5.3 Saline and sodic soils: causes, effects, and management

Salt-affected soils can wreak havoc on crops and land. These soils come in three flavors: saline, sodic, and saline-sodic, each with unique characteristics that impact soil structure, water availability, and plant growth.

Managing these tricky soils involves a mix of techniques. From leaching and drainage improvements to chemical amendments and smart crop selection, farmers have tools to combat salt issues. Regular soil testing is key to staying on top of potential problems.

Soil Salinity and Sodicity

Characteristics of salt-affected soils

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Top images from around the web for Characteristics of salt-affected soils

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  Sodic Soils | VRO | Agriculture Victoria View original

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• Saline soils accumulate high concentrations of soluble salts with EC > 4 dS/m, pH < 8.5, and SAR < 13 often forming white crust on soil surface (sodium chloride)

• Sodic soils contain high levels of exchangeable sodium with EC < 4 dS/m, pH > 8.5, and SAR > 13 appearing dark and greasy due to dispersed organic matter

• Saline-sodic soils combine saline and sodic properties with EC > 4 dS/m, pH < 8.5, and SAR > 13

• Formation processes involve salt accumulation from inadequate leaching for saline soils, high sodium content relative to calcium and magnesium for sodic soils, and combination of both for saline-sodic soils

Effects of salinity on soil and plants

• Soil structure impacts minimal in saline soils but severe in sodic soils causing clay dispersion, loss of structure, reduced infiltration and hydraulic conductivity

• Water availability decreases due to increased osmotic potential in saline soils reducing plant-available water and impairing root water uptake

• Plant growth suffers from osmotic stress hindering water absorption, specific ion toxicity (sodium, chloride), nutrient imbalances, and reduced crop yield and quality

• Salt-tolerant plants (halophytes) thrive in saline environments (saltbush, pickleweed)

Sources of soil salinity and sodicity

• Natural sources include weathering of primary minerals, marine sediments, and salt spray in coastal areas

• Irrigation water with high salt content leads to salt accumulation as water evaporates

• Groundwater causes salinity through capillary rise of saline water especially in arid regions with shallow water tables

• Human activities contribute through excessive fertilizer application, road salt use, poor drainage systems, and land clearing

Management of saline and sodic soils

• Leaching flushes salts using high-quality water calculated by leaching requirement formula $LR = \frac{EC_{iw}}{5(EC_{e}) - EC_{iw}}$

• Drainage improvement involves installing subsurface systems and enhancing surface drainage to prevent water ponding

• Chemical amendments include gypsum for sodic soil reclamation, sulfur for pH reduction, and calcium chloride as an alternative

• Crop selection focuses on salt-tolerant varieties (barley, cotton) with proper irrigation scheduling and mulching to reduce evaporation

• Phytoremediation uses halophytic plants to extract salts followed by biomass removal

• Monitoring and prevention requires regular soil testing for EC, pH, and SAR, water quality assessment, and implementing best management practices