)2),
green urea (GU: compound of urea coated by Neb26, USA)
and orange urea (OU: compound of urea coated by Agrotain, USA). The green and orange ureases are classified as
slow-release fertilisers, because they contain urea treated
with a urease inhibitor to delay the hydrolysis of urea into
NH3, thereby minimising losses to the atmosphere (IPL
2014). Top dressings of urea were applied on the same day
as Experiment 1, with 100 kg each for WU, GU and OU,
which equates to 46 kg N/ha.
Basic properties of the BIOC, compost and soils
of the study sites
The BIOC used in this study was produced from the rice
straw. The rice straw compost was applied at a rate of
10,000 kg ha-1 and BIOC at a rate of 4150 kg ha-1.
Samples were collected from the COMP and BIOC
treatment subplots and analysed for some chemical
Abbreviations
Dosage (kg ha-1)
N
P
K
BIOC
COMP
T1
Control
CONT
0
0
0
0
0
‘NPK
55
30
40
0
0
110
60
80
0
0
0
0
0
0
10,000
55
30
40
0
10,000
110
60
80
0
10,000
0
0
0
4150
0
55
30
40
4150
0
NPK ? BIOC
110
60
80
4150
0
NPK ? COMP ? BIOC
110
60
80
4150
10,000
T2
Half standard NPK rate
T3
Standard NPK
NPK
T4
COMP
COMP
T5
Half standard NPK ? COMP
‘NPK ? COMP
T6
Standard NPK ? COMP
NPK ? COMP
T7
BIOC
T8
Half standard NPK ? BIOC
BIOC
‘NPK ? BIOC
T9
Standard NPK ? BIOC
T10
Standard NPK ? COMP ? BIOC
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Paddy Water Environ
Table 2 Average chemical composition of biochar, compost and
topsoil used at the study sites
CH4 and N2O sampling and analysis
Constituent
The fluxes of CH4 and N2O were determined using the
techniques of static flux chamber and gas chromatography,
following the methods of Rochette and Eriksen-Hamel
(2008). The chamber consists of a permanently installed
base unit (open bottom) and a removable top. A stainless
steel base unit (45 cm length 9 40 cm width 9 40 cm
height) with a water groove (5 cm in depth) on the top was
placed 10 cm deep in the soil for 3 days before transplanting to avoid lateral gas diffusions. The removable top
(45 cm length 9 40 cm width 9 9 cm height) covered six
hills of rice, and the plant density inside the chamber was
the same as outside of the chamber (see www.climaviet.
org). Floodwater was used to seal the plexiglass top to the
base unit during gas sampling. A rubber septum, thermometer and two mini fans (12 V) were installed in the top
of the chamber (Ma et al. 2007). Pressure control (plastic
tube with 7.6 m length and 1.5 mm diameter) was also
installed to maintain an equilibrium gas pressure between
the inside and outside of the chamber and to minimise
mixing of the internal chamber gases with the exterior
atmosphere (Lindau et al. 1991). Removable wooden
boardwalks were set up in the early stages of the rice
season to avoid soil disturbances during gas sampling.
Gas sampling was usually performed between 08:00 and
11:30 am to prevent the effects of diurnal variation (Velthof and Oenema 1995). Three gas samples were withdrawn from each chamber headspace at 10 min intervals
(0, 10 and 20 min) using 60 ml syringes with three replications for every treatment in Experiments 1 and 2. The
collected gas samples were immediately transferred into
pre-evacuated vacuum glass containers. The concentration
of CH4 and N2O were analysed using gas chromatography
(Bruker 450-GC 2011, Canada) equipped with separate
electron capture and flame ionisation detectors. The CH4
was determined by flame ionisation detector and N2O by
electron capture detector. Helium (99.9 %) was used as
carrier gas for CH4 and argon (99.9 %) for N2O at a flow
rate of 60 ml min-1. Gas samplings were carried out five
times during the whole rice-growing season in summer
2014 at the TL commune (15, 45, 57, 66, and 72 DAT) and
RD farm (17, 43, 64, 70, and 77 DAT). In total (n = 1170),
gas samples were collected from TL and RD sites between
June and October 2014 for both Experiments 1 and 2. Out
of this, the total number of gas samples collected was 900
and 270 from Experiments 1 and 2, respectively.
Flux calculations for each of the N2O or CH4 were based
on the assumption that there was a linear increase in N2O
or CH4 concentration with time in the closed chambers
from sampling time 0 to 20 min. The change in N2O or
CH4 concentrations per unit time was estimated from the
slope of the line obtained by plotting for each N2O or CH4
Biochar
Compost
RD farm
(salic
fluvisols)
TL
commune
(thionic
fluvisols)
pH(KCl)
8.1
7.6
5.9
4.8
Corganic (%)
20.0
32.5
0.4
0.9
Ntotal (%)
0.26
1.36
0.11
Corganic: N
76.9
23.9
3.6
0.08
11.2
Ptotal (%)
0.32
2.80
0.14
Ktotal (%)
1.28
1.69
2.05
2.29
P2O5 available
(mg 100 g-1)
n.a.
n.a.
8.1
1.8
CEC (cmol kg-1)
11.0
n.a.
12.6
14.5
0.08
n.a not available, CEC cation exchange capacity
properties. The pH, organic carbon, N, P and K contents
of straw COMP and BIOC (on a dry weight basis) were
analysed before applying to the plots. Some of the basic
chemical properties of BIOC and straw COMP are given
in Table 2.
Soil sampling was carried out following the Vietnam
standard ‘‘Soil Quality, Sampling and General Requirements’’, including the quality assurance and quality
control regulations of the department of environmental
protection (TCVN 5297-1995). Before planting, composite soil samples (n = 2 for each site) were collected
from 0 to 20 cm depth from five points on two diagonal
lines in the study field, mixed thoroughly and about 1 kg
subsample was recovered for chemical analyses. The soil
pH (KCl) was determined using a pH meter (TCVN
5979:2007), total organic carbon by Walkley–Black
(TCVN 4050-1985), total N following the Kjeldahl
procedure (TCVN 6498:1999), available P2O5 by Bray 2
(TCVN 5256:1990) and cation exchange capacity of the
soils by acetate ammonium at pH 7 (TCVN 8568:2010).
The soils at the RD farm are light textured and classified as salic fluvisols (FAO 2006). They are slightly
acidic (average pH 5.9) and contain 0.4 % total organic
C and 0.11 % N in the topsoil. In contrast, soils at the
TL commune are heavy textured and acidic (averaging
pH 4.8), with 0.9 % total organic C and 0.08 % N.
