Influence of tillage practice on major pathways of CH4 emission in rice paddy field

Hiyori Namie, Kasane Shimada, Shuangshuang Zhao, Munehide Ishiguro, Ryusuke Hatano

Graduated school of Agriculture of Hokkaido University, Japan

April 19th-30th

EGU General Assembly 2021SSS8.6 _Soil gases : production, consumption and transport processes

Relationship between soil fertilizers and GHG emission in rice field

◼ Soil fertilizer is the basis for keeping high yields and high-quality rice.But, they are important factors affecting GHG emissions in rice field

(Liang X. et al 2013).

◼ CH4 producing bacteria actively work in anaerobic conditions→ Rice field is a hot spot for CH4 emissions.

◼ Organic matter supplied from rice straw, green manure, soil organic matter, paddy rice, etc become carbon resources of CH4 emitted from rice field (Akira

watanabe. et al 1999).

◼ Application of organic fertilizers may increase TOC content and promote CH4

emissions from rice field (Xie YQ. et al 2015) .

Rice cultivation accounts for about 58.8% of the consisted of CH4

generated agriculture in Japan ( UNFCCC Green house gas Inventory Data 2015 ).

1

Initiatives for fertilizer-free and pesticide-free rice fields◼ Several medium-tilling (weeding operations) which disturb the soil around

rice in fertilizer-free and pesticide-free paddy fields enables the same yield as conventional farming. （Kasubuchi.et al 2016）

◼ Effects of medium-tilling weeding

2

（Kasubuchi.et al 2019）Medium- tilling

Ecosystem conservation by pesticide-free

O2

weeding

machine

O2N

Efficiency of nutritional self-

sufficiency

Improvement of roots area and anaerobic environment

This way is sustainable but increasing C/N content → High GHG emissions?

CH4 gas dynamics in rice field

◼ CH4 produced in paddy soil during paddy rice cultivation is released into the atmosphere through three pathways: diffusion into the atmosphere (<1%), bubbles (<10%), and paddy rice bodies (>90%) (Yumite et al., 2019).

◼ There are few cases diffusion coefficient was measured for the soil under the water→ gas dynamics in rice field soils are not accurately understood.

3

Consideration of soil diffusion coefficient under the surface of the water

CH4 dynamics in rice field soilis able to more specific understanding.

CH4 gas from rice field soil to atmosphere is more accurate analysis

Paddy rice bodies

Diffusion

Bubble

Research Objectives

By comparing the conventional farming with the medium-tilling (weeding operation) rice field of fertilizer-free and pesticide-free farming,

The number of medium-tilling and the presence or absence of fertilizers and pesticides are how affect on CH4 dynamics?

Differences in gas dynamics in soil are how affect on major pathway of CH4 emission?

4

About the research site

Conventional Farming site（CF）

Midium-tilling and natural farming site （T0・T2・T5）

5

Rice field at Hokkaido University Northern Biosphere Field Science Center（N43°4′29″,E141°20′16″）

6

Capturing the space and time variation of CH4 flux

• Measure and compare CH4 flux in each sites (CF, T0, T2, T5)

• Measure CH4 flux throughout the year and compare by water

management in rice field

To identify the governing factor of CH4 flux,Examining the space and time variation of environmental factors

• Measure and compare environmental factors in each sites (CF, T0, T2, T5)

• Compare by water management in rice field as well as CH4 flux

◼The number of medium-tilling and the presence or absence of fertilizers and pesticides are how affect on CH4

dynamics?

◼ Differences in gas dynamics in soil are how affect on major pathway of CH4 emission?

Combine these to find answers!

Soil Physics : Greenhouse Gas FluxTransparent chamber Dark chamber

7

• Total gas flux

• Put 4 rice crops

• Collect 0,15,30

minutes of gas

• Plants and roots in the

base was removed

→ From rice field soil

gas flux

• Collect 0,15,30 minutes

of gas

◼Soil gasA soil gas sampling tube was installed at a depth of 0-5 cm

(oxide layer) and 5-10 cm deep (reduction layer) to collect soil air.

◼ Gas diffusion coefficient below the surface of the water

100cm3 core sampler is connected to collect 0-5cm and 5-10cm samples.

Oxygen electrodes developed by Osozawa and Kubota (1987) were used to measure gas diffusion.

