Three years of biochar and straw application could reduce greenhouse gas and improve rice productivity

Figures & data

Figure 1. Mean daily precipitation and air temperature during the rice cultivation year.

Table 1. Field management for rice cultivation.

Items	2015	2016	2017
Flooded period (days)	105	112	98
Rice transplanting (month/day)	5/28	5/24	5/27
Rice harvesting (month/day)	9/30	9/26	9/29
Barley straw biochar	○	×	×
Barley straw	○	○	○

○, application; ×, no application.

Table 2. Rice yield (mean ± SD) under different biochar and straw treatments during the 3 years of study.

Treatment	Rice yield (g m^−2)
	2015	2016	2017	Ave.
CN	515 ± 64.1b	508 ± 26.2b	473 ± 24.1c	499 ± 28.6b
BC	532 ± 17.2ab	536 ± 20.0b	497 ± 29.5bc	522 ± 18.7b
BS	516 ± 23.9b	524 ± 5.8b	528 ± 12.1b	523 ± 8.8b
BC+BS	593 ± 36.4a	583 ± 26.6a	602 ± 34.0a	592 ± 25.4a

Different letters within the same column indicate significant differences, as determined by Tukey’s test with p < 0.05.

Figure 2. Quantification of total bacterial 16S rRNA gene components after final rice harvesting. Different letters indicate significant differences among treatments at a 5% probability level. Error bars represent standard deviations (n = 12).

Table 3. Soil properties (mean ± SD) under different treatment sites after rice harvesting.

Treatment	Bulk density	pH	EC	SOC	TN	Avail. P2O5	CEC	Total bacteria
	(Mg m^−3)	(1:5 H2O)	(dS m^−1)	—– (g kg^−1) —–		(mg kg^−1)	(cmolc kg^−1)	(log10 copies g^−1)
CN	1.33 ± 0.1a^1	5.78 ± 0.0b	0.18 ± 0.2c	9.04 ± 0.7b	1.39 ± 0.1d	56.5 ± 3.1ab	6.25 ± 0.1b	6.90 ± 0.3b
BC	1.26 ± 0.0b	5.94 ± 0.0a	0.19 ± 0.2ab	9.60 ± 1.0ab	1.47 ± 0.0c	55.5 ± 3.3b	6.80 ± 0.3a	8.05 ± 0.3a
BS	1.25 ± 0.0b	5.93 ± 0.0a	0.18 ± 0.2bc	10.4 ± 0.7a	1.69 ± 0.1a	58.6 ± 2.7ab	6.62 ± 0.4ab	7.65 ± 0.1a
BC+BS	1.26 ± 0.0b	5.96 ± 0.1a	0.20 ± 0.2a	9.93 ± 0.6ab	1.55 ± 0.0b	60.0 ± 1.1a	6.74 ± 0.3a	7.68 ± 0.4a

^aDifferent letters within the same column indicate significant differences, as determined by Tukey’s test with p < 0.05.

Figure 3. Changes in CH₄ emission rates during each of the three rice-growing seasons. Error bars represent standard deviations (n = 3).

Figure 4. Changes in N₂O emission rates during each of the three rice-growing seasons. Error bars represent standard deviations (n = 3).

Table 4. Total CH₄ and N₂O fluxes, GWP, and GHGI (mean ± SD) during three rice-growing seasons.

Year	Treatment	Total fluxes (g m^−2)		GWP	GHGI
		CH4	N2O	(Mg CO2 ha^−1)
2015	CN	42.0 ± 1.7a^1	0.16 ± 0.0c	10.98 ± 0.1a	2.18 ± 0.4a
	BC	25.2 ± 0.7b	0.25 ± 0.0bc	7.03 ± 0.0b	1.32 ± 0.1b
	BS	38.8 ± 1.5a	0.37 ± 0.0a	10.81 ± 0.0a	2.11 ± 0.1a
	BC+BS	25.7 ± 1.4b	0.32 ± 0.0ab	7.38 ± 0.0b	1.25 ± 0.0b
2016	CN	38.0 ± 2.2b	0.22 ± 0.0b	10.15 ± 0.1b	2.00 ± 0.1b
	BC	26.9 ± 3.3c	0.28 ± 0.0b	7.56 ± 0.1c	1.41 ± 0.1d
	BS	45.3 ± 0.3a	0.47 ± 0.0a	12.72 ± 0.0a	2.43 ± 0.0a
	BC+BS	33.5 ± 2.7b	0.41 ± 0.0a	9.59 ± 0.1b	1.65 ± 0.1c
2017	CN	40.9 ± 4.0ab	0.22 ± 0.1b	10.88 ± 0.1ab	2.34 ± 0.3a
	BC	29.7 ± 3.1c	0.27 ± 0.0ab	8.25 ± 0.1c	1.68 ± 0.2b
	BS	43.9 ± 2.4a	0.37 ± 0.0a	12.09 ± 0.1a	2.30 ± 0.1a
	BC+BS	34.6 ± 3.5bc	0.33 ± 0.1ab	9.62 ± 0.1bc	1.59 ± 0.1b
Total	CN	120.8a	0.60c	32.01a
	BC	81.8b	0.80b	22.84c
	BS	128.0a	1.22a	35.63a
	BC+BS	93.8b	1.06a	26.60b
Statistical analysis^2
Year (A)		ns	ns	ns	ns
Treatment (B)		***	***	***	***
A × B		ns	***	ns	ns

^aDifferent letters within the same column indicate significant differences between treatments, as determined by Tukey’s test with p < 0.05.

^bns, *, **, and *** denote not significant (ns) and significant different differences at the 5, 1, and 0.1% levels, respectively.