Next Article in Journal
Eggshells Improve Soil pH and P Availability in Sandy Loam and Sandy Clay Loamy Soil
Previous Article in Journal
Assessing Organic Farming Adoption in Selected Districts of Tamil Nadu: Challenges, Practices, and Pathways for Growth
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agronomy
Volume 14
Issue 11
10.3390/agronomy14112538
agronomy-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Combined Application of Biochar and Calcium Superphosphate Can Effectively Immobilize Cadmium and Reduce Its Uptake by Cabbage

by
Xinlei Peng
1,
Md. Shoffikul Islam
2,
Qian Li
1,
Qingling Fu
1,
Jun Zhu
1 and
Hongqing Hu
1,*
1
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China
2
Department of Soil Science, University of Chittagong, Chattogram 4331, Bangladesh
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(11), 2538; https://doi.org/10.3390/agronomy14112538
Submission received: 16 September 2024 / Revised: 9 October 2024 / Accepted: 24 October 2024 / Published: 28 October 2024
(This article belongs to the Section Horticultural and Floricultural Crops)
Browse Figures
Versions Notes

Abstract

:
Biochar and phosphate fertilizer are commonly employed for the mitigation of soil cadmium (Cd) contamination. Nevertheless, there is a dearth of research regarding the mechanism behind their joint implementation. In this study, a combination of corn straw biochar (0 (C0), 5 (C5), and 10 (C10) g kg−1) and calcium superphosphate (0 (P0), 0.1 (P1), 0.2 (P2), 0.5 (P5), and 1.0 (P10) g kg−1) was applied in pot experiments, and the effects of the combined application on Cd bioavailability and its uptake by cabbage were investigated in Cd-contaminated soils. The results demonstrated that the combined treatment of applying biochar and Ca(H2PO2)2 yielded a significant decrease in the uptake of Cd by cabbage in alkaline soil, in contrast to the individual treatments of biochar or Ca(H2PO2)2. Compared to the CK treatment (C0P0), the Cd content in the shoots decreased by 46.26% and in the roots decreased by 24.81%, while the biomass of the cabbage demonstrated a noteworthy increase in C5P10 treatment. Compared to the CK treatment, the content of available phosphate (AP) in the soil increased by 17.57 mg kg−1, residual Cd increased by 22.02%, the exchangeable Cd decreased by 45.86%, and carbonate-bound Cd decreased by 20.55% in the C5P10 treatment. Therefore, it is advisable to use a combination of 5 g kg−1 biochar and 1 g kg−1 Ca(H2PO2)2 for the restoration of soil contaminated with Cd.

1. Introduction

With the progress being made within industrialization, a large amount of industrial waste can pile up on the soil surface, resulting in an increase in heavy metal content in the soil [1]. Heavy metal pollution mainly appears in the soils of cities, industrial mining areas, and agricultural planting areas, exhibiting a regional distribution [2,3]. Cadmium (Cd), a major pollutant, is commonly distributed in the soils of southern China [4]. Wang et al. [5] showed that about 10 million hectares of farmland soil in China were polluted by Cd. Excessive Cd content in plants manifests as yellow leaves and short plants [6]. The excessive accumulation of Cd can damage soil quality and reduce crop yield [7]. Vegetables are the main pathway for humans to ingest Cd [8]. Leafy vegetables are more likely to accumulate Cd [9,10]. The remediation of heavy metals in soil has consistently attracted the interest of numerous researchers. The focus of soil heavy metal remediation is to identify durable and efficient strategies for reducing the availability and mobility of Cd in soil over an extended period.
Remediation technology for soil heavy metal pollution mainly includes physical, chemical, and biological remediation [11]. Passivation has been studied by many researchers due to its simple operation and economic benefits [12]. Common passivators include biochar [13,14], phosphorous materials [15], clay materials [11,16], etc. These materials have different mechanisms and effects on the immobilization of heavy metals in soil [17]. Biochar is the product of agricultural wastes under relatively low-temperature pyrolysis [18]. Biochar has a porous structure and excellent carbon sequestration ability [19,20]. Studies have shown that the application of biochar can reduce the mobility of cadmium in contaminated soil [2]. The various oxygen functional groups on the surface of biochar play an important role in the adsorption and fixation of Cd in soil [21]. In addition, precipitation, electrostatic interactions, and functional group complexation also reduce the effectiveness of Cd [22,23]. An excessive application of biochar will lead to a rise in soil salinity and affect crop growth [24]. At the same time, the production cost of biochar is relatively high, which is a challenge for its practical application.
In Cd-contaminated soil, P fertilizer can reduce the plant uptake of soil Cd through adsorption and precipitation [25]. Heavy metal phosphate precipitation is relatively stable in soil at different pH conditions [26,27]. Additionally, phosphates also fix heavy metals through surface complexation and cation exchange [28,29]. Phosphate materials, such as diammonium phosphate and hydroxyapatite (HAP), are effective in adsorbing and stabilizing Cd and other heavy metals [30,31]. However, the excessive use of P fertilizer will lead to the eutrophication of surrounding water [32]; therefore, the application amount of P fertilizer in soil needs to be controlled.
The combined application of biochar and P fertilizer can effectively immobilize Cd in the soil and improve soil fertility [33]. Biochar effectively immobilizes Cd on its surface through adsorption [34]. The phosphate ions (PO43−) in biochar and P fertilizers contribute to the formation of insoluble Cd, such as Cd5(PO4)3OH/Cl and CdCO3 [35]. Among them, Cd orthophosphate and Cd pyrophosphate are the main forms of Cd precipitation with phosphorus [36]. Biochar alleviates nitrogen deficiency after P fertilizer application [37]. The structure of biochar is beneficial for improving the effectiveness of P fertilizer [38]. The cost of biochar is relatively high [17]. It is important to control the amount of P fertilizer and biochar reasonably for the remediation of heavy metals in soil.
Previous studies have mostly focused on the immobilization of Cd in soil by only biochar [39] or P fertilizer [40,41]. Studies on the passivation effect of biochar also focus on acidic soils. However, there are only a few studies on the combined application of biochar and P fertilizer on the Cd forms in the alkaline soil and plant Cd uptake [35]. Studying the effect mechanism of biochar and P fertilizer on the growth and Cd transport of cabbage is beneficial for filling the gap in this area. It was assumed that the addition of biochar helps to reduce P fertilizer loss, while the addition of P fertilizer also promotes the fixation of Cd in the alkaline soil. In this study, different proportions of biochar and calcium superphosphate (Ca(H2PO2)2) were added to Cd-contaminated soil (1) to explore the mechanism of combined biochar and Ca(H2PO2)2 on the availability of Cd in alkaline soil, (2) to study the impacts of combined biochar and Ca(H2PO2)2 on cabbage growth and cabbage Cd reduction, and (3) to investigate the optimal proportion of biochar and Ca(H2PO2)2 required to remedy Cd-contaminated soil to ensure food production safety.

