Fertilizer EC Contribution

Greenhouse tomato programs target 2.0–3.0 dS/m final solution EC in winter (vegetative growth) and may push to 4.0 dS/m in summer to throttle vegetative vigour and increase fruit Brix. Field crops generally see lower targets because they receive larger water volumes per dose, diluting the fertilizer contribution. Date palms — salt-tolerant with FAO DP29 threshold 4.0 but productive far above it with adequate leaching — tolerate solution EC well above 4.0 in irrigation, but Siwa-Oasis-grade water already at 4–6 dS/m is the limiting factor: any fertilizer added pushes the mix past root-damage thresholds for sensitive co-planted crops, so growers there separate fertigation events from leaching events temporally.

Operationally, the engine treats EC contribution as a planning hint, not a control loop. Real fertigation operators use an EC sensor on the manifold to dose injection in real time — when the sensor reads a target deviation > 0.2 dS/m, the pump rate adjusts. WiseYield's v1 engine emits the planned EC contribution (Σ kg × ecAt1GPerL / waterLiters) and a target final-solution EC; closing the loop with IoT sensors is Blueprint Enhancement #40. Until then, the formula transparency on each event lets the operator verify the math against their inline EC reading and flag drift.

Non-ionic fertilizers contribute near-zero EC: urea (the workhorse N source) and humic acid sit near 0. Ionic fertilizers contribute proportional to their charge density: ammonium sulfate ≈ 1.4, calcium chloride ≈ 2.4, sulfuric acid ≈ 1.95. Substituting low-EC sources matters in saline-water situations — replacing KCl with K2SO4 trades a Cl-toxicity risk for slightly lower EC contribution and identical K nutrition.