About Fertilizer Supplements and Plant Growth Stimulants

Introduction

Potato (Solanum tuberosum L.) cultivation requires meticulous nutrient management to attain optimal yields typically ranging from 30-50 t/ha, given the crop's shallow root system (20-40 cm depth) and substantial nutrient demands, such as 100-200 kg/ha of NPK. Fertilizer supplements, focusing on micronutrients, fill critical gaps in standard macronutrient regimens, mitigating yield reductions of up to 20-30% from deficiencies like zinc, which affects tuber formation. Plant growth stimulants, known as biostimulants, augment physiological functions without supplying primary nutrients, bolstering tolerance to stresses including drought, salinity and pathogens. In diverse regions such as the U.S. Midwest, Europe and India, where soil heterogeneity is prevalent, these adjuncts can elevate yields by 10-30%, diminish non-marketable tubers by 1-3 t/ha and support biofortification with elements like iron and zinc for nutritional enhancement.

When integrated with base fertilizers potentially substituting 50-70% they promote sustainable agriculture compliant with standards like USDA NOP or EU Organic Regulations, though soil testing is essential to avert toxicities. This guide explores their functions, classifications, advantages, application strategies and supporting evidence from field trials, advocating for integrated approaches to foster resilient potato farming. Additional considerations include the role of secondary nutrients like calcium, magnesium and sulfur, which support tuber quality and plant structure and the importance of monitoring environmental factors like soil organic matter to optimize uptake efficiency.

What Are Fertilizer Supplements?

Fertilizer supplements are specialized nutrient inputs, primarily consisting of micronutrients such as boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), chlorine (Cl) and nickel (Ni). They are applied in small quantities (typically 0.1–5 kg/ha) to correct specific nutrient deficiencies that primary macronutrients (NPK) alone cannot address. Unlike standard fertilizers, these supplements target secondary and trace nutrient needs, often supplied in chelated, sulfate or liquid formulations that enhance bioavailability achieving 70–90% uptake efficiency compared to 10–50% from conventional soil applications.

In potato cultivation, micronutrient deficiencies can lead to issues such as stunted growth due to manganese deficiency in alkaline soils or poor tuber quality caused by boron deficiency, which leads to internal browning or hollow heart. Fertilizer supplements play critical roles in enzyme activation, photosynthesis and hormone regulation, thereby enhancing overall plant vigor and productivity.

Experts, including those from Yara, emphasize maintaining soil pH between 6.0 and 6.5 to minimize nutrient antagonisms such as excessive iron interfering with zinc uptake. Certified supplements ensure low contaminant levels and proven efficacy, typically validated through tissue analysis, which has shown 15–25% yield improvements in nutrient-deficient conditions.

Beyond micronutrients, fertilizer supplements may also include secondary nutrients such as calcium (for tuber skin integrity and reduced hollow heart), magnesium (for chlorophyll synthesis) and sulfur (for protein formation). This integrated approach is particularly valuable in sandy or low-organic-matter soils prone to leaching, supporting both nutrient balance and sustainable potato production.

Types of Fertilizer Supplements for Potatoes

Supplements for potatoes are customized to developmental stages and include a range of micronutrients:

• Zinc (Zn): Applied at 1-3 kg/ha; vital for auxin production and tuber set; deficiency can slash yields by 20%, causing smaller tubers and delayed maturity.
• Boron (B): 1-1.5 kg/ha; supports cell wall integrity and pollen fertility; mitigates hollow heart and cracking.
• Manganese (Mn): 3-5 kg/ha; essential for chlorophyll and enzyme function; foliar sprays correct deficiencies in high-pH soils.
• Copper (Cu): 0.5-1 kg/ha; bolsters resistance to diseases like Rhizoctonia and improves lignin formation.
• Iron (Fe): 2-4 kg/ha; prevents chlorosis in alkaline conditions, aiding oxygen transport.
• Molybdenum (Mo): 0.1-0.2 kg/ha; facilitates nitrate reduction; crucial in acidic or sandy soils where availability is low. 

Commercial blends, such as YaraVita's micronutrient mixes containing Mn, Zn, B and Cu, or EDTA-chelated liquids, ensure balanced provision. Nano-formulations enhance uptake by 30%, reducing application rates and environmental impact. Missing from initial coverage are chlorine (Cl), which aids osmosis and disease suppression at trace levels and nickel (Ni), involved in urea metabolism. Secondary supplements like calcium nitrate prevent internal defects, while sulfur sources improve amino acid synthesis. In trials, phosphite-based supplements have shown promise as both nutrients and fungicide alternatives, enhancing root health.

What Are Plant Growth Stimulants (Biostimulants)? 

