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Article

Foliar Application of Manganese-Zinc Fertilizer Mitigated the Harmful Effects of Cadmium on Wheat and Reduced Human Health Risks

by
Ting Xie
1,2,
Mengjie Hao
1,2,
Qingyu Wang
1,2,
Bowen Wu
3,
Zhenguo Zhang
3,
Baoping Zhao
4,
Yufang Shao
5,* and
Meiying Liu
1,2,*
1
Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resources, College of Resources and Environmental Sciences, Inner Mongolia Agricultural University, Hohhot 010018, China
2
Key Laboratory of Agricultural Ecological Security and Green Development, College of Resources and Environmental Sciences, Inner Mongolia Agricultural University, Hohhot 010018, China
3
Cultivated Land Quality Protection Center of Bayan Nur, Bayannur 015000, China
4
College of Agriculture, Inner Mongolia Agricultural University, Hohhot 010018, China
5
Inner Mongolia Agriculture, Animal Husbandry, Fishery and Biology Experiment Research Centre, Rural Revitalization Research Institute, Inner Mongolia Agricultural University, Hohhot 010018, China
*
Authors to whom correspondence should be addressed.
Sustainability 2025, 17(7), 3058; https://doi.org/10.3390/su17073058
Submission received: 19 January 2025 / Revised: 4 March 2025 / Accepted: 28 March 2025 / Published: 30 March 2025
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Abstract

:
In recent years, the problem of Cd (cadmium) contamination in cultivated soils has grown worse, endangering food security and human health and impeding agricultural sustainability. The application of foliar fertilizer can effectively prevent and control the accumulation of Cd in crops, but the related effects of foliar fertilizer application on the accumulation of Cd in wheat and the risk to human health are not clear. On the Cd-polluted farmland, five foliar fertilizers (multi-element compound fertilizer (Me), manganese-zinc micro-fertilizer (MZ), sodium dihydrogen phosphate (P), water-soluble organic fertilizer (WO) and foliar silicon fertilizer (Si)) and CK (the fresh water was used as the control) were sprayed on wheat at different growth periods (spraying once at the tillering stage and spraying twice at the tillering stage and the booting stage) to investigate the effects of foliar fertilizer on wheat yield and the content of Cd in grains and human health risks. The results showed that the application of five types of foliar fertilizers can lead to an increase in wheat yield, an inhibition of the transfer of cadmium to the edible parts of wheat, and a reduction in the human health risk (THQ). Compared with the CK (the fresh water was used as the control), the impact of Cd stress on the yield of spring wheat was alleviated by the MZ treatment, and the largest yield increase of 24.2% was achieved when MZ was sprayed once. When compared with one application, two applications of foliar fertilizers were shown to effectively reduce the content of Cd in the leaves, glumes, and grains of wheat, while increasing the content of Cd in the roots and stems. Among all foliar fertilizers, the cadmium content in wheat grains was most effectively decreased using MZ2 (spraying twice at the tillering stage and the booting stage), with a reduction of 36.6%. At the same time, the target hazard coefficient (THQ) of foliar spraying was reduced, and using two bouts of foliar fertilizer spraying was more effective in reducing the health risks. In conclusion, MZ fertilizer sprayed twice was a desirable choice for wheat, which was conducive to the safe production of wheat on Cd-contaminated farmland and for contributing to the sustainable development of agriculture.

