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Article

Differential Effects of Four Materials on Soil Properties and Phaseolus coccineus L. Growth in Contaminated Farmlands in Alpine Lead–Zinc Mining Areas, Southwest China

by
Xiuhua He
1,
Qian Yang
1,
Weixi Meng
1,
Xiaojia He
1,
Yongmei He
1,
Siteng He
1,
Qingsong Chen
2,
Fangdong Zhan
1,
Jianhua He
3,* and
Hui Bai
4,*
1
Key Laboratory for Improving Quality and Productivity of Arable Land of Yunnan Province, College of Resources and Environment, Yunnan Agricultural University, Kunming 650201, China
2
Innovation Base for Eco-geological Evolution, Protection and Restoration of Southwest Mountainous Areas, Geological Society of China, Kunming 650111, China
3
Ecological Environment Monitoring Station in Nujiang State of Yunnan Provincial Ecological Environment Department, Lushui 673000, China
4
College of Architectural Engineering, Yunnan Agricultural University, Kunming 650201, China
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(11), 2467; https://doi.org/10.3390/agronomy15112467
Submission received: 24 September 2025 / Revised: 19 October 2025 / Accepted: 21 October 2025 / Published: 23 October 2025
(This article belongs to the Section Soil and Plant Nutrition)
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Abstract

Soils in alpine mining areas suffer from severe heavy metal contamination and infertility, yet little is known about the effects of different materials on soil improvement in such regions. In this study, a field experiment was conducted in farmlands contaminated by the Lanping lead–zinc mine in Yunnan, China, to compare the effects of four materials (biochar, organic fertilizer, lime, and sepiolite) on soil properties, heavy metal (lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) fractions and their availability, and the growth of Phaseolus coccineus L. Results showed that biochar and organic fertilizer significantly enhanced soil nutrient content and enzyme activities. Lime, biochar, and sepiolite effectively reduced heavy metal bioavailability by promoting their transition to residual fractions. Notably, biochar outperformed other materials by substantially increasing grain yield (by 82%), improving nutritional quality (sugars, protein, and starch contents raised by 20–88%), and reducing heavy metal accumulation in grains (by 36–50%). A comprehensive evaluation based on subordinate function values confirmed biochar as the most effective amendment. Structural equation modeling further revealed that biochar promoted plant growth and grain quality primarily by enhancing soil available nutrients and immobilizing heavy metals. These findings demonstrate the strong potential of biochar for remediating heavy metal-contaminated farmlands in alpine lead–zinc mining regions.

1. Introduction

During the mining and smelting of mineral resources, heavy metals disperse into surrounding soils via atmospheric deposition, surface runoff, and groundwater seepage and accumulate in farmland over the long term [1]. These accumulations of heavy metals cause soil degradation and compromise crop quality [2]. Therefore, heavy metal pollution in mining area soils has emerged as a major global environmental issue that demands immediate remediation.
In situ passivation technology is widely applied for remediating heavy metal-contaminated farmland soils [3]. Common passivation materials include lime, biochar, sepiolite, and organic fertilizers [4,5]. These materials primarily function through the following mechanisms: lime, biochar and sepiolite increase soil pH. Elevated soil pH has been shown to enhance heavy metal adsorption capacity [6], principally through increased surface negative charges that strengthen electrostatic interactions with metal cations [7]. This alkaline environment promotes precipitation reactions between heavy metals and soil constituents. These precipitation reactions effectively reduce the bioavailability and mobility of heavy metals [6]. Biochar and sepiolite exhibit excellent adsorption and ion-exchange capabilities because of their large specific surface areas and surface charges [8]. Beyond metal immobilization, these materials improve soil biological properties; for instance, they enhance nutrient availability and restore microbial functions as demonstrated in previous biochar studies [9], while also increasing plant nutrient utilization efficiency, a benefit particularly noted in sepiolite-amended soils [10]. In contrast, organic fertilizers are rich in organic matter and its functional groups, which can directly immobilize heavy metal ions through complexation and chelation while also significantly improving soil environmental quality by promoting soil biochemical processes [11].
Alpine mining regions worldwide present severe challenges for conventional remediation strategies due to their fragile ecosystems and unique climatic conditions [12,13]. These challenges stem from inherent environmental constraints: low temperatures, short growing seasons, and significant diurnal temperature fluctuations collectively suppress soil microbial activity, slow organic matter decomposition, and consequently lead to inherently low soil fertility and inefficient nutrient cycling [9,14]. Under these conditions, the effectiveness of remediation materials reliant on microbially driven chemical transformations (e.g., lime) may be compromised due to reduced reaction rates at low temperatures [15]. In contrast, materials with high specific surface areas and stable chemical properties (e.g., biochar) demonstrate greater potential for alleviating both heavy metal toxicity and low-temperature stress, owing to their inherent adsorption capabilities and capacity to improve the soil microenvironment [16]. This reveals that successful remediation in alpine environments must simultaneously address the dual stresses of heavy metal toxicity and soil nutrient limitation. Furthermore, the weak resistance of these regional ecosystems to disturbance [17], coupled with mining-induced soil acidification, further enhances heavy metal bioavailability. Concurrently, low temperatures severely constrain microbial-driven pollutant degradation and nutrient transformation processes [18]. Consequently, when evaluating remediation materials in a typical alpine lead-zinc mining area like the Lanping mine in Yunnan, it is essential to comprehensively consider their dual efficacy in synchronously enhancing soil fertility and immobilizing heavy metals—an aspect that remains understudied.
The Yunnan Lanping lead–zinc mine in southwestern China is a typical high-altitude mining area facing dual environmental pressures. First, the region experiences frequent seasonal freeze-thaw cycles, a process that disrupts soil structure and risks remobilizing heavy metals. Second, large-scale mining and smelting activities have introduced pollutants, including lead, cadmium, zinc, and copper [19], into farmland soils via atmospheric deposition and wastewater, threatening agricultural safety [20]. However, the interaction between these natural cyclic stresses and anthropogenic contamination creates a unique challenge, and the efficacy of soil amendments under such combined conditions is poorly understood. This knowledge gap forms the critical rationale for our investigation.
The Phaseolus coccineus L. was selected as the test plant for this study due to its comprehensive significance both locally and in broader regions. Agronomically and nutritionally, it is a legume crop of high nutritional value, with its seeds rich in protein, dietary fiber, vitamins, and minerals, serving as an important source of plant-based protein in the local diet [21,22]. Furthermore, in the high-altitude mountainous areas of Southwest China, its strong environmental adaptability and cold tolerance have established it as a key rotation or intercropping crop within local farming systems, playing a practical role in sustaining the livelihoods of smallholder farmers and ensuring regional food security [23]. More importantly, the symbiotic nitrogen-fixing association between legumes and rhizobia can effectively enhance soil fertility, which is particularly crucial for the ecological restoration of degraded farmland [24]. However, previous studies have indicated that leguminous plants often exhibit high sensitivity to heavy metal stress; their growth, nitrogen fixation efficiency, and the safety of agricultural products can be significantly compromised [25]. Therefore, investigating the physiological responses of Phaseolus coccineus L. in contaminated environments not only helps assess the potential safety risks of local produce but also allows for an indepth exploration of its potential and limitations within restorative agricultural systems.
In this context, the present work proposes the following clear objectives: (1) to evaluate and compare the effects of four amendments—lime, biochar, sepiolite, and organic fertilizer—on soil physicochemical properties, enzyme activities, and the chemical speciation and bioavailability of heavy metals (Pb, Cd, Cu, Zn) in the Lanping alpine lead-zinc mining area in Yunnan; (2) to elucidate how these materials influence the growth, mineral nutrient uptake, heavy metal accumulation, yield, and quality of the dominant crop, Phaseolus coccineus L.; and (3) to identify the optimal material that can synergistically achieve heavy metal immobilization and soil fertility enhancement through comprehensive evaluation. We hypothesized that (1) passivating materials would markedly reduce the bioavailable fractions of Pb, Cd, Cu, and Zn in soil by altering soil physicochemical properties and heavy metal speciation, thereby suppressing their accumulation in Phaseolus coccineus L.; (2) while decreasing heavy metal bioavailability, these amendments would increase mineral nutrient uptake and promote plant growth through improved soil nutrient.

