Climate changes have exacerbated the progression of drought conditions on a global scalethreating to crop production and heightening concerns over food security. Water scarcity enforces alterations in fundamental morphology, physiology and biochemical traits in crops. Consequently, it is imperative to identify environmentally sustainable alternative solutions to mitigate this problem and enhance overall plant performance.

Introduction

In recent years, changes in climate patterns have exerted a significant influence on agricultural regions, particularly manifesting notable impacts in arid, semi-arid, and coastal regions. Currently, approximately one-third of arable lands are categorized as arid or semi-arid regions, with the severity of drought exhibiting an escalating trajectory. Drought is a major abiotic stressor, exerting profound detrimental effects on crops worldwide. Forecasts predict a notable increase in mean air temperature by 5 ℃ in forthcoming years, further exacerbating the prevalence of drought occurrences and intensities.

The negative impact of drought stress on plants is contingent upon both the intensity and duration of the stress, with its severity intricately linked to the developmental stage of the plant. Drought stress elicits a spectrum of effects on plants at multiple levels of biological organization, encompassing anatomical and biochemical aspects(Figure 1).

In terms of morphology, the impact of water scarcity on crops is manifested by observable reductions in plant growth and hastened leaf senescence. These conspicuous phenotypic changes culminate in a pronounced deterioration in both the quality and quantity of yield, serving to underscore the profound deleterious effects of drought stress on agricultural productivity.

At the physiological level, water stress ‘pushes’ plants to close their stomata, a pivotal mechanism aimed at reducing water loss by transpiration and thus conserving water resources. This response inevitably limits the diffusion of carbon dioxide (CO2) into the leaf for photosynthetic assimilation. Furthermore, drought stress disrupts the hydraulic conductivity of plants, impeding the upward movement of water from roots to shoots. This disruption not only compromises the transport of water and essential nutrients but also disturbs the delicate balance of osmotic regulation within plant tissues.

At the biochemical level, the imposition of drought-induced water deficits triggers an elevation in the production of reactive oxygen species (ROS) within plant cells. This surge in ROS levels instigates oxidative stress, which can inflict damage on cellular structures and biomolecules. In response, plants activate an array of antioxidant defense mechanisms to scavenge excess ROS and mitigate oxidative injury, thereby preserving cellular integrity and function.

In the face of the escalating challenges posed by drought stress on crop productivity, the strategic application of biostimulants emerges as a compelling imperative. These substances and/or microorganisms offer a multifaceted approach to strengthen plant resilience, enhance physiological processes, and ameliorate the detrimental consequences of water deficit conditions on crop production. Under European Community Regulation (EU) 2019/1009, plant biostimulants have been delineated based on four distinct claims: Plant biostimulants are EU fertilizer products intended to stimulate plant nutrition processes regardless of the nutrient content of the product. Their primary objective is to improve one or more of the following plants and/or rhizosphere characteristics: (1) nutrient use efficiency, (2) tolerance and resistance to biotic and abiotic stressors, (3) quality attributes, or (4) availability of nutrients confined in the soil or rhizosphere. Under the current regulatory framework, biostimulants are subject to classification, a fundamental process designed to delineate their various constituents and functional attributes. Within this framework, biostimulants have been systematically categorized into two principal groups: microbial and non-microbial. The microbial classification encompasses organisms such as beneficial fungi and bacteria, while the non-microbial category encompasses a broad spectrum of substances, including plant and seaweed extracts, biopolymers, protein hydrolysates, amino acids, humic acids, and minerals. This classification schema is integral to regulatory coherence and scientific elucidation within the realms of agricultural and environmental jurisprudence, offering a structured framework for the assessment and management of biostimulant products.

The effectiveness of nonmicrobial biostimulants is mainly attributed to their rich repertoire of bioactive compounds, particularly amino acids and phytohormones. These constituents exert pronounced effects on plant growth dynamics by intricately modulating primary metabolic pathways. They also play a pivotal role in orchestrating secondary metabolic processes within plants.

Originally confined primarily to organic agricultural practices, plant biostimulants have undergone a notable expansion in their utilization, permeating various cropping systems, including conventional and integrated crop production methodologies. This evolution highlights a fundamental shift in the perception and application of biostimulant technologies, signifying their broader recognition and acceptance within the agricultural community. Such widespread adoption signifies a pivotal shift in agricultural practices, wherein biostimulants are increasingly acknowledged as valuable tools for enhancing crop productivity and sustainability across diverse farming paradigms.

