Effect of the long-term application of organic matter on soil carbon accumulation and GHG emissions from a rice paddy field in a cool-temperate region, Japan. -I. Comparison of rice straw and rice straw compost -

Figures & data

Table 1. Main soil physicochemical properties of the studied fields (0–15 cm, April 2010).

Field	Treatment	Bulk density (Mg m^−3)	pH (H2O)	Total-C (g kg^−1)	Total-N (g kg^−1)	C/N ratio	CEC (cmolC kg^−1)	Free ferric iron^†,‡ (g Fe kg^−1)
Initial application^§	-	0.882	5.36	22.1	2.09	10.6	25.9	15.7
Continuous application	No application	0.907	5.47	26.3	2.52	10.4	25.3
	Rice straw	0.878	5.33	29.9	2.87	10.4	23.5
	Rice straw compost	0.840	5.43	36.2	3.59	10.1	25.2

^†Determined by the Na₂S₂O₄–ethylenediamine-tetraacetic acid (EDTA) method as described by Shiratori et al. (2007). ^‡Measured value from an adjacent field. ^§Averaged value of three fields. The three fields had a similar history of cultivation management before the beginning of this study, and the field condition was similar. C, carbon; CEC, cation exchange capacity; N, nitrogen.

Table 2. Monthly air temperature and precipitation during the rice growing seasons.

	Air temperature (°C)						Precipitation (mm)
Year	May	Jun.	Jul.	Aug.	Sep.	Growing season^†	May	Jun.	Jul.	Aug.	Sep.	Growing season^†
2010	15.8	21.3	26.2	28.7	23.3	23.1	110	162	118	17	286	692
2011	16.7	21.5	26.5	26.6	22.8	22.8	183	239	184	153	315	1073
2012	16.4	20.5	25.6	27.8	24.5	23.0	67	58	177	73	247	620
30-year average^‡	16.6	20.6	24.6	26.3	22.0	22.0	96	145	211	150	206	808

^†Average for the air temperature and the total for precipitation. ^‡1981–2010.

Table 3. Date of cultivation management.

	2010		2011		2012
Practice	Initial	Continuous	Initial	Continuous	Initial	Continuous	Remarks
Compost application	20-Apr	16-Apr	14-Apr	14-Apr	16-Apr	16-Apr	1.5 kg m^−2
Basal fertilizer application	20-Apr	20-Apr	21-Apr	21-Apr	19-Apr	19-Apr	4-7-7 g m^−2 （N-P2O5-K2O）
Plowing	20-Apr	20-Apr	22-Apr	22-Apr	23-Apr	23-Apr
Submerging	20-Apr	20-Apr	22-Apr	22-Apr	24-Apr	24-Apr
Paddling	13-May	7-May	10-May	6-May	9-May	8-May
Transplantation	19-May	14-May	17-May	13-May	15-May	15-May
Start of mid-season drainage	18-Jun	29-Jun	21-Jun	21-Jun	22-Jun	22-Jun
Grooving	23-Jun	2-Jul	30-Jun	30-Jun	27-Jun	27-Jun
End of mid-season drainage	20-Jul	20-Jul	14-Jul	14-Jul	13-Jul	13-Jul	Afterwards, intermittent irrigation (saturated irrigation)
Fertilizer top-dressing	26-Jul	22-Jul	19-Jul	19-Jul	20-Jul	20-Jul	1.5-0-0 g m^−2 （N-P2O5-K2O）
Final drainage	1-Sep	1-Sep	30-Aug	30-Aug	3-Sep	3-Sep
Harvesting	16-Sep	16-Sep	14-Sep	14-Sep	14-Sep	14-Sep	Scattering rice straw (600 g m^−2) to the rice straw application plots after harvesting

Table 4. Physicochemical properties of rice straw and rice straw compost and estimated yield of rice straw compost production (3-year average).

