Effect of High pH Soils on Corn

High pH soils can be a problem in western corn growing regions due to the weathering or breakdown of soil parent material or by the use of poor quality irrigation water. Corn growth and yield potential can be limited on high pH soils.

Soil pH is measured on a scale of 0 to 14. Soils are considered acidic with a pH less than 7, and alkaline or basic with a pH greater than 7. A soil pH in the range of 5.6 to 7.5 is considered optimum for corn. Soil pH levels of 7.8 or greater can limit corn growth and yield potential.

High pH soil normally does not look any different than soil with a neutral pH (7). Sometimes high pH soil may have a powdery substance on the surface. Corn is considered a moderately susceptible crop to high pH and can exhibit nutrient deficiency symptoms on these soils. The availability of phosphorus and micronutrients such as iron and zinc are reduced in high pH soil. Yellow stripes on the middle to upper leaves are signs of iron and zinc deficiency. Dark green or purple coloring of the lower leaves and stems are signs of phosphorus deficiency. High pH soils can reduce corn height and ear size, ultimately reducing both grain and silage yield potential of the crop.

A soil test is the best way to accurately diagnose problems with the soil. High pH problems are often accompanied with high salt levels. Basic soil tests report the pH and electrical conductivity (EC), which measures salinity. Soil test results should also be evaluated for high carbonates (excess lime rating) and sodium levels. Soil tests can be helpful to determine management solutions with high pH soils. Also, if the site is being irrigated, collecting and analyzing a water sample will be helpful as well.

When it comes to high pH soils, it may be more difficult to lower the pH than to manage the availability of soil nutrients. This is because high pH is often caused by the parent material of the soil, which will continue to break down over time and buffer any attempts to acidify the soil. Soils that contain free carbonates are the most difficult to alter in terms of pH.

Management options for high pH soils are as follows:

  • Improve plant-available nutrients by adding fertilizers or chelates to the soil. A heavier reliance on starter fertilizers may be needed.
  • If the soil does not contain free carbonates, adding elemental sulfur, which is turned into sulfuric acid by bacteria in the soil, or directly adding sulfuric acid may help to acidify the soil over time. However, this is usually uneconomical for large acres as the amount required to lower the pH may be exceptionally high.
  • Adding organic matter in the form of manures or crop residue can lower the pH over time as the breakdown of organic matter releases acids while also providing essential nutrients, including micronutrients.
  • Limiting early irrigation events to prevent soils from sealing over. Wet soils may lead to more bicarbonate uptake by seedling roots which can block the uptake of other nutrients.
  • Select corn products that can tolerate high soil pH levels, maintain acceptable plant and ear height, and show optimum yield performance. Stalk strength and disease tolerance are also important agronomic traits to take into consideration.

Consult with your local DEKALB® agronomist or representative for corn product options to consider growing on high pH soils.

Sources: Waskrom, R., Bauder, T., Davis, J., and Andales, A. 2012. Diagnosing saline and sodic problems. Colorado State University Extension. Fact Sheet 0.521. http://extension.colostate.edu.; Managing high pH and salt issues in corn. agKnolwedge Spotlight. Bayer Crop Science. Web sites verified 9/26/2018 180928161422