**1 Scope**
This standard specifies the technical requirements, test methods, inspection rules, marking, packaging, transportation, and storage of organic fertilizers. It applies to organic fertilizers made from fermented and decomposed byproducts rich in organic matter, such as livestock and poultry manure, crop residues, and other similar by-products. This standard does not apply to green manure, farmyard manure, or other organic manures produced by farmers themselves.
**2 Normative References**
The following documents contain provisions that, through reference in this standard, constitute provisions of this standard. For dated references, subsequent amendments (excluding errata) or revisions do not apply to this standard. However, parties entering into agreements based on this standard are encouraged to consider using the latest versions of these documents. For undated references, the latest version applies.
- Preparation of Standard Solution for GB 601 Titration Analysis (Capacity Analysis)
- GB/T 1250: Limit Value Representation and Determination Method
- GB/T 6679: General Rules for Sampling of Solid Chemical Products
- GB 6682: Specifications and Test Methods for Analytical Laboratory Water
- GB 8172: Agricultural Waste Control Standard for Towns
- Determination of Free Water Content in GB 8576 Compound Fertilizer by Vacuum Oven Method
- GB/T 15063: Compound Fertilizer (Compound Fertilizer)
**3 Terminology**
Organic fertilizer refers to materials primarily derived from plant and/or animal sources, which are applied to the soil to provide essential nutrients for plant growth.
**4 Requirements**
4.1 **Appearance**: Organic fertilizer should be brown or gray-brown, granular or powdery, free from mechanical impurities and malodor.
4.2 **Technical Indicators**: The technical indicators of organic fertilizers must meet the requirements listed in Table 1.
**Table 1 – Technical Indicators for Organic Fertilizers**
| Item | Indicator |
|------|-----------|
| Organic Matter Content (on dry basis), % | ≥ 30 |
| Total Nutrient (N + P₂O₅ + K₂O) Content (on dry basis), % | ≥ 4.0 |
| Moisture (Free Water) Content, % | ≤ 20 |
| pH | 5.5 – 8.0 |
4.3 **Heavy Metal Content, Maggot Mortality, and E. coli Value**: These parameters must comply with the requirements specified in GB 8172.
**5 Test Methods**
All water used in the tests shall conform to the third-grade water specifications of GB 6682. Reagents are generally of analytical grade unless otherwise stated. Standard solutions are prepared according to GB 601.
**5.1 Visual Appearance and Odor**
Visually inspect the sample for color, texture, and presence of impurities. Smell the sample to detect any unpleasant odor.
**5.2 Determination of Organic Matter Content**
**5.2.1 Principle**
A known amount of potassium dichromate-sulfuric acid solution is used to oxidize the organic carbon in the fertilizer under heating conditions. Excess potassium dichromate is titrated with ferrous sulfate solution, and the organic carbon content is calculated. The result is multiplied by a coefficient of 1.724 to obtain the organic matter content.
**5.2.2 Instruments and Equipment**
Standard laboratory equipment.
**5.2.3 Reagents and Preparation**
- Silica (powdered)
- Concentrated sulfuric acid (Ï = 1.84)
- Potassium dichromate standard solution (c[1/6(K₂Cr₂O₇)] ≥ 1 mol/L)
- Ferrous sulfate standard solution (c(FeSOâ‚„) = 0.2 mol/L)
- O-phenanthroline indicator
**5.2.4 Measurement Procedure**
Weigh 0.3–0.5 g of air-dried sample (φ 0.5 mm) into a 500 mL flask, add 30.00 mL of 1 mol/L K₂Cr₂O₇ solution, shake well, and heat for 30 minutes. Cool, dilute, and titrate with FeSO₄ solution. Perform a blank test.
**5.2.5 Expression of Results**
Organic matter (%) = [100 × (c × (V₀ - V) × 0.003 × 1.724)] / (M × D × (1 - X₀))
Where: c = concentration of FeSOâ‚„, Vâ‚€ = volume of FeSOâ‚„ in blank, V = volume of FeSOâ‚„ in sample, M = mass of sample, Xâ‚€ = moisture content, D = dilution factor.
**5.2.6 Allowable Difference**
- Parallel determination: ±0.8% for organic matter ≤ 45%, ±1.0% for >45%.