1. Introduction

Wheat is one of the three most important food crops in the world [1]. With the irrational application of chemical fertilizer and pesticides for many years, as well as the continuous development of mining enterprises around farmland, many heavy metal pollutants enter farmland soil through atmospheric sedimentation and sewage discharge [2]. Compared with other heavy metal elements, Cd is more easily adsorbed by crops [3], is difficult to degrade [4], and has a high toxicity [5]. Cadmium (Cd) was ranked seventh in the Agency for Toxic Substances and Disease Registry (ATSDR) [6]. Farmland soil contaminated by Cd not only reduces soil fertility by disrupting biological and chemical processes in the soil, inhibiting soil enzyme activities and limiting the effectiveness of soil nutrients [7], but it also interferes with crop photosynthesis as well as water and nutrient uptake, ultimately leading to reduced crop yields [8]. After being absorbed by crops, Cd endangers the health and safety of humans and animals through the food chain and food web [9]. Therefore, it would be of great practical significance to understand the current status of heavy metal pollution in agricultural soils and take corresponding control measures to ensure the yield and quality of crops.
At present, remediation technologies for cadmium accumulation in crops mainly include soil passivation [10], biological remediation [11], foliar fertilization [12] and low-accumulation variety screening [13]. Among them, foliar fertilization is applied by spraying small organic or inorganic molecules on the surface of crop leaves [14]. By exploiting the antagonism [15] or synergism [16] between various elements and cadmium, the bioavailability of cadmium was reduced, the cadmium content in crops was reduced, the resistance of crops was improved and the yield of crops was increased [17,18,19]. When comparing different remediation techniques for farmland with moderate to mild cadmium pollution, foliar fertilization is the most economical. So, when should foliar fertilization be applied? What is the optimal dosage and frequency of application? Based on the previous studies on the effects of foliar fertilizer spraying once or twice on cadmium accumulation and absorption in wheat [20], it was found that the frequency of spraying may also be a factor affecting plant uptake and transport of cadmium. Therefore, this study was conducted.
The purpose of this study is to compare the absorption of heavy metal cadmium by different types of foliar fertilizer wheat at different fertilization times, and to evaluate the safety of cadmium in wheat grains. This research contributes to wheat safety and human health, and promotes agricultural sustainability by maintaining production viability and ecological balance.

2. Materials and Methods

2.1. Description of the Study Area

The experimental site was located in a heavy metal-contaminated farmland near a mining area in Inner Mongolia, China (41°6′ N, 107°6′ E). In this experiment, a spring wheat (Triticum aestivum L.) named Yongliang No. 4 was selected as the plant material, which was a characteristic wheat in the place where the research was conducted. The seeds were purchased from a local agricultural store. The soil is a Salic Calcic Solonetz (FAO classification) and the basic physical and chemical properties of the soil are as follows: pH = 8.02, total nitrogen (TN) 0.31 g⋅kg−1, total phosphorus (TP) 0.65 g⋅kg−1, total potassium (TK) 19.19 g⋅kg−1, alkaline-hydrolysis nitrogen (AN) 125.3 mg⋅kg−1, available phosphorus (AP) 43.6 mg⋅kg−1, available potassium (AK) 284 mg⋅kg−1, and organic matter 20.86 g⋅kg−1. The total cadmium (Cd) of soil in this study area was 1.19 mg⋅kg−1, which was cadmium-contaminated soil. The mean annual temperature was 14 °C and the total annual rainfall was 198.5 mm in this study area. A total of five foliar fertilizers were used in the present study, namely, multi-element compound fertilizer (Me), manganese-zinc micro-fertilizer (MZ), sodium dihydrogen phosphate (P), water-soluble organic fertilizer (WO) and foliar silicon fertilizer (Si).

2.2. Experimental Design

The experiment was conducted in a two-factor split-zone design and a Randomized Complete Block Design (RCBD) was used in this experiment. There were five foliar fertilizer treatments in the main treatment (Table 1) (including multi-element compound fertilizer (Me), manganese-zinc micro-fertilizer (MZ), sodium dihydrogen phosphate (P), water-soluble organic fertilizer (WO) and foliar silicon fertilizer (Si)), and fresh water was used as the control (CK)). There were two kinds of spraying times for the sub-treatments, including spraying once at the booting stage (CK1, Me1, MZ1, P1, WO1, Si1) and spraying twice at the tillering stage and the booting stage (CK2, Me2, MZ2, P2, WO2, Si2). A total of 12 treatments were set up (Table 1) and each treatment was replicated three times, with a plot area of 20 m2 (4 m ×5 m). The experiment consisted of 36 plots, with a 1 m wide pathway between each plot to prevent cross-contamination during spraying. Fertilizer was applied to the leaves after 4 pm on a sunny day using a hand-held sprayer. Equal amount of spraying was used between treatments, and equal amount of fresh water was used in the control group. The experiment was conducted over one planting season of wheat and wheat was sown at the end of March. The sowing rate of wheat was 450 kg·hm−2, and 375 kg·hm−2 of diammonium phosphate (N-P2O5 is 18-46) and 225 kg·hm−2 compound fertilizer (N-P2O5-K2O is 12-18-15) were applied as the basal fertilizer at the time of sowing. Urea 150 kg / hm2 was applied during the topdressing period, and watering was done three times during the whole growth period of the wheat.

