These soils are sometimes consolidated, blocky and poorly drained. The best indicator of sodicity in a soil is the sodium adsorption ratio or SAR, which compares the amount of sodium to calcium and magnesium. Generally, soils with SAR greater than 15 are considered sodic. The most common way to deal with sodic soils is to add another cation, such as calcium or magnesium, to displace the sodium. But good drainage is essential.
Alkalinity refers to the acidity of the soil.
The parameter most often used to refer to soil alkalinity is pH. Soils with pH greater than about 8.7 are considered alkaline. Alkalinity also is commonly associated with poorly drained sites. Hence, before any action can be taken to lower the pH, good drainage must be insured. Ample additions of organic matter, increased cropping intensity or large amounts of sulfur can be used to lower the pH and create more acidic conditions. You can have a soil with all of these conditions at the same time, though it is not likely.