2. Materials and Methods

2.1. Study Area

The experimental site is located on heavy metal-contaminated farmland adjacent to the Lanping lead–zinc mining area, Yunnan Province (99°28′33.47″ E, 26°27′23.91″ N; altitude: 2250 m), which is approximately 3 km from the mine. This region experiences a typical southern temperate monsoon climate characterized by distinct wet and dry seasons, with a mean annual temperature of 12.6 °C and an annual precipitation of 867 mm (Figure 1). The predominant crops cultivated in the region include common Phaseolus coccineus, maize, and potato. These crops are typically grown in areas with soil conditions comparable to our experimental site (3).
The fundamental properties of the experimental farmland soil were as follows: a pH of 7.2; a cation exchange capacity (CEC) of 33.83 cmol/kg; and an organic matter content of 74.01 g/kg. The total nitrogen, total phosphorus, and total potassium contents were 2.3, 12.1, and 12.4 g/kg, respectively. The alkaline hydrolyzable nitrogen, available phosphorus, and available potassium contents were 119, 45.24, and 144.85 mg/kg, respectively. The total contents of soil heavy metals (Pb, Cd, Cu, and Zn) were 3737, 32, 171, and 4520 mg/kg, respectively. According to the Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018) [26,27], the contents of Pb, Cd, and Zn significantly exceed their respective risk intervention values—reaching 4.3 times, 9.7 times, and 17.1 times the thresholds, respectively. In contrast, the Cu concentration (171 mg/kg) is slightly below its intervention threshold (200 mg/kg) (Table 1).

2.2. Plot Experimental Design and Sample Collection

In this study, lime, sepiolite, biochar, and organic fertilizer were used as passivating materials. The biochar used in this experiment was produced from rice straw. The organic fertilizer, sourced locally, contained organic matter ≥30% and total nutrients (N + P2O5 + K2O) ≥ 4%. The lime was also obtained from local suppliers. The biochar and sepiolite were purchased from Anning City, Yunnan Province, and Xiangtan Yuanyuan Sepiolite New Material Co., Ltd. (Xiangtan, China), respectively. their pH values and heavy metal contents are described in Table 2.
The field experiment comprised five treatments: a control treatment without the application of any passivator (CK), and four treatments with passivators applied: lime (L, 0.25 kg/m2), biochar (B, 1.5 kg/m2), sepiolite (S, 1.5 kg/m2), and organic fertilizer (O, 1.5 kg/m2).
These application rates were determined based on previously established effective doses for heavy metal immobilization found in the literature and are consistent with local agronomic practices for soil improvement [5,28]. While these specific doses were optimized for the soil properties and contamination levels of our experimental site, they provide a scientifically grounded and practical reference point for initial remediation efforts in similar alpine mining-affected areas. A completely randomized block design was implemented with three replicates per treatment, totaling 15 experimental plots. Each plot measured 5 m in length and 2 m in width, a size that is standard and adequate for field trials with row crops like Phaseolus coccineus L. Each plot contained 4 rows of plants, with a row spacing of 0.5 m. To minimize border effects, the two outer rows on each side were designated as border rows, and data (including soil and plant sampling) were collected exclusively from the two inner, central rows. Ten days prior to sowing, mechanical plowing was performed to uniformly incorporate the passivators into the 0–20 cm plow layer according to the prescribed application rates.
The test crop was Phaseolus coccineus L., a predominant cultivar in Yunnan’s high-altitude mountainous regions that was provided by the Food Crops Research Institute, Yunnan Academy of Agricultural Sciences. The crop was sown on 3 May 2020, and harvested at full maturity on 9 October 2020, resulting in a growth season of 160 days. Planting occurred during the growing season, using selected plump, uniformly sized seeds in hilled rows with the following specifications: a ridge height of 20 cm; a hill spacing of 30 cm; a hill width of 20 cm; a width of 10 cm from the plot edge; and 2–4 seeds per hill buried at a 3–5 cm depth. The total cultivation area spanned approximately 240 m2. Immediate irrigation followed sowing, with subsequent weeding postemergence and stake installation at 30 cm plant height. Harvest occurred uniformly at full maturity. Five-point sampling was used to select five representative plants. Rhizosphere soil was simultaneously collected (air-dried in the shade, homogenized through a 2 mm sieve, and stored). Each plant was separated into roots, stems and leaves, and grains. After sequential washing with tap water and deionized water, the samples underwent enzyme deactivation at 105 °C for 30 min, were dried at 75 °C to a constant weight, were finally ground through a 0.5 mm sieve, and were sealed for storage.
It is important to note that this field study was conducted at a single location over one growing season. The findings should therefore be considered preliminary, reflecting the specific soil, climatic, and management conditions of the experimental site. Further multi-location and multi-annual trials are necessary to validate the consistency and general applicability of these results.