		Rice straw	Rice straw compost
Moisture content (%)		42.1	69.7
Total C content (%)^†,‡		41.3	28.4
Total N content (%)^†,‡		0.56	2.15
C/N ratio^†,‡		74.0	13.2
SiO2 content (%)^†,§		11.4	36.3
Yield (%)^¶	Fresh weight basis	-	60
	Dry weight basis	-	31

^†Dry weight basis. ^‡N/C analyzer. ^§Gravimetric method after HNO₃-HClO₄ digestion. ^¶Estimated by assuming the amount of SiO₂ in rice straw was not lost throughout the compost production process. C, carbon; N, nitrogen; SiO₂, silicate.

Figure 1. Layout of the study fields. NA, no application; RS, rice straw, and SC, rice straw compost.

Table 5. Soil carbon (C) sequestration rate in the initial application field.

			Soil C sequestration rate by the organic matter application^‡
Treatment	Layer thickness (cm)	Bulk density^† (Mg m^–3)	(g C kg^–1 y^–1)	(kg C ha^–1 y^–1)
No application	15	0.882	-	-
Rice straw	15	0.882	0.368	487
Rice straw compost	15	0.882	0.906	1199

^†Mean value of three treatments. ^‡Estimated from regression lines during April 2010 and October 2012 in Fig. 2.

Table 6. Soil carbon (C) sequestration rate in the continuous application field.

Treatment	Application year^† (y)	Bulk density^‡ (Mg m^−3)	Layer thickness^§ (cm)	T-C^‡ (g kg^−1)	Soil C storage (Mg C ha^−1)	Soil C sequestration rate by the organic matter application^¶ (kg C ha^−1 y^−1)
No application	51	0.907	15.0	26.3	35.8	-
Rice straw	32	0.878	15.5	29.9	40.7	152
Rice straw compost	39	0.840	16.2	36.2	49.2	343

T-C, total carbon. ^†Application year before starting the experiment (2010). ^‡Measured in April 2010. ^§Calculated based on a soil mass basis to make that the dry soil mass of the rice straw and rice straw compost plots were equal to that of the no application plot (0−15 cm). ^¶Estimated by the following equation: (Soil C storage in the rice straw plot [or the rice straw compost plot] – Soil C storage in the no application plot)/application year/1000 (Fig. S1).

Figure 2. Changes in the total carbon (T-C) content of the surface soil in the initial application field.

Table 7. Averaged grain yield over three years.

	Grain yield (brown rice, g m^−2)
Treatment	Initial	Continuous
No application	511 ± 19 a	491 ± 14 a
Rice straw	498 ± 27 a	502 ± 48 a
Rice straw compost	544 ± 24 b	602 ± 31 b

Values represent the mean ± standard error for three years, and values within a column followed by different letters differ significantly among the treatments (Two-way ANOVA [year and treatment] followed by Tukey’s HSD test (p < 0.10, n = 3).

Figure 3. Seasonal variations in the soil Eh at the 5 cm depth (a), CH₄ flux (b) and N₂O (c). Bars for the CH₄ and N₂O fluxes indicate standard errors. C, continuous application; I, initial application; NA, no application; RS, rice straw; SC, rice straw compost. FD, final drainage; H, harvesting; MD, mid-season drainage; T, transplanting.

Table 8. Cumulative methane (CH₄) and nitrous oxide (N₂O) emissions for three years.

		CH4 emissions (kg C ha^−1)		N2O emissions (g N ha^−1)
Year	Treatment	Initial^†	Continuous	Initial^†	Continuous
2010	No application	135 a	200	20.9 a	84.0
	Rice straw	342 b	282	46.8 a	80.6
	Rice straw compost	165 a	267	108 a	346
2011	No application	233 a	353	−102 a	47.0
	Rice straw	305 a	462	−53.2 a	−50.5
	Rice straw compost	268 a	352	−12.3 a	−105
2012	No application	174 a	364	−176 a	183
	Rice straw	200 a	498	18.3 ab	77.5
	Rice straw compost	185 a	420	89.6 b	−41.8
Average^‡	No application	181 ± 28 a	306 ± 53 a	−85.7 ± 57.4 a	105 ± 40.5 a
	Rice straw	253 ± 53 b^§	414 ± 67 b	4.0 ± 29.7 ab	35.9 ± 43.2 a
	Rice straw compost	206 ± 31 a	347 ± 44 a	61.8 ± 37.4 b	66.3 ± 140.8 a

Positive values indicate net emissions to the atmosphere, and negative values indicate net uptake from the atmosphere.

