Magnetic field treatment on horticultural and agricultural crops: its benefits and challenges

Modern scientific and technological research results show that various life activities in the biological world are accompanied by electromagnetic phenomena. At present, bio-magnetic technology has attracted more and more attention and research interest from professionals and has been widely used in the fields of medicine, agriculture, horticulture, environmental protection and bioengineering (Özdinç and Yalçin, 2018). In medical science, magnetism has long been popularised to the stage of specific applications and has become an important medical detection method. In agricultural and horticultural areas, magnetic field (MF) effects on crops are being extensively explored.

Seeds/plants chemical treatments, including fertilisers, pesticides and fungicides, bio-stimulants, and so on, are widely used in agricultural and horticultural production. They effectively ensure the crop emergence rate, uniformity of emergence, plant growth rate in the following development stages and crop yield. However, chemical treatment has been controversial from the perspective of environment protection and food safety. More and more chemical reagents are deprecated or prohibited from being used. Under the general trend of environment-friendly agricultural and horticultural production, as an alternative to chemical treatment, physical treatments, such as MF, electric fields, microwave, and lasers, have attracted more and more attention (Aladjadjiyan, 2007; Chen et al., 2016).

Applying magnetic physical treatment in agricultural and horticultural production has always been a keenly observed method by agricultural and horticultural researchers. The use of artificial MF to treat cultivated crop seeds/plants improves their agronomical characteristics, promotes seed germination and vigour, increases yield, improves crop quality and enhances stress tolerance (Shine et al., 2011; Bhardwaj et al., 2012; Da Silva and Dobránszki, 2016; Kataria et al., 2017; Bahadir et al., 2018; Hozayn et al., 2018; Krawiec et al., 2018; Radhakrishnan, 2018; Anand et al., 2019; Baghel et al., 2019; Hozayn et al., 2019; Kataria et al., 2019; Liu et al., 2019; Menegatti et al., 2019; Alvarez et al., 2020; Kataria et al., 2020; Souza-Torres et al., 2020; Adetunji et al., 2021; Bukhari et al., 2021; Harb et al., 2021; Samarrai et al., 2022). This technology has the advantages of less physiological damage, low cost and easy operation and application. Moreover, it produces no pollution and has a high input–output ratio (Michalak et al., 2019; Nyakane et al., 2019; Abdel Latef et al., 2020; Johnson and Puthur, 2021; Pagano et al., 2023).

Although the main focus of MF application research is in the area of crop commercial trait improvement, still in recent years, more and more researchers have turned their attention to the application of MF treatment in the field of plant stress tolerance improvement. Both magnetopriming and magnetised water (MW) irrigation can enhance the tolerance and vitality of cultivated plants under various environmental stresses (Baghel et al., 2019; Hasan et al., 2020; Hozayn et al., 2021; Kataria et al., 2022, 2023). It ensures not only the ability of plants to survive under adverse stress conditions, but also the accumulation of heavy metals by plants grown in heavy metal soil; thus, it improves the ability of plants to help in soil restoration (Tang et al., 2022; Prajapati and Patel, 2023). MF treatment research in this direction provides great potential for the use of plants for heavy metal soil remediation.

At present, there are many reports in the area of magnetic effects on plants. The research not only involves the positive effects after treatment, but also provides some discussion about its mechanisms. However, there are also reports on some cases when application of MF on seeds was not successful or repeatable. For some crops, only in certain range(s) of the MF intensity and exposure time have caused the positive effects (Araújo et al., 2016; Farooq et al., 2019; Rifina et al., 2019; Sarraf et al., 2020;), while the other ranges have given weakened or even negative effects (Abdani Nasiri et al., 2018; Nair et al., 2018; Florez et al., 2019; Khaledi et al., 2019; Massah et al., 2019; Migahid et al., 2019; Júnior et al., 2020; Afzal et al., 2021). Due to the complexity of the interaction between the used MF and plants, the research of the mechanism is still in the exploration stage and needs further study (Radhakrishnan, 2019). Therefore, an in-depth study of the macroscopic regularity and mechanism of the regulation of plant physiological activities by magnetic treatment is still an area that needs to be vigorously developed. Meanwhile, the progress in MF treatment research will help reduce the use of traditional chemical reagents in agricultural and horticultural activity. Thus, the method has broad prospects in the development of environment-friendly agricultural and horticultural production and providing food-safety assurance.