These soils are classified as thionic fluvisols (FAO
2006).
The fields at the TL commune and RD farm were
planted with the TX111 rice variety on 21 July 2014. The
transplanting rice population was 40 hills per m2. Crop
yields were measured from each subplot to enable calculation of GHG emission intensities for each treatment. The
main cropping calendar and some field activities are presented in Table 3.
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Paddy Water Environ
Table 3 Main cropping calendar and field management in the TL commune and the RD farm during summer 2014
Date
DAT
RD farm
TL commune
July 10
–
–
First irrigation
July 20
–
–
Base fertiliser application
July 21
0
First irrigation, base fertiliser application, transplanting
Transplanting
July 28
7
First split fertiliser application
First split fertiliser application
August 5
15
–
First gas sampling
–
August 7
17
First gas sampling
September 2
43
Second gas sampling
–
September 4
45
–
Second gas sampling
September 10
51
First drainage
First drainage
September 12
53
–
Second split fertiliser application
September 15
September 16
56
57
Second split fertiliser application
–
–
Third gas sampling
September 23
64
Third gas sampling
–
September 24–27
65–68
Flowering
–
September 25
66
–
Fourth gas sampling
September 25–27
66–68
–
Flowering
September 27
68
Second irrigation
Second irrigation
September 29
70
Fourth gas sampling
October 1
72
October 4–6
75–77
Grain filling
–
October 6
77
Fifth gas sampling
–
October 4–7
75–78
–
Grain filling
October 8
79
Second drainage
Second drainage
October 8
79
Harvesting
Harvesting
Rice grain yield
–
2997–5870 kg ha-1
2713–5537 kg ha-1
Fifth gas sampling
The lowest yield was harvested from CONT and the highest yield from NPK ? COMP ? BIOC treatment from 20 m2 plot which was later
converted into ha
DAT days after transplanting
concentration in the headspace of the chamber versus the
sampling time. The gas fluxes (i.e. N2O or CH4) were
calculated using the following equation given by Smith and
Conen (2004):
hC
v
M
P
273
F¼
;
ð1Þ
ht
A
V
P0
T
where F is the gas flux (lg N2O-N m-2 h-1 or mg CH4-C
m-2 h-1), DC the change in the concentration of gas of
interest in the time interval Dt, v the chamber volume (L),
A the soil surface area (m2), M the molecular mass of the
gas of interest (i.e. N in N2O = 28 g N mol-1 and C in
CH4 = 12 g C mol-1), V the molecular volume occupied
by 1 mol of the gas (L mol-1) at standard temperature and
pressure, P the barometric pressure (mbar), P0 the standard
pressure (1013 mbar) and T the average temperature inside
the chamber during the deployment time.
The cumulative CH4 or N2O emissions were calculated
using the linear trapezoid formula (Angst et al. 2013) as
follows:
Cumulative flux of CH4 or N2 O
ðFta Ftb Þ
Ftb þ Ftc
þ ðtc tb Þ þ ...
¼ ðtb ta Þ 2
2
Ftn þ Ftx
;
ð2Þ
þ ðtn tx Þ 2
where ta, tb and tc are the dates of the first, second and third
sampling, tn is the date of the last sampling and tx is the
date before the last sampling. Fta, Ftb, Ftc, Ftx and Ftn are
the fluxes of the gas of interest at the ta, tb, tc, tx and tn
sampling day.
Estimation of GWP and GHG emission intensity
The cumulative emission of CH4 and N2O was multiplied
by a factor of 25 for CH4 and by a factor of 298 for N2O to
convert them into CO2 equivalents (IPCC 2007) to determine their respective total CO2e GWP over a 100-year
period. The CO2 emissions from the rice field under any of
the treatments were not included during the calculation of
123
Paddy Water Environ
total CO2 eq. GWP/tonne of rice grain due to their low
contribution (\1 %) to the GWP of agriculture (IPCC
2007). The GHG emission intensity expressed as CO2
eq. GWP tonne-1 of rice production from each of the
treatments was also calculated on the basis of total CO2
eq. GWP. The GWP and GHG emission intensities are
important factors to consider when assessing CH4 and/or
N2O mitigation options (Hinton et al. 2015). The following
equations were used to calculate the total CO2 eq. GWP
kg ha-1 and CO2 eq. GWP per unit of rice grain yield for
each of the treatments:
Total CO2 e GWP ¼ ð25 cumulative CH4 Þ
þ ð298 cumulative N2 OÞ;
ð3Þ
CO2 e GWP=ton of rice grain produced
Total CO2 e GWP
:
¼
Rice gain yield ðtonsÞ
ð4Þ
Statistical analysis
All statistical analyses of the data were performed using
SAS 9.1 (SAS Institute 1988). The effect of the different
treatments on CH4 and N2O emissions and CO2 equivalent
per grain yield were examined by one-way ANOVA. The
difference in means between the treatments were tested by
least square difference at p \ 0.05 significance level.
the order of treatments for the cumulative CH4-C fluxes
from TL commune and RD farm was NPK ? COMP
[ ‘NPK ? COMP [ NPK ? COMP ? BIOC [ COMP
[ NPK ? BIOC [ NPK [ ‘NPK ? BIOC [ ‘NPK [
CONT [ BIOC.
Application of BIOC alone (4.15 t ha-1) resulted in the
lowest CH4 emissions (4.8–59 mg C m-2 h-1) in the TL
commune and RD farm (13–40 mg C m-2 h-1). The
emissions were significantly (p \ 0.05) lower in the TL
commune compared with the RD farm. The CONT treatment also resulted in similarly low CH4 emissions (not
significantly different from BIOC). On the other hand, the
application of NPK ? COMP resulted in the highest
cumulative CH4 emission, increasing the CH4 emission
rates by 2.2-fold for the TL commune and 1.7-fold for the
RD farm. There were significant differences (p \ 0.05) in
cumulative CH4 emissions recorded by all treatments with
fertiliser as compared to no fertiliser (data not shown).
Overall, the BIOC and CONT treatments resulted in the
lowest emissions of CH4 at both sites. Various additions of
NPK and BIOC (NPK [ ‘NPK ? BIOC [ ‘NPK) further increased CH4 emissions at both sites. NPK ? BIOC
resulted in intermediate CH4 emissions at both sites.
