Soil pH
Soil pH is a measure of how acidic or alkaline a soil is, on a logarithmic scale from 0 to 14 where 7 is neutral. Most crops grow best between pH 6.0 and 7.0, where nutrients are most available. pH below 5.5 or above 7.5 can dramatically reduce yields by locking nutrients into forms plants cannot absorb.
How Soil pH Works
pH controls nutrient availability more than the absolute amount of nutrient in the soil. At pH below 5.5, phosphorus binds to aluminum and iron and becomes unavailable; at pH above 7.5, iron, manganese, and zinc become unavailable. This is why two fields with identical fertilizer application can show dramatically different crop growth if their pH differs.
Optimal pH ranges vary by crop: blueberries 4.5–5.5 (acidic), potatoes 5.0–6.0, corn and wheat 6.0–7.0, alfalfa and spinach 6.5–7.5. Match the crop to the field pH or amend the soil — adding agricultural lime raises pH, adding elemental sulfur or acidic compost lowers pH. Both amendments take months to fully shift pH, so soil testing should be done 6–12 months before planting.
A standard soil test (around €20–50 per sample through university extension labs) reports pH along with macronutrients (N, P, K), secondary nutrients (Ca, Mg, S), organic matter, and cation exchange capacity (CEC). The recommended amendment rate comes directly from this test. pH is one of the cheapest soil properties to correct — a €200/ha lime application can lift yields 20–30% on an acidic field — yet it is frequently overlooked because visible crop stress at low pH resembles nutrient deficiency. WiseYield links soil test results to crop selection and fertilizer recommendations automatically.
Sources
- USDA NRCS. Soil pH — soil quality indicator sheet.
- Penn State Extension (2023). Soil acidity and aglime.