Song et al.

Appl Biol Chem (2019) 62:70

https://doi.org/10.1186/s13765-019-0476-7

ARTICLE Open Access

Effect of straw incorporation on methane

emission in rice paddy: conversion factor
and smart straw management
Hyeon Ji Song1, Jin Ho Lee1, Hyun‑Cheol Jeong2, Eun‑Jung Choi2, Taek‑Keun Oh3, Chang‑Oh Hong4
and Pil Joo Kim1,5*

Abstract
Straw incorporation is strongly recommended in rice paddy to improve soil quality and mitigate atmospheric carbon
dioxide ­(CO2), via increasing soil organic carbon (SOC) stock. However, straw application significantly increased
methane ­(CH4) emission during rice cultivation, and then its incorporation area was not expanded effectively. To find
the reasonable straw management practice which can reduce ­CH4 emission without productivity damage, the effect
of straw incorporation season and method on ­CH4 emission was investigated at six different textured paddy fields
in South Korea for 2 years. A straw was applied right after rice harvesting in autumn, and the other right before rice
transplanting in spring. In the autumn application, straw was applied with two different methods: spreading over soil
surface or mixing with soil. Straw application significantly increased seasonal C ­ H4 flux by average 28–122% over 197–
590 kg ­CH4 ­ha−1 of the no-straw, but its flux showed big difference among straw applications. Fresh straw application
before transplanting increased seasonal ­CH4 flux by approximately 120% over the no-straw, but the autumn applica‑
tion reduced its ­CH4 flux by 24–43% over 509–1407 kg ­CH4 ­ha−1 of the spring application. In particular, the seasonal
­CH4 flux was approximately 24% lower in straw mixing with soil after autumn harvesting than 423–855 kg C ­ H4 ­ha−1
in straw spreading over surface. However, ­CH4 fluxes were not significantly discriminated by soil and meteorological
properties in the selected condition. Straw application slightly increased rice grain yield by approximately 4% over
the no-straw, but rice productivity was not statistically different among straw applications. Spring straw application
increased ­CH4 intensity which means seasonal ­CH4 flux per grain yield by the maximum 220% over the no-straw.
Autumn straw application significantly decreased ­CH4 intensity by average 24–65% over the spring straw application.
In particular, ­CH4 intensity in straw mixing with soil treatment was not statistically different with the no-straw. There‑
fore, autumn straw application with mixing inner soil could be a reasonable straw management practice to decrease
­CH4 emission impact with improving soil productivity.
Keywords: Greenhouse gas, Methane intensity, Straw application, Low land

Introduction ­CO2 securely inner soil layers [2], is getting a big atten-
Soil organic carbon (SOC) stock is accepted as the tion. Consequently, increasing SOC stock is recog-
most key parameter to decide soil health condition and nized as the most promised soil management strategy
sustainability [1]. With global warming, soil C seques- to achieve sustainable soil quality and mitigate global
tration, which means transferring a greenhouse gas warming [3, 4].
carbon dioxide ­(CO2) into long-lived pools and storing Several soil management practices such as tillage, fer-
tilizer, water, organic matter, winter cover crop, and crop
rotation managements were recommended to increase
*Correspondence: pjkim@gnu.ac.kr SOC stock in arable lands [5]. In particular, straw recy-
1
Division of Applied Life Science (BK 21+ Program), Gyeongsang
cling is accepted as the most reasonable agricultural
National University, Jinju 52828, South Korea
Full list of author information is available at the end of the article practice to increase SOC stock in mono-rice paddy [6].

