Last week in this column I briefly discussed soil testing. Soil pH is one piece of information received on a soil test report. Soil pH affects nutrient availability, herbicide activity, and crop development. Regular, periodic soil testing can tell you when a lime application is needed to raise soil pH. Fall is generally a good time of the year to apply lime if it is needed because the effect of lime on soil pH is not immediate. It may take 9 months or longer to reach the desired, target soil pH after a lime application. Ed Lentz, OSU Extension educator in Hancock County and Steve Culman, OSU Extension soil fertility specialist recently wrote an article about liming considerations. Here are a couple of points from that article:
What is the Effective Neutralizing Power of my lime source? An important item from a lime analysis report is the Effective Neutralizing Power (ENP) value, which is required for material sold as lime for agricultural purposes in Ohio. This value allows a producer to compare the quality among lime sources because ENP considers the purity, neutralizing power (including fineness) and moisture content. In other words, the ENP tells you how much of that ton of lime actually neutralizes soil acidity. The unit for ENP is pounds/ton (be careful not to use %ENP, which may also be on a lime analysis report). The ENP allows a producer to compare different lime sources because they can now determine price per pound or ton of actual neutralizing material.
Should I use “hi cal” or dolomitic lime? In most situations it does not matter, so a producer can select the least expensive of the two lime sources. Transportation is often the largest cost of a lime material, so generally the closest lime source (quarry) is often the most economical.
Several parts of the state are historically low in soil magnesium (eastern and southern Ohio). Adequate soil magnesium is important to reduce the risk of such problems as grass tetany for grazing animals. Soil test magnesium levels need to be greater than 50 ppm (100 lb.) for optimal corn, soybean, wheat, and alfalfa production. Often areas low in magnesium also need lime, which has made the application of dolomitic lime an economic solution for both concerns.
The ratio between calcium and magnesium is important. Soils should contain more calcium than magnesium. Extensive research has shown that crops yield the same over a wide range of calcium to magnesium ratios and will not affect crop production as long as the calcium to magnesium ratio is larger than 1. High calcium lime should be used in situations where the soil test calcium to magnesium ratio is less than 1, or in other words, the soil magnesium levels are greater than the soil calcium levels. We have not observed any Ohio soil tests where the magnesium levels are above the calcium levels. Also keep in mind that almost all dolomitic lime sources will contain more calcium than magnesium. Unfortunately, some producers have been led to believe that magnesium levels in dolomitic lime may be undesirable. The Ohio State University is currently investigating the importance of calcium to magnesium ratios in crop production since the last Ohio research was completed in the early 1980s. For now, the focus should be selecting lime on its Effective Neutralizing Power (ENP) rather than its calcium level.
How about gypsum as a lime source? Gypsum is not a lime source. It does not have the right chemical composition to neutralize soil acidity, such as carbonate (gypsum is calcium sulfate). Gypsum is used as an amendment for soil physical properties and/or as a fertilizer providing calcium and sulfur.
In summary, make sure you take a soil test to determine if lime is needed, determine if magnesium is needed, know the historic pH of your subsoil, and then use the ENP to select the most cost effective lime material. A soil test every three to four years will determine the lime requirements for your fields. Additional information on ENP and lime sources and liming rates may be found at the following location: http://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins/AGF505.pdf