Finally, addition of COMP in various combinations with
BIOC and NPK (NPK ? COMP [ ‘NPK ? COMP [
NPK ? COMP ? BIOC [ COMP) resulted in the highest
emissions of CH4 at both sites.
N2O-N fluxes
Results
Experiment 1: BIOC, compost and NPK fertilisers
CH4-C fluxes
CH4-C flux rates from paddy fields (at RD farm and TL
commune) that were treated with various combinations of
BIOC, COMP and/or NPK fertilisers are presented in
Table 4. The CH4-C fluxes varied widely among the ten
different treatments throughout the 2014 summer rice
season. Overall, the fluxes from the RD farm field ranged
from 6.06 to 93.83 mg C m-2 h-1 between 17 and 77
DAT, which is greater than that for the TL commune
(4.8–80.8 mg C m-2 h-1) between 15 and 72 DAT. The
CH4-C fluxes in all treatments exhibited similar trends and
the highest fluxes generally occurred at 66 DAT in TL and
64 DAT in the RD farm. All the treatments showed a
decreasing trend of CH4-C flux at 77 DAT in RD and 72
DAT in the TL commune, except for soils amended with
NPK ? COMP at the TL commune (Table 4). The CH4-C
emissions from the TL commune were slightly lower than
that in the RD farm in most of the treatments. In general,
123
The N2O-N fluxes from paddy fields treated with various
combinations of BIOC, COMP and/or inorganic fertilisers
are shown in Table 5. N2O-N fluxes across all treatments
ranged from 0.11 to 0.61 lg N m-2 h-1 at the RD farm,
and from 0.17 to 0.87 at the TL commune, excluding an
outlier (1.72 lg N m-2 h-1 from ‘NPK ? BIOC-amended TL commune). Hence, N2O emissions were lower at
the RD farm than at the TL commune. The rankings of
N2O-N fluxes across all treatments at the RD farm were in
the
following
order:
NPK [ ‘NPK [ ‘NPK ?
COMP [ NPK ? BIOC [ NPK ? COMP ? BIOC [ NPK
? COMP [ CONT [ COMP [ ‘NPK ? BIOC [ BIOC.
The rankings of N2O-N fluxes across all treatments at
the TL commune were in the following order: ‘
NPK ? BIOC [ NPK ? COMP ? BIOC [ NPK ? BIOC
[ COMP [ NPK [ NPK ? COMP [ ‘NPK ? COMP [
‘NPK [ BIOC [ CONT. While the treatment rankings
differed between the two sites, the BIOC and CONT treatments consistently exhibited low N2O emissions. However,
there were some clear anomalies in rankings between sites.
For example, the ‘NPK treatment exhibited one of the
highest N2O emissions at the RD farm (0.689), yet one of
the lowest at the TL commune (0.595). Further, the
Paddy Water Environ
Table 4 CH4-C fluxes from
paddy rice field in the RD farm
and the TL commune during
summer 2014
RD farm
CH4 emissions (mg C m-2 h-1) DAT
Cumulative CH4
(kg C ha-1)
17
43
64
70
77
CONT
29.47
26.53
20.68
35.63
15.56
‘NPK
21.97
22.42
73.65
23.29
6.06
569
NPK
30.60
40.15
53.11
26.16
14.88
692
COMP
22.39
25.72
44.07
93.83
51.98
753
521
‘NPK ? COMP
38.55
36.03
64.14
37.22
32.70
834
NPK ? COMP
47.54
42.90
54.37
64.77
14.38
886*
467*
BIOC
15.30
28.09
31.31
40.52
13.08
‘NPK ? BIOC
19.83
27.26
52.70
23.50
31.70
596
NPK ? BIOC
29.25
58.56
35.06
30.79
17.78
743
NPK ? COMP ? BIOC
30.81
41.23
61.25
44.04
30.77
805
TL commune
CH4 emissions (mg C m
-2
-1
h ) DAT
Cumulative CH4
(kg C ha-1)
15
45
57
66
72
CONT
12.12
10.79
41.93
46.30
11.83
409
‘NPK
17.60
24.60
28.90
35.06
26.98
507
NPK
25.59
69.19
38.33
30.70
10.85
676*
COMP
14.52
43.82
61.77
70.57
27.44
760
8.82
52.34
80.82
69.96
31.03
820
NPK ? COMP
34.85
37.22
66.28
17.72
72.06
894*
BIOC
‘NPK ? BIOC
12.43
13.47
4.78
34.99
59.12
38.06
26.65
51.13
17.33
19.81
391*
571
‘NPK ? COMP
NPK ? BIOC
36.91
20.24
50.83
60.42
27.05
746
NPK ? COMP ? BIOC
14.52
43.82
61.77
70.57
27.44
761
* Significantly different from each other at p \ 0.05
‘NPK ? BIOC treatment exhibited the highest N2O
emission rate at the TL commune (1.03), yet the second
lowest at the RD farm (0.495). This ‘site 9 treatment’
interaction suggests that differences in soil properties
between the two sites may have significantly affected N2O
emissions.
The N2O-N flux trend exhibits a similar pattern as the
CH4-C flux trend at both sites. In most of the treatments,
the highest flux was recorded at 66 DAT in the TL site and
70 DAT in the RD farm. Compared with the CONT, the
average N2O fluxes were higher by 8–72 % in all fertiliseramended soils, excluding BIOC-alone and ‘NPK ? BIOC
treatments.
Global warming potential (GWP)
The GWP of the treatments, expressed as CO2 equivalent
(CO2 eq.), were consistently higher at the RD farm than at
the TL commune (Fig. 1). The GWP was lowest from soils
treated with BIOC alone, and significantly lower at the TL
than at the RD site for this treatment. The addition of
‘NPK to BIOC (‘NPK ? BIOC treatment) increased
GWP by about 45 % relative to BIOC alone. GWP was
further increased by another 46 % with the addition of
compost (NPK ? COMP ? BIOC). The GWP was second
lowest in untreated (CONT) soils. The addition of various
combinations of NPK and compost increased GWP in the
following order: CONT \ ‘NPK \ NPK \ COMP \
‘NPK ? COMP \ NPK ? COMP. On average, each
treatment increased GWP by about 17 %, totalling to an
83 % increase from CONT to NPK ? COMP. These
results suggest that it should be possible to significantly
reduce GWP using various BIOC treatments.
