Organic acid accumulation under flooded soil conditions in relation to the incorporation of wheat and rice straws with different C:N ratios

Figures & data

Table 1 Composition of the straw materials used in the incubation experiments

Straw material	C:N ratio	N (%)	Sugar (%)^†	Hemi-cellulose (%)	Cellulose (%)	Lignin (%)
Wheat straw	82.77	0.79	10.86	38.47	34.66	16.23
Rice straw	42.52	0.82	15.85	35.02	33.69	15.20
^†Extracted with water at a 1:10 ratio (w/w) and measured using the phenol-sulfuric acid method (Dubois et al. 1956).

Figure 1  Effect of straw type and rate on the concentration of organic acids in soil at different incubation times.

Table 2 Comparison of the total concentration (µg C g−1 soil) of the four organic acids at each sampling date between the two straw materials

Straw material	Incubation days
	7			10			14
	Rate of straw incorporated (%)
	0.5	1	2	0.5	1	2	0.5	1	2
Wheat straw	2.21	11.99	123.38	3.98	26.58	112.46	3.49	5.04	9.86
Rice straw	0.23	4.52	29.14	0.19	15.41	33.87	0.12	0.17	0.22
	ns	*	**	ns	**	**	ns	ns	*
*P < 0.05.
**P < 0.01. ns, not significant.

Table 3 Soil pH value in the different straw treatments over the incubation period†

Treatment	Incubation days
	1	3	5	7	10	14	21
No straw	6.95a	7.30a	7.15a	6.97a	6.86a	6.80a	6.71a
Wheat straw	6.94a	7.29a	7.10a	6.94a	6.72b	6.63b	6.59b
Rice straw	6.92a	7.27a	7.08a	6.92a	6.75b	6.69b	6.60b
^†Different letters in the same column represent significant differences (least significant difference; P < 0.05).

Figure 2  Effect of straw incorporation on the soil redox potential detected at different incubation times. Errors bar are standard error.

Figure 3  Effect of the addition of N on in the soil solution under the different straw treatments. (A) No N added and (B) 0.4 g urea kg−1 soil. Errors bar are standard error.

Figure 4  Response of the organic acid concentration in soil solution at different incubation times to N addition. N0, N1 and N2 refer to 0, 0.2 and 0.4 g urea kg−1 soil, respectively. Bars labeled with different letters were significant (P < 0.05) within each incubation time. ns, not significant.

Figure 5  Effect of straw type and N addition on CH4 flux. (A) Wheat straw and (B) rice straw. N0, N1 and N2 refer to 0, 0.2 and 0.4 g urea kg−1 soil, respectively. Errors bar are standard error.

Figure 6  Effect of straw type and N addition on CO2 flux. (A) Wheat straw and (B) rice straw. N0, N1 and N2 refer to 0, 0.2 and 0.4 g urea kg−1 soil, respectively. Errors bar are standard error.

Fox , TR . 1995 . “ The influence of low-molecular-weight organic acids on properties and processes in forest soils ” . In Carbon Forms and Functions in Forest Soils , Edited by: McFee , WW and Kelly , JM . 43 – 62 . Madison : Soil Science Society of America .

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