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Saline And Sodic Soils

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  • 1. Saline and Sodic Soils • Salt Affected Soils – Occur when rainfall is not sufficient for adequate leaching of salts – Usually less than 20 "/yr precipitation – Common in arid regions • Western US • Irrigated agriculture – Not common in PA • Heavy salt application for ice melting • Land application of high salt waste materials – Can ruin soils for agriculture
  • 2. Saline and Sodic Soils • Salt Affected Soils – Common salt ions • Ca2+ • Mg2+ • Na+ • Cl- • SO4 2- • HCO3 - • CO3 2-
  • 3. Saline and Sodic Soils • Suelos afectados por sales Clasificación Conductivida d (mmhos/cm) pH % Na intercble Condiciones físicas SALINE > 4 < 8.5 < 15 Normal SODICO < 4 > 8.5 > 15 Pobre SALINO/SODICO >4 < 8.5 > 15 Normal Conductivity (EC) - Electrical conductivity of the soil water. Soluble salt ions will carry an electrical current. Therefore the higher the salt level the higher the conductivity. EC x 10 ≈ Soluble cations (meq/L) % Exch. Na - % saturation of Na on the soil CEC
  • 4. Saline and Sodic Soils • Saline Soil – High salt content in soil solution – “White Alkali” soils – salt accumulation at soil surface – EC > 4 mmhos/cm = 40 meq/L – Salts raise the osmotic potential of the soil solution reduces available soil water – Plants have to use more energy to get the water they need
  • 5. Saline and Sodic Soils • Saline Soil – Osmotic Effect – El agua se moverá desde donde la concentración de sal es baja hacia donde es alta Raíz Membrana Célula radical ALTA Sal BAJA Sal Suelo Normal Root Soil Solution High Salt High Salt Suelo SALINO Higher Salt Solución del suelo Membrana Célula radical
  • 6. Saline and Sodic Soils • Saline Soil – Effects on plants – Stunted growth – Wilting – Bluish-green color – Necrosis of leaf tips – Drought stress symptoms – Specific toxicities eg. Boron – Plant species vary in salt tolerance • See table 3.19 in Textbook
  • 7. Saline and Sodic Soils • Saline Soil – Management – Add enough irrigation water to leach salts below the root zone – Preferably drain the salty water away – Salts within 1m of the surface can move back into the rooting zone with evaporation – Quantity of irrigation water required: • Quality of irrigation water (Good quality = low salt) • Quality of drainage water • Soil water holding capacity • Rooting depth • Salt tolerance of plants • Formulas available to calculate the amount of water needed – .5 m water /m of soil will remove ~ 50% of salts – 1 m water / m soil will remove ~ 80% of salts
  • 8. Saline and Sodic Soils • Salt injury from fertilizer – High salt levels when high rates of fertilizer or manure applied – More serious when banded • Recommendation is no more than 70 lb/A of N + K2O within 2” of corn seed at planting • Recommendation is no more than 15 lb/A of N + K2O directly with corn seed at planting – Primarily germination and early growth problems – Usually temporary under our humid conditions
  • 9. Saline and Sodic Soils • Sodic Soil – High sodium > 15% CEC • ESP = Exchangeable Sodium Percentage – High pH > 8.5 • pH of Na2CO3 in water is 9.5 – “Black alkali” soils – dissolved OM and salt accumulation at the soil surface – Main problem is the effect of sodium on flocculation and aggregation of soil particles
  • 10. Saline and Sodic Soils • Sodic Soil – Sodium causes the soil particles to disperse – No aggregation of soil particles – Individual clay particles clog soil pores – Poor soil physical properties • Very difficult for water and air movement and root penetration – Plants cannot grow in sodic soils
  • 11. Saline and Sodic Soils • Sodic Soil – Flocculation Van der Waals Attraction – Short range attraction Ca2+ Ca2+ Na+ Flocculated Small hydrated ionic radius Dispersed Large hydrated ionic radius
  • 12. Saline and Sodic Soils • Sodic Soil Flocculated Aggregation Dispersed Sealing
  • 13. Saline and Sodic Soils • Sodic Soil –Reduced Hydraulic Conductivity 0 10 20 30 40 ESP % Hydraulic Conductivity
  • 14. Saline and Sodic Soils • Sodic Soil - Management – Leach with low Na+ , salty water to exchange Ca2+ for Na+ – Gypsum often added to create salty, low sodium water Na-Soil + CaSO4 → Ca-Soil + Na+ + SO4 2- – Leach with clean water to flush out Na+ & SO4 2- – Very difficult because you can’t get water into the soil to do the leaching!!!
  • 15. Saline and Sodic Soils • Sodic Soil - Management – Reduce ESP < 15 % of CEC – Use low sodium irrigation water • Sodium Adsorption Ratio (SAR) • Ion concentrations in irrigation water (meq/L) SAR = [Na+ ] / √ ([Ca2+ ] + [Mg2+ ])/2 ESR = 0.015 SAR SAR > 13 will give ESP > 15% • Figure 3.25 Textbook Classification of Irrigation Water
  • 16. Saline and Sodic Soils • Sodic Soil - Management – Use of Gypsum Na-Soil + CaSO4 → Ca-Soil + Na+ + SO4 2- • Provides Ca but doesn’t increase pH like limestone • Perception that adding Gypsum will always improve soil structure • True for sodic and saline/sodic soil but not in most other cases if Ca is adequate and Na is low • In acid soils we don’t have Na and we get plenty of Ca from limestone • Amount of Gypsum to provide equivalent Ca2+ to exchange with Na+ (Example in Textbook)
  • 17. Saline and Sodic Soils • Saline-Sodic Soil – High salt and high sodium – High sodium > 15% CEC • ESP = Exchangeable Sodium Percentage – High salt content in soil solution • EC > 4 mmhos/cm – pH < 8.5
  • 18. Saline and Sodic Soils • Saline-Sodic Soil – As long as the salts remain high these soils will remain floculated – Don’t have the serious physical properties that sodic soils have – Problems similar to saline soils – Can be come sodic very easily with improper management !!!
  • 19. Saline and Sodic Soils • Saline-Sodic Soil Management – Similar to sodic soil management • Leach with low sodium, saline water to exchange Na+ • This creates a saline soil • Then manage as a saline soil eg. Leach out the salts with clean water – Easier to manage than sodic soil – Very critical to use a high salt, low sodium water or it will become sodic
  • 20. Summary of Saline & Sodic Soils Figure 3.21 in Textbook Electrical Conductivity (mmhos/cm)

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