Macronutrient Ratios (Guidance Targets)

Why ratios matter

Uptake is governed by ion competition, CEC occupancy and root transport. A nutrient can be adequate in absolute terms but poorly available because another nutrient is dominating uptake pathways.

Ratios describe balance, not a fixed recipe.

Key ratios (guidance ranges)

Ca:K (meq basis)

Typical working range: 0.7–1.2 : 1
High K commonly suppresses Ca uptake and can reduce fruit quality and tissue strength.

Ca:Mg (meq basis)

Typical working range: 3–6 : 1
Low Ca:Mg can weaken structure; excessive Mg can suppress Ca movement.

K:Mg

Typical working range: 2–5 : 1
High K frequently induces Mg deficiency.

N:S

Typical working range: 10–15 : 1
Sulphur deficiency limits protein synthesis and reduces N use efficiency.

NO₃⁻:NH₄⁺

Typical substrate guidance: 80–95% NO₃⁻
Small NH₄⁺ proportions can be useful; excess NH₄⁺ suppresses Ca/Mg/K and can damage roots.

Interpretation

Ratios should be interpreted alongside EC, pH and Mulder’s interactions. They are most useful for explaining secondary deficiencies and guiding cautious correction.