Approaches of Biochar in Ecosystem Management: Current Scenario and Future Perspectives

Abstract

Agricultural crop growth and productivity are significantly influenced by a wide variety of biotic and abiotic factors. In order to address these shortcomings, substantial amounts of chemical fertilisers are administered to the land. The widespread use of chemical fertilisers has led to the degradation of ecosystems and various associated issues, including decreased nutritional quality of crops and the long-term decline in soil fertility. The excessive uses of fertilisers and pesticides have adverse implications for soil vitality, resulting in a substantial reduction in the biomass. Therefore, the use of biochar has been sustainable method and a potentially efficient strategy for improving soil quality and addressing the issue of heavy metal pollution in soil. Integrating biochar into the soil offers a significant chance to enhance soil quality and promote plant growth. The efficacy of biochar in enhancing nutrient cycles on agricultural lands is highlighted by its positive impact on plant growth and soil vitality, rendering it a practical instrument for mitigating nutrient deficiencies. The present chapter focuses on the utilisation of biochar and its impact on the soil microbial population, plant diseases, plant-parasitic nematodes, and insect pests and highlights the utility of biochar as an effective agent for plant protection.

1. Introduction

The growth and productivity of agricultural crops are profoundly impacted by a diverse range of biotic and abiotic factors [1, 2]. To address these deficiencies, significant quantities of chemical fertilisers are applied to the soil [3, 4]. However, it is crucial to acknowledge that plants possess a restricted capacity to assimilate water-soluble nutrients. The remaining elements undergo a transformation process, leading to the creation of forms that are not soluble. Consequently, it becomes imperative to periodically administer fertilisers in order to ensure a consistent provision of essential nutrients for the purpose of facilitating plant growth [5]. The extensive utilisation of chemical fertilisers has resulted in the deterioration of ecosystems and various related problems, such as diminished nutritional value of crops and the long-term reduction of soil fertility [6, 7]. Alongside fertilisers, pesticides provide a significant concern within the field of agriculture due to their noteworthy environmental consequences, which exert a major influence on the microbiological characteristics of soil. The overuse of fertilisers and pesticides, as well as their persistent presence in the soil, have negative consequences for soil health, leading to a significant decrease in the biomass of bacteria and fungus [8, 9]. Huang et al. [10] conducted a study to investigate the effects of prolonged exposure to inorganic fertilisers and/or organic manures on the structural diversity and dominant bacterial groups in agricultural soils. However, it is important to acknowledge that biofertilizers have the ability to enhance soil fertility by revitalising it. As a result, they present themselves as advantageous candidates for the promotion of sustainable agriculture and the mitigation of stress within agro-ecosystems. Moreover, the incorporation of organic soil supplements, particularly in the context of remediation, is occasionally justified based on their cost-effectiveness, often necessitating the implementation of alternative waste management methods (such as landfill deposition or cremation). In order to meet certain criteria, soil amendments must possess certain characteristics such as a strong capacity for binding, compatibility with the surrounding environment, and the lack of any detrimental impacts on soil structure, fertility, or the wider ecosystem [11]. The utilisation of biochar has been recognised as a sustainable approach and a potentially effective technique for enhancing soil quality and mitigating the problem of heavy metal contamination in soil [12]. When a bibliometric analysis was conducted using the key words “biochar”, “insect pest management” and “plant protection”, it was observed that the total number of publications was increased since 2001 (Figure 1a), while in agricultural, Veterinary and Food Sciences, Environmental Sciences and Biological Sciences related journals, this topic was focussed more (Figure 1b). Further, this topic was more focussed on diverse articles followed by book chapters and edited books (Figure 1c), while major articles were published in encyclopedia of the unsustainable development goals and the science of the total environment (Figure 1d), and bibliometric studies also indicated that biochars related to plant protection contributed higher to sustainable development goals (SDG) 2 (zero hunger) followed by SDG 13 (climate action) and SDG 15 (life on land) (Figure 1e). Thus, current study analyses the plant protection potential of biochar and its way forward in pest management.

Figure 1.

This figure depicts the total number of publications were increased since 2001 (a), while, in agricultural, veterinary and food sciences, environmental sciences and biological sciences related journals this topic was focussed more (b). Further, this topic was more focussed in diverse articles followed by book chapters and edited books (c), while, major articles were published in encyclopedia of the un sustainable development goals and the science of the total environment (d) and bibliometric studies also indicated that, biochars related to plant protection contributed higher to sustainable development goals (SDG) 2 (zero hunger) followed by SDG 13 (climate action) and SDG 15 (life on land) (e).

