Why Silicon Form Is Critical
K₂SiO₃ (potassium metasilicate):
- Concentrate pH 11–12
- Below pH 9 it converts to Si(OH)₄
- At pH 6.0–7.0 stable up to 100 mg/L; above 150–200 mg/L — polymerisation risk
K₂SiO₃ + Ca²⁺: immediately forms an insoluble calcium silicate precipitate — they are incompatible for direct mixing.
Stabilised silicic acid: compatible with Ca, no restrictions on addition order, but more expensive.
Benefits of Silicon for Plants
- Mechanical protection: leaves and stems become harder for thrips and mites to pierce (50–150 mg/L Si)
- Resistance to fungal disease: epidermal cell deposits provide a barrier against Botrytis, powdery mildew, and Fusarium
- Stress tolerance: improves water balance under heat and osmotic stress
Safe Application of K₂SiO₃
Option 1 — Separate tank C:
Dilute to EC <0.3 and pH <9.0, add to reservoir first, then add parts A and B.
Option 2 — Sequential addition:
Fill reservoir to 80–90% → add K₂SiO₃ → mix → adjust pH to 6.0–6.5 with acid → add parts A and B.
Option 3 — Stabilised form: no addition order restrictions.
Three Critical Mistakes
- Adding K₂SiO₃ directly into a solution containing calcium — results in a gel-like precipitate in pipes and drippers
- Not correcting pH after K₂SiO₃ addition — silicate raises pH to 8.0–9.5, causing iron and micronutrient precipitation
- Exceeding 200 mg/L — polymerisation risk increases sharply
Signs of a Correct Setup
- Solution remains clear immediately after addition and after 24 hours
- pH corrected to 5.8–6.2 before fertilisers are added
- No gel in drippers after one week