Saline and alkaline soils and their grading
The main problem in amending alkaline soils is their degraded structure and toxicity resulting from the presence of sodium. The first step in amending such soils is to apply large amounts of calcium in the form of small particles of calcium sulfate (several tons per hectare) to displace sodium by calcium. The smaller the particles of calcium sulfate are and the more uniformly they are incorporated into the soil, the better and more rapidly sodium will be replaced by calcium. After the soil is amended by the application of calcium sulfate and its permeability increases, it will be leached as saline soil (that is, it will be washed).
Soils are divided into the following grades based on their agricultural suitability:
- Grade zero: These soils are free of salt and do not limit plant growth.
- Grade 1: Soil salt content affects sensitive plants but does not hamper growth of halophytic plants.
- Grade 2: Soil salt content decreases normal growth of all plant species.
- Grade 3: Soil salt content is high and only a few plant species (salt resistant plants ) are resistant to the salt content of such soils.
Note: Soil electrical conductivity (EC), which is a function of soil salt content, is the criterion used to determine soil grade. Soil pH must also be measured when studying saline and alkaline soils. In most soils with pH values higher than 9 there is a large amount of exchangeable sodium.