A carbonaceous material with a sizable percentage of organic materials makes up biochar, an organic amendment. This chemical is produced as a byproduct of pyrolysis, a process that involves heating biomass to high temperatures and low oxygen levels. The process of pyrolysis, which includes the thermal breakdown of biomass materials like wood, dung, or leaves at high temperatures in an oxygen-poor atmosphere, produces biochar. The aforementioned procedure results in the production of biochar as the principal output, along with minor byproducts like as oil and gas. The extent of these remaining compounds is dependent on the specific processing parameters. Recent research have revealed that biochar, derived from the carbonisation of organic waste, possesses the potential to serve as a viable replacement material. The replacement of a certain element has consequences for the process of storing carbon in soil, as well as alterations to its physical, chemical, and biological characteristics [13]. The use of biochar shows promise in the production of renewable energy in agricultural regions, while also aligning with environmentally conscious principles. In a previous study, Verheijen et al. [14] observed that the use of biochar had discernible effects on the toxicity, transport, and destiny of specific heavy metals within soil. The primary cause of this phenomenon was predominantly ascribed to the enhanced soil adsorption capacity aided by the presence of biochar. Several key elements can be ascribed to the enhanced soil properties and heightened nutrient uptake by plants in soils treated with biochar. The nutrient and ash composition, expansive surface area, porous structure, and microbe habitat function are among the aspects that encompass biochar [15]. The research conducted by Rawat et al. [16] demonstrated that the use of biochar led to a reduction in soil compaction, indicating its potential to effectively mitigate this issue. Significant attention has been devoted to evaluating the advantages of introducing rhizobacteria into soil. Nevertheless, it is crucial to recognise that the incorporation of biochar into the soil can also enhance the availability of nutrients, hence providing benefits to agricultural products. Bhanse et al. [17] emphasise the utilisation of plant growth-promoting microorganisms in conjunction with biochar as the optimal approach for boosting the development and output of French beans. The integration of biochar into the soil presents a considerable opportunity to improve soil quality and stimulate plant growth, so making a valuable contribution to the development of a sustainable agricultural paradigm. Extensive research has been conducted to investigate the viability of utilising biochar additions for soil reclamation [18] and for the promotion of sustainable agriculture practises that aim to achieve high crop yield while mitigating environmental damage. The potential of biochar to increase nutrient cycles on farms is underscored by its good influence on plant growth and soil health, making it a realistic tool for addressing nutrient deficits. As a result, there has been a significant focus on examining the advantageous impacts of using biochar amendments in relation to soil stability and the facilitation of plant growth.

2. Role of biochar in plant protection

What are the processes by which biochar regulates plant diseases? There have been a minimum of five proposed mechanisms, namely: (i) the induction of systemic resistance in host plants; (ii) the augmentation of beneficial microorganisms in terms of their abundance and/or efficacy; (iii) modifications to soil quality with respect to nutrient accessibility and abiotic factors; (iv) the direct fungitoxic effect of biochar; and (v) the adsorption of allelopathic and phytotoxic compounds (Figure 2). The phenomenon of induced resistance in plants has been suggested as a potential mechanism for the regulation of disease suppression [19, 20]. The application of biochar was carried out in this study in a specific geographic region that was physically segregated from the infection sites. This purposeful dissociation was carried out in order to successfully eradicate any alternative mechanisms that may otherwise aid in the suppression of illness. More empirical support for the idea of induced resistance was offered by Harel et al. [21] and Mehari et al. [22], who showed that both the induced systemic resistance (ISR) and systemic acquired resistance (SAR) pathways were involved. According to a study by Harel et al. [21], adding biochar to substrates used to grow strawberry plants caused several genes to be noticeably upregulated. The genes contained in this collection encode three pathogenic-related proteins (FaPR1, Faolp2, and Fra a3), a lipoxygenase producing gene (Falox), and a trans-acting factor (FaWRKY1) gene from the WRKY family. Mehari et al. [22] investigated the role of jasmonic acid (JA) in biochar-induced systemic resistance (ISR) in tomato plants by looking at the S. lycopersicon-B. cinerea pathosystem. Nevertheless, the data presented by Mehari et al. [22] and Harel et al. [21] was insufficient to determine whether the introduction of biochar altered the rhizosphere microbiome’s composition and functions or whether specific chemical compounds present in biochar directly caused induced plant resistance.

Figure 2.

Representing how biochar is affecting plant defence against biotic stresses, (A) induction of systemic resistance in host plants, (B) augmentation of beneficial microorganisms, (C) modifications to soil quality, including nutrient accessibility and abiotic factors and (D) adsorption of allelopathic and phytotoxic compounds.

The second hypothesised mechanism for illness suppression involves the potential augmentation of beneficial bacteria’ proliferation and/or functions through the incorporation of biochar. Subsequently, these bacteria confer protection to the plant by mitigating the risk of pathogenic assaults. There is a growing body of empirical evidence that substantiates the proposition that biochar exerts a beneficial influence on various facets of microbial activity. Liang et al. [23] demonstrated that the application of biochar results in a significant augmentation of microbial biomass. Furthermore, the study conducted by Warnock et al. [24] has demonstrated that the application of biochar has a positive impact on the colonisation of roots by mycorrhizal fungi. In addition, Graber et al. [25] and Kolton et al. [26] have both provided evidence supporting the notion that biochar facilitates the proliferation of microbes that stimulate plant growth. Positive effects have been found to be correlated with both physiological and nutritional factors. According to Lehmann et al. [27], the porous structure and substantial specific surface area of biochar create an environment that is favourable and safe for many microorganisms, such as mites, collembolan, protozoans, and nematodes. Based on the findings of Downie et al. [28], it has been observed through empirical research that the porous composition of biochar can effectively serve as a refuge for bacteria and mycorrhizal fungus, enabling them to evade predators. The assertion is additionally corroborated by the research conducted by Warnock [24]. In terms of its nutritional implications, biochar possesses the capacity to provide organic carbon that can facilitate the proliferation of saprophytic microbes. Nevertheless, it is crucial to acknowledge that the impact of this phenomenon is expected to be considerably less prominent in comparison to other organic additions, such as agricultural wastes and composts. The biochemical compatibility of biomass with microbial needs undergoes a substantial decrease throughout the pyrolysis process. The main reason for this phenomenon can be attributed to the progressive exhaustion of carbon sources that can be easily broken down, coupled with the simultaneous accumulation of aromatic constituents that exhibit resistance to degradation [29]. Consequently, through the process of pyrolysis, biochar undergoes a conversion into an organic material that promotes agricultural productivity, albeit with restricted ability to facilitate microbial growth. The findings mentioned above collectively indicate that biochar has the potential to be a viable alternative to soil supplements such as agricultural wastes or composts. This is because biochar has the ability to enhance the functionality of beneficial microorganisms selectively, while also preventing the proliferation of pathogen populations and their detrimental impacts. Further investigation is required to explore this topic in greater depth, as the current body of research is limited in terms of establishing a clear link between changes in microbial communities resulting from biochar and the successful mitigation of diseases. This is despite the growing knowledge surrounding the influence of biochar on soil microbiomes, as highlighted by Lehmann et al. [27].