Yield-scaled GWP
Yield-scaled GWP is an integrated metric that addresses
the dual goals of environmental protection and food security (Linquist et al. 2012). Yield-scaled GWP (expressed in
CO2 eq. GWP per kg of grain yield) was almost 1.6-fold
greater with COMP-alone treatment than with NPK-alone
treatment (Fig. 2). The lowest CO2 eq. per kg rice grain
yield (*300 kg CO2 eq. ton-1 rice grain) was recorded in
the BIOC-alone treatment, while the highest was found in
the COMP treatment (*550 kg CO2 eq. ton-1 rice grain).
However, the grain yield harvested from BIOC-alone
treatment plot was lower than that of full NPK ? treatments (data not shown). Interestingly, there was little
123
Paddy Water Environ
Table 5 N2O-N fluxes from
paddy rice field in the RD farm
and the TL commune during
summer 2014
RD farm
N2O emissions (lg N m-2 h-1) DAT
Cumulative N2O
(kg N ha-1)
17
43
64
70
77
CONT
0.26
0.20
0.29
0.34
0.34
‘NPK
0.25
0.33
0.40
0.41
0.45
0.689
NPK
0.48
0.61
0.36
0.39
0.29
0.938*
COMP
0.25
0.22
0.33
0.32
0.28
0.539
‘NPK ? COMP
0.39
0.37
0.26
0.23
0.29
0.686*
NPK ? COMP
0.27
0.30
0.34
0.34
0.17
0.570
BIOC
0.15
0.21
0.20
0.17
0.26
0.397*
0.545
‘NPK ? BIOC
0.26
0.11
0.33
0.52
0.21
0.495
NPK ? BIOC
0.32
0.24
0.32
0.28
0.34
0.605
NPK ? COMP ? BIOC
0.28
0.27
0.33
0.35
0.28
0.591
TL commune
-2
N2O emissions (lg N m
-1
h ) DAT
Cumulative N2O
(kg N ha-1)
15
45
57
66
72
CONT
0.20
0.27
0.20
0.33
0.29
0.513
‘NPK
0.29
0.21
0.17
0.42
0.38
0.595
NPK
0.32
0.39
0.46
0.32
0.46
0.788
COMP
0.25
0.45
0.65
0.36
0.42
0.807
‘NPK ? COMP
0.31
0.30
0.27
0.34
0.35
0.648
NPK ? COMP
0.27
0.25
0.25
0.56
0.74
0.781
BIOC
‘NPK ? BIOC
0.25
0.28
0.31
0.37
0.21
1.72
0.38
0.44
0.25
0.28
0.569*
1.030*
NPK ? BIOC
0.38
0.21
0.87
0.39
0.33
0.812
NPK ? COMP ? BIOC
0.67
0.39
0.21
0.53
0.33
0.985
* Significantly different from each other at p \ 0.05
difference in yield-scaled GWP between CONT, ‘NPK
and NPK treatments, suggesting that yield increases were
off-setting GWP with increasing NPK increments. Yieldscaled GWP was slightly higher in the RD farm than in the
TL commune. Generally, the yield-scaled GWP trends in
the RD farm and TL commune displayed a similar pattern.
CH4 emissions among the three treatments in the TL
commune (437–451 kg C ha-1 season-1) was lower than
that in the RD farm (506–573 kg C ha-1 season-1), as
shown in Table 6.
Experiment 2: slow-release urea fertilisers
The N2O-N flux trend increased from 0.14 (at 17 DAT) to
0.49 g N m-2 h-1 (at 77 DAT) in the TL commune and
from 0.29 (at 17 DAT) to 0.49 g N m-2 h-1 (at 70 DAT) in
the RD farm (Fig. 4). Green and orange urea amendments
showed significantly (p \ 0.05) lower cumulative N2O
emissions compared to WU at the RD farm sites, but only
OU at the TL commune. Furthermore, cumulative N2O
emissions were lower with the application of OU than GU
at both the study sites (Table 6; Fig. 4).
CH4-C fluxes
The CH4-C fluxes from paddy fields in the TL commune
and RD farm amended with WU, GU and OU fertilisers are
presented in Fig. 3. The CH4-C flux rate among the treated
urea displayed a large variation across the growing stages
of rice in the RD farm and TL commune. For example in
the TL commune, the CH4-C flux trend increased from 5.2
(at 15 DAT) to 52–71 mg C m-2 h-1 (at 57 DAT), but then
decreased sharply to 0.7–2.8 mg C m-2 h-1 (at 72 DAT).
Similar CH4-C flux trends were also displayed for the RD
farm. However, no significant differences were detected in
cumulative CH4-C emissions among WU, GU and OU
fertilisers at both the study sites (Table 6). The cumulative
123
N2O-N fluxes
Yield-scaled GWP
Slow-release urea fertilisers render lower yield-scaled
GWP (B250 kg CO2 eq. emitted per tonne rice grain,
Fig. 5) than BIOC-amended soils (*300 kg CO2
eq. emitted per tonne rice grain, Fig. 2). As in Experiment
Paddy Water Environ
Fig. 1 GWP (kg CO2 eq. ha-1
season-1) among the ten
different treatments at the RD
farm and the TL commune
27000
GWP (kg CO 2 eq. ha-1
season-1)
24000
RD
TL
21000
18000
15000
12000
9000
6000
3000
0
CONT
Fig. 2 Yield-scaled GWP in
the RD farm and the TL
commune. Refer Table 1 for the
treatment descriptions
7
6
½ NPK
NPK
COMP
½
NPK+COMP
NPK+
COMP
BIOC
½ NPK+
BIOC
NPK+BIOC
Yield-Scaled GWP (kg
CO2 eq. kg-1 rice grain)
RD
NPK+
BIOC+
COMP
TL
5
4
3
2
1
0
CONT
NPK
COMP
½
NPK+COMP
NPK+
COMP
BIOC
½ NPK+
BIOC
NPK+BIOC
NPK+
BIOC+
COMP
160
15
140
CH4 flu x (mg C m-2 h -1 )
Fig. 3 CH4 emission rates from
paddy rice field in the RD farm
and the TL commune over the
growing stages
½ NPK
45
57
66
72 DAT
120
100
80
60
40
20
0
White urea
Green urea
Orange urea
RD
1, yield-scaled GWP was also slightly higher in the RD
farm than in the TL commune in all the treatments. At the
TL commune site, there was a trend for lower yield-scaled
GWP with GU and OU, compared with WU, although the
differences were not significant at P = 0.05 (Fig. 5). There
were also no differences in yield-scaled GWP among fertiliser treatments at the RD farm. However, the average rice
yield harvested from a plot treated with OU was higher
than GU and WU in the RD farm as well as the TL commune (Table 6).