2. Materials and Methods

2.1. Materials and Characterization

The testing soil (0–20 cm) was collected from Yangxin county, Huangshi city, Hubei province (N 29°48′40″; E 115°25′53″). The soil is classified as paddy soil. After collection, the soil samples were air-dried and cleared of any loose stones, roots, and other debris. A portion of the samples was passed through a 0.15 mm sieve to determine the basic physical and chemical parameters, while the other half was passed through a 2 mm sieve for the subsequent pot experiment. The Supplementary Materials include instructions for determining soil pH, organic carbon (OC), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and total Cd (Method part 1). The soil pH, OC, TN, TP, AP, and total Cd levels were 8.13, 13.71 g kg−1, 1.63 g kg−1, 0.50 g kg−1, 11.63 mg kg−1, and 3.61 mg kg−1, respectively (Table S1).
The biochar used for treating contaminated soil was obtained from Henan Lize Environmental Protection Technology Co. (Zhengzhou, China). This biochar was produced from corn stover through pyrolysis at 500 °C. Before use in the experiment, the biochar samples were dried at 40 °C for 48 h, ground using a mortar and pestle to pass through a 2 mm sieve, and stored in a sealed nylon bag. The manufacturer provided the main physical and chemical characteristics of the biochar, which are presented in Table S1. The biochar exhibited pH, OC, TN, TP, and AP values of 9.17, 404.78 mg kg−1, 8.45 mg kg−1, 5.29 g kg−1, and 122.69 mg kg−1, respectively. The total Cd content was below the detection limit (0.003 mg kg−1) (Table S1).
The phosphate fertilizer used was calcium superphosphate (Ca(H2PO2)2) with chemical purity, purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Some physical and chemical properties of Ca(H2PO2)2 were provided by the manufacturer (Table S1). The pH of the Ca(H2PO2)2 compound was 2.78, the P2O5 concentration was 15.0%, and the Cd concentration was less than the detection threshold (0.003 mg kg−1) (Table S1).
The cabbage (Brassica rapa L.) used was purchased from Hunan Hezhiyuan Seed Industry Co., Ltd. (Changsha, China), and the variety was Hua’nai Shanghaiqing.

2.2. Experiment Design and Methods

The pot experiment was conducted in a completely randomized design in the greenhouse of Huazhong Agricultural University in summer 2021. In this experiment, the Cd content of soil is 3.61 mg kg−1. Each plastic pot (diameter 12 cm, height 11.5 cm) received a 1 kg air-dried soil sample. Then, three levels of biochar treatment (0, 5, 10 g kg−1), denoted as C0, C5, and C10, and five levels of Ca(H2PO2)2 treatment (0, 0.1, 0.2, 0.5, and 1.0 g kg−1), denoted as P0, P1, P2, P5, and P10, were added in combination to the pot. A control treatment (CK) with no biochar material or phosphate fertilizer was added. In total, there were 13 treatments, and each treatment was replicated three times, which were as follows: (1) CK, (2) C0P5, (3) C0P10, (4) C5P0, (5) C5P1, (6) C5P2, (7) C5P5, (8) C5P10, (9) C10P0, (10) C10P1, (11) C10P2, (12) C10P5, and (13) C10P10. The pots were placed in the greenhouse at random. In each pot, 0.15 g kg−1 urea and 0.06 g kg−1 potassium chloride were added as recommended by Wang et al. [42]. In each pot, ten cabbage seeds (Brassica rapa L.) were sowed. After 10 days, three cabbage plants with the same growth were selected and kept, while the other seedlings were removed. During the growing season in summer, water was given on a daily basis up to 60–70% of field capacity.
The cabbage plants were harvested after 50 days of sowing. The cabbage samples were cleaned with deionized water, separated into roots, stems, and leaves, and their fresh weight was determined. Half of the plant samples were frozen with liquid nitrogen and stored in a refrigerator at −80 °C. The second half was oven-dried at 105 °C for 30 min before heating at 60 °C until it attained a steady weight. Then, their dry weight was determined, and the grind-dried cabbage sample was passed through 100 sieves.
To determine the Cd concentrations in the plant roots and shoots (stems + leaves), they were digested with HNO3-HClO4 (3:1) [33]. The concentrations of Cd in the extracts were determined using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) (Agilent 5110, Santa Clara City, CA, USA). The detailed steps of digestion were described in the Supplementary Materials (Methods part 1).
The levels of antioxidative enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)) in the plant leaves were measured following the methods reported in the Supplementary Materials (Methods part 4).
After harvesting the plants, 100 g of soil was collected from each pot. The samples were then mixed, air-dried, ground, and sieved by 0.25 mm and 1 mm to determine the soil chemical properties and Cd fractions, respectively. The pH, AP, and enzyme activity (phosphatase, urease, and catalase) of the post-harvest soil were measured as the same methods of pH, AP, and enzyme activity of the studied soil (Method parts 1 and 3 in the Supplementary Materials).
The mobile Cd in the soil was determined by extracting the soil with a diethylenetriamine pentaacetate acid (DTPA) solution, as described by Lahori et al. [43]. The Tessier sequential extraction procedure [44] was adopted to classify soil Cd into five forms, namely exchangeable Cd, carbonate-bound Cd, Fe–Mn oxides Cd, organic matter-bound Cd, and residual Cd. The detailed methods of Cd speciation in the soil are described in the Supplementary Materials section (Method part 2 and Table S2).

2.3. Data Analysis

All values were processed in triplicate and expressed as the mean ± standard deviation using Excel 2010. In all tests, a p  <  0.05 test was considered statistically significant. The analysis of variance (ANOVA) among different treatments was proceeded by SPSS 21 software and Duncan’s method. The Origin 2018 software was used for drawing.

3. Results

3.1. Cd Uptake by Cabbage Under Amendment Application

The application of the C5P10 treatment resulted in a 40.0% decrease in Cd levels in the shoots and a 17.2% decrease in Cd levels in the roots compared to the C5P0 treatment (Figure 1). The shoots and roots of cabbage had 0.30 and 0.80 mg kg−1 of Cd, respectively, when treated with 10 g kg−1 of biochar (C10P0). Comparing the C10P10 treatment to the C10P0 treatment, the Cd concentrations in the shoots and roots decreased by 32.7% and 17.8%, respectively. The concentration of Cd in the shoots and roots of cabbage exhibited an inverse relationship with the application amount of Ca(H2PO2)2 while keeping the biochar application quantity constant. Furthermore, the concentration of Cd in the roots was greater than that in the shoots.