2.3. Determination of Soil Physicochemical and Biological Properties

Soil sampling was conducted at the maturity stage of the plants. In each plot, five soil cores were randomly collected from the 0–20 cm plow layer using a stainless-steel auger (Kunming, China). This sampling depth was selected because it represents the primary root zone for Phaseolus coccineus L. and the layer where the passivators were incorporated. The five sub-samples from each plot were then thoroughly mixed to form one composite sample, ensuring it was representative of the entire plot. After removing visible plant debris and stones, the composite sample was air-dried, ground, and passed through nylon sieves for subsequent physicochemical analysis. Soil pH was determined by homogenizing 10.0 g of air-dried soil (<1 mm) with CO2 free distilled water (water to soil ratio 2.5:1) using a pH meter (Shanghai, China). The soil organic matter content was measured via the potassium dichromate volumetric method with external heating using 0.1 g of soil (<0.149 mm). Cation exchange capacity was analyzed by the cobalt hexamine trichloride spectrophotometric method with 3.5 g of air-dried soil. Available nutrients were quantified in 2.50 g of air-dried soil (<1 mm): alkali-hydrolyzable nitrogen by alkali diffusion, available phosphorus by sodium bicarbonate extraction followed by molybdenum–antimony colorimetry (UV-5800 spectrophotometer, Shanghai, China), and available potassium by ammonium acetate extraction with flame photometry (FP6410, Shanghai, China). All the above indices were measured according to the method described by Bao [29].
Soil sucrase activity was determined by the 3,5-dinitrosalicylic acid (DNS) colorimetric method [30]. Hydrogen peroxidase activity was assayed via potassium permanganate titration [31]. Urease activity was quantified using indophenol blue colorimetry [32]. Acid phosphatase activity was analyzed by p-nitrophenyl phosphate hydrolysis [32].

2.4. Determination of Soil Heavy Metal Forms and Bioavailability

The available fractions of Pb, Cd, Cu, and Zn were extracted from 5.0 g of air-dried soil (<2 mm) using 0.1 mol·L−1 CaCl2 solution and quantified by flame atomic absorption spectrometry (FAAS; Thermo ICE™ 3300, Thermo Fisher Scientific, Waltham, MA, USA) [28]. The chemical speciation of Pb, Cd, Cu, and Zn was determined through BCR sequential extraction of 1.0 g of air-dried soil, with each fraction analyzed by FAAS (Thermo ICE™ 3300, Thermo Fisher Scientific, Waltham, MA, USA) [33].

2.5. Determination of Phaseolus coccineus L. Biomass, Nutrient Content, Yield, Quality, and Heavy Metal Content

Five Phaseolus coccineus L. plants were randomly selected per plot. Roots, stems and leaves, and grains were separated. The tissue samples were subsequently washed with deionized water, heated at 105 °C for 30 min to inactivate enzymes, and then transferred to a 75 °C oven to dry to constant weight; the biomass was subsequently recorded. Dried samples were ground and sieved through 0.5 mm nylon mesh (Kunming, China). A 0.1 g aliquot of the powder was digested with 5 mL of H2SO4-H2O2 digestion solution. The total nitrogen, total phosphorus, and total potassium contents were determined using Nessler’s reagent colorimetry, the molybdenum–antimony colorimetric method, and flame spectrophotometry, respectively [29]. Additionally, seeds from 10 plants per plot were collected, air-dried, and weighed. The grain yield was calculated as kg·hm−2 on the basis of a plot area of 10 m2. The quality of grain components (reducing sugars, soluble sugars, proteins, starch, and vitamin C) was analyzed using commercial kits (Suzhou Grace Biotechnology Co., Ltd, Suzhou, China. The heavy metal contents (Pb, Cd, Cu, and Zn) in 0.5 g of ground plant tissue digested with HNO3-HClO4 were quantified by flame atomic absorption spectrometry [29].

2.6. Data Processing and Analysis

2.6.1. Statistical Analysis

The experimental data were processed using Microsoft Excel 2010, charts were created using Origin 2024b. All data presented in the figures are expressed as the mean ± standard deviation (SD) of three independent replicates (n = 3). The data were analyzed using SPSS 21.0 for one-way analysis of variance (ANOVA) and correlation analysis. Multiple comparisons between groups were performed using the LSD and Duncan models, with a significance level of p < 0.05 and a correlation level of 0.05. Statistical analysis and graphing were performed using IBM SPSS Statistics 27.0, R (version 4.2.2; R Core Team, Vienna, Austria), and Amos 27 (IBM Corporation, Chicago, IL, USA).

2.6.2. Calculation of Subordinate Function Values

The subordinate function values were used to evaluate the properties of different material treatments. These values combined parameters such as Phaseolus coccineus L. biomass, nutrient content, heavy metal content, and soil heavy metal availability and nutrient content. The attribute function values of each process are calculated by using the following formula [34]. The weighting of the individual parameters (e.g., plant biomass, nutrient content, heavy metal content) in this integration was objectively determined by their contributions in the Principal Component Analysis (PCA). Specifically, the variance contribution rates of the significant principal components and the loadings of the original variables on these components were used to derive the implicit weights, ensuring that the data structure itself dictated the importance of each indicator.
(Xi − Xmin)/(Xmax − Xmin)
where Xi denotes the measured value and Xmin and Xmax represent the minimum and maximum values, respectively. Comparison of ordinal function values across treatments enables the ranking of their relative efficacy in remediating heavy metal-contaminated soils and identification of the optimal strategy.

2.6.3. Structural Equation Modeling (SEM) Analysis

Principal component analysis (PCA) was performed on the data using the FactoMineR package in R for dimensionality reduction. A structural equation model (SEM) based on maximum likelihood estimation was constructed by using Amos 27 to explore the effects of different treatments on Phaseolus coccineus L. biomass. The goodness of fit of the SEM was evaluated using a suite of standard indices. The final model was selected based on its excellent fit to the data, meeting the following criteria: the ratio of chi square to degrees of freedom (χ2/df) < 3, the comparative fit index (CFI) > 0.95, the goodness of fit index (GFI) > 0.90, and the root mean square error of approximation (RMSEA) < 0.08. The best SEM reveals the interactive network of abiotic and biotic factors affecting yield changes. The bioavailable contents of heavy metals in soil include Pb, Cd, Cu, and Zn. The soil nutrient content includes soil alkali-hydrolyzable nitrogen, available phosphorus, and available potassium contents. The contents of heavy metals in plants include the contents of Pb, Cd, Cu, and Zn in the roots, stems and leaves, and grains of plants. The contents of plant nutrients include the total nitrogen, phosphorus, and potassium contents in the roots, stems and leaves, and grains of plants. Plant biomass includes root biomass, stem and leaf biomass and grain biomass.

