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Article

Dependence of Metolachlor Adsorption by Biochar on Soil Properties in South China

by
Lan Wei
†,
Lianxi Huang
†,
Xiang Li
,
Yufen Huang
,
Weisheng Chen
,
Rui Ma
and
Zhongzhen Liu
*
Key Laboratory of Plant Nutrition, and Fertilizer in South Region, Ministry of Agriculture, Guangdong Key Laboratory of Nutrient Cycling and Farmland Conservation, Institute of Agricultural Resources and Environment, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2024, 14(6), 1290; https://doi.org/10.3390/agronomy14061290
Submission received: 17 May 2024 / Revised: 8 June 2024 / Accepted: 13 June 2024 / Published: 14 June 2024
(This article belongs to the Section Agricultural Biosystem and Biological Engineering)
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Abstract

:
Sorption is the most important process influencing the amount of herbicide retained in soils. The special properties of biochar could influence the soil retention of pollutants through adsorption. However, the detailed sorption mechanisms as influenced before and after applying biochar to soils with different properties are unclear. This study examined the sorption characteristics of metolachlor using soil samples collected from South China. Sorption experiments were conducted using a batch equilibration method. After comparing the metolachlor sorption constants observed for all soil samples, our results showed that the application of biochar significantly increased the capacity of metolachlor adsorption. Without biochar, sorption capacity (Kf) was positively related to soil organic matter and to a soil particle size of 0.002–0.02 mm in soils developed from granite, of 0.002–0.02 mm in soils developed from delta shockwaves, and of 0.002–0.02 mm, together with complex iron oxide and total iron content, in soils developed from arenaceous shale. Moreover, sorption capacity (Kf) with biochar was positively related to peroxidase in soils developed from granite and to dissociative iron oxide and total iron content in soils developed from arenaceous shale. Our results show that biochar greatly affects metolachlor sorption behavior, probably because of qualitative differences in the structural characteristics of soils with different developmental parent materials and properties.

1. Introduction

Metolachlor (2-chloro-N-(6-rthyl-o-tolyl)-N-((1RS)-2-methoxy-1-methy-lethyl) is a selective pre-emergence herbicide used worldwide for controlling annual weeds in tomato, soybean, corn and potato fields. However, because of its high water solubility (20,530 mg L−1) and long half-life (126.0–135.9 d), metolachlor poses a high risk to aquatic ecosystems (REF). A few reports have shown that metolachlor has significant toxic effects on both rice and daphnia [1,2]. It is also listed as a possible cancer-causing substance by the World Health Organization. Herbicide absorption could prevent these substances from leaching into groundwater, especially in areas with high precipitation or sandy soils. The adsorption and desorption of metolachlor by the soil is largely determined by the physical behavior of pesticides in the environment, although most soils have a low affinity to metolachlor. Soil characteristics are known to play an important role in metolachlor sorption [3]. Soil minerals and soil organic matter (SOM) are major components that influence the sorption magnitude of organic chemicals, including pesticides. The results of Wu et al. [4] showed that the adsorption coefficient was significantly correlated with the SOM content (r = 0.990, p < 0.01). It has also been shown that SOM governs the extent to which sorption processes occur [5]. Moreover, reactive mineral components, such as silicate clays, oxyhydroxides and amorphous materials of Fe and Al, affect the adsorption of herbicides [6,7].
Numerous studies have shown that biochar and soil conditions are the most important factors influencing the efficiency of applied amendments to soil [8]. For example, the application of biochar to soil can affect the soil’s properties, such as its nutrient storage and release and its water and carbon storage. Biochar is a product obtained from the pyrolysis of waste biomass from agricultural and forestry production [9,10]. Many studies have demonstrated that given biochar’s highly aromatic nature, high surface area and micropore volume and abundance of polar functional groups, it is effective in increasing the uptake of a variety of organic chemicals, including pesticides, PAHs and emerging contaminants, such as steroidal hormones [11]. Among the positive effects of biochar are its ability to increase organic matter content, increase herbicide persistence in soils and improve soil physical properties. The addition of biochar increases the soil carbon content by a factor of at least 2. In White’s study, the addition of biochar to soil increased the soil’s adsorption capacity for metronidazole and dimethalin [12]. Wang et al. [13] observed that biochar-enhanced soil adsorption of the herbicide terbuthylazine was much greater in soil with low organic matter than in soil with a higher organic matter content. However, most studies have found that the adsorption of metolachlor depends mainly on SOM and is generally weak in most soils [1,14]. The weak adsorption of metolachlor results in a high likelihood of this herbicide moving downward through the soil with percolating water. Herbicidal compounds, along with their metabolites, are frequently detected in surface and ground waters as a result of their high leachability, which leads to a potential long-term threat to the environment because of their persistence in the environment [1]. Soil is the main medium through which metolachlor can pollute water and poison animals and plants. Therefore, controlling the leaching of metolachlor from soil is an effective method of controlling its distribution [15]. As such, the adsorption of organic pollutants in the soil–crop system is considered to be a determining factor controlling plant uptake and, therefore, public health risk through food chain transfers in the “soil–water environment” system [16]. After the adsorption of herbicides by biochar in soil, microorganisms can be used to help degrade organic pollutants [17]. Therefore, it is necessary to understand the adsorption effect of biochar addition to soils with different properties on metolachlor. This research is beneficial for improving agricultural soil quality and sustainable development.
Less information is available on the effect of soil physicochemical properties on biochar’s adsorption of organic pollutants. Thus, it is necessary to determine which factors are important in determining biochar’s increased adsorption of metolachlor in different soils. Therefore, knowledge of herbicide sorption in relation to the characteristics of different parent soils with biochar addition is very important, albeit limited.
Biochar is an important organic amendment that has the potential to influence soil structure, but its effects on specific soil types and properties have not been fully investigated. Most previous studies have focused on the influences of sorption in biochar–soil mixtures compared to soil only. The effects of soil characteristics on herbicide sorption in biochar–soil mixtures have rarely been investigated. We aimed to determine whether the effect of biochar addition on soils’ isothermal adsorption of metolachlor depends on specific soil characteristics. We hypothesized that the influence of biochar on soils’ isothermal adsorption of metolachlor may depend on specific soil properties, which are greatly affected by biochar addition. The research objectives are as follows: (1) to determine the characteristics of metolachlor adsorption of 22 typical farmland soils in the study region and their relationship with soil characteristics; and (2) to identify the effects of biochar addition on the metolachlor adsorption behavior of 22 soils and its mechanisms.

2. Materials and Methods

2.1. Soils and Biochar Addition

Twenty-two soils were sampled from the surface (0–20 cm) of typical croplands in Guangdong Province, China (Figure 1). These soils covered four parent materials and two cropping systems, and presented wide ranges of soil texture, extractable iron oxides, extractable Al, pH levels, organic matter and other chemical parameters. Soil samples were air-dried and passed through a 1-mm sieve. Parts of the samples served as soils without biochar, while other parts were thoroughly mixed with peanut shell-derived biochar at a mass ratio of 5% and served as soils with biochar. According to WRB Reference Soil Groups classification, the 22 soil samples belong to haplic ferralsol, dystric fiuvisol and rhodic ferralsol.

2.2. Biochar

Biochar was prepared using the pyrolysis of peanut shells at 300 °C for 2–3 h in a muffle furnace with nitrogen. The elemental contents of C, H, O, N and S were 45.83%, 1.88%, 50.78%, 1.06% and 0.45%, respectively.