The third hypothetical mechanism posits that modifications in soil characteristics, specifically pertaining to nutrient accessibility and abiotic factors, have the potential to impact the overall dynamics of plant-pathogen interactions. In accordance with the findings of Gaskin et al. [30], the addition of biochar supplements generally enhances the concentrations of essential soil cations, including calcium (Ca²⁺), magnesium (Mg²⁺), and potassium (K⁺). Furthermore, the study conducted by Yuan and Xu [31] revealed that the use of biochar amendments has a tendency to increase soil pH levels. Nevertheless, the impact of bioavailability on crucial plant nutrients, such as nitrogen and phosphorus, remains a subject of significant debate [32]. The biochar generated by the pyrolysis process frequently has an elevated carbon-to-nitrogen (C/N) ratio in comparison to the initial feedstocks. This is primarily attributed to the selective elimination of nitrogen in favour of organic carbon during the pyrolysis procedure. The C/N ratio of the biochar produced is determined by various factors, including the temperature used during the pyrolysis process and the initial characteristics of the biomass used. Schofield et al. [33] posited that the incorporation of organic materials characterised by a high carbon-to-nitrogen (C/N) ratio into soil leads to the augmentation of microbial activity. The heightened microbial activity that ensues consequently restricts the accessibility of mineral nitrogen, thereby impeding the saprophytic abilities of pathogens and hence inhibiting the progression of illness. Based on the aforementioned data, it may be deduced that biochar exhibits considerable potential in impacting the interactions between plants and pathogens. However, it is crucial to acknowledge that, based on current knowledge, there exists a dearth of definitive empirical data from research studies that definitively establish a causal relationship between the augmentation of soil nutrient levels or modifications in soil abiotic factors, such as the liming effect, through the utilisation of biochar, and the effective mitigation of diseases.

One plausible mechanism that may account for the decline in illnesses is the direct fungitoxic effect of biochar. Significant chemical transformations take place during the process of biomass pyrolysis, resulting in the degradation of O-alkyl carbons found in carbohydrates. Concurrently, there is a simultaneous generation of aliphatic and aromatic carbon compounds. In addition, it has been noted by Spokas et al. [34] that pyrolysis produces a diverse range of organic compounds that possess the capacity to demonstrate fungitoxic characteristics. However, studies investigating the precise fungitoxic properties of biochar have indicated that its ability to prevent fungal growth is often minimal or insignificant. An example of this may be seen in the study conducted by Jaiswal et al. [35], where it was observed that various forms of biochar effectively inhibited the occurrence of damping-off disease caused by Rhizoctonia solani on Phaseolus vulgaris. However, numerous tests conducted in vitro and in vivo have consistently demonstrated that biochar has a limited or insignificant direct inhibitory effect on R. solani. The research group achieved similar results in their tests investigating the impact of Medicago sativa hay and wood biochars on hyphal growth in Aspergillus niger, Fusarium oxysporum, Penicillium italicum, and Rhizoctonia solani.

