How does soil pH impact zinc availability?

Soil pH controls zinc availability via chemical reactions determining nutrient solubility. Zinc is chemically bound in alkaline soils with a pH above 7.0 as insoluble compounds, which plants cannot take up. Acidic pH conditions, with a pH below 6.0, leach zinc out of root zones. Most zinc uptake occurs in slightly acidic soil with a pH of 6.0-6.5.

Zinc fixation occurs in alkaline soils due to reactions with calcium carbonate (CaCO3). At pH 7.5, zinc is incorporated into zinc carbonates, resulting in a 80% reduction in solubility. Calcareous soils may require pH correction before applying zinc. I have measured that the available zinc fell from 2.0 mg/kg to 0.3 mg/kg when the pH increased from 6.5 to 8.0.

To ensure the effectiveness of zinc fertilizers, ensure you have the ideal pH level before applying. To lower the soil pH in alkaline soils, use elemental sulfur at rates of 5-10 pounds per 1,000 square feet. To raise soil pH in acidic soils, use lime at recommended rates. Check the pH every year, as it is constantly changing. Measure zinc availability 4 weeks after adjusting pH.

Different crops can tolerate different pH ranges. For instance, citrus has been shown to effectively absorb zinc when the soil pH remains at or below pH 7.2. At the same time, corn requires soil pH levels below 6.8 for effective zinc absorption. Adjust targets based on the plant's sensitivity. After adjusting the pH, check for new growth and look for symptoms. Soil testing will always remain a crucial component of precision agriculture.

Read the full article: Zinc Deficiency Plants: Symptoms and Solutions