3.2. Plant Biomass Under Amendment Application

In comparison to the CK treatment, the fresh weight of the cabbage shoots increased by 1.03 g under the C0P10 treatment and by 1.65 g under the C10P0 treatment (Figure S2). The impact was most pronounced when subjected to the C10P10 treatment, resulting in a 5.19 g rise in shoot fresh weight and a 0.50 g increase in root fresh weight. Compared to the CK treatment, the fresh weight of the cabbage shoots and roots increased by 4.56 g and 0.35 g in the C5P10 treatment, respectively.
Under the C10P10 treatment, the dry weights of the cabbage shoots and roots were 0.95 g and 0.062 g (Figure 2). Compared to the CK treatment, the dry weight of the cabbage shoots and roots increased by 0.80 g and 0.053 g in the C5P10 treatment, respectively. The dry weight of the cabbage roots showed a favorable correlation with the amount of phosphorus applied when the cabbage was planted for 50 d using the same amount of biochar application. The combined treatment significantly promoted the growth of cabbage.

3.3. Physiological Indexes and Phosphorus Content of Cabbage Under Amendments Application

Under the condition of 10 g kg−1 biochar application, the SOD, CAT, and POD activities decreased to 92.43, 0.32, and 3.39 U g−1 (Table 1). Under the treatment of 0.5 g kg−1 phosphate fertilizer, the SOD activity in cabbage leaves increased to 108.8 U g−1. After biochar application, the SOD, CAT, and POD activity in cabbage leaves decreased, and the CAT and POD activity was negatively correlated with the biochar application amount. When the application amount of biochar was constant, the SOD content in cabbage leaves was positively proportional to the application amount of Ca(H2PO2)2, while the CAT and POD contents were inversely proportional.
Applying just Ca(H2PO2)2 and biochar significantly boosted the phosphorus concentration in the cabbage, as shown in Figure 3. Applying 10 g kg−1 biochar resulted in a significant increase in the cabbage’s ability to absorb phosphorus. The cabbage exhibited the highest phosphorus level under the C10P10 treatment, with a 16.46% increase compared to the phosphorus content under the C5P10 treatment. An increase in the application of biochar resulted in a decrease in the phosphorus content of cabbage, assuming that the amount of Ca(H2PO2)2 remains constant.

3.4. DTPA-Cd and Cd Fractionation for Contaminated Soil Under Amendments Application

Within the CK treatment, 11.94% of the Cd was exchangeable, 22.90% was bound to carbonate, 10.21% was associated with Fe-Mn oxides, 4.43% was linked to organic material, and 50.53% remained as residual Cd (Figure 4). Compared to the CK treatment, the exchangeable Cd decreased by 9.38%, the carbonate-bound Cd increased by 4.91%, and the Fe-Mn oxides bound Cd increased by 2.13% in the C10P0 treatment. When biochar was added to the soil, the amount of exchangeable Cd went down, but the amounts of carbonate-bound Cd and Fe-Mn oxides bound Cd went up. Compared to the CK treatment, with the C0P10 treatment, we observed that the exchangeable Cd in the soil decreased by 2.18%, the carbonate-bound Cd decreased by 5.28%, and the residual Cd increased by 8.76%. The use of Ca(H2PO2)2 facilitated the transformation of exchangeable Cd and carbonate-bound Cd into residual Cd inside the soil.
Compared to the CK treatment, the exchangeable Cd decreased by 45.86%, the carbonate-bound Cd decreased by 20.55%, and the residual Cd increased by 22.02% in the C5P10 treatment. When biochar and Ca(H2PO2)2 were applied together, increasing the amount of Ca(H2PO2)2 resulted in a drop in the proportion of exchangeable Cd and Fe-Mn oxides bound Cd. Meanwhile, the proportion of residual Cd increased and the proportion of organic matter Cd initially increased and subsequently decreased. The ratio of carbonate-bound Cd to Fe-Mn oxides bound Cd in the soil increased in direct proportion to the biochar application amount, whereas the exchangeable Cd decreased in an inverse proportion to the biochar application rate when the phosphate application rate remained constant.
The application of either biochar or phosphate to the soil after cabbage planting resulted in a considerable reduction in the concentration of DTPA-Cd in the soil (Figure 5). Compared to the CK treatment, the DTPA-Cd content decreased by 16.80% in the C5P10 treatment. The DTPA-Cd content in the soil decreased when the application amounts of Ca(H2PO2)2 increased.

3.5. Chemical Properties of Soil Under Amendments Application

In the soil after cabbage planting, the alkaline phosphatase activity showed a decreasing trend with the increase in Ca(H2PO2)2 application (Figure 6a). Compared to CK, the alkaline phosphatase activity increased by 4.44% in C10P0. At a 10 g kg−1 biochar application amount, the alkaline phosphatase activity in the C10P10 treatment was significantly decreased by 17.0% compared to the C10P0 treatment. The alkaline phosphatase activity was positively correlated with the biochar application amount under the same phosphate fertilizer content.
The soil urease activity increased by 4.44% in C5P0 and 61.64% in C0P10 (Figure 6b). The application of Ca(H2PO2)2 and biochar also significantly increased the activity of urease in the soil. When the biochar application amount was the same, the urease activity increased first and then decreased with the phosphorus application amount.
The catalase activity increased by 5.8% under the C10P0 treatment compare to CK (Figure 6c). This meant that the application of biochar increased the catalase activity in the soil. Under the same application amount of biochar, the catalase activity in the soil was inversely proportional to the application amount of phosphate fertilizer.
Table 2 shows that the addition of biochar and Ca(H2PO2)2 significantly increased the content of AP in the soil. After the addition of biochar, the gap in AP between different phosphorus application levels decreased, which may be caused by the fact that biochar application promoted the growth of cabbage and uptake of phosphorus from the soil.
In this experiment, the effect of biochar on soil pH was not significant (Table 2). This may be due to the high pH of the soil. Compared with the CK treatment, the soil pH increased insignificantly after 5 g kg−1 biochar was applied. At a 10 g kg−1 biochar application amount, the soil pH decreased with the increase in the amount of phosphorus applied. At a biochar application amount of 5 g kg−1, there was no significant change in the soil pH with the increase in the Ca(H2PO2)2 application.
A significant positive relationship was found between organic matter-bound Cd and carbonate-bound Cd (Figure 7). Applying biochar to the soil can lead to an increase in organic carbon and carbonate-bound Cd content. This increase in carbonate-bound Cd content helped to decrease the bioavailability of Cd. In Figure 7, there was a substantial negative association between the available phosphorus and Cd contents in the shoots and roots. A strong positive correlation was seen between the DTPA-Cd content and the Cd content in both the shoots and roots of cabbage. This suggest that the simultaneous use of Ca(H2PO2)2 and biochar could mitigate the toxicity of Cd by enhancing the concentration of available phosphorus in the soil.