Biostimulants are non-nutritive substances or microorganisms that enhance plant physiological processes, improving growth, nutrient uptake efficiency (NUE by 20–40%) and stress tolerance without acting as direct fertilizers. According to EU Regulation 2019/1009, biostimulants include humic and fulvic acids, seaweed extracts, amino acids and microbial inoculants that function through mechanisms such as hormone signaling, modulation of gene expression and stimulation of beneficial rhizosphere microbiota.

In potato cultivation, biostimulants promote root elongation by 20–30%, enhance tuber uniformity and strengthen resistance against abiotic stresses (e.g., drought, heat, salinity) as well as biotic stresses (e.g., pathogens). Unlike agrochemicals, they possess low toxicity and are compatible with organic and sustainable farming systems. Field studies have demonstrated yield improvements of 10–26%, alongside increased tuber dry matter and marketable yield. Certain compounds such as flavonoids and phenolic extracts further elevate plant antioxidant capacity, thereby improving physiological resilience.

Biostimulants also play a role in carbon sequestration and soil health improvement by enhancing photosynthetic efficiency and microbial activity, contributing to climate-resilient agriculture. Emerging categories now include protein hydrolysates, silicon-based products and microbial consortia (e.g., Bacillus, Trichoderma), which reinforce cell wall structure, stimulate root exudation and improve water-use efficiency.

Types of Plant Growth Stimulants for Potatoes 

Biostimulants are classified by source and action: 

• Seaweed Extracts (e.g., Kelpak SL from Ascophyllum nodosum): Contain auxins and cytokinins; boost root growth (up to 30%) and tuber count (+15-20%).
• Amino Acid Mixtures (e.g., Pilatus): Derived from hydrolysates; enhance protein synthesis and stress recovery; increase dry matter by 5-10%.
• Humic/Fulvic Acids (e.g., HumiPlant): Amend soil structure and chelate nutrients; improve potassium uptake (+10-15%).
• Chitosan (biopolymer): Induces defense pathways; cuts non-marketable yield by 1-2 t/ha and curbs pathogens.
• Flavonoid-Based (e.g., quercetin, chlorogenic acid extracts): Provide antioxidant support; yield gains of 10-25% in trials.
• Inorganic (e.g., potassium silicate): Reinforce cell walls; enhance resistance to lodging and mechanical damage.
• Microalgal (e.g., Algifol): Stimulate via amino acids; improve NUE under heat stress. 

Blends like Asahi SL (phenolics) offer synergy. Additional types include microbial biostimulants (e.g., mycorrhizal fungi, PGPR) that colonize roots for better nutrient absorption and protein hydrolysates that act as signaling molecules for growth promotion. Silicon-based stimulants are gaining traction for improving drought tolerance in potatoes.

Benefits of Fertilizer Supplements and Plant Growth Stimulants in Potato Production 

The integration of fertilizer supplements and plant growth stimulants (biostimulants) in potato production has demonstrated 10–30% yield improvements through a combination of nutrient deficiency correction, enhanced physiological efficiency and improved stress resilience.

Yield and Quality Enhancement: Micronutrient supplements significantly enhance tuber quality and nutritional value. For instance, zinc and iron supplementation can increase Fe/Zn concentrations in tubers by 20–50%, contributing to biofortification and improved human nutrition. These inputs also reduce tuber bruising, improve skin finish and elevate specific gravity, ensuring 18–22% dry matter content, which is desirable for processing industries (e.g., chips and fries). Boron and calcium applications further strengthen cell walls and reduce internal necrosis, improving overall marketable yield.

Nutrient Use Efficiency and Soil Health: Biostimulants enhance nutrient use efficiency (NUE) to 40–60%, compared to 20–30% under conventional fertilizer use. This improvement not only boosts yield but also reduces fertilizer requirements by 20–30%, leading to substantial cost savings. Long-term use enhances soil microbial diversity by up to 50%, promoting nutrient cycling, organic matter buildup and overall soil fertility.

Environmental Sustainability: By improving nutrient uptake and reducing losses, these technologies decrease nitrous oxide (N₂O) emissions by 20–40% and minimize fertilizer runoff, thereby reducing the risk of groundwater contamination. Biostimulants containing humic substances and microbial consortia also improve carbon sequestration, contributing to sustainable and climate-smart potato production systems.

Stress Tolerance and Disease Resistance: Certain biostimulants, such as chitosan, activate natural defense pathways, suppressing pathogens like Verticillium and Rhizoctonia. Seaweed extracts and amino acid formulations mitigate abiotic stresses particularly drought, salinity and heat by regulating osmotic balance and enhancing antioxidant enzyme activity. Collectively, these effects improve plant resilience under variable climatic conditions.

