Nitrogen-enriched biochar co-compost for the amelioration of degraded tropical soil

Figures & data

Table 1. Physical and chemical properties of biochar.

Parameter	Rice straw biochar	Maize stover biochar	Gram residue biochar
pH	8.20b^§ ± 1.34	7.86c ± 1.28	9.51a ± 1.55
EC (ds m^−1)	6.19b  ± 1.01	4.16c ± 0.68	6.56a ± 1.07
CEC [cmol (p^+) kg^−1]	56.5a  ± 9.23	54.2b ± 8.85	57.8a ± 9.44
CCE (%)	36.6b  ± 5.98	29.7c ± 4.85	42.1a ± 6.88
BD (Mg m^−3)	0.21b  ± 0.03	0.23b ± 0.04	0.27a ± 0.04
PD (Mg m^−3)	0.40b  ± 0.07	0.43b ± 0.07	0.57a ± 0.09
Porosity (%)	48b  ± 7.84	47b ± 7.68	53a ± 8.66
Moisture (%)	5.86b  ± 0.96	6.80a ± 1.11	3.20c ± 0.52
MWHC (%)	593b  ± 96.8	586b ± 95.7	660c ± 107.8
Volatile matter (%)	27.0a ± 4.41	23.0b ± 3.76	21.0c ± 3.43
Ash (%)	37.1b ± 6.06	31.1c ± 5.08	39.1a ± 6.39
C (%)	57.6c ± 9.41	62.6a ± 10.2	58.4b ± 9.54
N (%)	0.68b ± 0.11	0.67b ± 0.11	1.69a ± 0.28
C:N	85:1b ± 0.41	94:1a ± 0.49	35:1c ± 0.05

^§ Data followed by different lower-case letters in a row representing specific property is significant according to Duncan’s Multiple Range Test at p = .05. Data followed by ± represent standard error (n = 3). EC: Electrical conductivity; CEC: Cation exchange capacity; CCE: Calcium carbonate equivalent; BD: Bulk density; PD: Particle density; MWHC: Maximum water holding capacity.

Table 2. Physical and chemical properties of biochar co-composts.

Biochar co-compost	Residue-biochar ratio	pH	EC (dS  m^−1)	CCE	C (%)	N (%)	C:N
RS + RSBC	7:1	8.50a^§ ± 1.39	3.97c ± 0.65	27.1de ± 4.43	16.7abc ± 2.73	0.93bcd ± 0.16	17.9de ± 2.92
	9:1	8.42c ± 1.37	3.57f ± 0.58	26.5efg ± 4.33	15.3bc ± 2.5	0.91def ± 0.15	16.9ef ± 2.76
	11:1	8.35cd ± 1.36	3.24g ± 0.53	27.1de ± 4.43	12.5d ± 2.04	0.81h ± 0.13	15.5fg ± 2.53
RS + MSBC	7:1	8.24ef ± 1.35	3.22g ± 0.52	25.9ghi ± 4.23	18.1a ± 2.96	0.91cde ± 0.15	19.9abc ± 3.25
	9:1	8.16gh ± 1.33	3.91cd ± 0.64	25.5hi ± 4.16	15.6bc ± 2.55	0.88defg ± 0.15	17.6e ± 2.87
	11:1	7.94i ± 1.3	3.53f ± 0.58	25.3i ± 4.13	15.5bc ± 2.53	0.86fgh ± 0.14	18.0cde ± 2.94
RS + GRBC	7:1	8.86a ± 1.45	4.20b ± 0.69	29.3b ± 4.79	16.7abc ± 2.73	0.96bc ± 0.16	17.4e ± 2.84
	9:1	8.50b ± 1.39	3.90cd ± 0.64	28.2c ± 4.61	17.4ab ± 2.84	0.98b ± 0.16	17.9de ± 2.92
	11:1	8.30de ± 1.36	3.71e ± 0.6	28.2c ± 4.61	17.4ab ± 2.84	0.96bc ± 0.16	18.1cde ± 2.96
MS + RSBC	7:1	7.88ij ± 1.29	2.95h ± 0.48	27.1de ± 4.43	17.4ab ± 2.84	0.86efg ± 0.14	20.2ab ± 3.3
	9:1	7.83j ± 1.28	2.91h ± 0.47	28.2c ± 4.61	17.4ab ± 2.84	0.83gh ± 0.14	20.9a ± 3.41
	11:1	7.67k ± 1.25	2.25i ± 0.37	27.6de ± 4.51	16.2abc ± 2.65	0.81h ± 0.13	20.1ab ± 3.28
MS + MSBC	7:1	8.22efg ± 1.34	2.25ij ± 0.37	26.5efg ± 4.33	16.2abc ± 2.65	0.86fgh ± 0.14	18.8bcde ± 3.07
	9:1	8.18fgh ± 1.34	2.21j ± 0.36	26.1fgh ± 4.26	16.0abc ± 2.61	0.83gh ± 0.14	18.0cde ± 2.94
	11:1	8.12h ± 1.32	2.10k ± 0.34	26.8ef ± 4.38	15.9abc ± 2.6	0.81gh ± 0.13	19.7abcd ± 3.22
MS + GRBC	7:1	8.42c ± 1.37	4.70a ± 0.77	30.5a ± 4.98	16.9abc ± 2.76	0.93bcd ± 0.16	18.2cde ± 2.97
	9:1	8.20fgh ± 1.34	3.84d ± 0.63	29.1b ± 4.75	16.0abc ± 2.61	0.92cd ± 0.15	17.5e ± 2.86
	11:1	8.17fgh ± 1.33	4.23b ± 0.69	29.3b ± 4.79	15.1c ± 2.47	1.05a ± 0.17	14.4g ± 2.35

