The multicellular, microscopic algae known as seaweeds are found in maritime environments. Although there are more than 9 thousand macroalgae species in the waters, they can be generically categorized into three classes: Rhodophyta (red algae), Chlorophyta (green algae), and Phaeophyta (brown algae) (1). Seaweeds are naturally rich in nutrients, including beneficial lipids, enzymes, polysaccharides, proteins, and bioactive peptides (2). Additionally, they produce various stress-related bio-compounds to withstand and lessen various pressures in their natural habitats (3). Because of their rich resource content, seaweeds are useful as plant modifiers that can increase agricultural output. For many years, seaweeds have been employed in agriculture as bio-stimulants. According to the oldest reports, seaweeds were employed for centuries as soil conditioners before being used as biofertilizers and bio-stimulants (1). Seaweeds aren’t currently being used directly for either commercial or agricultural purposes. The best nutrient sources are seaweed extracts, full of the valuable micronutrients and macronutrients present in seaweeds (3). Since more than one-third of the global bio-regulator market is made up of seaweed extracts, their use as a preferred bio-regulator has caused a boom in the agribusiness sector (4). The growing urbanization, lack of groundwater, climate change, and a general reduction in arable land are some of the toughest challenges that the world’s agriculture is currently experiencing. Together, they represent a greater threat to meeting the world’s population’s rising food needs.

On the one hand, farmers and producers utilize excessive chemicals to increase crop output. On the other side, overusing these chemicals has resulted in several health risks and environmental safety concerns, as well as deteriorating quality of the rhizosphere (5). Therefore, it is urgent to find a strategy to reduce the use of harmful chemicals in agriculture if they are not eliminated. In this regard, the seaweed extract-based bio-stimulants provide a novel and substitute method for increasing agricultural crop productivity without using chemical fertilizers or pesticides (Shukla et al., 2019). Extract preparation from seaweeds can be directly applied onto the soil, just like chemical fertilizers or pesticides, or they can be used as foliar spray on plants (6). Applications made to the soil can create soil microflora, leading to soil retention and remediation (7). On plants, seaweed extracts can affect phytohormone homeostasis and reduce nutrient shortage (6). It is evident from the existing literature that seaweeds play a crucial role in both agriculture and daily life. Most seaweed deposits are found throughout the world’s coastlines and should be used wisely and effectively. Plants can benefit from the physiological processes of biostimulants, which can be synthetic or natural compounds (8). These processes include improved tolerance to various abiotic stressors and nutrient absorption and translocation (9). Plants can benefit from the physiological processes of biostimulants, which can be synthetic or natural compounds generated from microorganisms and/or plants. These processes include improved tolerance to various abiotic stressors and nutrient absorption and translocation (10). Creating bio-stimulants based on seaweed extract is one method of efficient use of seaweed biomass. However, farmers should be made aware of and encouraged to use these seaweed-based bio-regulators in their fields in place of standard chemical fertilizers and pesticides (11). Therefore, using seaweed-based solutions can be a sustainable way to enhance integrated pest management and organic farming (Wan et al., 2018). Even though there have been numerous reviews on its bio-regulator-based use in agricultural advancements, this review paper concentrates on a detailed understanding of the updates regarding the extraction methods for seaweed extract-based bio-regulator and their mechanisms of action for enhancing plant as well as soil health. We have also discussed the value of seaweed extracts in other fields, such as horticulture and floriculture. Additionally, the prospects for seaweed extract-based bio-stimulants are given in-depth, with a strong emphasis on the economic side.

Rapid population expansion should lead to an increase in agro-based products. As one of the key components in increasing food production, the fertilizer industry will unavoidably grow alongside agro-based goods. There is now a 3–4 million tons fertilizer shortfall worldwide (12). Seaweeds are frequently used as manure throughout the world, particularly in regions close to the ocean. Seaweeds can be composted or used directly as organic manure (13). Two things determine how vital seaweed fertilizer is. First and foremost, seaweeds include significant concentrations of micronutrients besides Ca, N, P and K. Growth hormones like auxin, gibberellin, and cytokinin as well as oligo elements like Zn, Cu, etc. are also present (14). The presence of diverse mucopolysaccharides, which aid in soil conditioning by adding organic matter to the soil and increasing its moisture-retaining capacity, is a second distinguishing quality of seaweeds. Numerous seaweeds can be utilized as manure in all regions of the country, either directly or in the form of compost, due to their abundance of nutritional value for plant growth ( Figure 1 ). When manure with seaweed compost was applied, efficient observations were also obtained with several crops such as cereals, fruits, and vegetables; crotons also thrived with its application; high nitrogen levels can also be maintained with its treatment.

