Amy Shober, Nutrient Management and Environmental Quality Extension Specialist; ashober@udel.edu, Richard Taylor, Extension Agronomist; rtaylor@udel.edu, Josh McGrath, Extension Soil Specialist University of Kentucky and Edwin Ritchey, Extension Soil Specialist University of Kentucky
Maintaining soil pH in the proper range is one of the most important parts of soil fertility management. Soil pH is considered the “master variable” because it influences many of the chemical and biological functions of the soil. Recall that pH is a measure of the activity or concentration of hydrogen ions (H+), which is represented mathematically as pH = –log[H+]. The more hydrogen ions present in the soil solution the lower the pH value. Values below 7.0 are considered acidic and values above 7.0 are considered alkaline. The target soil pH for crops grown in Delaware is crop specific but, in general, is as follows:
- Grain crops (corn, soybean, small grains): 6.0
- Forages (alfalfa, corn silage, grass/legume mixtures): 6.0 to 6.8.
- Vegetable crops (beans, peas, peppers, etc.): 6.0 to 7.0
In this soil pH range, the essential mineral macro- and micro-nutrients are in a chemical form that is most available for uptake by growing plants. At pH below 5.0, soluble aluminum (Al), iron (Fe), and manganese (Mn) may be toxic to the growth of some plants and phosphorus (P) availability is decreased.
Delaware soils are naturally acidic. In addition, nitrogen (N) fertilizers that contain urea or ammonium (NH4+) also contribute to soil acidity when NH4+ is converted to nitrate (NO3–), releasing many H+ ions into the soil solution. Therefore, periodic liming may be required to maintain Delaware soils in the optimum pH for grain and vegetable crops. Remember to have your soil tested before applying any lime to the soil. The lime requirement test is offered as part of the routine soil analysis by the University of Delaware soil testing lab and many private labs in the region. You need both the water pH and the lime requirement (buffer pH) test run to obtain an accurate estimate of the quantity of lime needed to raise the pH back to the target pH.
Recently, colleagues at the University of Kentucky alerted us that Kentucky growers were being marketed an “alternative” liquid lime product. After a little investigation, they identified that the material being marketed as a liquid lime was actually calcium chloride (CaCl2). Unfortunately, CaCl2 provides NO liming value and is in fact not “liquid lime.” Calcium chloride is used for many purposes including road salt or tractor tire ballast, but it cannot be used to neutralize soil acidity. Therefore, we thought it would be useful to provide some information on liming materials, how liming materials increase soil pH, and explain why CaCl2 is not a viable alternative to agricultural lime.
What is Lime?
Liming materials are typically oxides (O2-), hydroxides (OH–), carbonates (CO32-) or silicates (SiO44−) of calcium (Ca) or magnesium (Mg). Some examples include calcitic lime or calcium carbonate (CaCO3), dolomitic lime (CaMg(CO3)2), quick lime (CaO), and hydrated lime (Ca(OH)2). The reason these materials work or “lime” a soil (i.e. neutralize acidity) is NOT due to the Ca or Mg in the material. The oxide, hydroxide, carbonate, or silicate anions in these materials are the active liming agents. When these liming materials dissolve in water, the acidity (H+) reacts with the negatively charged anions (O2-, OH–, CO32-, or SiO44−), thereby reducing the concentration of acid (H+) in the soil solution. The Ca or Mg cation does nothing to reduce soil acidity. Land application of Ca and/or Mg liming agents does, however, serve as a source of these macronutrients to growing plants.
Available Liming Materials
Many common liming materials are available in solid form. It is important to know the liming ability of any material, which is expressed as calcium carbonate equivalents (CCE), because some materials are more effective at neutralizing acidity. High quality solid limes have a small particle size allowing them to dissolve in water more readily.
Liquid lime products are also available. Liquid lime is simply a very finely ground solid liming product that is dissolved in water. Liquid lime usually has a high relative neutralizing ability allowing it to modify soil pH quickly. However, since lime is dissolved in water, it typically consists of approximately 50% lime and 50% water by weight. Therefore, one ton of liquid lime would be equivalent to applying ½ ton of solid lime. If you need 2 tons per acre of 100% CCE lime (based on request of a lime requirement soil test), you would likely need to apply over 4 tons per acre of the liquid lime, which is well in excess of 700 gallons per acre. This large volume of water would require multiple applications of liquid lime throughout the year to get the amount of effective lime on the field as recommended by the soil test. However, because liquid lime is very fast acting (you don’t have to wait for the rain to dissolve the lime), in some cases it may be a good option for growers when only a small amount of lime is required.
Buyer Beware
If purchasing “liquid lime”, read the label to be sure that the material is actually an oxide (O2-), hydroxide (OH–), carbonate (CO32-), or silicate (SiO44−) form of calcium (Ca) or magnesium (Mg). The CaCl2 being marketed to growers in Kentucky is not liquid lime and has no liming ability. Remember, the Ca (and or Mg in some liming materials) is not responsible for neutralizing soil acidity. And while CaCl2 can provide plant available Ca to the soil, Ca deficiencies are not common in grain or vegetable crops grown in Delaware when proper pH management practices are followed. If you do need Ca or Mg, a calcitic or dolomitic limestone source is a great way to meet those needs. Be a savvy customer when purchasing liming materials and don’t forget to get your soil tested before applying lime.