Which nutrient is less available in high-pH soils?

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Multiple Choice

Which nutrient is less available in high-pH soils?

Explanation:
When soil pH is high, the availability of many nutrients changes, but iron is the most affected. Iron in soils is usually present as Fe3+, and as pH rises it readily forms insoluble hydroxides, such as Fe(OH)3, which precipitate and are not easily taken up by roots. This makes iron increasingly unavailable in alkaline conditions and commonly leads to iron chlorosis in plants, especially on new shoots. Other nutrients don’t show this same dramatic drop in availability with rising pH. Nitrogen and potassium remain comparatively more available across a wider pH range, and zinc (while it does become less available as pH increases) isn’t affected as severely as iron. That combination is why iron is the nutrient that is least available in high-pH soils.

When soil pH is high, the availability of many nutrients changes, but iron is the most affected. Iron in soils is usually present as Fe3+, and as pH rises it readily forms insoluble hydroxides, such as Fe(OH)3, which precipitate and are not easily taken up by roots. This makes iron increasingly unavailable in alkaline conditions and commonly leads to iron chlorosis in plants, especially on new shoots.

Other nutrients don’t show this same dramatic drop in availability with rising pH. Nitrogen and potassium remain comparatively more available across a wider pH range, and zinc (while it does become less available as pH increases) isn’t affected as severely as iron. That combination is why iron is the nutrient that is least available in high-pH soils.

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