4. Discussion

The phytotoxicity of Cd on plants primarily relied on the concentration of DTPA-Cd present in the soil [42,43]. The incorporation of biochar and phosphate fertilizer resulted in a significant decrease in DTPA-Cd levels in the soil and facilitated the conversion of mobile Cd into more stable fractions within the soil [27,28]. The biochar treatment resulted in a decrease in the amount of exchangeable Cd in the soil compared to the CK treatment. Additionally, there was a significant increase in the content of carbonate-bound Cd and Fe-Mn oxides bound states in the soil. The addition of biochar to soil contaminated with Cd resulted in a negligible increase in the concentration of Cd bound to organic matter in the soil. There was a positive correlation between the amount of biochar applied and the content of carbonate-bound Cd [45].
Ca(H2PO2)2 greatly decreased the amount of exchangeable Cd in the soil and dramatically increased the amount of residual Cd. Phosphates facilitate the conversion of heavy metals into stable forms primarily by causing metal phosphate precipitation and ion exchange [28,31]. Nevertheless, many investigations had yielded opposite findings about the impact of P fertilizer on the bioavailability reduction in Cd in soil [46]. This could be attributed to the competition between Ca2+ and Mg2+ ions present in the P fertilizer and Cd ions in the soil for adsorption sites [43]. The impact of P fertilizer on cadmium was dependent on the quantity of phosphate application, soil characteristics, and features [32].
There was a decrease in the levels of carbonate-bound Cd and Fe-Mn oxides bound Cd in the soil as the application amount of Ca(H2PO2)2 applied increased. Meanwhile, the residual Cd increased (Figure 4). Adding biochar and P fertilizer to cadmium-contaminated soil would form Cd5(PO4)3OH/Cl on the surface of biochar [35]. Chen et al. [47] found that the abundant surface groups of biochar, such as hydroxyl and amino, can adsorb nanohydroxyapatite (nHAP) and prevent the polymerization of nHAP. Meanwhile, the presence of nHAP also enhanced the adsorption capacity of biochar [31,48]. Therefore, the combined application of biochar and Ca(H2PO2)2 improved the immobilization capacity. When Ca(H2PO2)2 application was low, the use of Ca(H2PO2)2 increased the amount of organically bound Cd in the soil. Conversely, when phosphorus application was high, it decreased the amount of organic matter Cd in the soil. Under high Ca(H2PO2)2 treatment, the content of residual Cd was higher than that under low phosphorus treatment, and exchangeable Cd was lower than that under low phosphorus treatment [36]. Combined application led to the transformation of mobile Cd in the soil into an insoluble state [49].
The exchangeable state had a direct impact on the plants’ ability to absorb heavy metals, with the residue state being the most stable [20]. Under appropriate conditions, the carbonate-bound state and organic matter state could undergo a transformation into exchangeable states, and then they would be assimilated by plants [50]. The impact of the quantity of biochar applied on the levels of exchangeable and residual Cd was found to be insignificant in alkaline soil. The combined use of biochar and Ca(H2PO2)2 resulted in a notable increase in the concentration of AP in the soil. This, in turn, facilitated the conversion of free Cd into phosphate precipitation within the soil [51]. The utilization of both phosphate fertilizer and biochar exhibited a heightened level of stability and a long-lasting impact on the immobilization of Cd in soil, as demonstrated by Li et al. [36].
Some studies showed that biochar can change the accumulation of organic carbon in soil [52]. Biochar can promote soil fertility and crop growth [3]. Cd promoted oxidative loss in plants by increasing the production of reactive oxygen species (ROS) [53], and plant cells reduce ROS levels through a variety of protective mechanisms, including the antioxidant enzyme system. Under high Cd stress, the activity of antioxidant enzymes in plants increased, and the contents of SOD, POD, CAT, and other stress-resistant indexes increased [54]. The addition of biochar alleviated the toxicity of soil Cd to plants. The application of biochar significantly increased the biomass of cabbage and reduced the content of Cd in cabbage, which was the same as the findings of Bian et al. [55]. The synergistic effect of combining biochar with Ca(H2PO2)2 on plant growth surpassed that of applying phosphate fertilizer or biochar alone, and it exhibited a certain level of stability.

5. Conclusions

The concurrent utilization of biochar and phosphate fertilizer resulted in a significant decrease in the DTPA-Cd concentration in the soil, suppressed the uptake of Cd by cabbage, and enhanced the growth of cabbage. Furthermore, the application of biochar and phosphate fertilizer enhanced the transformation of exchangeable Cd into more enduring forms such as carbonate-bound and residual Cd, hence diminishing the availability of Cd for plants. Therefore, to address heavy metal contamination in soil, it is recommended to use a combination of 5 g kg−1 of corn stalk biochar and 1.0 g kg−1 of superphosphate. This treatment has been found to have a positive impact on the environment and provide economic advantages. Moreover, the suggested application quantities were evidently reduced in comparison to prior reports. Nevertheless, it is imperative to take into account long-term investigations in forthcoming assessments. Furthermore, the presence of Cd in phosphate fertilizer might exacerbate Cd contamination. Conducting field studies is crucial to accurately assessing the impact of biochar and phosphate fertilizer on soil Cd rehabilitation.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy14112538/s1. Figure S1. Effect of the combined application of biochar and phosphate fertilizer on the growth of cabbage at 50 days of growth. Figure S2. Effect of the combined application of biochar and phosphate fertilizer on the fresh weight of cabbage at 50 days of growth. Figure S3 Effect of the combined application of biochar and phosphate fertilizer on the photosynthetic pigment in cabbage leaves at 50 days of growth. Table S1. Some physical and chemical properties of soil, biochar, and Ca(H2PO2)2 used in the experiment. Table S2. Sequential fractionation of Cd in soils [56,57].

Author Contributions

X.P.: conceptualization, methodology, data curation, writing; M.S.I.: writing, reviewing and editing; Q.L.: reviewing and editing, data curation; Q.F.: reviewing and editing; J.Z.: methodology, reviewing; H.H.: funding acquisition, supervision, project administration, reviewing. All authors have read and agreed to the published version of the manuscript.

Funding

The work was supported by the National Natural Science Foundation of China (No. U21A20237).

