Greenhouse gas emissions from rice straw burning and straw-mushroom cultivation in a triple rice cropping system in the Mekong Delta

Figures & data

Table 1 Ignition loss of carbon (C) and nitrogen (N) at each straw burning condition (straw of Jasmine 85 harvested in February 2012)

Straw burning condition					Straw-ash after burning			Ignition loss
	Dry weight	Moisture	Carbon content	Nitrogen content	Dry weight	Carbon content	Nitrogen content	Calculated carbon loss*	Calculated nitrogen loss*
Condition	(kg)	(%)	(kg)	(kg)	(kg)	(kg)	(kg)	(g C kg dry straw^−1)	(g N kg dry straw^−1)
Harvested straw	5	12.6	1.85	0.05	1.01	0.04	0.002	361	9.1
	5	23.1	1.85	0.05	1.07	0.06	0.003	357	8.9
	5	30.9	1.85	0.05	1.24	0.09	0.004	352	8.7
	5	52.2	1.85	0.05	1.50	0.06	0.003	358	8.8
	10	19.8	3.70	0.09	1.83	0.10	0.005	360	8.9
	10	23.6	3.70	0.09	2.11	0.08	0.005	362	8.9
	10	32.0	3.70	0.09	2.26	0.12	0.005	358	8.9
	10	50.9	3.70	0.09	2.40	0.08	0.003	362	9.1
	20	12.6	7.40	0.19	3.74	0.31	0.013	354	8.7
	20	20.6	7.40	0.19	3.69	0.20	0.009	360	8.9
	20	33.7	7.40	0.19	3.88	0.13	0.006	363	9.1
	20	65.0	7.40	0.19	4.53	0.21	0.008	360	9.0
	40	17.1	14.80	0.38	7.58	0.38	0.016	360	9.0
	40	29.0	14.80	0.38	8.02	0.23	0.010	369	9.1
	40	38.1	14.80	0.38	6.89	0.18	0.008	384	9.2
	40	61.4	14.80	0.38	9.54	0.17	0.004	362	9.3
Mushroom beds	10	18.2	3.42	0.20	4.62	1.16	0.086	225	11.2
	20	18.2	6.83	0.40	6.81	0.90	0.076	297	16.0

*See text (Eq. 1).

Figure 1 Straw stack dynamics: (A) internal temperature and (B) emission factors of carbon dioxide (CO₂), (C) carbon monoxide (CO), (D) methane (CH₄), (E) non-methane volatile organic carbon (NMVOC) and (F) nitrous oxide (N₂O) during the combustion of (a) 5 kg, (b) 10 kg, (c) 20 kg and (d) 40 kg (oven-dried weight) straw stacks with different moisture contents (12.6, 23.1, 30.9 and 52.2%; mass basis).

Figure 1 (Continued).

Table 2 Greenhouse gas emissions derived from straw burning. Emission factors are expressed as the amounts of carbon (C) or nitrogen (N) emitted per 1 kg oven-dried weight of straw or mushroom beds. Values in parentheses show relative gas emission per calculated C or N loss

Straw burning condition			Carbon emission									Nitrogen emission
	Dry-weight	Moisture	CO2-C		CO-C		CH4-C		NMVOC		MCE*	N2O-N
Burned straw	(kg)	(%)	(g C kg^−1)		(g C kg^−1)		(g C kg^−1)		(g C kg^−1)		(%)	(g N kg^−1)
Harvested straw	5	12.6	322	(89%)	36	(11%)	2.7	(0.8%)	0.15	(0.04%)	90	0.076	(0.84%)
	5	23.1	302	(84%)	52	(15%)	2.8	(0.8%)	1.27	(0.35%)	85	0.092	(1.04%)
	5	30.9	273	(78%)	65	(19%)	12.3	(3.5%)	0.95	(0.27%)	81	0.026	(0.30%)
	5	52.2	204	(57%)	124	(35%)	21.0	(5.9%)	8.60	(2.40%)	62	0.073	(0.83%)
	10	19.8	317	(88%)	38	(10%)	4.8	(1.3%)	0.24	(0.07%)	89	0.067	(0.75%)
	10	23.6	300	(83%)	55	(15%)	6.5	(1.8%)	0.79	(0.22%)	84	0.043	(0.48%)
	10	32.0	292	(81%)	57	(16%)	8.6	(2.4%)	0.83	(0.23%)	84	0.015	(0.17%)
	10	50.9	295	(81%)	57	(16%)	9.3	(2.6%)	1.18	(0.33%)	84	0.014	(0.15%)
	20	12.6	314	(89%)	26	(7%)	14.4	(4.1%)	0.38	(0.11%)	92	0.163	(1.86%)
	20	20.6	290	(81%)	59	(16%)	10.2	(2.8%)	0.73	(0.20%)	83	0.037	(0.41%)
	20	33.7	283	(78%)	60	(16%)	19.7	(5.4%)	1.08	(0.30%)	83	0.023	(0.25%)
	20	65.0	302	(84%)	48	(13%)	8.4	(2.3%)	1.22	(0.34%)	86	0.006	(0.07%)
	40	17.1	300	(83%)	53	(15%)	6.8	(1.9%)	0.59	(0.16%)	85	0.030	(0.33%)
	40	29.0	293	(81%)	57	(16%)	12.8	(3.5%)	0.92	(0.25%)	84	0.078	(0.85%)
	40	38.1	305	(84%)	48	(13%)	10.7	(2.9%)	1.05	(0.29%)	86	0.025	(0.27%)
	40	61.4	313	(86%)	43	(11%)	9.2	(2.5%)	0.62	(0.17%)	88	0.030	(0.32%)
Mushroom beds	10	18.2	199	(87%)	21	(9%)	8.7	(3.8%)	0.00	(0.00%)	90	0.035	(0.31%)
	20	18.2	268	(90%)	25	(8%)	3.7	(1.2%)	0.00	(0.00%)	92	0.031	(0.20%)

