By: Dan Kaiser, Extension nutrient management specialist
Deciding whether to lime the soil can be a difficult choice, especially in rental situations, since the impact of liming can extend beyond short-term rental situations. The benefits of liming may not be achieved until two or more years post-application, so determining where lime is most economical can be difficult to assess. In addition, Minnesota maintains two separate lime recommendations depending on sub-soil acidity, which reflects differences in the parent material that formed the soils across the state.
A current study is underway which will help assess the long-term benefits of lime applications in Minnesota. The study will also look into the rationale for parts of the current lime guidelines to determine whether changes should be made to better represent current cropping practices across the state.
The history behind Minnesota’s lime guidelines
The benefits of liming have been demonstrated through cooperative work between farmers and the University of Minnesota for over 100 years. What has changed since then is our understanding of where lime is needed and how we come about suggesting lime application rates across the state.Early work found differences in lime needs across the state and the current split for the lime guidelines can be found in Extension publications dating back to around 1970. However, more recent work has me questioning whether the split for the state should be where it is or farther to the east to encompass much of the area consisting of Des Moines Lobe till, where soils like the Clarion-Nicollet-Webster series persist.
One major change around 1970 was the use of the buffer pH for lime recommendations instead of water pH. I get questions about buffer pH from time to time. The buffer pH method adds a solution with a known pH. The Sikora buffer method has a starting pH of 7.7. When added to an acid soil, the pH of the buffer solution decreases and the amount the pH decreases is related to the amount of lime required to neutralize the soil. Many times, the buffer pH will be over 7.0 even though the water pH is below 6.0, which is normal. What that means is that it should not take as much lime to neutralize the acidity of the soil to a target level. Getting to the target level does take time, so it is important to consider liming one or more years ahead of when a crop more sensitive to low pH is planted in a field.
Research is currently being funded by the Minnesota Soybean Research and Promotion Council looking at the current guidelines to determine where changes may need to be made. One question we are trying to determine is whether more of central Minnesota should be considered in Area II as some fields include low pH soils in upland positions but higher pH soils (that would not need lime) in depressional areas of the field.
Fields needed for new research studies
We are looking for three additional field locations to establish trials in the fall of 2024 or spring of 2025 on farmers’ fields. The sites are around 0.6 acres in size. I am looking for one additional sandy location, one location east of the I-35 corridor in southern MN, and one location west of I-35 in southern MN. We are targeting sites with surface soil pH close to 5.0 or less.Traditional ag lime, pell lime, and precipitated calcium carbonate from the Southern MN Beet Sugar Cooperative will be applied at different rates and we will measure yield for five cropping seasons after application. The intention is to have the grower manage the field as normal other than not applying additional lime. Yield data will be collected by the University of Minnesota from the fields.
Interested farmers and ag professionals can contact Extension nutrient management specialist Daniel Kaiser at dekaiser@umn.edu.
There are currently seven field locations that have already been established, three in 2023 and four in 2024. We will be providing updates from the study as we go along. All sites were planted to soybean in 2023, and we did not find any significant yield benefits from the lime, but a large change in soil pH was not expected in the initial year after application, especially with most sites being impacted by the drought in 2023. We will be monitoring these fields and reporting results over the next three to four years to determine the extent of the impact that lime has and how well it pays at various locations across the state of Minnesota.
Additional resources:
- Liming and pH: Timing, economics, materials, and more (October 2024 podcast episode)
- Soil test pH and liming: Common questions and answers
- Lime needs in Minnesota
- Liming materials for Minnesota soils
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If you have questions or comments, please email us at nutmgmt@umn.edu.
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