2.3. Sample Collection

The S-shaped samples were taken from 0 to 20 cm of pre-sowing soil, which was naturally air-dried indoors and then passed through 2 mm and 0.149 mm sieves to determine the basic physical and chemical properties of the soil as well as the Cd content.
At the maturity stage of wheat, plant height, spike length and number of grains per spike, thousand kernel weight and wheat yield were measured in each plot. Whole wheat plants in the plots were collected using the three-point sampling method and disassembled into plant roots (washed with water followed by distilled water), stems, leaves, glumes, and kernels, and fresh weight was determined. Dry weight was determined after drying at 105 °C for 30 min and then at 70 °C to constant weight. The organs were ground in a high-speed grinder and sieved through a 0.149 mm sieve for the determination of cadmium concentration.

2.4. Determination of Soil Physiochemical Parameters

Soil pH was determined with a pH meter in a 1:2.5 soil-water suspension. Soil organic carbon (TOC) was determined with wet oxidation via K2Cr2O7 + H2SO4 and titration with FeSO4. Soil total nitrogen (TN) was determined using an element analyzer. Available phosphorus (AP) in the soil was extracted using 0.5 M NaHCO3 and determined via the molybde-num-antimony anti-colorimetric method. Available potassium (AK) was measured using 1 M NH4OAC with flame photometry.

2.5. Determination of Cd Concentrations in Plants

A total of 0.5 g of plant samples were weighed to digest the dried samples with a mixture of HNO3 and HClO4 (3:1, v/v), while a blank group and a standard sample were made, and the digested samples were kept in a constant volume with deionized water. Inductively coupled plasma mass spectrometry (ICP-MS 7500c, Agilent, Santa Clara, CA, USA) was used to determine Cd concentration.
The transport factor (TF) from the lower parts to the upper parts of the plants was calculated:
TFi.j = Cj/Ci
where i, j are the two plant parts being compared from the root, to stem, to leaf, to grain [21].

2.6. Human Health Risk Assessment in Plants

The Target Hazard Factor THQ is used for the assessment of the risk of dietary exposure to heavy metals in humans which is the ratio of the Exposure Dose (EDI) to the Reference Oral Dose (Rf D) [22]. The THQ value of <1 indicates that there is no risk of non-carcinogenic effects, while on the other hand, the THQ value of >1 indicates that there is a potential risk of non-carcinogenic effects and that intervention and protective measures are required. The specific calculation formula is as follows:
EDI = (C × IRD × EF × ED)/(365 × Bw × AT)
THQ = EDI/Rf D
where C is the heavy metal content in grain, µg·kg−1; IRD is the daily grain intake per person, (adults for 266.4 g·person−1·d−1) [23]; EF is the frequency of exposure, and is taken as 365 d·a−1; ED is the number of years of exposure, and is taken as 70 a; Bw is the average body mass of adults, and is taken as 65 kg·person−1; AT is the expectation of life, taken as 70 a; 365 is the conversion factor; and Rf D is the oral reference dose value (the Rf D of Cd is 1.0 µg·kg−1·d−1) [24].

2.7. Statistical Analysis

Origin 2024 (Origin Lab Corporation, Northampton, MA, USA) was used for graphical work performance. Data were analyzed using SPSS 24.0 (SPSS Inc., Chicago, IL, USA). Differences between treatments were analyzed using a one-way ANOVA and two-way ANOVA for comparisons between groups. Duncan’s Multiple Range Test (DMRT) was used for significance analysis. Differences were considered statistically significant when p-values < 0.05.

3. Results

3.1. Effects of Different Foliar Fertilizers and Spraying Times on Wheat Growth Status

There was no statistically significant effect of spraying foliar fertilizer on plant height and spike length of wheat at a p < 0.05 level (Figure 1a,b), but there were significant differences in the plant height of the same foliar fertilizer sprayed at different times. All of the foliar fertilizer sprays significantly increased the number of grains in wheat compared to CK1, with the MZ1 treatment significantly increasing the number of grains by 10.4%, which was the largest increase (Figure 1c). Compared with CK1, MZ1 and WO1 treatments significantly increased the thousand-grain weight of wheat, which were 1.9% and 5.6%, respectively, and only the MZ2 treatment resulted in a significant increase in the thousand-grain weight of wheat compared with CK2 (Figure 1d). Foliar spraying of different fertilizers reduced the effect of Cd stress on wheat yield (Figure 1e). The spraying of different foliar fertilizers significantly increased the economic yield of wheat compared to CK1, with the largest increase of 24.2% in MZ1 (Figure 1e), and compared to CK2, the Me2, MZ2 and Si2 treatments increased the yield of wheat by 17.8%, 15.7% and 16.9%, respectively (Figure 1e). At the same time, there were significant differences (p < 0.01) in the yield of the same foliar fertilizer sprayed at different times.