Humic Acids

Origin and Effectiveness of Humic Acids as Biostimulants in Agriculture

Humic substances (HS) are the product of intricate chemical and biological processes involving the incorporation of organic materials derived from plant and animal residues, along with microbial metabolism. Humic substances represent the predominant reservoir of organic carbon within Earth’s terrestrial ecosystems. Constituting over sixty percent of soil organic matter, they serve as a fundamental component in organic fertilizers. For this reason, HS are recognized for their significant nutrient content. Humic substances, integral components of soil and natural organic matter, are traditionally categorized into distinct classes, namely humic acids (HA), fulvic acids (FA), and humins. This classification is mainly based on the solubility behavior of these substances in aqueous environments. Due to their chemical reactivity, ability to resist microbial interactions, and lower degradation, researchers have turned their focus to humic acids for their remarkable ability to improve fertility and promote soil health in a relatively short time. The structure of HAs comprises numerous functional groups, with phenolic (OH) and carboxylic (COOH) groups being predominant.

Humic acids represent a constituent of organic matter serving as a precursor to humic compounds, and they exhibit solubility under acidic conditions. The presence of several functional groups in humic acids results in unique characteristics that can promote plant development by inducing carbon uptake and metabolism. In addition to its role in carbon cycling, the utilization of HAs has been shown to augment nitrogen metabolism by enhancing the activities of key enzymes such as nitrate reductase (NR), glutamate dehydrogenase (GDH), and glutamine synthetase (GS), all of which are integral to nitrogen assimilation pathways.

At the soil level, HA supplementation enhances the physicochemical properties of the soil, improving its structure, texture, microbial abundance, water-holding capacity (WHC) and soil nutrient availability. As a result, root growth is stimulated, promoting the exudation of molecular weight organic anions by roots, which culminates in the release of soil micronutrients such as Fe, Mn and Zn. Humic acids have been observed to facilitate crop growth through a myriad of metabolic mechanisms. These include increased cell membrane permeability, enhanced mineral assimilation, elevated rates of photosynthesis and respiration, and enhanced protein synthesis and hormonal activities. The increased promotion of root and leaf growth and development has a considerable impact on the commercial quality and market value of plant products. The impact of HA on soil and crop dynamics is contingent upon the specific source of HS utilized. The selection of an HA source is predicated upon a multitude of factors, including its nutritional composition, method of production, functional group distribution, and intended application purpose. A comparative analysis of five distinct HA sources, scrutinized for their efficacy in influencing crop agronomic parameters, revealed a hierarchical trend in their effectiveness.

Morphological, Physiological, and Biochemical Changes Induced from Humic Acids to Mitigate Drought Stress in Agriculture Crops

Drought stress poses a significant threat to global agricultural productivity, necessitating the exploration of innovative strategies to mitigate its adverse effects. Among these strategies, the application of humic acids has garnered attention due to their multifaceted beneficial effects on plant growth and stress tolerance. The application of HAs has been correlated with discernible morphological alterations in plants experiencing drought stress. Their ability to augment stomatal conductance and improve water use efficiency contributes to the amelioration of water loss and the preservation of cellular hydration status. Additionally, HAs have been demonstrated to upregulate the enzymatic scavenging of ROS, thereby enhancing the antioxidant defense mechanisms within plant cells.

As shown in Table 1, humic acid improves the utilization of various crop physiological and biochemical reactions under water-deficient conditions. It is investigated the impact of drought stress on Cucumis melo cultivated under greenhouse conditions. Plants were subjected to drought stress (100% and 50% of field capacity irrigation) from 35 to 77 days after seed sowing. Aiming to mitigate the effects of water scarcity, plants received liquid humic acid at a dose of 2000 mg L−1 applied via irrigation. The findings obtained revealing an increase in leaf SOD, CAT, and GR activities and a reduction in leaf H2O2 concentration. Also it is assessed the performance of onions cultivated under greenhouse conditions and subjected to three different levels of water stress (80, 70 and 60% field capacity). Drought stress was imposed during both vegetative and reproductive stages. To mitigate the adverse effects of water scarcity, solid humic acid powder (1 g per pot) was applied. The results demonstrated that onion plants showed increased leaf protein content as well as enhanced SOD and POD activities.

