Alkaline Soil

Soil with a pH value greater than 7 when precisely described. Practically it is the soil with a pH value greater than 7.5.  The term is usually used for surface layers or root zones, but it is also used for a horizon in these areas or a soil sample taken from them.

Alkaline Soil refers to soil with a pH level greater than 7. It is often characterized by the presence of calcium carbonate (lime), low acidity, and a tendency to limit the availability of certain essential nutrients for plants. Alkaline soils are commonly found in arid and semi-arid regions where there is minimal rainfall to leach soluble salts from the soil.

Characteristics of Alkaline Soil:

1. High pH:

   • pH levels typically range from 7.5 to 10.
   • The soil's alkalinity is often due to the presence of sodium, calcium, or magnesium carbonates.

2. Texture:May vary from sandy to clayey, but alkaline soils often contain higher levels of clay.

3. Nutrient Imbalances:

   • Deficiency of micronutrients like iron, zinc, manganese, and phosphorus, which become less available to plants at higher pH levels.
   • High concentrations of soluble salts or sodium can also lead to salinity or sodicity issues.

4. Drainage:Alkaline soils, especially when high in clay, may have poor drainage and compacted structure.

5. Color:

   • Often light in color due to high lime content.
   • May appear white or dusty when dry.

Causes of Alkaline Soil:

1. Parent Material:Soils derived from limestone, marl, or other calcium-rich rocks tend to be alkaline.

2. Climate:Found in areas with low rainfall where salts and bases are not leached out.

3. Irrigation Practices:Irrigating with water high in bicarbonates or carbonates can increase soil alkalinity over time.

4. Accumulation of Soluble Salts:Occurs in poorly drained areas or regions with high evaporation rates.

Effects of Alkaline Soil on Plants:

1. Nutrient Deficiency:

   • Iron chlorosis is common, where leaves turn yellow while veins remain green due to iron unavailability.
   • Phosphorus and zinc deficiencies may also occur.

2. Poor Growth:Alkaline soil can limit plant growth by restricting root access to essential nutrients.

3. Salt Stress:In extreme cases, high alkalinity may be coupled with salinity, further inhibiting plant growth.

Management of Alkaline Soil:

1. Lowering Soil pH:

   • Add Organic Matter: Incorporating compost, manure, or peat moss can increase acidity and improve soil structure.
   • Apply Sulfur or Sulfates: Elemental sulfur, aluminum sulfate, or iron sulfate can reduce soil pH over time.
   • Acidic Fertilizers: Use ammonium-based fertilizers, which can lower pH as they break down.

2. Improving Nutrient Availability:

   • Chelated Micronutrients: Use chelated forms of iron, zinc, or manganese to provide nutrients directly to plants.
   • Foliar Sprays: Apply iron or zinc sprays to address immediate nutrient deficiencies.

3. Improve Soil Drainage:In poorly drained soils, install drainage systems or use deep tillage to prevent waterlogging.

4. Leaching Salts:Flush out excess salts by applying sufficient water to move them below the root zone (only effective with good drainage).

5. Mulching:Mulching with organic materials helps retain soil moisture, improve structure, and enhance nutrient cycling.

6. Grow Alkaline-Tolerant Plants:

   • Select crops and plants adapted to high pH conditions. Examples include:
     • Trees: Olive, cedar, juniper.
     • Shrubs: Forsythia, lilac, barberry.
     • Vegetables: Asparagus, beets, spinach.
     • Flowers: Lavender, dianthus, geranium.

Alkaline Soil Indicators:

1. Plants Symptoms:

   • Yellowing of leaves (chlorosis) while veins stay green.
   • Stunted growth or poor flowering.

2. Soil Testing:

   • Conduct a pH test to confirm alkalinity.
   • Test for salinity or sodicity if necessary.

3. Efflorescence:A white, powdery residue of salts on the soil surface indicates high alkalinity or salinity.

Reclamation of Alkaline Soils:

1. For Mild Alkalinity:Use organic amendments like compost or manure to gradually lower pH.

2. For Sodic Soils:Apply gypsum (calcium sulfate) to replace sodium with calcium, which improves soil structure and permeability.

3. For Highly Alkaline Soils:Combine gypsum application with leaching and the addition of sulfur-based amendments.

4. Phytoremediation:Grow salt-tolerant and alkaline-tolerant plants to reduce salinity and gradually improve soil health.

Conclusion:

Managing alkaline soil involves improving its fertility, structure, and nutrient availability through amendments, better water management, and proper plant selection. With consistent effort, these soils can be made productive and suitable for a wide range of plants.