Grain crops play a pivotal role in global food production, serving millions of people as a primary source of nutrition and livelihood. However, the conventional use of chemical fertilizers and pesticides in production and pest management has raised significant concerns regarding human health risks and environmental sustainability. As a result, there is an increasing demand for sustainable and eco-friendly alternatives that can ensure optimal crop yield and quality. Among these alternatives, vermicompost (VC) and its derived products have emerged as a promising solution, offering numerous benefits for grain crop production and effective pest management.

Maize, wheat, barley, rice, and pearl millet are important cereal crops worldwide, contributing significantly to the 9.5 billion tons of global food production in 2021 and the 54% increase in food production since 2000 [1]. Between 2020 and 2021, global cereal production increased by 2.1%, driven by a 4.1% surge in maize production, with maize, wheat, and rice contributing to 90% of the total cereal output [2]. Additionally, pearl millet, the sixth major cereal crop, is vital in agriculture, covering approximately 30 million hectares in arid and semi-arid tropical regions of Asia and Africa, accounting for nearly half of global millet production [2]. Maize, the most produced grain globally, has high nutritional value with protein, carbohydrates, oil, fiber, and ash content [3]. Wheat, a similarly vital source of protein for billions of people, often suffers from nutrient deficiencies in soils, adversely affecting human nutrition. Zinc and iron deficiencies are prevalent in agricultural soils globally [4]. Wheat grain is rich in starch, protein, fat, cellulose, minerals, and vitamins, making it nutritionally valuable.

To meet the ever-growing demands for food, maximizing crop yield per unit area has become imperative. Organic fertilizers such as VC present a sustainable approach to achieving this goal. VC, produced through the symbiotic interactions between microorganisms and earthworms, represents a cost-effective and environmentally friendly process that enhances soil quality and improves microbial biodiversity ^{[5][6][7][8][9][10]}[5,6,7,8,9,10]. Incorporating VC into agricultural systems has shown great potential for boosting grain crop productivity while minimizing environmental impacts.

A balanced supply of nutrients is crucial to ensure high productivity and nutritional value in grain crops. Combining chemical and organic fertilizers, including VC, has been recommended to address nutrient deficiencies and mitigate soil quality deterioration caused by intensive crop cultivation practices ^[3][11][3,11]. Farmers can improve soil fertility, enhance nutrient availability, and promote sustainable long-term productivity in grain crops by incorporating VC, crop residues, and cover crop biomass.

Micronutrient malnutrition poses a significant challenge to global public health, affecting a substantial portion of the population. Ensuring the enrichment of widely consumed cereals with essential nutrients has become imperative. VC offers a natural solution enriched with crucial nutrients, humic acids, plant growth-regulating hormones, and enzymes, which positively influence plant nutrition, photosynthesis, and the nutrient content of various plant parts ^[12][13][12,13]. Moreover, VC has been shown to enhance crop tolerance against pests and diseases, making it a favorable alternative to inorganic fertilizers in agricultural and horticultural practices.

Overreliance on mineral fertilizers in cereal production has led to severe soil degradation and environmental problems. Integrated nutrient management practices, including VC, mitigate these issues. VC is vital in improving soil quality, sequestering organic carbon, and reducing excessive CO₂ emissions associated with intensive agricultural practices ^{[14][15][16][17]}[14,15,16,17]. Farmers can achieve sustainable agriculture practices by implementing VC -based strategies while reducing environmental impacts.

VC has been recognized as an effective organic fertilizer for reducing the accumulation of cadmium (Cd) and arsenic (As) in crops and soil. The study by ^[18][87] found that adding VC significantly reduced the CaCl₂-extractable Cd in the soil through Cd adsorption onto VC (Figure 1) and increased soil pH. The effectiveness of organic amendments, including VC, in reducing Cd accumulation depends on factors such as plant species, type and dosage of organic materials, and modifications in the physicochemical and biological characteristics of the rhizosphere. Organic amendments, including VC, have also shown promise in reducing As bioavailability in soils through the chelation of organo-As compounds, thus lowering As accumulation in plants ^[19][32]. The complexation of As with humic acid and binding mechanisms involving cation bridges contribute to As immobilization. Machine learning algorithms, particularly random forest (RF), have been used to predict As concentrations in rice grains, considering soil parameters such as soil As, pH, organic carbon (OC), and soil phosphorus (P) concentration ^[19][32].