Economic and Post-Harvest Benefits: The combined use of supplements and stimulants results in 1–3 t/ha reduction in non-commercial tubers, increases the proportion of marketable (medium-sized) tubers by 20%, and provides a return on investment (ROI) of 5–10:1. Enhanced calcium and boron nutrition also improve post-harvest shelf life, reduce storage losses and minimize physiological disorders such as blackheart and hollow heart.

Contribution to Global Food Security: Through improved nutrient efficiency, stress tolerance and quality enhancement, these tools contribute to sustainable intensification producing more food with fewer inputs thus supporting global food security and environmental protection.

Application Methods: Foliar and Soil Incorporation 

Efficient application methods are crucial to maximize the benefits of fertilizer supplements and plant growth stimulants in potato production. Selection depends on nutrient type, soil characteristics, and crop growth stage.

Foliar Application: Foliar sprayssuch as zinc or boron solutions at 0.5–2 L/ha provide rapid absorption, achieving 70–90% uptake efficiency, making them ideal for mid-season corrections during the vegetative growth or tuber initiation phases. Spraying should be done using low-pressure nozzles and non-ionic surfactants or adjuvants to ensure even leaf coverage and minimize runoff. Applications should preferably occur during cooler hours (morning or late afternoon) to avoid leaf scorching and maximize uptake. Foliar feeding is particularly effective for micronutrients like Fe, Mn, Zn and B, which have limited soil mobility.

Soil Incorporation and Banding: Soil incorporation through banding or side-dressing provides a more gradual and sustained nutrient release, particularly for less mobile elements such as molybdenum and calcium. For instance, Mo applied at 0.1 kg/ha during planting enhances early enzyme activity and nitrogen metabolism. Mixing supplements with organic matter or compost improves nutrient mobility, reduces fixation and supports microbial activity. Band placement near the root zone ensures better accessibility and minimizes nutrient losses through leaching or volatilization.

Fertigation and Biostimulant Delivery: For biostimulants, fertigation (e.g., seaweed extracts via drip irrigation at 1–3 L/ha) is highly effective, achieving up to 80% utilization efficiency by synchronizing nutrient availability with irrigation cycles. This method enhances root-zone interaction, improves absorption uniformity and supports continuous stimulation throughout growth. Humic acids, amino acid blends and microbial formulations are particularly well-suited for fertigation due to their compatibility with irrigation systems.

Precision and Smart Technologies: Emerging precision agriculture tools, including drones, multispectral sensors and variable-rate applicators, allow for site-specific nutrient and biostimulant applications. These technologies help identify localized deficiencies, optimize input use and reduce application rates by 15–25%, contributing to sustainability and cost efficiency.

Seed and In-Furrow Treatments: Seed-piece treatments where micronutrients or biostimulants are applied directly to potato seed pieces promote early vigor, root initiation and disease resistance. Similarly, in-furrow applications at planting position nutrients close to emerging roots, ensuring immediate availability during early establishment. These techniques are particularly beneficial for immobile nutrients like phosphorus, zinc and calcium.

Compatibility Considerations: When mixing supplements and biostimulants, avoid chemical incompatibilities for example, iron (Fe) should not be mixed with phosphate-based fertilizers, as it can lead to precipitation and reduced availability. Always perform a jar test before tank-mixing different formulations and maintain correct pH levels (typically 5.5–6.5) for optimal stability and efficacy.

Timing and Rates for Applications 

Effective scheduling of nutrient and biostimulant applications is vital to support balanced growth and optimize tuber yield during the potato’s 90–120 day growth cycle. Applications should always be aligned with both soil and tissue analyses to ensure that nutrients are applied only when required, preventing deficiencies or toxic buildup.

Pre-Planting Stage: During the pre-planting stage, boron and molybdenum are critical for early root establishment and enzyme activation. Typically, 1–1.5 kg/ha of boron and 0.1–0.2 kg/ha of molybdenum are applied through soil incorporation or in-furrow blending with organic matter to enhance nutrient mobility. Maintaining a soil pH between 6.0 and 6.5 is important, as acidic conditions can reduce molybdenum availability. These applications lay the foundation for strong early vegetative growth and efficient nutrient uptake.

Vegetative Growth Stage (20–40 DAP): At the vegetative stage, the crop requires manganese and iron to promote chlorophyll synthesis and photosynthetic efficiency. Foliar applications of 3–4 kg/ha manganese and 2–4 kg/ha iron ensure vigorous canopy growth and better light interception. Low-pressure foliar spraying with surfactants allows uniform coverage while preventing leaf scorching. Complementary use of humic acid or microbial biostimulants during this phase can further strengthen root activity and soil microbial balance.