2.3. Adsorption Experiments

Isothermal adsorption of metolachlor was performed using a batch equilibrium experiment. Briefly, portions of both control and biochar-amended soils, each weighing 1 g, were thoroughly mixed with a series of 10 mL metolachlor solutions to obtain a series of initial metolachlor concentrations of 0, 10, 20, 30, 50 and 80 mg kg−1. The ratio of soil to metolachlor solution was selected to achieve measurable sorption of the original chemical. In glass centrifuge tubes (30 mL) with Teflon-lined caps, 1 μL of each concentration of metolachlor solution (0, 10, 20, 30, 50 and 80 mg kg−1) was added to 1 g of control soil or 1 g of soil including 5% biochar. Following horizontal shaking at 20 ± 2 °C for 24 h in a dark room, the supernatants obtained at 1280 g for 15 min were filtered through a 0.45 μm PTFE filter and then analyzed for metolachlor content using a high-performance liquid chromatograph (Waters Alliance e2695, Waters Company, Milford, MA, USA) fitted with a UV detector [18].

2.4. Fitting of Adsorption Isotherm Equation

The adsorption data were fitted with the Langmuir and Freundlich models, respectively, using the following fitting equations:
Langmuir :   Q e q = Q m b C e q 1 + b C e q
Freundlich :   Q e q = K f C e q 1 n
In Equations (1) and (2), Qeq and Ceq are the solid phase equilibrium concentration (mg kg−1) and liquid phase equilibrium concentration of metolachlor (mg L−1), respectively; Qm is the theoretical maximum adsorption capacity, mg g−1; b is the constant of the Langmuir isotherm equation, L mg−1; and Kf and n are constants of the Freundlich isothermal equation, mg1−n Ln kg−1 (Table 1).
These two equations are the most commonly used descriptive equations for adsorption processes. The Langmuir model assumes single-layer adsorption, that is, that adsorption only occurs on the outer surface of the adsorbent. The Freundlich equation can be applied to both single-layer adsorption and nonuniform surface adsorption. The Freundlich equation can properly describe the adsorption mechanism of nonuniform surfaces and is more suitable for situations involving low adsorption concentrations, allowing the explanation of experimental results over a wider concentration range.

2.5. Analytical Methods

Chemical and ultimate analyses were performed to determine pH, soil organic matter, cation exchange capacity (CEC), total and available nitrogen, and phosphorus and potassium (TN/AN, TP/AP and TK/AK, respectively) [19] (Table 2). The particle size distribution was estimated using micropipette texture analysis. The determination of soil enzymes mainly adopts the improved method of Dick [20]. All the iron oxides in the soil were extracted and determined by flame spectrophotometry using the method of Lu [19]. The determination method of Al forms is based on the method of Yu et al. [21].

2.6. Data Processing and Statistics

The experimental data were analyzed using an Origin 8.0 fitting cooperation chart and SPSS 19.0. Duncan multiple comparisons were used for the significance analysis, with a significance level of 0.05.

3. Results

3.1. Isothermal Adsorption Characteristics in the 22 Soils without Biochar Additions

The fitting results of the Langmuir and Freundlich models are shown in Table 1. And we take GZ-2 and ST-3 as examples to describe the adsorption isotherm of metolachlor onto different soils (Figure 2). In soil without biochar addition, the fitting degree was R2 (Freundlich) (0.87–1.00) > R2 (Langmuir) (0.74–1.00). The Freundlich equation was more suitable than the Langmuir equation for describing the adsorption characteristics of soil for metolachlor. The adsorption constant Kf of the Freundlich model represents the magnitude of the soil’s ability to adsorb metolachlor. In the soils without biochar addition, the numerical range of Kf was 0.01–63.18 mg1−n Ln kg−1, with an average value of 11.58 and a median of 7.72 mg1−n Ln kg−1.
The value of n represents the reversibility of the adsorption process and the degree of nonuniformity. In the soil system without biochar addition, the numerical range of n was 0.32–3.16, with an average of 0.96 and a median of 0.79. n indicates the degree of surface nonuniformity, which is the energy distribution of adsorption sites caused by their heterogeneity. When 0 < n < 1, the adsorption process is favorable; if n > 1, this indicates that the adsorption process is unfavorable.
The 22 types of soils collected were mostly acidic, within a pH range of 4.13–7.06 and with a median value of 5.53. The soil organic matter (SOM) content was 8.33–46.27 g kg−1, with an average of 22.46 g kg−1 and a median of 19.55 g kg−1. The average and median total nitrogen (N), phosphorus (P) and potassium (K) contents were 1.44 and 1.40 g kg−1, 1.32 and 1.14 g kg−1, and 18.57 and 19.47 g kg−1, respectively. According to the American soil texture classification system, among the 22 soils, loam accounts for 90.91% of the samples, loam and clay account for 22.73%, sandy loam accounts for 40.91% and sandy clay accounts for 9.09% (Table 2).
The activity ranges of dehydrogenase (DHO), peroxidase (POD), polyphenol oxidase (PPO), invertase (INV), protease (PRO), phosphatase (ACP), catalase (CAT) and urease (EC) in the soil samples were 6.15–193.97 mg g−1, 221.13–8230.16 mg 100 g−1, 20.70–1896.56 mg 100 g−1, 0.08–0.28 mL g−1, 521.62–9828.59 µg g−1, 0.43–139.79 mg 100 g−1, 0.07–0.52 mmol 100 g−1 and 4.08–71.70 mg 100 g−1, respectively. The average and median values were 101.99 and 89.13 mg g−1, 4881.70 and 5421.09 mg 100 g−1, 460.83 and 266.21 mg 100 g−1, 0.16 and 0.15 mL g−1, 3473.26 and 2731.22 µg g−1, 48.28 and 41.47 mg 100 g−1, 0.24 and 0.19 mmol 100 g−1, 23.17 and 14.81 mg 100 g−1, respectively (Table 2).
There were significant differences in the contents of iron and aluminum in different forms of soil across the different regions. The content of free iron oxide in the soil ranged from 697.48 to 3351.56 mg kg−1, with an average of 3416.02 mg kg−1. The content of amorphous iron oxide ranged from 1296.56 to 7776.34 mg kg−1, with an average of 3595.49 mg kg−1. The content of complex iron oxide ranged from 243.03 to 901.51 mg kg−1, with an average of 584.14 mg kg−1. The total iron content ranged from 2998.89 to 9728.86 mg kg−1, with an average of 6065.84 mg kg−1.
The soluble aluminum content in the soil ranged from 0.10 to 9.87 mg kg−1, with an average of 2.32 mg kg−1. The exchange state aluminum content ranged from 0.55 to 13.71 mg kg−1, with an average of 4.24 mg kg−1. The content of monomeric hydroxyl aluminum ranged from 0.04 to 1.10 mg kg−1, with an average of 0.39 mg kg−1. The content of acid-soluble inorganic aluminum ranged from 356.68 to 1764.78 mg kg−1, with an average of 1117.44 mg kg−1. The organic complex aluminum content ranged from 9.32 to 37.79 mg kg−1, with an average of 20.14 mg kg−1. The content of aluminum humate ranged from 39.79 to 2311.81 mg kg−1, with an average of 1074.36 mg kg−1. The total aluminum content was between 705.59 and 3742.82 mg kg−1, with an average of 2218.90 mg kg−1 (Table 2).
The collected soil samples could be divided into arenaceous shale (7), delta sediment (5), granite (7) and alluvial deposits (2) according to the different parent materials [22]. The parent material had a significant impact on the different forms of soil organic matter, textures and iron contents, which were also the main factors influencing the soil’s adsorption of metolachlor. The average organic matter contents of soil developed by arenaceous shale, delta sediment, granite and alluvial deposits were 19.20, 27.96, 20.07 and 29.29 g kg−1, respectively. Moreover, 59.47%, 29.84%, 62.29% and 23.00% of soils from each parent material had a particle size of 2–0.02 mm; 24.56%, 35.96%, 20.57% and 44.30% had a particle size of 0.02–0.002 mm; and 15.97%, 34.20%, 17.14% and 32.70% had a particle size <0.002 mm. The dissociative iron oxide contents of the four soil parent materials were 1610.49, 1841.61, 1925.28 and 226.04 mg kg−1, respectively. The complex iron oxide contents were 612.34, 561.13, 542.35 and 689.19 mg kg−1, respectively. The total iron contents were 4712.25, 7117.72, 360.67 and 7141.80 mg kg−1, respectively.

