What is the optimal soil pH range for most cool-season turfgrasses, and which nutrients are affected when pH moves outside this range?

• A. pH 5.0–6.0; nitrogen availability decreases in alkaline soils; phosphorus decreases in alkaline soils; calcium toxicity occurs in acidic soils
• B. pH 7.5–8.5; iron and manganese increase in alkaline soils; phosphorus unaffected; aluminum toxicity in alkaline soils
• C. pH 6.0–7.0; iron and manganese availability decreases in alkaline soils; phosphorus availability can be limited in acidic soils; aluminum toxicity in strongly acidic soils
• D. pH 4.5–5.5; potassium and sulfur become unavailable; magnesium toxicity occurs

Answer: (C)

Nutrient availability in soil is driven by pH. Cool-season turfgrasses grow best when the soil pH is around 6.0 to 7.0 because at this range nutrients are most accessible to roots.

When the pH climbs above this range, iron and manganese become less soluble and available, so even if the soil contains these micronutrients, the turf may show deficiency symptoms due to reduced uptake. Conversely, when the pH drops below this range, phosphorus can become less available because it binds with iron and aluminum to form insoluble compounds; in the most acidic soils, aluminum becomes soluble and can be toxic to roots, hindering growth and nutrient uptake.

Thus the statement aligns with the typical pattern: the optimal range is 6.0–7.0; iron and manganese availability declines in alkaline soils; phosphorus availability can be limited in acidic soils; and aluminum toxicity occurs in strongly acidic soils.