Effects of environmental factors on temporal variation in annual carbon dioxide and nitrous oxide emissions from an unfertilized bare field on Gray Lowland soil in Mikasa, Hokkaido, Japan

Figures & data

Figure 1 Seasonal variations in (a,b) monthly precipitation and (c,d) mean monthly air temperature.

Figure 2 Seasonal variations in (a) CO2, (b) N2O and (c) NO fluxes in 2000, 2002 and 2003. Arrows indicate the timing of plowing. sd, standard deviation.

Figure 3 Seasonal variations in (a) CO2, (b) N2O and (c) NO fluxes from 2004 to 2007. Arrows indicate the timing of plowing. sd, standard deviation.

Figure 4 Seasonal variations in (a,f) soil temperature, (b,g) water-filled pore space (WFPS), (c,h,i) soil NH4+-N, (d,j) NO3−-N and (e,k) water-soluble organic carbon (WSOC) concentrations.

Table 1 Correlation coefficients for the relationships between CO2 or N2O fluxes and soil physical and chemical properties

Year	Soil temperature† (°C)		WFPS (%)		NH4 ^+-N (H2O) (mg N kg^−1)		NH4 ^+-N (KCl) (mg N kg^−1)		NO3 ^−-N (mg N kg^−1)		WSOC mg N kg^−1		CO2 flux mg C m^−2  h^−1
	n	R	n	R	n	R	n	R	n	R	n	R	n	R
CO2 flux (mg C m^−2 h^−1)
2000	19	0.54*	19	−0.17	19	−0.25	ND	ND	19	0.56*	ND	ND	–	–
2002	51	0.37*	43	0.09	33	−0.47**	ND	ND	33	0.08	33	0.06	–	–
2003	34	0.68**	30	−0.51**	13	0.56*	ND	ND	13	0.66*	13	−0.27	–	–
2004	26	0.68**	24	−0.34	18	−0.35	ND	ND	18	0.71**	18	−0.08	–	–
2005	24	0.35	24	0.09	24	−0.37	ND	ND	24	0.33	22	0.37	–	–
2006	27	0.31	29	0.22	29	−0.05	29	0.15	28	0.10	29	0.13	–	–
2007	25	0.13	21	−0.11	ND	ND	21	−0.22	22	0.12	22	−0.60*	–	–
N2O flux (mg N m^−2 h^−1)
2000	22	0.54**	19	−0.19	22	−0.23	ND	ND	22	0.68**	ND	ND	23	0.59**
2002	51	0.26	43	−0.11	33	−0.30	ND	ND	33	0.04	33	0.08	60	0.74**
2003	34	0.25	30	−0.42*	13	0.52	ND	ND	13	0.36	13	−0.34	39	0.51**
2004	26	0.50**	24	−0.32	18	−0.36	ND	ND	18	0.78**	18	0.03	29	0.71**
2005	24	0.19	24	0.28	24	−0.28	ND	ND	24	0.14	22	0.49*	28	0.79**
2006	28	0.21	29	0.09	29	−0.01	29	0.10	28	0.23	29	−0.10	32	0.55**
2007	24	−0.11	21	0.23	ND	ND	21	−0.20	22	−0.37	22	−0.37	25	0.27
*P < 0.05, **P < 0.01; ND, no significant difference; †Exponential curve regression analysis between CO2 flux and soil temperature. WFPS, water-filled pore space.

Figure 5 Relationships between (a) CO2 or (b) N2O fluxes and water-filled pore space (WFPS).

Figure 6 Relationship between N2O flux and the N2O-N:NO-N ratio.

Table 2 Annual CO2 and N2O emissions from unfertilized bare soil in an onion field in Mikasa

Year	Annual precipitation (mm year^−1)	Mean annual air temperature (°C)	Period day	CO2 emission (Mg C ha^−1 year^−1)	Uncer-tainty (%)	Q10	N2O emission (kg N ha^−1 year^−1	Unvcer- tainty (%)
2000	1576	7.7	302	3.32^a	14.2	2.38	4.60^bc	18.8
2002	1187	7.7	251	2.42^abc	16.9	2.03	3.94^bc	23.6
2003	986	7.4	318	2.04^c	20.7	1.80	2.01^c	74.0
2004	1294	8.4	280	2.48^bc	13.2	1.73	7.34^b	15.0
2005	1398	7.5	297	2.95^ab	21.2	1.53	12.1^a	19.0
2006	1124	7.8	271	2.25^bc	22.8	1.38	1.62^c	106
2007	1015	8.2	256	2.20^bc	58.9	1.11	2.56^c	153
Average	1226	7.81	282	2.53	24.0	1.71	4.88	58.5
Values within the same column with different lowercase letters differ significantly (P < 0.05). Q10, relative increase in CO2 flux for a 10°C change in soil temperature.

Figure 7 Relationship between CO2 emission and annual precipitation.

Figure 8 Relationship between the slope of the monthly CO2 emission against mean monthly temperature and precipitation from April to October.

Figure 9 Relationship between monthly CO2 emission and N2O emission from April to October.