Various studies have explored the effectiveness of VC, biochar, and humic substances in mitigating Cd accumulation in plants ^[20][88]. These natural materials have demonstrated the potential to retain Cd in soils, with VC -derived humic substances exhibiting the highest retention capacity for Cd²⁺. The interaction between these materials and roots, along with acid exudation and rhizosphere acidification, may influence the release of weakly or superficially retained Cd²⁺. The assimilation of Cd²⁺ in plants grown on different substrate materials has varying toxicity levels and impacts plant growth. VC and VC-derived humic substances show less inhibition of root and shoot growth than biochar and humin.

Furthermore, the co-application of VC and selenium (Se) has further reduced Cd concentrations in rice tissues compared to treatments with single organic amendments ^[21][56]. This suggests the potential of combined approaches to enhance the remediation of Cd contamination in crops.

Using chemical fertilizers and pesticides in agriculture has resulted in soil degradation and environmental contamination with heavy metals such as Cd, Pb, and As ^[22][89]. These heavy metals can originate from natural sources and human activities, including industrial processes and waste disposal, which has led to heavy metal accumulation in the tissues of earthworms such as Eisenia fetida. However, VC, produced through vermicomposting, has been shown to reduce toxic metal levels and enhance soil fertility.

A study conducted on Eisenia fetida examined the concentration of Co, Cr, and Pb in different combinations of animal dung used in the initial feed mixture and the resulting VC. The results revealed that Co levels decreased the most when the soil was combined with cow dung VC inoculated with Eisenia fetida. The concentration of Cr was significantly increased in the earthworm body when the soil was combined with horse dung VC. On the other hand, Pb levels showed the maximum decrease when the soil was mixed with cow dung VC inoculated with Eisenia fetida. This indicates that Eisenia fetida contributes to the accumulation of heavy metals from various combinations of soil and VC during vermicomposting ^[22][89].

Eisenia fetida, through its feeding and microbial activity during vermicomposting, has shown effectiveness in reducing cobalt levels in different waste materials. Vermicomposting can be a suitable metal remediation technology, particularly in urban sludges. Buffalo dung is a good feed material for earthworms, with a higher accumulation of Co in the gizzard compared to the posterior region of the intestine. However, concerns arise when VC derived from municipal solid waste (MSW) containing heavy metals is applied to soil, as the earthworms can absorb these metals and potentially affect crop yield, long-term soil quality, and human health. Despite these concerns, inoculating Eisenia fetida in crop fields can help decompose various wastes and improve soil conditions. Therefore, vermibiotechnology offers a valuable approach to managing heavy metals in soil and waste materials, safeguarding human health and the environment ^[22][89].

The application of VC can introduce heavy metal contamination into soil and crops, mainly when sourced from feedstock materials such as municipal solid waste, sewage sludge, and manures ^[23][90]. This contamination poses risks to soil organisms, plants, and potentially human or animal health, depending on the concentrations of heavy metals involved.

A recent study by ^[24][30] investigated the effects of VC contaminated with heavy metals (Cd, Cr, Cu, and Zn) on mudflat soil and barley crops. The study revealed increased concentrations of these heavy metals in the soil and crops following VC application. However, it is essential to note that the concentrations remained within permissible limits set by the National Environmental Quality Standard for Soils China, indicating no immediate risk to the environment or human health. Nevertheless, using domestic sludge as the VC source limited the earthworms’ capacity to fully remediate heavy metals, resulting in their persistence within the VC. It is crucial to consider that different VC sources can yield varying levels of heavy metal contamination. In this case, the high concentrations introduced outweighed the potential benefits of VC application in mudflat soils.

While most VC research has focused on soil micro- and macronutrients, micronutrient responses and their transfer to crops have received less attention. A study by ^[23][90] investigating the accumulation of micronutrients in soil and their uptake by rice plants after long-term VC application revealed an enhanced uptake of trace elements. However, the increase in uptake did not consistently occur with extended application periods, possibly due to variations in soil properties such as acidity and organic carbon. Long-term fertilization practices can modify soil characteristics, including pH, organic matter, and nutrient levels, subsequently influencing the behavior of micronutrients in soil and crops ^[23][90].