3.2. Effects of Foliar Fertilizer and Spraying Times on Plant Cd Contents

The Cd content in wheat roots showed an increasing trend after spraying with foliar fertilizer compared to the control (Figure 2). Compared with CK1, one application of foliar fertilizer did not contribute significantly (p < 0.05) to the Cd content in the root system of wheat at the statistical level (Figure 2a), but MZ2 and Me2 significantly increased the Cd content in the root system of wheat compared with CK2 (Figure 2b), with the most increase of Cd content in the root system of wheat treated with MZ2 of 41.7%.
Different from the changes in the root system, the Cd content in stems, leaves, glumes, and grains of wheat tended to decrease with the spraying of foliar fertilizer. Compared with CK1, cadmium reduction in wheat leaves with spraying once with foliar fertilizer was not significant at the p < 0.05 statistical level (Figure 2a). The three treatments of MZ2, Me2 and P2 resulted in a significant reduction of Cd in wheat leaves by 34.8%, 30.6% and 24.3%, respectively, compared with CK2 (Figure 2b). By analyzing the stems and glumes of wheat, it could be found that MZ1, WO1 and P1 could significantly reduce Cd content in stems compared with CK1, and at the same time, MZ1 and P1 also significantly reduced the Cd content in wheat glumes (Figure 2a), among which the most obvious effect of Cd reduction was achieved by MZ1, which reduced Cd content of wheat stems by 63.5% and Cd content of wheat glumes by 34.0%, respectively. Meanwhile, two foliar sprays of different fertilizers did not produce significant changes (p < 0.05) (Figure 2b).
When sprayed once with foliar fertilizer, both MZ1 and WO1 reduced the Cd content of wheat grains to the range of food contaminant criterion values (≤0.1 mg/kg) (Figure 2a). The application of five foliar fertilizers reduced the content of Cd in wheat grains using MZ2, P2, and WO2 was significant compared with that of CK2, and MZ2 was the most effective for the reduction of Cd in the grains, lowering the Cd content by 36.6% compared with that of CK2 (Figure 2b).
According to the distribution ratio of Cd in various organ tissues of wheat, Cd was mainly distributed in the roots, leaves and glumes of wheat, and different types of foliar fertilizer and times of application changed the distribution pattern of Cd in wheat (Figure 3). Two applications of foliar fertilizer (CK1, Me1, MZ1, P1, WO1, and Si1) clearly reduced the percentage of Cd in leaves, glumes and grains of wheat, and increased the percentage of Cd in the roots and stems of wheat compared to a single application of foliar fertilizer (CK2, Me2, MZ2, P2, WO2, and Si2) (Figure 3).

3.3. Effects of Foliar Fertilizers and Spraying Times on Cd Transport Factor (TF)

The transport factor (TF) can reflect the Cd transport capacity among plant organs under Cd stress. The results showed that the TF of Cd in leaf-glumes and glumes-grains did not change significantly (p < 0.05) with the foliar application of different fertilizers in wheat (Figure 4). However, there were significant changes in Cd migration within roots, stems and leaves of wheat with the foliar application of different fertilizers in wheat (Figure 4). It indicated that the Cd-reducing effect of foliar fertilizer was mainly through the inhibition of Cd mobility through three organs, namely, the roots, stems and leaves in wheat. Compared with CK1, the TF root-stem of Cd was reduced by spraying foliar fertilizer once, in which the TF root-stem of Cd was significantly reduced in MZ1, P1 and WO1, and the maximum reduction was 67.6% in MZ1, while only the TF stem-leaf of Cd in MZ1 was significantly changed and improved by 1.5% (Figure 4a). Compared to CK2, Me2, MZ2 and WO2 significantly reduced the TF root-stem of Cd, and the MZ2 reduced maximum was 33.8%. MZ2, Me2 and P2 significantly reduced the TF stem-leaf of Cd, and MZ2 reduced maximum was 30.6% (Figure 4b).
The inhibition of translocation was directly reflected in the decrease in Cd content of the whole wheat plant. It was found that spraying foliar fertilizer significantly reduced Cd content in whole wheat plants compared to CK, and it was more effective to reduce Cd by spraying twice than spraying once (Figure 5). Compared with CK1, the total Cd content of wheat was significantly reduced by Me1, MZ1, P1 and WO1 (p < 0.05), with MZ1 showing the greatest reduction of 36.9% (Figure 5a). Compared with CK2, the total Cd content of wheat was significantly reduced by MZ2, P2, WO2 and Si2 (p < 0.05), with MZ2 showing the greatest reduction of 39.9% (Figure 5b).

