Nutrient Solution Preparation for Soilless Culture: Stock Solutions, Working Solutions, and Operating Procedures

Nutrient Solution Preparation for Soilless Culture: Stock Solutions, Working Solutions, and Operating Procedures

The correct preparation of nutrient solution is one of the key technologies in soilless culture. Improper preparation may cause certain nutrient elements to precipitate, resulting in nutrient loss, imbalance in root absorption, or even plant death. Therefore, strict procedures and accurate calculations are essential.

3.3.1 Preparations Before Nutrient Solution Preparation

1. Select and Adjust the Nutrient Solution Formula

The nutrient solution formula should be selected and adjusted based on the following factors:

• Crop species and growth stage (especially N–P–K requirements)

• Local water quality and climate conditions

• Fertilizer purity

• Cultivation method (e.g., substrate culture)

• Production cost

Key considerations:

• Regional differences in water quality and fertilizer purity directly affect nutrient composition.

• Different crops and growth stages require different nutrient ratios.

• Substrate cultivation may alter nutrient composition due to substrate adsorption and inherent nutrients.

• Formula selection should balance nutritional requirements and economic feasibility.

👉 Nutrient formulas should be flexibly selected, adjusted, tested, and validated before large-scale application.

2. Review Relevant Materials

Before preparation:

• Carefully read fertilizer and chemical labels.

• Confirm molecular formulas, water of crystallization, and purity.

3. Select Appropriate Fertilizers

Choose fertilizers that:

• Provide balanced nutrient content and proportions

• Have high solubility

• Feature high purity and low impurities

• Are cost-effective

4. Select Water Source

• Choose a suitable water source.

• Conduct water quality testing if necessary to guide formula adjustments.

5. Prepare Equipment

Nutrient solutions are typically prepared as 100–1000× concentrated stock solutions.

Required equipment includes:

• 2–3 stock solution tanks (25 L or 50 L, preferably dark/lightproof)

• Plastic buckets and basins

• Beakers

• Balances (top-loading and analytical)

• pH meter

• Electrical conductivity (EC) meter

• A storage tank for preparing the working solution

3.3.2 Methods for Nutrient Solution Preparation

(1) Preparation of Stock Solutions

Basic process:
Calculation → Weighing → Dissolution & Volume Fixing → Recording & Storage

① Calculation

Using the Japanese Garden Test Nutrient Solution as an example (Table 3-14), calculate the actual dosage of each compound based on the required concentration factor.

Important notes:

• Most fertilizers used in soilless culture are agricultural or industrial grade, containing moisture or impurities; adjust calculations based on actual purity.

• In hard water areas:

  • Subtract Ca²⁺ and Mg²⁺ already present in water from Ca(NO₃)₂·4H₂O and MgSO₄·7H₂O dosages.

  • Supplement reduced nitrogen using HNO₃, which also neutralizes water alkalinity.

  • If pH remains high, reduce phosphate and use phosphoric acid for neutralization.

  • If solution is too acidic, increase KNO₃ and reduce K₂SO₄.

  • Reduced MgSO₄·7H₂O lowers SO₄²⁻, but hard water generally contains sufficient sulfate; supplement with H₂SO₄ if needed.

Table 3-14. Japanese Garden Test Nutrient Solution

② Weighing

• Weigh each fertilizer separately

• Store in clean containers or plastic bags

• Accuracy requirement: ±0.1 g

③ Dissolution, Mixing, and Volume Fixing

• Dissolve fertilizers that do not cause precipitation together

• Stir continuously until fully dissolved

Stock solution tanks:

• Tank A (Ca-based): Fertilizers compatible with Ca²⁺

• Tank B (Phosphate-based): Fertilizers compatible with PO₄³⁻

• Tank C (Fe-based):

  • Prepare chelated Fe solution first

  • Dissolve trace elements separately

  • Slowly add trace elements to Fe solution while stirring

Fill each tank to the final volume and mix thoroughly.

④ Recording and Storage

• Label each stock solution clearly

• Maintain preparation records for future reference

• For long-term storage:

  • Adjust solution pH to 3–4 using HNO₃

  • Store in plastic containers in a cool, dark place

Stock Solution Label (Example)

• Stock solution ID

• Concentration factor

• Preparer

• Preparation date

• Storage condition: Cool, dark place

• Long-term storage: Adjust pH to 3–4 with HNO₃

Table 3-15. Stock Solution Preparation Record

(2) Preparation of Working Solutions

① Dilution of Stock Solutions

Steps:

1. Calculate required stock solution volume:
   V₂ = V₁ / n

2. Adjust water pH as required.

3. Add 60–70% of final volume to storage tank.

4. Add Tank A solution and circulate for 30 min.

5. Slowly add Tank B solution with water flow; fill to 80%.

6. Add Tank C solution; fill to final volume and circulate.

7. Measure and adjust pH and EC.

8. Allow solution to stand ≥30 min, circulate again, and recheck.

9. Complete preparation records.

⚠️ Avoid rapid addition to prevent local high concentrations and precipitation.

② Direct Preparation of Working Solutions

For large-scale production:

• Weigh fertilizers directly according to formula.

• Prepare Tank C stock solution.

• Add fertilizers in A → B → C sequence.

• Circulate, test, adjust pH and EC, and record data.

3.3.3 Operating Procedures for Nutrient Solution Preparation

To minimize errors:

• Carefully verify fertilizer names, formulas, and purity.

• Label all materials and containers clearly.

• Calculation results must be verified three times by three staff members.

• Ensure all materials and tools are ready before preparation.

• Use non-metal tools for handling NH₄NO₃ and KNO₃.

• Maintain complete records for traceability and optimization.

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