pH is a measure of the acidity or alkalinity of your soil, a logarithmic scale on which 7 is neutral. Soil pH has a major impact upon nutrient uptake. Most minerals are most available to the plant at a soil pH of 6.4, so this is considered the ideal soil pH. Acidic soils will render some minerals less available and alkaline soils will also compromise nutrient uptake. Please see the diagram below highlighting this phenomenon. An oversupply of hydrogen drives soil acidity, but hydrogen disappears from the equation when the soil pH is above 7 (neutral).
If you have inherited a high pH soil, driven by an excess of magnesium, or sodium, or both, then it is a good strategy to bypass the associated soil lockups via direct route into the leaf. In this case it is always a productive strategy to foliar spray iron, manganese and boron at least twice per season, as they are the minerals most impacted by high pH soils. If your soil pH is 8.0, for example, it can be tremendously effective and profitable to compensate with foliar applications of iron, manganese and boron (in cereal crops, usually at the five leaf stage and again immediately before flowering).