Effects of coated slow-release fertilizers on nitrous oxide emission from winter wheat field in a cool-temperate region in Japan

Figures & data

Table 1. Dates of agricultural practices in the experimental field from 2018 to 2020

Treatment	Basal fertilization	Wheat seeding	Supplemental fertilization	Flowering	Harvest
1st cultivation
U	18/09/12 (40)		19/04/08 (90) 19/05/24 (60)
CU	18/09/12 (190)	18/09/13	–	ca. 19/05/30	19/07/10
CC	18/09/12 (190)		–
NN	18/09/12 (0) *		–
2nd cultivation
U	19/09/26 (40)		20/04/15 (90) 20/05/19 (60)
CU	19/09/26 (130)	19/09/27	20/05/19 (60) ^†	ca. 20/06/10	20/07/20
CC	19/09/26 (130)		20/05/19 (60) ^†
NN	19/09/26 (0) *		–

Value in parentheses shows N fertilization rate in kg N ha⁻¹. U, CU, CC, and NN are the treatments with urea, coated urea, coated calcium nitrate, and no nitrogen applications, respectively. *Only phosphate and potassium fertilizers were applied in the NN treatment. ^†Urea was applied as the supplemental fertilizer.

Figure 1. Seasonal courses of daily mean air temperature and precipitation (a), N₂O flux (b), water-filled pore space (WFPS) of the soil at depths of 0–12 cm (c), and NH₄- and NO₃-N contents of the topsoil (d, e) in the experimental field during the first wheat cultivation period in autumn of 2018 (left) and from spring to summer of 2019 (right). U, CU, CC, and NN indicate the treatments with urea, coated urea, coated calcium nitrate, and no nitrogen applications, respectively. More details of the treatments are described in Table 1. The vertical error bars of the N₂O flux and soil NH₄- and NO₃-N contents represent the standard deviations of three replicates. For better clarity of the figures, only the upper halves of the error bars are shown. Data on the WFPS are shown as the mean of all the replicate plots of the four treatments (two sites per plot: 24 sites in total), with error bars as the standard deviations of 24 replicates. For better clarity of the figures, only the upper halves of the error bars are shown. The vertical arrows with ‘BF,’ ‘SF,’ and ‘H’ represent the dates of basal and supplemental fertilizations and the wheat harvest, respectively. Note that the supplemental fertilizations were conducted only in the U treatment.

Figure 2. Seasonal courses in daily mean air temperature and precipitation (a), N₂O and NO fluxes (b, c), water-filled pore space (WFPS) of the soil at depths of 0–12 cm (d), and NH₄- and NO₃-N contents of the topsoil (e, f) in the experimental field during the second wheat cultivation period in autumn of 2019 (left) and from spring to summer of 2020 (right). U, CU, CC, and NN indicate the treatments with urea, coated urea, coated calcium nitrate, and no nitrogen applications, respectively. More details of the treatments are described in Table 1. The vertical error bars of the N₂O and NO fluxes and soil NH₄- and NO₃-N contents represent the standard deviations of three replicates. For better clarity of the figures, only the upper halves of the error bars are shown. Data on the WFPS are shown as the mean of all the replicate plots of the four treatments (two sites per plot: 24 sites in total), with error bars as the standard deviations of 24 replicates. For better clarity of the figures, only the upper halves of the error bars are shown. The vertical arrows with ‘BF,’ ‘SF,’ and ‘H’ represent the dates of basal and supplemental fertilizations and the wheat harvest, respectively. Note that the supplemental fertilization in April was conducted only in the U treatment, whereas the supplemental fertilization in May was conducted in the U, CU, and CC treatments.

Figure 3. Relationships among N₂O flux, water-filled pore space (WFPS) of the soil at depths of 0–12 cm, and daily minimum air temperature in the experimental field with wheat cultivation. The magnitude of N₂O flux is proportional to the size (area) of each circle . Data obtained from mid to late autumn after the first N₂O flux peak ended (October 2–12 November 2018 and October 21–22 November 2019) are plotted. U, CU, CC, and NN indicate the treatments with urea, coated urea, coated calcium nitrate, and no nitrogen applications, respectively. More details of the treatments are described in Table 1.

Table 2. Cumulative N₂O and NO emissions from the experimental field from 2018 to 2020

2018–2019

Treatment

Cumulative N2O emission

N2O emission in the autumn

Emission factor

(2018/09/15–11/12, 2019/03/29–08/19)

(2018/09/15–11/12)

(2018/09/15–11/12, 2019/03/29–08/19)

kg N ha^−1

kg N ha^−1

%

U

0.88

±

0.49

n.s.

0.70

±

0.52

n.s.

0.14

±

0.27

n.s.

CU

0.85

±

0.19

n.s.

0.68

±

0.12

n.s.

0.12

±

0.11

n.s.

CC

0.70

±

0.29

n.s.