Data Availability Statement

All data are included within the manuscript.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

  1. Jiang, Y.; Liu, Y.; Yi, X.T.; Zeng, P.; Liao, B.H.; Zhou, H.; Gu, J.F. Regulation of rhizosphere microenvironment by rice husk ash for reducing the accumulation of cadmium and arsenic in rice. J. Environ. Sci. 2023, 136, 1–10. [Google Scholar] [CrossRef] [PubMed]
  2. Wu, J.; Huang, D.; Liu, X.M.; Meng, J.; Tang, C.X.; Xu, J.M. Remediation of As(III) and Cd(II) co-contamination and its mechanism in aqueous systems by a novel calcium-based magnetic biochar. J. Hazard. Mater. 2018, 348, 10–19. [Google Scholar] [CrossRef]
  3. Yang, Y.H.; Xiao, C.F.; Wang, F.; Peng, L.; Zeng, Q.R. Assessment of the potential for phytoremediation of cadmium polluted soils by various crop rotation patterns based on the annual input and output fluxes. J. Hazard. Mater. 2022, 423, 127183. [Google Scholar] [CrossRef]
  4. Liu, X.J.; Tian, G.J.; Jiang, D.; Zhang, C.; Kong, L.Q. Cadmium (Cd) distribution and contamination in Chinese paddy soils on national scale. Environ. Sci. Pollut. Res. 2016, 23, 17941–17952. [Google Scholar] [CrossRef]
  5. Wang, H.Y.; Teng, Y.G.; Lu, S.J.; Wang, Y.Y.; Wang, J.S. Contamination features and health risk of soil heavy metals in China. Sci. Total Environ. 2015, 512–513, 143–153. [Google Scholar]
  6. Gupta, D.K.; Pena, L.B.; Romero-Puertas, M.C.; Hernández, A.; Inouhe, M.; Sandalio, L.M. NADPH oxidases differentially regulate ROS metabolism and nutrient uptake under cadmium toxicity. Plant Cell Environ. 2017, 40, 509–526. [Google Scholar] [CrossRef]
  7. Wu, J.Z.; Li, Z.T.; Huang, D.; Liu, X.M.; Tang, C.X.; Parikh, S.J.; Xu, J.M. A novel calcium-based magnetic biochar is effective in stabilization of arsenic and cadmium co-contamination in aerobic soils. J. Hazard. Mater. 2020, 387, 122010. [Google Scholar] [CrossRef] [PubMed]
  8. Bashir, S.; Hussain, Q.; Akmal, M.; Riaz, M.; Hu, H.H.; Ijaz, S.; Iqbal, M.; Abro, S.; Mehmood, S.; Ahmad, M. Sugarcane bagasse-derived biochar reduces the cadmium and chromium bio-availability to mash bean and enhances the microbial activity in contaminated soil. J. Soils Sediments 2018, 18, 874–886. [Google Scholar] [CrossRef]
  9. Huang, L.K.; Wang, Q.; Zhou, Q.Y.; Ma, L.Y.; Wu, T.J.; Liu, Q.Z.; Wang, S.; Feng, Y. Cadmium uptake from soil and transport by leafy vegetables: A meta-analysis. Environ. Pollut. 2020, 264, 114677. [Google Scholar] [CrossRef]
  10. Pan, S.; Ji, X.; Xie, Y.; Liu, S.; Tian, F.; Liu, X. Influence of soil properties on cadmium accumulation in vegetables: Thresholds, prediction and pathway models based on big data. Environ. Pollut. 2022, 304, 119225. [Google Scholar] [CrossRef]
  11. Zhang, F.F.; Liu, M.H.; Li, Y.; Che, Y.Y.; Xiao, Y. Effects of arbuscular mycorrhizal fungi, biochar and cadmium on the yield and element uptake of Medicago sativa. Sci. Total Environ. 2019, 655, 1150–1158. [Google Scholar] [CrossRef] [PubMed]
  12. Li, F.; Liu, H.; Zhong, H.; Dong, L.; Tang, Y.; Ge, Y. Effects of biochar combined with nitrogen fertilizer on ryegrass remediation of cadmium-contaminated soil. Int. J. Environ. Sci. Technol. 2024, 21, 4201–4212. [Google Scholar] [CrossRef]
  13. Zong, Y.; Chen, H.; Malik, Z.; Xiao, Q.; Lu, S. Comparative study on the potential risk of contaminated-rice straw, its derived biochar and phosphorus modified biochar as an amendment and their implication for environment. Environ. Pollut. 2022, 293, 118515. [Google Scholar] [CrossRef] [PubMed]
  14. Bashir, S.; Hussain, Q.; Shaaban, M.; Hu, H. Efficiency and surface characterization of different plant derived biochar for cadmium (Cd) mobility, bioaccessibility and bioavailability to Chinese cabbage in highly contaminated soil. Chemosphere 2018, 211, 632–639. [Google Scholar] [CrossRef] [PubMed]
  15. Gomes, F.P.; Soares, M.B.; Amoozegar, A.; Alleoni, L.R.F. How Does the Use of Biochar, Phosphate, Calcite, and Biosolids Affect the Kinetics of Cadmium Release in Contaminated Soil? Water Air Soil Pollut. 2023, 234, 439. [Google Scholar] [CrossRef]
  16. Amirahmadi, E.; Ghorbani, M.; Moudrý, J. Effects of Zeolite on Aggregation, Nutrient Availability, and Growth Characteristics of Corn (Zea mays L.) in Cadmium-Contaminated Soils. Water Air Soil Pollut. 2022, 233, 436. [Google Scholar] [CrossRef]
  17. Guo, J.; Wang, L.; Qu, G.; Liu, X.; Lian, Y.; Hou, D. Soil health improvement in a karst area with geogenic Cd enrichment using biochar and clay-based amendments. J Soils Sediments 2024, 24, 230–243. [Google Scholar] [CrossRef]
  18. Liang, J.; Yang, Z.X.; Tang, L.; Zeng, G.M.; Yu, M.; Li, X.D.; Wu, H.P.; Qian, Y.Y.; Li, X.M.; Luo, Y. Changes in heavy metal mobility and availability from contaminated wetland soil remediated with combined biochar-compost. Chemosphere 2017, 181, 281–288. [Google Scholar] [CrossRef]
  19. Lehmann, J.; Rillig, M.C.; Thies, J.; Masiello, C.A.; Hockaday, W.C.; Crowley, D. Biochar effects on soil biota—A review. Soil Biol. Biochem. 2011, 43, 1812–1836. [Google Scholar] [CrossRef]
  20. Ahmad, M.; Rajapaksha, A.U.; Lim, J.E.; Zhang, M.; Bolan, N.; Mohan, D.; Vithanage, M.; Lee, S. Biochar as a sorbent for contaminant management in soil and water: A review. Chemosphere 2014, 99, 19–33. [Google Scholar] [CrossRef]
  21. Zong, Y.T.; Xiao, Q.; Lu, S.G. Biochar derived from cadmium-contaminated rice straw at various pyrolysis temperatures: Cadmium immobilization mechanisms and environmental implication. Bioresour. Technol. 2021, 321, 124459. [Google Scholar] [CrossRef] [PubMed]