© The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creat​iveco​mmons​.org/licen​ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.
Song et al. Appl Biol Chem (2019) 62:70 Page 2 of 13

The Korean government has strongly recommended and Juk-dong, Daejeon, South Korea, respectively. In the
straw recycling to increase SOC stock. However, its recy- Honam area, loam and silt clay loam having rice paddies
cling area was not expanded rapidly in the fields. Most of were selected as the experimental sites in Wanju-gun and
rice straw was removed for cattle feeding in rice cropping Gimje-si, respectively. In Youngnam area, two rice pad-
area. This removal significantly decreased SOC stock dies having clay loam and silt loam textures were selected
with the lapse of year, and then deteriorated soil quality in Jinju-si and Sacheon-si, respectively.
[7, 8]. Two paddy soils of the central part (Daejeon) of Korea
In the negative side, straw addition as organic mat- had slightly acidic pH (5.4–5.5) and low fertility with
ter source markedly increased the emission of methane 8–12 g kg−1 of SOC concentration before the experi-
­(CH4), which is an important greenhouse gas (GHG) and ment. In comparison, two soils of Honam area had rela-
has 28 times higher global warming potential (GWP) than tively high pH (7.0–7.7). Silt clay loam in Gimje-si had
­CO2 over a 100-year time horizon [9], during the flooded high SOC content (19.1 g kg−1), but loam soil in Wanju-
rice cultivation [10]. Methane is biologically produced by gun had low fertility with 8.0 g kg−1 of SOC. However,
methanogenic archaea during anaerobic decomposition two rice paddies in Youngnam area had general chemi-
of organic matter [11]. Flooded rice cropping is assumed cal properties of Korean paddy soils with pH 6.1–6.2 and
to cover approximately 10% of anthropogenic ­CH4 emis- 14–17 g kg−1 of SOC content.
sion [12]. Therefore, sustainable straw management prac- However, any apparent difference on meteorologi-
tices which can increase SOC stock and decrease C ­ H4 cal properties of three different locations was not found
emission during rice cultivation should be developed. for the last 30 years. Mean annual temperatures of the
In the several field studies [13, 14], the application of selected locations were ranged within 12.9–13.6 °C with-
rice straw aerobically digested during the fallow sea- out big difference. Annual precipitation was slightly
son was very effective to decrease ­CH4 flux during the higher in Youngnam area with average 1528 mm, and
flooded rice cropping season, comparing with ­ CH4 comparatively lower in Honam area with 1223–1289 mm.
emission in fresh straw application. However, rice straw Sunshine hours were approximately 200 h per year higher
is generally applied in farmer’s fields with two different in Youngnam and Central areas than Honam area [15].
methodologies. For example, rice straw is mechanically
chopped at harvesting stage and immediately applied as Experimental plot installation and rice cultivation
organic amendment. The chopped straw is spread over To evaluate the effect of straw application on seasonal
the soil surface and digested under upland condition dur- ­CH4 flux, straw recycling and removal plots were selected
ing the cold follow season. On the other hand, the straw as the main treatments (Table 2). In the straw recycling
is mixed with soil via plowing and then digested. How- treatment, straw was applied with three different meth-
ever, the effect of two different straw managements on ods surface spreading after rice harvesting in autumn,
­CH4 emission was not clear. mixing with soil in autumn, and recycling right before
In order to evaluate the effect of rice straw manage- rice transplanting in spring. In the selected experiment
ments on ­CH4 emission in Korean rice paddies, rice straw fields, all plots were designed with 100 m2 size, and total
was applied with three different methodologies. The 12 plots (4 treatments and 3 replicates) were arranged
chopped fresh straw was incorporated in spring before with randomized complete block design.
transplanting. In the other treatments, straw was applied The average yield of straw in the selected location was
with two different methodologies in autumn right after considered with straw application level, and the same lev-
harvesting and aerobically digested during the fallow sea- els of straw was applied for 2-year field studies (Table 3).
son. The one chopped straw was spread over the surface For example, 9.0, 6.0 and 8.0 Mg ha−1 of straw were
layer, and the other straw was mixed with soil right after applied in Central, Honam, and Youngnam area of south
rice harvesting. Korean Peninsula, respectively. The straw harvested
in the mid October was mechanically chopped with
Materials and methods 5–10 cm length, and then applied in two autumn treat-
Experimental site selection ments. The one was spread over soil surface layer, and the
To evaluate the effect of straw managements on seasonal other was mixed by mechanical plowing with surface soil
­CH4 flux in Korean rice fields, six typical rice paddies (0–15 cm depth). In the spring recycling treatment, the
having different soil texture were selected in three dif- chopped straw was stored inner warehouse during the
ferent locations (Central, Honam, and Youngnam area) fallow season and then applied as organic amendment
of south Korean Peninsula (Table 1). As the central part right before flooding. All treatments were mechanically
of Korea, two different textured experiment plots (sand plowed and puddled under the same condition before
clay loam and sandy loam) were installed in Noeun-dong rice transplanting in the late May-the early June.
Song et al. Appl Biol Chem (2019) 62:70 Page 3 of 13