3.4. Effects of Foliar Fertilizer and Spraying Times on Human Health Risks

Generally, the value of THQ of wheat under each treatment was <1 (Figure 6), indicating that Cd in wheat grains would not cause cancer in humans. According to the results of the two-way ANOVA, there was a non-significant (p > 0.05) interaction between the frequency of spraying and types of foliar fertilizer on the THQ of wheat grains (Table 2). However, the main effect of the frequency of spraying and types of foliar fertilizer both reached significant levels (p < 0.05) (Table 2). The THQ of wheat sprayed with twice foliar fertilizer was clearly lower than that of spraying once with foliar fertilizer (Figure 6). Me1, MZ1, P1, WO1 and Si1 THQ were significantly reduced compared to CK1, and THQ was significantly reduced under MZ2, P2 and WO2 treatments compared to CK2. The values of THQ for MZ1 and MZ2 treatments showed an obvious reduction which was 36.5% and 91.4%, thus, MZ2 treatment was the most effective (Figure 6).

4. Discussion

4.1. Effects of Different Foliar Fertilizers on the Growth of Wheat

The biomass of plants decreases under Cd stress [25]. This is why monitoring wheat growth is one of the key measures for testing whether the application of fertilizer reduces the effects of Cd pollution on crop stress. In this experiment, it was found that spraying foliar fertilizer could alleviate Cd stress in wheat to different degrees. Overall, two applications of foliar fertilizer at the tillering stage and booting stage were more effective in alleviating Cd stress in wheat than one application of foliar fertilizer at the booting stage. The greatest contribution of MZ and WO to the growth conditions of wheat under Cd stress was observed. This is because Mn-Zn fertilizer could promote wheat growth, improve photosynthesis and increase wheat resistance. In this study, compared with the control, both MZ1 and MZ2 significantly increased wheat thousand grain weight and promoted wheat growth to some extent, which was consistent with the results of Wang and Cai [26,27]. This is because Mn-Zn fertilizer can promote wheat growth, improve photosynthesis and enhance the resistance of wheat. A large number of studies have shown that the application of organic fertilizer can effectively improve the growth of crops [28,29]. Organic acids, humus and microbial activity in organic fertilizer could form complexes with heavy metals, reducing the absorption of heavy metals and the toxic effects on plants [29]. In particular, water-soluble organic fertilizer was more easily absorbed and utilized by crops, which is consistent with the results of this study. However, there was no significant effect of foliar fertilizer on plant height and spike length, but the difference in plant height was significant (p < 0.05) for different numbers of sprays with the same fertilizer. This result may be related to the climate. Some studies have shown that lower temperature and insufficient light during wheat growth may lead to a decrease in the efficiency of leaf photosynthesis, which makes it difficult to significantly promote the morphological development of plant height and spike length even when supplemented with foliar nutrients [30,31].
It was also concluded that Me, MZ and Si were effective in increasing wheat yield in the study. It has been shown that Mn can improve the photosynthetic capacity of wheat leaves and promote the growth and development of wheat [32]. Zinc was able to promote the synthesis of growth hormones in the plant root system, thus, improving the development of the wheat root system [33]. On the other hand, the antagonistic effect of Mn and Zn with Cd can slow down the toxic effect of Cd on plant growth [34]. It was found that foliar sprays of Mn-Zn fertilizer significantly reduced Cd content in wheat grain and increased wheat yield, which was consistent with the results of this study [35]. Another study confirmed that foliar spraying with Si fertilizer could increase crop yield under Cd stress [36], which was similar to the results of this study. There was a significant effect on the growth and development, yield and disease resistance of crops using Si. Moreover, the physiological barrier between Si and Cd may also greatly alleviate the cadmium stress of crops [34,37]. Multi-element compound fertilizer contained various micro-elements required for wheat growth, which can improve the photosynthetic capacity of wheat leaves, carbon metabolism and the development of the root system, thereby inhibiting Cd in wheat, and eventually promoting the growth of wheat and increasing the economic yield of wheat under Cd dress [38,39].