  22. Zhang, Y.; Chen, Z.; Xu, W.; Liao, Q.; Zhang, H.; Hao, S.; Chen, S. Pyrolysis of various phytoremediation residues for biochars: Chemical forms and environmental risk of Cd in biochar. Bioresour. Technol. 2020, 299, 122581. [Google Scholar] [CrossRef] [PubMed]
  23. Yang, T.; Meng, J.; Jeyakumar, P.; Cao, T.; Liu, Z.; He, T.; Cao, X.; Chen, W.; Wang, H. Effect of pyrolysis temperature on the bioavailability of heavy metals in rice straw-derived biochar. Environ. Sci. Pollut. Res. Int. 2021, 28, 2198–2208. [Google Scholar] [CrossRef]
  24. Kiros, G.T.Y.; Hailu, A.M.; Asfaw, S.L.; Mekonnen, S.Y. The effect of brewery sludge biochar on immobilization of bio-available cadmium and growth of Brassica carinata. Heliyon 2020, 6, e05573. [Google Scholar]
  25. Sigua, G.C.; Novak, J.M.; Watts, D.W.; Johnson, M.G.; Spokas, K. Efficacies of designer biochars in improving biomass and nutrient uptake of winter wheat grown in a hard setting subsoil layer. Chemosphere 2016, 42, 176–183. [Google Scholar] [CrossRef]
  26. Tao, Q.; Zhao, J.W.; Li, J.X.; Liu, Y.K.; Luo, J.P.; Yuan, S.; Li, B.; Li, Q.Q.; Xu, X.F.; Huang, H.; et al. Unique root exudate tartaric acid enhanced cadmium mobilization and uptake in Cd-hyperaccumulator Sedum alfredii. J. Hazard. Mater. 2020, 383, 121177. [Google Scholar] [CrossRef]
  27. Zeng, G.; Wan, J.; Huang, D.; Hu, L.; Huang, C.; Cheng, M.; Xue, W.; Gong, X.; Wang, R.; Jiang, D. Precipitation, adsorption and rhizosphere effect: The mechanisms for Phosphate-induced Pb immobilization in soils—A review. J. Hazard. Mater. 2017, 339, 354–367. [Google Scholar] [CrossRef] [PubMed]
  28. Liu, M.; Zhao, Z.; Chen, L.; Wang, L.; Ji, L.; Xiao, Y. Influences of arbuscular mycorrhizae, phosphorus fertiliser and biochar on alfalfa growth, nutrient status and cadmium uptake—Sciencedirect. Ecotoxicol. Environ. Saf. 2020, 196, 110537. [Google Scholar] [CrossRef]
  29. He, M.; Shi, H.; Zhao, X.; Yu, Y.; Qu, B. Immobilization of Pb and Cd in contaminated soil using nano-crystallite hydroxyapatite. Procedia Environ. Sci. 2013, 18, 657–665. [Google Scholar] [CrossRef]
  30. Kim, S.U.; Owens, V.N.; Kim, Y.G.; Lee, S.M.; Park, H.C.; Kim, K.K.; Joo, S.H.; Hong, C.O. Effect of phosphate addition on cadmium precipitation and adsorption in contaminated arable soil with a low concentration of cadmium. Bull. Environ. Contam. Toxicol. 2015, 95, 675–679. [Google Scholar] [CrossRef]
  31. Feng, Y.; Gong, J.L.; Zeng, G.M.; Niu, Q.Y.; Zhang, H.Y.; Niu, C.G.; Deng, J.H.; Yan, M. Adsorption of Cd (II) and Zn (II) from aqueous solutions using magnetic hydroxyapatite nanoparticles as adsorbents. Chem. Eng. J. 2010, 162, 487–494. [Google Scholar] [CrossRef]
  32. Lai, W.W.; Wu, Y.Y.; Zhang, C.N.; Dilinuer, Y.; Pasang, L.; Lu, Y.Q.; Wang, Y.H.; Chen, H.M.; Li, C. Combination of Biochar and Phosphorus Solubilizing Bacteria to Improve the Stable Form of Toxic Metal Minerals and Microbial Abundance in Lead/Cadmium-Contaminated Soil. Agronomy 2022, 12, 1003. [Google Scholar] [CrossRef]
  33. Liu, M.H.; Che, Y.Y.; Wang, L.Q.; Zhao, Z.J.; Zhang, Y.C.; Wei, L.L.; Xiao, X. Rice straw biochar and phosphorus inputs have more positive effects on the yield and nutrient uptake of Lolium multiflorum than arbuscular mycorrhizal fungi in acidic Cd-contaminated soils. Chemosphere 2019, 235, 32–39. [Google Scholar] [CrossRef]
  34. Jin, S.; Hu, Z.; Huang, Y.; Hu, Y.; Pan, H. Evaluation of several phosphate amendments on rare earth element concentrations in rice plant and soil solution by X-ray diffraction. Chemosphere 2019, 236, 124322. [Google Scholar] [CrossRef]
  35. Yin, C.R.; Lei, W.X.; Wang, S.J.; Xie, G.X.; Qiu, D. Biochar and arbuscular mycorrhizal fungi promote rapid-cycling Brassica napus growth under cadmium stress. Sci. Total Environ. 2024, 953, 953176034. [Google Scholar] [CrossRef]
  36. Li, J.F.; Zhang, S.R.; Ding, X.D. Biochar combined with phosphate fertilizer application reduces soil cadmium availability and cadmium uptake of maize in Cd-contaminated soils. Environ. Sci. Pollut. Res. 2021, 29, 25925–25938. [Google Scholar] [CrossRef]
  37. Wang, Y.Z.; Peng, X.Y.; Lai, L.Y.; Li, H.; Zhang, X.Y.; Chen, H.X.; Xie, L.T. Phosphorus fertilization regimes and rates alter Cd extractability in rhizospheric soils and uptake in maize (Zea mays L.). Chemosphere 2022, 298, 134288. [Google Scholar] [CrossRef] [PubMed]
  38. Lu, K.P.; Yang, X.; Gielen, G.; Bolan, N.; Yong, O.S.; Niazi, N.K.; Xu, S.; Yuan, G.D.; Chen, X.; Zhang, X.K.; et al. Effect of bamboo and rice straw biochars on the mobility and redistribution of heavy metals (Cd, Cu, Pb and Zn) in contaminated soil. J. Environ. Manag. 2017, 186, 285–292. [Google Scholar] [CrossRef]
  39. Islam, M.S.; Gao, R.; Gao, J.; Song, Z.T.; Ali, U.; Hu, H.Q. Cadmium, lead, and zinc immobilization in soil using rice husk biochar in the presence of citric acid. Int. J. Environ. Sci. Technol. 2022, 19, 567–580. [Google Scholar] [CrossRef]
  40. Islam, M.S.; Kashem, M.A.; Moniruzzaman, M.; Parvin, A.; Das, S.; Hu, H.Q. Cadmium, lead, and zinc immobilization in the soil using a phosphate compound with citric acid present. Environ. Technol. 2023, 29, 1–18. [Google Scholar] [CrossRef]
  41. Islam, M.S.; Rezwan, F.; Kashem, M.A.; Moniruzzaman, M.; Parvin, A.; Das, S.; Hu, H.Q. Impact of a phosphate compound on plant metal uptake when low molecular weight organic acids are present in artificially contaminated soils. Environ. Adv. 2024, 15, 100468. [Google Scholar] [CrossRef]