^†Values within a column followed by the different letters differ significantly among the treatments for each year (Tukey’s HSD test [p < 0.10, n = 3]). ^‡Values represent the mean ± standard error for three years, and the values within a column followed by different letters differ significantly among the treatments (Two-way ANOVA [year and treatment] followed by Tukey’s HSD test (p < 0.10, n = 3). ^§CH₄ emissions in 2010 were excluded from the average due to high emissions caused by the rice straw application in the spring (see text in 3.3 CH₄ and N₂O emissions).

Table 9. Changes in net greenhouse gas (GHG) balance due to the application of organic matter.

		Initial			Continuous
		NA	RS	SC	NA	RS	SC
Application year		3	3	3	51^†	32^†	39^†
CH4 emission^‡,§ (A)	(Mg CO2-eq ha^–1 y^–1)	8.21	11.47	9.34	13.87	18.77	15.73
N2O emission^‡,§ (B)		−0.04	0.00	0.03	0.05	0.02	0.03
Soil carbon sequestration rate by the organic matter application (C)		-	1.79	4.40	-^¶	0.56^¶	1.26^¶
Net GHG balance^§ (A + B – C)	(Mg CO2-eq ha^–1 y^–1)	8.17	9.69	4.97	13.92	18.23	14.50
Changes in net GHG balance by the organic matter application (RS or SC – NA)		-	1.52	−3.19	-	4.31	0.58
Combination effect of rice straw removal and rice straw compost application (SC – RS)		-	-	−4.71	-	-	−3.72
Yield-scaled net GHG balance^§	(Mg CO2-eq Mg^–1 grain)	1.60	1.94	0.91	2.84	3.63	2.41

NA, no application; RS, rice straw; SC; rice straw compost. ^†Application year before starting the experiment (2010). ^‡Calculated from Table 8 with the GWP of CO₂:CH₄:N₂O = 1:34:298 (IPCC 2013). ^§Positive values indicate net emissions to the atmosphere and negative values indicate net uptake from the atmosphere. ^¶With an assumption that the soil carbon content in C-NA did not change throughout the application period.

Figure 4. Effects of rice straw removal and compost application on net greenhouse gas balance (CO₂ equivalent) evaluated by taking compost production into consideration. Positive values indicate net emissions to the atmosphere, and negative values indicate net uptake from the atmosphere. To produce 15 Mg of rice straw compost applied to 1 ha of paddy field, 24.83 Mg of rice straw was estimated to be collected from 4.14 ha (calculated from the Table 4 by assuming negligible SiO₂ loss during the composting process with the rice straw application rate of 6.0 Mg ha⁻¹). Changes in CH₄ and the soil carbon due to the rice straw removal (4.14 ha) and rice straw compost application (1.00 ha) were estimated from Table 9. CH₄ emissions during composting were calculated using a factor estimated by Miura (2003). N₂O emissions during compositing were excluded from the evaluation because it was not observed with no nitrogen addition (Miura 2003). Changes in N₂O emissions by the organic matter application were excluded from the evaluation because the values were very small.

Shiratori Y, Watanabe H, Furukawa Y, Tsuruta H, Inubushi K 2007: Effectiveness of a subsurface drainage system in poorly drained paddy fields on reduction of methane emissions. Soil Sci. Plant Nutr., 53, 387–400.

 Web of Science ®Google Scholar

IPCC (Intergovernmental Panel on Climate Change 2013: In Climate change 2013: the physical science basis, chapter 8 anthropogenic and natural radiative forcing. contribution of working group i to the fifth assessment report of intergovernmental panel on climate change. Ed. T Stocker, et al. http://www.ipcc.ch/report/ar5/wg1/ (December 2018)

 Google Scholar

Miura Y 2003: Rice straw management for mitigation of methane emission from paddy field. Spe. Bull. Fukushima Pref. Agric. Exp. Stn., 7, 1–38. in Japanese.

 Google Scholar