3. Biochar in plant-biotic interactions

3.1 Biochar in insect pest management

The existing body of research has extensively examined the positive impacts of biochar on soil in terms of chemical, physical, and microbiological enhancements. However, the potential indirect consequences of biochar on plant diseases and herbivorous insects in soils modified with biochar have not been thoroughly investigated (Figure 3). While several studies have demonstrated the potential of biochar applications in reducing infections caused by soilborne pathogens like Fusarium and Ralstonia solanacearum in crop plants, as well as mitigating foliar fungal infections such as Botrytis cinerea and minimising damage caused by pests like the broad mite (Polyphagotarsonemus latus Banks), there is a noticeable lack of research focusing on the effects of biochar on herbivorous insect pests. The utilisation of biochar in soil has attracted considerable attention owing to its capacity to mitigate greenhouse gas emissions, improve soil fertility, and enhance agricultural productivity. Nevertheless, there has been a relative lack of attention given to the impact of biochar additions on herbivorous insect pests. The objective of this study was to examine the potential impact of biochar supplementation on the developmental and reproductive outcomes of the rice brown planthopper (Nilaparvata lugens) while its feeding on rice plants. Biochar generated from wheat straw through the process of pyrolysis was utilised in the application of soils originating from a fallow rice field, with different amounts of application. Subsequently, the aforementioned treated soils were employed for the cultivation of rice seedlings within compact containers, hence facilitating the examination of the life cycle of N. lugens. The findings of the study indicate that the application of a substantial amount of biochar (200 g/kg of soil) resulted in a significant delay in the development of nymphs and a decrease in the survival rates of nymphs transitioning into adulthood. Moreover, the fertility of herbivores across their lifespan exhibited a decline with increasing rates of biochar application. Specifically, the number of eggs produced reduced from 256 eggs in the control circumstances to 69 eggs at the maximum biochar concentration. The egg-hatching rates exhibited a notable decrease when the biochar content reached its maximum value of 200 g/kg, in contrast to the lower biochar levels. The findings of this study indicate that the addition of biochar to rice fields, especially when applied at high rates, could potentially have negative consequences on the development and reproductive abilities of rice brown planthoppers [36]. In an independent investigation, considerable impacts on the population of Cnaphalocrocis medinalis, a prevalent pest, were identified as a result of incorporating biochar. In particular, the addition of biochar resulted in the prolongation of the larval development phase, an elevation in larval death rates, a drop in the final body weight of fully developed larvae, a reduction in the intake of rice leaves by the larvae, and a decrease in the adult lifespan of C. medinalis. It is important to note that, irrespective of the different levels of biochar treatment, there was no discernible variation in the ability to reproduce among the female insects that were able to mature. Another study that showed how biochar affected C. medinalis populations was a two-year study carried out in rice fields. In the first year, the use of charcoal resulted in a decrease in theC. medinalis population. The population level was discovered to be comparable to the control group in the second year, although. The study’s results offer strong proof that using biochar can successfully impede C. medinalis’s development and proliferation, possibly resulting in a decrease in the species’ population size [37]. A further investigation was undertaken to examine the efficacy of nanoscale and conventional biochar amendments in eliciting resistance in Nicotiana benthamiana when exposed to the pathogen Phytophthora nicotianae [38]. Nanoscale biochar derived from maize straw, produced at a temperature of 350°C and a concentration of 400 mg L⁻¹, with particle sizes of around 160 nm, exhibited a positive impact on enhancing the active immunity of N. benthamiana plants via the ethylene pathway. Consequently, this led to increased resistance against P. nicotianae infection. In the leaf assays conducted, the utilisation of nanoscale biochar led to a significant decrease of 9.26% in lesion sizes as compared to the control samples. The introduction of biochar nanoparticles resulted in a 20.3% rise in reactive oxygen species (ROS) through a mechanistic process, which in turn triggered the activation of the ethylene pathway. The activation event was subsequently accompanied by the manifestation of systemic acquired resistance (SAR), which was produced by the application of salicylic acid (SA). It is worth mentioning that the immune response caused by SA showed a significant rise of more than ten times in both treatments involving biochar nanoparticles. Furthermore, the biochar nanoparticles exhibited a much higher level of PR1-a expression compared to conventional biochar particles. In a conducted experiment, the utilisation of biochar nanoparticles as a delivery system for the plant elicitor 5-methoxyindole yielded notable enhancements in plant development. In particular, the use of biochar nanoparticles and 5-methoxyindole as seed treatments resulted in a significant enhancement of shoot length by more than 105.3% and root length by 41.2% when compared to untreated control samples. This work highlights the effective application of exogenous nanoscale biochar amendment in stimulating plant defence responses and improving resistance against the prominent pathogen P. nicotianae. The aforementioned methodology exhibits significant potential as an innovative tactic for safeguarding plants in the realm of sustainable nano-enabled agriculture, as outlined by Kong et al. [39]. Biochar serves a multifaceted purpose beyond the mere sequestration of carbon in soil over an extended period. It possesses the capability to significantly enhance agricultural production. The white-backed plant hopper (WBPH) is well recognised as a significant agricultural pest due to its substantial consumption of rice, a staple crop that provides sustenance for a significant portion of the global population. The researchers initiated a scientific endeavour with two primary goals: Initially, embark on a quest to ascertain the optimal biochar formulation for two distinct rice cultivars, namely ‘Cheongcheong’ and ‘Nagdong.’ Furthermore, this study aimed to investigate the impact of several biochar blends on the growth and resistance of two rice cultivars, when exposed to the persistent threat of the white-backed planthopper (WBPH). Upon doing a comprehensive analysis of the ideal levels of biochar, the findings yielded remarkable insights. The use of biochar at a 10% ratio in the rooting media proved to be quite beneficial, as it substantially enhanced the physiological well-being of both rice cultivars. The introduction of these plants provided a significant boost in their vitality. Nevertheless, deviating excessively beyond this optimal range, such as by incorporating biochar levels of 1%, 2%, 3%, or 20%, resulted in adverse outcomes. The experience resembled indulging excessively in a desirable entity until its desirability diminished. Now, this is the point at which it becomes quite fascinating. The two rice cultivars, Cheongcheong and Nagdong, exhibited contrasting responses in the presence of the persistent white-backed planthopper (WBPH). Nagdong, when reinforced with biochar, exhibited robust growth and resilience in the presence of White-backed Planthopper (WBPH) infestation. In contrast, Cheongcheong exhibited a less favourable response when faced with comparable situations. The expansion of the entity was impeded, appearing to be overpowered by the very strength and adaptability it aimed to possess. It is noteworthy that the impact caused by WBPH was notably reduced in Nagdong and notably increased in Cheongcheong, in comparison to their respective untreated equivalents. The phenomenon of biochar’s “priming effect” was shown to result in a significant increase in the production of jasmonic acid in response to the presence of white-backed planthopper (WBPH). In the context of Nagdong, this phenomenon can be interpreted as a catalyst for bolstering fortitude and facilitating personal development. However, in the region of Cheongcheong, there appeared to be an excessive abundance of favourable conditions, which resulted to an unfavourable reaction that hindered development and diminished the ability to withstand WBPH [40]. To determine how biochar amendments affected the English grain aphid Sitobionavenae’s ability to reproduce, more research was done. The study subsequently examined the expression of defence-related genes in wheat plants, specifically exploring the impact of biochar amendments and aphid feeding on this expression. When compared to the control group, the inclusion of biocahr modifications led to a decrease in aphid lifetime fertility by 9.09% and 20.23% for amendment levels of 3% and 5%, respectively. In addition, the utilisation of biocahr amendments resulted in a decrease in the aphid population by 18.68%, 21.69%, and 28.70% at amendment concentrations of 1.5%, 3%, and 5%, correspondingly. The silicon concentration in wheat plants increased significantly with the usage of biochar, surpassing a 40% elevation. Additionally, using biochar caused wheat plants to activate four defence-related genes (AOS, LOX, PAL, and PR), extending the time that aphids may feed on the plant. Our study’s findings indicate that adding biochar to soil may have a negative effect on aphids that infest wheat crops by reducing their ability to reproduce. The greater activation of plant defence mechanisms caused by applying biochar in response to aphid infestation is responsible for the reported negative effects [41].

