What is the pH of the soil?
All soils fall into one of three categories: acid, neutral, or alkaline. A pH number describes the degree of acidity or alkalinity in a soil. The pH scale runs from 0 to 14. A pH of less than 7.0 is considered acidic, 7.0 is neutral, and greater than 7 is alkaline. Thus, an acidic soil has a pH of 5.8, whereas an alkaline soil has a pH of 7.9.
As pH values below 7.0 drop numerically, soils become more acidic (see Fig. 1). In fact, every whole pH unit decrease results in a ten-fold rise in acidity. A soil with a pH of 5.5, for example, is ten times more acid than one with a pH of 6.5, while a soil with a pH of 4.5 is 100 times more acid than one with a pH of 6.5.
Similarly, there is a ten-fold rise in alkalinity for every whole unit increase in pH over 7. On a soil test report, pH values are normally provided to the nearest 1/10th of a complete unit ie. 6.2, 7.0, 8.5.
Many plant species have a preference for certain soil pH levels. Rhododendrons and azaleas prefer soils with a pH of 5.2 to 5.5, while cool-season turf grasses prefer soils with a pH of 6.0 to 7.2. Kentucky bluegrass, Pennsylvania’s most popular cool-season turf grass, thrives in soil pH ranges of 6.5 to 7.2. Fine fescues, bent grasses, turf-type perennial ryegrasses, and turf-type tall fescues are more acid-tolerant than Kentucky bluegrass on mildly acid soils (6.0 to 6.5).
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Factors affecting Soil pH
Natural processes and human actions both contribute to the acidification of soils. The amount of rainfall determines the pH of most soils. Rainfall percolates through the soil in humid locations like the north eastern United States, draining ions like calcium and magnesium that keep the soil from becoming acidic and replacing them with acidic ions like hydrogen and aluminium.
Fertilization with ammonium-containing fertilizers and pollution of industrial by-products such as sulphur dioxide and nitric acid, which infiltrate the soil through acid rain, are examples of human activities that enhance soil acidity. Changes in soil pH, whether driven by natural processes or human activity, occur slowly in most circumstances.
This is due to most mineral soils’ extraordinary buffering capacity (resistance to pH shift).
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How soil pH impacts turf health
The availability of plant nutrients and other elements, thatch decomposition, some turf grass pests, and pesticide activity are all influenced by soil pH.
Strongly acid soils (pH less than or equal to 5.5) can cause calcium, magnesium, and phosphorus deficits, as well as an increase in the availability of aluminium and manganese, which can be harmful to turf grasses. In acid soils, liming improves plant nutrient availability while also reducing toxicity issues.
The development of insoluble tri calcium phosphate renders phosphorus inaccessible to plants in very alkaline soils (pH more than or equal to 8.5). Some plants growing in high-pH soils may develop iron chlorosis, a symptom of iron deficiency.
In highly acidic soils, many beneficial soil microbes cannot flourish. Certain nitrogen fertilizers are broken down by some of these bacteria, releasing the nitrogen for utilization by the turf grass. Fertilizers derived from urea form, sulphur-coated urea, or natural organic sources are ineffective unless specific microbes are present in adequate numbers.
Decomposition of thatch and grass clippings is aided by soil microbes. Thatch is a thick layer of organic material that forms beneath the grass on the soil surface. The circulation of air, water, nutrients, and pesticides into the soil is restricted by a coating of thatch. Microbial activity is increased and thatch is reduced when soil pH is between 6.0 and 7.0. Soil pH has an impact on several turf grass diseases. Although the causes for this are unknown, there is evidence that the populations of microorganisms that control harmful fungi are reduced in very acidic soils.
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Furthermore, due of nutritional deficits or aluminium toxicity, plants growing in acid soils may be more prone to disease. In acid soils, on the other hand, at least two turf grass diseases (take-all patch and Fusarium patch) are reduced. These pathogens, fortunately, rarely cause issues in home lawns.
Although a pH of 6.0 to 7.0 will not prevent turf grass disease, it will help to lessen the severity of the infestation.
Acidic soils encourage the growth of certain weed species. Moss, one of the most common and difficult-to-control weeds, thrives in moderately to strongly acidic soils rather than neutral or slightly acidic soils.
Shepherds purse is a common lawn weed that indicates moderately acidic to extremely acidic soils. Although lime applications cannot control weeds, applying lime before soils get too acidic is one way to prevent serious weed infestation.
The pH of the soil influences the activity of several insecticides. Some turf grass herbicides and insecticides are less effective in highly acidic soils.