3. Results

3.1. Effects of the Four Materials on the Physicochemical Properties of Contaminated Farmland Soil in the Lanping Lead–Zinc Mining Area

The organic fertilizer and biochar treatments significantly increased the available nutrient contents in the contaminated farmland soil (p < 0.05). Among the four materials, organic fertilizer demonstrated the most comprehensive effect in enhancing soil available nutrients. Specifically, at the maturity stage of Phaseolus coccineus L., soil pH, cation exchange capacity, alkali-hydrolyzable nitrogen, available phosphorus, and available potassium under the organic fertilizer treatment were all significantly higher than those in the CK, with increases of 11%, 7%, 32%, 112%, and 407%, respectively. It is noteworthy that the effectiveness of organic fertilizer in increasing available phosphorus was significantly superior to that of the biochar treatment. The biochar treatment primarily significantly increased the contents of soil organic matter, alkali-hydrolyzable nitrogen, available phosphorus, and available potassium (by 25%, 37%, 30%, and 398%, respectively, but had no significant effect on soil pH or cation exchange capacity); however, its effectiveness in enhancing available phosphorus was significantly lower than that of organic fertilizer (Figure 2). When compared with crop nutritional requirements, the reported available nutrient contents are at favorable levels.

3.2. Effects of the Four Materials on Soil Enzyme Activity in Contaminated Farmland

Biochar and organic fertilizer significantly enhanced soil enzyme activities, with their effects varying notably by enzyme type (Figure 3). Among the four materials, biochar was significantly more effective than organic fertilizer in stimulating sucrase activity, increasing it by 52% compared to CK, which was significantly greater than the 28% increase induced by organic fertilizer. Conversely, organic fertilizer was the most effective treatment for boosting urease and acid phosphatase activities. It increased urease activity by 67%, significantly outperforming biochar (35%), and dramatically elevated acid phosphatase activity by 160%. However, biochar had no significant effect on soil acid phosphatase activity. For catalase activity, biochar also demonstrated a superior effect, producing a 26% increase that was significantly greater than the 18% increase observed in the organic fertilizer treatment.

3.3. Effects of the Four Materials on the Chemical Forms of Heavy Metals in Contaminated Farmland Soil

Lime, biochar, and sepiolite all reduced the bioavailability of heavy metals in the contaminated farmland soil to varying degrees (Figure 4). Among the four materials, lime was significantly more effective than sepiolite and biochar in reducing the acid-extractable fraction of Pb. Compared to the CK, the lime treatment reduced the proportions of the acid-extractable fractions of soil Pb, Cd, and Cu by 11%, 12%, and 15%, respectively. Furthermore, sepiolite showed the best performance in increasing the residual fraction of Zn. This treatment reduced the acid-extractable fractions of Pb, Cu, and Zn by 15%, 10%, and 9%, respectively, while increasing the proportions of the residual fractions of Pb and Zn by 11% and 13%, respectively.

3.4. Effects of the Four Materials on Bioavailable Heavy Metals Content in Contaminated Farmland Soil

Lime, biochar, and sepiolite treatments all significantly reduced the bioavailable fractions of heavy metals in the soil, though their effectiveness varied substantially depending on the specific metal (Figure 5). All data represent the relative reduction compared to the CK. Among the treatments, biochar was most effective in immobilizing Pb, showing a significantly greater reduction (57%) in the bioavailability of Pb than both sepiolite (40%) and lime (33%). For Cd, sepiolite demonstrated the best performance, achieving a significantly higher reduction in bioavailability (53%) than lime (37%). However, biochar had no significant effect on the bioavailable Cd concentration. In reducing Cu bioavailability, lime and sepiolite showed comparable immobilization effects (with reductions of 37% and 34%, respectively), and both treatments were significantly more effective than other amendments. In contrast, lime was the most effective in immobilizing Zn, producing a significantly larger reduction (73%) than both sepiolite (66%) and biochar (30%).

3.5. Effects of the Four Materials on Heavy Metal Accumulation in Phaseolus coccineus L.

The application of lime, biochar, and sepiolite significantly reduced heavy metal accumulation in various tissues of Phaseolus coccineus L. (Figure 6), with their remediation efficacy varying by metal type and plant organ (All data represent relative changes compared to the CK). sepiolite was the most effective treatment for reducing Pb content in the roots, achieving a significantly greater reduction (59%) than biochar (45%). In contrast, biochar was more effective than sepiolite in inhibiting Pb translocation to the grains, reducing Pb content by 50%, compared to a 45% reduction by sepiolite. Furthermore, biochar provided the most comprehensive reduction in heavy metals in the grains, significantly decreasing not only Pb but also Cd, Cu, and Zn contents (by 36%, 35%, and 36%, respectively), an effect not observed with sepiolite. In contrast, the concentrations of Cd and Cu in the stems and leaves remained unaffected by biochar amendment, showing no significant difference from the CK. These results demonstrate the tissue-specific and metal-specific remediation efficacy of the different amendments.

3.6. Effects of the Four Materials on the Nutrient Content and Biomass of Phaseolus coccineus L.

Among the four tested materials, biochar, sepiolite, and organic fertilizer significantly promoted the growth and increased the mineral nutrient content of scarlet Phaseolus coccineus L., with biochar and organic fertilizer demonstrating distinct and complementary advantages (Figure 7). Organic fertilizer was significantly more effective than biochar in enhancing total phosphorus content across all plant parts, with its increases relative to CK (63–217%) being substantially greater than those of biochar (16–40%). Conversely, biochar exhibited a stronger effect on biomass accumulation, with increases relative to CK in roots, stems, and leaves (37–55%) being significantly higher than those of organic fertilizer (16–36%). For total potassium content in grains, the increase relative to CK induced by biochar (49%) was also significantly greater than that of organic fertilizer (34%). Despite this, the total potassium in the roots and total nitrogen in the stems and leaves were not significantly increased by biochar. These results highlight the differential capabilities of the various amendments: organic fertilizer is particularly effective in improving phosphorus nutrition, whereas biochar excels in promoting overall plant growth and potassium accumulation in grains.

3.7. Effects of the Four Materials on the Quality and Yield of Phaseolus coccineus L.

Biochar and sepiolite treatments differentially improved the grain quality of Phaseolus coccineus L., while all four tested materials significantly increased grain yield (Figure 8). (All data represent relative changes compared to the CK). Among the materials, biochar was the only treatment that significantly enhanced protein content, with an 88% increase. Although sepiolite showed a numerically greater improvement in reducing sugars (29%) than biochar (20%), this difference was not statistically significant. In contrast, biochar showed no significant effect on soluble sugar content in the grains. For amylose content, biochar demonstrated significantly better improvement (37% increase) compared to sepiolite (20%). In terms of yield, organic fertilizer and biochar were the most effective treatments, achieving yield increases of 104% and 94%, respectively.

