Early mid-season drainage can mitigate greenhouse gas emission from organic rice farming with green manure application

Figures & data

Table 1. Soil characteristics in chemical fertilizer applied (CF) and green manure (GM) applied paddy fields in 2017

Treatment	Depth	Available phosphorus content^‡	Ex. K content	Ex. Mg content	Ex. Ca content	CEC^§	Free Fe oxides content	Carbon content	Nitrogen content	C:N ratio	Sand	Silt	Clay
	(cm)	(g P2O5 kg^−1)	(mg kg^−1)	(mg kg^−1)	(g kg^−1)	(cmolc kg^−1)	(g Fe kg^−1)	(%)	(%)		(%)	(%)	(%)
CF	0–5	2.10	94.7	129	1.40	10.9	5.46	1.74	0.18	9.46	73.1	14.2	12.7
	5–10	2.15	86.7	124	1.35	10.3	5.21	1.52	0.16	9.28	71.7	13.1	15.2
	10–20	2.20	54.9	123	1.41	9.73	10.9	1.12	0.13	8.48	71.7	15.0	13.3
	20–30	1.05	51.8	136	1.11	8.48	12.8	0.37	0.05	7.89	69.7	13.2	17.2
GM	0–5	0.96	109	196	1.32	11.6	8.09	1.52	0.17	9.04	74.5	9.10	16.4
	5–10	1.07	123	180	1.41	10.1	7.85	1.44	0.16	8.99	70.5	13.8	15.7
	10–20	0.92	62.7	193	1.33	9.76	9.25	1.04	0.12	8.45	72.0	12.8	15.2
	20–30	0.29	31.2	201	1.60	8.16	10.3	0.24	0.05	4.54	71.9	12.0	16.2

‡ Bray II method, § Cation exchange capacity.

Figure 1. Seasonal variation in mean daily air temperature and precipitation (a), CH₄ (b), CO₂ (c), and N₂O (d) fluxes in chemical fertilizer (CF) and green manure (GM) applied treatments in 2017. F, T, P, TP, W, and H represents chemical fertilizer application, tillage, puddling, transplanting, weeding, and harvest, respectively

Table 2. Dry matter and nitrogen input from plant in GM in 2017

		Aboveground		Root	Total
		White clover	Other plant
Dry matter	(Mg ha^−1)	0.72 ± 0.78 c	3.36 ± 1.42 b	6.66 ± 0.98 a	10.7 ± 0.60
N content	(%)	2.62 ± 0.42 a	1.65 ± 0.62 b	1.47 ± 0.13 b	ND
C:N ratio		16.1 ± 2.48 b	30.5 ± 7.04 a	26.2 ± 3.12 a	ND
N application rate	(kg N ha^−1)	19.7 ± 21.5 b	61.0 ± 44.2 ab	97.4 ± 11.4 a	178 ± 24.9

Values are represented by Average ± Standard deviation.

Different letters represent significant difference between white clover, other plant, and root. ND: no data.

Table 3. Carbon budget (kg C ha⁻¹) from June 11 to October 15 in 2017

			Treatment
			CF	GM	P value
Input	Aboveground	White clover	0	296 ± 217	NA
		Other plant	0	1649 ± 734	NA
	Root		0	2543 ± 357	NA
	Total		0	4488 ± 211	NA
Output	CH4 emission		194 ± 71.7	1535 ± 420	< 0.05
	Rh		2094 ± 429	2610 ± 204	0.39
	Total		2288 ± 364	4145 ± 421	< 0.01
C budget			−2288 ± 364	343 ± 632	< 0.01

NA: not available.

Values are represented by Average ± Standard deviation.

Positive and negative values represent net C sink and source of atmospheric C, respectively.

Table 4. Global warming potentials (GWP) and net greenhouse gas emission (NGHGE) (Mg CO₂eq ha⁻¹) from June 11 to October 15 in 2017

		Treatment		P value
		CF	GM
GWPIN	GWPGM of white clover	0	−1.09 ± 0.80	NA
	GWPGM of other plant	0	−6.04 ± 2.69	NA
	GWPGM of root	0	−9.32 ± 1.31	NA
	Total	0	−16.5 ± 0.77	NA
GWPOUT	GWPCH4	8.82 ± 3.25	69.6 ± 19.1	< 0.05
	GWPRh	7.68 ± 1.57	9.57 ± 0.75	0.16
	GWPN2O	0.51 ± 1.15	1.46 ± 1.26	0.39
	Total	17.0 ± 2.02	80.6 ± 18.2	< 0.05
NGHGE		17.0 ± 2.02	64.2 ± 18.9	0.05

NA: not available.

Values are represented by Average ± Standard deviation.

Positive and negative values represent acceleration or mitigation of global warming, respectively.

Figure 2. Seasonal variation in mean daily air temperature (a), CH₄ (b), CO₂ (c), and N₂O (d) fluxes in green manure (G) fertilization, green manure fertilization at 1 (GE1) and 3 (GE3) weeks earlier treatments and combination of green manure fertilization and earlier mid-season drainage (GED) in 2018. HV, T, P, and H represents hairy vetch application, tillage, puddling, and harvest, respectively

Table 5. Carbon budget (kg C ha⁻¹) from May 5 to October 11 in 2018

		Treatment
		G	GE1	GE3	GED
Input	Hairy vetch^§	2112	1690	1056	2112
Output	CH4 emission	276 ± 185 abc	300 ± 56.9 a	171 ± 34.1 b	90.4 ± 30.7 c
	Rh	1675 ± 185 a	1751 ± 223 a	1449 ± 203 a	1778 ± 489 a
	Total	1951 ± 211 a	2051 ± 260 a	1620 ± 210 a	1688 ± 468 a
Carbon budget		161 ± 211 a	−361 ± 260 ab	−664 ± 210 b	244 ± 468 ab

Values are represented by Average ± Standard deviation.

