PO 36: Define the following terms

Buffer pH is used to estimate a soil's exchangeable acidity; the degree of change in buffer pH is related to lime needs.  Buffering occurs when an acid (for instance, H⁺) and a base (for instance, OH^-) react and form a neutral product (in this case, H⁺ + OH^- → H₂O).

Alkalinity is the term used to describe the amount of base in a soil when the pH is above 7.  At higher alkalinity, there are fewer hydrogen ions (H⁺), and more hydroxyl ions (OH^-).

Basically, pH is a measure of active acidity, telling you whether you need lime or not.  Buffer pH and exchangeable acidity measure the buffer capacity, telling you how much lime you need to add.

There are several causes of soil acidity, including the leaching of basic cations (Ca²⁺, Mg²⁺, K⁺; leaving behind Al³⁺, which is acidic), crop uptake of basic cations and release of acids, decay of plant residues, acid rain, and the reaction of nitrogen fertilizer.

There are many benefits of liming: it prevents the toxic effects of aluminum, increases availability of essential nutrients, supplies plant needs for Ca and Mg, improves soil conditions for microorganisms, increases effectiveness of some key herbicides, and improves soil texture.