3.8. Correlations Between Phaseolus coccineus L. Growth and Soil Available Nutrients and the Bioavailability of Heavy Metals

The treatments with different materials reduced heavy metal accumulation in plants and grains by decreasing the bioavailability of heavy metals in soil. The soil available Pb content exhibited a highly significant positive correlation with root and grain Pb concentrations. The available Cd concentration was significantly positively correlated with the root Cd concentration. Soil available Cu was significantly positively correlated with grain Cu. Soil available Zn was strongly positively correlated with root Zn and significantly positively correlated with grain Zn (Figure 9a). These consistent positive correlations demonstrate the direct transfer of heavy metals from soil to plant tissues, with their bioavailability in soil being the primary factor controlling internal accumulation.
These materials enhanced Phaseolus coccineus L. growth by improving soil physicochemical properties. Soil pH was highly significantly positively correlated with available K and available P. CEC was significantly positively correlated with organic matter and available P and K contents. Soil organic matter was significantly positively correlated with shoot biomass. Alkaline-hydrolyzable N content was significantly positively correlated with shoot and root biomass. The grain N content correlated significantly positively with root biomass. The shoot K content was significantly positively correlated with root K, grain K, and root biomass. The grain K content was significantly positively correlated with root biomass. Shoot biomass was highly significantly positively correlated with grain biomass (Figure 9b). The strong interdependence among soil properties, nutrient availability, and plant growth underscores that these amendments promoted crop productivity through a synergistic improvement of the soil–plant system.
The materials improved grain quality. The reducing sugar content exhibited a highly significant negative correlation with grain Cd and a significant positive correlation with protein. The protein content was highly significantly negatively correlated with Cd. The starch content was significantly negatively correlated with grain Pb and Cd, highly significantly negatively correlated with Zn, and highly significantly negatively correlated with Cu (Figure 9c). The prevalent negative correlations between heavy metals and key quality components reveal that metal stress adversely affects grain nutritional quality, likely by disrupting biosynthetic pathways or inducing metabolic toxicity.

3.9. Structural Equation Modeling

Structural equation modeling elucidated the interrelationships and mechanisms through which distinct materials influence soil nutrient availability, heavy metal content, and Phaseolus coccineus L. growth in farmland adjacent to lead–zinc mining regions. The results demonstrated that lime treatments primarily increased Phaseolus coccineus L. biomass by regulating soil pH (0.74 ***); biochar amendment significantly reduced heavy metal bioavailability and accumulation in Phaseolus coccineus L. through increasing soil available nutrients (0.71 ***) and organic matter content (0.72 ***); sepiolite addition increased Phaseolus coccineus L. nutrient content (0.96 ***), consequently increasing biomass; and organic fertilizer treatments elevated both soil available nutrient (0.91 ***) and Phaseolus coccineus L. nutrient content (0.98 ***), further increasing biomass(Figure 10). Collectively, these materials improved soil nutrient status, reduced heavy metal bioavailability, and increased Phaseolus coccineus L. nutrient content, synergistically promoting Phaseolus coccineus L. biomass accumulation.

3.10. Applicability Assessment of the Four Materials for Heavy Metal Remediation

Subordinate function value analysis was performed to evaluate Phaseolus coccineus L. growth, plant nutrient contents, heavy metal accumulation, and bioavailable soil heavy metal and nutrient contents across the four treatments. The overall average value for the biochar treatment was the highest (0.70), indicating that it had a better restoration effect (Table 3).

4. Discussion

4.1. Effects of the Four Materials on the Bioavailability of Heavy Metals in Contaminated Farmland Soil and the Accumulation of Heavy Metals in Crops

The co-contamination of Pb, Cd, Cu, and Zn in the farmland soils of lead‒zinc mining regions can enter food chains via crop uptake, which can threaten food security [35]. In alpine lead–zinc mining regions such as Lanping, Yunnan, special environmental conditions further exacerbate this risk; frequent freeze‒thaw cycles disrupt soil structure and mobilize heavy metals [36], whereas permafrost layers impede vertical metal migration, causing contaminant accumulation in topsoil [37]. Consequently, conventional remediation materials require reevaluation for alpine treatments. To address these challenges, our field study demonstrated that lime, biochar, and sepiolite significantly reduce the bioavailable heavy metal content in soil and suppress Pb, Cd, Cu, and Zn uptake in Phaseolus coccineus L., with strong positive correlations between soil bioavailability and plant metal content. This conclusion is supported by the consistent efficacy of such amendments in reducing metal uptake across various crops, as observed in the reduction in Cd and Pb in cabbage by lime and biochar [38], demonstrated by the suppression of Cd, Zn, Pb, and Cu uptake in maize using rice straw and date palm biochars [39], and consistent with the decreased Cu, Zn, and Cd concentrations in rice grains following the application of silicate-based amendments and sepiolite [40]. Although all three materials effectively immobilize Pb, Cd, Cu, and Zn, their underlying mechanisms are fundamentally distinct. It should be noted that the findings of this study are based on a preliminary investigation at a specific site, and their broader applicability requires validation through future multi-site and multi-year studies.
The lime treatments increased the soil pH [41], promoting the formation of hydroxide or carbonate precipitates of Pb, Cd, Cu, and Zn. This resulted in a reduced proportion of acid-soluble fractions (e.g., an 11% decrease in Pb) and an increased proportion of residual fractions (e.g., a 15% increase in Cd), accompanied by significant reductions in both soil available heavy metal contents and Pb, Cd, Cu, and Zn concentrations in Phaseolus coccineus L. plants. Sepiolite, leveraging its large specific surface area and surface charge properties [8], reduced the available contents of Pb and Cd by 40% and 53%, respectively, through physical adsorption while achieving heavy metal immobilization via speciation transformation (e.g., a 15% decrease in acid-soluble Pb and an 11% increase in residual Pb). Biochar, as an organic material, has multiple advantages in soil remediation within alpine environments. Its loose, porous structure effectively mitigates physical damage to soil caused by freeze–thaw cycles [42,43], while concurrently immobilizing heavy metal contaminants (e.g., Pb, Cu, Zn) through integrated mechanisms including electrostatic adsorption, ion exchange [44], surface complexation [45,46], and chemical precipitation. A representative example is the formation of stable lead carbonate precipitates resulting from reactions between biochar-derived carbonate ions and soluble Pb2+ in the soil solution, which significantly reduces lead bioavailability [47]. Collectively, these synergistic mechanisms substantially minimize the risk of heavy metal remobilization during freeze–thaw cycles in high-altitude mining areas [48].