4.2. Effect of Different Foliar Fertilizers on the Transport Factor of Cd in Wheat

In this study, it was observed that foliar fertilizers significantly inhibited Cd transport in the root-stem (TF root-stem) and stem-leaf (TF stem-leaf), but had no significant effect on glume-to-seed transport (TF leaf-glumes/glumes-grains) (Figure 4). This finding is in accordance with the “dual-channel theory” of Cd translocation in plants. Specifically, the transportation of Cd in vegetative organs (roots, stems, and leaves) predominantly depends on the symplastic pathway propelled by xylem flow, while the redistribution of Cd in reproductive organs (glumes and grains) is intricately linked to phloem transport [35]. There was a more obvious inhibition of cadmium in the whole wheat plant when applying foliar fertilizer twice compared to one application of foliar fertilizer (Figure 5). This may be due to the fact that multiple sprays prolong the duration of action of foliar fertilizers, enhancing chelation and barrier effects. On the other hand, the reason might be that the expression of cadmium transporter genes could be continuously suppressed by epigenetic regulation during repeated application of foliar fertilizers [40].
Heavy metals are absorbed by wheat and then stored and accumulated in various parts of wheat [41]. There was the greatest decrease of 67. 6% in MZ1 treatment compared to CK1 and 33.8% in MZ2 compared to CK2 in this study about Cd transport from roots to stems. It indicated that the spraying of Mn-Zn fertilizer enriched Cd in roots and was the most suitable way to prevent Cd translocation to above ground parts of the crops. In this study, it was concluded that spraying foliar fertilizer under Cd stress had a blocking effect on the absorption of Cd in wheat and prevented the transport of Cd from roots to leaves. Consequently, the Cd content of the edible part of wheat above ground was reduced, which achieved the safe production and utilization of wheat cultivation in the low and medium Cd-contaminated areas. According to the experimental results, the application of foliar fertilizers significantly reduced the Cd content of wheat grains, with the most significant effect of MZ2 treatment (36.6% reduction). The high efficiency of MZ2 may be related to its optimization of the inhibitory pathway of Cd fixation or transport under specific climatic conditions (suitable temperature and moderate precipitation). It has been shown that suitable temperatures enhance the absorption of foliar fertilizers, while low or high temperatures may reduce the rate of absorption [42].
In this study, the Cd content of wheat grains was reduced to different degrees and also met the safe edible standard of wheat grains (0.1 mg/kg). In all treatments, the Cd content of grains was reduced more by spraying twice with foliar fertilizer compared to spraying once. Among five foliar fertilizers, spraying Mn-Zn fertilizer and sodium dihydrogen phosphate were more effective in reducing the Cd content of grains. The application of Mn-Zn fertilizer can reduce the cadmium content in crops [43,44]. This may be due to the antagonism between cadmium and zinc because zinc and cadmium have similar chemical properties and enter the root cells of crops through the same absorption channels and transporters, and are then transported from the xylem to the phloem [26,34]. At the same time, Mn also competes with Cd for these carriers, leading to the inhibition of Cd2+ uptake in wheat [45]. However, the mechanism of spraying phosphorus fertilizer to reduce Cd content in wheat grains was different from that of Mn-Zn fertilizer. The phosphorous fertilizer anchored more Cd by increasing the thickness of the cell wall [46]. Moreover, phosphorus fertilizer can increase the activity of antioxidant enzymes and lessen the damage to the photosynthetic system to lower the cadmium content in crops [47,48,49]. It was similar to the findings of this study.