White urea
Green urea
Orange urea
TL
Discussion
The effects of BIOC on CH4 and N2O emissions
Several studies on CH4 emissions from BIOC-amended
rice fields have shown contradicting results. Some
researchers reported increased CH4 emissions (Zhang et al.
2010; Wang et al. 2012), while other studies have found a
decrease (Liu et al. 2011) following BIOC additions. The
discrepancy of the effects of BIOC on CH4 emissions is
123
Paddy Water Environ
the BIOC (at a dose of 4.15 tonnes ha-1) and CONT
treatments resulted in the lowest emissions of CH4 at the
TL commune and the RD farm study sites. Various
additions of NPK and BIOC (NPK [ ‘NPK ?
BIOC [ ‘NPK) further increased CH4 emissions at both
sites, suggesting that the replacement of NPK with BIOC
could be an effective way to reduce CH4 emissions in rice
production systems (Table 4). One possible explanation for
lower CH4 emissions with BIOC-alone-amended soils is
that BIOC addition combined with subsequent frequent
drainage and irrigation of the paddy soils may have
improved the soil aeration status, resulting in the oxidation
of CH4 which, in turn, enhances CH4 adsorption (Zhang
et al. 2010), thereby leading to reductions in CH4 emissions
from the soils (Pandey et al. 2014).
The effects of BIOC on N2O emissions are also inconsistent. A number of studies demonstrated that N2O emissions from a BIOC-amended soil were lower than those
from the control (Zhang et al. 2010). However, Clough
et al. (2010) found that BIOC application had no effect on
N2O emissions. Others have reported that BIOC
Table 6 Cumulative CH4 N2O emission from paddy rice field in the
RD farm and the TL commune and average grain yield
Cumulative
CH4 (kg C
ha-1season-1)
Cumulative
N2O (kg N
ha-1season-1)
Rice yield
(kg ha-1)
5633
RD farm
White urea, WU
506
0.931*
Green urea, GU
541
0.581
6000
Orange urea, OU
573
0.533*
6160
White urea, WU
443
0.619*
5330
Green urea, GU
451
0.510
5860
Orange urea, OU
437
0.439*
5963
TL commune
The rice yield is from 20 m2 plot converted into ha
* Significantly different from each other at p \ 0.05
likely due to a range of factors, including differences in the
original biomass types, the temperature used for its production and the duration of its incorporation in the soil
(Zhang et al. 2010; Feng et al. 2012). In the current study,
2,5
17
N2 O-N flu x (g N m-2 h -1 )
Fig. 4 N2O-N emission rates
from paddy rice fields in the RD
farm and the TL commune over
the growing stages
43
64
70
77 DAT
2,0
1,5
1,0
0,5
0,0
White urea
Green urea
Orange urea
White urea
RD
Orange urea
TL
3,0
RD farm
Yield-scaled GWP (kg CO2 eq. kg -1 rice grain)
Fig. 5 Yield-scaled GWP of
white, green and orange urea
fertilisers in the RD farm and
the TL commune
Green urea
TL commune
2,5
2,0
1,5
1,0
0,5
0,0
White Urea
123
Green Urea
Yellow Urea
Paddy Water Environ
application even increased N2O emissions when compared
with the control treatment (Sánchez-Garcı́a et al. 2014;
Verhoeven and Six 2014). In the present study, the
cumulative N2O emissions from the BIOC-alone treatment
were lower than those treatments without BIOC at the RD
farm site. Cumulative N2O emissions were also low with
the BIOC treatment at the TL commune site, but exceeded
the control and were equivalent to the ‘NPK ? COMP
and ‘NPK treatments. Overall, our findings agree with
previous studies on soils amended with and without BIOC
(Zhang et al. 2010). The higher C/N ratio of biochar (*77/
1 in Table 2), compared to the compost, might have slowed
down the nitrogen decomposition, thereby reducing N2O
emissions from the BIOC-alone treatment and may
enhance NH4-N in the soil and plant uptake (Steiner et al.
2010). Wang et al. (2012) also reported that the depressed
nett N mineralisation of paddy soils following BIOC
addition without NPK and/or compost might contribute to
the decreased N2O emissions. All measurements in the
control treatment (except for 72 DAT) showed slightly
lower N2O emissions than the BIOC-alone treatment at the
TL commune (Table 5).
The current study also indicates that differences in soil
properties at the two sites may have significantly affected
N2O emissions. For example, the ‘NPK ? BIOC treatment exhibited the highest N2O emission rate at the TL
commune (1.03), yet the second lowest at the RD farm
(0.495). A key conclusion from these results is that the
application of BIOC to mitigate N2O emissions must be
considered in the context of the soil to which it is applied.
In other words, the effectiveness of BIOC in mitigating
N2O emissions is dependent on soil type.
Effect of compost on CH4 and N2O emissions
Compost-amended treatments (that were applied alone or
in combination with BIOC and/or NPK) exhibited higher
CH4 emissions than the control treatment (Table 4). This
was the case both for the cumulative rates and for single
measurements of CH4 emissions that were carried out at
different intervals during the rice-growing period. In general, application of organic materials such as compost to
rice fields significantly increase the rate of CH4 emissions
compared to control plots with no fertiliser applications
(Khosa et al. 2010). The higher CH4 emissions from
compost-amended treatments may be due to the increased
organic matter content, which provides particular methanogenic populations with a carbon source, thereby
enhancing their growth. The average organic C in the
compost used in this study was 32.5 %, compared with
only 20 % in the BIOC (Table 2). Hence, compost, either
alone or in combination with NPK and/or BIOC, consistently increased CH4 emissions, with the addition of NPK
to compost resulting in the highest emissions (NPK ?
COMP [ ‘NPK ? COMP [ NPK ? COMP ? BIOC
[ COMP).
Contrasting results for N2O emissions rates from compost-amended soils were found between the RD farm and
the TL commune. The cumulative N2O emissions from the
compost-alone-applied soils were not significantly different
from the control treatment at the RD farm site. However, in
the case of the TL commune, cumulative N2O emissions
from compost-amended soils were greater than in the
control (Table 5). This was also the case for single measurements at 15, 45, 57, 66 and 72 DAT. The higher
cumulative N2O emissions exhibited by compost treatments relative to the control could be due to the lower C/N
ratio in the rice straw compost used in this study (i.e. 24/1
in Table 2). Under such conditions, the available N is
readily used in microbial processes, thereby enhancing
microbial activity and increasing N2O production.