Figure 3.

Depicting biochar in plant-biotic interactions like insect pest management, controlling plant pathogens and increasing soil microbial community.

3.2 Biochar effect on the soil microbial community

The planet’s soil ecosystems are home to the widest variety of terrestrial communities, and soil microorganisms are largely responsible for this extraordinary diversity [42]. Therefore, it is imperative to understand how biochar affects the soil microbiota, as Ng and Cavagnaro [43] pointed out. Because of its porous structure, biochar has microsites that can host soil microorganisms and provide them with a fresh environment (Figure 3). Since little is known about how biochar affects different organisms selectively, its potential as a microbial habitat is yet unknown. Furthermore, it is unknown how other elements like food availability and predation affect microbial response to biochar [43]. It has been noted that adding biochar to several experiments causes a significant increase in microbial biomass. It has been observed that the microbial communities’ composition and the activity of the enzymes are significantly altered by the ensuing increase in microbial biomass. A number of adjustments can be made to clarify the possible biogeochemical effects of biochar, including how it affects crop development, plant disease prevention, and nutrient cycling [27, 44]. One of the ways that biochar promotes microbial activity is through its porous nature. Furthermore, the abundance and availability of dangerous compounds are altered by biochar, changing abiotic variables like pH and giving some microbial communities an edge over others. Moreover, microbes can use biochar as a feasible energy source or as a way to obtain necessary mineral components [45]. There are several documented instances of interactions between soil, bacteria, and biochar that can have both positive and negative consequences. For instance, adding biochar made from wheat husks to temperate soils increased the diversity of microbes. Since the biochar’s organic carbon utilisation and metabolic activity were determined to be negligible, the rise was mostly due to physicochemical factors [46]. In tomato plants, the introduction of biochar made from eucalyptus wood chips at a concentration of 1% (wt/wt) increased bacterial diversity and altered the plants’ ability to metabolise nutrients. This was the conclusion of a study carried out by Kolton et al. [47]. Similar results were seen by Kolton et al. [26] when pepper plants were cultivated with citrus wood-derived biochar. By using biochar made from red spruce pellets and grapevine residues, Taskin et al. [48] report that the growth and enzyme activity of ligninolytic fungi living in the soil were enhanced. According to Wong et al. [49], the application of biochar derived from peanut shells and wheat straw to a recently constructed landfill cover topsoil resulted in an augmentation of soil bacterial community diversity. In contrast, certain biochar variants that had elevated levels of phosphorus, such as those derived from chicken sources, exhibited a notable decrease in the colonisation of roots by mycorrhizal fungi. However, it is worth noting that this reduction did not have any discernible impact on crop productivity, as indicated by Solaiman et al. [50]. Furthermore, the utilisation of rice straw-derived biochar was observed to elicit detrimental consequences on the model organism Caenorhabditis elegans. This was evident through the manifestation of neurotoxic attributes, which can be attributed to the activation of oxidative stress responses within the nervous system and the identification of free radicals within the biochar [51]. An further advantageous consequence of biochar implementation is its capacity to mitigate the environmental repercussions associated with metal(loid) pollutants through interactions with microorganisms. The study conducted by Wang et al. [52] demonstrated that the utilisation of bamboo-derived biochar in soils contaminated with cadmium (Cd) resulted in a notable reduction in the uptake and accumulation of Cd in rice plants. This effect was attributed to the biochar’s ability to modify the composition of the bacterial population in the rhizosphere. In a study conducted by Meng et al. [53], it was shown that the application of biochar derived from wheat straw in soils contaminated with herbicides resulted in an increase in microbial diversity and a subsequent improvement in the performance of wheat plants.