The main aim of this review was to firstly highlight research findings with relevance to seeds or/and plants growing under the influence of a constant or alternating MF and MW and the impact on seed germination, plant growth, yield and their quality in horticultural and agricultural crops, enzyme activity, stress tolerance, and genome stability. Secondly, it was done to elucidate the molecular mechanism regarding the MF interaction based on the existing published results.

As magnetism becomes more and more widely used in agriculture and horticulture, we believe that it becomes necessary to summarise the latest and most-important scientific research results in the related fields and the results of further in-depth research on its mechanism. This could serve as a guide to relevant scientists and will attract more agricultural researchers to pay attention to this field of plant science. By studying selected papers in English and Chinese, we aimed to gain an understanding of past research results and come out with conclusions and recommendations for both the future MF experiments and its applications.

The English literature cited in this paper was mainly obtained through Google Scholar, whereas the Chinese ones came from the collection of the China National Knowledge Infrastructure (CNKI) platform. The searched keywords were ‘effect of MF and MW on plants’, ‘effect of MF on seeds’ and ‘application of MF and MW in agriculture and horticulture’. The present paper consists of five chapters discussing the points of concern for researchers in related fields. These are: ‘Materials and methods of the use of MF treatment’, ‘Plant parameters enhanced by MF’, ‘Molecular mechanisms understanding the response to MF treatments’, ‘Difficultly in application’ and ‘Conclusions and recommendations’. Afterwards, based on the experimental subjects, methods and results collected from the literature, several sub-chapters were further sub-divided into some chapters. For example, in the chapter ‘Plant parameters enhanced by MF’, five sub-chapters were sub-divided, with a focus on explaining the impact of MF on various aspects of plant’s development. They included ‘Increase of seed germination and seeding growth’, ‘Increase of crop yield and quality’, ‘Enhancement of enzyme activity’, ‘Increase of the tolerance to environmental stress’ and ‘Impact on genomic stability’. In each chapter or sub-chapter, representative experimental results, from the collected papers, were elaborated in detail. Their aim was to provide more specific information for researchers in related fields and to provide an experimental results data foundation for future research and application. The present paper integrated information related to MF with a large amount of data by using a table. Photographs were also used to make the relevant descriptions more concrete and easier for readers to understand. All this allowed us to make final conclusions and recommendations.

The MF processing technical parameters, for different methods of using, mainly include: MF intensity, exposure time, frequency of change (for alternating MF), and the number of cutting magnetic lines (for MW). So far, the MF treatment of cultivated crops can be roughly divided into three categories: (1)

The first method is to treat seeds/plants directly with MF, depending on the experimental design, the processing time ranges from tens of minutes to several days (Hołubowicz et al., 2014; Hozayn et al., 2018; Baghel et al., 2019; Farooq et al., 2019; Jin et al., 2019; Menegatti et al., 2019; Radhakrishnan, 2019; Xia et al., 2020; Bukhari et al., 2021; Himoud et al., 2022). The types of MF that can be used include static MF or varying MF. Static MF is mostly provided by permanent magnets made of alloys such as iron, cobalt and nickel, and it obtains a wide magnetic induction. The varying MF can be obtained according to the MF principle – the alternating current passes through the coil to generate an alternating MF, and the pulsating current passes through coil to generate a pulsating MF. Other types of varying MF are rotating MF, translational MF and gradient MF. Figure 1 shows examples of two devices used in agricultural and horticultural research to generate MF: the Viofor machine which has been patented and previously used in human magnetotherapy (Figure 1, above) and magnets plates (Figure 1, below).

Figure 1.

Figure 2.