Effect of slow-release urea fertilisers on N2O
emissions
The average cumulative N2O emissions from slow-release
urea fertilisers were as follows: WU [ GU [ OU in RD
farm and TL commune (Table 6). The difference between
OU and WU in the cumulative N2O emission rate was
significant (p \ 0.05), although the difference between GU
and OU was not. The GU and OU were actually more
effective in reducing yield-scaled GWP than white urea,
probably because both were treated with a urease inhibitor
that delays hydrolysis of urea into unstable forms (which
otherwise may have been lost to the atmosphere), thereby
reducing emissions. Several studies have also reported that
lower cumulative N2O emissions in the SRU treatments
were due to urease inhibitors that prevent or suppress the
transformation of amide-N in urea to ammonium hydroxide
and ammonium through the hydrolytic action of the
enzyme urease (Turner et al. 2008; Trenkel 2010; Jamil
et al. 2014; IPL 2014). In this regard, our data suggest that
slow-release urea fertilisers are an effective strategy to
mitigate N2O emissions in rice paddy systems.
Opportunities to reduce GWP and yield-scaled
GWP
In the present study, the higher GWP of emissions from
rice paddies were largely driven by CH4 emissions
(Table 4), despite the small contribution of CH4 to GWP
(only *8 %). This is because methanogenic bacteria thrive
well in paddy rice soils and produce methane anaerobically
(Segers 1998). Extremely high CH4 emissions in excess of
20,000 kg CO2 eq. ha-1 season-1 were also reported from
rice paddy soils in China (Ma et al. 2007; Shang et al.
123
Paddy Water Environ
2011). Our result is consistent with agronomic assessment
of GWP for rice by Linquist et al. (2012). However, the
GWP of the rice paddy soils amended with BIOC at the RD
farm and TL commune (and yield-scaled GWP) were
smaller than that of all the other treatments due to the
additive mitigation effects of BIOC on CH4 and N2O
emissions (Figs. 2, 3). Furthermore, slow-release urea
fertilisers (Fig. 5) exhibited even lower yield-scaled GWP
than BIOC-amended soils (Fig. 2), with a trend for the
lowest yield-scaled GWP in OU at the TL commune site.
Hence, the combined application of BIOC (which contains
not only N, but also other essential plant nutrients like P
and K) with orange or green urea provides a potential win–
win situation for both rice growers and the environment.
In rice paddy systems, it is a common practice to apply
water continuously throughout the growing season, but
draining rice fields at some point during the growing season, sometimes called alternate wetting and drying (AWD),
has gained increased attention as a means of reducing CH4
emissions from rice paddy soils (Uprety et al. 2012; Jain
et al. 2013). However, AWD has trade-off effects that
increase aeration in the soils, resulting in higher N2O
emissions (Jain et al. 2013). Despite the negating effects of
AWD on N2O emissions, several studies have found that
the GWP (accounting for both CH4 and N2O) in drained
rice fields is lower than in continuously flooded fields (e.g.
Zou et al. 2005; Jain et al. 2013). Moreover, AWD fields
have been found to decrease yield-scaled GWP by about
34 % compared with continuously flooded fields, without
significantly affecting rice yields (Linquist et al. 2012).
Hence, applying AWD in rice paddy soils at the TL
commune and the RD farm could be another feasible
mitigation option to reduce GHG emissions while maintaining rice yield. However, it is worth mentioning that the
effect of AWD in reducing CH4 emissions and total GWP
was not studied in this research, mainly because it is
beyond the scope of the research objectives.
Conclusions
This study demonstrated that the combined application of
COMP and NPK gave the highest CH4 fluxes, while the
application of BIOC alone gave the lowest CH4-C flux
rates. The BIOC-alone treatment showed significantly
(p \ 0.05) lower cumulative CH4 emissions compared to
all other treatments. Application of BIOC alone also
resulted in the lowest N2O emissions at the RD farm and
relatively low emissions at the TL commune. The results
indicated that the incorporation of straw compost, either
alone or in combination with NPK, increased GWP. In fact,
the yield-scaled GWP of rice production was highest with
the addition of compost alone. In contrast, BIOC exhibited
123
the lowest GWP and yield-scaled GWP of rice production
compared with all other treatments, suggesting that application of BIOC is an effective mitigation strategy, at least
at the two sites tested in this study. Green urea and orange
urea reduced N2O fluxes significantly (p \ 0.05) compared
to conventional urea, but no significant differences were
found with respect to CH4-C fluxes.
Instead of burning the straw and rice residues, farmers
should be trained to make use of BIOC, which has dual
benefits, i.e. to mitigate GHG emissions and as a supplement to inorganic fertilisers. The application of BIOC and/
or orange/green urea could be a viable option to mitigate
both CH4-C and N2O-N emissions from paddy fields at the
TL commune and the RD farm. Future studies are required
to confirm these results for other seasons, soil types and
irrigation methods on a long-term basis.
Acknowledgments The authors would like to thank the Ministry of
Foreign Affairs of Norway for the financial support provided through
the Royal Norwegian Embassy in Hanoi to carry out the research as
part of the ClimaViet project. We thank also Dr. Bo and the two
anonymous reviewers for the helpful comments on an earlier version
of the manuscript.
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
interest.
References
Akiyama H, Yan X, Yagi K (2010) Evaluation of effectiveness of
enhance deficiency fertilizers as mitigation options for N2O and
NO emissions from agricultural soils: meta-analysis. Glob
Change Biol 16:1837–1846. doi:10.1111/j.1365-2486.2009.