3.3 The use of biochar against plant pathogens

Research findings have provided intriguing revelations concerning the influence of biochar on plant diseases. According to Frenkel et al. [54], it has been observed that lower concentrations (≤1%) of biochar have the ability to suppress a range of disorders. Conversely, greater concentrations (>3%) tend to be ineffective, leading to a dose-response pattern that resembles an inverted U-shaped curve. In order to maintain a consistent and replicable impact of biochar on agricultural practises, it is advisable for biochar manufacturers to establish uniformity in the selection of feedstocks and concentrations, while also taking into account the potential implications on plant diseases [55]. The significance of this matter lies in its relevance, as the varied source and treatment of raw materials utilised in the production of biochar can result in variable outcomes with regards to disease suppression in agricultural systems (Figure 3). Biochar utilises various mechanisms to safeguard plants against diseases. These mechanisms encompass the facilitation of plant growth through nutrient provision, the augmentation of soil-microbial diversity, the adsorption of toxins generated by pathogens (such as extracellular enzymes and organic acids), the stimulation of antibiotic or fungitoxic compound production, the modification of root exudate chemistry, and the initiation of systemic plant defence mechanisms via chemical compounds acting as elicitors or microorganisms residing in microhabitats [56, 57]. Biochar has demonstrated efficient utilisation in combatting a diverse array of plant diseases, including those present in the air or soil, as well as many types of pests. Moreover, the research conducted by Lou et al. [58] has validated the growth-enhancing characteristics of biochar water-wash extracts, which contain a substantial amount of organic and inorganic chemicals. These findings indicate the need for additional investigation in this area. It is noteworthy that the advantageous impacts of biochar are occasionally more closely associated with its ability to enhance plant development rather than eliciting plant defence mechanisms. An experiment was conducted to investigate the effects of applying poplar woodchip biochar on the growth of Arabidopsis thaliana, a model plant, and lettuce, a crop plant. The results showed a notable enhancement in plant growth for both species, accompanied by the activation of genes associated with growth-promoting hormones such as auxins and brassinosteroids. These hormones are believed to play a role in mediating the observed growth effects. Nevertheless, the utilisation of global gene expression arrays and metabolomics techniques unveiled a significant decrease in the expression of multiple plant defence genes. These genes encompass those responsible for the synthesis of jasmonic acid, as well as genes encoding defensins and various classes of secondary metabolites that play a crucial role in safeguarding plants against insects and pathogens [59].

3.4 Biochar for the control of plant-pathogenic bacteria

The primary focus of utilising biochar as a mitigation technique for plant diseases caused by bacterial pathogens has been on tackling the specific issue of bacterial wilt disease, predominantly attributed to the pathogen Ralstonia solanacearum. The illness in question presents a substantial obstacle to the cultivation of vegetables on a worldwide level [60]. In light of the restricted accessibility of data, multiple sources were employed in the production of biochars with the aim of addressing bacterial concerns. The biochars utilised in this study were applied at a consistent rate of 2–3% (weight/weight). The results of the study indicated that these biochars were effective in reducing the incidence of bacterial wilt in tomato and tobacco crops. The protective effect of biochar is ascribed to multiple mechanisms, including the improvement of soil physicochemical qualities and the proliferation of bacteria and actinomycetes in the rhizosphere. The studies [61, 62, 63] also provide evidence for the combined impact of these processes on the decrease in swarming motility and root colonisation capacity of Ralstonia solanacearum.

3.5 Biochar for the control of plant-pathogenic fungi

Fungi are widely recognised as a prominent and highly deleterious category of plant pathogens [64], hence presenting a substantial agricultural risk. Soilborne infections, caused by the presence of Fusarium species, exert a substantial influence on a wide range of crops in different climatic zones [12]. As per the findings of Summerell [65], it has been established that Fusarium has the ability to produce mycotoxins in conserved plant-based goods. The aetiology of crown and root rot disease in asparagus can be ascribed to two fungal infections, specifically Fusarium oxysporum f. sp. asparagi and Fusarium proliferatum. Furthermore, the gravity of this ailment is augmented by the emission of allelopathic pollutants into the soil. The application of hardwood biochar resulted in a significant increase in the populations of antagonistic organisms, including Pseudomonas and arbuscular mycorrhizal fungi (AMFs) [66]. Furthermore, the latter have been recognised as agents that induce systemic resistance [12]. Additional research is necessary in order to have a comprehensive understanding of the fundamental mechanisms at play. Nevertheless, the results strongly suggest that biochars exert a substantial influence on nutrient availability and soil characteristics, as well as on the stimulation of soil microbial communities [66, 67]. The study conducted by Eo et al. [68] yielded similar results when investigating Panax ginseng plants cultivated on soil that was enriched with rice husk biochar. Similar effects were observed against F. solani and Ilyonectriadestructans, and these effects were ascribed to changes in the rhizosphere-microbial community. In a similar vein, the application of green waste biochar, along with compost, has been observed to yield advantageous effects in the reduction of F. oxysporum f. sp. lycopersici wilt. The aforementioned phenomenon was observed throughout a spectrum of intensities, ranging from 0% to 3% (w/w).According to Akhter et al. [69], the introduction of chlamydospores in tomato plants led to a notable augmentation in advantageous bacteria. These bacteria can exercise their influence through two mechanisms: direct antagonism or indirect activation of systemic resistance in the plant. The potential beneficial effects of biochar produced from beech wood chips or garden waste residues on the inhibition of F. oxysporum f. sp. lycopersici in tomato plants are likely due to the alteration of plant root exudates. These exudates may have a significant impact on the plant’s response to stress caused by disease [70]. Furthermore, the use of biochar alongside gaseous pesticides, which are generally referred to as fumigants, has promise for efficiently reducing fumigant emissions in the agricultural industry. The usage of two different types of biochar, obtained from a blend of hardwoods and Eupatorium adenophorum, in combination with dimethyl disulfide, is exemplified by an illustration. In the study conducted by Wang et al. [71], it was observed that the application of these chemicals at rates lower than 0.5% (by weight) did not have any detrimental effects on the control of Fusarium spp. Nevertheless, a significant reduction in the emission of dimethyl disulfide into the surrounding ecosystem was observed. The necrotrophic fungus Rhizoctonia solani is a soilborne pathogen that holds significant economic importance due to its ability to cause seedling illnesses in crop plants [12]. While the specific processes underlying the suppression of R. solani by biochar remain unclear, it has been determined that direct toxicity is not the primary factor. The utilisation of a 1% (wt/wt) biochar derived from eucalyptus wood and greenhouse wastes shown a notable decrease in disease occurrence among cucumber and bean plants, as observed in previous studies conducted by Jaiswal et al. [72, 73]. On the other hand, it was observed that the use of biochar derived from maple bark resulted in an increase in the incidence of R. solani damping-off disease across many plant species. This effect can be attributed to the existence of various organic chemicals within the biochar, which are believed to augment the pathogen’s fundamental metabolic processes [74]. Hence, it should be noted that not all biochar sources have a favourable capacity for disease suppression.