Humic Acids Description	Crop	Growing Conditions	Drought Stress Treatment	Plant Growth Stage at the Stress Treatment Application	Effects of Humic Acids on Stressed Crops
Humic acid (C9H9NO6, seeds soaking for 12 h (0, 50, 100, 200 and 300 mg L−1))	Setaria italica Beauv.	Potted experiment under field conditions	3–5 leaf stage (set as 0 d), water application was stopped	10 d after drought treatment	Reduction in H2O2 and MDA content and SOD and POD activities increase,
Humic acid (5 mM) applied via fertigation	Fragaria ananassa	Glasshouse	100, 70 and 40% field capacity	From 4 weeks after sowing until 12 weeks after sowing	Increase in Chl content, reduction in leaf proline and MDA content
Humic acid (as 3-ethoxy-4-hydroxybenzaldehyde (foliar application (dose 5 mL per plant)) at 1 mM	Zea mays L.	Hydroponic	10% (w/v) PEG-6000 to achieve −0.15 MPa osmotic potential	Only 18 days	Reduction in electrolyte leakage and increased leaf membrane stability. Increase in pigments concentration.
Humic acid foliar application at different concentrations: 0, 3, and 6 mg L−1)	Brassica napus L.	Field	Drought treatments: 60, 100, and 140 mm evaporation from class A pan	Vegetative and early flowering stages	Increase in APX and POD activities and MDA level and soluble protein content
Humic acid application at 0, 2, 4 and 6 L per ha	Zea mays L.	Field	Three irrigation levels after depleting 30, 40 and 50% of field capacity (optimum irrigation, moderate stress and severe stress)	From 30 days after planting to 25 days before harvest (60 days approximately)	Higher yield and SOD and CAT activities
Humic acid foliar application (0, 150 and 300 ppm)	Triticum aestivum	Field	Complete irrigation, irrigation withholding at stem elongation stage, irrigation withholding at flowering stage and irrigation withholding at seed setting stage	Stem elongation, flowering and seed setting stages	Higher SOD and GPX activities and lower MDA content
Humic acid, foliar application in the volume of 4.5 L per one thousand liters of water	Oryza sativa	Field	Well-watered conditions, water restriction at the tillering stage and grain filling stage	Tillering and grain filling stages	Lower leaf proline content, reduced CAT activity and increased APX activity
Humic acid application through irrigation water (0 and 4 kg ha−1). two times during vegetative growth of roselle (15 and 35 days after emergence).	Hibiscus sabdariffa L.	Field	Water regimes [irrigation after pan evaporation of 100 mm (normal irrigation) and 200 mm (deficit irrigation)]	After the first week of seed sowing until the harvest (approximately 7 months)	Enhanced acidity and maturity index in calyx of roselle
Humic acid application through irrigation water (0 and 4 kg ha−1).	Zea mays	Greenhouse	100 and 60% water holding capacity	28 days after seedlings establishment	Enhanced photosynthesis by increasing the electron transport rate (ETR) of photosystem II (PSII) and the ratio between effective photochemical quantum yield to non-photochemical quenching (Y(II)/Y(NPQ)
Humic acid drenched in the soil (0, 250, 500 and 1000 mg kg−1)	Echinacea purpurea	Field	100, 80, 60 and 40% field capacity	After three months of sowing	Enhanced relative water content, electrolyte leakage reduction and higher content of total phenolic and flavonoid content in shoot

Genes Involved in Drought Tolerance in Agriculture Crops Treated with Humic Acids

The application of HAs in agriculture has been proved to alter genes expression in crops contributing to various physiological and biochemical changes that enhance plant growth, stress resilience, and yield. Stress-responsive genes, nutrient uptake genes, hormone-related genes, defense-related genes and genes expression networks can be stimulated under the application of HAs as briefly presented in Table 2.

Biostimulant	Crop	Growing Conditions	Drought Stress Treatment	Genes Activated by Drought Stress
Liquid phase, rate of 60 Kg ha−1 in 3 equally doses (first in germination, second two weeks later and third: initiation of flowering)	Vigna radiata	Field	No irrigation after 15 days from the vegetative stage until the reproductive stage	Upregulation of VrHsfA6a genes and VrDREB2a, and VrBZIP17 transcription factors
Foliar spray of HA at increasing concentrations (50, 100, 200, 300, and 400 mg L−1)	Setaria italica Beauv.	Field	Dry region simulating a drought environment	Upregulation of SETIT_021707mg, SETIT_016840mg, and SETIT_015030mg genes and downregulation of SETIT_004913mg and SETIT_016654mg genes
Drenching into the soil with two different rates: 0 and 45 Kg ha−1	Zea mays	Field	Drought stress (W1, 45–60% soil water holding capacity (SWHC)) and well-watered (W2, 75–100% SWHC).	Upregulation of psbQ and psbP genes (encoding the extrinsic proteins of PS II complexes) and genes involved in the Calvin cycle regulation
Foliar spray of HA at 1% w/v	Triticum aestivum	Hydroponic	After the 7th day of drought stress treatments (MD, moderate drought (−6 bar PEG6000); HD, high drought (−8 bar PEG6000)	Downregulation of miR396-targeted growth-regulating factor (GRF) and AP2 gene (miRNA Apetala 2) in root and upregulation in leaf

