Nitrous oxide emissions and nitrogen cycling in managed grassland in Southern Hokkaido, Japan

Figures & data

Table 1 The botanical composition of grassland (dry matter weight percentage) on the study site

	Gramineae			Leguminosae (White clover)	Broad-leaved weed
	Reed canarygrass	Meadow foxtail	Others
Fertilizer plot	77.9	14.4	7.7	0.0	0.0
Manure plot	49.8	48.7	1.2	0.0	0.4
Control plot	54.8	41.9	0.3	2.9	0.1

Figure 1 Location of the study site (a) and the layout of the experimental plots (b).

Table 2 The applied date and the application rates of chemical fertilizer and manure

Treatment	Date	Fertilizer type	Application rates (kg ha^−1)
			T-C	T-N	P2O5	K2O
Fertilizer	May 2005	Chemical fertilizer^†	0	103	23	168
	July 2005	Chemical fertilizer^†	0	61	23	97
	May 2006	Chemical fertilizer^†	0	124	50	177
	July 2006	Chemical fertilizer^†	0	59	18	97
Manure	May 2005	Manure^‡	5833	236	191	266
	July 2005	Chemical fertilizer^†	0	133	7	70
	May 2006	Manure^‡	5958	310	212	167
	May 2006	Chemical fertilizer^†	0	71	0	33
	July 2006	Chemical fertilizer^†	0	59	6	97
^†Chemical fertilizer is comprised of ammonium sulfate, ammonium phosphate, potassium sulfate and potassium magnesium sulfate. ^‡Beef cattle manure with bedding litter (bark) is applied in manure plot.

Table 3 Mineralization rates from the cattle manure

Year	Mineralization rate^† from						Estimated supply rate (kg ha^−1)
	Manure applied in 2005			Manure applied in 2006
	T-N (%)	P2O5 (%)	K2O (%)	T-N (%)	P2O5 (%)	K2O (%)	T-N	P2O5	K2O
2005	13	20	70	–	–	–	31	38	186
2006	7	10	10	13	20	70	57	62	144
^†The N mineralization rates were estimated based on the Uchida’s model (Shiga et al. 1985), which was developed in Japan and were 13.2% and 7.0% in the first and second years after application, respectively. The P and K mineralization rates from the manure were estimated based on the handbook of animal waste management and utilization in Hokkaido 2004 (Hokkaido Prefectural Experiment Stations and Hokkaido Animal Research Center 2004).

Figure 2 Seasonal variations in meteorological variables and the N2O and NO flux; Daily precipitation and daily maximum snow depth (a), soil temperature at a 5-cm depth (b), water-filled pore space (WFPS) (c), N2O flux (d) and NO flux (e). Data of soil temperature, WFPS, N2O flux and NO flux represent means ± standard deviation (SD) (n = 6). The arrows indicate the timing of fertilizer or manure application.

Table 4 N deposition, gross N mineralization of soil (GMs), root-litter (GMl) and manure (GMm), and mineral N pool during each growing season (G1, G2 and G3) and non-growing season (NG) (kg N ha−1 period−1)

	2005				2006				2005	2006
	G1	G2	G3	NG	G1	G2	G3	NG
N deposition	12	2	1	1	1	1	2	1	15	4
Gross N mineralization of soil
Fertilizer plot	60	115	155	37	62	122	115	32	367	331
Manure plot	62	115	155	36	59	129	116	32	369	336
Control plot	64	120	161	37	61	132	121	34	382	348
Bare plot	67	132	150	34	67	153	104	31	384	356
Gross N mineralization of root-litter
Fertilizer plot	88	44	0	13	104	10	0	13	145	126
Manure plot	103	51	0	11	101	11	0	10	165	122
Control plot	68	27	0	13	75	6	0	13	108	94
Gross N mineralization of manure	13	30	39	6	13	43	34	6	88	96
G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season.

Table 5 N uptake in aboveground biomass during each growing season (G1, G2 and G3) and non-growing season (NG) (kg N ha−1 period−1)

	2005				2006				2005	2006
	G1	G2	G3	NG	G1	G2	G3	NG
Fertilizer plot	138	94	20	−2	137	70	22	−9	249	219
Manure plot	57	133	36	−10	122	52	30	−3	215	201
Control plot	42	55	24	−11	85	41	10	−1	109	134
G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season.