Table 1 Characteristics of the selected soils before plot installation, and meteorological properties for the last 30 years
Parameter Field location

Central Honam Youngnam

Noeundong Jukdong Wanju Gimje Jinju Sacheon

Location (GPS) 36° 22′ 20.4″ N, 36° 22′ 23.7″ 35° 49′ 43.76″ 36° 22′ 23.7″ 35° 14′ 05.25″ 35° 10′ 82.33″
127° 19′ 52.0″ E N, 127° 19′ N, 127° 02′ N, 127° 19′ N, 128° 09′ N, 128° 11′
39.5″ E 39.03″ E 39.5″ E 59.89″ E 64.87″ E
Soil properties
Soil texture Sand Clay Loam Sandy Loam Loam Silt Clay Loam Clay Loam Silt Loam
Sand (%) 57 66 37 14 39 26
Silt (%) 22 17 40 53 33 53
Clay (%) 21 16 22 33 29 21
­ 2O)
pH (1:5, H 5.5 5.4 7.7 7.0 6.5 6.6
Soil organic C (g kg−1) 11.6 8.5 8.03 19.1 14.2 17.1
Available P (mg kg−1) 110.9 133.4 102.1 123.1 108.1 110.4
Exchangeable cation ­(cmol+ ­kg−1)
K+ 0.38 0.55 0.53 0.67 0.23 0.21
Ca2+ 1.73 1.64 5.30 5.11 6.23 6.11
Mg2+ 0.62 0.71 1.50 0.91 1.52 1.81
Meteorological properties
Annual mean temperature (°C) 13.0 13.0 12.9 13.6 13.4 13.2
Annual precipitation (mm) 1366 1366 1289 1223 1533 1528
Annual sunshine hours (h) 2229 2229 2078 2076 2250 2244

Table 2 Field managements and rice cultivation

Season No-straw treatment Straw recycling treatment
Spring recycling Autumn recycling
Spreading Mixing

After harvesting (Autumn) Straw removed Straw removed Straw spread over soil Straw mixed
surface with soil
Before transplanting (Following spring) – Straw application – –
Plowing and irrigation
Fertilizing (NPK), puddling, and rice transplanting

In the selected experimental fields, rice was cultivated Methane gas sampling and analysis
under the same condition, except for straw application. During rice cultivation period, C­ H4 emission rates were
Shindongjin cultivar (Japonica) was selected as the target determined using a closed chamber method [18]. Three
rice cultivar. The same levels (N–P2O5–K2O = 90–45– pairs of six hexahedra transparent acrylic chamber (W.
57 kg ha−1) of chemical fertilizers were applied in all treat- 60 cm × L. 60 cm × H. 120 cm) were installed in each plot
ments, according to the guidelines of rice cultivation of after rice transplanting. Total eight hills of rice seedling
RDA, Korea [16]. The fields were constantly flooded with were transplanted inner the chamber with the same space
5–7 cm depth from soil surface by 1 month before har- interval out of the chamber. A fan and a thermometer were
vesting. Three-week old rice seedlings were manually placed inner the chambers to circulate gas and monitor the
transplanted with 15 cm × 30 cm space interval in the late temperature of inside chambers, respectively. The lips of the
May-the early June. Rice was harvested at maturing stage chambers were only closed during the sampling period and
in the mid-October. Rice growth and yield properties kept open during the whole experimental period to mini-
were investigated at harvesting stage, based on the Korean mize chamber effects. Gas was sampled every week interval
standard [17].
Song et al. Appl Biol Chem (2019) 62:70 Page 4 of 13

Table 3 Straw application rate and chemical properties of straw in each location
Year Parameter Field location

