Estimation of global warming potential from upland cropping systems in central Hokkaido, Japan

Figures & data

Figure 1  Seasonal variations in (a) weather conditions, and fluxes of (b) N2O and (c) CH4 from cultivated soils at the study sites. Error bars indicate the standard deviation (n = 3).

Table 1 Basic characteristics of the topsoil (0–20 cm) at the study sites

Site	A	B	C	D	E	F	G
Land use	Grass	Wheat	Maize	Wheat	Onion	Wheat	Soybean
Soil type	BF	GL	BL	BF	BL	BL	BL
pH (H2O)	5.42	5.08	5.76	5.32	5.30	5.94	5.73
Total C (g kg^−1)	17.2	19.8	24.1	16.2	37.4	26.2	16.0
Total N (g kg^−1)	1.36	1.82	2.20	1.34	1.80	2.15	1.54
CEC (cmol c kg^−1)^†	17.2	28.5	26.1	19.7	21.8	27.9	24.1
Texture	CL	LiC	CL	CL	CL	CL	CL
^†Ammonium acetate method. BF, brown forest soils; BL, brown lowland soils; CL, Clay Loam; GL, gray lowland soils; LiC, Light Clay.

Table 2 Mean† and cumulative‡ fluxes of N2O and CH4 from different cultivated soils

Site	N2O flux			CH4 flux
	Mean (µg N m^−2 h^−1)	Cumulative (g N m^−2)	% of fertilized N	Mean (µg C m^−2 h^−1)	Cumulative(g C m^−2)
A	2.84a	0.02	0.63	−16.9a	–0.08
B	11.4ab	0.09	1.96	−1.88cd	−0.01
C	22.1ab	0.16	0.79	−4.32c	−0.02
D	119c	0.62	4.44	−11.1b	−0.07
E	59.3b	0.29	1.3	−1.47cd	−0.01
F	7.70a	0.04	0.35	−3.48cd	−0.02
G	15.6ab	0.07	1.94	0.34d	0
^†The mean fluxes of a gas followed by different letters are significantly different using Tukey's test (P < 0.05).
‡The cumulative number of days is 209 for Site G and 269 for the other sites.

Table 3 Net primary production (NPP), amount of carbon in harvested products, microbial respiration (Rm) and soil carbon sequestration during the study period for different cropping systems

Site	NPP (g C m^−2)	Carbon in harvested products (g C m^−2)	Rm(g C m^−2)	Carbon sequestration(g C m^−2)
A	218	151	301	−235
B	252	117	328	−193
C	180	62	346	−227
D	294	136	568	−410
E	349	305	393	−348
F	454	210	498	−255
G	304	126	464	−287
Negative values of carbon sequestration indicate net CO2 emission from soils.

Table 4 Global warming potential (GWP) for the different cropping systems based on soil carbon sequestration and trace gas fluxes

Site	CO2 ^†	N2O	CH4	Net GWP
A	862 (99.21)	9.30 (1.07)	−2.45 (−0.28)	869
B	708 (94.45)	41.9 (5.59)	−0.31 (−0.04)	749
C	832 (91.86)	74.4 (8.21)	−0.61 (−0.07)	906
D	1,503 (84.01)	288 (16.11)	−2.15 (−0.12)	1,790
E	1,276 (90.46)	135 (9.56)	−0.31 (−0.02)	1,411
F	935 (98.11)	18.6 (1.95)	−0.60 (−0.06)	953
G	1,052 (97.00)	32.6 (3.00)	0 (0)	1,085
^†Soil net CO2 emissions are equivalent to the negative values of soil carbon sequestration. Units are CO2 equivalents (g m^−2) based on IPCC (2001) conversion factors. The values in parentheses indicate the contribution percentage to the net GWP. Negative values indicate mitigation of global warming potential.

IPCC . 2001 . “ Climate Change 2001Synthesis Report: Summary for policymakers ” . http://www.ipcc.ch

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