- Inter-laboratory difference: ±1.5% for ≤45%, ±2.0% for >45%.
**5.3 Determination of Total Nitrogen Content**
**5.3.1 Methodology**
Organic nitrogen is digested with sulfuric acid and hydrogen peroxide, converted to ammonium nitrogen, and distilled. Ammonia is absorbed in boric acid and titrated with standard acid.
**5.3.2 Reagents**
- Sulfuric acid (Ï = 1.84)
- 30% hydrogen peroxide
- Sodium hydroxide (40%)
- Boric acid (2%)
- Mixed indicator (bromocresol green + methyl red)
- Standard acid solution (0.05 mol/L)
**5.3.3 Instrument**
Nitrogen distillation apparatus.
**5.3.4 Procedure**
Digest 0.5 g of sample with Hâ‚‚SOâ‚„ and Hâ‚‚Oâ‚‚. Distill, absorb ammonia in boric acid, and titrate with standard acid.
**5.3.5 Expression of Results**
Total Nitrogen (N) (%) = [100 × (V - V₀) × c × 0.014] / (M × D × (1 - X₀))
**5.3.6 Allowable Difference**
- Parallel results: ±0.05% for N ≤ 1.00%, ±0.10% for >1.00%.
**5.4 Determination of Total Phosphorus Content**
**5.4.1 Methodology**
Phosphorus is digested with Hâ‚‚SOâ‚„ and Hâ‚‚Oâ‚‚, then reacted with ammonium vanadomolybdate to form a yellow complex. Absorbance is measured at 440 nm.
**5.4.2 Reagents**
- Sulfuric acid (Ï = 1.84)
- Nitric acid
- 30% hydrogen peroxide
- Ammonium vanadomolybdate reagent
- Phosphorus standard solution (50 μg/mL)
- 2,4-Dinitrophenol indicator
**5.4.3 Calibration Curve**
Prepare standards at 0–15 μg/mL and plot absorbance vs. concentration.
**5.4.4 Expression of Results**
Total Phosphorus (P₂O₅) (%) = [100 × c × V × 2.29] / (M × D × (1 - X₀))
**5.4.5 Allowable Difference**
- Parallel results: ±0.05% for P₂O₅ ≤ 1.00%, ±0.10% for >1.00%.
**5.5 Determination of Total Potassium Content**
**5.5.1 Methodology**
Potassium is digested with Hâ‚‚SOâ‚„ and Hâ‚‚Oâ‚‚, then measured using flame photometry.
**5.5.2 Reagents**
- Sulfuric acid (Ï = 1.84)
- 30% hydrogen peroxide
- Potassium standard stock solution (1 mg/mL)
- Potassium standard solution (100 μg/mL)
**5.5.3 Calibration Curve**
Standards at 0–20 μg/mL are measured, and a linear regression is performed.
**5.5.4 Expression of Results**
Total Potassium (K₂O) (%) = [100 × c × V × 1.20] / (M × D × (1 - X₀))
**5.5.5 Allowable Difference**
- Parallel results: ±0.05% for K₂O ≤ 1.20%, ±0.10% for >1.20%.
**5.6 Determination of Moisture Content**
Moisture is determined using the vacuum oven method as described in GB 8576.
**5.7 Determination of pH**
pH is measured by immersing the sample in water and measuring directly with a pH meter.
**5.8 Heavy Metal, Maggot Mortality, and E. coli Values**
These are determined according to GB 8172.
**6 Inspection Rules**
6.1 Quality indicators are evaluated using the "repair value comparison method" from GB/T 1250.
6.2 Manufacturers must ensure all products meet the standard and include quality certificates.
6.3 Users have the right to inspect products against the standard.
6.4 If a batch fails, it is retested; if still fails, the batch is rejected.
6.5 Sampling methods depend on the number of bags, with specific numbers provided in Table 2.
6.6 Disputes are resolved according to product quality arbitration regulations.
**7 Packaging, Labeling, Transport, and Storage**
7.1 Organic fertilizers are packed in plastic woven bags with inner polyethylene lining. Net weights include 50 kg, 40 kg, and 25 kg.
7.2 Packaging must indicate product name, trademark, organic matter content, total nutrients, net weight, standard number, company name, and location.
7.3 Store in cool, dry places and protect during transport from moisture, sunlight, and damage.
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