Central Honam Youngnam

Noeundong Jukdong Wanju Gimje Jinju Sacheon

1st Straw application rate (Mg ha−1) 9.0 9.0 6.0 6.0 8.0 8.0
C (%) 38.6 38.5 35.9 34.0 38.5 38.1
N (%) 0.6 0.6 0.4 0.5 0.6 0.6
C/N ratio 64.3 64.2 89.8 68.0 64.2 63.5
2nd Straw application rate (Mg ha−1) 9.0 9.0 6.0 6.0 8.0 8.0
C (%) 36.9 38.1 35.5 35.3 37.4 37.1
N (%) 0.5 0.5 0.4 0.5 0.5 0.5
C/N ratio 73.8 76.2 88.8 70.6 74.8 74.2

at 10:00–10:30. Gas samples were collected using 60 ml gas- (i − 1)th and ith sampling, and n is the number of sam-
tight syringes at 0 and 30 min after chamber closing. pling time.
The gas samples were transferred into 30 ml air-evacu- To figure out the impact of straw application practices
ated glass vials closed by a butyl rubber septum. The C ­ H4 on ­CH4 emission during rice production, C ­ H4 intensity
concentrations in the collected gas samples were analyzed which means C ­ H4 seasonal fluxes per rice grain produc-
by gas chromatography (Shimadzu, GC-2010, Japan) with a tivity were evaluated.
Porapak NQ column (Q 80–100 mesh). A flame ionization  
detector (FID) were utilized for quantifying the C ­ H4 con- CH4 intensity kg CH4 kg−1 grain
centrations in samples. The temperatures of column, injec- 
tor, and detector were controlled at 35, 200 and 250 °C, = Seasonal CH4 flux Grain yeild
respectively. Hydrogen and helium gases were used as the To compare the effect of straw recycling method-
burning and carrier gases, respectively. ologies on ­CH4 emission rate, conversion factor which
The ­CH4 emission rates were calculated using the implies the relative C
­ H4 emission weight to the control
increased ­CH4 concentration in the headspace of closed (straw application right before transplanting in spring)
chambers [18, 19]. was calculated by 2006 IPCC Guideline [21]. Methane
  emission factor means average daily C ­ H4 emission rate
CH4 emission rate mg m−2 h−1
(kg ­CH4 ­ha−1 day−1) during rice cropping period. Based
on ­CH4 emission factor at the straw incorporated shortly
        
= C t × V A × ρ × 273 T
(< 30 days) before cultivation, the conversion factor was
where ΔC (­ m3 m−3) is the increased C­ H4 concentrations comparatively calculated using ­ CH4 emission factor
in the headspace of closed chamber during the sampling under different straw recycling condition.
period, Δt is the chamber closing hour for gas sampling, 
V ­(m3) and A ­(m2) are the headspace volume and the Conversion factor = EFT EFC
surface area of closed chamber, respectively, ρ is the gas
where ­EFT and ­EFC mean the ­CH4 emission factor (kg
­ H4 at a standardized state (mg cm−3), and T
density of C
­CH4 ­ha−1 day−1) of straw treatments and the control
(K) is the absolute temperature of closed chamber at gas
(straw incorporated shortly (< 30 days) before cultiva-
sampling.
tion), respectively.
The seasonal ­CH4 fluxes which means the cumulative
­CH4 emission rates during the entire experiment period
were calculated [20].
Soil, straw and statistical analysis
n
   Air temperature, precipitation and sunshine hour data
Seasonal CH4 flux kg ha−1 = (Ri × Di ) during rice cultivation were collected from the database
i
of Korea Meteorological Administration [15]. In addi-
­ H4 flux per day (g m−2 day−1)
where ­Ri is the rate of C tion, soil redox potential (Eh value) was determined at
in the ith sampling, ­Di is the interval days between the 5–10 cm soil depth during rice cropping season with Eh
Song et al. Appl Biol Chem (2019) 62:70 Page 5 of 13

