pH Management inside Greenhouse

Maintaining proper soil/substrate and irrigation water pH inside a greenhouse is critical for nutrient availability, microbial activity, root health, and overall crop growth. Unlike open-field conditions, the closed and intensive system of greenhouse cultivation makes pH management more challenging but also more controllable.

Importance of pH in Greenhouse Cultivation

a. Nutrient availability:

• Most nutrients (N, P, K, Ca, Mg, S, micronutrients) are optimally available at pH 5.5–6.8.
• At low pH (<5.5): micronutrient toxicity (Fe, Mn, Al).
• At high pH (>7.5): micronutrient deficiencies (Fe, Zn, Mn, Cu).

b. Microbial activity: Beneficial microbes (Rhizobium, nitrifiers, decomposers) work best near neutral pH.

c. Root system growth: Optimum pH improves root proliferation and water uptake.

d. Pesticide & fertilizer efficiency: Certain agrochemicals lose effectiveness outside the optimum pH range.

Factors Affecting pH inside Greenhouses

• Irrigation water alkalinity (carbonate/bicarbonate content).
• Type of growing medium (soil, cocopeat, perlite, rockwool).
• Fertilizer used:

a. Ammonium-based fertilizers → lower pH.

b. Nitrate-based fertilizers → raise pH.

• Crop species: Blueberry prefers acidic soil (pH 4.5–5.5), while tomato/cucumber need near-neutral pH.
• Accumulation of salts in closed irrigation systems.

Techniques for pH Management inside a greenhouse

a. Monitoring and Testing

• Regular pH measurement of soil/substrate, irrigation water, and nutrient solution.
• Tools: pH meter, pH test kits, digital sensors.

b. Lowering pH (Acidification)

• Acid injection into irrigation water:

Sulfuric acid (H₂SO₄): common in commercial systems.

Phosphoric acid (H₃PO₄): also supplies P.

Nitric acid (HNO₃): supplies N.

• Elemental sulfur application: Converted by microbes to sulfuric acid.
• Ammonium-based fertilizers (ammonium sulfate, ammonium nitrate).

c. Raising pH (Alkalinization)

• Lime application: Agricultural lime (CaCO₃), dolomitic lime (CaMg(CO₃)₂).
• Potassium carbonate or bicarbonate for minor adjustments.
• Nitrate-based fertilizers (Ca(NO₃)₂, KNO₃).

d. Buffering Capacity of Growing Medium

• Use substrates with good buffering capacity (peat, cocopeat with lime correction).
• Avoid inert substrates (perlite, rockwool) unless nutrient solution is precisely managed.

e. Integrated Fertigation Management

• Balance between ammonium-N and nitrate-N to stabilize pH.
• Continuous fertigation with acidified water prevents pH drift.