*See Eq. 3.

Notes: [Carbon composing carbon dioxide (CO₂-C), carbon monoxide (CO-C) and methane (CH₄-C), non-methane volatile organic carbon (NMVOC), modified combustion efficiency (MCE: emissions ratio of CO₂-C/(CO-C + CO₂-C)) and nitrogen composing nitrous oxide (N₂O)].

Figure 2 Correlations between straw moisture content (x) and (A) hours after ignition to reach a 100°C straw stack internal temperature; (B) modified combustion efficiency (MCE). Lines of significant regressions are given for straw stacks with different masses (5, 10, 20 and 40 kg dry straw; p < 0.05, n = 4 each).

Figure 3 Correlations between straw moisture content or modified combustion efficiency (MCE) and emission ratios of (A, D) methane (CH₄), (B, E) non-methane volatile organic carbon (NMVOC) and (C, F) nitrous oxide (N₂O) per calculated carbon (C) or nitrogen (N) loss (mass basis). Solid lines of significant regressions are given (p < 0.05, n = 16).

Table 3 Carbon (C) and nitrogen (N) contents in straw immediately after being harvested from rice paddies, straw after straw-mushroom [Volvariella volvacea (Bul. ex Fr.) Singer] cultivation, harvested straw-mushroom and ash of straw that was used for straw-mushroom cultivation as mushroom beds and then burned. Contents of carbon and nitrogen are expressed as the amounts of C or N contained in 1 kg of oven-dried straw (n = 3, mean ±standard deviation)

	Harvested straw from rice paddies			Straw after straw-mushroom cultivation (mushroom beds)			Harvested straw-mushroom			Straw-ash after straw-mushroom cultivation and burning**
Straw harvested Season*	Dry weight(t ha^−1)	Total C(g C kg^−1)	Total N(g N kg^−1)	Dry weight(t ha ^−1)	Total C(g C kg ^−1)	Total N(g N kg ^−1)	Dry weight(t ha^−1)	Total C(g C kg^−1)	Total N(g N kg^−1)	Dry weight(t ha^−1)	Total C(g C kg^−1)	Total N(g N kg^−1)
Winter- Spring	3.72 (± 0.71)	352 (± 15)	11 (± 1)	1.67 (± 0.51)	342 (± 27)	20 (± 3)	0.005 (± 0.001)	347 (± 20)	21 (± 5)	0.43 (± 0.08)	133 (± 18)	11 (± 3)
Spring- Summer	3.10 (± 0.80)	366 (± 87)	8 (± 1)	1.52 (± 0.29)	352 (± 14)	15 (± 2)	0.007 (± 0.001)	348 (± 20)	14 (± 3)	0.35 (± 0.07)	139 (± 23)	11 (± 3)
Summer- Autumn	2.22 (± 0.67)	354 (± 48)	7 (± 2)	1.10 (± 0.19)	331 (± 23)	14 (± 2)	0.005 (± 0.001)	345 (± 21)	18 (± 4)	0.25 (± 0.04)	129 (± 19)	9 (± 4)

*Winter–spring: First cropping season after flooding (the driest season, November–February; rice cultivar: Jasmine 85).

Spring–summer: Second cropping season after flooding (March–May; rice cultivar: OM4218).

Summer–autumn: Third cropping season after flooding (the rainy season, June–September; rice cultivar: OM4218).

**After straw-mushroom cultivation, mushroom beds were burned using farmers’ conventional practice. Mushroom beds were left on the upland for a couple of weeks to be air-dried, and then piled up and burned.