electrode and Eh meter (PRN-41, DKK-TOA Corpora- average 20–40% over that in the control. In particular,
tion, Japan). ­C H4 emission factor was much lower in the straw mix-
Total C and N contents of the used soil and straw ing with soil right after rice harvesting in autumn with
were determined using CHNS Analyzer (CHNS-932, 3.42 ± 1.04 kg ha−1 day−1, which was not comparable
Leco, Saint Joseph, MI, USA). Soil properties were deter- with 4.51 ± 1.10 kg ha−1 day−1 in the straw spreading
mined following as the Korean standard [22]; soil texture over soil surface in autumn.
(pipette method), pH (1:5 with H ­ 2O), available P (Lan- In the 2006 Revised IPCC Guideline [21], the
caster method), and exchangeable cation content (1 M ­C H4 emission rate in straw incorporated shortly
­NH4-acetate extraction at pH 7). (< 30 days) before rice cultivation was proposed as
All statistical analyses were performed using IBM the control with conversion factor 1.0 (error range
SPSS statistics 25.0 (IBM Corp., Armonk, NY, USA). The 0.97–1.04). Comparing with C ­H4 emission factor
impact of parameters (treatments and year) was deter- (5.94 ± 1.90 kg ha−1 day−1) at the control treatment,
mined through one- and two-way analysis of variance straw application over the surface right after rice har-
(ANOVA), and Tukey’s test. vesting decreased average 20% of ­C H4 emission and
then had 0.8 of conversion factor (Fig. 4). In compari-
son, straw mixing with soil right after rice harvesting
Results reduced average 40% of ­C H4 emission and then had 0.6
Methane emission during rice cultivation of conversion factor.
Irrespective with soil amendments, similar ­CH4 emission
patterns were observed in each field during rice cropping
seasons (Fig. 1). Methane emission rates were sharply Rice productivity and methane intensity
increased with flooding and rice transplanting. This high The same rice cultivar was cultivated in the whole inves-
­CH4 emission rates were maintained to rice flowering tigation sites. However, under the same soil amendments,
stage at approximately 80–90 days after transplanting, rice yield properties showed differences among rice fields
and thereafter, slowly decreased to the background level. and cropping years (Table 5). We could not find any
Methane emission patterns were reversely changed correlation between grain yields and soil and meteoro-
with changes of soil Eh values (Fig. 2). Irrespective with logical properties in this study. In six different soils, the
soil amendments, soil Eh values were sharply decreased mean grain yield was 6.5 ± 0.8 Mg ha−1 in the no-straw
to less than minus 200 mV within 1–2 week after trans- treatment (NPK) for 2 years. Straw application slightly
planting. This low Eh values were continued to rice increased rice grain productivity by average 4% over the
flowering stage, and thereafter steadily increased up no-straw application. However, the average grain produc-
to 200 mV at harvesting stage. However, soil Eh value tivities were not significantly different among straw man-
changes were not clearly discriminated among soil agements. Its productivity was the highest with average
amendments. 6.7 Mg ha−1 in the straw spreading over soil surface at
harvesting stage, and then followed by the straw mixing
Methane factor and conversion factor with soils with 6.6 Mg ha−1.
Under the same soil amendments, C ­ H4 emission factor Rice productivities did not show any meaningful rela-
which means the average daily ­C H4 emission rate dur- tionship with ­CH4 emission factor in this study. Meth-
ing cropping season [21] showed big differences among ane intensity which indicates seasonal ­CH4 flux per grain
soil textures and experimental field locations. However, yield (kg ­CH4 ­kg−1 grain) was average 0.06 kg ­CH4 ­kg−1
this emission factor was not correlated with clay or grain in no-straw treatment, but straw application signifi-
organic matter contents of soils. The average ­C H4 emis- cantly increased this intensity by approximately 24–114%
sion factor was ranged within 2.67 ± 0.91 kg ha−1 day−1 over that of no-straw application (Fig. 5). Fresh straw
in the no-straw treatment, and straw applications sig- application right before rice transplanting in spring sig-
nificantly increased this emission factor by 1.3–2.2 nificantly increased C­ H4 intensity by average 114% over
times over that in the no-straw (Table 4, and Fig. 3). that of no-straw application. Straw spreading over sur-
Among straw application treatments, ­C H4 emission face in autumn increased C ­ H4 ­kg−1
­ H4 intensity (0.1 kg C
factor was the highest with 5.94 ± 1.90 kg ha−1 day−1 in grain) by around 65% over the no-straw, but straw mix-
the straw application right before rice transplanting in ing with soil in autumn decreased this intensity to the
spring (control). However, straw application in autumn similar level (0.07 kg C­ H4 ­kg−1 grain) with the no-straw
and its aerobic digestion during the off-cropping sea- treatment.
son significantly decreased ­ C H4 emission factor by
Song et al. Appl Biol Chem (2019) 62:70 Page 6 of 13