The research materials include all seeds, seedlings or plants of agricultural, horticultural and other cultivated plants, for example, maize (Zea mays) (Kataria et al., 2017; Baghel et al., 2019; Himoud et al., 2022), rice (Oryza sativa) (Chen et al., 2016; Florez et al., 2019), wheat (Triticum aestivum) (Massah et al., 2019; Hassen et al., 2020; Selim et al., 2022), triticale (×Triticosecale Wittmack) (Alvarez et al., 2019, 2020), barley (Hordeum vulgare) (Hozayn et al., 2018; Ehtaiwesh et al., 2019; Hozayn et al., 2021), soybean (Glycine max) (Shine et al., 2011; Kataria et al., 2017; Özdinç and Yalçin, 2018; Radhakrishnan, 2018; Kataria et al., 2019, 2020; Michalak et al., 2019), common bean (Phaseolus vulgaris) (Da Silva and Dobránszki, 2016; Sarraf et al., 2020), mung bean (Vigna radiata) (Nair et al., 2018; Sarraf et al., 2020), faba bean (Vicia faba spp. minor) (Podleśna et al., 2019), chickpea (Cicer arietinum) (Da Silva and Dobránszki, 2016; Samarrai et al., 2022), pepper (Capsicum annuum) (Liu et al., 2003), head cabbage (Brassica oleracea var. capitata) (Cui et al., 2014), Chinese cabbage (Brassica rapa subsp. pekinensis) (Han et al., 2008), lettuce (Lactuca sativa) (Abdel Latef et al., 2020), radish (Raphanus sativus) (Xia et al., 2020), tomato (Solanum lycopersicum) (Da Silva and Dobránszki, 2016; Souza-Torres et al., 2020), eggplant (Solanum melongena) (Cui et al., 2020; Kishore et al., 2022), sugar beet (Beta vulgaris) (Faiyad and Hozayn, 2020), sunflower (Helianthus annuus) (Afzal et al., 2021; Bukhari et al., 2021), passion fruit (Passiflora edulis) (Menegatti et al., 2019) and cotton (Gossypium spp.) (Da Silva and Dobránszki, 2016), Sedum alfredii (Tang et al., 2022).

According to current reports, the effects of MF treatment on plants are mainly reflected in the following aspects.

A deep understanding of the cellular and molecular pathways triggered upon exposure to MF, responsible for the observed biological reactions, is required to provide improved rationale bases for the design of tailored seed invigoration treatments. The current state of the art highlights multiple pathways and targets, disclosed mainly by studies on animal and human systems (Xu et al., 2021).

An intriguing aspect is related to MF perception that has been suggested to occur according to the ‘radical pair mechanism’ (Hammad et al., 2020). Cryptochromes, highly conserved blue light-absorbing flavoproteins acting as photoreceptors during plant development, have been associated to MF perception in plants, flies, and humans. In the presence of MF, cryptochrome modulates ROS levels and, consequently, the cellular redox reactions. This process, conserved in both plants and animals, affects gene expression (Parmagnani et al., 2022a, 2022b).

In the attempt to explain the impact of MF on biological processes, Binhi and Prato (2017) developed the ‘molecular gyroscope mechanism’ based on the rotation of large fragments of macromolecules or amino acid residues with distributed electric charges in response to MF. The biological effect is related to the reaction yield, the number of gyroscopes that enter this reaction, or those that are in a state of equilibrium. The theoretical model elaborated by Vaezzadeh et al. (2006) is based on the oscillation of ferritin under the influence of MF. A common feature of these models is the hypothesis that the MF energy is absorbed by the cells, affecting the mobility and uptake of ions with important roles in cellular homeostasis.

Information about MF mechanism in plants is still scanty, and the published reports generally focus on the plant response rather than on seed germination. In a recent review, Salentnik et al. (2022) described the effects of MF on plant gene expression, underlining the potential of the technique for applications in the agri-food sector. The few reports, so far contributing to expand the knowledge in plant field, use the model system Arabidopsis thaliana. Jin et al. (2019) investigated the impact of static MF on Arabidopsis seedling growth and evidenced that root growth was promoted according to intensity and direction-dependent profiles by increasing auxin levels in the root tip. Transcriptomics showed that MF caused upregulation of the AUX1 gene coding for an auxin influx transporter as well as downregulation of the PIN3 gene encoding an auxin efflux transporter. The MF-shaped Arabidopsis transcriptome revealed up-regulation of genes participating in the flavonoid biosynthetic pathway, cell wall organisation and nitrate transport.