Table 4 Carbon (C) and nitrogen (N) emitted from straw-mushroom (Oryza sativa L.), cultivation. Emission rates are expressed as the amounts of C or N emitted per 1 kg oven-dried weight of straw

Straw harvested season*	Emission from mushroom beds during the cropping process		Ignition loss of mushroom beds		Total emission
	Carbon	Nitrogen	Carbon	Nitrogen	Carbon	Nitrogen
	(g C kg^−1)	(g N kg^−1)	(g C kg^−1)	(g N kg^−1)	(g C kg^−1)	(g N kg ^−1)
Winter–spring (Jasmine 25)	199	2.0	138	7.7	337	9.7
Spring–summer (OM4218)	194	0.6	157	6.1	351	6.7
Summer–autumn (OM4218)	190	0.6	149	5.9	339	6.5

*Winter–spring: First cropping season after flooding (the driest season, November–February; rice cultivar: Jasmine 85).

Spring–summer: Second cropping season after flooding (March–May; rice cultivar: OM4218).

Summer–sutumn: Third cropping season after flooding (the rainy season, June–September; rice cultivar: OM4218).

Figure 4 Dynamics of (A–C) carbon dioxide (CO₂), (D–F) methane (CH₄) and (G–I) nitrous oxide (N₂O) emitted by microbial decomposition of mushroom beds during straw-mushroom [Volvariella volvacea (Bul. ex Fr.) Singer] cultivation, which is conducted with straw harvested in (A, D, G) winter–spring, (B, E, H) spring–summer and (C, F, I) summer–autumn rice cropping seasons. Error bars show standard deviations (n = 3).

Figure 5 Greenhouse gas emissions derived from straw-use [(A) straw burning and (B) straw-mushroom [Volvariella volvacea (Bul. ex Fr.) Singer] cultivation] from different straw stack masses, and their moisture contents (moisture contents of burned mushroom beds were 16% in the winter–spring season, 17% in the spring–summer season and 22% in the summer–autumn season). Each gaseous species’ emissions factor was integrated with respect to each direct and indirect global warming potential [1.0 for carbon dioxide (CO₂), 1.9 for carbon monoxide (CO), 25 for methane (CH₄), 0.81-7.47 for non-methane volatile organic carbon (NMVOC], and 298 for N₂O; mass basis referring to IPCC 2007). Error bars illustrate the ranges of the NMVOC’s global warming potential.

Table 5 Straw production, amount of harvested straw, its use and greenhouse gas emissions from the harvested straw-use in a triple rice (Oryza sativa L.) cropping system of Tan Loi 2 hamlet, Thot not, Can Tho city, Viet nam from 2007 to 2011

	Straw production		Use of harvested straw			Greenhouse gas emission from the harvested straw-use
Rice cropping season*	Total straw production (including stumps)(t dry-straw ha-paddy^−1)	Harvested straw (except stumps)(t dry-straw ha-paddy^−1)	Burned straw with scattered on the paddy soil(t dry-straw ha-paddy^−1)	Burned haystack of straw(t dry-straw ha-paddy^−1)	Used as mushroom beds for mushroom cultivation(t dry-straw ha-paddy^−1)	Straw burning(t CO2-eq. ha-paddy^−1)	Straw-mushroom cultivation(t CO2-eq. ha-paddy^−1)
Winter–spring	7.05 ± 1.64	3.78 ± 0.88	3.78 ± 0.88	0	0	6.39 ± 1.49^a	0^d
Spring–summer	6.59 ± 1.25	3.14 ± 0.60	0.10 ± 0.03	0.58 ± 0.11	2.47 ± 0.47	1.16 ± 0.22^c	3.53 ± 0.67^b
Summer–sutumn	5.82 ± 1.67	2.32 ± 0.67	0	0.03 ± 0.01	2.30 ± 0.66	0.06 ± 0.01^d	3.11 ± 0.89^b
Annual	19.46 ± 2.66	9.24 ± 1.26	3.88 ± 0.88	0.61 ± 0.11	4.82 ± 0.81	7.60 ± 1.50	6.65 ± 1.12

*Winter–spring: First cropping season after flooding (the driest season, November–February; rice cultivar: Jasmine 85).

Spring–summer: Second cropping season after flooding (March–May; rice cultivar: OM4218).

Summer–autumn: Third cropping season after flooding (the rainy season, June–September; rice cultivar: OM4218).

The quantitative information on straw production and use of harvested straw is from Hong Van et al. (2014). Referring to Fig. 8, greenhouse gaseous emission factors (t CO_2-equivalent t dry-straw⁻¹) were calculated as 1.69 ± 0.17 for straw burning (n = 16), 1.36, 1.46 and 1.38 for straw-mushroom cultivation in the winter–spring, the spring–summer and the summer–autumn rice cropping season respectively.

Greenhouse gas emissions from the use of harvested straw are not significantly different from each other when they are marked with the same letter above the bars, based on Tukey–Kramer honestly significant difference (HSD) test (p < 0.05, n = 35).

IPCC (Intergovernmental Panel for Climate Change) 2007: Climate Change 2007: The Physical Science Basis. Cambridge University Press, Cambridge.

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Hong Van NP, Nga TT, Arai H, Hosen Y, Chiem NH, Inubushi K 2014: Rice straw management by farmers in a triple rice production system in the Mekong Delta, Vietnam. Trop. Agr. Develop., 58, 155–162.

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