Fertigation Mixing Order and Precipitation Risk
Build a verified fertigation solution without concentrating incompatible salts, losing nutrients to precipitates, or creating avoidable worker and equipment hazards.
Educational reference · evidence, sources, and limits shown below
Build a verified fertigation solution without concentrating incompatible salts, losing nutrients to precipitates, or creating avoidable worker and equipment hazards.
Terms to know
- Stock solution
- Concentrated fertilizer solution designed for controlled dilution before crop delivery.
- Precipitate
- Solid formed from dissolved ions after a chemical reaction or solubility limit is exceeded.
- Compatibility
- Ability of products and water chemistry to remain stable and usable at the intended concentration and temperature.
- Injector ratio
- Relationship between stock volume drawn and final irrigation volume delivered.
Core science
Mixing order is chemistry control. Calcium salts can react with concentrated phosphate or sulfate to form poorly soluble solids. Micronutrients can precipitate or become unstable at unsuitable pH, and hard or alkaline source water can increase risk. A clear tank does not prove complete recovery, while visible sediment is an immediate deviation.
Commercial programs commonly separate incompatible concentrates into A and B stocks, then inject them into moving water at sufficient dilution. Each salt is dissolved according to manufacturer solubility and compatibility information. Concentrates are never combined casually, and fertilizer is added to an adequate water volume under controlled mixing rather than creating localized supersaturation.
The safe sequence is site-specific because products, acids, disinfectants, water, temperature, injector design, and materials differ. Acid handling and oxidizer compatibility belong under dedicated SDS- and manufacturer-based procedures. Fertilizers, pesticides, sanitizers, and concentrated acids must not be improvised into one stock system.
Why this matters in cultivation
- Precipitation silently changes the delivered formula, clogs emitters, distorts EC, damages injectors, and creates nonuniform deficiency even when the recipe calculation was correct.
- Verification samples should be collected from final delivery points after the system stabilizes, not only from stock tanks or the mixing reservoir.
Measure and record
Water prerequisite
Temperature, pH, alkalinity, hardness, Ca/Mg, sulfate, bicarbonate, EC, and filtration.
Product identity
Exact product, lot, analysis, solubility, compatibility chart, SDS, and expiry or storage state.
Stock preparation
Tank, water volume, product mass, sequence, mixing time, final volume, temperature, and operator.
Injection
A/B assignment, injector ratio and calibration, interlocks, flow, pressure, and stabilization time.
Verification
Stock appearance, filters, emitter pH/EC, laboratory ion check when needed, uniformity, and deviation action.
Common misconceptions
Correction: Compatible individual solubility does not prevent reactions between concentrated ions.
Correction: A precipitate can change specific ions while the remaining solution still conducts electricity.
Correction: Formulations, concentrations, water chemistry, acids, and equipment require product-specific instructions.
Evidence limits
This lesson defines controls, not a universal chemical recipe. Site procedures must follow product labels, SDSs, equipment manuals, qualified water analysis, and applicable worker-safety requirements.
Related encyclopedia topics
- THC-ENC-086, THC-ENC-123-136, THC-ENC-138-140, and THC-GROW-080.
Source notes
- University of Tennessee Extension. Plant Nutrition and Fertilizers for Greenhouse Production.
- University of Georgia Extension. Fertilizer Injectors: Selection, Maintenance and Calibration.
- Penn State Extension. Interpreting Irrigation Water Tests.
- THC Cultivation SOP Source Materials Packet v1.0 (project source, May 2026).
This lesson summarizes the source material and its evidence limits for education. Use direct measurement, controlled comparison, and the cited sources when conditions differ or a decision carries meaningful risk.