3.2. Isothermal Adsorption Characteristics in the 22 Soils with Biochar Additions

The fitting degree on the biochar + soil samples was R2 (Freundlich) (0.73–1.00) > R2 (Langmuir) (0.78–1.00)(Table 3), which was similar to the soil samples without biochar addition. And we take GZ-4 and ZH-2 as examples to describe the adsorption isotherm of metolachlor onto different soils + biochar (Figure 3). The Freundlich model was more suitable than the Langmuir model to describe the adsorption characteristics of soil + biochar for metolachlor. In the soil + biochar system, the Kf range was 0.01–82.27 mg1−n Ln kg−1, with an average value of 32.41 mg1−n Ln kg−1 and a median of 29.04 μg1−1/n mL1/n g−1. In the soil + biochar system, the numerical range of n was 0.28–2.16, with an average of 1.13 and a median of 1.03.
Table 3. Isotherm constants for metolachlor adsorption onto different biochar + soil.
Table 3. Isotherm constants for metolachlor adsorption onto different biochar + soil.
FreundlichLangmuir
Kf
(mg1−n Ln kg−1)		nR2b
(L mg−1)		Qm
(mg g−1)		R2
GZ-133.80 ± 1.411.17 ± 0.011.00141.62 ± 9.323540.73 ± 125.241.00
GZ-282.27 ± 1.110.41 ± 0.010.9419.01 ± 1.25583.34 ± 85.420.93
TS-121.00 ± 0.980.85 ± 0.020.982.53 ± 0.0513.09 ± 0.850.94
TS-256.35 ± 1.031.77 ± 0.020.7339.87 ± 0.25945.86 ± 69.320.78
TS-323.75 ± 0.780.89 ± 0.040.952.20 × 1015 ± 0.01 × 10158.11 × 1016 ± 0.02 × 10160.94
HZ-10.80 ± 0.210.56 ± 0.020.971.33 × 1016 ± 0.01 × 10162.02 × 1017 ± 0.01 × 10170.81
HZ-232.23 ± 0.231.63 ± 0.050.9251.12 ± 0.35735.25 ± 99.250.95
HZ-360.29 ± 0.141.10 ± 0.040.88148.25 ± 8.258000.36 ± 253.410.89
DG-130.06 ± 0.111.81 ± 0.040.9540.70 ± 0.69487.18 ± 17.320.97
DG-228.99 ± 0.140.95 ± 0.020.993.42 × 1015 ± 1.41 × 10151.17 × 1017 ± 0.02 × 10170.99
HZ-413.23 ± 0.110.84 ± 0.030.846.29 × 1014 ± 0.02 × 10141.67 × 1016 ± 0.01 × 10160.91
HZ-522.58 ± 0.091.30 ± 0.050.93129.07 ± 1.411648.12 ± 154.250.91
GZ-311.62 ± 0.110.77 ± 0.071.001.19 × 1016 ± 0.04 × 10163.84 × 1017 ± 0.02 × 10170.95
GZ-423.58 ± 0.151.44 ± 0.110.9678.34 ± 1.58926.29 ± 142.310.97
GZ-530.59 ± 0.120.95 ± 0.080.891.68 × 1004 ± 0.08 × 10046.14 × 105 ± 0.02 × 1050.88
HS-129.10 ± 0.082.16 ± 0.140.9427.15 ± 0.14280.94 ± 1.410.99
JM-156.28 ± 0.171.36 ± 0.050.9976.53 ± 0.272530.87 ± 100.880.99
ZH-276.86 ± 0.311.38 ± 0.070.9962.61 ± 0.522882.66 ± 99.261.00
ST-125.29 ± 0.180.90 ± 0.060.993.33 × 1014 ± 0.26 × 10141.26 × 1016 ± 0.03 × 10160.98
ST-243.97 ± 0.211.51 ± 0.080.9960.92 ± 1.981324.82 ± 111.540.99
ST-310.25 ± 0.230.80 ± 0.070.982.62 × 1015 ± 0.10 × 10156.51 × 1016 ± 0.01 × 10160.95
Compared with the soil samples without biochar addition, the addition of a small amount of biochar increased the soil’s adsorption of metolachlor, with an increase ratio ranging from 64% to 300,500%. The most significant increase was in soils from arenaceous shale (44,904 times), followed by granite (985 times), and the lowest increase was in soils developed from delta sediments (237 times).
In our experiment, the average value of n in the adsorption equation of metolachlor by soil without biochar was 0.955, and the average value of n after biochar addition was 1.211. We believe that the content of organic matter and clay particles has the greatest impact on the adsorption of metolachlor under different soil conditions. Marín-Benito’s [16] research also showed that the isothermal adsorption curve of metolachlor in soil with higher organic matter was linear, characterized by an n value close to 1, which is consistent with our research. However, when biochar was added to the soil, although the direct effect of biochar on the adsorption of metolachlor was not significant, biochar affected the adsorption of herbicides by combining with iron oxides and aluminum oxides. Under the action of different adsorption mechanisms, the isothermal adsorption curve was nonlinear, and the n value deviated from 1.

3.3. The Relationships between Isothermal Adsorption Parameters and Soil Properties

Figure 4 shows that the main factors affecting the adsorption of metolachlor in soils developed from arenaceous shale parent materials were organic matter and particles with a diameter of 0.002–0.02 mm, with correlation coefficients of 0.7972 and 0.8510 (p < 0.05), respectively. The main influencing factor on the development of soils developed from delta sediments was particles with a size of 0.002–0.02 mm, which had a positive correlation coefficient of 0.8860 (p < 0.05). The main influencing factors of soils developed from granite affecting the adsorption of metolachlor were particles with sizes of 0.002–0.02 mm and complex iron oxide and total iron contents, with correlation coefficients of 0.8212, 0.7682 and 0.8140 (p < 0.05), respectively (data sourced from Figure 5). The main influencing factor of soils developed from delta shockwave affecting the adsorption of metolachlor was a diameter of 0.002–0.02 mm (Figure 6). However, when we compared all soils together, the number of factors that affected the adsorption of metolachlor in the soil increased (Figure 7). The 0.002–0.02 mm particle size, <0.002 mm particle size, dissociative iron oxide content and total iron content were significantly positively correlated with Kf (p < 0.05), while the 0.02–2 mm particle size was significantly negatively correlated with the adsorption constant Kf (p < 0.05).
After the biochar was added to the soil, the main factors affecting the adsorption of metolachlor in the soil from arenaceous shale parent materials development were no longer organic matter and particle size, but were significantly negatively correlated with the content of soil peroxidase and soil urease, with correlation coefficients of −0.7731 and −0.8578 (p < 0.05) (data sourced from Figure 8). There was no significant correlation between the adsorption of metolachlor and all physicochemical properties of the soil developed from delta sediments after biochar addition. The addition of biochar to soil developed from granite mainly affected the adsorption of metolachlor via the dissociative iron oxide and total iron content, with correlation coefficients of 0.8055 and 0.7790 (p < 0.05), respectively. When we compared all soil types together, the organic matter, CEC content, 0.002–0.02 mm particle size and <0.002 mm particle size showed a significant positive correlation (p < 0.05) with Kf after biochar addition, while the 0.02–2 mm particle size showed a significant negative correlation (p < 0.05) with the adsorption constant Kf.