1st year 2nd year

No straw Noeundong-Central
2500 Straw : Spring recycling
Straw : Autumn spreading
2000 Straw : Autumn mixing
1500
1000
500
0

Jukdong-Central
2500
2000
1500
1000
500
0

Wanju-Honam
2500
2000
CH4 emission rate (mg m day )
-1

1500
-2

1000
500
0

Gimje-Honam
2500
2000
1500
1000
500
0

Jinju-Youngnam
2500
2000
1500
1000
500
0

Sacheon-Youngnam
2500
2000
1500
1000
500
0

30 60 90 120 30 60 90 120

Day after transplanting (DAT)

Fig. 1 Changes of ­CH4 emission rates under different condition of straw amendments during cropping seasons
Song et al. Appl Biol Chem (2019) 62:70 Page 7 of 13

1st year 2nd year

No straw Sand Loam Noeundong-Central
200 Straw : Spring recycling
Straw : Autum spreading
100 Straw : Autumn mixing
0
-100
-200
2D Graph 13
-300

Sand Clay Loam Jukdong-Central

200 200

100 100

Y Data
0

-100 -100

-200 -200

-300 -300

Wanju-Honam
200
100
0
Soil Eh value (mV)

-100
-200
-300
Gimje-Honam
200
100
0
-100
-200
-300
Jinju-Youngnam
200
100
0
-100
-200
-300
Sacheon-Youngnam
200
100
0
-100
-200
-300

30 60 90 120 30 60 90 120
Day after transplanting (DAT)
Fig. 2 Changes of soil Eh values under different condition of straw amendments during cropping seasons
 Song et al. Appl Biol Chem

Table 4 CH4 emission factors of each location under different methods of straw application
Year Treatment CH4 emission factor (kg ha−1 day−1)
(2019) 62:70

Straw addition Application season Application method Noeun (SCL) Jukdong (SL) Wanju (L) Gimje (SiCL) Jinju (CL) Sacheon (SiL) Mean

1st No straw – – 2.21b 2.87c 3.71b 3.99b 1.40b 1.58c 2.63b

Straw Spring – 3.46a 5.87a 5.92a 7.26a 4.42a 5.39a 5.39a
Straw Autumn Spreading 3.66a 4.47b 4.56b 3.47b 4.54a 6.11a 4.47a
Straw Autumn Mixing 2.50b 2.57c 3.62b 2.92b 2.96ab 4.55ab 3.19b
2nd No straw – – 1.88c 2.23c 2.59c 3.57c 2.64c 3.38c 2.71c
Straw Spring – 4.49a 4.34a 8.10a 10.13a 5.79a 6.83a 6.61a
Straw Autumn Spreading 2.99b 3.50b 6.15ab 5.08b 4.35ab 4.88ab 4.49b
Straw Autumn Mixing 2.36bc 2.15c 5.64b 4.16bc 3.87bc 3.78bc 3.66bc
Mean No straw – – 2.05b 2.55b 3.15c 3.78b 2.02c 2.48c 2.67c
Straw Spring – 3.98a 5.10a 7.01a 8.70a 5.11a 6.11a 5.94a
Straw Autumn Spreading 3.32a 3.98a 5.36ab 4.28b 4.44a 5.50a 4.51b
Straw Autumn Mixing 2.43b 2.36b 4.63bc 3.54b 3.41b 4.16b 3.42c
Statistical analysis
Year (A) ns *** *** *** *** ns *
Treatment (B) *** *** *** *** *** *** ***
A×B *** *** *** *** ns *** ns
All treatments were plowed before flooding in spring
Different letters on same column indicate significant difference at level of p < 0.05 within the treatments
Page 8 of 13
Song et al. Appl Biol Chem (2019) 62:70 Page 9 of 13