4.3. Effect of Different Foliar Fertilizers on Health Risk Assessment of Wheat Grain

Heavy metal toxicity can lead to adverse effects in agricultural soil ecosystems, and the uptake of soil heavy metal elements by plants can lead to health risks in humans [50,51]. THQ is widely used as a method for assessing the uptake of heavy metals by humans through food. Values of THQ greater than one indicate a serious health hazard to humans, while values of THQ less than one indicate no serious health hazard to people [52]. Within this study, all treatments had a THQ less than one, indicating that Cd in wheat grain did not pose a serious health risk. Meanwhile, sprayed foliar fertilizer resulted in a significant reduction of THQ (Cd) in wheat kernels compared to the control, with MZ1 and MZ2 reducing THQ the most, and MZ2 treatment was more effective than MZ1 treatment. Therefore, from the point of view of food security, spraying foliar fertilizer to wheat in Cd-contaminated farmland is an efficient method to reduce the risk of Cd to human health, and Mn-Zn Fertilizer is more suitable to be widely promoted.
Due to the relatively small amount of foliar fertilizer used, the cost and application amounts of the five types of foliar fertilizers are not significantly different. Only spraying twice will result in slightly higher operating costs than spraying once. If automatic sprinkler irrigation equipment is used for fertilizer spraying in the future, foliar fertilizer will follow the sprinkler irrigation system, which is economically feasible. Based on these conclusions, it is suggested that the technical specifications for foliar spraying in Cd-contaminated areas (including the optimal spraying stage and dosage parameters) can be made in the future to provide a scientific basis, especially for the use of manganese and zinc fertilizers. Moreover, a dynamic monitoring system should be established to combine THQ assessment with soil heavy metal content detection to ensure the safe production of wheat in Cd-contaminated areas and to promote the sustainable development of agriculture.

5. Conclusions

The application of five foliar fertilizers was observed to increase wheat yield and reduce the migration of Cd into the edible portion of wheat. In addition, the application of foliar fertilizer reduced human health risk (THQ). Compared with one application of foliar fertilizer, two applications of foliar fertilizer were shown to be significantly more effective in increasing yield, preventing the transport of Cd and mitigating the human health risk. As a result, the MZ2 was the most effective treatment in increasing yield and mitigating Cd accumulation in wheat. This suggests that spraying wheat with MZ2 fertilizer in two separate applications at the tillering stage and booting stage is an ideal solution for safely growing wheat in Cd-polluted farmland. It is expected that these results provide the theoretical basis for further research on the use of foliar fertilizer to ensure the safe production of wheat and human health. However, this experiment was conducted for only one growth period of wheat, and it was not possible to determine the stability of the foliar fertilizer.

Author Contributions

Methodology, T.X., M.H., Q.W., B.W., Z.Z. and Y.S.; Writing—original draft, T.X., M.H. and M.L.; Writing—review and editing, B.Z., Y.S. and M.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the National Modern Agricultural Industrial Technology System Project of China (CARS-07).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets used during the current study are available from the first author on reasonable request.