Seaweed Extract

Origin and Effectiveness of Seaweed Extracts as Biostimulants in Agriculture

Macroalgae belong to Phaeophyta, Rhodophyta, and Chlorophyta classes, also known as brown, red, and green algae, respectively based on their color. Their use by humans has deep roots. They have been used in medicine, cosmetics, and in agriculture as food to feed animals and as fertilizers, since the ancient Romans. The use of algae extracts instead has more recent uses. They have been called plant biostimulants for their ability to promote plant growth and improve the nutritional aspect and shelf life. The biostimulant action of algae extracts has not been attributed to their nutritional content (macronutrients) but to elicitor compounds capable of activating the physiological responses of the treated plants. Algae extracts regulate plant growth similarly to phytohormones as they stimulate, or slow down growth based on their concentration. The phytohormone-like activity is due to the content of indole acetic acid, cytokinin, gibberellic acid, polyamines, and abscisic acid in the seaweed extracts. They are rich in phenolic compounds with antioxidant activity, osmolytes such as mannitol and betaines, amino acids, vitamins. They also contain polysaccharides (alginates and laminarins) that promote plant growth and act as elicitors of plant defense against pathogenic infections.

The concentration of these substances and hormonal activity depends on the type of seaweed, seasonality, extraction method, and the type of processing they undergo.

Seaweed extracts are generally in liquid or soluble powder form. In liquid form, the extracts can be mixed into irrigation water and applied as drip irrigation to the crops, or as foliar sprays. Seaweed extracts effectively depends on the growth stage of the plants and is highest when the stomata are open.

Ascophyllum nodosum, Ecklonia maxima, Macrocystis pyrifera, and Durvillea potatorum are the main brown macroalgae (Phaeophyta) used to produce extracts intended for agriculture and horticulture. The main bioactive compound found in these macroalgae are summarized in the Table 3.

Species	Main Bioactive Compound	Cellular Action
Ascophyllum nodosum	Indoleacetic acid; Abscisic acid	Increase of roots number and length; regulation of stomata closure
Ecklonia maxima	1-aminocyclo-propane-1-carboxylic acid; Abscisic acid	Precursor of ethylene synthesis, it promotes flowering and fruit ripening; regulation of stomata closure
Macrocystis pyrifera	Molecules with auxin-like activity	Increase of roots, fruit setting
Durvillea potatorum	Fibres, alginic acid, laminarin, fucoidan, mannitol	Regulation of response to pathogens

Brown algae extracts are found to improve the soil water retention capacity, root growth and soil microbial activity. Some extracts have modified the acidification activity of the plasma membrane proton pumps by inducing the secretion of H+ ions, the rhizosphere, and increasing the solubility of some useful ions for plants. Brown algae extract increased the absorption of copper, iron, calcium, potassium, and magnesium in grapevine, lettuce, cucumbers, and tomatoes, especially when the plants are in sub-optimal growth conditions or under environmental stresses. Higher nitrogen and sulfur uptake were detected, too.

The bioactive compounds in the algae extracts are considered responsible for the increased tolerance to biotic and abiotic stresses of numerous crops. Ascophyllum nodosum extracts applied to strawberry and lettuce plants allowed increased plant and root growth under salinity conditions. Yield and antioxidant defense increases were found in tomato plants grown in saline conditions and treated with Dunaliella salina extracts. Chickpea plants treated with Sargassum muticum extracts had a greater tolerance to salinity due to the restoration of the ionic balance, a better antioxidant defense, and better regulation of the amino acids synthesis, compared to plants not treated with a biostimulant.

