The exponential increase in the human population has placed immense pressure on the Earth’s resources and ecosystems (Tal, 2025). Particularly food scarcity and water shortages, which have become more prevalent in many regions around the world (Saleem et al., 2025). Food scarcity results from the decline in natural soil fertility due to the insufficiency of space for other traditional systems of farming, such as shifting cultivation and slash-and-burn agriculture (Serrani et al., 2022). Also, population blooms have led to increased competition for limited land resources for other purposes such as urbanization and industrialization, further exacerbating the issue of food scarcity. This has led to an increased reliance on intensive farming practices such as monoculture and the use of chemical fertilizers and pesticides to maximize crop yields (Satterthwaite et al., 2010). This is because chemical fertilizers such as nitrogen, phosphorus, and potassium provide a direct, potent, and rapidly available nutrient source that boosts crop productivity, ensuring that more food can be grown on existing farmland (Govindasamy et al., 2023). The nitrogen provided by fertilizers promotes vigorous leaf and stem growth, resulting in a larger, more productive plant. Adequate phosphorus is essential for root development and overall plant health, while potassium helps regulate water uptake and nutrient transport within the plant. Therefore, fertilizer helps to correct soil deficiencies and imbalances, ensuring that crops have access to all the necessary nutrients for optimal growth. This increases yield per unit of land and contributes to global food security by maximizing the efficiency of agricultural production (Ma et al., 2023).

Continuous dependence on chemical products for agricultural practices has created an inconsistency that boosts short-term yield and creates long-term ecological consequences (Ahmad et al., 2024). For example, the Haber-Bosch process for ammonia synthesis consumes vast amounts of fossil fuels, contributing to greenhouse gas emissions and climate change. Also, only about 30-50% of applied N-P-K fertilizers are actually taken up by crops, with the rest leaching into waterways or remaining in the soil, leading to nutrient pollution and degradation of ecosystems (Laje et al., 2019). This highlights the need for the growing interest in sustainable farming practices such as crop rotation and organic farming. Despite its substantial role in enhancing soil health and decreasing dependence on environmentally detrimental agrochemicals (Al-Shammary et al., 2024). The transition to sustainable farming practices can be difficult for farmers due to initial costs and potential decrease in yields during the transition period (Gamage et al., 2024). The switch towards biofertilizers and biostimulants is a better and easy alternative for farmers looking to adopt sustainable practices without sacrificing productivity. This is because the transition to biofertilizers and biostimulants can help improve soil health and crop yield while also reducing the reliance on synthetic fertilizers and pesticides (Miranda et al., 2024). The gradual incorporation of these products into farming practices enhance the benefits of sustainable agriculture without causing major financial or yield challenges (Roy and Medhekar, 2025). This is because biofertilizers and biostimulants allow the continuous cultivation of crops of interest without the need for crop rotation, leading to increased efficiency and cost savings in the long run (Mahmud et al., 2021). Despite the significance of biostimulants and biofertilizers, issues such as variable environmental factors, poor adaptability, and competition with native microbes hinder the use of biofertilizers and biostimulants in agricultural industries (Ferreyra-Suarez et al., 2024). To counteract this limitation, it is crucial to focus on improving the formulation and effectiveness of biofertilizers and biostimulants using different biomass. The identification of specific strains of microbes that are better suited for different environmental conditions will help enhance the performance and efficacy of biofertilizers and biostimulants in agricultural settings (Boutahiri et al., 2024).

Different bioresources have been used as biofertilizers and biostimulants to enhance crop productivity and soil health. For example, Plant Growth-Promoting Rhizobacteria (PGPR) have been shown to fix atmospheric nitrogen, solubilize phosphorus/potassium, produce phytostimulants, and improve plant growth and stress tolerance (Khoso et al., 2024). Humic substances have been linked to the enhancement of soil structure by increasing nutrient and water retention, leading to the stimulation of root growth and plant metabolic processes (Trevisan et al., 2010). Seaweed extracts have been shown to be rich in micronutrients, amino acids, and plant hormones that can enhance plant growth, yield, and stress tolerance (Yasmeen et al., 2025). Whereas protein hydrolysates have been shown to provide nitrogen in a readily absorbable form, which can promote rapid plant growth and improve overall plant health (Colla et al., 2017). Microalgae and cyanobacteria are a superior option for use in biofertilizers and biostimulants due to their unique properties that enable the dual function of simultaneously acting as both a biofertilizer and a biostimulant (Nur et al., 2025). This is because they have the ability to provide essential nutrients and also the capability to produce a range of bioactive compounds, such as phytohormones, that are linked to the enhancement of plant growth, development, and stress resilience (Ugya et al., 2024a). Also, the potential circularity of microalgae cultivation makes them a sustainable and environmentally friendly option for agricultural practices, as they can be grown using waste nutrients and carbon dioxide from various industries (Ugya et al., 2024c, 2023). This not only reduces the environmental impact but also contributes to the overall sustainability of food production systems (Rahman et al., 2025). Despite the significance of microalgae resources as a tool for biofertilizers and biostimulants, challenges such as scale-up production, cost viability, harvesting, and processing have limited the widespread adoption of these sustainable alternatives in agriculture (Samoraj et al., 2024). This review aimed to identify the key strategies and technologies that can address these challenges and promote the successful integration of microalgae-based biofertilizers and biostimulants in agricultural practices.