4. Discussion

4.1. The Characteristics of Metolachlor Adsorption in the 22 Soils

The adsorption and leaching behavior of herbicides in soil were mainly affected by the characteristics of the herbicides and the soil’s physical and chemical properties. Generally, the higher the content of organic matter in the soil, the stronger its ability to adsorb herbicides [4]. Previous studies have shown that the adsorption of herbicides in soil is mainly influenced by soil organic carbon and mineral contents, but that different herbicides have varying degrees of control in different soils [23]. The adsorption of metolachlor in soil was positively correlated with organic matter [24], clay content [25] and soil surface area [26], and negative correlations with clay content have also been reported [27]. Our experimental results also showed that the adsorption behaviors of metolachlor by soils collected from different regions of Guangdong Province were significantly different. However, there was no significant positive correlation between soil organic matter and adsorption capacity Kf. In general, the correlation analysis showed that the Kf value, representing the adsorption capacity in the Freundlich isotherm model, had a positive correlation with the percentage of different particle sizes, the content of dissociative iron oxides and total iron oxides. In our study, soils with low organic matter content, such as arenaceous shale and granite soils, had much lower adsorption constants for metolachlor than soils rich in organic matter content, such as soils derived from delta and fluvial sediments. This might be due to the fact that organic matter provides an order of magnitude higher adsorption capacity than clay minerals, resulting in clay minerals not playing a major role in the adsorption of metolachlor in these soils. Therefore, in soils rich in organic matter soil formed by alluvial materials, the adsorption constant of metolachlor was much higher than in the other two soil types. This was consistent with the research findings by Paszko et al. [17], who found that both the neutral and the anionic forms of phenoxyalkanoic acid herbicides were absorbed, primarily by organic matter.
Studies conducted on pure minerals revealed that the anionic forms of phenoxyalkanoic acids are sorbed on ferrihydrite, goethite and lepidocrocite; on α-alumina; and on complexed Al(OH)x-montmorillonite [17,28,29]. In soils with low organic matter content, mineral content and soil particle size composition might be the main factors affecting the adsorption of metolachlor. The content of clay in soil solid matter was generally composed of aluminosilicate and its oxides. Soil clay of small particle sizes has a larger specific surface area and greater surface electrification and cation exchange. Therefore, small soil particle sizes, especially in clay minerals, serve as strong adsorbents. In this experiment, the soil particle size composition was significantly positively correlated with Kf in soils developed from arenaceous shale and granite. The adsorption of herbicides by soil particles was mainly based on van der Waals forces, and the surface area might be an important factor in the different herbicide adsorption effects of different soil particles. As a result, there was a significant positive correlation between the soil particle size occupancy of 0.002–0.02 mm and the adsorption constant Kf for all soil types.
When the organic matter content in the soil was low, minerals, especially iron oxides, also played a leading role in the adsorption of herbicides [30]. Janniche et al.’s [31] study showed that the adsorption of isoproterenol and acetochlor in heterogeneous limestone was more controlled by mineralogy than by organic carbon content. The content of mineral elements in soils developed from different parent materials varies greatly. Barré et al. [32] speculated that the differences in the physical properties and composition of soils developed from four parent materials not only directly affect the mineralization process of organic carbon but may also affect soil retention of organic matter by changing the particle size distribution of aggregates and the distribution of organic carbon. At the same time, the adsorption capacity of isoprene by kaolin was greater than that of quartz, calcite, alumina [29] and iron oxides [28], indicating that its adsorption was more related to the clay content and the adsorption of herbicides in the soil [33,34]. Moreover, for a nonionic compound such as metolachlor, the soil’s solid phase components, such as iron, aluminum oxides and layered silicate minerals, exhibit hydrophilicity in the interlayer space due to the strong hydration of inorganic ions, resulting in weak affinity for most nonionic organic compounds [35]. Chang et al. [36] found that the distribution of herbicides in soil was influenced by soil particle size and geological setting.
Various forms of iron oxide have been found to be important mineral cementitious materials in soil, playing bridging or connecting roles in the formation of soil structures. Dissociative iron oxide and amorphous iron oxide are the main carriers of variable charges in soil. Dissociative iron oxides have a specific adsorption of some metal ions and multivalent oxyacid roots, which is generally positively correlated with the content of soil clay [37]. Therefore, in addition to organic matter and soil clay particles, the different forms of iron content in the soil were also important factors affecting metolachlor adsorption.

4.2. The Impacts of Biochar Addition on Metolachlor Adsorption of the 22 Soils

Spokas et al. [38] studied the sorption of acetochlor, another chloroacetanilide herbicide, and reported greater absorption in the soil amended with biochar, increasing the Freundlich Kf value from 4.1 to 6.6 mg1−n Ln kg−1 with the amendment. In our experiment, the average Freundlich Kf value of the 22 soils was 12.13 mg1−n Ln kg−1, but after applying biochar to the soils, the average Freundlich Kf value increased to 33.95 μg1−1/n mL1/n g−1. However, the adsorption Kf of the combination of biochar and soil on metolachlor in this test was lower than that in other studies. The reason for this might be that the biochar used in this study was prepared at 300 °C. Yang et al. [39] posited that temperature is more important than feedstock material in determining the effectiveness of a biochar for the treatment of contaminated soils.
Wang et al.’s [13] research revealed that the adsorption of metolachlor in soil was mainly controlled by hydrogen bonding with alcohol, phenol and acid hydroxyl groups on the surface of humic acid. However, biochar could change the content of humic acid and other active substances in soil OM. Therefore, the organic matter content was significantly positively correlated with the Kf value of all types of soils with biochar addition.
In addition to SOM, the sorption of metolachlor was also related to CEC and soil clay particle size in this study. Tang et al. [40] showed that after biochar products were added to the soil, the adsorption capacity of the modified soil increased with the increase in the total amount of biochar/compost added, which was positively correlated with the SOM, CEC and EC of the modified soil. Biochar addition increases the content of CEC in soil and thus increases the soil’s adsorption of metolachlor. Therefore, in the mixture of soil and biochar, the correlation of metolachlor adsorption with CEC increased. Álvarez-Benedí et al. [41] discovered that the sorption of tribenuron-methyl, chlorsulfuron and imazamethabenz-methyl was correlated with OM and clay content. In our research, whether or not biochar was added to the soil, the distribution of silt (0.02–0.002 mm) and clay (<0.002 mm) particles had a significant positive correlation with Kf. Meanwhile, after biochar was added to the soil, this correlation tended to increase, and the relationship between clay and Kf showed a very significant positive correlation. After biochar is applied to the soil, it reacts with various soil components in a short time, especially with a large and wide variety of soil minerals, combining with these components in a variety of ways to form numerous biochar–mineral complexes [42]. The application of biochar to soil can significantly change the total porosity and pore size distribution of the soil, reducing the influence of particle size on adsorption constants in soils with different parent material development. Research has shown that the addition of biochar improves soil surface aggregates and mineral structure, leading to an increase in hydrophobicity, which is beneficial for the adsorption of metolachlor as a nonionic compound [43]. Therefore, the application of biochar increases the soil’s adsorption capacity for metolachlor.
However, after adding biochar to soil, the increased adsorption capacity differs with different parent materials. For delta sediment and river sediment soils, both of which have high organic matter contents, the addition of biochar makes it easy for soluble organic matter in the soil to interact with the surface of biochar, limiting the availability of adsorption sites on the biochar’s surface. Therefore, biochar addition cannot significantly increase the adsorption of metolachlor on the surface of these soils [44], and there was no significant correlation between Kf and organic matter or other physicochemical properties in the delta sediment and river sediment soils. For soil types with low organic matter contents, such as granite and arenaceous shale, biochar first combines with inorganic colloids (clay particles and free oxides) to form water-stable microaggregates with smaller particle sizes [45,46]. Then, the increased organic carbon introduced by the biochar first enters the microaggregates and gradually transfers to the macroaggregates for storage [47]. Soil aggregates have a certain physical protective effect on organic carbon and promote the accumulation of organic carbon at different particle sizes in the soil [48]. Furthermore, the adsorption capacity of soil + biochar for metolachlor increases. Wang et al. [49] found that the addition of biochar significantly increased the content of aggregates >0.25 mm by 47.32%. Xue et al. [50] analyzed the soil structure by adding biochar and straw to three types of soil and found that the proportions of large aggregates (2–0.5 mm) and medium aggregates (0.5–0.25 mm) significantly increased and the stability index of the soil aggregates was better than the control’s. The application of biochar reduced soil bulk density [51], provides a large amount of organic matter and enhances the activity of roots and soil microorganisms, thereby increasing the quantity and size of soil macroaggregates. This was also the main reason why there was still a correlation between the overall Kf and particle size after adding biochar to the soil.
Lehmann et al. [52] believed that -COO and aromatic functional groups contained in biochar might coordinate with soil minerals, especially goethite. Our previous research showed that biochar prepared at lower temperatures had more available adsorption points, such as aromatic groups and -COO, enabling it to adsorb metolachlor better [18]. After biochar is added to the soil, it combines with free iron oxides to form more active functional groups that contain free radicals, hydrophilic groups and other functional groups. It can be combined with herbicides, especially nonionic herbicides, better than other components of the soil [23]. Shi et al. [53] found that the vibration intensity of the characteristic peak of biochar/Fe(OH)3 composite surface functional groups was significantly stronger than that of the original biochar, indicating that there were more functional groups on the surface of the composites. The combination of biochar and dissociative iron oxide weakened the correlation between the adsorption constant Kf and dissociative iron oxide.
Both soil peroxidase and dehydrogenase, mainly derived from microorganisms, are closely related to the synthesis of soil humus components and soil formation processes [54,55]. The reproduction of microorganisms helps to open the pores blocked by biochar, increasing the sites where soil + biochar can adsorb herbicides [54]. However, in our study, no soil enzyme activities were significantly correlated with Kf values before or after the application of biochar. The reason for this might be that the experimental time was too short and the impact on soil microbial activity had not yet been fully revealed.

