Effects of biochar returning on soil pH and CEC
The application of biochar increased the pH value of uncontaminated sugarcane soil and manganese-contaminated sugarcane soil (Fig. 1), and the pH increased with the increase of biochar application ratio, but the change was not obvious with time. In the soil of uncontaminated sugarcane field soil, the pH value of uncontaminated sugarcane field with 0.5% biochar decreased with the culture time, while the pH value of soil with 2% and 5% biochar did not change significantly with time. In the soil of manganese-contaminated sugarcane soil, the pH value of the soil of 0.5% biochar manganese-contaminated sugarcane soil decreased first and then increased with time, and the pH value of the soil of 2% and 5% biochar manganese-contaminated sugarcane soil decreased with time. The pH value of sugarcane soil was higher than that of manganese contaminated sugarcane soil. Biochar application had little effect on soil pH of manganese contaminated sugarcane field.
It can be seen from Fig. 2 that the CEC of uncontaminated sugarcane field soil was 3.56 ~ 61.01 cmol·kg− 1 higher than that of manganese-contaminated sugarcane soil 3.62 ~ 49.13 cmol·kg− 1 during the whole culture period. Compared with the control, the cation exchange capacity of uncontaminated sugarcane soil increased by 4.57 ~ 27.39%, 10.80 ~ 73.13% and 17.57 ~ 74.80% when treated with 0.5%, 2% and 5% biochar for 0 ~ 40 days, respectively. After 60 days of culture, it increased slowly and gradually stabilized. The CEC of control (0%ZSB) increased to 61.01 cmol·kg− 1, higher than other treatments. The CEC of biochar treatment in manganese-contaminated sugarcane soil increased with the proportion of biochar and increased with time. Compared with the control (0%MSB), the CEC of 0.5%, 2% and 5% biochar treatment increased by 0.87 ~ 50.83%, 7.30 ~ 65.11% and 26.59 ~ 175.64%, respectively, and increased slowly after 40 days of culture and gradually stabilized.
Effects Of Biochar Returning On Soil Nutrients (Dup: Abstract ?)
From Fig. 3, it can be seen that during the whole culture process, the content of AP in uncontaminated sugarcane soil and manganese-contaminated sugarcane soil increased with the increase of biochar ratio. Compared with the control, the application of biochar can significantly increase the content of AP in soil. The relationship of the content of AP in the unpolluted sugarcane field was 5%ZSB > 2%ZSB > 0.5%ZSB > 0%ZSB. The content of AP in the soil treated with 0.5%, 2% and 5% biochar increased by 143.85%, 417.06% and 663.32% respectively compared with the control (0%ZSB). The content of AP in the soil treated with 2% and 5% biochar was significantly higher than that of 0.5% biochar. When biochar was applied to manganese-contaminated sugarcane soil, the available phosphorus content in each treatment changed little during 0 ~ 40 days. After 40 days, the increase of 5%MSB was the largest, followed by 2%MSB, and 0.5%MSB was the smallest, which was significantly higher than that of the control (0%MSB). The increase of AP content was 5%MSB > 2%MSB > 0.5%MSB > 0%MSB. The ability of biochar to improve the content of AP in two kinds of sugarcane field soil was unpolluted soil > manganese polluted soil.
It can be seen from Fig. 4 that during the whole culture process, different biochar ratios applied to uncontaminated sugarcane field soil and manganese-contaminated sugarcane soil can increase the AK content in the soil to varying degrees, which is manifested as 5%ZSB > 2%ZSB > 0.5%ZSB > 0%ZSB, 5%MSB > 2%MSB > 0.5%MSB > 0%MSB. During the incubation period, the content of AK in uncontaminated sugarcane soil with 0.5%, 2% and 5% biochar increased by 5.95%, 48.85% and 117.42% on average compared with the control (0%ZSB). Compared with the control (0%MSB), the content of AK in manganese-contaminated sugarcane soil treated with 0.5%, 2% and 5% biochar increased by 54.82%, 210.11% and 251.66% on average, and the content of AK in the soil treated with biochar was significantly higher than that in the control. The ability of biochar to increase the AK content in uncontaminated sugarcane field soil was greater than that in manganese-contaminated sugarcane soil.
