Sodium in irrigation water

High sodium ions in water affects permeability of soil and causes infiltration problems. Sodium when present in the soil in exchangeable form replaces Calcium and Magnesium adsorbed on clay soils and causes dispersion of soil particles. 

This dispersion results in breakdown of soil aggregates, the soils become hard and compact when dry and reduces infiltration rates of water and air (aeration) into the soil therefore affecting soil structure. 

Other problems caused to crops by excess Sodium ions include the formation of crusting seedbeds, temporary saturation of the soil surface, high pH, and an increased potential for diseases, weeds, soil erosion, lack of Oxygen and inadequate nutrient availability.