Rice yield and soil carbon dynamics over three years of applying rice husk charcoal to an Andosol paddy field

Figures & data

Table 1. Physicochemical properties of the paddy soil before commencing the experiment, and of the rice husk charcoal and rice husk applied.

Physicochemical property	Paddy soil		Rice husk charcoal		Rice husk
Bulk density (g cm^−3)	0.61	(0.06)	0.12	(0.01)	0.11	(0.00)
pH	5.80	(0.00)	9.19	(0.76)	6.59	(0.52)
EC (mS cm^−1)	0.11	(0.00)	0.52	(0.15)	0.66	(0.15)
Total C (g kg^−1)	73.2	(0.29)	396	(34.4)	369	(10.6)
Total N (g kg^−1)	5.42	(0.03)	3.40	(0.56)	3.26	(0.15)
C/N ratio	13.5	(0.05)	118	(9.66)	116	(1.46)
Si (g kg^−1)	na		215	(24.8)	106	(13.1)
K (g kg^−1)	na		8.35	(1.19)	4.36	(0.16)
Ca (g kg^−1)	na		2.18	(0.24)	0.97	(0.02)
Mg (g kg^−1)	na		0.65	(0.04)	0.33	(0.10)

Notes: EC, electrical conductivity; N, nitrogen; C, carbon; Si, silicon; K, potassium; Ca, calcium; Mg, magnesium and na, not analyzed. pH and EC were measured in a material to water solution at a ratio of 1:10. Figures in parentheses indicate standard deviation (n = 3–6).

Table 2. Growth, yield, and yield components of rice plants as affected by three years of application of rice husk charcoal (RC) or rice husk (RH).

Factor	Culm length (cm)	Panicle length (cm)	Aboveground weight (gDW m^−2)		Grain-straw ratio (%)	Panicle number (m^−2)	Spikelet number (panicle^−1)	Percentage of ripened grains (%)	1000-grain weight (g)	Grain yield (g m^−2)
			Panicle	Straw
Treatment
CONT	82.1 ab	19.5	605.9	722.0 b	81.3 a	351.2	76.4	81.9	27.6	602.0
RC0.02	82.2 ab	20.0	584.1	696.4 b	82.3 a	339.7	76.9	82.2	27.7	589.9
RC0.2	81.5 b	19.9	574.5	709.5 b	78.1 ab	335.9	77.4	81.6	27.5	579.1
RC2	85.3 a	19.8	639.4	822.3 a	73.6 b	360.2	80.8	79.1	27.4	625.7
RH0.2	83.3 ab	19.6	582.9	717.7 b	78.9 ab	343.8	76.6	80.8	27.7	582.7
Application year
1st year	80.3 b	20.8 a	612.0 a	685.9 b	81.3 a	347.6 b	78.4 a	76.4 c	28.1 a	582.9 b
2nd year	87.7 a	19.3 b	639.5 a	879.0 a	72.9 b	401.6 a	74.8 b	82.0 b	27.2 b	667.7 a
3rd year	80.6 b	19.2 b	540.7 b	635.9 b	82.3 a	289.3 c	79.6 a	85.0 a	27.5 b	537.0 b
ANOVA
Treatment	*	NS	NS	**	**	NS	NS	NS	NS	NS
Application year	**	**	**	**	**	**	**	**	**	**
Interaction	NS	**	NS	NS	NS	NS	NS	NS	NS	NS

Notes: Panicle and straw weight indicated on a dry weight basis. 1000-grain weight and grain yield were adjusted to have a moisture content of 14%.

**, * and NS denote significantly different at p < 0.01, p < 0.05 and not significant, respectively, according to analysis of variance (ANOVA).

Means followed by the same letter within each column are not significantly different at the 5% level in Tukey’s HSD test.

Table 3. Nutrient concentration and uptake in mature rice straw as affected by rice husk charcoal (RC) or rice husk (RH) application.