5. Conclusions

There were significant differences in the capacities of soils developed from different parent materials to adsorb metolachlor. The application of biochar to soils in South China would significantly increase their capacity for metolachlor adsorption. Regardless of whether or not biochar was applied to the soil, particle size was the most important factor affecting the soil’s adsorption of metolachlor, especially the soil particle size of 0.002–0.02 mm. This particle size (0.002–0.02 mm) was significantly positively correlated with Kf in all soils with different parent materials. However, after the addition of biochar, the effect of this particle size (0.002–0.02 mm) on soils with different parent materials weakened. In addition, the ability of soil without biochar to adsorb metolachlor (Kf) was significantly positively correlated with the content of free iron oxides and total iron, while Kf after adding biochar was also positively correlated with CEC and soil organic matter. This study provides scientific evidence for the response to herbicides in different soils with biochar application, which can elucidate the complex roles that biochar plays in various environmental contexts for organic pollution control.

Author Contributions

Methodology, X.L.; Software, R.M.; Validation, Y.H.; Data curation, W.C.; Writing—original draft, L.W.; Writing—review & editing, L.H.; Project administration, Z.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Low Carbon Agriculture and Carbon Neutralization Research Center, GDAAS (XT202220).

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy concerns.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Liu, L.; Dai, Y. Strong adsorption of metolachlor by biochar prepared from walnut shells in water. Environ. Sci. Pollut. Res. 2021, 28, 48379–48391. [Google Scholar] [CrossRef]
  2. Liu, L.; Yuan, M.; Wang, X.; Li, X.; Dai, Y. Biochar aging: Properties, mechanisms, and environmental benefits for adsorption of metolachlor in soil. Environ. Technol. Innov. 2021, 24, 101841. [Google Scholar] [CrossRef]
  3. Zhang, Y.; Yang, C.; Zheng, Z.; Cao, B.; You, F.; Liu, Y.; Jiang, Z. Mechanism for various phytotoxicity of atrazine in soils to soybean: Insights from soil sorption abilities and dissolved organic matter properties. J. Environ. Manag. 2021, 297, 113220. [Google Scholar] [CrossRef] [PubMed]
  4. Wu, L.; Zhao, L.; Bi, E. Predicting the effect of dissolved humic acid on sorption of benzotriazole to biochar. Biochar 2022, 1, 203–215. [Google Scholar] [CrossRef]
  5. Weber, J.; Mckinnon, E.; Swain, L. Sorption and mobility of 14C-labeled imazaquin and metolachlor in four soils as infuenced by soil properties. J. Agric. Food Chem. 2003, 51, 5752–5759. [Google Scholar] [CrossRef]
  6. Wang, Y.; Zhang, X.; Zhang, X.; Meng, Q.; Gao, F.; Zhang, Y. Characterization of spectral responses of dissolved organic matter (DOM) for atrazine binding during the sorption process onto black. Soil Chem. 2017, 180, 531–539. [Google Scholar] [CrossRef] [PubMed]
  7. Yang, X.; Zhang, S.; Liu, L. Study on the long-term effects of DOM on the adsorption of BPS by biochar. Chemosphere 2020, 242, 125165. [Google Scholar] [CrossRef]
  8. De Jesus Duarte, S.; Glaser, B.; Cerri, C. Effect of Biochar Particle Size on Physical, Hydrological and Chemical Properties of Loamy and Sandy Tropical Soils. Agronomy 2019, 9, 165. [Google Scholar] [CrossRef]
  9. Chen, H.; Qin, P.; Yang, X.; Bhatnagar, A.; Shaheen, S.; Rinklebe, J.; Wu, F.; Xu, S.; Che, L.; Wang, H. Sorption of diethylphthalate and cadmium by pig carcass and green waste-derived biochars under single and binary systems. Environ. Res. 2021, 193, 110594. [Google Scholar] [CrossRef]
  10. Houssou, A.; Jeyakumar, P.; Niazi, N.; Zwieten, L.; Li, X.; Huang, L.; Wei, L.; Zheng, X.; Huang, Q.; Huang, Y.; et al. Biochar and soil properties limit the phytoavailability of lead and cadmium by Brassica chinensis L. in contaminated soils. Biochar 2022, 1, 58–72. [Google Scholar] [CrossRef]
  11. Askeland, M.; Clarke, B.; Cheema, S.; Mendez, A.; Gasco, G.; Paz-Ferreiro, J. Biochar sorption of PFOS, PFOA, PFHxS and PFHxA in two soils with contrasting texture. Chemosphere 2020, 249, 126072. [Google Scholar] [CrossRef]
  12. White, J.; Potter, T.; Lima, I. Sugarcane bagasse and pine wood biochar effects on aerobic soil dissipation of metribuzin and pendimethalin. In Proceedings of the American Chemical Society Fall 2011 National Meeting and Exposition, Denver, CO, USA, 28 August–2 September 2011. [Google Scholar]
  13. Wang, H.; Lin, K.; Hou, Z.; Richardson, B.; Gan, J. Sorption of the herbicide terbuthylazine in two New Zealand forest soils amended with biosolids and biochars. J. Soils Sediments 2010, 10, 283–289. [Google Scholar] [CrossRef]
  14. Sigmund, G.; Castan, S.; Wabnitz, C.; Bakkour, R.; Huffffer, T.; Hofmann, T.; Elsner, M. NO2 and natural organic matter affect both soot aggregation behavior and sorption of S-metolachlor. Environ. Sci. Process. Impacts 2019, 21, 1729. [Google Scholar] [CrossRef]
  15. Sun, Y.; Zhao, L.; Li, X.; Xu, H.; Weng, L.; Yang, L.; Li, Y. Response of soil bacterial and fungal community structure succession to earthworm addition for bioremediation of metolachlor. Ecotoxicol. Environ. Saf. 2020, 189, 109926. [Google Scholar] [CrossRef]
  16. Marín-Benito, J.; Herrero-Hernandez, E.; Ordax, J.; Sanchez-Martín, M.; Rodríguez-Cruz, M. The role of two organic amendments to modify the environmental fate of S-metolachlor in agricultural soils. Environ. Res. 2021, 195, 110871. [Google Scholar] [CrossRef]
  17. Paszko, T.; Muszy’nski, P.; Materska, M.; Bojanowska, M.; Kostecka, M.; Jackowska, I. Adsorption and degradation of phenoxyalkanoic acid herbicides in soils: A review. Environ. Toxicol. Chem. 2016, 35, 271–286. [Google Scholar] [CrossRef]
  18. Wei, L.; Huang, Y.; Huang, L.; Li, Y.; Huang, Q.; Xu, G.; Müller, K.; Wang, H.; Ok, Y.; Liu, Z. The ratio of H/C is a useful parameter to predict adsorption of the herbicide metolachlor to biochars. Environ. Res. 2020, 184, 109324. [Google Scholar] [CrossRef]