The Padina gymnospora seaweed extract improved the salinity tolerance of tomato plants due to the increase in photosynthetic activity, stomatal conductance, and the content of antioxidant enzymes. Brassica juncea plants under thermal stress conditions had better growth and yield and less membrane impairment when treated with seaweed extract (3 mL L^-1 and 5 mL L^-1). The positive effect of seaweed extracts under salt stress conditions was also observed in pepper plants. Extracts of Ascophyllum nodosum and Sargassum spp. sprayed on barley plants increased the plants’ tolerance to cold through proline and non-structural carbohydrates increase, and osmotic adjustment.

Seaweed extracts have antifungal properties against Macrophomina phaseolina (Tassi) Goid., and Fusarium oxysporum, blocking the growth of their mycelium. The mycelial growth of four plant pathogenic fungi (Botrytis cinerea, Aspergillus niger, Penicillium expansum, and Pyricularia oryzae) was blocked using Gracilariopsis persica extract at 1000 μL .

Others examined the response of Thompson seedless grapes (Vitis vinifera L.) to the extracts of Ascophyllum nodosum in an experiment conducted over three years. The extract was applied as a spray at different stages: before and after flowering, before and during the sizing stage, during veraison, and in pre-harvest. For all three years of the experiment, the authors obtained a positive effect of the treatment on the total number of fruits, on the uniformity and weight of the berries, on the number of primary bunches, on the number of berries per bunch, with increases in yields, compared to untreated control plants.

However, the activity and mechanisms of action of algae and algae extracts on plants depend on various factors, such as the type of algae, the extraction mechanism, and the plant species. For future studies, it would be interesting to understand the possible synergistic effect of extracts from different algae. Likewise, the plants stage should be understood to have the best benefits following the application of the extract.

Morphological, Physiological, and Biochemical Changes Induced from Seaweed Extracts to Mitigate Drought Stress in Agriculture Crops

Broccoli and spinach plants treated with A. nodosum extracts had better resistance to drought stress due to an increase in gaseous exchange parameters, compared to untreated plants. Another symptom of drought stress is leaf yellowing caused by chlorophyll degradation. Extracts of A. nodosum have been shown to increase the chlorophyll content in tomato plants subjected to water stress. Drought-stressed tomato plants had improved plant height, root length, and the number and area of the leaves when treated with a microalgae-based biostimulant.

Extracts of A. nodosum reduced wilting, increased WUE, and accelerated recovery of several drought-stressed vegetables. Extracts of A. nodosum also increased the water potential of almond plants under high-temperature conditions. According to some authors, the cytokine-like activity and the increase in K⁺ absorption induced in the plants treated by seaweed extracts explained the tolerance of creeping bentgrass to heat.

Foliar application of brown algae extract (A. nodosum) alleviated drought stress by increasing the synthesis of antioxidant enzymes, the accumulation of defense metabolites, and growth and sugar production in sugarcane plants.

Someone applied marine algae extracts to 12 blueberry species grown in greenhouse pots under controlled stress conditions (the substrate was maintained at 40% field water). The authors showed an increase in the activity of antioxidant enzymes (peroxidase and catalase) in plants subjected to water deficit, compared to untreated control plants, with no differences in nutrient and chlorophyll content between treated and control plants. Similarly, others showed that fertilization of blueberry fruit plants with algae increased the content of antioxidant molecules (anthocyanins and total polyphenols) in drought-stressed plants.

An increase in phenolic, proline, and flavonoid content was also shown in ornamental plants (Spiraea nipponica and Pittosporum eugenioides) subjected to mild drought stress condition. Citrus sinensis L. drought-stressed improved water use efficiency when treated with extracts of A. nodosum.

Some other examples are summarized in Table 4.