Fig. 3 Methane emission factors under different condition of straw amendments during cropping seasons. (Different letters on the same column
indicate significant difference at level of p < 0.05 among treatments)

Fig. 4 Conversion factor of ­CH4 flux under different condition of straw amendments during cropping seasons. (Different letters on same column
indicate significant difference at level of p < 0.05 among treatments)

Table 5 Grain yields under different methods of straw application in different location
Year Treatment Grain yield (Mg ha−1)
Straw addition Application Application Noeun (SCL) Jukdong (SL) Wanju (L) Gimje (SiCL) Jinju (CL) Sacheon (SiL)
season method

1st No straw – – 6.1 5.7 6.2 8.1 5.6 6.9

Straw Spring – 6.4 5.9 6.7 8.4 6.0 7.4
Straw Autumn Spreading 6.3 6.1 6.6 8.2 6.0 7.0
Straw Autumn Mixing 6.9 6.0 6.5 8.3 6.1 7.3
2nd No straw – – 5.9 6.2 6.3 7.6 5.9 7.0
Straw Spring – 6.0 6.4 6.7 7.9 5.5 6.9
Straw Autumn Spreading 6.4 6.1 6.5 7.7 6.0 7.3
Straw Autumn Mixing 6.3 6.2 6.6 7.7 5.8 7.1

Discussion seasonal ­CH4 flux by average 122% over no-straw appli-

In this field experiments which were studied in six dif- cation [23]. Methane emission is basically decided by the
ferent soils for 2 years, the effect of straw application on difference between ­CH4 production and oxidation [24].
­CH4 emission was highly different depending on straw Methanogens produce C ­ H4 under extremely reduced
application timing and methods (Fig. 1). Straw applica- soil condition, and organic C availability can impor-
tion right before flooding in spring significantly increased tantly affect ­CH4 production. In the flooded rice fields,
Song et al. Appl Biol Chem (2019) 62:70 Page 10 of 13

Fig. 5 Total ­CH4 flux, grain yield, and ­CH4 intensity under different condition of straw amendments during cropping seasons. (Different letters on
same column indicate significant difference at level of p < 0.05 among treatments)
Song et al. Appl Biol Chem (2019) 62:70 Page 11 of 13