  19. Lu, R.K. Soil Agricultural Chemical Analysis and Method; Chinese Agriculture Science and Technology Press: Beijing, China, 2000. (In Chinese) [Google Scholar]
  20. Dick, R. (Ed.) Methods of Soil Enzymology; Soil Science Society of America: Madison, WI, USA, 2011; pp. 71–84. [Google Scholar]
  21. Yu, J.; Yu, Y.; Fang, L.; Shu, H. Effects of low molecular weight organic acids on the pH and the form of aluminum of forest soils. J. Fujian Coll. For. 2005, 245, 243–246. (In Chinese) [Google Scholar]
  22. Shi, X.; Yu, D.; Warner, E.; Pan, X.; Petersen, G.; Gong, Z.; Weindorf, D. Soil Database of 1:1,000,000 Digital Soil Survey and Reference System of the Chinese Genetic Soil Classification System. Soil Surv. Horiz. 2004, 45, 129–136. [Google Scholar] [CrossRef]
  23. Spark, K.; Swift, R. Effect of Soil Composition and Dissolved Organic Matter on Pesticide Sorption. Sci. Total Environ. 2002, 298, 147–161. [Google Scholar] [CrossRef]
  24. Si, Y.; Takagi, K.; Iwasaki, A.; Zhou, D. Adsorption, desorption and dissipation of metolachlor in surface and subsruface soils. Pest Manag. Sci. 2009, 65, 956–962. [Google Scholar] [CrossRef] [PubMed]
  25. Kodešová, R.; Kočárek, M.; Kodeš, V.; Drábek, O.; Kozák, J.; Hejtmánková, K. Pesticide adsorption in relation to soil properties and soil type distribution in regional scale. J. Hazard. Mater. 2011, 186, 540–550. [Google Scholar] [CrossRef] [PubMed]
  26. Peter, C.; Weber, J. Adsorption, Mobility, and Efficacy of Alachlor and Metolachlor as Influenced by Soil Properties. Weed Sci. 1985, 33, 874–881. [Google Scholar] [CrossRef]
  27. Bedmar, F.; Daniel, P.; Costa, J.; Giménez, D. Sorption of acetochlor, S-metolachlor, and atrazine in surface and subsurface soil horizons of Argentina. Environ. Chem. 2011, 30, 1990–1996. [Google Scholar] [CrossRef] [PubMed]
  28. Clausen, L.; Fabricius, I. Atrazine, isoproturon, mecoprop, 2,4-D, and bentazone adsorption onto iron oxides. J. Environ. Qual. 2001, 30, 858–869. [Google Scholar] [CrossRef] [PubMed]
  29. Clausen, L.; Fabricius, I.; Madsen, L. Adsorption of pesticides onto quartz, calcite, kaolinite, and α-alumina. J. Environ. Qual. 2001, 30, 846–857. [Google Scholar] [CrossRef] [PubMed]
  30. Zhao, Y.; Geng, J.; Wang, X.; Gu, X.; Gao, S. Tetracycline Adsorption on Kaolinite: pH, Metal Cations and Humic Acid Effects. Ecotoxicology 2011, 20, 1141–1147. [Google Scholar] [CrossRef]
  31. Janniche, G.; Mouvet, C.; Albrechtsen, H. Vertical small scale variations of erosion and mineralization of three herbicities in subsurface limestone and sandy acquirer. J. Contam. Hydrol. 2011, 123, 167–177. [Google Scholar] [CrossRef] [PubMed]
  32. Barré, P.; Plante, A.; Cécillon, L.; Lutfalla SBaudin, F.; Bernard, S.; Christensen, B.; Eglin, T.; Fernandez, J.; Houot, S. The energetic and chemical signatures of persistent soil organic matter. Biogeochemistry 2016, 130, 1–12. [Google Scholar] [CrossRef]
  33. Coquet, Y.; Vachier, P.; Labat, C. Vertical variation of near-saturated hydraulic conductivity in three soil profiles. Geoderma 2005, 126, 181–191. [Google Scholar] [CrossRef]
  34. Cheng, H.; Zhang, R.; Chen, G. Sorption of four s-triazine herbicides on natural zeolite and clay mineral materials with microporosity. Fundam. Res. 2021, 1, 285–295. [Google Scholar] [CrossRef]
  35. Chaara, D.; Bruna, F.; Ulibarri, M.; Draoui, K.; Barriga, C.; Pavlovic, I. Organic/layered double hydroxide nanohybrids used to remove non ionic pesticides. J. Hazard. Mater. 2011, 196, 350–359. [Google Scholar]
  36. Chang, J.; Fang, W.; Chen, L.; Zhang, P.; Zhang, G.; Zhang, H.; Liang, J.; Wang, Q.; Ma, W. Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review. Chemosphere 2022, 307, 136006. [Google Scholar] [CrossRef] [PubMed]
  37. Gupta, K.; Joshi, P.; Gusain, R.; Hatri, O. Recent advances in adsorptive removal of heavy metal and metalloid ions by metal oxide-based nanomaterials. Coord. Chem. Rev. 2021, 445, 214100. [Google Scholar] [CrossRef]
  38. Spokas, K.; Koskinen, W.; Baker, J.; Reicosky, D. Impacts of woodchip biochar additions on greenhouse gas production and sorption/degradation of two herbicides in a Minnesota soil. Chemosphere 2009, 77, 574–581. [Google Scholar] [CrossRef] [PubMed]
  39. Yang, X.; Ying, G.; Peng, P.; Wang, L.; Zhao, J.; Zhang, L.; Yuan, P.; He, H. Influence of biochars on plant uptake and dissipation of two pesticides in an agricultural soil. J. Agric. Food Chem. 2010, 58, 7915–7921. [Google Scholar] [CrossRef] [PubMed]
  40. Tang, S.; Liang, J.; Gong, J.; Song, B.; Yang, Z.; Fang, S.; Zhang, P.; Cao, W.; Li, J.; Luo, Y. The effects of biochar/compost for adsorption behaviors of sulfamethoxazole in amended wetland soil. Environ. Sci. Pollut. Res. Int. 2021, 28, 49289–49301. [Google Scholar] [CrossRef]
  41. Álvarez-Benedí, J.; Cartón, A.; Fernández, J. Sorption of Tribenuron-methyl, Chlorsulfuron, and Imazamethabenz-methyl by Soils. J. Agric. Food Chem. 1998, 46, 2840–2844. [Google Scholar] [CrossRef]
  42. Ye, J.; Zhang, R.; Nielsen, S.; Joseph, S.; Huang, D.; Thomas, T. A Combination of Biochar–Mineral Complexes and Compost Improves Soil Bacterial Processes, Soil Quality, and Plant Properties. Front. Microbiol. 2016, 7, 372. [Google Scholar] [CrossRef]
  43. Shattar, S.; Zakaria, N.; Foo, K. One step acid activation of bentonite derived adsorbent for the effective remediation of the new generation of industrial pesticides. Sci. Rep. 2020, 10, 20151. [Google Scholar] [CrossRef]
  44. Li, X.; Zhang, C.; Deng, J.; Xu, G.; Wei, M.; Wei, L.; Liu, Z. The effect of biochar on butachlor adsorption isotherm and mechanism in different soils. J. Agro-Environ. Sci. 2024. (In Chinese) [Google Scholar]
  45. Adnan, M.; Xu, M.; Syed, A.; Muhammad, M.; Nan, S.; Wang, B.; Cai, Z.; Qudsia, S.; Muhammad, N.; Khalid, M.; et al. Soil aggregation and soil aggregate stability regulate organic carbon and nitrogen storage in a red soil of southern China. J. Environ. Manag. 2020, 270, 110894. [Google Scholar]