Microalgae and cyanobacteria have gained significant attention as sustainable biofertilizers due to their rich nutrient content, growth-promoting properties, and environmental benefits (Gonçalves et al., 2023). The presence of proteins, amino acids, lipids, polysaccharides, vitamins, and minerals makes them ideal for use in agriculture. Microalgae and cyanobacteria are able to supply macro- and micronutrients such as nitrogen, phosphorus, potassium, iron, and magnesium, which are essential for plant growth and development (Ugya et al., 2024b). Also, microalgae and cyanobacteria can help improve soil structure and enhance water retention, leading to increased crop yields and overall soil health. Their ability to produce antimicrobial compounds that suppress soil-borne pathogens also contributes to healthier plants and reduced need for chemical pesticides (Ramakrishnan et al., 2023).

The benefit of using microalgae and cyanobacteria for agriculture is not only their nutrient-rich composition but also their potential to contribute to sustainable farming practices by reducing the reliance on synthetic fertilizers and pesticides. Additionally, microalgae cultivation can be done in a way that minimizes environmental impact, making them a promising option for eco-friendly agriculture. Whereas the production of synthetic fertilizer and pesticides leads to negative carbon footprints (Jurado-Flores et al., 2025). Different studies have reported the positive impact of microalgae on crop yield and quality, as well as their ability to enhance soil health and biodiversity. By incorporating microalgae into agricultural practices, farmers can not only improve the health of their crops but also contribute to a more sustainable and environmentally friendly food production system. For example, Zhang et al. reported that the use of extracts from Chlorella sp. and Anabaena sp. causes 81.7% and 58.3% increases in the length of cucumber seedling stems, respectively. The microalgal extract inhibited primary root elongation while concurrently promoting the development of lateral and fibrous root systems (Zhang et al., 2024b). The ideal of microalgae biofertilizer is to provide essential nutrients to crops through direct and indirect mechanisms. This mechanism includes nitrogen fixation, phosphorus solubilization, potassium and micronutrient cycling, and organic matter contribution as shown in Figure 1.

The ability of microalgae and cyanobacteria to act as biostimulants and biopesticides involves a complex mechanism (Parmar et al., 2023). This complex mechanism is linked to their rich biochemical composition, which directly influences plant physiology and soil health. For example, microalgae produce metabolites such as vitamins, amino acids, phytohormones, betaines, and alginate-derived oligosaccharides, which can act as biostimulants by improving seed germination, root development, chlorophyll synthesis, and overall plant growth (Zhang et al., 2024a). They also increase stress tolerance in plants by enhancing antioxidant activity and promoting nutrient uptake (Brito-Lopez et al., 2025). Microalgae also produce antimicrobial compounds that can help protect plants from pathogens and diseases. These antimicrobial compounds are able to assist plants to suppress fungal pathogens such as Fusarium oxysporum and Rhizoct onia solani. For example, Schmid et al. (2022) reported the ability of the extract of Scenedesmus obliquus to inhibit the growth of Sclerotium rolfsii by 32%. While the extract of Phaeodactylum tricornutum suppressed the growth of Rhizoctonia solani by 18.35%. This result indicates the prospect of microalgae biopesticide in the reduction of the synthetic pesticides utilization in agriculture, which can help minimize the environmental impact of chemical pesticides (Schmid et al., 2022). The mechanism of microalgae in the enhancement of nutrient uptake and assimilation in plants is primarily through the release of organic compounds that stimulate root growth and increase nutrient availability in the soil. For example, microalgae secrete organic acids such as citric and gluconic acids, which chelate nutrients in the soil, making them more accessible to plants. They also produce phytohormones such as auxins, cytokinins, and gibberellins that stimulate root branching and lengthening, further enhancing the plant’s ability to absorb nutrients (Prisa and Spagnuolo, 2023).