4.2. Improving Effects of the Four Materials on the Properties of Heavy Metal-Contaminated Soil

Soils in lead‒zinc mining regions typically exhibit nutrient deficiency and low enzyme activity [9]. In alpine mining regions, these challenges are exacerbated by low temperatures, frequent freeze-thaw cycles, and short growing seasons. Under low-temperature conditions, enzyme activity is inhibited, and the mineralization of organic matter slows, leading to reduced rates of nutrient release [49]. Moreover, freeze‒thaw action can damage soil structure, increasing the risk of nutrient leaching [50]. To meet the demands of a short growing season, ensuring a rapid and effective nutrient supply is essential. In this study, organic fertilizer and biochar resulted in the most significant improvements in soil physicochemical properties and biological functions. This is closely related to their material characteristics and mechanisms of action, which exhibit distinct advantages in high-altitude environments.
Organic fertilizer increased the soil available potassium content by 407% and the available phosphorus content by 112%. Similarly, the organic fertilizer treatments significantly increased the soil nitrogen, available phosphorus, available potassium, total nitrogen, and total phosphorus contents [51]. This may be because organic fertilizer is produced from biomass resources such as animal and plant residues and excreta through composting processes. Its composition includes essential elements for crop growth, such as N, P, K, Ca, and Mg [52], which can be directly supplemented into the soil to increase the soil nutrient content. This bypasses the slow mineralization process at low temperatures and rapidly meets crop nutrient demands during the short growing season. Organic fertilizer also contains large amounts of humic acid, which fixes nutrients through ion exchange, reducing the degree of leaching caused by freeze‒thaw cycles [53]. Additionally, the organic fertilizer treatments significantly increased the soil cation exchange capacity, which was significantly positively correlated with the soil available phosphorus and potassium contents. Similarly, Sun et al. [54] reported that organic fertilizer treatments significantly increased the cation exchange capacity (51.98%), available nitrogen (234.56%), phosphorus (20.09%), and potassium (67.65%), indicating that organic fertilizer can also increase the soil nutrient content by increasing the cation exchange capacity. Biochar significantly increased the soil organic matter content, alkaline-hydrolyzable nitrogen content, available phosphorus content, and available potassium content by 25%, 37%, 30%, and 398%, respectively. Similarly, the biochar treatments significantly increased the soil total carbon, total nitrogen, available phosphorus, and available potassium contents [55].These enhancements stem from biochar’s dual function: as a direct source of mineral nutrients and as a porous adsorbent that retains cations (e.g., NH4+, K+) via its functional groups (e.g., -COOH, -COH), reducing leaching [56,57]. Additionally, this porosity helps buffer freeze–thaw stress, maintaining soil structure and porosity for improved water and nutrient retention in alpine regions [58]. Changes in soil enzyme activity further reflect the improvement in soil functionality in alpine mining regions caused by the amendments. Biochar increased invertase and urease activities by 52% and 35%, respectively, whereas organic fertilizer increased urease and acid phosphatase activities by 67% and 160%, respectively (Figure 3). This occurs because, against the background of low-temperature-limited microbial activity in alpine regions, both materials provide carbon sources and habitats for microorganisms [59]. Moreover, increased activities of invertase (which is involved in carbon metabolism) and urease (which is involved in nitrogen transformation) directly increase the efficiency of soil nutrient conversion [60].

4.3. Effects of the Four Materials on Crop Yield and Quality in Contaminated Soil

The accumulation of heavy metals in soil reduces crop biomass and yield by inhibiting photosynthesis, disrupting enzyme activities, and impairing nutrient uptake while degrading grain quality [61]. Alpine environments inherently impose stress on crop growth through factors such as low temperatures, short growing seasons, and intense radiation. Heavy metal pollution compounds this stress, generating combined stress. In this study, all four materials significantly promoted Phaseolus coccineus L. growth through improvements in the soil environment—specifically by increasing nutrient availability or reducing heavy metal bioavailability. Nevertheless, their effects on yield and quality significantly varied and were closely linked to each material’s mechanism of action and regulatory efficacy in the soil–plant system.
All amendments significantly increased grain yield of Phaseolus coccineus L., with improvements ranging from 56% to 104%. Organic fertilizer achieved the highest yield enhancement (104%), followed by biochar (82%), with sepiolite and lime showing more moderate effects. These differential outcomes align with each material’s capacity to improve soil nutrient status and alleviate heavy metal stress. Under the constraints of short alpine growing seasons, organic fertilizer provides immediate access to essential macronutrients (particularly N, P, and K), directly supporting vegetative growth and grain filling while overcoming the inherent limitation of slow nutrient mineralization in cold soils. Biochar improved crop productivity through comprehensive enhancements in soil physical conditions, heavy metal immobilization, and nutrient utilization efficiency. Its characteristic porous architecture improves soil aeration and moisture retention, creating optimal conditions for root system development. Simultaneously, biochar effectively diminishes heavy metal bioavailability while improving nutrient acquisition, collectively stimulating plant growth and yield formation [62,63]. Structural equation modeling (Figure 10) verified that biochar promotes biomass accumulation through two interconnected pathways: optimizing plant nutritional status and reducing soil heavy metal bioavailability, with this synergistic interaction proving particularly beneficial in alpine ecosystems.
In terms of quality regulation, biochar and sepiolite showed superior effectiveness, while organic fertilizer and lime had more limited effects. Biochar treatment significantly increased the contents of grain-reducing sugars (20%), protein (88%), and starch (37%). Similarly, Du et al. [64] reported that biochar treatments increased head rice yield and protein content in main and ratoon rice crops by 16.5% and 13.5%, respectively. These quality improvements stem from two mechanisms: biochar enhances nitrogen uptake and utilization, promoting protein synthesis and accumulation in grains particularly important under low-temperature conditions where protein metabolism is often inhibited [65]. Additionally, biochar substantially reduces heavy metal accumulation in grains, as shown by a 36% decrease in Cd content (Figure 6). Correlation analysis demonstrated strong negative correlations between grain Cd concentration and both protein and starch contents (Figure 9c), indicating that heavy metal stress reduction alleviates the inhibition of enzymes involved in starch and protein synthesis [66].
The remediation mechanisms identified in this study suggest potential applicability to other crops in alpine regions. For instance, the heavy metal immobilization capabilities of biochar and sepiolite could benefit staple cereals like highland barley (Hordeum vulgare) and oats (Avena sativa), which are widely cultivated in similar environments and have been shown to accumulate heavy metals in contaminated soils [67]. Similarly, the rapid nutrient supply from organic fertilizer may be particularly advantageous for root crops such as potatoes (Solanum tuberosum) during their critical tuber bulking stage as rapid nutrient availability is crucial for tuber yield formation [68]. However, crop-specific responses should be considered, as variations in root architecture, metal translocation efficiency, and nutrient requirements may influence the effectiveness of each amendment across different species.
In alpine mining regions where dietary diversity is limited, the nutritional composition of grains is particularly crucial for local residents [69]. The substantial increase in protein content (88%) is likely to provide economic advantages for farmers, as higher protein levels typically command better market prices for legume crops [70]. Meanwhile, the concurrent increases in starch (37%) and reducing sugars (20%) are expected to enhance cooking quality and palatability, thereby improving consumer acceptance. Starch, being the primary component of grains, significantly influences cooking and eating quality [71]. While these improvements demonstrate clear potential for enhancing both market value and consumer satisfaction, further socioeconomic studies would be valuable to precisely quantify their perceived significance among local farmers and consumers.
In summary, while organic fertilizer was most effective for yield improvement, biochar proved to be the most comprehensive amendment for simultaneously enhancing both crop productivity and grain quality in contaminated farmlands of alpine lead–zinc mining regions, due to its dual capacity to improve nutrient availability and immobilize heavy metals. However, the practical implementation of biochar at scale faces several challenges that warrant consideration. Firstly, the production cost of high-quality biochar through pyrolysis remains higher than that of conventional amendments like lime and organic fertilizer, which could limit its economic feasibility for local farmers. Secondly, accessibility to standardized biochar products may be constrained in remote alpine regions due to underdeveloped supply chains and logistical barriers. Finally, the properties and effectiveness of biochar can vary significantly depending on the feedstock source and pyrolysis conditions, creating uncertainty in its long-term performance. Future research should therefore focus on developing low-cost production techniques utilizing local biomass wastes, optimizing transport and application protocols, and establishing quality standards to ensure consistent remediation effects in alpine mining areas.
Beyond technical efficacy, the socioeconomic implications of implementing these soil amendments are crucial for their practical adoption. The yield and quality improvements demonstrated in this study could directly enhance farmers’ income through increased marketable produce, potentially offsetting the initial investment in amendments. Specifically, the 82–104% yield increase and significant grain quality enhancement may improve food security and economic resilience for local farming communities. While organic fertilizer offers the advantage of local availability and immediate yield gains, biochar’s long-term soil improvement and metal immobilization benefits could provide sustained economic and environmental returns. Successful implementation would require supportive policies, such as subsidies for amendment procurement and extension services to educate farmers about proper application techniques. Future work should integrate cost–benefit analyses and engage with local stakeholders to co-develop feasible implementation strategies.
These improvements are closely linked to the dual mechanisms of action of biochar. First, biochar enhances crop nitrogen uptake by increasing soil nitrogen availability and promoting protein synthesis and accumulation in grains [65]. This effect is particularly critical when protein metabolism may be inhibited at low temperatures. Second, it significantly reduces the heavy metal content in grains, as exemplified by a 36% reduction in Cd (Figure 6). Correlation analysis revealed strong negative relationships between grain Cd and both protein and starch contents (Figure 9c), indicating that alleviation of heavy metal stress mitigates the inhibition of starch synthases and proteases [66], thereby indirectly improving quality. In conclusion, biochar is optimal for enhancing both crop yield and grain quality in alpine mining regions. Through its dual functions of supplying soil nutrients and alleviating heavy metal stress, it has emerged as a promising material for simultaneously improving agricultural productivity and grain quality in contaminated farmlands of alpine lead‒zinc mining regions.