^§ Data followed by different lower-case letters in a column representing specific property is significant according to Duncan’s Multiple Range Test at p = .05. Data followed by ± represent standard represent standard error (n = 3). EC: Electrical conductivity; CCE: Calcium carbonate equivalence; RS: Rice straw; MS: Maize stover; RSBC: Rice straw biochar; MSBC: Maize stover biochar; GRBC: Gram residue biochar.

Figure 1. XRD patterns of rice straw biochar (RSBC), maize stover biochar (MSBC), and gram residue biochar (GRBC).

Figure 2. SEM images of (a) rice straw biochar (RSBC), (b) maize stover biochar (MSBC), and (c) gram residue biochar (GRBC).

Figure 3. FTIR spectra of (a) rice straw biochar (RSBC), (b) maize stover biochar (MSBC), and (c) gam residue biochar (GRBC).

Table 3. Effect of biochar, biochar co-compost and lime amendments on pH, electrical conductivity, cation exchange capacity, exchangeable acidity, exchangeable Al³⁺ and exchangeable H⁺ contents in soil.

Treatment	pH	EC (ds m^−1)	CEC [c mol (p^+) kg^−1]	Exchangeable acidity [c mol (p^+) kg^−1]	Exchangeable Al^3+ [c mol (p^+) kg^−1]	Exchangeable H^+ [c mol (p^+) kg^−1]
RS + RSBC (7:1)	6.43cd^§ ± 0.00	0.51d^§ ± 0.083	9.25fg^§ ± 0.03	1.23c^§  ± 0.02	0.96b^§ ± 0.07	0.26c^§ ± 0.05
RS + GRBC (7:1)	6.63b ± 088	0.73c ± 0.056	10.1d ± 0.03	0.88e ± 0.06	0.71c ± 0.08	0.17cd ± 0.04
RS + GRBC (9:1)	6.32de ± 030	1.20a ± 0.057	9.61ef ± 0.04	1.35b ± 0.09	0.97b ± 0.06	0.38a ± 0.12
RS + GRBC (11:1)	6.23e ± 098	1.13a ±  0.05	9.45efg ± 0.06	1.18d ± 0.01	0.91b ± 0.04	0.27bc ± 0.03
MS + GRBC (7:1)	6.76a ± 085	0.94b ± 0.11	9.88de ± 0.03	1.02e ± 0.01	0.63cd ± 0.07	0.38a ± 0.07
MS + GRBC (11:1)	6.41cd ± 155	0.36e ± 0.036	9.75de ± 0.05	1.13d ± 0.07	0.64cd ± 0.01	0.38a ± 0.07
RSBC	6.46c ± 010	0.69c ±  0.035	10.59c ± 0.28	0.77g ± 0.07	0.53e ± 0.05	0.23c ± 0.01
MSBC	6.32de ± 010	0.68c ± 0.030	10.62c ± 0.75	0.88f ± 0.06	0.64cd ± 0.01	0.24c ± 0.06
GRBC	6.86a ± 025	0.58d ±  0.025	12.01b ± 0.03	0.90f ± 0.02	0.62d ± 0.01	0.28bc ± 0.02
2/3rd LR	6.88a ± 030	0.55d ± 0.025	12.72a ± 0.07	0.83fg ± 0.02	0.72c ± 0.02	0.11d ± 0.02
Control	5.05f ± 050	0.31e ± 0.050	9.12g ± 0.12	1.50a ± 0.00	1.10a ± 0.00	0.40a ± 0.00

^§ Data in the same column followed by different lower-case letters (a–g) are significantly different according to Duncan’s Multiple Range Test at p = .05. Data followed by ± represent standard error (n = 3). EC: Electrical conductivity; CEC: cation exchange capacity; RS: Rice straw; MS: Maize stover; RSBC: Rice straw biochar; MSBC: Maize stover biochar; GRBC: Gram residue biochar; LR: Lime requirement.