According to Mirparsa et al. (15), seaweeds are known to supplement the macronutrients (N, P, K, etc.) as well as a variety of micronutrients in amounts sufficient for plant growth ( Table 1 ). The mineral content of various seaweed species from different taxonomic groupings, including red, green, and brown algae, was investigated. ( Table 2 ). This indicated the presence of several mineral elements, including Ca, Mg, Na, K, Fe, Mn and Zn (19). In addition, several organic compounds, such as vitamins, cellulose, hemicelluloses, cellulose, fat, and amino acids, are rich in seaweed. It has also been shown that seaweeds have a greater mineral composition than terrestrial plants (20). Several researchers have identified a wide variety of polysaccharides as cell wall and storage component elements (21), indicating a high concentration of soluble and insoluble fibers. Seasonal variations, temperature, salinity, light, and the availability of nutrients are only a few examples of how the environment affects chemical composition (22). Between the wet winter and the warm summer, a considerable shift in composition was seen (23). More diverse amounts of phycobiliproteins, chlorophyll, and carotenoids were also detected (24).

Seaweed biomass and seaweed meal have been applied to horticultural crops using a variety of application techniques. The type of seaweed product utilized determines the type of application. Seaweed species are found in tropical, temperate, and polar parts of the world’s coastal climates (Sarkar et al., 2016). Near the seaside, where seaweeds are abundant, the usage of whole seaweed biomass or meal is widespread. Whole seaweeds or seaweed meal are spread on the ground and usually incorporated into the soil to speed up the microbial decomposition of the seaweed. Because soil bacteria reduce nitrogen during the decomposition process, causing a temporary nutrient immobilization that may adversely affect plant growth, seaweeds are introduced into the soil well before planting crops. As an organic matter, the decomposed seaweed generally enhanced the soil’s physical and chemical characteristics, its ability to hold water and its microbial activity. Additionally, it shielded plants from environmental hazards including extreme temperatures and water stress (36).

Seaweed extracts, which are either in a soluble powder form or as liquid extracts, are readily available and are the most commonly utilized seaweed product on agricultural and horticultural crops. Applying drip irrigation to crops while mixing liquid extracts with irrigation water it is possible to apply extracts close to the plant’s roots. Seaweed extracts are also used as foliar sprays on various floral, vegetable, and tree crops (37). Leaf stomata opening in the morning appears to be the best time for foliar administration of seaweed extracts. The plant’s stage of growth has an impact on how effective seaweed extracts are. For instance, Dwelle and Hurley (38) discovered that seaweed extract had the most significant effect on potato yield when applied two weeks after tuber start.

Seaweed extract includes vitamins, auxins, gibberellins, antibiotics, trace elements, and other chemical substances. To protect the crops, it is crucial to preserve some of the components as heat decomposes others. When making commercial seaweed extracts and evaluating the conflicting field trial findings that have been reported, it is known that several seaweed constituents experience significant seasonal fluctuations (12).

The positive properties of seaweed-based organic manure are attributed to the extensive spectrum of bioactive substances found in seaweed extract, including vitamins, auxins, gibberellins, antibiotics, trace elements, and amino acids. The species employed and the extraction technique may significantly impact the activity that promotes plant growth. Many seaweed components are said to experience seasonal fluctuations, and these variations are taken into account in the commercial manufacture and testing of organic seaweed manure. Surprisingly, despite the intended use of the extraction methods, there is a shortage of precise and thorough information about extraction techniques and procedures for agricultural purposes. This is partly because ownership dossiers for production and extraction techniques are rarely published and maintained (41). Extracts are frequently created by grinding at low temperatures, using water, acid, or alkali, or by physically disrupting the material (42). The most economical and practical approach for releasing micro- and macronutrients necessary for producing organic manure and bio-regulators appears to be the water-based method (43). Numerous publications indicate that water or an alkaline seaweed extract has a bio-stimulant impact on grains, legumes, vegetables, etc. (44). Species include Ascophyllum nodosum, Fucus vesiculata, Hypnea musciformis, Sargassum plagiophyllum, Ulva lactuca, Sargassum wightii, Laminaria saccharina, Padia tetrastomatica, and Ecklonia radiata have purportedly been used to manufacture liquid seaweed fertilizer (45).

The right balance of phytohormones, humic acids, and phytonutrients in seaweed characterizes it as superior organic manure. In addition to boosting soil fertility, applying seaweed fertilizers improves the soil’s ability to retain moisture and provides sufficient micronutrients for plant growth (45). The development of liquid-based seaweed fertilizer is a result of current attention being paid to the spray application of plant nutrients, which improves nutrient absorption efficiency (46). Seaweed extracts are applied to the soil, utilized as a foliar spray, and used to soak seeds before planting. It has been suggested that using seaweed-based fertilizers will lower the nitrogen, phosphorus, and potash fertilizer doses. It is known that about 59 species of seaweed can increase crop output and growth, as well as seed germination and other growth factors, more effectively than artificial fertilizers (47) ( Table 3 ).