02031.x
Angst TE, Patterson CJ, Reay DS, Anderson P, Peshkur TA, Sohi SP
(2013) Biochar diminishes nitrous oxide and nitrate leaching
from diverse nutrient sources. J Environ Qual 42:672–682
Borrell AK, Garside AL, Fukai S, Reid DJ (1998) Season, nitrogen
rate and plant type affect nitrogen uptake and nitrogen use
efficiency in rice. Aust J Agric Res 49:829–843
Briggs CM, Breiner JM, Graham RC (2005) Contributions of Pinus
ponderosa charcoal to soil chemical and physical properties.
http://nature.berkeley.edu/classes/es196/projects/2005final/Briggs.
pdf. Accessed 10 Oct 2015
Bruun EW, Müller-Stöver D, Ambus P, Hauggaard-Nielsenet H
(2011) Application of biochar to soil and N2O emissions:
potential effects of blending fast-pyrolysis biochar with anaerobically digested slurry. Eur J Soil Sci 62:581–589
Clough T, Bertram J, Ray J, Condron L, O’Callaghan M, Sherlock R,
Wells N (2010) Unweathered wood biochar impact on nitrous
oxide emissions from a bovine-urine-amended pasture soil. Soil
Sci Soc Am J 74(3):852. doi:10.2136/sssaj2009.0185
Corton TM, Bajita JB, Grospe FS, Pamplona RR, Asis CA Jr,
Wassmann R, Lantin RS, Buendia LV (2000) Methane emission
from irrigated and intensively managed rice fields in Central
Luzon (Philippines). Nutr Cycl Agroecosyst 58:37–53
Cuong TV, Trinh MV, Ha PQ, Khai PM (2012) Influence of biochar
on rice yield and acrisols properties. J Nat Sci 28–4S:19–25
Paddy Water Environ
FAO (2006) World reference base for soil resources 2006: a
framework for international classification, correlation and communication. World Soil Resources Report No. 103, Rome
FAO (2013) The database of FAOSTAT. http://faostat3.fao.org/
faostat-gateway/go/to/download/G1/*/E. Accessed 15 May 2015
Feng Y, Xu Y, Yu Y, Xie Z, Lin X (2012) Mechanisms of biochar
decreasing methane emissions from Chinese paddy soils. Soil
Biol Biochem 46:80–88
Hamer U, Marschner B, Brodowski S, Amelung W (2004) Interactive
priming of black carbon and glucose mineralization. Org
Geochem 35:823–830
Hinton NJ, Cloy JM, Bell MJ, Chadwick DR, Topp CFE, Rees RM
(2015) Managing fertiliser nitrogen to reduce nitrous oxide
emissions and emission intensities from a cultivated Cambisol in
Scotland. Geoderma Reg 4:55–65
IPCC (2007) Climate change 2007: synthesis report. Contribution of
working groups I, II and III to the fourth assessment report of the
Intergovernmental Panel on Climate Change. Geneva, pp 104.
https://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_full_
report.pdf. Accessed 30 April 2016
IPL (2014) IPL sustainability report products and services research
and development. http://www.incitecpivot.com.au/*/media/
Files/IPL/Sustainability/Online%20Report/Report%20Sections/
Products%20and%20Services/Research%20and%20Develop
ment.pdf. Accessed 5 Mar 2016
Jain N, Dubey R, Dubey DS, Singh J, Khanna M, Pathak H, Bhatia A
(2013) Mitigation of greenhouse gas emission with system of
rice intensification in the Indo-Gangetic Plains. Paddy Water
Environ. doi:10.1007/s10333-013-0390-2
Khan JM, Malik A, Zaman M, Khan Q, Habib ur Rehman (2014)
Nitrogen use efficiency and yield of maize crop as affected by
agrotain coated urea in arid calcareous soils. Soil Environ
33(1):1–6
Khosa MK, Sidhu BS, Benbi DK (2010) Effect of organic materials
and rice cultivars on methane emission from rice field. J Environ
Biol 31:281–285
Laird D, Fleming P, Wang BQ, Horton R, Karlen D (2010) Biochar
impact on nutrient leaching from a Midwestern agricultural soil.
Geoderma 158:436–442
Lehmann J, Da Silva JP, Steiner C, Nehls T, Zech W, Gllaser B
(2003) Nutrient availability and leaching in an archaeological
anthrosol and a ferralsol of the Central Amazon basin: fertilizer,
manure and charcoal amendments. Plant Soil 249:343–357
Lindau CW, Bollich PK, Delaune RD, Patrick WH Jr, Law VJ (1991)
Effect of urea fertilizer and environmental factors on methane
emissions from a Louisiana, USA rice field. Plant Soil
136:195–203
Linquist B, van Groenigen KJ, Adviento-Borbe AM, Pittelkow C, van
Kessel C (2012) An agronomic assessment of greenhouse gas
emissions from major cereal crops. Glob Change Biol
18:194–209
Liu C, Shi B, Zhou J, Tang C (2011) Quantification and characterization of microporosity by image processing, geometric measurement and statistical methods: application on SEM images of
clay material. Appl Clay Sci 54:97–106
Liu G, Zotarelli L, Li Y, Dinkins D, Wang Q, Ozores-Hampton M
(2014) Controlled-release and slow-release fertilizers as nutrient
management tools. http://edis.ifas.ufl.edu/pdffiles/HS/HS125500.
pdf. Accessed 10 Aug 2015
Ma J, Li XL, Xu H, Han Y, Cai ZC, Yagi K (2007) Effects of nitrogen
fertiliser and wheat straw application on CH4 and N2O emissions
from a paddy rice field. Aust J Soil Res 45(5):359–367
Major J, Steiner C, Downie A, Lehmann J (2009) Biochar effects on
nutrient leaching. Chapter 15. In: Lehmann J, Joseph S (eds)
Biochar for environmental management: science and technology.
Earthscan, London, p 271
Meijide A, Dı́ez JA, Sánchez-Martı́n L, López-Fernández S, Vallejo
A (2007) Nitrogen oxide emissions from an irrigated maize crop
amended with treated pig slurries and composts in a Mediterranean climate. Agric Ecosyst Environ 121:383–394
Ministry of Natural Resources and Environment (MoNRE) (2014)
The initial biennial updated report of Viet Nam to the United
Nations framework convention on climate change, Viet Nam
Publishing House of Natural Resources, Environment and
Cartography,
Hanoi.
http://unfccc.int/resource/docs/natc/
vnmbur1.pdf. Accessed 30 April 2016
Miura Y, Kanno T (1997) Emissions of trace gases (CO2, CO, CH4,
and N2O) resulting from rice straw burning. Soil Sci Plant Nutr
43(4):849–854
Nash RP, Motavalli PP, Nelson KA (2012) Nitrous oxide emissions
from claypan soils due to nitrogen fertilizer source and tillage/
fertilizer placement practices. Soil Sci Soc Am J 76:983–993
Pandey A, Mai VT, Vu DQ, Bui TPL, Mai TLA, Jensen LS, de
Neergaard A (2014) Organic matter and water management
strategies to reduce methane and nitrous oxide emissions from
rice paddies in Vietnam. Agric Ecosyst Environ 196:137–146
Peng X, Ye LL, Wang CH, Zhou H, Sun B (2011) Temperature- and
duration-dependent rice straw-derived biochar: characteristics
and its effects on soil properties of an Ultisol in southern China.
