Microbial activity and metabolic quotient of microbes in soils amended with biochar and contaminated with atrazine and paraquat

Figures & data

Table 1. Some physico-chemical properties of the soils and biochar used for the greenhouse incubation study.

Properties	Sand (%)	Silt (%)	Clay (%)	Textural class	Bulk density (mg/m³)	pHw (H₂O)	pHs (0.01 CaCl₂)	OC (g/kg)	Total nitrogen (g/kg)	C:N ratio	Available phosphorus (mg/kg)	CEC (cmol/kg)
Alfisol	70.3	7.2	22.5	Sandy clay loam	1.31	5.4	4.9	6.0	1.09	5.50	4.8	8.12
Vertisol	47.1	5.4	47.5	Sandy clay	1.4	7.6	6.2	9.1	0.91	10	8.93	37.6
CHB	____	____	____	____	0.36	10.4	10.8	256.0	3.5	73.14	3897.7	81.67
RHB	____	____	____	____	0.22	7.4	7.6	291.0	1.4	212.14	531	38.8

Figure 1. XRD spectra of biochars (CHB and RHB). Note: A = silica (SiO₂), F = periclase (MgO), G = magnesium oxide (MgO), H = magnesium carbonate (MgCO₃), I = potassium hydrogen carbonate (KHCO₃), J = aluminium iron (iii) oxide (AlFeO₃), K = iron oxide hydroxide (FeOOH), P = magnesium hydroxide (Mg[OH]₂).

Figure 2. (a) Ammonia released from soils of different clay contents, (b) soils amended with biochar of different feed stocks and (c) soils contaminated with different rates of pesticides (atrazine and paraquat) in a greenhouse incubation study.

Figure 3. (a) Nitrate released from soils of different clay contents, (b) soils amended soil with biochar of different feed stocks, (c) soils contaminated with different rates of pesticides (atrazine and paraquat) and (d) soil × pesticide interaction during a greenhouse incubation study.

Table 2. Ammonification, nitrification and carbon mineralization rates of soils amended with biochar of different feed stocks and contaminated with pesticides (atrazine and paraquat) of various rates.

Soil type	Biochar type	Level of pesticide applied	Mean ammonification rate (µg/g soil/day)	Mean nitrification rate (µg/g soil/day)	Mean carbon mineralization rate (µg/g soil/day)
Alfisol	Un-amended^a	Paraquat at 0 ×	0.10	0.57	15.28
	Un-amended	Paraquat at 10×	0.38	1.06	15.61
	Soil amended with CHB	Paraquat at 0×	0.48	1.13	17.88
	Soil amended with CHB	Paraquat at 10×	0.39	1.78	18.53
	Soil amended with RHB	Paraquat at 0×	0.44	1.71	17.96
	Soil amended with RHB	Paraquat at 10×	0.20	2.30	17.80
	Un-amended	Atrazine at 0×	0.10	0.67	14.98
	Un-amended	Atrazine at 10×	0.30	1.19	17.73
	Soil amended with CHB	Atrazine at 0×	–0.59	1.19	17.30
	Soil amended with CHB	Atrazine at 10×	0.64	2.34	23.79
	Soil amended with RHB	Atrazine at 0×	0.44	1.17	16.27
	Soil amended with RHB	Atrazine at 10×	0.41	2.44	19.68
Vertisol	Un-amended	Paraquat 0×	0.44	0.49	16.66
	Un-amended	Paraquat at 10×	0.80	1.78	20.31
	Soil amended with CHB	Paraquat at 0×	0.99	1.79	19.65
	Soil amended with CHB	Paraquat at 10×	0.84	2.39	22.23
	Soil amended with RHB	Paraquat at 0×	1.00	1.83	17.48
	Soil amended with RHB	Paraquat at 10×	0.12	3.13	20.78
	Un-amended	Atrazine at 0×	0.73	0.97	16.13
	Un-amended	Atrazine at 10×	0.54	1.90	23.06
	Soil amended with CHB	Atrazine at 0×	0.67	1.84	19.76
	Soil amended with CHB	Atrazine at 10×	0.89	3.98	34.44
	Soil amended with RHB	Atrazine at 0×	0.63	1.77	17.65
	Soil amended with RHB	Atrazine at 10×	0.29	4.31	26.97

Notes: For ammonification rates, p < .001 for soil, p = .022 for biochar, p < .001 for pesticide, p < .001 for soil × biochar interaction, p < .001 for soil × pesticide interaction, p < .001 for biochar × pesticide interaction and p = .06 for soil × biochar × pesticide interaction.

For nitrification rates, p < .001 for soil, p < .001 for biochar, p < .001 for pesticide, p = .191 for soil × biochar interaction, p = .055 for soil × pesticide interaction, p = .161 for soil × biochar interaction, p = .915 for soil × biochar × pesticide interaction.

For carbon mineralization rates, p < .001 for soil, p < .001 for biochar, p < .001 for pesticide, p < .001 for soil × biochar interaction, p < .001 for soil × pesticide interaction, p < .001 for biochar × pesticide interaction and p < .001 for soil × biochar × pesticide interaction.

The ammonification rate was calculated as follows:

The nitrification rate was calculated as follows:

The carbon mineralization rate was calculated as follows:

^aUn-amended soil means no biochar was added.

Figure 4. (a) Microbial biomass carbon of soils of different clay content, (b) soils amended with biochar of different feed stocks, (c) soils contaminated with different rates of pesticides (namely atrazine and paraquat) and (d) soil × biochar interaction during an incubation study in the greenhouse.

Figure 5. (a) Basal respiration as measured as carbon dioxide carbon evolved from soils of different clay contents, (b) soils amended with biochar of different feed stocks, (c) soils contaminated with pesticides (atrazine and paraquat) at different rates and (d) soil × pesticide interaction during an incubation study in the greenhouse.

Figure 6. (a and b) Carbon mineralization in the alfisol and vertisol when no has been pesticide applied (i.e. 0 kg a.i/ha atrazine and paraquat applied), (c) carbon mineralization in the alfisol contaminated with 10× the normal rate of atrazine and paraquat and (d) carbon mineralization in the vertisol contaminated with 10× the normal rate of atrazine and paraquat during a greenhouse incubation study.

Figure 7. (a) Metabolic quotient of soils of different clay content, (b) soils amended with biochar of different feed stocks and (c) soils contaminated with different rates of pesticides (atrazine and paraquat) during an incubation study in the greenhouse.

Figure 8. (a–c) Correlation between micobial biomass carbon and basal respiration at days 20, 30 and 50. (d–f) Correlation between microbial biomass carbon and nitrate released at days 20, 30 and 50 days of incubating soils with different biochar amendments and polluted with pesticides. r is the correlation coefficient.