When soluble carbonate salts are found, the soils generally have coarse textures. When the soil pH is greater than 9.5 live plant roots are vulnerable to deterioration. High pH affects plant growth by reducing availability of some plant nutrients. Phosphates are most avail-able to the plant at a pH between 6 and 7. Micronutrients such as iron, manganese, zinc, copper, and cobalt are all much less available at a pH greater than 7.
Permeability is the ease of air and water movement through soils.
This is needed for good plant growth. A dense layer of clay occurs at or near surface of sodic soils. This natural layer, often called a claypan, is a barrier to roots. Most roots are restricted to the topsoil above the claypan, because movement of water, nutrients, and gases is too slow in the claypan. A dry claypan can be hard enough to physically restrict root penetration.