SOIL222 - Lecture 3: Salinity and Sodicity Overview

Salinity and Sodicity Overview

Salinity

  • Affects natural environments and agricultural production

  • Saline soils have excess soluble salts

  • Sodic soils have excess sodium

  • Sources: Weathering of parent material, fossil salts, sea salt, poor irrigation practices, fertilizers, wastewater

Soil Classification by Salinity

  • Non-saline, non-sodic: pH 7.9, ECa 0.84 dS/m, Exch. Na+ 0.5

  • Saline, non-sodic: pH 8.0, ECa 12.0 dS/m, Exch. Na+ 0.9

  • Non-saline, sodic: pH 9.6, ECa 3.16 dS/m, Exch. Na+ 10.1

  • Saline, sodic: pH 7.8, ECa 16.7 dS/m, Exch. Na+ 10.5

  • Critical saturated paste EC values: 2-10 dS/m

Area of Salt-affected Soils in Australia

  • Total area: 2,383,200 km² (32.9% total land)

  • Saline Kandosols: 386,300 km²

  • Sodic Vertosols: 666,400 km²

  • Dryland salinity affects 1-3 million ha of irrigated soils

Plant Effects of Salinity

  • Reduces growth due to osmotic and specific ion effects

  • Competition for ions can affect nutrient uptake

  • Salinity tolerance varies among crops (e.g., high tolerance: barley, wheat; low tolerance: lettuce, potato)

Salinity Testing and Reclamation

  • Detection of salinity via field signs, EC measurement

  • Reclamation methods include: planting salt-tolerant species, improving irrigation water quality, draining saline areas

Sodicity

Sodicity Assessment

  • Measured using Sodium Adsorption Ratio (SAR): SAR=racNa(Ca+Mg)/2SAR = rac{Na}{(Ca + Mg)/2}

  • Classification: Very sodic >15; sodic 6-14; pH >8.5 indicates sodicity

Effects on Plants

  • Dispersive effects of Na+ on soil structure impact root development

  • High pH limits nutrient availability

Reclamation of Sodicity

  • Gypsum application can manage surface sodicity; difficult for subsoil sodicity.

Land Use Impacts

  • Changes in land management can lead to saline soil development.