◼Gas diffusion flux (※Calculated from the following equation）

Soil Physics : Greenhouse Gas Flux8

(Fujikawa.et al 2008)

Statistical analysis

◼ One-way ANOVA(p<0.05)

→ To test for significant differences in sites intervals

◼ Tukey-HSD

→ To determine which sites intervals are the significant differences confirmed in One-way ANOVA

9

CH4 flux for distinguishing between rice cultivation period and sites

◼ By rice cultivation period

Total CH4 flux tends to increase during flooding period and intermittent irrigation period.

Total CH4 flux tends to decrease since the drainage season→The major pathway of CH4

is rice bodies.

◼ By sites

High emissions in CF and T5 sites where the content of C and N was considered to be high

10CF区: ① Flooding 5/30~7/12 ② Mid-drying 7/13~7/19

③ Intermittent irrigation 7/20~8/25

T区: ① Flooding 5/30~7/27 ② Mid-drying 7/28~8/1

③ Intermittent irrigation 8/2~8/25

CF/T区: ④ Drainage:8/26~10/9 ⑤ Fallowing 10/10~11/12 ⑥Snowing 11/13∼

Total

Soil

Gas

diffusion

Flooding Mid-drying

Intermittent irrigation Drainage Fallowing Snowing

Gas diffusion flux

Bubbles+

Generateand supply

Bubbleaccumulation

+Consumption

Soil flux

CH4

CO2

Total flux

Rice bodies flux

11

Create CH4 emission model

Total flux Soil flux Rice bodies flux

Gas diffusion

flux

Total flux

Positive value

Negative value

Bubbles

Generate and supply

Bubble accumulation

consumption

12

CH4 emission model :CF 2,791 (μgC/m2/h)

1,316

613

2,178

1,475

14,613

Mid- drying

10,364

7,417

22,030

4,249

13,966

Intermittent

irrigation

10,199

29,522

3,767

15,556

7,619

7,393

226

3,264

4,355

79

7,298

7,219

Drainage Fallowing Snowing※2020/10/22

Rice straw

spraying-60

2,978

3,038

※期間Total

（中干し期除く）

Total period

(excluding the

mid-drying)

Flooding

13415 (μgC/m2/h)

419

38

377

-4

958

897

61

2,025

1,150

16

875

1,242

349

893

61

1,181

115

-125

-123

17

140

2,009

240

※期間Total

（中干し期除く）

CH4 emission model :T0

Total period

(excluding the

mid-drying)

Mid- drying Intermittent

irrigation

Drainage Fallowing Snowing

Flooding

※2020/10/22

Rice straw

spraying

14374 (μgC/m2/h)

316

14

360

58

2,051

1,468

583

2,166

2,183

320

-17

1,512

552

960

-11

1,523

75

3,070

2,995

-43

293

336

1,846

CH4 emission model :T2

Total period

(excluding the

mid-drying)

Mid- drying Intermittent

irrigation

Drainage Fallowing Snowing

Flooding

※2020/10/22

Rice straw

spraying

15858 (μgC/m2/h)

796

-322

1,180

62

4,811

4,333

478

3,854

3,714

16

140

2,416

2,456

-40

-10

2,426

107

4,168

4,061

-19

93

3,838

74

Total period

(excluding the

mid-drying)

Mid- drying Intermittent

irrigation

Drainage Fallowing Snowing

Flooding

※2020/10/22

Rice straw

spraying

CH4 emission model :T5

Ｓｐａｃｅ and ｔｉｍｅ variation of CH4 flux

◼ Comparison of sites at the water management stage

①The peak of total CH4 flux was confirmed during the mid-drying or intermittent irrigation period.Rice pathways accounted for more than half of the total CH4 flux.

Order→CF区＞T5区＞T2区＞T0区

②Bubble CH4 flux was confirmed during flooding or drainage period.Pathway of bubble accounted for more than half of the total CH4 flux.

Order→CF区＞T5区＞T2区＞T0区

③Most of the diffusely moved CH4 was easily oxidized to CO2.

◼ Comparison of CH4 dynamics between sites

Total emissions order→CF区＞T5区＞T2区＞T0区Significantly higher CH4 emissions were shown in CF sites.

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Summary of CH4 flux by this natural farming method17

• The capture of organic matter into the soil in the conventional farming

method tended to increase CH4 emissions.

• The major pathway of CH4 emissions was through rice bodies, and

emissions were greatly affected by medium-tilling.

It was suggested that the source of the bubbles may be organic

decomposition of weeds mixed in rice straw and soil.