January 13, 2023
Soil pH is defined as the negative logarithm of the hydrogen ion activity where a pH of 7.0 is neutral, below 7.0 is acidic, and above is alkaline.1 Because the pH scale is logarithmic, each full point change in pH equals a 10-fold increase in hydrogen ion activity. The level of acidity or alkalinity can:
- reduce the availability of key nutrients for crops (Figure 1)
- decrease beneficial microbial activity and deterioration of soil health
- reduce overall crop performance and health.
Nutrient availability is the number one concern when looking at pH management strategies to help optimize crop performance. Crops stressed due to pH often show symptoms of nutrient deficiencies. Common symptoms are shorter, yellow plants with interveinal necrosis in more severe cases.
The best management strategies depend on the soil type and pH levels.
Figure 1. Nutrient availability related to soil pH. Image courtesy of and used with the permission of Dr. Emerson Nafziger, University of Illinois.
Managing Acidic (Low pH) Soils
The factors contributing to acidification are root respiration, organic matter decomposition, nitrification of ammonium ions, acid rain, and the replacement of base cations (Ca, Mg, etc.) with hydrogen during plant uptake. As pH levels fall to the 5.0 to 6.5 range, the most effective strategy is to apply lime to help neutralize the acidity. Below pH 5.0, aluminum is the dominant acidifier and should be treated differently.
Fall applications are preferred. Application recommendations generally range from 1 to 4 tons per acre depending on soil type and level of acidity and may take a few years of lime application to correct.2 It is best to reference local university extension publications for lime recommendations as these vary state to state.
Managing Alkaline (High pH) Soils
Alkaline soils often contain calcareous materials such as limestone and are characterized based on the amounts and kinds of salts present (Table 1). Saline soils can be identified by the “white” areas in fields. These salts are mostly sulfates and/or chlorides of calcium and magnesium.3 Good drainage and good water quality can leach the harmful salts in saline soils. Planting corn products with good drought stress can also help.
Sodic soils are more challenging. Though lower in total salts, they have high levels of exchangeable sodium. These soils can be sticky when wet, have poor water drainage, and have a crust when dry. Management strategies in sodic soils are longer term strategies that must address high pH, the excess sodium, and poor soil structure.
Gypsum application and incorporation combined with water can help to displace and leach the sodium beyond the root structure. Applications of elemental sulfur, aluminum sulfate, or iron sulfate can be considered to help address the high pH but are costly. Manure applications can help lower pH and improve soil structure.
Each field is unique. Managing pH starts with soil sampling to understand the type of pH and other soil factors that can influence product performance. Consider adding essential micronutrients to your starter fertilizer and foliar applications along with implementing pH management strategies.
Lastly, work closely with your local Channel Seedsman to select the best corn and soybean products with pH tolerance to optimize your performance potential.
Table 1. Salt-Affected Soil Classification*
Classification |
Electrical Conductivity (MS/cm) |
Soil pH |
Exchangeable Sodium Percentage |
Soil Physical Condition |
|
| Saline | >4.0 | <8.5 | <15 | Normal | |
| Sodic | <4.0 | >8.5 | >15 | Poor | |
| Saline-sodic | >4.0 | <8.5 | >15 | Normal | |
| > = Greater than; < = Less than. | |||||
| *Table from Management of Saline and Sodic Soils. MF1022, K-State Research and Extension, Kansas State University. Used with the permission of Dr. Diaz and Dr. Presley, Kansas State University. |
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Sources
1 Adamchuk, V.I. and Mulliken, J. Site-specific management of soil pH (FAQ). Precision Agriculture. EC o5-705. University of Nebraska-Lincoln Extension. https://cropwatch.unl.edu/documents/Site-Specific%20Management%20of%20Soil%20pH%20%28FAQ%29%20-%20EC705.pdf/.
2 Mamo, M., Wortmann, C.S., and Shapiro, C.A. Revised 6/2015. Lime use for soil acidity management. G1504. NebGuide. University of Nebraska-Lincoln. https://extensionpublications.unl.edu/assets/pdf/g1504.pdf.
3 Diaz, D.R. and Presley, D. 2017. Management of saline and sodic soils. MF1022. K-State Research and Extension. Kansas State University. https://bookstore.ksre.ksu.edu/pubs/MF1022.pdf/.
Additional source:
Truog, E. 1947. Soil reaction influence on availability of plant nutrients. Soil Science Society of America Journal. Volume 11, Issue C:305-308
Web sites verified 11/15/22.
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