4.4. Practical Implications and Future Perspectives

This study demonstrates that the large-scale application of the four amendments in contaminated farmland of alpine mining areas depends not only on their remediation efficacy, but also on local availability, cost, and long-term ecological and economic benefits. In typical alpine mining areas such as Lanping, Yunnan, organic fertilizer—sourced locally from livestock farming—is the lowest-cost option and significantly increases crop yield (by up to 104%), though its effect on reducing heavy metal concentrations in crops was not statistically significant. Lime can be sourced locally from nearby quarries at moderate cost and effectively reduces heavy metal activity. In contrast, biochar and sepiolite currently rely mainly on external supply, resulting in higher costs. However, biochar excels in synergistically improving soil quality and immobilizing heavy metals, while sepiolite shows outstanding adsorption capacity for specific metals such as lead and cadmium.
Based on these differences, we propose tiered remediation strategies: for moderately to lightly contaminated farmland, organic fertilizer is recommended as the primary amendment to balance yield and economic benefits; for areas with prominent heavy metal contamination, biochar or its combination with organic fertilizer is suggested. Although the initial investment is higher, the comprehensive benefits for soil health and agricultural product safety are more substantial.
It should be noted that the present findings are based on a single growing season pot experiment, and the long-term stability of the amendments and their applicability to other crops have not been fully verified. Future research should focus on the following directions: conducting multi-season continuous monitoring to evaluate the persistence of remediation effects under the dynamic environmental conditions of alpine regions; and extending the study to different crop types, particularly staple food crops, to establish safe utilization strategies suitable for diverse agricultural systems in alpine mining areas.

5. Conclusions

This study demonstrates that four amendments significantly enhanced the remediation of contaminated farmland in an alpine lead–zinc mining area. Organic fertilizer and biochar improved soil fertility by increasing available nutrient content (e.g., organic fertilizer raised available phosphorus and potassium by 112% and 407%, respectively) and enhancing soil enzyme activities (e.g., biochar increased invertase and urease activities by 52% and 35%, respectively). Meanwhile, lime, biochar, and sepiolite effectively reduced heavy metal bioavailability (e.g., lime decreased available Pb, Cd, and Cu by 33–37%) and promoted their stabilization. Comprehensive evaluation revealed that biochar exhibited the best overall remediation performance, integrating dual functions of nutrient enhancement and heavy metal immobilization. While promoting the growth of Phaseolus coccineus L., increasing yield by 82%, and improving grain quality, it also reduced heavy metal accumulation in grains by 36–50%. Thus, biochar is an ideal material for the synergistic remediation of heavy metal contamination and soil fertility improvement in alpine mining areas. The other amendments showed distinct advantages: organic fertilizer achieved the most notable rapid yield increase, lime was most effective in elevating soil pH, and sepiolite exhibited superior adsorption capacity for Pb and Cd, serving as alternative options for targeted remediation.