Factor	Concentration (%)					Nutrient uptake (g m^−2)
	N	Si	K	Ca	Mg	N	Si	K	Ca	Mg
Treatment
CONT	0.60 a	4.92 c	1.28	0.32	0.110 ab	4.34	34.9 b	11.3	2.81	0.97
RC0.02	0.57 ab	5.56 bc	1.28	0.30	0.111 a	3.91	38.5 b	10.4	2.48	0.91
RC0.2	0.54 ab	6.07 b	1.30	0.32	0.109 ab	3.81	42.6 b	11.1	2.71	0.93
RC2	0.50 b	8.35 a	1.30	0.24	0.095 c	4.13	68.2 a	12.6	2.37	0.91
RH0.2	0.56 ab	5.82 bc	1.30	0.24	0.108 b	3.96	41.5 b	11.3	2.13	0.94
Application year
1st year	0.63 a	6.20 ab	na	na	na	4.33 a	43.1 b	na	na	na
2nd year	0.51 b	5.66 b	1.29	0.28	0.107	4.47 a	50.1 a	11.3	2.50	0.93
3rd year	0.52 b	6.58 a	na	na	na	3.29 b	42.1 b	na	na	na
ANOVA
Treatment	*	**	NS	NS	**	NS	**	NS	NS	NS
Application year	**	**	–	–	–	**	**	–	–	–
Interaction	NS	NS	–	–	–	NS	NS	–	–	–

Notes: na, not analyzed as the K, Ca, and Mg concentrations were analyzed only in the 2nd year of experiment.

**, * and NS denote significantly different at p < 0.01, p < 0.05 and not significant, respectively, according to analysis of variance (ANOVA).

Means followed by the same letter within each column are not significantly different at the 5% level in Tukey’s HSD test.

Table 4. Effects of three years of application of rice husk charcoal (RC) or rice husk (RH) on paddy soil physicochemical properties.

Factor	Bulk density (Mg m^−3)	Porosity (%)	pH	EC (mS m^−1)	TN (g kg^−1)	TC (g kg^−1)		C/N ratio
						0–10 cm	10–20 cm
Treatment
CONT	0.70 a	72.6 a	5.91	88.4	4.08	54.0 b	49.8 b	13.2 c
RC0.02	0.68 ab	73.5 a	5.96	85.8	3.99	53.2 b	49.2 b	13.3 c
RC0.2	0.70 a	72.5 a	5.99	85.5	4.07	56.6 b	50.6 ab	13.9 b
RC2	0.65 b	73.9 a	5.92	86.0	4.16	79.6 a	59.1 a	19.1 a
RH0.2	0.69 a	73.0 a	5.99	82.5	4.05	54.9 b	47.6 b	13.5 bc
Application year
1st year	0.71 a	71.6 b	5.91 b	82.5 b	4.23 a	59.6 ab	na	14.1 c
2nd year	0.71 a	72.1 b	5.92 ab	71.7 b	3.95 b	57.6 b	na	14.6 b
3rd year	0.63 b	75.7 a	6.03 a	102.9 a	4.03 b	61.7 a	51.3	15.2 a
ANOVA
Treatment	**	*	NS	NS	NS	**	**	**
Application year	**	**	*	**	**	**	–	**
Interaction	NS	NS	NS	NS	NS	**	–	**

Notes: EC, electrical conductivity; TN, total nitrogen; TC, total carbon; C/N ratio, carbon to nitrogen ratio; na, not analyzed. Total carbon contents of paddy soil at a depth of 10–20 cm were measured only in the 3rd year of experiment. C/N ratio was calculated using total C and N contents at the top 10 cm layer of paddy soil.

**, * and NS denote significantly different at p < 0.01, p < 0.05 and not significant, respectively, according to analysis of variance (ANOVA).

Means followed by the same letter within each column are not significantly different at the 5% level in Tukey’s HSD test.

Figure 1. Increase in soil carbon content compared to that in the control plots over three years of rice husk charcoal (RC) or rice husk (RH) applications. Vertical bars indicate standard errors of three replicates. The regression equation shown in the figure was calculated from the data from RC2 plots.