Effects Of Biochar Returning On Soc Mineralization
It can be seen from Fig. 5 that compared with the control, the application of biochar significantly reduced the CO2 emission rate in both sugarcane fields, and decreased with the increase of biochar ratio. During the whole incubation period, the CO2 emission rates of biochar application in the two sugarcane fields were lower than that of control. In the early stage of culture, the order of carbon dioxide emission rate of biochar applied in uncontaminated sugarcane soil was 0%ZSB > 0.5%ZSB > 2%ZSB > 5%ZSB; the order of carbon dioxide emission rate of biochar applied in manganese-contaminated sugarcane soil was 0%MSB > 0.5%MSB > 2%MSB > 5%MSB. In the uncontaminated sugarcane field soil, the CO2 emission rate decreased rapidly within 0 ~ 10 days. Compared with the control (0%ZSB), the application of 0.5%, 2% and 5% biochar decreased by 17.83 times, 18.27 times and 25.08 times, respectively. In the manganese-contaminated sugarcane soil, the application of 0.5%, 2%, and 5% biochar decreased by 14.74 times, 17.42 times, and 19.17 times, respectively, compared with the control (0%MSB). During the whole incubation period, the CO2 emission rate of each treatment can be divided into three stages: the soil CO2 emission rate is in a rapid decline stage in 0 ~ 10 days, the soil CO2 emission rate decreases slowly in 10 ~ 40 days, and the CO2 emission rate gradually stabilizes after 40 days.
It can be seen from Fig. 6 that the cumulative CO2 emissions in the two sugarcane fields decreased with the increase of biochar application ratio. After 0 ~ 40 days of incubation, the cumulative CO2 emissions of each treatment group increased rapidly and gradually stabilized. During the whole incubation process, the cumulative CO2 emissions in the uncontaminated sugarcane soil treated with different proportions of biochar were significantly lower than those in the control (0%ZSB) treatment. At the end of the incubation, the cumulative CO2 emissions in the ZSB treatment soil were 0%ZSB > 0.5%ZSB > 2%ZSB > 5%ZSB; the cumulative emission of soil carbon dioxide in MSB treatment was 0%MSB > 0.5%MSB > 2%MSB > 5%MSB. Compared with the control (0%ZSB), the cumulative CO2 emissions of uncontaminated sugarcane soil treated with different proportions of biochar decreased by 35.29 ~ 57.29%, respectively. Compared with the control (0%MSB), the cumulative CO2 emission of manganese-contaminated sugarcane soil treated with different proportions of biochar decreased by 15.78 ~ 36.87%.
As shown in Table 2, the first-order kinetic equation accurately simulated the mineralization dynamics of SOC during the 100 days incubation period. In general, the potential mineralization amount (C0) of organic carbon in different proportions of biochar treatments was significantly different. The soil range of ZSB biochar treatment was 481.268 ~ 1140.45 µg·g− 1, and the soil range of MSB biochar treatment was 486.594 ~ 740.359 µg·g− 1. It can be seen that the mineralization potential of soil decreased with the increase of biochar proportion. However, the soil carbon mineralization rate constant (k) showed an opposite trend. The k value of ZSB biochar treated soil varied between 0.069 and 0.135 d− 1, while that of MSB biochar treated soil varied between 0.089 and 0.101 d− 1.
