At the end of this section, you should know: Common alternative liming materials including their effectiveness and limitations.NOTE: Each state has its own laws concerning the use of alternative liming materials. The intent of this section is to serve as a guide regarding the strengths and weaknesses for using these materials but does not address the legal restrictions for each state. The state laws governing the use of any of these alternate materials should be consulted before application.
Ground agricultural limestone has been the traditional material for liming acid soils in the Southeastern U.S. Farmers usually refer to this as "lime" but technically it is "ground limestone" or "ag limestone". Most of the time we just call it "aglime". There are two fundamental reasons for using aglime (1) to neutralize soil acidity (increase soil pH) and (2) add calcium and magnesium to the soil. Ground limestone does this well since it is mostly CaCO3 or CaCO3 + MgCO3. However, since carbonates are not very soluble in water, limestone must be ground very finely and mixed with the soil to be effective at neutralizing soil acidity. Although ground limestone may have a calcium carbonate equivalency (CCE) of 100% (pure CaCO3), it may be only 67% effective at neutralizing soil acidity because of some coarse particles. Most soil testing laboratories take this into consideration when making routine soil liming recommendations.
There are many other products and by-products which may also be used to neutralize soil acidity and supply Ca, Mg, and other plant nutrients.
Quick lime, burned lime, or oxide limeIn the strict chemical terminology, "lime" refers to this product which is calcium oxide (CaO) with or without magnesium oxide (MgO). Ground limestone is heated in a kiln to drive off CO2. This leaves a highly concentrated calcium oxide or calcium and magnesium oxide.
Pure CaO has a molecular weight of 56 grams per mole compared to a molecular weight of 100 for pure CaCO3. Therefore it is 1.78 times more reactive (178% CCE) compared to pure calcium carbonate (e.g. 100/56 = 1.78) and could be almost 3 times more effective at neutralizing soil acidity compared to ground limestone. This is the highly reactive, caustic lime used by the steel industry, paper industry, and construction industry where a highly caustic, alkaline material is needed. When oxide lime comes in contact with water, an intense, exothermic (heat producing) reaction occurs. Oxide lime may be used to rapidly increase soil pH. However, it must be carefully handled to avoid breathing the dust and to avoid contact with the skin and eyes. When mixed with soil, oxide lime is nearly 100% effective.
(Figs. 1 and 3)
Hydrated limeWhen water is added to calcium oxide, heat and Ca(OH)2 , calcium hydroxide or hydrated lime, is produced.
This is the "lime" that is used for cement, mortar, and soil stabilization. Like oxide lime, hydrated lime may also be used to dry out manure piles and treat animal carcasses to reduce insect and odor problems. It is also the "lime" used to make pickles. Like oxide lime, it is more reactive than ground limestone but is a little easier to handle than oxide lime. Pure calcium hydroxide has a molecular weight of 74 so it is 1.35 times more reactive (135% CCE) than pure calcium carbonate and may be almost twice as effective, pound for pound, at neutralizing soil acidity compared to ground limestone.
Marl or Selma chalkMarl is a natural, chalky substance that is sometimes used as a liming material. It is a granular or loosely consolidated earthy material comprised largely of shell fragments and calcium carbonate precipitated in ponds. Marl may also contain aluminum silicate clay, silt and sand as impurities. However, since the calcium carbonate component is often amorphous, it may be more reactive in the soil than ground limestone. In Alabama and Mississippi, marl is called "Selma chalk" and is the parent material of the alkaline, prairie-like soils of the Black Belt. Selma chalk is around 80% CCE and is an acceptable alternative to ag lime. However, Selma Chalk contains very little Mg and because of its clay content, can be difficult to handle if it becomes wet.
Oyster shellsSince shells are mostly calcium carbonate, they are about as effective as ground limestone when finely ground and used as a soil amendment.
Egg shellsDried egg shells are about 60% CCE. However, since the shells are a crystalline calcium carbonate, like limestone, they are ineffective at neutralizing soil acidity unless they are finely ground (Fig. 2).
Basic slag or blast furnace slagBasic slag or calcium silicate slag is a by-product of the steel industry. Lime (or limestone) is used to remove impurities from molten iron ore. The slag that remains is crushed and, historically, has been used as a soil amendment. According to the American Association of Plant Food Control Officials, basic slag must contain at least 12% total phosphoric acid (P2O5) or be labeled "low phosphate". Most basic slag in agricultural use today contains very little phosphorus and is used primarily as a soil liming material. It may contain between 50% and 70% CCE and some micronutrients.