Tuber Initiation Stage (40–60 DAP): As tubers begin to form, zinc and copper become essential for hormonal regulation and enzyme activation. Application of 1–3 kg/ha zinc and 0.5–1 kg/ha copper helps improve tuber set, stress tolerance and disease resistance. Seaweed extracts at 2 L/ha, applied via foliar or fertigation, can further stimulate tuber initiation and uniform bulking. Care should be taken to avoid mixing copper-based products with phosphates or sulfur, as these can form insoluble precipitates that reduce nutrient availability.

Bulking Stage (60–90 DAP): The bulking stage represents the period of maximum nutrient demand, particularly for potassium, which influences tuber size, starch accumulation and overall yield. Around 250–300 kg/ha of potassium is typically supplied during this phase. Application of amino acids or chitosan-based biostimulants at 1–2 L/ha enhances nutrient use efficiency, stress resilience and uniform tuber development. Balanced nutrient and biostimulant supply during this phase ensures maximum conversion of photosynthates into tuber biomass.

Maturation Stage (90–120 DAP): In the final growth phase, the emphasis shifts to maintaining foliage vitality and improving tuber quality traits such as skin texture and storability. A low-dose foliar spray of seaweed or silicon-based biostimulants during this period can enhance skin firmness and improve post-harvest shelf life. Excessive nitrogen should be avoided, as it can delay maturity and negatively affect skin setting.

General Application Considerations: Across the entire growth period, total micronutrient inputs usually range from 5–15 kg/ha, with approximately 40% applied through soil and 60% via foliar routes. Biostimulants are best applied 3–5 times at rates of 1–3 L/ha depending on crop stress conditions and growth dynamics. Tissue testing remains a valuable diagnostic tool for instance, leaf zinc concentrations below 20 ppm indicate the need for supplementary application. On sandy soils, more frequent split doses are preferred to minimize leaching, whereas clay soils respond better to banded applications for localized nutrient availability. Nitrogen management should be split, with 50–70% applied at emergence and the remaining portion at 35–40 DAP, ensuring synchronization between nutrient release and plant uptake.

Considerations and Challenges 

The use of fertilizer supplements and biostimulants in potato cultivation offers substantial benefits but also presents several agronomic and management challenges that require careful consideration.

Nutrient Imbalance and Toxicity Risks: Excessive application of certain micronutrients can lead to phytotoxic effects that compromise yield and quality. For example, boron applied above 2 kg/ha may cause leaf tip burn and necrosis, while excessive copper can induce iron and zinc deficiencies by interfering with their uptake. Maintaining a soil pH of 6.0–6.5 is critical for nutrient availability, as acidic soils reduce molybdenum and calcium uptake, whereas alkaline soils restrict iron, manganese and zinc absorption. Balanced formulations and split applications help minimize such risks.

Variable Biostimulant Efficacy and Cost Constraints: The performance of biostimulants is highly dependent on formulation type, environmental conditions and application timing, with efficacy variations often ranging between 10–30%. Factors such as temperature, soil moisture and microbial activity strongly influence product performance. Although biostimulants are typically 15–40% more expensive than conventional inputs, their higher return on investment (ROI) is justified through enhanced yield stability and improved soil health. However, field validation through small-scale testing under local conditions remains essential before large-scale adoption.

Pathogen Interactions and Integrated Pest Management (IPM): Some micronutrients, such as copper, provide dual benefits by supplying nutrition and suppressing pathogens like Phytophthora infestans (late blight). However, indiscriminate use can lead to soil accumulation and microbial imbalance. Integrating nutrient management with IPM practices ensures synergy between disease control and plant nutrition, preventing overreliance on single compounds.

Environmental and Regulatory Challenges: Emerging formulations such as nano-fertilizers and nano-biostimulants show promising efficiency but face increasing regulatory scrutiny due to potential ecological and toxicity concerns. Ensuring environmental safety and compliance with regional guidelines is becoming a key part of sustainable nutrient management strategies.

Climatic and Soil-Related Constraints: Drought conditions can significantly reduce the effectiveness of foliar sprays, as nutrient absorption through stomata depends on adequate leaf hydration. Similarly, soils with excessive potassium levels can trigger secondary magnesium deficiencies, affecting photosynthetic performance and tuber development. Climate variability manifested through erratic rainfall and temperature extremes further challenges consistent nutrient uptake and biostimulant performance, demanding adaptive management and precision monitoring.

Sustainable Management Strategies: To mitigate these challenges, integrated practices such as routine soil and tissue testing, the adoption of hybrid organic–inorganic fertilization systems and the use of crop rotations are recommended. These strategies maintain nutrient equilibrium, promote soil microbial diversity and reduce dependency on external inputs. Continuous site-specific trials and the development of localized nutrient response databases will further refine application protocols, supporting both productivity and sustainability goals.