Table 2
Kinetic parameters of soil carbon mineralization in biochar treatment
Different Treatments | Fitting Parameter |
C0/µg·g− 1 | k/d− 1 | R2 |
0%ZSB | 1140.45 ± 48.48 | 0.069 ± 0.009 | 0.95 |
0.5%ZSB | 758.529 ± 26.68 | 0.076 ± 0.010 | 0.95 |
2% ZSB | 627.780 ± 20.03 | 0.099 ± 0.012 | 0.96 |
5% ZSB | 481.268 ± 16.32 | 0.135 ± 0.019 | 0.94 |
0%MSB | 740.359 ± 24.49 | 0.089 ± 0.010 | 0.95 |
0.5% MSB | 634.238 ± 15.97 | 0.101 ± 0.010 | 0.97 |
2% MSB | 635.116 ± 14.48 | 0.100 ± 0.008 | 0.97 |
5%MSB | 486.594 ± 9.368 | 0.091 ± 0.006 | 0.98 |
Note: ZSB is biochar applied to uncontaminated sugarcane field soil, MSB is biochar applied to manganese-contaminated sugarcane soil, C0 represents soil carbon mineralization potential, and k represents soil carbon mineralization rate constant. |
Effects Of Biochar Returning On Different Carbon Fractions In Soil
Adding different proportions of biochar to uncontaminated sugarcane field soil and manganese-contaminated sugarcane soil could increase the content of SOC, and increased with the increase of biochar proportion (Fig. 7). At the end of incubation, different proportions of biochar were added to the uncontaminated sugarcane field soil. Compared with the control, the addition of 5% and 2% biochar significantly increased the content of SOC by 100% and 58.87%, respectively. The addition of 0.5% biochar did not significantly increase the content of organic carbon. The relationship of SOC content in each treatment was 5%ZSB > 2%ZSB > 0.5%ZSB > 0%ZSB. The SOC content in the manganese-contaminated sugarcane soil with 5%, 2%, and 0.5% biochar increased by 132.70%, 114.56%, and 33.41%, respectively, compared with the control. The relationship between the organic carbon content is 5%MSB > 2%MSB > 0.5%MSB > 0%MSB. Applying biochar in two kinds of sugarcane field soil, the SOC content in unpolluted soil is higher than that in manganese polluted soil.
From Table 3, it can be seen that the stability coefficient of SOC in the uncontaminated sugarcane field soil is greater than that in the manganese-contaminated sugarcane soil, and the stability coefficient of SOC in the two sugarcane fields generally increases with the increase of biochar application ratio.
Table 3
Two stability coefficients of SOC (soil organic carbon)
Stability Factors | 0% | 0.5% | 2% | 5% |
ZSB | 0.47 | 0.51 | 0.48 | 0.54 |
MSB | / | 0.07 | 0.50 | 0.53 |
Figure 8 shows the changes of MBC in uncontaminated and manganese-contaminated sugarcane soils with different biochar application rates. During the whole culture period, the MBC in the soil increased with the increase of biochar application ratio, and increased with the increase of culture time. At the end of incubation, the MBC content of 5%, 2% and 0.5% biochar applied to the uncontaminated sugarcane soil was 39.42 mg·kg− 1,37.92 mg·kg− 1 and 28.49 mg·kg− 1, respectively. Compared with the control (0%ZSB), the MBC content increased by 117.55%, 109.29% and 57.23%, respectively, and the increase was 5%ZSB > 2%ZSB > 0.5%ZSB. The MBC content of 5%, 2% and 0.5% biochar in manganese-contaminated sugarcane soil was 15.10 mg·kg− 1,13.71 mg·kg− 1 and 12.72 mg·kg− 1, respectively. Compared with the control (0%MSB), the MBC content increased by 180.15%, 154.36% and 135.99%, respectively. The increase was 5%MSB > 2%MSB > 0.5%MSB. Applying biochar to the two sugarcane fields, the MBC in the uncontaminated sugarcane field was greater than that in the manganese-contaminated sugarcane soil.
As shown in Fig. 9, the content of soil DOC increased first and then decreased with time when different proportions of biochar were applied to the uncontaminated sugarcane field. During the whole culture period, 0%, 0.5%, 2% and 5% biochar were applied, and the variation range of DOC was 32.24 ~ 14.99 mg·kg− 1,37.03 ~ 15.64 mg·kg− 1,43.50 ~ 16.11 mg·kg− 1 and 50.30 ~ 17.37 mg·kg− 1, respectively. The soil DOC content of 0%, 0.5% and 2% biochar reached the maximum of 32.24 mg·kg− 1,37.03 mg·kg− 1 and 43.50 mg·kg− 1 on the 10 th day of culture, respectively. The application of 5% biochar reached the maximum of 50.30 mg·kg− 1 on the 20 th day. Different proportions of biochar were applied to the soil of manganese-contaminated sugarcane soil, and the content of soil DOC decreased with the increase of biochar. During the whole culture period, 0%, 0.5%, 2% and 5% biochar were applied, and the variation range of DOC was 43.82 ~ 13.96 mg·kg− 1, 34.44 ~ 13.59 mg·kg− 1, 30.95 ~ 13.00 mg·kg− 1 and 26.27 ~ 11.94 mg·kg− 1, respectively. On the 15 th day, 0.5% and 2% biochar were applied. The DOC content reached the maximum of 34.44 mg·kg− 1 and 30.95 mg·kg− 1, respectively. When 0% and 5% biochar were applied, the DOC content reached 43.82 mg·kg− 1 and 26.27 mg·kg− 1, respectively, on the 20 th day of culture. The effect of biochar on DOC in two sugarcane fields was uncontaminated sugarcane field soil > manganese-contaminated sugarcane soil.
