Time to Lime, but first…

By Tommy Brannon

If your pastures and hay fields are overgrown with broom sedge or other undesirable grasses, it may be an indication of topsoil that is too acidic. Topsoil in the mid-south tends to be acidic because it is mainly comprised of decomposed deciduous leaves, pine needles, as well as wood, bark, and cut grasses. Even in the areas of the mid-south where there are limestone outcroppings, the soil may acidic on the surface.

First a quick chemistry lesson: Acidity and alkalinity are measured as pH levels (potential of hydrogen).The pH scale ranges from 0 to 14. The readings are based around a pH of 7, which is neutral, like pure water: A pH below 7 is acidic. A pH higher than 7 is alkaline or basic. The pH of human skin is between 4.5 and 6.2. This scale might seem small, but each level is 10 times bigger than the next. For example, a pH of 9 is 10 times more alkaline than a pH of 8. A pH of 2 is 10 times more acidic than a pH of 3, and 100 times more acidic than a reading of 4.  

Agricultural lime consists mainly of ground limestone (Calcium Carbonate, CaCo3) in various sized particles so that it has different dissolving rates. The application usually is effective up to three years. Dolomitic lime (calcium magnesium carbonate, CaMg (CO3)2) is often substituted for Ag lime and has the advantage of adding magnesium to the soil. It is lighter than Calcium Carbonate so the application rate of tons per acre is different. Since no two limestone quarries have exactly the same chemical makeup, the quality of Ag lime is measured by two different systems: Calcium Carbonate Equivalent (CCE) and the Effective Calcium Carbonate Equivalent (ECCE). These give a numeric value to the effectiveness of different liming materials, as compared to pure calcium carbonate. Granular size is measured by the fineness of the mesh that it can pass through. By combining the chemistry of a particular product (CCE) and its particle size the Effective Calcium Carbonate Equivalent (ECCE) is determined.

Some effects of agricultural lime on soil are: it increases the pH of the soil, reducing soil acidity and increasing alkalinity. It provides a source of calcium for plants and improves water penetration for acidic soils. It improves the uptake of major plant nutrients, such as nitrogen, phosphorus, and potassium. 

“Test – Don’t Guess” is the starting point for just about anything that needs repair or improvement, be it mechanical, animal, vegetable, or mineral. “You don’t know where to go or how to get there until you know where you are.” This axiom especially holds true for farm management.  If you want to improve the quality of the forage for your animals, it is a waste of time, money, and resources to just apply some lime and fertilizer without knowing how much is needed and for what purpose. The rate of application would be different, for example, for converting land into pasture that has been in row crop, as opposed to rejuvenating established pastures. Likewise, just because you have done something a certain way in the past doesn’t necessarily mean it would be the most effective way to do it now.Depending on where you live in the mid-south, a University Extension Service agent can assist you in getting your soil tested.

 The University Of Tennessee Extension Service, the Mississippi State Extension service, the Arkansas Experiment Station, and the University of Kentucky Soil Testing Lab all have the information and materials for you to test your soil.

Pre-addressed small boxes are provided for you to mail to the laboratory and there is a place to indicate to the lab what the field is used for, i.e., pasture, hay production, row crop, etc. There is a nominal charge for the service and turnaround time is about two weeks.

It is a good idea to sample each field separately because the application rate may vary from field to field. There are different types of top soil in the mid-south and two fields side by side may have different soil types. The USDA has soil maps available by county. Your extension agent can help you with that as well.  

 A composite sample consisting of small portions of soil from approximately 20 locations should be collected for each field. Collect samples in a zig-zag pattern. One can use a soil tube or probe, a shovel, a spade, or a sharp shooter. Dig to a depth of about six inches and remove any organic debris, grass, rocks, or trash. Thoroughly mix the soil in a bucket that is not zinc coated so that you don’t get a false reading of zinc. When sampling for nitrate-nitrogen, the sample should be air-dried thoroughly within 36 hours to obtain the best results.

Fall is the best time to test and apply Ag lime because the fields are usually dryer and, thus, more accessible. Since the lime is slow release, it has the entire wet winter to dissolve before the growing season starts. In addition, the equipment used to distribute the lime is quite big and heavy.  It can make pretty big ruts in a wet pasture. The loader that dumps the lime in the spreader truck can make a lot of ruts as well. As the normal application rate is about two tons per acre, it will take several dump truck loads to properly lime the fields.  Make sure the place that the lime is dumped is easily accessed by the dump trucks and that it is on high enough ground that it will remain dry throughout the entire process. Be sure that that your gates are wide enough for the equipment to pass through easily and that there are no trees or other obstacles in the way. It’s not fun to have to repair a gate or fence, or even worse to not get a particular field limed, because the machinery could not access the field. For smaller fields you may want to use a broadcast spreader on a tractor.

For good pasture management, test your soil every two years and maintain a pH level that will promote healthy growth of the desirable grasses and legumes and discourage the less nutritious and palatable ones.

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