What are the nutritional indicators of fish protein fertilizers?
The nutritional specifications for fish protein fertilizers are categorized into four core areas-organic nutrients, macronutrients, secondary and micro-nutrients, and bioactive substances-alongside mandatory safety limit standards.
Organic Nutrient Specifications
These constitute the core nutritional components of fish protein fertilizers. In accordance with the Ministry of Agriculture and Rural Affairs' current industry standard for "Fish Protein Fertilizers" and the 2024 updated technical specifications for aquatic-derived fertilizers, key testing parameters include total free amino acids, crude protein, and the proportion of small-molecule peptides. For liquid formulations, the total free amino acid content must be ≥80 g/L, while for powder formulations, it must be ≥30%. Crude protein content must be ≥150 g/L for liquid fertilizers and ≥50% for powders. Small-molecule peptides must account for at least 30% of the total free amino acids; these small-molecule nutrients can be directly absorbed by crop roots and foliage without requiring further breakdown.
Macronutrient Specifications
These primarily refer to the total content of nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O). The combined N+P₂O₅+K₂O content must be ≥50 g/L for liquid fish protein fertilizers and ≥20% for powders. In high-quality products, amino nitrogen accounts for at least 60% of the total nitrogen; this form of amino nitrogen-derived from fish protein hydrolysis-is more easily absorbed and utilized by crops than inorganic nitrogen fertilizers and is less likely to result in soil nitrogen residues.
Secondary and Micro-nutrient Specifications
These include essential secondary and micro-nutrients such as calcium, magnesium, sulfur, iron, zinc, boron, and manganese. Specifications require a total secondary and micro-nutrient content of ≥20 g/L for liquid formulations and ≥6% for powders. Most of these nutrients exist in chelated or free forms to prevent soil fixation and enhance crop absorption efficiency. Some products tailored for specific crops feature enhanced levels of certain elements; for instance, formulations designed for fruits and vegetables often contain higher levels of boron and zinc to promote flowering and fruit set.
Bioactive Substance Specifications
These are the distinctive parameters that set fish protein fertilizers apart from conventional chemical fertilizers. They primarily include natural plant growth regulators (such as indole-3-acetic acid, gibberellins, and cytokinins), betaine, and polysaccharides. In accordance with industry standards, liquid fertilizers must contain at least 0.1 g/L of indole-3-acetic acid and a total polysaccharide content of at least 50 g/L; these substances regulate crop growth and enhance resistance to cold and drought.
Safety Limit Indicators
In compliance with the Ministry of Agriculture and Rural Affairs' fertilizer safety standards, heavy metal limits must be clearly stated-specifically, lead ≤5 mg/L, arsenic ≤2 mg/L, and cadmium ≤1 mg/L. Additionally, the moisture content of powder products must not exceed 15%, and the pH value of liquid products must be maintained between 5.5 and 8.5 to ensure no harm is caused to soil or crops during use.
