Your soil is likely alkaline due to a few key reasons, including the natural weathering of calcium-rich materials, over-liming, or alkaline irrigation water.
Here's a breakdown of the primary causes:
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Calcium Carbonate-Rich Parent Material: The most common cause is the natural weathering of parent material rich in calcium carbonate (like limestone) in arid or dry environments. These environments don't have enough rainfall to leach away the carbonates, leading to alkaline soil.
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Over-Liming: Adding too much lime (calcium carbonate) to acidic soil in an attempt to raise the pH can inadvertently make the soil alkaline. Lime is used to neutralize soil acidity, but excessive application will increase the alkalinity.
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Alkaline Irrigation Water: Using irrigation water with high levels of alkaline minerals can gradually increase the soil's pH over time, especially in poorly drained soils.
In summary, your soil alkalinity is probably a result of the inherent properties of the underlying rock material, excessive use of lime, or alkaline irrigation water. Identifying the specific cause can help you determine the best course of action for managing your soil's pH.