Furthermore, biochar has been found to enhance the ability of plants to fight foliar plant pathogenic fungus. The primary mechanism observed for the phenomenon of induced resistance is the systemic activation of defence mechanisms, as described by Shirai and Eulgem [75]. Botrytis cinerea is a fungal pathogen with a broad host range, capable of inducing necrotic disease on numerous plant species spanning various taxonomic groups [76]. Grey mould, a commercially detrimental disease, is caused by B. cinerea in strawberries [76]. The application of biochar derived from holm oak in strawberry fields has been found to enhance the bacterial variety within the rhizosphere, as demonstrated by De Tender et al. [77]. This increased bacterial diversity has the potential to induce systemic resistance against pathogens, hence mitigating the incidence of diseases. Kolton et al. [47] reported comparable outcomes in the suppression of B. cinerea when biochar derived from eucalyptus wood chips was administered to tomato plants. This application resulted in heightened microbial diversity and metabolic activity in the rhizosphere, consequently bolstering the defence mechanisms of the tomato plants. In a study conducted by Poveda et al. [12], it was shown that the application of biochar derived from greenhouse waste on tomato plants resulted in the activation of both early- and late-acting defence mechanisms against B. cinerea. Several factors were observed in this study, including the upregulation of genes associated with jasmonic acid and ethylene responses, as well as a significant increase in the presence of active oxygen species like H₂O₂. These findings are of great importance in understanding the mechanisms behind resistance to B. cinerea, as reported by De Tender et al. [77]. In a study conducted by Al-Juboory et al. [78], it was observed that the application of biochar derived from citrus wood at concentrations ranging from 1% to 5% exhibited significant reduction in the incidence of two plant diseases, namely B. cinerea and Leveillulataurica, which is responsible for powdery mildew. This reduction in disease occurrence is likely attributed to the activation of systemic induced resistance elicitors. Consistent with this, the utilisation of biochar derived from pepper plant wastes demonstrated efficacy in combating various fungal pathogens, including Colletotrichum acutatum and Podosphaeraaphanis [21] that are responsible for causing anthracnose and powdery mildew in strawberries, respectively.

3.6 Biochar for the control of plant-pathogenic oomycetes

Oomycetes exhibit characteristics that facilitate their effective infection and subsequent mortality of several plant species, including those of considerable economic importance as food and cash crops [79]. In parallel to the investigation of plant-pathogenic bacteria, there exists a restricted corpus of scholarly inquiry pertaining to the use of biochar for the purpose of oomycete management. The utilisation of biochar as a means of addressing plant disease caused by Phytophthora has been mostly focused on species that infect trees. Previous studies have shown evidence that the application of biochar generated from pine plant tissues at a concentration of 5% (vol/vol) can enhance the activation of plant defence systems through the induction of systemic resistance. The phenomenon described has been documented in Quercus rubra plants subjected to Phytophthora cinnamomi, as well as in Acer rubrum plants subjected to Phytophthora cactorum. As a result, the utilisation of biochar has been discovered to effectively reduce the advancement of diseases and alleviate physiological strain in these particular plant species [20]. In contrast, the utilisation of softwood biochar led to an increase in the colonisation of Pythium ultimum in the roots of sweet pepper, lettuce, basil, and geranium plants. Nevertheless, the investigation carried out by Gravel et al. did not reveal any observable adverse impacts on the root system or general growth of the plants [80].