Author Contributions

Conceptualization, S.H.; methodology, W.M.; software, Q.Y.; formal analysis, Q.C.; resources, Y.H.; data curation, X.H. (Xiaojia He); writing—original draft preparation, X.H. (Xiuhua He); writing—review and editing, J.H. and H.B.; funding acquisition, F.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (42177381, 42267002), Expert Workstation of Jian Liu in Yunnan Province (202305AF150126) the Natural Science Foundation of Yunnan Province(202401AS070087), Heavy Metal Pollution and Ecological Restoration in Lanping Lead-Zinc Mining Area, Observation and Research Station of Yunnan Province (202505AM340006), Expert Workstation of Longhua Wu in Yunnan Province (202305AF150042).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Acknowledgments

We thank Y.H. and F.Z. from Yunnan Agricultural University for experimental design guidance. We also thank the editors and anonymous reviewers for their great support.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Climate Diagram of the Experimental Site (2020).
Figure 1. Climate Diagram of the Experimental Site (2020).
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Figure 2. Effects of the four materials on soil physicochemical properties. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
Figure 2. Effects of the four materials on soil physicochemical properties. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
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Figure 3. Effects of the four materials on soil enzyme activity. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
Figure 3. Effects of the four materials on soil enzyme activity. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
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Figure 4. Effects of the four materials on soil heavy metal chemical forms. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer.
Figure 4. Effects of the four materials on soil heavy metal chemical forms. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer.
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Figure 5. Effects of the four materials on the bioavailable content of heavy metals in contaminated farmland soil. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
Figure 5. Effects of the four materials on the bioavailable content of heavy metals in contaminated farmland soil. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
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Figure 6. Effects of the four materials on heavy metal content in roots, stems and leaves, and grains of Phaseolus coccineus L. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
Figure 6. Effects of the four materials on heavy metal content in roots, stems and leaves, and grains of Phaseolus coccineus L. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
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Figure 7. Effects of the four materials on nutrient content and biomass of roots, stems and leaves, and grains of Phaseolus coccineus L. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
Figure 7. Effects of the four materials on nutrient content and biomass of roots, stems and leaves, and grains of Phaseolus coccineus L. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
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Figure 8. Effects of the four materials on grains quality and yield of Phaseolus coccineus L. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
Figure 8. Effects of the four materials on grains quality and yield of Phaseolus coccineus L. The abbreviations are CK, the control; L, lime; B, biochar; S, sepiolite; O, organic fertilizer. Different lowercase letters above the bars indicate statistically significant differences among treatments according to Duncan’s multiple range test at p < 0.05. Treatments sharing the same letter are not significantly different.
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Figure 9. Correlation analysis between the available forms of heavy metals in soil and their concentrations in plant tissues (a), between soil physical and chemical properties and plant growth (b), and between grain quality and heavy metal concentrations (c).
Figure 9. Correlation analysis between the available forms of heavy metals in soil and their concentrations in plant tissues (a), between soil physical and chemical properties and plant growth (b), and between grain quality and heavy metal concentrations (c).
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Figure 10. Structural equation modeling analysis of the effects of the four materials on Phaseolus coccineus L. biomass. In the model, positive and negative values on arrows indicate positive and negative relationships between variables, respectively; solid and dashed arrows denote significant and no significant pathways, respectively. Blue arrows represent positive relationships, and red arrows represent negative relationships. *** p < 0.001, ** p < 0.01, * p < 0.05.
Figure 10. Structural equation modeling analysis of the effects of the four materials on Phaseolus coccineus L. biomass. In the model, positive and negative values on arrows indicate positive and negative relationships between variables, respectively; solid and dashed arrows denote significant and no significant pathways, respectively. Blue arrows represent positive relationships, and red arrows represent negative relationships. *** p < 0.001, ** p < 0.01, * p < 0.05.
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Table 1. The Nutrient Classification Criteria of the Second National Soil Survey.
Table 1. The Nutrient Classification Criteria of the Second National Soil Survey.
IndicatorExtremely RichRichRelatively RichModeratePoorExtremely Poor
Organic matter(g/kg)>4030~4020~3010~206~10<6
Total N (g/kg)>21.5~21~1.50.75~10.5~0.75<0.5
Total P (g/kg)>10.8~10.6~0.80.4~0.60.2~0.4<0.2
Total K (g/kg)>2520~2515~2010~155~10<5
Available N (mg/kg)>150120~15090~12060~9030~60<30
Available P (mg/kg)>4020~4010~205~103~5<3
Available K (mg/kg)>200150~200100~15050~10030~50<30
Note: The criteria are based on the second national soil survey, with the upper limits of each nutrient index determined according to the measured values in this study.
Table 2. pH value, Pb, Cd, Cu, and Zn content of the test materials.
Table 2. pH value, Pb, Cd, Cu, and Zn content of the test materials.
MaterialspHPb (mg/kg)Cd (mg/kg)Cu (mg/kg)Zn (mg/kg)
L (Lime)12.201.390.21——
B (Biochar)8.845.41———
S (Sepiolite)9.352.72———
O (organic fertilizer)7.8918.22.27156245
Note: “—” means below the detection limit of the instrument.
Table 3. Ranking of soil heavy metal remediation effects based on subordinate functional values.
Table 3. Ranking of soil heavy metal remediation effects based on subordinate functional values.
IndexLBSO
Plant biomass0.150.720.480.43
Plant nutrient0.530.680.860.91
Plants heavy metal0.720.910.940.33
Soil available heavy metal0.860.740.910.09
Soil available nutrient0.470.440.120.85
Mean value0.550.700.660.52
Ranking number3124
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He, X.; Yang, Q.; Meng, W.; He, X.; He, Y.; He, S.; Chen, Q.; Zhan, F.; He, J.; Bai, H. Differential Effects of Four Materials on Soil Properties and Phaseolus coccineus L. Growth in Contaminated Farmlands in Alpine Lead–Zinc Mining Areas, Southwest China. Agronomy 2025, 15, 2467. https://doi.org/10.3390/agronomy15112467

AMA Style

He X, Yang Q, Meng W, He X, He Y, He S, Chen Q, Zhan F, He J, Bai H. Differential Effects of Four Materials on Soil Properties and Phaseolus coccineus L. Growth in Contaminated Farmlands in Alpine Lead–Zinc Mining Areas, Southwest China. Agronomy. 2025; 15(11):2467. https://doi.org/10.3390/agronomy15112467

Chicago/Turabian Style

He, Xiuhua, Qian Yang, Weixi Meng, Xiaojia He, Yongmei He, Siteng He, Qingsong Chen, Fangdong Zhan, Jianhua He, and Hui Bai. 2025. "Differential Effects of Four Materials on Soil Properties and Phaseolus coccineus L. Growth in Contaminated Farmlands in Alpine Lead–Zinc Mining Areas, Southwest China" Agronomy 15, no. 11: 2467. https://doi.org/10.3390/agronomy15112467

APA Style

He, X., Yang, Q., Meng, W., He, X., He, Y., He, S., Chen, Q., Zhan, F., He, J., & Bai, H. (2025). Differential Effects of Four Materials on Soil Properties and Phaseolus coccineus L. Growth in Contaminated Farmlands in Alpine Lead–Zinc Mining Areas, Southwest China. Agronomy, 15(11), 2467. https://doi.org/10.3390/agronomy15112467

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