Figure 3 The relationship between N2O fluxes and the N2O-N/NO-N rate.

Table 6 The cumulative N2O flux during each growing season (G1, G2 and G3) and non-growing season (NG) (kg N ha−1 period−1)

	2005				2006				2005	2006
	G1	G2	G3	NG	G1	G2	G3	NG
Fertilizer plot	0.2 (0.1)	1.8 (0.4)	0.8 (0.3)	0.1 (0.0)	1.0 (1.0)	1.3 (0.5)	0.6 (0.3)	0.2 (0.1)	2.8 (0.7)	3.0 (0.8)
Manure plot	0.5 (0.3)	1.9 (0.9)	1.2 (0.7)	0.0 (0.0)	2.5 (2.1)	1.9 (1.6)	0.5 (0.3)	0.1 (0.1)	3.6 (1.3)	4.9 (3.0)
Control plot	0.1 (0.0)	0.2 (0.1)	0.3 (0.4)	0.0 (0.0)	0.1 (0.1)	0.3 (0.3)	0.2 (0.1)	0.1 (0.1)	0.7 (0.5)	0.6 (0.3)
Bare plot	0.2 (0.1)	1.4 (0.8)	2.5 (2.9)	0.1 (0.0)	0.8 (0.6)	1.4 (1.8)	0.7 (0.6)	0.4 (0.5)	4.2 (3.3)	3.3 (2.1)
Data represent means ± (uncertainties/100 × means). G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season.

Figure 4 The cumulative N2O flux for each seasons (G1, G2, G3 and non-growing season [NG]) compared with the cumulative CO2 flux. G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season. Data of the cumulative N2O flux represent means ± (uncertainties/100 × means). The cumulative CO2 flux was referred to Shimizu et al. (2009).

Figure 5 N uptake in aboveground biomass during each growing season (G1, G2, G3) compared with the external mineral N supply (a) and total mineral N supply (b). The external N supply is composed of N deposition, chemical fertilizer application and the gross N mineralization of applied manure. The total mineral N supply is composed of the external N supply, gross N mineralization of soil and gross mineralization of root-litter. G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season. The data of N uptake in aboveground biomass represent means ± (uncertainties/100 × means). The dashed-line indicates a regression model for all values, N uptake in aboveground biomass = 0.58 × total mineral N supply – 47; R2 = 0.68; P < 0.01.

Figure 6 The cumulative N2O flux for each season (G1, G2, G3 and non-growing season [NG]) compared with the total mineral N supply (a) and the mineral N surplus (b). The total mineral N supply is composed of the external N supply (N deposition, chemical fertilizer application and gross N mineralization of applied manure), gross N mineralization of soil and gross mineralization of root-litter. The mineral N surplus was estimated as the difference between the mineral N pool and N uptake in aboveground biomass. G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season. The data of cumulative N2O flux represent means ± (uncertainties/100 × means). The regression model shown in Fig. 6a is for all values, Cumulative N2O flux = 0.0059 × (total mineral N supply) – 0.103; R2 = 0.37; P < 0.01. The regression model shown in Figure 6b is for all values, Cumulative N2O flux = 0.0120 × (mineral N surplus) – 0.537; R2 = 0.50; P < 0.01.

Figure 7 The N2O emission factor to mineral N surplus for each season (G1, G2, G3 and non-growing season [NG]) compared with mean precipitation. The mineral N surplus was estimated as the difference between the mineral N pool and N uptake in aboveground biomass. G1 is the period from the beginning of the growing season to the first crop harvest, G2 is the period from the first harvest to the second harvest and G3 is the period from the second harvest to the end of the growing season. The data of N2O emission factor to mineral N surplus represent means ± (uncertainties/100 × means). The regression line is for all values, Cumulative N2O/mineral N surplus × 100 = 0.195 × mean precipitation – 0.055; R2 = 0.21; P < 0.01.

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