Table 4. Effect of biochar, biochar co-compost and lime amendments on activities of dehydrogenase, β-Glucosidase and leucine aminopeptidase enzymes in soil.

Treatment	Dehydrogenase activity (µg TPF g^−1 soil h^−1)	β-glucosidase activity (µg PNP g^−1 soil h^−1)	Leucine aminopeptidase activity (µmol MUC g^−1 soil h^−1)
RS + RSBC (7:1)	1.80ab^§ ± 0.105	83.7cd^§ ± 2.111	3.22bc^§ ± 0.01
RS + GRBC (7:1)	1.87a ± 0.128	90.5c ± 3.872	1.74f ± 0.013
RS + GRBC (9:1)	1.84a ± 0.087	81.2cd ± 1.927	2.23e ± 0.059
RS + GRBC (11:1)	1.57b ± 0.093	83.1cd ± 3.207	2.76d ± 0.04
MS + GRBC (7:1)	1.56b ± 0.054	84.8cd ± 2.01	3.05c ± 0.048
MS + GRBC (11:1)	1.60b ± 0.108	77.6d ± 4.542	2.36e ± 0.058
RSBC	1.92a ± 0.093	88.9c ± 2.043	2.34e ± 0.005
MSBC	1.89a ± 0.111	110b ± 3.895	3.01c ± 0.165
GRBC	1.98a ± 0.047	155a ± 4.861	3.52a ± 0.139
2/3rd LR	1.21c ± 0.072	105b ± 3.461	3.31ab ± 0.033
Control	0.95d ± 0.113	14.1e ± 0.716	1.10g ± 0.03

^§ Data in the same column followed by different lower-case letters (a–i) are significantly different according to Duncan’s Multiple Range Test at p = .05. Data followed by ± represent standard error (n = 3). RS: Rice straw; MS: Maize stover; RSBC: Rice straw biochar; MSBC: Maize stover biochar; GRBC: Gram residue biochar; LR: Lime requirement; MUC: L-Leucine-7-amido-4-methylcoumarin hydrochloride.

Table 5. Correlation coefficients (r) among different chemical and biological properties of soil.

	pH	EC	CEC	TA	Ex-Al	Ex-H	DHA	BG	LAP
pH	1
EC	0.26	1
CEC	0.61*	−0.16	1
TA	−0.74**	0.02	−0.71*	1
Ex-Al	−0.69*	0.06	−0.55	0.89**	1
Ex-H	−0.50	0.06	−0.63*	0.72*	0.34	1
DHA	0.56	0.33	0.06	−0.46	−0.50	−0.16	1
BG	0.83**	0.17	0.71*	−0.72*	−0.65	−0.47	0.67*	1
LAP	0.74**	0.14	0.56	−0.48	−0.42	−0.34	0.36	0.79**	1

EC: Electrical conductivity; CEC: Cation exchange capacity; TA: Total acidity; Ex-Al: Exchangeable Al³⁺; Ex-H: Exchangeable H⁺; DHA: Dehydrogenase activity; BG: β-glucosidase activity; LAP: Leucine amino peptidase activity; *Significant at p = .05; **Significant at p = .01.

Figure 4. Correlation biplots and identification of most important contributing parameters based on principal component analysis (PCA) depicting the relationship among the physicochemical and microbial properties of soil amended with biochar, biochar co-composts, and lime. Abbreviations: T1 − RS + RSBC (7:1), T2 − RS + GRBC (7:1), T3 − RS + GRBC (9:1), T4 − RS + GRBC (11:1), T5 − MS + GRBC (7:1), T6 − MS + GRBC (11:1), T7 − RSBC, T8 − MSBC, T9 − GRBC, T10 − 2/3rd LR, T11 − Control, RS − Rice straw; MS − Maize stover; RSBC − Rice straw biochar; MSBC − Maize stover biochar; GRBC − Gram residue biochar; LR − Lime requirement; EC − Electrical conductivity (ds m⁻¹), CEC − Cation exchange capacity, EXAC − Exchange acidity, EXAL − Exchangeable Al³⁺, EXH − Exchangeable H⁺, DHA − Dehydrogenase activity, BGA − β-glucosidase activity, LAP − Leucine amino peptidase activity.

Data availability statement

All data generated or analyzed during this study are included in this published article and its supplementary information file.