Soil Tillage Res 112:159–166
Rajkovich S, Enders A, Hanley K, Hyland C, Zimmerman AR,
Lehmann J (2011) Corn growth and nitrogen nutrition after
additions of biochars with varying properties to a temperate soil.
Biol Fertil Soils 48:271–284. doi:10.1007/s00374-011-0624-7
Rochette P, Eriksen-Hamel NS (2008) Chamber measurements of soil
nitrous oxide flux: are absolute values reliable? Soil Sci Soc Am
J 72(2):331–342
Sánchez-Garcı́a M, Roig A, Sánchez-Monedero MA, Cayuela ML
(2014) Biochar increases soil N2O emissions produced by
nitrification-mediated pathways. Environ Sci 2(article 5):1–9.
doi:10.3389/fenvs.2014.00025
SAS Institute (1988) SAS technical report: P-174 changes and
enhancements to the SAS system release 5.16 for the VSE
operating system
Segers R (1998) Methane production and methane consumption: a
review of processes underlying wetland methane fluxes. Biogeochemistry 41:23–51
Shang Q, Yang X, Gao C et al (2011) Net annual global warming
potential and greenhouse gas intensity in Chinese double ricecropping systems: a 3-year field measurement in long-term
fertilizer experiments. Glob Change Biol 17:2196–2210
Singh B, Singh BP, Cowie AL (2010) Characterisation and evaluation
of biochars for their application as a soil amendment. Aust J Soil
Res 48(7):516–525
Smith KA, Conen F (2004) Measurement of trace gas, I: gas analysis,
chamber methods and related procedures. In: Smith KA, Cresser
MS (eds) Soil and environmental analysis: modern instrumental
technical, 3rd edn. Marcel Dekker, New York
Soares JR, Cantarella H, Vargas VP, Carmo JB, Martins AA, Sousa
RM, Cristiano A, Andrade CA (2015) Enhanced-efficiency
fertilizers in nitrous oxide emissions from urea applied to
sugarcane. special section: improving nitrogen use efficiency in
crop and livestock production. J Environ Qual 44:423–430.
doi:10.2134/jeq2014.02.0096
Steiner C, Das KC, Melear N, Lakly D (2010) Reducing nitrogen loss
during poultry litter composting using biochar. J Environ Qual
39(4):1236–1242. doi:10.2134/jeq2009.0337
Trenkel ME (2010) Slow- and controlled-release and stabilized fertilizers: an option for enhancing nutrient efficiency in agriculture, 2nd
edn. International Fertilizer Industry Association, Paris
Truc NTT, Sumalde ZM, Espaldon MVO, Pacardo EP, Rapera CL,
Palis FG (2012) Farmers’ awareness and factors affecting
123
Paddy Water Environ
adoption of rapid composting in Mekong Delta, Vietnam and
Central Luzon, Philippines. J Environ Sci Manag 15:59–73
Turner D, Edis R, Chen D, White B, Christie R (2008) Nitrogen loss
from top-dressing fertilisers to wheat. BGC 2000 season research
results. http://www.farmtrials.com.au/trial/13971. Accessed 10
April 2016
UN (United Nation-Vietnam) (2013) Greenhouse gas emissions and
options for mitigation in Viet Nam, and the UN’s responses.
http://www.un.org.vn/en/publications/cat_view/130-un-viet-namjoint-publications/209-climate-change-joint-un-publications.html.
Accessed 15 Mar 2016
Uprety DC, Dhar S, Hongmin D, Kimball BA, Garg A, Upadhyay J
(2012) Technologies for climate change mitigation: agriculture
sector. Department of Management Engineering, Technical
University of Denmark, Kongens Lyngby
van Zwieten L, Singh B, Joseph S, Kimber S, Cowie A, Chan Y
(2009) Biochar and emissions of non-CO2 greenhouse gases
from soil. In: Lehmann J, Joseph S (eds) Biochar for environmental management: science and technology. Earthscan, London, p 227
van Zwieten L, Kimber S, Morris S, Chan KY, Downie A, Rust J,
Joseph S, Cowie A (2010) Effects of biochar from slow pyrolysis
of paper mill waste on agronomic performance and soil fertility.
Plant Soil 327(1–2):235–246
Velthof GL, Oenema O (1995) Nitrous oxide fluxes from grassland in
the Netherlands: I. Statistical analysis of flux-chamber measurements. Eur J Soil Sci 46:533–540
Verhoeven E, Six J (2014) Biochar does not mitigate field-scale N2O
emissions in a Northern California vineyard: an assessment
across two years. Agric Ecosyst Environ 191:27–38
123
Wang J, Pan X, Liu Y, Zhang X, Xiong Z (2012) Effects of biochar
amendment in two soils on greenhouse gas emissions and crop
production. Plant Soil 360:1–2. doi:10.1007/s11104-012-1250-3
Yamato M, Okimori Y, Wibowo IF, Anshori S, Ogawa M (2006)
Effects of the application of charred bark of Acacia mangium on
the yield of maize, cowpea and peanut, and soil chemical
properties in South Sumatra, Indonesia. Soil Sci Plant Nutr
52:489–495
Yanai Y, Toyota K, Okazaki M (2007) Effects of charcoal addition on
N2O emissions from soil resulting from rewetting air-dried soil
in short-term laboratory experiments. Soil Sci Plant Nutr
53(2):181–188
Yao Z, Zhou Z, Zheng X, Xie B, Mei B, Wang R, Bahl KB, Zhu J
(2010) Effects of organic matter incorporation on nitrous oxide
emissions from rice–wheat rotation ecosystems in China. Plant
Soil 327:315–330
Zhang A, Cui L, Pan G, Li L, Hussain Q, Zhang X, Zheng J, Crowley
D (2010) Effect of biochar amendment on yield and methane and
nitrous oxide emissions from a rice paddy from Tai Lake plain,
China. Agric Ecosyst Environ 139:469–475
Zimmerman AR, Gao B, Ahn MY (2011) Positive and negative
carbon mineralization priming effects among a variety of
biochar-amended soils. Soil Biol Biochem 43:1169–1179
Zou J, Huang Y, Jiang J, Zheng X, Sass RL (2005) A 3-year field
measurement of methane and nitrous oxide emissions from rice
paddies in China: effects of water regime, crop residue, and
fertilizer application. Glob Biogeochem Cycles 19(2):GB2021.
doi:10.1029/2004GB002401