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Got Low pH? Adjust Soil for Corn Production

Categories: GROWING, CORN
Soil pH is the universal measure of its acidity (lower pH) or alkalinity (higher pH). Processes that are crucial to crop performance, such as soil microbial activity and nutrient availability, are very sensitive to soil pH. 

Unfortunately, the effect of soil pH on production agriculture is often underrated, and many farmers may not realize soil pH is limiting their yields. Each year, Golden Harvest agronomists pull soil samples from producers’ fields, and results have shown 74% of samples test outside the optimum pH range.

Both high and low pH may limit corn and soybean yields, but cornfields with low soil pH can be managed. Low soil pH affects corn health and performance in several ways:
  • Causing soluble metals, such as iron, aluminum and manganese, to be released too quickly and become toxic to plants
  • Reducing the transformation of nitrogen, sulfur and phosphorus into useable forms
  • Enabling calcium to become deficient, especially in soils with low CEC
  • Decreasing weed control by some herbicides
  • Resulting in poor soil structure and soil tilth, especially in soils with low organic matter 
  • Increasing carryover problems with some herbicides
  • Allowing crop residues to build up due to slowing decomposition from decreased biological activity

  Source: University of Wisconsin Extension

What is the Ideal Soil pH for Corn?
The best way to determine if your fields have a low pH issue is to take a soil sample and have it analyzed. The optimum pH range for a corn/soybean rotation is 5.8 to 6.2. Any soil pH below this level is considered low. 

Corn health may be visibly affected by low pH, but it is usually manifested as a nutrient deficiency. For example, if your corn is showing a phosphorus deficiency symptom, it’s very possible your soil has plenty of phosphorus, but its low pH is restricting the production form of phosphate that can be taken up by the crop. For nutrient deficiency symptoms, a soil test is the only way you'll know if you need to apply fertilizer or lime, or both, to adjust your pH.

Why Does Soil pH Drop?
There are several reasons soil may become more acidic, or drop in pH:
  • Minerals that control acidity are removed when crops are harvested
  • Alkaline minerals leach out of the root zone when soils become saturated during rainy periods
  • Acid residues are deposited with the use of some nitrogen fertilizers
How Can I Fix Low pH?
Testing soil every 3 to 4 years is a good strategy to keep tabs on soil pH. If pH drops, applying lime is the best way to correct it. Lime can be applied any time the application does not disturb the crop. Fall applications are preferred to avoid planting delays and compacting the soil. Maintaining soil pH at optimal levels (5.8 to 6.2) should be a priority. If pH is allowed to fall considerably below this range, it could take years to get it back to target levels and help boost yields, because pH reacts slowly to conventional liming materials, such as aglime

Lime rate recommendations vary from state to state. Reference Extension publications for local recommendations. Liming rates are based on:
  • Cropping system
  • Buffer pH provided on the soil report: Soil pH only tells if you have a problem
  • Soil type: Higher clay and organic matter content requires more lime
  • Depth of incorporation tillage: Deeper tillage requires more lime
  • Limestone chemical composition: For example, dolomitic lime, calcific lime, etc.
  • Limestone grind: Finer limestone will change pH faster

Take care to apply lime evenly at the target rate to minimize overlaps. Incorporating lime with tillage is highly recommended, because lime moves slowly through the soil. For fields with variable soils, consider variable rate liming since it is considered one of the most economical applications of precision farming. Without variable rate application, lime may be under applied in heavier soils and over applied in sandier soils, with the latter causing high pH injury.

Managing Low pH in No-Till Systems
In no-till fields, maintaining soil pH at optimal levels through the top 6 inches is even more important than conventional fields. Without tillage, lime will eventually move downward very slowly. Before giving up tillage to initiate a no-till field strategy, test the soil and consider applying lime to get pH levels back to pre-no-till years. 

If you decide to not incorporate lime, reduce lime rates by one-third to one-half, and apply over several years. If you try to push lime rates to catch up, soil pH may become stratified and be very high at the surface, and acidic further down in the soil. Stratified pH can easily be fixed by taking the field out of no-till for a few years, and tilling to incorporate the surface lime.

pH Management Resources
There are several Extension resources that can provide more agronomic insights on managing low soil pH fields, including photos and management recommendations:
Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.

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