3.7 Biochar for the control of plant-parasitic nematodes

Singh et al. [81] have reported that the occurrence of plant-parasitic nematodes (PPNs) has been linked to an average decline in agricultural productivity by roughly 12.3%. Biochar is widely recognised as an ecologically sustainable strategy for mitigating the impact of plant-parasitic nematodes (PPNs) by employing various techniques. For instance, modifications in the biodiversity of nematode populations residing in the soil have exhibited effectiveness in mitigating the impact of plant-parasitic nematodes (PPNs). The effect of incorporating biochar produced from wheat straw on the variety of soil nematodes was assessed in a microcosm experiment. According to Zhang et al. [82], the phenomenon resulted in a rise in the population of fungivorous nematodes and a decline in plant-parasitic nematodes (PPNs) from different genera such as Coslenchus, Hirschmanniella, Rotylenchus, and Tylenchus. The effectiveness of utilising biochar produced from burned log wood has been demonstrated in reducing the populations of Pratylenchuscoffeae, a migratory endoparasitic nematode that inflicts substantial harm to banana roots [83]. The decrease in nematode populations was seen at a concentration of 4% (wt/wt) [84]. The utilisation of biochar derived from poultry litter in the cultivation of grapevines led to a significant reduction in soil populations of plant-parasitic nematodes (PPNs), such as Meloidogyne javanica, Tylenchulus semipenetrans, Pratylenchus spp., Helicotylenchus spp., and Criconemoid spp. The decrease in plant growth can be ascribed to the increased abundance of several species that have been found to be advantageous for plant development, as documented by Rahman et al. [85]. The activation of plant defence mechanisms is an effective strategy utilised to combat Pratylenchus spp. As an example, the application of biochar produced from coniferous wood and spelt husks at a concentration of 5% (volume/volume) led to an enhanced resistance to Pratylenchus penetrans in carrot plants. The increased resistance seen can be ascribed to the activation of plant defence mechanisms. Nevertheless, it is crucial to acknowledge that the potential mechanism of direct toxicity or alteration of soil pH should not be overlooked [86]. Furthermore, the researchers successfully controlled the presence of the endoparasitic root-knot nematode Meloidogyne graminicola in rice agrosystems by introducing biochar generated from oak wood. This intervention involved the application of biochar at a concentration of 1.2% (wt/vol), as reported by Mondal et al. [87]. According to Huang et al. [88], it was discovered that the observed phenomena was linked to a concentrated accumulation of H₂O₂ in a specific area, as well as an upregulation of genes related to ethylene. This led to the alteration of plant defence genes. One intriguing application of biochar involves its effectiveness in reducing fumigant emissions while simultaneously controlling nematodes. In a study conducted by Cheng et al. [89], it was demonstrated that the use of a combination of 1,3-dichloropropene and chloropicrin, along with biochar derived from coconut shell, exhibited a sustained ability to manage plant-parasitic nematodes (PPNs) from various genera including Pratylenchus, Meloidogyne, Tylenchorhynchus, Tylenchidae, Trichodorus, and Mesocriconema. Moreover, this methodology additionally led to a decrease in the emission of detrimental atmospheric pollutants. Another example, as mentioned earlier, of managing Fusarium spp. is the application of biochar produced from hardwood and Eupatorium adenophorum. The aforementioned method has exhibited effectiveness in managing root-knot nematodes when administered at a concentration of 0.5% in relation to the soils weight. In addition, it is worth noting that the utilisation of this application rate has led to a significant reduction in fumigant emissions [90].

4. Conclusion

Knowledge of the role of biochar in plant protection can be highly beneficial in the context of advanced pest management for several reasons:

Increased availability of nutrients: enhancing the fertility and availability of nutrients in the soil through the use of biochar can lead to healthier plant development. Generally speaking, robust plants are better equipped to resist against pests and illnesses. You can contribute to the creation of an environment that is less favourable to pest infestations by implementing biochar into soil management techniques.

Advanced biological control: beneficial microorganisms in the soil, such particular bacteria and mycorrhizal fungi, can flourish when supported by biochar. Pathogenic organisms can be inhibited, consumed, or engaged in competition with these bacteria. Biochar aids in pest management indirectly by promoting a robust microbial population in the soil.

Reduction in chemical use: pesticides and fertilisers can be absorbed and retained by biochar, preventing them from leaking into the environment. This may result in less chemical pesticide being used, which is advantageous for the environment and may also help stop the emergence of pests that are resistant to pesticides.

Modification of pest behaviour: according to specific research, biochar may have an impact on how certain pests behave. Pests may find it more difficult to discover and infest crops if it interferes with the chemical cues that they utilise to locate their host plants.

Increased plant immunity: plants that have been exposed to biochar have been shown to develop systemic acquired resistance (SAR). Plants can repel a wide variety of diseases thanks to a defence system called SAR. Plant resistance to pests and diseases may rise as a result.

Sustainable agriculture: eco-friendly and sustainable methods are critical in this day of sophisticated pest control. By enhancing soil quality, lowering the demand for chemical inputs, and lessening the detrimental effects of agriculture on the environment, biochar can contribute to sustainable agriculture. In addition, insect patterns are changing due to climate change, and crop pressure is rising. By boosting their general health and stress tolerance, biochar can help plants become more resilient to these shifting environmental circumstances.

Thus, knowing how biochar protects plants is important for advanced pest management because it provides a comprehensive strategy that enhances soil health, plant vitality, sustainability, and direct insect control. It is feasible to lessen the need for chemical pesticides, support healthier ecosystems, and improve agricultural systems’ overall resistance to pests and other environmental problems by using biochar into pest management techniques.