Also, extracts produced from microalgae contain auxins, cytokinins, gibberellins, brassinosteroids, and jasmonates that can promote plant growth, increase resistance to stress, and improve overall health. These bioactive compounds have shown promising results in agricultural applications, offering a sustainable and eco-friendly alternative to traditional synthetic plant growth regulators, as shown in Table 3 (Mazzafera, 2025). For example, studies have demonstrated that microalgae extracts can enhance seed germination rates, root development, and nutrient uptake in various crops. These extracts have been found to stimulate the production of plant hormones and enzymes involved in stress response mechanisms, leading to improved crop productivity and resilience. For example, microalgae synthesize antioxidants such as carotenoids, phenolics, vitamin E, and glutathione that can help plants combat oxidative stress and increase their tolerance to environmental challenges such as drought, salinity, UV, and temperature (Prisa et al., 2024). Microalgae also have the capacity to supply compatible solutes such as proline and polysaccharides that can help plants maintain cellular osmotic balance and survive under extreme conditions (Ren et al., 2025). They also have the potential to trigger Systemic Acquired Resistance (SAR) in plants, thus activating defense-related enzymes such as peroxidase, polyphenol oxidase, chitinase, and β-1,3-glucanase in plants. This can enhance the plant’s immune response and overall resilience to biotic stressors such as pathogens and pests (Yu et al., 2022).

The mechanisms of microalgae biopesticides are based on the production of bioactive compounds that can disrupt the growth and development of pests. These compounds can act as repellents, toxins, or growth inhibitors, providing an eco-friendly alternative to synthetic pesticides. The metabolites produced by microalgae include secondary metabolites such as phenolics, terpenoids, alkaloids, fatty acids, and peptides (Chaïb et al., 2021). These compounds exhibit antibacterial, antifungal, and antiviral activity because they cause the disruption of pathogen cell membranes, inhibit enzymatic processes, or interfere with cellular communication by blocking bacteria quorum sensing. This enhances plant yield because they help protect plants from harmful pathogens and pests, allowing them to grow more efficiently and produce higher yields. Certain microalgae are able to produce allelochemicals that can also suppress weed growth and competition, further benefiting plant growth. These allelochemicals can help improve soil health and reduce the need for synthetic herbicides, making microalgae a sustainable option for enhancing agricultural productivity (Bhardwaj et al., 2025). Microalgae also produce fatty acids and pigments such as astaxanthin and β-carotene, which have insecticidal and nematicidal effects. These compounds can help reduce the reliance on chemical pesticides in agriculture, promoting a more environmentally friendly approach to pest management. Also, microalgae can be easily integrated into existing farming practices, making them a convenient and cost-effective solution for improving crop yields (Casanova et al., 2023).

Microalgae are increasingly recognized as sustainable alternatives to chemical fertilizers and synthetic plant growth regulators due to their ecological benefits, nutrient content, and potential for circular bioeconomy integration. The waste-to-resource model of microalgae increases its utilization for biofertilizer because it allows for the conversion of organic waste into valuable nutrients for plants. For example, microalgae can utilize nutrients from agricultural runoff, municipal wastewater, or industrial effluents for biomass production, which can then be used as a nutrient-rich biofertilizer for crops. This not only helps in reducing waste and pollution but also promotes sustainable agriculture practices by closing the nutrient loop in a circular economy. The cultivating of Chlorella sp. in wastewater recovery has led to the recovery of more than 90% of nitrogen and 80% of phosphorus. These recovered nutrients are then slowly released back into the soil, providing a continuous source of nourishment for plants (Ortega-Blas et al., 2025). Also, the ability of microalgae to sequester carbon makes them a promising solution for reducing greenhouse gas emissions. They are able to fix atmospheric CO₂ through photosynthesis at approximately 1.8 tons of CO₂ per ton of algal biomass produced. This allows for integration of microalgae cultivation with industrial emissions, thus reducing the cost of microalgae biofertilizer production. This increases the sustainability of both the agricultural and industrial sectors because it aligns with the concept of a circular economy (Geng et al., 2025).

The high nutrient density per input of microalgae biomass also contributes to its potential as a sustainable biofertilizer for enhancing crop productivity. This is attributed to the fact that microalgal biomass is highly concentrated with essential nutrients and bioactive compounds compared to traditional compost or manure. Also, the rapid growth rate of microalgae allows for continuous production of biomass, making it a reliable source of biofertilizer. This can help reduce the reliance on chemical fertilizers, promoting environmentally friendly agricultural practices (Atzori et al., 2020). Microalgae biofertilizer reduced the dependence on nonrenewable inputs, which are associated with mined phosphate or Haber–Bosch nitrogen, leading to a shift towards agricultural sustainability (Slocombe et al., 2020). This transition addresses the severe environmental and economic costs embedded in conventional fertilizers (Ugya et al., 2021). This is because chemical fertilizers depend on phosphate and nitrogen mined from phosphate rock and Haber-Bosch nitrogen (Asadu et al., 2024). The Haber-Bosch process for nitrogen fixation requires high energy inputs, contributing to greenhouse gas emissions and environmental degradation (Ladha et al., 2022). Similarly, phosphate rock mining is unsustainable and leads to habitat destruction and water pollution (Amann et al., 2018). Also, the application of chemical fertilizers can lead to soil degradation and nutrient runoff, further exacerbating environmental issues (Nuruzzaman et al., 2025). Microalgae biofertilizer offers a sustainable alternative by utilizing nutrient-rich algae to provide essential nutrients for plant growth. This method not only reduces reliance on harmful chemical fertilizers but also helps to improve soil health and minimize environmental impact (Hoque et al., 2025).

