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Finding the Right pH Level for Your Corn's Soil

Categories: GROWING, CORN
Soil pH classified as “alkaline” typically has higher levels of calcium, magnesium and sodium. High soil pH is considered higher than what your cornfields need for optimal growth and affects corn health and performance in several ways:
  • Reduces the availability of several nutrients, especially phosphorus, zinc, iron (most common), and manganese, causing stunted plant growth.
  • Decreases weed control by some herbicides.
  • Increases carryover problems with some herbicides.
  • Allows crop residues to build up due to slower decomposition from decreased biological activity.

​​​​​​​Is Acidic Soil Good for Corn?

Soil pH is the foundation of soil fertility because it dictates how available soil nutrients are to the plant. If soil pH is too low or acidic, microbial processes shut down and applied nutrients are not as available to the corn plant. The ideal soil pH for corn is between 6 and 6.5.

What pH Level is Too High for Corn?
The best way to determine if you have a high pH issue is to analyze a soil sample. The optimum pH range is 5.8 to 6.2 for a corn/soybean rotation. Any soil pH above this level is considered high, especially if it is greater than 7. Corn health may be visibly affected by high pH, but it is usually manifested as a nutrient deficiency. For example, if your corn is showing an iron deficiency symptom, it’s very possible your soil has plenty of iron, but high pH has restricted the form of iron production corn can use. For nutrient deficiency symptoms, a soil test is the only way to know if fertilizer is needed to fix the issue.

Reasons for High Soil pH
Soils become alkaline typically because they contain calcareous materials, such as limestone. In arid crop areas, such as the Great Plains, high pH is often associated with saline soils. These soils contain high levels of soluble salts, which reduce potential water uptake in plant cells. Crop response to saline soils is similar to drought stress and may be associated with a white, salty crust on the soil surface. Planting hybrids with good drought tolerance is the best way to deal with high salinity. 
Corn with drought injury on saline soil. Source: Golden Harvest

Sodic soils are saline soils that have a high sodium content and often have a pH greater than 8.4. These soils often have a black, dusty residue on the soil surface. Corn grown in sodic conditions may exhibit abnormal growth, stunting, and poor kernel set and weight. Planting hybrids with good tolerance to both drought and high pH is recommended for sodic or saline soils with a high pH. 

In non-arid areas of the Corn Belt, hybrid response to high pH is not nearly as dramatic as in arid areas. For hybrids that are typically chlorotic and stunted in arid high pH, the corn may show little or no symptomology in non-arid fields with the same pH. 

Fixing Soil with High pH Issues
If over-liming caused high soil pH, simply stop applying lime for several years, and pH levels will come down. If your field pH is higher than 7.4 for other reasons, the pH can be reduced by applying elemental sulphur, aluminum sulfate or iron sulfate. Unfortunately, it is not economically feasible to treat soils with these materials in fields that have a naturally high pH, such as calcareous soils. Adding organic matter with manure or crop residue can lower pH, but it takes several years to impact corn performance.        

Hybrid response differences in high pH soil. Source: Golden Harvest
The best way to manage corn in high pH soil is to plant hybrids with excellent tolerance to high pH. To avoid herbicide carryover issues, double-check product labels and adjust application rates for high pH, as needed. 

Soil pH Management Photo and Resource Links
There are several Extension resources that can provide more agronomic insights on managing high soil pH fields, including:
Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.

Photos are either the property of Syngenta or used under agreement.

Syngenta hereby disclaims liability for third-party websites.


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