Seaweed Extracts Description	Crop	Growing Conditions	Drought Stress Treatment	Plant Growth Stage at the Stress Treatment Application	Effects of Protein Hydrolysates on Stressed Crops
Ascophyllum nodosum/ Foliar spray	Solanum lycopersicum (cv. Moneymaker)	Growth into pots placed in a growth room and filled with vermiculite/perlite and slow releaser fertilizer	Interruption of watering for 7 days	35-day-old tomato plants	Increase in: RWC, plant growth, foliar area, chlorophyll, proline, soluble sugars Decrease in lipid peroxidation
Ascophyllum nodosum/aminoacidic Soil application/foliar spray	Brassica oleracea var. italica	Growth into pots placed in a growth chamber and filled with peat and complex fertilizers	Interruption of watering for 2 days	Seven weeks after planting	Increase in photosynthesis, stomatal conductance, and chlorophyll content
Ascophyllum nodosum/ foliar and drench	Spinach (cv. Bloomsdale)	Growth into pots filled with sand and topsoil, placed in a growth chamber	100% (full irrigation) and 50% (drought stress) evapotranspiration	3 weeks after sowing	Increase in plant growth, leaf relative water content, area, fresh weight, dry weight, and specific leaf area, improvement of gas exchange parameters Decrease in ferrous ion chelating ability
Ascophyllum nodosum/ Foliar application	Saccharum spp.	Field	driest period of the year	late-harvest sugarcane	Increase in biomass production and stalk yield, sugar yield, antioxidant enzyme activity, and cellular redox balance Decrease in malondialdehyde content
Extracts from Fucus spiralis, Ulva lactuca, Laminaria ochroleuca, and Ascophyllum nodosum/soil drench and foliar spray	Vicia faba (cv. Super Aguadulce)	Growth into pots filled with natural soil and placed in a covered shelter	Water withholding for 10 days	40 days after sowing	Increase in plant biomass, relative water content, proline content, and soluble sugars content Decrease in malondialdehyde content
Ascophyllum nodosum	Soybean	Growth into pots irrigated with nutrient solution and placed in a growth chamber	75 h of water interruption	14 days after transplanting	Increase in relative water content, stomatal conductance, and antioxidant activity
Ecklonia maxima	Chicorium intybus	Growth into pots filled with peat and placed in a greenhouse	Moderate (60–70% of water holding capacity) and severe (30–40% water holding capacity) stress	7 days after transplanting	Increase in fresh biomass, relative water content, water use efficiency, nitrogen use efficiency, P, K, Ca and Mg content, chlorophyll content, proline and total polyphenols content Decrease in plant growth traits and yield and N content

Genes Involved in Drought Tolerance in Agriculture Crops Treated with Seaweed Extracts

Seaweed extracts have been found to increase chalcone isomerase, the plant phenylpropanoid precursor enzyme involved in plant defense against stress.

A. nodosum extract was found to increase the gene expression encoding the nitrate and auxin transporter NRT1.1. in Arabidopsis thaliana. In this way, the extract caused an increase in the growth of lateral roots and the assimilation of nitrate. Furthermore, commercial A. nodosum extract was found to increase the expression of the NodC rhizobial bacterial gene. This gene is involved in the rhizobia-plant interaction and the induction of root nodule formation. Therefore, in the presence of the extract, leguminous plants had a greater number of nodules and fixed more nitrogen. Extracts from a commercial brown algae extract increased the expression of genes encoding enzymes regulating nitrogen metabolism, antioxidant activity, and glycine betaine synthesis in treated spinach plants. The increase in these enzymes was associated with an increase in phenolic compounds, total soluble proteins, and the antioxidant capacity of plants.

Biostimulant Super Fifty obtained from Ascophyllum nodosum repressed the stress-responsive negative growth regulator (RD26) in Arabidopsis thaliana plants subjected to drought stress. In this way, the plants had an active cell cycle during stress. Furthermore, stressed plants treated with the biostimulant increased the expression of CYCP2;1, a gene that promotes meristem cell division.

Conclusions

The biostimulants ability to enhance soil health, promote nutrient uptake, and mitigate drought stress renders them highly attractive in the pursuit of sustainable, climate-resilient agriculture. The scientific community has placed significant emphasis on biostimulants due to their potential to enhance plant growth and resilience, particularly under stressful conditions such as drought.

Several promising areas warrant further investigation in future research on the role of biostimulants as alleviators of drought stress in plants. For instance, conducting long-term, multi-season field trials is crucial to assess the sustained efficacy of biostimulants and to address the poor lab-to-field translation, as well as the lack of robustness across varying climatic conditions. Moreover, the optimization of biostimulant formulations, alongside precise tailoring of their timing and dosage, should be adapted to specific crops, soil types, and environmental conditions to maximize drought-mitigation potential. Emphasizing the agroecological perspective of these products through a range of field experiments, particularly in the contexts of organic farming, agroforestry, and regenerative agriculture practices is essential. Such studies are key to developing resilient agricultural systems in drought-prone regions, ensuring that biostimulants align with sustainable farming principles and contribute to long-term environmental and agricultural sustainability.

In any case, it should be made clear that the application of biostimulants, regardless of their origin, will not be able to replace synthetic fertilizers but could help reduce their use by improving the sustainability of agricultural production.

Dora Agri is a leading company focused on researching and promoting natural, organic biostimulants and bio fertilizers for sustainable agriculture and horticulture.

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