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Corn Response to High Soil pH Levels

Categories: GROWING, CORN
  • Soil pH is a critical factor that can influence soil nutrient availability.
  • Corn hybrid response to soil pH depends on genetic tolerance and actual pH level.
What is Soil pH?
pH is a measurement of the concentration of hydrogen ions. Soil pH is measured on a scale of 0 to 14, with pH less than 7 considered acidic and pH greater than 7 considered alkaline or basic. Precipitation, temperature and soil composition, both physically and chemically, play a role in soil pH. Rain, specifically, is naturally slightly acidic due to atmospheric CO2. The soil composition foundation or the parent material will determine subsoil pH based on chemical composition.

Other factors related to crop management also directly impact soil pH. Nitrogen fertilizers may form ammonium in the soil, which, if not absorbed by a plant, will cause soil acidification. Legumes like soybeans and alfalfa will uptake more positive-charged cations than negative-charged anions, which leads to soil acidification. The application of lime (calcium carbonate) to soil will cause a chemical reaction forming a strong base (calcium hydroxide) and a weak acid (carbonic acid), raising the pH level and making the soil more alkaline.

Why is Soil pH Important?

Soil pH plays a major role in crop production as plants obtain 14 of their 17 essential nutrients exclusively from the soil. Soil pH influences those nutrients’ solubility, and thus availability, in the soil (Figure 1), which can lead to plant stress from deficiencies (Figure 2) or toxicities. Basic soils (pH > 7) lead to toxicity of aluminum while acidic soils lead to toxicity of manganese where these elements are present in sufficient amounts. Slightly acidic soils quickly begin to hold on more tightly to essential elements like phosphorus, calcium and magnesium, which makes them less available to the plant.

Soil pH can also impact potential plant pests and pathogens, such as certain fungi and soybean cyst nematode (SCN). Many fungi, Pythium spp. in particular, seem to perform well in slightly acidic soils. According to Michigan State University studies, basic soils have been shown to harbor higher populations of SCN than slightly acidic and neutral soils. Low pH in soils causes many plant nutrients to be less accessible but can also interfere with the breakdown of certain pesticides, leading to carryover issues and reduced efficacy. Low pH in soils can be managed by applying lime. 

The optimum soil pH range for corn is 5.6 to 7.5. Soil pH levels of 7.8 or greater can limit corn growth and yield potential. The severity of corn response to soil pH higher than 7.8 is greatly influenced by the amount of available calcium (also expressed as excess lime and/or percent carbonate) and sodium in the soil solution. Greater amounts of one or both of these elements are typically more detrimental to the crop. If soil pH is high enough to influence corn development, plants often appear stunted and chlorotic (yellowing leaves) and yields can be reduced. High pH tolerance due to genetic variation among corn hybrids can result in stark physical differences (Figure 3). Hybrids that are not tolerant to high pH will appear stunted and pale or bleached in color.

When selecting hybrids for high pH soils, farmers should consider taking the following steps:

1. Document soil pH
  • Utilize yield maps, aerial imagery and/or plant symptoms to identify potential high pH areas of a field.
  • Use soil sample results to evaluate pH, excess lime rating and sodium levels. Understanding the relationship between calcium, sodium and salt in the soil is important in properly classifying a soil saline (high salt), sodic (high sodium), or saline-sodic, with each classification carrying different management implications. Saline soils make water uptake more difficult and are best managed by selecting a hybrid with an optimal drought tolerance rating.
  • Create a soil map from results to visualize pH distribution in the field.
2. Match hybrid to field
  • Select hybrids based on pH severity profile of the field (Table 1).

Consider hybrid performance, not just for pH, but also for ear and plant height. In drought conditions, a taller plant with higher ear placement may perform better and have more harvestable ears than a shorter hybrid or a hybrid with ears too low to the ground which can be exacerbated by soil pH.

For more information on soil pH management, contact your local Golden Harvest Seed Advisor.

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