Soil Health · January 2025 · 5 min read
Soil pH is one of the most fundamental factors controlling nutrient availability in your fields. Even with perfect fertilizer rates, a pH that is too high or too low can lock up essential nutrients and slash yields. Understanding and managing pH is a low-cost, high-return practice every farmer should prioritize.
The pH scale runs from 0 to 14, with 7.0 being neutral. Most field crops perform best in a slightly acidic to neutral range of 6.0 to 7.0. Below 5.5, aluminum and manganese can reach toxic levels, while above 7.5, phosphorus, iron, and zinc become increasingly unavailable.
Each full point on the pH scale represents a tenfold change in acidity, so a soil at 5.0 is ten times more acidic than one at 6.0. Small shifts can have outsized effects on crop performance.
When pH drifts out of the optimal range, nutrients already present in the soil become chemically bound and unavailable to plant roots. This is known as nutrient lockout. Phosphorus is especially sensitive, becoming tied up with aluminum at low pH and calcium at high pH.
To raise pH, apply agricultural lime (calcium carbonate) or dolomitic lime if magnesium is also low. Lime reacts slowly, so apply it at least three to six months before planting for best results. Typical rates range from one to three tons per acre depending on soil buffer pH.
To lower pH, eleite sulfur or ammonium-based fertilizers are the most common options. Elemental sulfur is oxidized by soil bacteria into sulfuric acid, gradually reducing pH over several months. Always base application rates on a proper soil test and buffer index.
🧶 Analyze your soil numbers with our free tool:
Try the Soil Test InterpreterTest your soil pH every two to three years to track trends and catch problems early. Sample to a consistent depth of six to eight inches, and pull cores from at least 15 locations per field to get a representative average.
For the most accurate results, test at the same time of year each cycle. Fall testing gives you time to apply lime before the following growing season, letting it react through winter moisture and freeze-thaw cycles.