The question has been raised over and over by Michigan’s Upper Peninsula farmers, but it’s not only an Upper Peninsula issue. Farmers in all areas where soil pH is naturally low, or where magnesium levels are low (or high), have concerns about getting their soil out of “calcium/magnesium balance.” In some areas, the local and most economical source of agricultural lime is from a dolomitic limestone quarry. Calcitic lime may need to be trucked a longer distance, or vice versa. Either way, one source of lime may be cheaper than the other. In this case, it may have been applied repeatedly over many years. The end result of repeated applications of dolomitic lime can be a build-up of soil magnesium level shown in soil test reports. The basic question is: Is magnesium build-up from use of dolomitic lime a problem?
The short answer? Very unlikely.
Calcitic lime is derived from deposits of primarily calcium carbonate. Dolomitic lime is derived from deposits of calcium carbonate combined with magnesium carbonate and contains much higher levels of magnesium. The key factors in deciding which of these types of lime should be applied to your soil is the soil pH and magnesium level. There is little difference between lime types in their respective ability to neutralize soil acidity. Also, as long as the amount of each is adequate, the balance of magnesium and calcium can vary quite a lot and have little or no impact on crop performance. Making the decision based on the calcium to magnesium ratio can be a mistake.
Recommendations from University of Wisconsin Extension’s publication, “Soil calcium to magnesium ratios – Should you be concerned?,” include the following:
Wisconsin research also indicates that, as long as soil magnesium levels are adequate, variations in the calcium to magnesium ratio are unlikely to affect alfalfa yields.
If you have serious concerns about which type of lime to use based on soil test report information, feel free to contact your local Michigan State University Extension educator for research-based information before you invest in the application.
Additional resources on this topic can be found at:
Source: Jim Isleib, Michigan State University Extension
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