Boiler wood ash and fireplace ashesWhenever wood is burned, oxides and hydroxides of calcium, magnesium, potassium, sodium, etc. are formed. These alkaline compounds are effective at neutralizing soil acidity. However, industrial boilers may also burn coal, gas, oil, or other biomass fuels which result in a less alkaline ash. Ash may be collected at different points in the boiler (bottom, stack, etc.) and handled differently. Therefore, boiler wood ash and mixed ash from different industries may vary considerably in their neutralizing values. Samples of 19 boiler ashes from Alabama pulp and paper mills had CCEs that ranged from 0 to 70% (hardwood) with a mean of 38%. However, when used based on the CCE of the ash, most are highly effective at neutralizing soil acidity. Other plant nutrients, especially K, are added in the boiler ash (Fig. 1).
Boiler Wood Ash
For a more detailed discussion about the use of wood ashes see: Recommended Practices for Using Wood Ash as an Agricultural Soil Amendment Best Management Practices for Wood Ash as Agricultural Soil Amendment
Flue dust or cement kiln dustFlue dust is very fine, calcareous, alkaline material collected as a by-product from the manufacture of Portland cement. It often contains some potassium (1 to 28% K2O), sulfate-sulfur (4 to 10% S), magnesium (0.6-2.8% Mg), and micronutrients. Because it contains a high percentage of oxides and hydroxides compared to carbonates and is very fine, it is more reactive than ground limestone. However, flue dust may only be 60 to 80% CCE. Nevertheless, Alabama research has shown that ton for ton, flue dust appears equal to standard, ground agricultural limestone as a soil liming.
Paper mill lime or lime mudWaste lime from the paper manufacturing process is often transported in a slurry to a lagoon, where lime settles out of suspension. This material is mostly precipitated calcium carbonate with smaller amounts of carbonates and hydroxides of Ca, Mg, and Na. It may have a CCE between 91 and 109% (dry basis) and is more effective than ground limestone in neutralizing soil acidity (Fig. 3). However, most of this "lime mud" is not used for agricultural purposes because of it's poor physical characteristics. It must be dredged from ponds, dried, and crushed to be spread by conventional, dry, lime spreaders.
Grits and dregsOther, coarser, lime by-products of the pulp and paper industry are known collectively as grits and dregs. Dregs, in particular, may be higher in sodium than other paper mill by-products (25-90 mg Na/kg) and lower in total alkalinity than grits. However, both grits and dregs have neutralizing values ranging from 80 to 120% CCE (Fig. 1).
Carbide lime or acetylene limeCarbide lime is a by-product obtained in the generation of acetylene from calcium carbide. It may be called acetylene lime, carbide sludge, lime sludge, lime hydrate, etc.
Carbide lime is a potentially high quality hydrated lime because of the high quality of the original raw materials in the process. But it is often washed into settling ponds where a lime mud is created. This mud is difficult to recover for agricultural spreading. However, once dried, it makes an excellent alternative soil liming material comparable in quality to regular hydrated lime.
Minor sourcesMany other by-products and amendments used on the soil may also contain alkaline compounds which may increase soil pH and add Ca and Mg to the soil. These include poultry broiler litter (10% CCE), layer litter (up to 30% CCE), lime-stabilized municipal biosolids (sludges), lime-stabilized septage, composted alkaline materials, etc. When these organic sources of plant nutrients are used, the soil pH must be monitored to avoid excessively high soil pH.
Laboratory Incubation Study ResultsThe following three figures show the results from laboratory incubation studies with conventional and non-conventional soil liming materials applied to an acid, sandy loam, Coastal Plain soil. All materials were applied at equivalent rates based solely on their CCE in order to compare their effective neutralizing value. Other lime products (Fig. 3) were: (1) a commercially available oxide lime, (2) a commercially available, ground, dolomitic limestone (Dol. Limestone), (3) a commercially available, pelletized, ground, dolomitic limestone (Pellet limestone), (4) a waste lime-sludge mixture from a paper mill (Lime-sludge), (5) fly ash from a wood-burning boiler, and (6) a commercial mixture of paper mill lime and boiler ash used as a soil amendment. In all tests, the control is the soil without any amendment.
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