  42. Wang, T.; Song, J.X.; Liu, Z.; Liu, Z.; Cui, J. Melatonin alleviates cadmium toxicity by reducing nitric oxide accumulation and IRT1 expression in Chinese cabbage seedlings. Environ. Sci. Pollut. Res. 2020, 28, 15394–15405. [Google Scholar] [CrossRef] [PubMed]
  43. Lahori, A.H.; Zhang, Z.; Guo, Z.; Li, R.; Mahar, A.; Awasthi, M.K. Beneficial effects of tobacco biochar combined with mineral additives on (im)mobilization and (bio)availability of Pb, Cd, Cu and Zn from Pb/Zn smelter contaminated soils. Ecotoxicol. Environ. Saf. 2017, 145, 528–538. [Google Scholar] [CrossRef] [PubMed]
  44. Tessier, A.; Campbell, P.G.C.; Bisson, M. Sequential extraction procedure for the speciation of particulate trace metal. Anal. Chem. 1979, 51, 844–851. [Google Scholar] [CrossRef]
  45. Gong, Z.L.; Liu, L.Q.; Chou, Z.Y.; Deng, S.; Tang, T.; Xiang, W.L.; Chen, X.J.; Li, Y. Efficient cadmium-resistant plant growth-promoting bacteria loaded on pig bone biochar has higher efficiency in reducing cadmium phytoavailability and improving maize performance than on rice husk biochar. J. Hazard. Mater. 2024, 249, 135609. [Google Scholar] [CrossRef]
  46. Wang, Y.B.; Zhu, C.F.; Yang, H.F.; Zhang, X.W. Phosphate fertilizer affected rhizospheric soils: Speciation of cadmium and phytoremediation by Chlorophytum comosum. Environ. Sci. Pollut. Res. 2017, 24, 3934–3939. [Google Scholar] [CrossRef]
  47. Chen, Y.; Li, M.; Li, Y.; Liu, Y.; Chen, Y.; Li, H. Hydroxyapatitemodified sludge-based biochar for the adsorption of Cu2+ and Cd2+: Adsorption behavior and mechanisms. Bioresour. Technol. 2021, 321, 124413. [Google Scholar] [CrossRef]
  48. Zhang, Z.; Liu, B.; He, Z.; Pan, P.; Wu, L.; Lin, B.; Li, Q.; Zhang, X.; Wang, Z. The Synergistic Effect of Biochar-Combined Activated Phosphate Rock Treatments in Typical Vegetables in Tropical Sandy Soil: Results from Nutrition Supply and the Immobilization of Toxic Metals. Int. J. Environ. Res. Public Health 2020, 19, 6431. [Google Scholar] [CrossRef]
  49. Ren, J.; Zhao, Z.X.; Ali, A.; Guan, W.D.; Xiao, R.; Wang, J.J.; Ma, S.R.; Guo, D.; Zhou, B.Y.; Zhang, Z.Q.; et al. Characterization of phosphorus engineered biochar and its impact on immobilization of Cd and Pb from smelting contaminated soils. J. Soils Sediments 2020, 20, 3041–3052. [Google Scholar] [CrossRef]
  50. Huang, R.; Li, Y.; Li, F.; Yin, X.; Li, R.; Wu, Z.; Li, Z. Phosphate fertilizers facilitated the Cd contaminated soil remediation by sepiolite: Cd mobilization, plant toxicity, and soil microbial community. Ecotoxicol. Environ. Saf. 2022, 234, 113388. [Google Scholar] [CrossRef]
  51. Hamid, Y.; Tang, L.; Sohail, M.I.; Cao, X.R.; Hussain, B.; Aziz, M.Z.; Usman, M.; He, Z.L.; Yang, X.E. An explanation of soil amendments to reduce cadmium phytoavailability and transfer to food chain. Sci. Total Environ. 2019, 660, 80–96. [Google Scholar] [CrossRef] [PubMed]
  52. Zhao, T.; Wang, L.; Yang, J.X. Synergistic effects of combined application of biochar and arbuscular mycorrhizal fungi on the safe production of rice in cadmium contaminated soil. Sci. Total Environ. 2024, 951, 175499. [Google Scholar] [CrossRef] [PubMed]
  53. Carvalho, M.E.A.; Piotto, F.A.; Franco, M.R.; Borges, K.L.; Gaziola, S.A.; Castro, P.R.; Azevedo, R.A. Cadmium toxicity degree on tomato development is associated with disbalances in B and Mn status at early stages of plant exposure. Ecotoxicology 2018, 27, 1293–1302. [Google Scholar] [CrossRef] [PubMed]
  54. He, Y.H.; Lin, H.; Jin, X.N.; Dong, Y.B.; Luo, M.K. Simultaneous reduction of arsenic and cadmium bioavailability in agriculture soil and their accumulation in Brassica chinensis L. by using minerals. Ecotoxicol. Environ. Saf. 2020, 198, 110660. [Google Scholar] [CrossRef]
  55. Bian, R.J.; Joseph, S.; Cui, L.Q.; Pan, G.X.; Li, L.Q.; Liu, X.Y.; Zhang, A.F.; Rutlidge, H.; Wong, S.W.; Chia, C.; et al. A three-year experiment confirms continuous immobilization of cadmium and lead in contaminated paddy field with biochar amendment. J. Hazard. Mater. 2014, 272, 121–128. [Google Scholar] [CrossRef]
  56. Shidan, B. Soil Agrochemical Analysis; China Agriculture Press: Beijing, China, 2000. [Google Scholar]
  57. Xiaofang, L.; Zhiliang, Z. Plant Physiology Experiment Guidance; Higher Education Press: Beijing, China, 2016. [Google Scholar]
Agronomy 14 02538 g001
Figure 1. Effect of the combined application of biochar and calcium superphosphate on the Cd content of cabbage at 50 days of growth. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Figure 1. Effect of the combined application of biochar and calcium superphosphate on the Cd content of cabbage at 50 days of growth. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Agronomy 14 02538 g001
Agronomy 14 02538 g002
Figure 2. Effect of the combined application of biochar and calcium superphosphate on the dry weight of cabbage at 50 days of growth. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Figure 2. Effect of the combined application of biochar and calcium superphosphate on the dry weight of cabbage at 50 days of growth. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Agronomy 14 02538 g002
Agronomy 14 02538 g003
Figure 3. Effect of the combined application of biochar and calcium superphosphate on the shoot phosphorus content of cabbage at 50 days of growth. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Figure 3. Effect of the combined application of biochar and calcium superphosphate on the shoot phosphorus content of cabbage at 50 days of growth. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Agronomy 14 02538 g003