Different letters represent significant difference between the treatments.

Positive and negative values represent net C sink and source of atmospheric C, respectively.§ differences in carbon input by hairy vetch incorporation was not statistically analyzed due to artificial application.

Table 6. Global warming potentials (GWP) and net greenhouse gas emission (NGHGE) (Mg CO₂eq ha⁻¹) from May 5 to October 11 in 2018

		Treatment
		G	GE1	GE3	GED
GWPIN	GWPGM^§	−7.74	−6.20	−3.87	−7.74
GWPOUT	GWPCH4	12.5 ± 8.39 abc	13.6 ± 2.58 a	7.75 ± 1.55 b	4.10 ± 1.39 c
	GWPRh	6.14 ± 0.68 a	6.42 ± 0.82 a	5.31 ± 0.74 a	6.52 ± 1.79 a
	GWPN2O	0.57 ± 0.40 a	0.56 ± 0.50 a	0.37 ± 0.17 a	0.66 ± 0.28 a
	Total	19.2 ± 8.30 ab	20.6 ± 2.78 a	13.4 ± 1.93 b	11.3 ± 1.53 b
NGHGE		11.5 ± 8.30 ab	14.4 ± 2.78 a	9.55 ± 1.93 a	3.53 ± 1.53 b

Values are represented by Average ± Standard deviation.

Different letters represent significant difference between the treatments.

Positive and negative values represent acceleration or mitigation of global warming, respectively.

§ differences in carbon input by green manure, which was hairy vetch, incorporation was not statistically analyzed due to artificial application.

Figure 3. Seasonal variation in soil Eh at 5-cm depth (a), soil Fe₂⁺ (b), NH₄⁺, and NO₃⁻ contents in chemical fertilizer (CF) and green manure (G) applied treatments in 2017. F, T, P, TP, W, and H represents chemical fertilizer application, tillage, puddling, transplanting, weeding, and harvest, respectively

Figure 4. Seasonal variation in soil Eh at 5-cm depth (a), soil Fe₂⁺ (b), NH₄⁺, and NO₃⁻ contents in green manure (G) fertilization, green manure fertilization at 1 (GE1) and 3 (GE3) weeks earlier treatments and combination of green manure fertilization and earlier mid-season drainage (GED) in 2018. HV, T, P, and H represents hairy vetch application, tillage, puddling, and harvest, respectively

Table 7. Yield component and quality of rice in 2017

	Unit	Treatment		P value
		CF	GM
Grain weight	(g m^−2)	650 ± 68.2	538 ± 23.8	0.09
Straw weight	(g m^−2)	1080 ± 95.6	889 ± 19.6	0.07
Grain/Straw		0.60 ± 0.04	0.60 ± 0.03	0.98
Panicle number	(number m^−2)	311 ± 14.8	273 ± 5.13	< 0.05
1000 grain weight^§	(g)	22.8 ± 0.41	23.8 ± 0.18	< 0.05
Brown rice yield^§	(g m^−2)	537 ± 54.8	416 ± 31.3	< 0.05
Protein content^§	(%)	5.50 ± 0.30	5.40 ± 0.26	0.69
Perfect grain ratio	(%)	83.5 ± 0.86	76.8 ± 6.88	0.23

Values are represented by Average ± Standard deviation.

§ 15% of moisture.

Table 8. Yield component and quality of rice in 2018

	Unit	Treatment
		G	GE1	GE3	GED
Grain weight	(g m^−2)	606 ± 25.6 a	568 ± 56.0 ab	521 ± 30.0 b	598 ± 23.8 a
Straw weight	(g m^−2)	694 ± 9.01 a	719 ± 86.1 a	643 ± 44.0 a	700 ± 23.4 a
Grain/Straw		0.87 ± 0.03 a	0.79 ± 0.04 a	0.81 ± 0.02 a	0.85 ± 0.04 a
Panicle number	(number m^−2)	378 ± 13.8 a	372 ± 25.7 a	352 ± 29.0 a	369 ± 21.6 a
1000grain weight^§	(g)	20.8 ± 0.14 a	21.0 ± 0.24 a	21.1 ± 0.13 a	21.1 ± 0.08 a
Brown rice yield^§	(g m^−2)	369 ± 8.16 a	349 ± 37.9 ab	317 ± 19.8 b	363 ± 25.0 ab
Protein content^§	(%)	7.15 ± 0.26 ab	7.00 ± 0.08 a	6.89 ± 0.16 ab	6.66 ± 0.06 b
Perfect grain ratio	(%)	83.2 ± 1.52 a	84.8 ± 0.54 a	85.9 ± 2.40 a	86.2 ± 1.00 a

Values are represented by Average ± Standard deviation.

Different letters represent significant difference between the treatments.

§ 15% of moisture.