Impacts of alternate wetting and drying on greenhouse gas emission from paddy field in Central Vietnam

Figures & data

Table 1. Soil properties of the experimental site.

Property
pH (H2O)	4.18
Total carbon (%)	1.92
Total N (%)	0.19
Total P2O5 (%)	0.013
Total K2O (%)	0.40
Available P2O5 (mg 100 g^−1)	3.50
Available K2O (mg 100 g^−1)	2.40
Texture	Loam
Clay (%)	17.8
Sand (%)	49.3
Silt (%)	32.9
Bulk density (g cm^−3)	1.01
Active Fe (%)	1.23
Active Mn (%)	0.0027

Table 2. Rice cropping calendar in the winter–spring (WS) and summer–autumn (SA) seasons.

Season	WS1	SA1	WS2	SA2	WS3	SA3
Plowing	−22 DAS	−13 DAS	−22 DAS	−7 DAS	−10 DAS	−8 DAS
Sowing	0 DAS (16 January 2014)	0 DAS (28 May 2014)	0 DAS (20 January 2015)	0 DAS (26 May 2015)	0 DAS (20 January 2016)	0 DAS (9 June 2016)
Organic fertilizer	0 DAS	0 DAS	0 DAS	0 DAS	0 DAS	0 DAS
First chemical fertilizer	0 DAS (18.4–72–0)^a	0 DAS (18.4–72–0)	0 DAS (18.4–72–0)	0 DAS (18.5–72–0)	0 DAS (18.4–72–0)	0 DAS (18.5–72–0)
Herbicide	2 DAS	1 DAS	1 DAS	2 DAS	2 DAS	2 DAS
Second chemical fertilizer	21 DAS (55.2–0–28)	19 DAS (59–0–36)	14 DAS (46–0–36)	21 DAS (46–0–36.6)	26 DAS (46–0–33.6)	27 DAS (46–0–36.5)
Third chemical fertilizer	43 DAS (27.6–0–33.6)	42 DAS (41.4–0–42)	49 DAS (32.2–0–42)	50 DAS (27.4–0–39.2)	56 DAS (34–0–40)	42 DAS (28–0–40)
Total N applied (kg ha^−1)	101	119	97	92	98	92
Harvest	114 DAS (10 May 2014)	96 DAS (1 September 2014)	104 DAS (4 May 2015)	96 DAS (30 August 2015)	120 DAS (19 May 2016)	91 DAS (8 September 2016)

DAS: days after sowing.

^aIn parentheses for chemical fertilizer, the application rates of urea (kg N ha⁻¹), super phosphate (kg P₂O₅ ha⁻¹), and potassium chloride (kg K₂O ha⁻¹).

Table 3. Seasonal CH₄ and N₂O emissions, GWP, rice grain yield, yield-scaled GWP, total water use, and water productivity as affected by cropping season and water management.

			CH4 (kg CH4 ha^−1)		N2O (kg N2O ha^−1)		GWP (kg CO2 ha^−1)		Grain yield (Mg ha^−1)		Yield-scaled GWP (Mg CO2 Mg^−1 grain)		Water use (m^3 ha^−1)		Water productivity (kg grain m^−3)
Treatment			WS	SA	WS	SA	WS	SA	WS	SA	WS	SA	WS	SA	WS	SA
CF			500	644	0.281	0.698	17,030	23,540	4.41	4.44	3.49	4.89	8127	8394	0.556	0.540
AWD			351	491	0.208	0.574	11,867	18,186	4.89	4.67	2.37	3.83	6936	7133	0.727	0.687
AWDS			353	490	0.206	0.455	11,704	17,227	4.84	4.60	2.27	3.81	6984	7147	0.721	0.671
Season mean			401	542	0.232	0.576	13,534	19,651	4.71	4.57	2.71	4.18	7349	7558	0.668	0.632
			Treatment mean
CF			572a		0.489a		20,285a		4.42a		4.19a		8260a		0.548b
AWD			421b		0.391a		15,026b		4.78a		3.10b		7035b		0.706a
AWDS			421b		0.330a		14,466b		4.72a		3.04b		7066b		0.694a
			p-Value
Source of variation	df1	df2^c
CS	5	3	***		*		***		***		***		***		***
WS or SA (WS–SA)^a	1	1	^†		**		^†		^†		^†		*		*
WS^a	2	1	0.229		^†		*		***		0.344		***		***
SA^a	2	1	***		0.265		***		***		***		***		***
Main plot error	10	6
T	2	2	**		0.812		**		0.114		*		***		***
T × CS	10	6	0.900		0.994		0.763		0.287		0.772		0.108		^†
T × WS–SA^b	2	2	0.925		0.986		0.940		0.708		0.934		0.852		0.792
T × WS^b	4	2	0.646		0.745		0.387		0.142		0.575		0.214		*
T × SA^b	4	2	0.723		0.983		0.571		0.354		0.399		*		0.152
Split-plot error	24	16

Different lower characters indicate significant treatment differences.

CS: cropping season; WS: winter–spring; SA: summer–autumn; T: treatment; AWD: alternate wetting and drying; CF: continuous flooding; AWDS: site-specific AWD.

^aSub-division of variation among cropping seasons.

^bSub-division of variation among T × CS interactions.

^cdf for N₂O, GWP, and yield-scaled GWP in which WS3 and SA3 were not included in the analyses.

^†p < 0.10; *p < 0.05; **p < 0.01; ***p < 0.001.

Figure 1. Seasonal variations in daily rainfall (A, B, C), daily maximum and minimum air temperature (D, E, F), mean surface water level (G, H, I), CH₄ flux (J, K, L), and N₂O flux (M, N, O) for three water management practices in the first, second, and third winter–spring seasons (WS). Error bars for CH₄ and N₂O fluxes indicate the standard error (n = 3). Vertical dotted lines indicate the application timing of nitrogen fertilizer.

Figure 2. Seasonal variations in daily rainfall (A, B, C), daily maximum and minimum air temperature (D, E, F), mean surface water level (G, H, I), CH₄ flux (J, K, L), and N₂O flux (M, N, O) for three water management practices in the first, second, and third summer–autumn seasons (SA). Error bars for CH₄ and N₂O fluxes indicate the standard error (n = 3). Vertical dotted lines indicate the application timing of nitrogen fertilizer.