Answer:
a. SAR is the Sodium adsorption ratio of the water used for irrigation purpose. SAR is ratio of sodium concentration to that of calcium and magnesium concentration.This value is also useful while managing soils that have high concentration of sodium which can occur naturally in some soils. Although sodium is a macro-nutrient for plants, higher concentration of sodium can cause the displacement of the calcium and magnesium ions in soil which can affect the soil structure by preventing aggregation of clay in the soil resulting in a decrease in the infiltration rates.
b. EC is the electrical conductivity of the soil which depends on the salinity of the soil. High salinity means more solutes in water and this increases the osmotic potential of the soil solution making it difficult for plants to absorb water.