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PH and Liming

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objective

Monitor soil pH regularly and manage it effectively with good liming practices.

Monitor soil pH and maintain at a level appropriate for turfgrass species and site use.

  • Soil testing labs offer convenient and cost effective pH analysis, and provide recommendations for correcting adverse pH conditions.
  • Both acid and alkaline conditions can affect nutrient availability to turfgrass plants.
  • Acid conditions can increase mobility of heavy metals and pesticides.
  • Many soil organisms function best when pH values are moderately acidic to near neutral.
  • pH can significantly affect the composition of the turfgrass stand, and can influence incidence of many weed species.

Know the significance of soil pH, soil acidity and buffering capacity to determine lime requirements.

  • Soil pH is only a measure of active acidity, that is, the concentration of hydrogen ions (H+) in soil solution. Active acidity is an indicator of current soil conditions.
  • There are also acidic cations (H+ and Al3+) adsorbed on soil colloids (the cation exchange capacity, or CEC) which can be released into the soil solution. This is called exchangeable acidity. Exchangeable acidity is much larger than active acidity.
  • The most effective way to manage soil acidity is to apply agricultural limestone. The quantity of lime required is determined by the target pH (based on turfgrass species and management) and the soil's buffering capacity.
  • Buffering capacity refers to the tendency of a soil to resist changes in pH. The buffering capacity of a soil depends on factors such as the soil's clay and organic matter contents and type of clay present. Soils with a high clay and organic matter content can hold greater levels of exchangeable acidity and will require greater amounts of limestone than sandy soils lower in clay content and organic matter.

Do not apply more than 50-70 pounds per 1000 sq. ft. (1.5 tons per acre) of limestone to established turf in a single treatment.

  • If a soil testing lab recommendation is more than this, then the limestone should be applied in several treatments on a semi-annual or annual basis until the recommended quantity of limestone is met.
  • Applications in excess of 50-70 pounds per 1000 sq. ft. will not increase the rate at which pH changes, can be difficult to manage, and excessive limestone is often visible and can impact turf aesthetics.
  • Aeration in conjunction with lime application will increase 'access' to the root zone, thereby increasing the effectiveness of lime and raising pH faster.
  • When preparing soil for new plantings at the time of establishment, incorporate limestone pre-plant to increase its effectiveness.

Adjust application rates based on the calcium carbonate (CaCO3) equivalent (CCE) of the liming material being used.

  • Limestone recommendations from a soil testing lab are based on material with a 100% CCE value, however commercially available lime is never 100% pure.
  • Divide the recommended limestone amount by the CCE of your liming material (usually provided on the bag):

Example 1:
Calcium carbonate equivalent (CCE) on the bag = 85%
Laboratory recommended limestone treatment = 50 pounds per 1000 sq. ft.
Limestone required = (50/85) x 100 = 59 pounds per 1000 sq. ft.
Example 2:
Calcium carbonate equivalent (CCE) on the bag = 79%
Laboratory recommended limestone treatment = 1800 pounds per acre
Limestone required = (1800/79) x 100 = 2278 pounds per acre

Apply limestone at intervals appropriate for the soil type and drainage on the site.

  • A sandy soil needs to be limed more frequently because of its lower buffering capacity relative to a soil higher in clay and organic matter.
  • A soil that is poorly drained requires less frequent liming than a well-drained soil because of the reduced leaching of alkaline soil components.

Account for the CCE of fertilizer materials being used.

  • As covered previously, the calcium carbonate equivalent (CCE) indicates the degree to which a material reacts to change the soil pH.
  • In the case of fertilizer, CCE is defined as the amount of calcium carbonate (limestone) needed to neutralize the acidity caused by a specific amount of the fertilizer material.
  • Information on CCE can be found on the fertilizer label.
  • Some fertilizer sources (e.g. ammonium sulfate, urea, mono- and di-ammonium phosphate, superphosphate, and many composts and organic fertilizers) can cause a lowering of soil pH (positive CCE).
  • Some fertilizers (e.g. poultry feather meal and poultry manure-based composts and fertilizers) can cause an increase in soil pH (negative CCE).