Acknowledgments

The authors would like to thank Shiyu Guan and Zhenhan Liu for their help in conducting the experiment.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Effects of different foliar fertilizer sprays and different frequencies of spraying on the growth and yield of wheat. Specifically, (a) shows their effect on wheat plant height; (b) shows their effect on spike length, (c) shows their effect on number of grains per spike, (d) shows their effect on thousand grain weight, and (e) shows their effect on wheat yield. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level. * and **, respectively, indicate that there were significant differences between the two spraying frequencies of the same foliar fertilizer at the level of p < 0.05 and p < 0.01.
Figure 1. Effects of different foliar fertilizer sprays and different frequencies of spraying on the growth and yield of wheat. Specifically, (a) shows their effect on wheat plant height; (b) shows their effect on spike length, (c) shows their effect on number of grains per spike, (d) shows their effect on thousand grain weight, and (e) shows their effect on wheat yield. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level. * and **, respectively, indicate that there were significant differences between the two spraying frequencies of the same foliar fertilizer at the level of p < 0.05 and p < 0.01.
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Figure 2. Cd content in tissues of wheat with different fertilizers on leaf surface. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level.
Figure 2. Cd content in tissues of wheat with different fertilizers on leaf surface. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level.
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Figure 3. Effect of different foliar fertilizers and different frequencies of spraying on the distribution of cadmium in wheat tissues. Values are mean ± standard error (n = three). Different lowercase letters indicate significant differences in the same organ under different treatments (p < 0.05).
Figure 3. Effect of different foliar fertilizers and different frequencies of spraying on the distribution of cadmium in wheat tissues. Values are mean ± standard error (n = three). Different lowercase letters indicate significant differences in the same organ under different treatments (p < 0.05).
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Figure 4. Effect of different foliar fertilizer sprays and different frequencies of spraying on the transport factor of cadmium in wheat tissues. (a,b) refer to the effect of spraying once and spraying twice on the transport factor of cadmium content in various parts of wheat, respectively. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level.
Figure 4. Effect of different foliar fertilizer sprays and different frequencies of spraying on the transport factor of cadmium in wheat tissues. (a,b) refer to the effect of spraying once and spraying twice on the transport factor of cadmium content in various parts of wheat, respectively. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level.
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Figure 5. Effect of different foliar fertilizer sprays and different frequencies on the cadmium content of whole wheat plants. (a,b) refer to the effect of the once sprayed and twice sprayed on whole plant cadmium content in wheat, respectively. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level.
Figure 5. Effect of different foliar fertilizer sprays and different frequencies on the cadmium content of whole wheat plants. (a,b) refer to the effect of the once sprayed and twice sprayed on whole plant cadmium content in wheat, respectively. Values are mean ± standard error (SE) (n = three). Within each column, values followed by different letters indicate significant differences at the p < 0.05 level.
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Figure 6. Effects of different foliar fertilizers and frequencies of spraying on human health risks in wheat grains. Values are means ± SE (n = three). Different letters indicate significant differences among various treatments at p < 0.05.
Figure 6. Effects of different foliar fertilizers and frequencies of spraying on human health risks in wheat grains. Values are means ± SE (n = three). Different letters indicate significant differences among various treatments at p < 0.05.
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Table 1. Five kinds of foliar fertilizer details.
Table 1. Five kinds of foliar fertilizer details.
CodeFoliar FertilizerSpraying
Concentration		Spraying TimeSpraying Amount
MeMulti-element compound fertilizer2 mL/L1. Spraying once at the booting stage3.5 L liquid per cell at tiller stage and 7 L liquid per cell at booting stage
MZManganese-zinc fertilizer8 g/L
PSodium dihydrogen phosphate0.5 g/L2. Spraying twice at tillering stage and booting stage
WOWater-soluble organic fertilizer2 mL/L
SiFoliar silicon fertilizer6 mL/L
Table 2. The two-way analysis of variance (ANOVA) for THQ of wheat grains.
Table 2. The two-way analysis of variance (ANOVA) for THQ of wheat grains.
SourceType III Sum of SquaresDegrees of FreedomMean SquareF-Valuep-Value
Frequency of spraying0.03910.0397.1150.013
Types of Foliar Fertilizer0.19450.0397.0370.001
Types of Foliar Fertilizer *
Frequency of spraying		0.00850.0020.2740.923
Note: “Types of Foliar Fertilizer * Frequency of spraying” represents the interaction between the two factors. A value of p < 0.05 is considered significant.
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Xie, T.; Hao, M.; Wang, Q.; Wu, B.; Zhang, Z.; Zhao, B.; Shao, Y.; Liu, M. Foliar Application of Manganese-Zinc Fertilizer Mitigated the Harmful Effects of Cadmium on Wheat and Reduced Human Health Risks. Sustainability 2025, 17, 3058. https://doi.org/10.3390/su17073058

AMA Style

Xie T, Hao M, Wang Q, Wu B, Zhang Z, Zhao B, Shao Y, Liu M. Foliar Application of Manganese-Zinc Fertilizer Mitigated the Harmful Effects of Cadmium on Wheat and Reduced Human Health Risks. Sustainability. 2025; 17(7):3058. https://doi.org/10.3390/su17073058

Chicago/Turabian Style

Xie, Ting, Mengjie Hao, Qingyu Wang, Bowen Wu, Zhenguo Zhang, Baoping Zhao, Yufang Shao, and Meiying Liu. 2025. "Foliar Application of Manganese-Zinc Fertilizer Mitigated the Harmful Effects of Cadmium on Wheat and Reduced Human Health Risks" Sustainability 17, no. 7: 3058. https://doi.org/10.3390/su17073058

APA Style

Xie, T., Hao, M., Wang, Q., Wu, B., Zhang, Z., Zhao, B., Shao, Y., & Liu, M. (2025). Foliar Application of Manganese-Zinc Fertilizer Mitigated the Harmful Effects of Cadmium on Wheat and Reduced Human Health Risks. Sustainability, 17(7), 3058. https://doi.org/10.3390/su17073058

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