It can be seen from Fig. 10 that the application of different proportions of biochar can increase the content of ROC in uncontaminated sugarcane field soil and manganese contaminated sugarcane field soil, and it increases with the increase of biochar application proportion. Biochar was applied to uncontaminated sugarcane soil. The content of ROC increased slowly with time from 0 ~ 40 days. After 40 days, the increase of 2% and 5% biochar was more obvious, 2% increased from 1.23 mg·g− 1 to 2.20 mg·g− 1, 5% increased from 1.37 mg·g− 1 to 2.25 mg·g− 1, increased by 78.86% and 64.23%, respectively. The content of ROC ranged from 1.11 to 2.25 mg·g− 1 during the whole culture period. The content of ROC in the soil of manganese-contaminated sugarcane soil increased with the increase of biochar application ratio, and increased with the increase of culture time. The application of 0.5%, 2% and 5% biochar increased by 6.63%, 17.13% and 27.07% respectively compared with the control (0%MSB). The content of ROC in uncontaminated soil was generally higher than that in manganese-contaminated soil.
Effect Of Biochar Returning On Soil Enzyme Activity
As shown in Fig. 11, the application of biochar in both sugarcane fields could increase the content of catalase. With the increase of biochar application ratio, the content of catalase in uncontaminated sugarcane fields was much higher than that in manganese-contaminated sugarcane soils. The content of catalase activity in the soil of uncontaminated sugarcane field increased with time. At the end of culture, compared with the control (0%ZSB), the catalase activity of 0.5%, 2% and 5% treatments increased by 1.24 times, 1.33 times and 1.47 times, respectively. The content of catalase in the soil of manganese-contaminated sugarcane soil increased with time. At the end of culture, the catalase activity of 0.5%, 2% and 5% treatments increased by 2.19 times, 3.44 times and 4.48 times respectively compared with the control (0%MSB). The catalase activity in manganese-contaminated sugarcane soil was significantly lower than that in uncontaminated sugarcane field soil.
As shown in Fig. 12, the application of different proportions of biochar in uncontaminated sugarcane field soil and manganese-contaminated sugarcane soil could increase urease activity, and increased with time. The urease activity was 5%ZSB > 2%ZSB > 0.5%ZSB > 0%ZSB, 5%MSB > 2%MSB > 0.5% MSB > 0%MSB. In the uncontaminated sugarcane field soil, the application of 5% biochar reached the maximum value of 0.43 mg·g− 1·h− 1 on the 80 th day. At the end of the culture, the urease activities of 0.5%, 2% and 5% biochar treatments were 0.28 mg·g− 1·h− 1, 0.34 mg·g− 1·h− 1 and 0.42 mg·g− 1·h− 1, respectively, which were 1.05 times, 1.29 times and 1.59 times higher than those of the control (0%ZSB). In the manganese-contaminated sugarcane soil, at the end of the culture, the urease activities of 0.5%, 2%, and 5% biochar treatments were 0.56 mg·g− 1·h− 1, 0.59 mg·g− 1·h− 1, and 0.60 mg·g− 1·h− 1, respectively, which were 1.03 times, 1.08 times, and 1.10 times higher than the control (0%MSB). This experiment showed that biochar had a greater effect on soil urease activity in manganese-contaminated sugarcane soils.
Correlation Analysis
It can be seen from Fig. 13 that when biochar was applied to sugarcane field soil, CEC and ROC were significantly positively correlated with AP, CEC was significantly positively correlated with ROC, urease and catalase were significantly positively correlated with MBC. When biochar was applied to manganese-contaminated sugarcane soil, AK was significantly positively correlated with SOC, CEC and AP were significantly positively correlated with ROC, urease and catalase were significantly positively correlated with MBC, and pH was negatively correlated with cumulative CO2 emissions.