Which Is Better: Humic Acid, Amino Acids, Fish Protein, or Seaweed Extracts?

In today’s market, there is a growing range of “new-generation” water-soluble fertilizers and functional additives-humic acids, amino acids, fish protein hydrolysates, seaweed extracts, and more. Many growers find them difficult to distinguish, and even some distributors and manufacturers struggle to explain their differences clearly.

In reality, these products are not “nutrient fertilizers” in the traditional sense. They are derived from different sources and work through different mechanisms. Most of them fall under biostimulants or bioactive organic substances-acting as fertilizer efficiency enhancers, soil conditioners, or plant physiological regulators rather than direct suppliers of large amounts of N, P, and K.

According to internationally recognized definitions:

• FAO and the European Commission indicate that biostimulants mainly work by improving nutrient use efficiency, enhancing stress tolerance, and supporting quality performance-rather than providing substantial nutrient quantities.

  
  

• The EU regulation Regulation (EU) 2019/1009 recognizes plant biostimulants as an independent product category with dedicated management requirements.

In agricultural practice, humic acids, amino acids, fish protein, and seaweed extracts are commonly used as:

• Growing media or soil amendment additives

• Rooting and root-strengthening additives

• Soil conditioners

• Plant growth regulators (in a broad practical sense)

• Foliar fertilizer formulation components

• Anti-stress agents (cold, drought, salinity, etc.)

• Efficiency enhancers for compound fertilizers

Below is a structured overview of each category and how to choose the most suitable option.

1. Humic Acid Fertilizers

1.1 Background and Production

Humic acid fertilizers are widely produced and used in China and many other markets. They are typically manufactured using raw materials such as peat, lignite (brown coal), and weathered coal, processed by different extraction or conversion methods to produce products rich in humic substances. These products are often formulated together with nutrients such as nitrogen, phosphorus, potassium, and certain micronutrients.

In practice, humic acid fertilizers can be viewed as a type of organic–inorganic hybrid product: they contribute to soil improvement, support nutrient availability, and stimulate crop growth performance.

1.2 Key Functional Characteristics

(1) Enhancing Nitrogen Efficiency

Nitrogen fertilizers commonly include ammonium-based nitrogen and urea. Ammonium nitrogen is relatively unstable and can be prone to volatilization losses. Humic substances contain functional groups (such as carboxyl and phenolic groups) with ion-exchange and adsorption capacity, which can help reduce ammonium nitrogen loss when used in combination.

(2) Enhancing Phosphorus Efficiency

Water-soluble phosphorus fertilizers may be rapidly fixed in soil. Adding humic substances can help reduce fixation of soluble phosphorus, slow down the conversion from available forms to less available forms, and support better phosphorus uptake by roots.

(3) Enhancing Potassium Efficiency

Humic substances can adsorb and store potassium ions, reducing leaching in sandy or highly permeable soils and reducing potassium fixation in heavy soils. Certain low-molecular humic fractions (such as fulvic acids) may also promote gradual potassium release from potassium-bearing minerals.

(4) Enhancing Micronutrient Availability

Soils may contain significant micronutrient reserves, but only a small portion is plant-available. Humic substances can react with sparingly soluble micronutrients to form complexes that are more soluble and easier for plants to absorb. This can support both root uptake and foliar uptake, and facilitate nutrient redistribution within the plant.

(5) Indirect Soil Improvement

Humic substances can improve soil structure and help reduce cracking and erosion.

• Physical effects: improve water-holding capacity, increase drought resilience, darken soil color which can support heat absorption.

• Chemical effects: help regulate pH, improve nutrient and water uptake, and act as natural chelators under alkaline conditions to support uptake of certain elements.

  
  

Fish Protein Fertilizers (Fish Protein Hydrolysates)

2.1 What They Are

Fish protein fertilizers are produced by crushing or grinding fish and shrimp by-products and using endogenous enzymes or microbial digestion to break down proteins into small peptides and amino acids.

They are used in various product forms, including fertigation products, foliar fertilizers, and water-soluble formulations. Some formulations also include micronutrients, plant growth factors, enzymes, or microbial catalysts.

In many markets, fish-protein-related products are often produced by smaller or medium-sized companies, frequently originating from traditional coastal fish-processing and fish-protein raw material industries.

