Which type of acidity is most important in determining the required lime rate?

The type of acidity that is most important in determining the required lime rate is residual acidity. Residual acidity represents the acid that persists in the soil even after the active acidity (measured by pH) has been neutralized. It accounts for the total acid content of the soil, including that which is held on soil particles and is not readily available to neutralization through a simple addition of lime.

When assessing the need for lime, understanding residual acidity helps determine how much lime is necessary to not only raise the soil pH to the desired level but also to effectively combat the long-term acidity that can affect soil health and crop production. Correctly estimating this requires analyzing soil samples to gauge both the active and residual acidity levels.

Active acidity refers to the hydrogen ions in the soil solution and provides an immediate measure of soil pH, whereas potential acidity considers the total acidity that can affect soil chemistry but is less relevant when determining lime needs. Saline conditions are characterized by high levels of soluble salts and do not directly relate to the acidity constraints. Thus, it is the residual acidity that plays the pivotal role in calculating the proper lime rate for effective soil management.