Despite the potential heavy metal contamination risks, VC produced through the digestion of sewage sludge by earthworms has been found to have beneficial effects on soil fertility and nutrient availability in mudflat salt-affected soils ^[24][30]. Applying VC improved the soil’s physical and chemical properties, including increased bulk density, pH, organic matter, and organic carbon, while decreasing electrical conductivity (EC) ^[24][30]. Higher rates of VC application also increased nutrient content, such as total nitrogen, alkaline nitrogen, total phosphorus, and available phosphorus in the soil ^[24][30]. Therefore, applying VC contaminated with heavy metals can affect soil and crop health. To minimize heavy metal contamination, carefully selecting high-quality VC sources becomes crucial, considering the variations in contamination levels among different sources. Continuous research and monitoring are necessary to develop effective risk mitigation strategies and ensure agricultural practices’ sustainability in the face of potential heavy metal contamination from VC applications.

In addition to improving soil properties, VC application promoted the growth of barley plants in mudflat environments, resulting in increased plant height, total biomass yield, and grain yield ^[24][30]. This positive effect can be attributed to VC’s rich organic matter and organic colloid content, which form a good soil structure with increased porosity and decreased bulk density. These soil conditions reduce capillary tension and limit the upward movement of water and salt, thereby inhibiting soil resalinization. Furthermore, the acidity of VC and the production of small-molecule organic acids during decomposition contribute to the decrease in electrical conductivity observed after its application ^[24][30]

Research conducted by ^[25][91] demonstrated that VC and water treatment residuals (WTR) positively affect saline-sodic soils and wheat yield. Adding VC and WTR improved soil structure, water retention, and nutrient uptake, ultimately enhancing crop productivity. Similarly, ref. ^[26][92] found that VC, combined with WTR, effectively reduced soil salinity and sodicity while enhancing soil physical properties and nutrient availability. Although not directly addressing pest management, reducing soil salinity and improving soil conditions through VC and WTR applications indirectly benefit pest control in cereal crops. Another study by ^[27][93] assessed the effectiveness of VC and sorghum water extract ^[28][94] in mitigating salt stress in maize seedlings. The combined application of VC and SWE alleviated the adverse effects of salt stress, improving plant growth, photosynthetic efficiency, and nutrient uptake in salt-affected soils.

Adopting suitable crop patterns can help reduce greenhouse gas (GHG) emissions from fields ^[29][95]. In rice cultivation, VC has shown promising results in reducing GHG emissions and increasing grain yield. The study by [11] found that the VC-IPNSF (integrated plant nutrient system fertilization) treatment in a triple rice cropping system reduced CH₄ emissions by approximately 14% compared to the cow dung-IPNSF treatment. The VC-IPNSF treatment also led to a 5–13% increase in grain yield and significant reductions in CH₄, CO₂, and N₂O emission factors. GHG intensity was reduced by approximately 16–24%, and the global warming potential decreased by 13–17% with VC-IPNSF compared to cow dung treatment. These findings suggest that VC is a better carbon source than cow dung and can potentially reduce GHG emissions while improving rice yield [11].

In a comparison between VC and synthetic fertilizers in rice cultivation, ref. ^[30][24] observed that VC-fertilized plots emitted more methane during the early and active vegetative stages but less methane during the panicle initiation and maturity stages than plots fertilized with synthetic fertilizers. Although the overall difference in methane flux was not statistically significant, the study highlighted that VC-fertilized rice cultivation might result in lower net GHG emissions due to the higher nitrous oxide emissions associated with synthetic fertilizers. This emphasizes the potential of VC to reduce GHG emissions in rice cultivation ^[30][24].

Organic amendments like biochar have also shown positive effects on reducing GHG emissions. The study by ^[31][59] compared the impacts of biochar and VC on various factors, including GHG emissions. Both amendments suppressed methane, nitrous oxide, and carbon dioxide emissions. VC application positively affected the soil organic carbon pool, crop yield, and nitrogen loss reduction. However, the effectiveness of biochar varies depending on feed materials, production processes, and soil types ^[31][59].

It is important to note that specific greenhouse gas emissions from rice cultivation patterns amended with VC are not widely available. Further research is needed to explore alternative organic substances and fine-tune the VC application rate to minimize GHG emissions while enhancing rice yield and soil health [11].