Parmagnani et al. (2022b) explored the transcriptomics and metabolomics of ROS production in roots and shoots of A. thaliana plants exposed to MF. Upregulation of several oxygenase-coding genes was observed in the tested tissues, including AERO2 involved in the oxidative protein folding in the endoplasmic reticulum (Fan et al., 2019) and GulLO1 involved in the production of the antioxidant and redox molecule L-ascorbic acid (Maruta et al., 2010). Developmental changes in ROS production occurring in MF-treated plants were associated to the upregulation of genes coding for enzymes involved in ROS production, for example, respiratory burst oxidase homolog H, J and G (RBOHH, RBOHJ and RBOHG) (Parmagnani et al., 2022b). Metabolomics provided insights into the dynamics of antioxidant molecule accumulation, such as polyphenols. Furthermore, increased H₂O₂ production in MF-exposed plants was associated with progressively decreased polyphenols levels (Parmagnani et al., 2022b). Kataria et al. (2022) proved in their experiment on magnetoprimed soybean seeds that the enhanced NO production lowered the Na⁺/K⁺ ratio to increase the salt tolerance index in soybean seeds. The enhanced NO production came from the upregulation of genes of enzymes related to nitric oxide NOS-like and NR along with their enhanced activities after soybean seeds magnetopriming. The GmNOS-like 2 and GmNR1 genes can be ideal candidates to be characterised towards their involvement in the NO production in soybean.

The complexity of the molecular networks underlying the response of plant cells to MF has been so far partially disclosed. The mechanisms of plant perception and signalling and related molecular players still need to be defined as well as the downstream targets (effectors) that contribute to the physiological responses (growth, antioxidant protection). Efforts should be expanded to gain insights into the way the seed pre-germinative metabolism reacts at the molecular level to MF treatments. In this way, it will be possible to design more rationale and controlled MF-based protocols for agri-food applications.

It is important to note that a large number of research results showed that different optimal MF intensities and exposure time for different cultivated crops, cultivars and target traits were found. The excessive intensity and exposure time will lead to weakened positive effects, and even in some crops – to negative effects (Table 1). As in the table below, listed crops, including agricultural, horticultural and herbal plants, all showed positive effects in certain range(s) of the MF intensity and exposure time, while there did exist the adverse dose, which led to negative effects (Table 1). After studying the table, one should be aware that in the past, many researchers who had tried and failed to use MF or MW in their experiments with plants had never reported it. Some of these old experiments could be repeated today when our technical equipment is much better than before. Moreover, many of such reports were published in other-than English languages and, therefore, could have been missed by ones who only follow papers published in English. Another serious difficulty that came from this review is lack of one main way of using MF in practical agriculture and horticulture as it had affected various organs of plants. Therefore, for some species, cultivars and target traits, only by a large number of screening experiments to determine the best treatment conditions, can MF treatment achieve the purpose of effectively improving the target traits of plants.

In recent years, the application of magnetism in agriculture and horticulture has been paid more and more attention to, especially in the field of MF treatment on both seed germination and the physiology of seedlings. In the application research of MF effects on seeds, for certain species and cultivars, only after a large number of screening tests to determine optimal dosage, can we achieve positive effects and income improvement. This is the main challenge we currently face for the commercial MF application in plants.

In the current application research of MF effects, much of the work, so far, has focused on how to improve economic traits and increase economic output. At the same time, more and more researchers have moved their attention to using seed MF treatment or MW irrigation to improve the plant stress tolerance under salt or heavy metal stresses, in order to achieve the purpose of soil restoration by plant heavy metal accumulation. At present, there have been many reports that MF treatment can successfully improve plant tolerance to various environmental stresses. They have all proved the potential of MF application in this area and provide new environmentally friendly ideas for soil restoration and environment protection. In addition, there are also reports on MF effect on seed anti-ageing ability, which imply that the magnetic treatment may also have a technical potential applied to seed storage.

On one hand, the future research direction is still to study in-depth the mechanism of MF effects on seed germination and cultivated crops growth promotion. It would help us to understand or even effectively predict the possible improvement of the crops’ parameters enhanced by the treatment. On the other hand, further research and development on the use of MF to improve plant stress tolerance are needed to achieve the application in soil remediation and environment protection on a large scale. Through these two aspects of further study and development can we make MF treatment more effective and targeted in agricultural and horticultural production and environment restoration.