applied straw provides a C source for methanogenesis conversion factor. However, in this studies, the conver-
and develops strictly anaerobic soil conditions [25, 26]. sion factor for straw applied in autumn was approxi-
This changed soil condition stimulates ­CH4 production, mately 0.6 and 0.8 in the straw mixing with soil and the
inhibits ­CH4 oxidation, and then increases ­CH4 emission straw spreading over surface layer, respectively (Fig. 4).
[27, 28]. They were much bigger than the IPCC default value
Aerobic digestion of amended straw during off-crop- (0.29) to straw incorporated long (> 30 days) before cul-
ping season significantly decreased ­CH4 emission during tivation [21].
rice cropping season. However, straw mixing with soil at Besides the effect of straw incorporation on increas-
rice harvesting stage was more effective to reduce ­CH4 ing ­CH4 emission, straw application makes a number of
emission than straw spreading over surface during fallow other effects. The effect of straw amendments on rice
season. In the several field studies [13, 14], the applica- growth and productivity might be positive or negative,
tion of rice straw digested during the off-cropping sea- depending on incorporation methodology and timing,
son was very effective to decrease C ­ H4 emission during chemical and physical properties of straw, and fertiliza-
rice cropping season, comparing with ­CH4 emission in tion backgrounds [31, 32]. In this field studies, rice straw
straw applied shortly (< 30 days) before cultivation. The recycling slightly increased rice grain productivity by
changes of organic constituent composition in rice straw approximately 4% over that of the no-straw treatment,
during the off-cropping season might be related to this but there was no statistic difference among straw appli-
decrease of ­CH4 emission rates. Rice straw contained cation seasons and methods (Fig. 5). However, long-term
approximately 25–35% of cellulose, 32–37% of hemicel- straw application can increase SOC stock, which might
lulose, and 6–10% of lignin [29]. Aerobic decomposition further offset the negative effect of straw application, due
of straw during the off-cropping upland season decreases to increased C ­ H4 emission [33]. For example, straw appli-
the concentration of readily available C substrates like cation increased SOC content by 20–30% in the long-
cellulose and hemicellulose for methanogenesis, and then term straw application field [34].
decreases ­CH4 emissions in the following rice cropping With developing intensive farming structure, rice pro-
season [26, 30]. This decomposition effect might be much ductivity increase is limited largely by the deterioration of
higher under the condition of straw mixing with soil than soil quality, due to decrease of soil organic matter (SOM)
straw spreading over surface layer. stock [35, 36]. Straw recycling as organic matter source
In the 2006 Revised IPCC guidelines [21], a daily ­CH4 is accepted as the most reasonable management practice
emission factor (­ EFi) is calculated by multiplying baseline to improve SOM stock and increase crop productivity
­CH4 emission factor ­(EFc) and scaling factors (SF) (Eq. 1). [33]. Rice straw application can improve soil fertility [37].
Scaling factors mean the conversion factor of ­CH4 emis- This improved soil quality might reduce the dependence
sion factor against that in the control treatment [21], and of chemical fertilizers [38] and increases rice productivity
are specified with several SF for water regime during the [39]. The positive effect of rice cropping industry that is
cultivation period (­SFw), water regime in the pre-season not related to GHG emission should be also considered.
­(SFp), organic amendment applied ­(SFo), soil type ­(SFs), For example, comparing with straw burning in the open
and rice cultivar ­(SFR). field, straw recycling leads to favorable effects on envi-
ronment quality and human health [40]. Straw applica-
EFi = EFc × SFw × SFp × SFo × SFS × SFS,r (1) tion can boost soil biota activity, which will improve soil
where ­EFi and E­ Fc are a daily emission factor for i con- biodiversity and health condition [41]. Therefore, agri-
dition (kg C­ H4 ­ha−1 day−1) and baseline emission factor cultural policy decisions including straw management
(kg ­CH4 ­ha−1 day−1), respectively. ­SFW, ­SFP, ­SFO and S
­ FS,r should consider a number of trade-offs between positive
mean scaling factors for water regime during the culti- and negative effects of straw application on rice produc-
vation period, water regime in the pre-season, organic tivity and environment impact.
amendment applied and soil type and rice cultivar, Acknowledgements
respectively. This work was supported by Cooperative Research Program for Agriculture
Science & Technology Development (Project title: Study on ammonia emission
Scaling factor for organic amendment applied (­SFo) is
inventory establishment in paddy rice, Project No. PJ014205032019), National
estimated with application rate of organic amendment in Academy of Agricultural Science, Rural Development Administration and
fresh weight (Mg ha−1) and conversion factor for organic Basis Science Program (NRF-2015R1A6A1A03031413), the National Research
Foundation, the Ministry of Education, Republic of Korea.
amendment [21]. For example, in Tier 1 level, IPCC pro-
posed 1.0 (error range 0.97–1.04) as the conversion factor Authors’ contributions
for straw incorporated shortly (< 30 days) before cultiva- HJS and JHL conducted all the research works and data analyses. HCJ, E-JC,
T-KO, and COH were co-PI on the project and contributed to data analyses.
tion. In comparison, straw incorporated long (> 30 days)
before cultivation had 0.29 (error range 0.20–0.40) of
Song et al. Appl Biol Chem (2019) 62:70 Page 12 of 13

PJK developed the concepts, led the research, contributed to data analyses a mono-rice cultivation system as influenced by fallow season straw
and wrote the paper. All authors read and approved the final manuscript. management. Environ Sci Pollut Res 23:315–328. https​://doi.org/10.1007/
s1135​6-015-5227-7
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768.1993.10419​187
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