TITUTE


HELPFUL HINTS


FROM THE LAWN INSTITUTE


FROM THE LAWN INSTITUTE SOIL pH: THE MASTER VARIABLE


these changes occur, not only can elemental toxicity become a concern, but so too can elemental deficiency. For example, N (Nitrogen), P (Phosphorus), K, Mg, and S (Sulfur) all can become deficient in acidic soils, while Fe (Iron), Mn, P, and B (Boron) are examples of nutrients that can be deficient in alkaline soils. Mineralization of organically bound nitrogen and phosphorus can also be affected by soil pH in that the soil microorganisms involved in these processes are limited in acidic soils. As a result, turfgrasses may not be able to take advantage of these nutrients, thus requiring increased fertilization.


Soils are the foundation of terrestrial plant life, and almost everything that plants need to survive and thrive can be obtained from them. Tey are complex systems that provide physical, chemical, and biological support for plant growth. Of all the processes and factors affecting soil health, few are as intertwined with them all as soil pH.


Soil pH, often referred to as the master variable, is one of the most commonly measured soil characteristics at soil testing labs throughout the world. It is defined as -log [H+


So, what do we do when soil pH is too low or high? Limestone can effectively raise the pH of acidic soils and is often applied in pelletized form. Sources include calcitic limestone and dolomitic limestone, with the latter containing magnesium in addition to calcium. Inversely, to lower the pH of alkaline soils, applications of sulfur and/or acidifying nitrogen fertilizers such as ammonium sulfate can often be effective.


], or a measure of hydrogen ion activity in soil solution


and impacts almost every aspect of growing healthy turfgrass. It can affect nutrient availability and balance, nutrient toxicity, microbial populations, and even herbicide or insecticide performance.


Te scale for soil pH ranges from 0 to 14 with 7 being neutral. Any values below 7 are considered acidic (H+ donors), while values above 7 are considered alkaline (H+ acceptors). One of the most important things about soil pH that is often overlooked is the fact that this scale is logarithmic. As a result, a pH of 6 is not 1 unit more acidic than a pH of 7 but in fact it is 10 times more acidic than a pH of 7. Similarly, a soil pH of 5 is 100 times more acidic, a soil pH of 4 is 1,000 times more acidic, and so on. Tis is important to recognize because drastic changes in pH such as this can have a negative impact on turfgrass health.


Most turfgrasses perform best in a soil pH of 6.5 to 7. As soils become more acidic, cations such as Mn (Manganese) and Al (Aluminum) can become toxic, and as they become more alkaline, cations including Ca (Calcium), Mg (Magnesium), K (Potassium), and Na (Sodium) can be more dominant. As


care and helpful “How to” tips, visit The Lawn Institute at: ww.TheLawnInstitute.org.


TPI Turf News May/June 2018


For more information on lawn care and helpful “How to” tips, visit The Lawn Institute at: www.TheLawnInstitute.org.


For more information on lawn care and helpful “How to” tips, visit The Lawn Ins www.TheLawnInstitute.org.


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It is important to note that soils have a high buffering capacity, which is their resistance to chemical change. Tis is good in the sense that soils resist immediate changes from rainfall or irrigation, but is bad in that acidic or alkaline soils may often take months or even years to adjust. Te master variable of soil pH is one of the most important factors impacting turfgrass health and should always be monitored routinely as part of turfgrass management programs.


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