  46. Wang, Y.; Wang, Y.; Li, L.; Li, S. Composition Characteristic of Soil Aggregates and Their Stability in Red Soils As Affected by the Soil Parent Materials and Land Use Types. Chin. J. Soil Sci. 2013, 44, 776–784. (In Chinese) [Google Scholar]
  47. Wang, H.; Guan, D.; Zhang, R.; Chen, Y.; Hu, Y.; Xiao, L. Soil aggregates and organic carbon affected by the land use change from rice paddy to vegetable field. Ecol. Eng. 2014, 70, 206–211. [Google Scholar] [CrossRef]
  48. Barré, P.; Durand, H.; Chenu, C.; Meunier, P.; Montagne, D.; Castel, G.; Billiou, D.; Soucémarianadin, L.; Cécillon, L. Geological control of soil organic carbon and nitrogen stocks at the landscape scale. Geoderma 2017, 285, 50–56. [Google Scholar] [CrossRef]
  49. Wang, Y.; Pang, J.; Zhang, M.; Tian, Z.; Wei, T.; Jia, Z.; Ren, X.; Zhang, P. Is adding biochar be better than crop straw for improving soil aggregates stability and organic carbon contents in film mulched fields in semiarid regions? -Evidence of 5-year field experiment. J. Environ. Manag. 2023, 338, 117711. [Google Scholar] [CrossRef]
  50. Xue, P.; Fu, Q.; Li, T.; Liu, D.; Hou, R.; Li, Q.; Li, M.; Meng, F. Effects of biochar and straw application on the soil structure and water-holding and gas transport capacities in seasonally frozen soil areas. J. Environ. Manag. 2022, 301, 113943. [Google Scholar] [CrossRef]
  51. Laird, D.; Fleming, P.; Davis, D.; Horton, R.; Wang, B.; Karlen, D. Impact of biochar amendments on the quality of a typical Midwestern agricultural soil. Geoderma 2010, 158, 443–449. [Google Scholar] [CrossRef]
  52. Lehmann, J. A handful of carbon. Nature 2007, 447, 143–144. [Google Scholar] [CrossRef]
  53. Shi, J.; Han, H.; Xu, C. A novel enhanced anaerobic biodegradation method using biochar and Fe(OH)3 biochar for the removal of nitrogen heterocyclic compounds from coal gasification wastewater. Sci. Total Environ. 2019, 697, 134052. [Google Scholar] [CrossRef]
  54. Rahman, M.; Zhu, Q.; Zhang, Z.; Zhou, H.; Peng, X. The roles of organic amendments and microbial community in the improvement of soil structure of a vertisol. Appl. Soil Ecol. 2017, 111, 84–93. [Google Scholar] [CrossRef]
  55. Zhao, S.; Zhang, Q.; Zhang, C.; Ji, L.; OK, Y. Biochar–microbial interactions in contaminated soil remediation: A review. J. Agro-Environ. Sci. 2023, 42, 1423–1435. (In Chinese) [Google Scholar]
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Figure 1. Sampling map of the soils used in the experiment.
Figure 1. Sampling map of the soils used in the experiment.
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Figure 2. Adsorption isotherm of metolachlor onto different soils (Taking GZ-2 and ST-3 as examples).
Figure 2. Adsorption isotherm of metolachlor onto different soils (Taking GZ-2 and ST-3 as examples).
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Figure 3. Adsorption isotherm of metolachlor onto different soils + biochar (Taking GZ-4 and ZH-2 as examples).
Figure 3. Adsorption isotherm of metolachlor onto different soils + biochar (Taking GZ-4 and ZH-2 as examples).
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Figure 4. The correlation between soil Kf and SOM/the proportion of 0.02–0.002 mm in arenaceous shale soil.
Figure 4. The correlation between soil Kf and SOM/the proportion of 0.02–0.002 mm in arenaceous shale soil.
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Figure 5. The correlation between soil Kf and the proportion of 0.02–0.002 mm (a)/amorphous iron oxide (b)/total iron (c) in granite soil.
Figure 5. The correlation between soil Kf and the proportion of 0.02–0.002 mm (a)/amorphous iron oxide (b)/total iron (c) in granite soil.
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Figure 6. The correlation between soil Kf and the proportion of 0.02–0.002 mm in delta shockwave soil.
Figure 6. The correlation between soil Kf and the proportion of 0.02–0.002 mm in delta shockwave soil.
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Figure 7. The correlation between soil Kf and soil physicochemical properties in soils. * in a row indicate that the difference is significant at 0.05 level using LSD test.
Figure 7. The correlation between soil Kf and soil physicochemical properties in soils. * in a row indicate that the difference is significant at 0.05 level using LSD test.
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Figure 8. The correlation between soil Kf and soil physicochemical properties in soil + biochar. * in a row indicate that the difference is significant at 0.05 level using LSD test.
Figure 8. The correlation between soil Kf and soil physicochemical properties in soil + biochar. * in a row indicate that the difference is significant at 0.05 level using LSD test.
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Table 1. Isotherm constants for metolachlor adsorption onto different soils.
Table 1. Isotherm constants for metolachlor adsorption onto different soils.
FreundlichLangmuir
Kf
(mg1−n Ln kg−1)		nR2b
(L mg−1)		Qm
(mg g−1)		R2
GZ-116.41 ± 0.051.08 ± 0.010.88818.31 ± 10.8710,773.55 ± 632.140.83
GZ-216.28 ± 0.031.46 ± 0.020.9274.11 ± 5.63608.47 ± 12.360.93
TS-10.39 ± 0.010.62 ± 0.010.962.53 ± 0.8813.09 ± 0.020.94
TS-225.41 ± 0.041.63 ± 0.040.8961.00 ± 6.36635.07 ± 21.550.83
TS-34.41 ± 0.020.66 ± 0.011.002.23 × 1015 ± 0.01 × 10155.99 × 1016 ± 0.10 × 10160.89
HZ-10.19 ± 0.010.57 ± 0.010.872.30 ± 0.0113.99 ± 0.220.74
HZ-22.62 ± 0.040.88 ± 0.020.984.09 × 1016 ± 0.02 × 10161.77 × 1017 ± 0.08 × 10170.96
HZ-310.25 ± 0.070.77 ± 0.010.981.35 × 1015 ± 0.01 × 10154.07 × 1016 ± 0.04 × 10160.93
DG-10.01 ± 0.000.32 ± 0.011.001.79 ± 0.0219.08 ± 0.080.87
DG-217.69 ± 0.040.99 ± 0.050.97906.84 ± 20.3517,192.23 ± 569.210.96
HZ-41.44 ± 0.010.98±0.040.965.10 × 1013 ± 0.02 × 10137.98 × 1013 ± 0.03 × 10130.96
HZ-563.18 ± 0.113.16 ± 0.080.9711.79 ± 0.05272.15 ± 10.770.87