0.54

±

0.20

n.s.

0.05

±

0.02

n.s.

NN

0.61

±

0.26

n.s.

0.40

±

0.15

n.s.

–

2019–2020

Treatment

Cumulative N2O emission

N2O emission in the autumn

Emission factor

(2019/09/29–11/22, 2020/03/27–08/24)

(2019/09/29–11/22)

(2019/09/29–11/22, 2020/03/27–08/24)

kg N ha^−1

kg N ha^−1

%

U

1.59

±

0.39

n.s.

1.43

±

0.35

n.s. *

0.32

±

0.33

n.s.

CU

1.43

±

0.32

n.s.

1.28

±

0.32

n.s. *

0.23

±

0.29

n.s.

CC

1.02

±

0.05

n.s.

0.78

±

0.06

n.s. *

0.02

±

0.14

n.s.

NN

0.99

±

0.29

n.s.

0.88

±

0.15

n.s. *

–

2019–2020

Treatment

Cumulative NO emission

NO emission in the autumn

Emission factor

(2019/09/29–11/22, 2020/03/27–08/24)

(2019/09/29–11/22)

(2019/09/29–11/22, 2020/03/27–08/24)

kg N ha^−1

kg N ha^−1

%

U

0.62

±

0.21

a

0.16

±

0.02

a

0.26

±

0.12

n.s.

CU

0.35

±

0.04

ab

0.12

±

0.03

a

0.12

±

0.03

n.s.

CC

0.29

±

0.03

b

0.04

±

0.01

b

0.09

±

0.00

n.s.

NN

0.12

±

0.03

b

0.04

±

0.01

b

–

Values are shown as the mean ± standard deviation of three replicates. Cumulative emission for the entire wheat cultivation period and that in the autumn are shown separately. U, CU, CC, and NN are the treatments with urea, coated urea, coated calcium nitrate, and no nitrogen applications, respectively. More details of the treatments are described in Table 1. Different letters in each panel indicate significant differences among the treatments (P < 0.05) and ‘n.s.’ indicates nonsignificant differences. *The P value was 0.07 by two-way analysis of variance. Differences among the blocks were found to be nonsignificant for all the data on the N₂O and NO emissions.

Table 3. Grain yield and nitrogen and carbon contents of the wheat in the experimental field from 2018 to 2020

2018–2019
Treatment	Grain yield				Nitrogen				Carbon
	t ha^−1				g N kg^−1				g C kg^−1
U	7.47	±	0.07	a	23.2	±	1.5	a	451.7	±	0.9	a
CU	5.41	±	0.46	b	18.7	±	1.3	b	451.4	±	0.1	a
CC	6.04	±	0.66	b	21.7	±	0.6	a	453.2	±	0.7	b
NN	3.21	±	0.21	c	15.3	±	0.5	c	448.8	±	0.7	c
2019–2020
Treatment	Grain yield				Nitrogen				Carbon
	t ha^−1				g N kg^−1				g C kg^−1
U	7.67	±	0.44	a	24.4	±	0.4	a	439.2	±	0.3	a
CU	7.15	±	0.27	a	22.6	±	1.4	b	437.8	±	1.2	ab
CC	6.87	±	0.37	a	21.6	±	0.3	b	437.6	±	0.2	ab
NN	3.50	±	0.33	b	16.6	±	0.5	c	435.6	±	1.2	b

Values are shown as the mean ± standard deviation of three replicates. U, CU, CC, and NN are the treatments with urea, coated urea, coated calcium nitrate, and no nitrogen applications, respectively. More details of the treatments are described in Table 1. Different letters in each panel indicate significant differences among the treatments (P < 0.05). Differences among the blocks were found to be nonsignificant for all the data on the wheat grain yield and carbon and nitrogen contents.

Table 4. Presence of recognizable increase in N₂O flux from soils with winter wheat cultivation in Hokkaido reported in previous and present studies

Period			Reference
BF	SM	SF
–	++	–	Koga et al. (2004)
+++	++	–	Nagata et al. (2009)
– ~ + *	– ~ ++ *	–	Koga (2013)
++, –	++, ++	++ ^†, –	Shioaku et al. (2019) ^§
+ ~ ++ *, ++	–, –	–, –	This study ^§

BF, SM, and SF are the periods after basal fertilization in autumn, around snowmelt period in the next early spring, and after supplemental fertilizations in the next spring and summer, respectively. ‘+++,’ ‘++,’ and ‘+’ indicate the approximate local maxima of N₂O flux of > 1000, 100–1000, and 30–100 µg N m⁻² h⁻¹, respectively, whereas ‘–’ indicates the absence of recognizable increases in N₂O flux. *The levels of the local maxima of N₂O flux differed among the experimental treatments. ^†The increase in N₂O flux was found only after the first supplemental fertilization immediately after the end of snowmelt. ^§The reports included field experiments two times.

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