Regarding carbon sequestration, ref. ^[32][43] evaluated different treatments to assess their impact on organic carbon stock, total carbon stock, and organic carbon sequestration in grain crops. The treatment involving the application of poultry manure (PM) at a rate of 5 t ha⁻¹ with a 50% recommended dose (RD) of chemical fertilizer yielded the highest values in these parameters. This treatment resulted in an organic carbon stock of 18.70 t ha⁻¹, 20.81 t ha⁻¹, and organic carbon sequestration of 1.75 t ha⁻¹. The second-highest values were observed in the VC treatment, at a rate of 5 t ha⁻¹ with 50% RD of chemical fertilizer. These findings highlight the significant enhancement of organic carbon accumulation in the soil of cereal crops when PM or VC is incorporated at the specified rates. These practices have promising implications for mitigating carbon emissions and promoting sustainable agricultural systems. However, the effectiveness of these treatments may vary depending on factors such as soil type, crop species, and local conditions. Further research is needed to determine the optimal application strategies for different scenarios to maximize the benefits.

The environmental consequences of contaminants such as personal-care and pharmaceutical products (PPCPs), microplastics (MPs), and emerging contaminants (ECs) have necessitated innovative strategies for their remediation and mitigation. Vermicomposting, harnessing the capabilities of earthworms, has emerged as a promising approach for achieving these objectives. A study by ^[33][96] investigated the bioremediation of organic contaminants, with a focus on polycyclic aromatic hydrocarbons (PAHs) and heavy-phase hydrocarbons found in automotive residual oil. Their study revealed that introducing earthworms significantly enhanced the removal of PAHs from contaminated soils. Similarly, ref. ^[34][97] employed vermiremediation by harnessing the power of earthworms to address PAH-contaminated soil, demonstrating the earthworms’ ability to accelerate the transformation of PAHs into less toxic metabolites. The resulting nutrient-rich worm castings were suitable for use as a soil amendment. However, the response of earthworms to PAH toxicity varied depending on factors such as PAH type, concentration, exposure duration, and earthworm species involved.

The effectiveness of vermicompost application in mitigating hydrocarbon-contaminated soil is underscored by studies conducted by ^[35][98] and ^[36][99]. A study by ^[35][98] integrated vermicompost into contaminated soil, leading to a remarkable 34.4% degradation of hydrocarbons. This enhanced degradation was attributed to mechanisms such as adsorption and sequestration, wherein the vermicompost bound PAHs, limiting their availability for uptake by microorganisms or plants. In addition, ref. ^[36][99] targeted the remediation of soils contaminated with polychlorinated biphenyls (PCBs) using biological sewage sludge and Eisenia fetida earthworms, effectively reducing highly chlorinated PCB contamination in soils.

Another study by ^[37][100] demonstrated a substantial reduction in PPCPs during vermicomposting of sewage sludge, attributed to the transformative influence of earthworms on the humification process. This transformation led to the generation of humic-like and fulvic-like substances known for their proficiency in binding organic and inorganic pollutants, further contributing to contaminant mitigation. Furthermore, ref. ^[38][101] compared the efficiency of vermifiltration, which employs earthworms, to conventional activated sludge methods in removing PPCPs from hospital effluent. The study highlighted the significant role played by earthworms in biodegrading organic compounds, heavy metals, and solids in sewage. Vermifiltration proved nearly as efficient as activated sludge in removing PPCPs. Also, ref. ^[39][102] explored the interaction between earthworms and PPCPs and found that their physicochemical properties and soil characteristics influenced the uptake of these compounds.

Moreover, ref. ^[40][103] investigated the mineralization of ciprofloxacin in soils and demonstrated that adding earthworms could enhance mineralization up to eightfold when introduced into the soil. In another context, ref. ^[41][104] employed vermicompost to create an environment conducive to the proliferation of fungi capable of degrading 3,4-dichloroaniline (DCA) in winery wastes. These fungi, such as Aspergillus niger and two Fusarium sp. strains, indirectly facilitated the growth of earthworms and offered an alternative for bioremediation techniques focused on DCA degradation and environmental impact reduction. Furthermore, ref. ^[42][105] introduced vermifiltration as a method where earthworms break down organic matter and remove ECs from wastewater. Earthworms played a crucial role in enhancing aeration and water flow within the system, effectively mitigating ECs through physical and biological processes, including adsorption, biodegradation, and bioaccumulation. Therefore, VC application offers valuable solutions to address the environmental challenges posed by these contaminants, ultimately contributing to cleaner and healthier ecosystems.