Fertilizer Compatibility

The Ca-P precipitation rule is the single most common cause of clogged drip lines in real operations. Calcium nitrate is the standard fertigation Ca source, MAP/DAP/MKP are standard P sources — and operators new to fertigation routinely pre-mix them in one stock tank "to save labour". The precipitate forms within minutes, drops out of solution as a milky suspension, and cements in the emitters within hours. Recovery requires acid flushing the entire system; the cost in lost flow uniformity often exceeds the original fertilizer cost. The rule is absolute: separate Ca tanks from P/S tanks, inject through different ports, or split the events temporally (Ca on Mon, P on Thu).

The K-vs-Mg ratio rule is subtler. Programs with high-K stages (fruit-set, fruit-development) push K2O totals to 200+ g per palm per week — beneficial for fruit quality but problematic when soil Mg is already marginal. Calcium and potassium compete with magnesium for root-uptake sites; an applied K:Mg ratio above 4:1 by mass starts to suppress Mg uptake even when soil Mg looks adequate on paper. The engine flags this as a warning (not critical) and suggests adding MgSO4 to bring the ratio toward 4:1.

The chloride rule is the connection point between §9.2 salinity and §9.3 fertigation. KCl is the cheapest K source globally — but on saline irrigation water (water EC > 3 dS/m) the chloride load from KCl stacks on top of the chloride already in the irrigation water, pushing leaf %Cl above the 0.5–1.0 toxicity threshold. The engine flags this and proposes K2SO4 substitution: same K nutrition, no Cl load, modestly higher cost.

The pH rules govern P availability and irrigation-system longevity. Above pH 7.5, soluble phosphate precipitates as Ca/Mg phosphates within hours of contact with calcareous soil; chelated P or banded placement compensates. Above 2 meq/L bicarbonate, drip emitters scale with carbonate precipitates that progressively degrade flow uniformity. The mitigation in both cases is acid injection — phosphoric, sulfuric, or nitric — to bring irrigation pH to ~6.0. WiseYield's engine emits an inline tip when bicarbonate exceeds 2 meq/L on a drip system.