Agronomy 14 02538 g004
Figure 4. Effect of the combined application of biochar and calcium superphosphate on the Cd content of different forms of soil after cabbage planting. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1; P0, P1, P2, P5, P10 represent calcium superphosphate application amounts of 0, 0.1, 0.2, 0.5, 1.0 g kg−1).
Figure 4. Effect of the combined application of biochar and calcium superphosphate on the Cd content of different forms of soil after cabbage planting. Data are mean ± SE (n = 3) (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1; P0, P1, P2, P5, P10 represent calcium superphosphate application amounts of 0, 0.1, 0.2, 0.5, 1.0 g kg−1).
Agronomy 14 02538 g004
Agronomy 14 02538 g005
Figure 5. Effect of the combined application of biochar and calcium superphosphate on the DTPA-extractable Cd of soil after cabbage planting. Data are mean ± SE (n = 3). (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Figure 5. Effect of the combined application of biochar and calcium superphosphate on the DTPA-extractable Cd of soil after cabbage planting. Data are mean ± SE (n = 3). (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Agronomy 14 02538 g005
Agronomy 14 02538 g006
Figure 6. Effect of the combined application of biochar and calcium superphosphate on the alkaline phosphatase (a), urease (b), and catalase (c) of soil after cabbage planting. Data are mean ± SE (n = 3). (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Figure 6. Effect of the combined application of biochar and calcium superphosphate on the alkaline phosphatase (a), urease (b), and catalase (c) of soil after cabbage planting. Data are mean ± SE (n = 3). (C0, C5, and C10 represent biochar application amounts of 0, 5, 10 g kg−1. Different lower case letters above columns indicate statistical differences at p  <  0.05).
Agronomy 14 02538 g006
Agronomy 14 02538 g007
Figure 7. Correlation between Cd content in cabbage, soil chemical properties, and Cd forms (** significant at level p < 0.01; * significant at level p < 0.05. F1, F2, F3, F4, and F5 represent exchangeable Cd, carbonate-bound Cd, Fe-Mn oxides bound Cd, organic matter-bound Cd, and residual Cd).
Figure 7. Correlation between Cd content in cabbage, soil chemical properties, and Cd forms (** significant at level p < 0.01; * significant at level p < 0.05. F1, F2, F3, F4, and F5 represent exchangeable Cd, carbonate-bound Cd, Fe-Mn oxides bound Cd, organic matter-bound Cd, and residual Cd).
Agronomy 14 02538 g007
Table 1. Effect of the combined application of biochar and calcium superphosphate on the enzymes of cabbage leaves.
Table 1. Effect of the combined application of biochar and calcium superphosphate on the enzymes of cabbage leaves.
TreatmentSOD (U g−1)CAT (U g−1)POD (U g−1)
CK103.89 ± 6.15abc0.96 ± 0.030a5.86 ± 0.88a
C0P5108.78 ± 2.79ab0.04 ± 0.001h5.31 ± 0.82ab
C0P10115.27 ± 7.35a0.04 ± 0.018h5.44 ± 0.55ab
C5P098.64 ± 9.58bcd0.12 ± 0.002ef4.84 ± 0.21b
C5P1109.24 ± 7.48ab0.15 ± 0.038de2.25 ± 0.44def
C5P2115.69 ± 7.48a0.16 ± 0.017d1.78 ± 0.47def
C5P599.19 ± 8.10bc0.09 ± 0.011fg1.49 ± 0.24f
C5P1089.67 ± 6.98cd0.06 ± 0.023gh2.00 ± 0.29def
C10P092.43 ± 9.27cd0.32 ± 0.048b3.39 ± 0.37c
C10P185.07 ± 10.25de0.22 ± 0.013c2.58 ± 0.40d
C10P292.36 ± 10.98cd0.23 ± 0.020c3.42 ± 0.04c
C10P516.78 ± 4.45f0.06 ± 0.027gh2.48 ± 0.20de
C10P1072.82 ± 6.31e0.04 ± 0.001h1.65 ± 0.46ef
Different lower case letters above columns indicate statistical differences at p  <  0.05.
Table 2. Effect of the combined application of biochar and calcium superphosphate on the pH and available phosphorus of soil after planting.
Table 2. Effect of the combined application of biochar and calcium superphosphate on the pH and available phosphorus of soil after planting.
TreatmentpHAvailable Phosphorus (mg kg−1)
CK8.24 ± 0.01ab6.50 ± 0.49g
C0P58.24 ± 0.05ab20.36 ± 1.43b
C0P108.21 ± 0.05ab25.83 ± 1.88a
C5P08.24 ± 0.03ab8.99 ± 0.25f
C5P18.25 ± 0.03ab11.38 ± 0.65def
C5P28.25 ± 0.07ab11.94 ± 0.86de
C5P58.28 ± 0.04ab15.18 ± 0.51c
C5P108.23 ± 0.05ab24.07 ± 0.57a
C10P08.24 ± 0.06ab9.65 ± 0.54ef
C10P18.23 ± 0.06ab12.43 ± 0.24d
C10P28.18 ± 0.05ab12.05 ± 1.06d
C10P58.17 ± 0.02b17.19 ± 0.93c
C10P108.14 ± 0.03b21.17 ± 2.56b
Different lower case letters above columns indicate statistical differences at p  <  0.05.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Peng, X.; Islam, M.S.; Li, Q.; Fu, Q.; Zhu, J.; Hu, H. Combined Application of Biochar and Calcium Superphosphate Can Effectively Immobilize Cadmium and Reduce Its Uptake by Cabbage. Agronomy 2024, 14, 2538. https://doi.org/10.3390/agronomy14112538

AMA Style

Peng X, Islam MS, Li Q, Fu Q, Zhu J, Hu H. Combined Application of Biochar and Calcium Superphosphate Can Effectively Immobilize Cadmium and Reduce Its Uptake by Cabbage. Agronomy. 2024; 14(11):2538. https://doi.org/10.3390/agronomy14112538

Chicago/Turabian Style

Peng, Xinlei, Md. Shoffikul Islam, Qian Li, Qingling Fu, Jun Zhu, and Hongqing Hu. 2024. "Combined Application of Biochar and Calcium Superphosphate Can Effectively Immobilize Cadmium and Reduce Its Uptake by Cabbage" Agronomy 14, no. 11: 2538. https://doi.org/10.3390/agronomy14112538

APA Style

Peng, X., Islam, M. S., Li, Q., Fu, Q., Zhu, J., & Hu, H. (2024). Combined Application of Biochar and Calcium Superphosphate Can Effectively Immobilize Cadmium and Reduce Its Uptake by Cabbage. Agronomy, 14(11), 2538. https://doi.org/10.3390/agronomy14112538

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop