Relationships between methane emissions and soil microorganisms in a double-rice field in southern subtropical China

Figures & data

Figure 1. Location of the long-term greenhouse gas monitoring site in Hunan province.

Figure 2. Daily air temperature and precipitation of the experimental site in the rice-growing season of 2008–2009.

Table 1. Design of the field experiment (kg ha^{- 1}).

	N (Urea)		P2O5		K2O		Controlled-release urea		High stubble^3		Rice straw^3		Irrigation	Tillage
E^1	L^2	E	L	E	L	E	L	E	L	E	L
CWS, conventional tillage + without straw residues + urea	150	180	90	45	90	112.5							MSD^4	CT^6
NWS, no tillage + without straw residues + urea	150	180	90	45	90	112.5							MSD	NT^7
SCU, conventional tillage + without straw residues + controlled-release urea			90	45	90	112.5	441	529					MSD	CT
HN, high stubbles + no tillage + urea	97.8	127.8	76.05	31.2	32.55	54.9			4500	4500			MSD	NT
HC, high stubbles + conventional tillage + urea	97.8	127.8	76.05	31.2	32.55	54.9			4500	4500			MSD	CT
SN, straw cover + no tillage + urea	97.8	127.8	76.05	31.2	32.55	54.9					4500	4500	MSD	NT
SNF, straw cover + no tillage + urea + continuous flooding	97.8	127.8	76.05	31.2	32.55	54.9					4500	4500	CF^5	NT
Note: ^1E represents early rice, ^2L represents late rice. ^3By the nutrient content (N,P,K) of rice straw, we use the same amount of pure straw (equivalent). ^4MSD represents the mid-season drainage, ^5CF represents continuous flooding. ^6CT represents conventional tillage and ^7NT represents no-till.

Figure 3. Schematic diagram of the static chamber.

Figure 4. Effect of different field practices on methane flux (MF) and total activities of soil microbes (TASM) and the populations of methanogens (PMET) from double-rice paddy. The definition of each practice is demonstrated in Table 1. The data are the average daily observed value of MF, TASM, and PMET during the two years.

Table 2. Results of the two-way ANOVA.

		SS	df	MS	F	P-value	F crit	Significance
Methane flux	Date	7330.25	5	1466.05	3.77	0.00353	2.3	0.01
	Treatment	82863.33	21	3945.87	10.14	6.25E-17	1.66	0.001
	Error	40845.43	105	389
	Total	131039	131
TASM	Date	0.19	5	0.04	2.79	0.020851	2.3	0.05
	Treatment	13.03	21	0.62	46.47	1.26E-43	1.66	0.001
	Error	1.4	105	0.01
	Total	14.62	131
PMET	Date	375.28	5	75.06	2.33	0.047512	2.3	0.05
	Treatment	3781.02	21	180.05	5.59	1.01E-09	1.66	0.001
	Error	3382.68	105	32.22
	Total	7538.97	131

Figure 5. Correlation coefficient matrix of methane flux (MF) and total activities of soil microbes (TASM) and the populations of methanogens (PMET) under the effect of different field practices. (A) MF with TASM and (B) MF with PMET. The definition of each practice is demonstrated in Table 1. The data for the correlation analysis of MF, TASM, and PMET are the observed daily values of each practice during the two years.

Table 3. Results of monadic and multivariate regression analyses.

	Regression model	R-squared	P-value	Significance
MSD	MF = −27.69 × T + 38.21 × T^2	0.39	0.00283	**
	MF = −1.9895 × 10^−4 × P + 0.4129 × 10^−8 × P^2	0.82	1.25E-08	***
	MF = −10.53 − 69.49 × T + 32.03 × exp(T)−5.27 × 10^−4 × P + 0.57 × 10^−8 × P^2	0.80	1.36E-06	***
SNF	MF = 28.12 × T + 0.4451 × T^2	0.44	0.001093	**
	MF = 5.0202 × 10^−4 × P−0.04621 × 10^−8 × P^2	0.87	5.03E-10	***
	MF = 65.81 × T − 22.07 × exp(T) + 4.29 × 10^−4 × P− (2.011E-18) × exp(P × 10^−4)	0.88	6.32E-09	***
General	MF =−35.32 + 19.1 × exp(T)	0.31	0.004311	**
	MF = 5.24 − 2.65 × 10^−4 × P + 0.41 × 10^−8  × P^2	0.97	1.61E-15	***
	MF = 2.048 × exp(T)− 2.5724  ×  10^−4 × P + 0.3973 × 10^−8 × P^2	0.98	5.91E-16	***
Note: MSD represents the mid-season drainage, SNF represents the continuous flooding, MF represents methane flux, T represents the total activities of soil microbes (TASM), and P represents the populations of methanogens (PMET). Significance: **significant at 0.01 level and ***significant at 0.001 level.