Effect of crop residue C:N ratio on N₂O emissions from Gray Lowland soil in Mikasa, Hokkaido, Japan

Figures & data

Table 1 Chemical properties of the soil horizons

Horizon	Depth (cm)	pH (H2O)	CEC cmolc kg^−1	Sand (%)	Silt (%)	Clay (%)	C (g kg^−1)	N (g kg^−1)	C:N
Ap1	0–10	5.8	25.5	12.1	51.2	36.7	32.1	2.80	11.5
Ap2	10–33	5.2	24.6	11.3	50.9	37.8	35.1	2.80	12.7
Bg	33–64	4.4	27.1	2.90	47.9	49.2	49.1	3.10	16.0
C	64–100	4.7	33.1	6.10	56.3	37.6	76.6	4.40	17.4
Cation exchange capacity (CEC).

Table 2 Quantities of nitrogen and carbon applied in crop residues in each treatment

Treatment (plot name)	N (%)	C (%)	C:N	N application (g m^−2)	C application (g m^−2)
Onion leaf	3.39	39.3	11.6	9.30	108
Soybean stem & leaf	2.98	43.3	14.5	11.6	168
Rice straw	0.63	39.2	62.3	1.76	110
Wheat straw	0.37	40.5	110	1.28	141
No residue	0	0	–	0	0

Figure 1  Outline of the chamber and base used in the closed chamber method.

Figure 2  Variations in (a) N2O flux, (b) CO2 flux, (c) soil temperature, (d) water-filled pore space (WFPS), (e) soil -N, (f) -N, (g) water-soluble organic carbon (WSOC) and (h) NO flux from plots treated with onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS), wheat straw (WS) or no residue (NR). SD, standard deviation.

Figure 3  Relationships between N2O and CO2 fluxes from plots treated with (a) onion leaf (OL) and soybean stem and leaf (SSL) and (b) rice straw (RS), wheat straw (WS) or no residue (NR).

Figure 4  Relationships between N2O (a–e) and CO2 (f–j) fluxes and soil temperature at 5 cm (a,f), water-filled pore space (WFPS) (b,g), soil -N (c,h), -N (d,i) and water-soluble organic carbon (WSOC) (e,j) in plots treated with onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS), wheat straw (WS) or no residue (NR).

Table 3 Measured N2O and CO2 emissions, and estimated EF_N2O and EF_CO2 in five treatments

Treatment (plot name)	N2O emission (mg N m^−2)		CO2 emission (g C m^−2)		EFN2O (%)	EFCO2 (%)
	Mean	SD	Mean	SD
Onion leaf	84.5 a	28.8	98.0 a	10.6	0.86	45.4
Soybean straw & leaf	89.1 a	12.6	93.6 a	3.59	0.73	26.6
Rice straw	0.91 b	1.47	42.7 b	5.38	−0.18	−5.77
Wheat straw	−1.44 b	1.02	56.2 b	10.5	−0.43	5.08
No residue	4.11 b	2.17	49.0 b	3.87
Different letters indicate significant differences (P < 0.01). SD, standard deviation.

Figure 5  Relationships between N2O flux and N2O-N/NO-N in plots treated with onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS), wheat straw (WS) and no residue (NR).

Figure 6  Relationships between (a) and (b) and crop residue C:N ratio.