10/27/2009 - By Dr. Raymond Snyder

By Raymond Snyder, Ph.D.

Soil pH is arguably the most important factor in essentially all aspects of soil science. Many chemical and biological reactions are dependent on the levels of acidity (hydrogen ions [H+] ) and alkalinity (hydroxide ions [OH-]) in the soil. These levels influence the availability to turfgrass of many essential elements such as iron (Fe), manganese (Mn), phosphorus (P), zinc (Zn), and molybdenum (Mo). Diverse biological activity is also affected by pH. For example, highly acid soils generally have less bacterial activity, resulting in increased thatch accumulation and algal growth, while nutrient cycling is reduced.

The recommended soil pH range for turfgrass is 5.5 to 6.5. Maintaining optimum soil pH can be accomplished using either acidifying or liming materials. Acidifying materials such as elemental sulfur, ammonium, and sulfuric acid decrease soil pH by releasing H+ ions which lower pH. Liming materials are those which contain or form carbonate ions that neutralize acidity. Examples of liming materials include calcium carbonate, dolomitic limestone, calcitic lime, and calcium oxide. Liming materials increase soil pH by removing H+ ions in the soil.

Decreasing soil pH can be more difficult than increasing soil pH due to the potential for plant-tissue burn associated with acidifying materials. Small, frequent applications of elemental sulfur can be safely used to decrease soil pH in established turf. Up to 5 pounds of elemental sulfur can be applied per 1,000 sq ft on fairways and roughs. Applications to low cut turf such as tees and greens should not exceed ½ pound per 1000 sq ft. Applications to high and low cut turf should be spaced at least 3-4 weeks apart. Total applications should not exceed 10 pounds per 1000 sq ft yearly. Ammonium based fertilizers, such as ammonium sulfate, can also be used to lower soil pH. Again, low, frequent applications are advised due to the potential for tissue burn and excessive growth associated with the nitrogen content of these materials. See Table 1 for specific rates.

Increasing soil pH is more easily and safely accomplished than decreasing soil pH in established turf. Liming requirement is based on the soil texture and organic matter content, and the change of soil pH desired. Rates generally do not exceed 50 to 100 pounds per 1000 sq ft. Liquid liming products which can be applied more uniformly and with less dust than dry, granular lime are also available. Dolomitic limestone is recommended when soil pH is low and also deficient in magnesium. Application rates of dolomitic limestone are similar to that of calcitic limestone. See Table 2 for specific rates.