GZ-37.09 ± 0.040.78 ± 0.040.991.75 × 1016 ± 0.02 × 10163.48 × 1017 ± 0.03 × 10170.95
GZ-42.09 ± 0.051.04 ± 0.060.991108.62 ± 88.362103.32 ± 95.630.98
GZ-58.36 ± 0.040.76 ± 0.041.001.69 × 1016 ± 0.02 × 10164.43 × 1017 ± 0.05 × 10170.95
HS-10.27 ± 0.010.77 ± 0.030.981.03 ± 0.017.92 ± 0.020.98
JM-115.48 ± 0.090.72 ± 0.020.992.24 × 107 ± 0.01 × 1071.23 × 109 ± 0.01 × 1090.91
ZH-235.05 ± 0.101.06 ± 0.080.95493.53 ± 15.3615,091.69 ± 264.360.94
ST-111.47 ± 0.050.80 ± 0.040.945.52 × 1015 ± 0.02 × 10151.54 × 1017 ± 0.02 × 10170.89
ST-213.65 ± 0.061.18 ± 0.070.99198.46 ± 33.651874.80 ± 99.361.00
ST-33.06 ± 0.020.69 ± 0.060.994.58 ± 0.027.91 ± 0.050.97
Table 2. (a) The basic physical–chemical properties of the tested soils. (b) The content of soil enzymes in the 22 tested soils. (c) The contents of different forms of iron and aluminum in the 22 tested soils.
Table 2. (a) The basic physical–chemical properties of the tested soils. (b) The content of soil enzymes in the 22 tested soils. (c) The contents of different forms of iron and aluminum in the 22 tested soils.
(a)
SoilpHSOM
(g kg−1)		Total N
(g kg−1)		Total P
(g kg−1)		Total K
(g kg−1)		Available N
(mg kg−1)		Available P
(mg kg−1)		Available K
(mg kg−1)		CEC
(cmol (+)kg−1)		2–0.02
(mm)		0.02–0.002
(mm)		<0.002
(mm)
DG-16.1214.341.241.857.387.186.71234.004.9368.022.49.6
DG-24.6918.641.161.6726.3824.4126.45247.509.1642.030.427.6
GZ-16.8238.542.090.6724.047.328.1264.2913.3032.038.030.0
GZ-25.5218.291.373.2121.1511.8411.18202.086.1126.038.036.0
GZ-37.0618.071.520.9115.887.107.56121.006.7354.022.423.6
GZ-45.5415.201.410.9223.000.981.06315.008.7148.024.427.6
GZ-55.4216.061.421.4211.7510.4911.48240.005.4372.014.413.6
HZ-15.3715.481.091.1710.2510.2711.46196.505.0068.016.415.6
HZ-24.1329.541.390.9122.505.264.47151.505.7648.032.419.6
HZ-36.1524.081.461.3812.884.564.94135.508.2142.024.433.6
HZ-44.7419.211.211.1026.752.911.38165.005.0770.016.413.6
HZ-54.5122.941.161.488.132.622.34257.505.2936.038.425.6
JM-15.9630.631.370.7820.567.888.5984.0010.6910.050.239.8
JM-25.928.330.510.4934.2216.9218.06119.003.4172.316.311.4
JM-36.0219.161.143.8920.195.745.5053.574.2674.016.010.0
JM-44.9627.281.721.3116.831.280.9641.075.3340.038.010.0
JM-54.5325.251.451.2112.5011.1811.3841.073.3756.030.014.0
ST-15.1923.121.491.6520.3510.4111.5958.059.0072.014.413.6
ST-25.0219.881.600.3520.0314.5014.9755.536.7436.038.425.6
ST-36.8617.571.180.7216.948.178.4341.9311.0154.022.423.6
ST-46.8226.281.880.8917.8815.7114.8044.958.4856.030.014.0
ZH-16.0746.272.721.0418.9119.0923.47119.0017.7372.049.043.8
(b)
SoilDHO
(mg g−1)		POD
(mg 100 g−1)		PPO
(mg 100 g−1)		INV
(ml g−1)		PRO
(ug g−1)		ACP
(mg 100 g−1)		CAT
(mmol g−1)		EC
(mg 100 g−1)
DG-155.094675.641572.290.083225.6055.080.299.85
DG-26.156021.09914.750.11521.6239.150.0938.70
GZ-1136.705402.91158.120.17784.328.170.1010.05
GZ-2153.574339.28194.150.146284.3938.280.1317.34
GZ-3157.515912.00293.230.154087.234.980.0813.39
GZ-4120.148230.16275.210.162206.0137.990.0731.41
GZ-585.496211.99266.210.168294.8647.260.137.93
HZ-189.135421.09239.180.173512.8173.900.1562.18
HZ-2127.713884.74113.080.141559.7847.550.2512.58
HZ-333.674793.8295.060.131413.2249.580.2214.81
HZ-496.706966.53131.090.142731.229.610.1723.82
HZ-5183.675430.181049.860.172586.2441.470.2810.05
JM-172.964630.191896.560.286355.6996.490.4238.09
JM-284.786757.44248.190.202256.747.300.2012.78
JM-3177.968048.34527.420.162520.3429.960.1943.56
JM-4193.976048.36626.510.10609.250.430.1421.39
JM-546.00221.1320.700.145756.00124.850.526.81
ST-140.44221.13113.080.169828.59139.790.4712.99
ST-283.37693.8632.010.263653.81116.070.4971.70
ST-359.531612.03284.220.141979.9643.140.384.08
ST-4137.216993.81626.510.132770.762.770.1923.11
ZH-155.094675.641572.290.083225.6055.080.299.85
(c)
SoilDissociative iron oxide
(mg kg−1)		Amorphous iron oxide
(mg kg−1)		Complex iron oxide
(mg kg−1)		Total iron
(mg kg−1)		Soluble aluminum
(mg kg−1)		Exchangeable aluminum
(mg kg−1)		Hydroxyl aluminum content of monomer
(mg kg−1)		Acid-soluble inorganic aluminum
(mg kg−1)		Organic complex aluminum
(mg kg−1)		Aluminum humate
(mg kg−1)		Total aluminum
(mg kg−1)
DG-11567299784254050.211.540.8694117.862841245
DG-22506539958584893.756.140.11121324.1113542601
GZ-11120777683297290.660.550.44115413.712141384
GZ-21696533142674537.0213.711.10176535.361471969
GZ-3697282260141210.101.540.06107724.1112852387
GZ-41683315633051690.211.750.43116237.7919553157
GZ-52150336556960851.042.410.43124623.6623123586
HZ-11696255951847722.922.410.43114524.1114092583
HZ-21556190390243606.258.550.2291620.9812502202
HZ-31254300131845730.422.190.22145021.8822683743
HZ-41949370161662660.832.410.2282314.7310761917
HZ-52922414588779545.008.550.09122116.5213632614
JM-12730310849263290.211.750.22149215.1815113021
JM-21410168558236763.337.890.043579.3710321409
JM-31713222376947051.211.320.77122412.611831423
JM-43352542250792811.975.040.8869412.8863778
JM-52271383150266049.8710.860.886359.3240706
ST-11749553624375270.630.880.09171322.328152551
ST-2964123136025552.925.920.8673013.3911451898
ST-31867418249165400.211.320.11111119.648491982
ST-41091129761229992.296.140.4392422.779971953
ZH-12633206864453450.632.190.22120424.1121553386
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MDPI and ACS Style

Wei, L.; Huang, L.; Li, X.; Huang, Y.; Chen, W.; Ma, R.; Liu, Z. Dependence of Metolachlor Adsorption by Biochar on Soil Properties in South China. Agronomy 2024, 14, 1290. https://doi.org/10.3390/agronomy14061290

AMA Style

Wei L, Huang L, Li X, Huang Y, Chen W, Ma R, Liu Z. Dependence of Metolachlor Adsorption by Biochar on Soil Properties in South China. Agronomy. 2024; 14(6):1290. https://doi.org/10.3390/agronomy14061290

Chicago/Turabian Style

Wei, Lan, Lianxi Huang, Xiang Li, Yufen Huang, Weisheng Chen, Rui Ma, and Zhongzhen Liu. 2024. "Dependence of Metolachlor Adsorption by Biochar on Soil Properties in South China" Agronomy 14, no. 6: 1290. https://doi.org/10.3390/agronomy14061290

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