The scale-up of microalgae biofertilizer is hindered by a complex interconnected set of challenges ranging from production economics, product efficacy, and regulatory frameworks (Zhang et al., 2025a). The production economics basically involve the costs of cultivation, harvesting, processing, and distribution, which critically shape how widely and effectively microalgae-based biofertilizers can be adopted. This has limited the adoption of microalgae biofertilizer because for maximum biomass production, microalgae cultivation requires controlled environments with adequate light, nutrients, carbon dioxide, and water. Thus, depending on the system used, the capital and operational costs can vary significantly, making it challenging for producers to achieve cost competitiveness with traditional fertilizers. For example, open pond systems are cheaper to build but yield lower productivity due to contamination and environmental fluctuations (Skifa et al., 2025). But closed photobioreactor systems offer higher productivity but come with higher initial investment costs. Also, the cost of the nutrient inputs can greatly impact the overall expenses of microalgae cultivation, as high-quality nutrients can be expensive. Therefore, finding a balance between cost and productivity is crucial for successful microalgae production (Magalhães et al., 2022). Another issue affecting production economics is harvesting and downstream processing, due to labor and energy intensity. This is because techniques such as centrifugation, filtration, or flocculation are required. Although for biofertilizer purposes cheaper methods such as gravity sedimentation or bioflocculation can be used because lower purity is needed compared to other applications like pharmaceuticals. However, optimizing these processes to maintain nutrient content and biological activity while reducing energy input is key to economic viability (Anthony et al., 2013).

The efficacy of a microalgae-based biofertilizer is another limitation to scale-up production. For example, microalgae are known for their rich biochemical composition, including proteins, amino acids, phytohormones, and micronutrients (Miranda et al., 2024). However, the real-world application of this biofertilizer may not always result in the expected crop yield increase due to various factors such as environmental conditions, soil type, and application method (Cao et al., 2023). Also, microalgal performance varies depending on species selection, cultivation conditions, and formulation stability. For example, environmental factors such as pH, light availability, and soil microbiota interactions can affect the bioavailability of algal nutrients and metabolites. Therefore, a lot of questions remain regarding the optimization of microalgal biofertilizers for different agricultural settings and crops (Ugya et al., 2025b).

The regulatory framework also influences the development and application of microalgae as biofertilizers. This is attributed to the need to determine the classification, safety standards, and market approval processes of microalgae-based fertilizer. The high regulation on biofertilizer imposed by many countries creates a barrier for the scale-up production of microalgae-based biofertilizer. Also, the complex regulatory requirements may also impact the cost-effectiveness and commercial viability of microalgae biofertilizers (Santos et al., 2024). To counteract these limitations, the following strategies can be implemented to improve the overall effectiveness of microlagae-based biofertilizer.

Microalgae and cyanobacteria act through several mechanisms as biofertilizers by fixing atmospheric nitrogen, solubilizing phosphorus, and releasing essential nutrients. This has the potential to reduce the reliance on chemical fertilizers, decrease environmental pollution, and improve soil health. Furthermore, the use of microalgae and cyanobacteria as biofertilizers can also enhance crop productivity and increase resilience to environmental stressors. They also act as biostimulants through the secretion of plant growth hormones like gibberellins that enhance seed germination, root development, and crop biomass. This biostimulant potential has led to increased interest in utilizing microalgae and cyanobacteria in sustainable agriculture practices as a natural alternative to synthetic growth promoters. Their role as biopesticides involves enriching the soil with beneficial microorganisms that control plant pathogens, and they can also directly contribute to the biodegradation of environmental pesticide residues. These biopesticides are considered environmentally friendly alternatives to chemical pesticides, as they do not harm beneficial insects or contaminate water sources. Despite the benefits of microalgae-based biofertilizer, large-scale application is limited by production economics, product efficacy, and regulatory frameworks. Thus, warranting further research and development to address these challenges and maximize the potential of microalgae biofertilizers in sustainable agriculture practices.