Salt content, hydraulic conductivity, sunlight, temperature, and availability of nutrients are a few of the primary environmental elements that impact seaweeds. The relationships between sessile animals and their epiphytic bacteria, fungi, algae, and other sessile animals, as well as the connections between herbivores and plants and predators, including humans, are examples of biological interactions. All of these elements working together have an overall impact on the individual patterns of growth, morphology, and reproduction. The physicochemical environment of an organism, which is made up of all the external abiotic factors that affect it, is extremely complicated and continually changing. The saltwater density is influenced by temperature and salinity, mixing nutrient-rich bottom water with nutrient-depleted migration of epiphytic animal larvae. Turbidity, siltation, and the availability of nutrients can all be impacted by water velocity. These are illustrations of how one environmental factor influences another. The interaction of temperature and photoperiod controls growth and reproduction in many seaweed species. Additionally, interactions between physicochemical and biological components are more often than not. Factor interaction through sequential effects is the last type of interaction. Red algae may catabolize some phycobiliproteins due to a lack of nitrogen, lowering their capacity to absorb light. Therefore, many seaweed species and genera within seaweed floras inhabiting more or less constrained regions of the world’s seacoast are more or less identical.

The United States, United Kingdom, Canada, New Zealand, Australia, Ireland, Scotland, England, France, and Spain are just a few of the nations that regularly employ seaweed fertilizers. Green, brown, and red seaweed extracts are offered for sale in South Africa to soil conditions. Hypnea, Ulva, and Enteromorpha are frequently employed in Brazil, while the Sargassum is utilized in China and the Hypnea in the West Indies.

As previously mentioned, coastal agricultural soils have been treated with seaweed for millennia, either in their fresh or sun-dried state. However, a variety of simple (compost, flour) or more complicated seaweed-based fertilizers are being offered commercially (bio-stimulant extracts). Since the middle of the 20th century, many types of extracts have replaced seaweed-based fertilizers as bio-stimulants in contemporary agriculture (93). The increased usage of extracts is likely due to their convenience in storage and transportation and the quick effects of their active ingredients on plants (94). The horticulture industry has already used seaweed extracts to a large extent (94), and horticultural crops have been the subject of the majority of studies on seaweed usage in agriculture. To enhance the economic and environmental balances, several seaweed extracts are utilized to boost the effectiveness of traditional fertilizer by decreasing doses. Through cryo processing, cell rupturing under high pressure, or extraction with water, acid, or an alkali, bioactive chemicals in seaweed can be recovered (42). All of these techniques prevent the target products from degrading.

Long-term use and the high salt content of seaweeds may result in salinity issues. Utilizing purified preparations may help to mitigate this problem. These problems can be avoided by adopting sporadic pauses in the application of seaweed and allowing a rain rinse phase to minimize salt content. The use of seaweeds from contaminated locations as fertilizer or soil conditioner would increase the pollutants in soil and plants because seaweeds are efficient heavy metal accumulators in marine and other ecosystems (95). Seaweed contamination levels must therefore be assessed before application. Additionally, sulfides produced by the anaerobic breakdown of sulfur compounds in seaweed may cause soil acidification as they are microbially oxidized to sulfates (96). Carrageenans, laminarins, and ulvans are the distinctive organic components of seaweed that set them apart from other major plants’ polymeric carbon compounds like cellulose, hemicellulose, and lignin. The soil microbial community also experiences these novel compounds, which may be resistant to biodegradation (97). In such cases, a thorough analysis of the long-term effects of seaweed use on the local microbial population of the soil should be conducted. Additionally, seaweeds are known to support a variety of microbial communities that generate antibacterial chemicals (98). It is crucial to determine the depth to which this microbial community has established itself in the soil. The seaweed-associated microbial population that has been introduced may boost soil nutrient turnover, which could form the cornerstone of better plant and soil health.

This review highlights the significance of seaweed-based bio-regulators derived from red, brown, and green algae in agricultural disease management. Seaweed extracts (SEs) offer a natural and sustainable alternative to synthetic chemicals, reducing the environmental impact of conventional agrochemicals while enhancing plant health. Their bioactive compounds stimulate plant defense mechanisms by activating pathogen-responsive genes, transcription factors, and defense-related enzymes, thereby improving disease resistance. Standardizing extraction techniques, application rates, and treatment methods is crucial to maximizing the effectiveness of SEs, as variations in composition influence their efficacy against different plant diseases. Further research is needed to evaluate and compare diverse seaweed species to determine their optimal use in various agricultural conditions. By refining dosage, method, and application frequency, SEs can be integrated into modern farming systems to enhance plant growth, improve soil health, and boost stress tolerance. This approach will strengthen confidence in SEs as reliable bio-regulators, promoting their widespread adoption in sustainable agriculture and contributing to eco-friendly crop management strategies.