2.2 Typical Benefits

1. Supplementing bioactive organic nutrition (peptides and amino acids)

2. Helping relieve soil compaction issues caused by long-term heavy use of mineral fertilizers (in practice, mainly through organic input and microbial stimulation)

3. Promoting soil microbial growth, activating soil nutrients, and improving soil fertility

4. Enhancing stress tolerance, including cold and drought resilience

In recent years, improved marine resource utilization and extraction processes have reduced raw material costs, and fish protein products have become more affordable than in the past.

Amino Acid Fertilizers

3.1 What They Are

Amino acids are major organic nitrogen compounds in soils and can originate from microorganisms, plants, animals, and their metabolites. Amino acids are also important nutrient sources for soil microbes and may serve as precursors for substances involved in plant growth regulation.

Commercial amino acid fertilizers are often produced as amino acid chelated multi-micronutrient fertilizers, sometimes derived from animal hair hydrolysates (including by-product streams after cystine extraction). Amino acids may also be extracted from animal hair or plant protein sources and then combined with micronutrients using specific chemical synthesis processes, forming organic-form multi-micronutrient products.

3.2 Key Functional Characteristics

When used as fertilizer components, amino acids mainly serve as:

• A supplementary organic nitrogen source

• Chelating/complexing agents for metal ions

Amino acids can complex metal ions and help carry micronutrients (Ca, Mg, S, B, Mn, Zn, Fe, Cu, Mo, Se, etc.) into plant tissues, improving nutrient use efficiency.

Main features:

1. Mixed amino acids often perform better than single amino acids; mixtures can show stronger effects than equal-nitrogen applications of inorganic nitrogen sources in certain contexts.

2. Fast response: amino acids may be absorbed directly by plant organs, delivering quicker visible effects compared with some fertilizers that require mineralization or transformation.

3. Support plant metabolic processes: amino acids are closely linked to enzyme formation and metabolic regulation.

4. Amino-acid-chelated micronutrients can enhance uptake efficiency, improve yields, and contribute to quality improvements.

   
   

Seaweed Fertilizers (Seaweed Extracts)

4.1 What They Are

Seaweed extracts are produced through biotechnological extraction from seaweed. They typically contain bioactive components such as plant-growth-regulator-like substances (often discussed as cytokinin-like and gibberellin-like activity), along with alginic acid, vitamins, oligosaccharides, minerals, and other marine bioactive compounds.

Seaweed extracts may also contain significant amounts of non-nitrogen organic substances and naturally accumulated minerals (K, Ca, Mg, Fe, Zn, etc.) from the marine environment.

Seaweed fertilizers are available as powders, liquids, or dehydrated dry products, and are generally positioned as green and environmentally friendly inputs.

4.2 Typical Benefits

1. May promote rapid cell division and growth (linked to hormone-like activities)

2. Improve nutrient status and enhance stress tolerance

3. Promote root development, support yield improvement, and quality enhancement

4. Activate beneficial soil microbial communities and improve fertilizer utilization efficiency

5. Improve soil physicochemical properties and help reduce soil compaction

6. Compatible with many fertilizer programs, supporting synergistic use

   
   

Comparison Table

Item	Humic Acid	Amino Acids	Fish Protein	Seaweed Extract
Raw material source	Lignite, peat, weathered coal	Hydrolyzed plant/animal proteins	Hydrolyzed marine fish proteins	Seaweed (e.g., brown algae)
Main components	Humic acid, fulvic acid	Free amino acids, small peptides	Small peptides, amino acids	Alginates, polysaccharides, hormone-like bioactives
Primary function	Soil conditioning, nutrient retention	Fast absorption, micronutrient chelation	Soil + microbial activation	Stress tolerance, rooting, physiological activation
Typical application	Base application, fertigation	Foliar spray, fertigation	Fertigation, drip irrigation	Foliar spray, drip irrigation
Speed of response	Medium to slow	Fast	Medium	Fast
Stress tolerance	Medium	Medium	Medium	Strong
Best for base application	Excellent	Moderate	Good	Moderate

How to Choose the Right Type

There is no universally “best” option-only the most suitable choice for your specific agronomic goal and field conditions.

Practical selection guidelines:

• Soil compaction, low organic matter, weak structure → prioritize humic acids

• Rapid micronutrient delivery or foliar correction → amino acids are often more suitable

• Organic farming and quality-oriented production, microbial stimulation → fish protein

• Drought, low temperature, salinity, transplant shock, or other stress conditions → seaweed extracts

A mature fertilization strategy typically follows this principle:

Mineral nutrition as the foundation, and functional bioactive substances as adjustment tools.

In other words, these inputs work best when integrated into a balanced nutrient program rather than used as stand-alone solutions.