Q112: Most hazardous element in the irrigation water in relation to... - Water Resources, Hydrology, Watershed Management & Water Quality - ICAR AIEEA PG 2024 - Water Science and Technology | Agrigyan

Sodium ($Na^+$) is the most hazardous element/ion in irrigation water. An excess of sodium relative to divalent cations ($Ca^{2+}, Mg^{2+}$), evaluated via the Sodium Adsorption Ratio (SAR), causes dispersion of clay aggregates, slaking, hard-setting, crusting, and drastic loss of soil permeability and aeration. Sodium also causes specific ion toxicity in crops and induces sodicity/alkalinity.