Soil anchors plant roots and serves as a storehouse for nutrients. The term ‘pH’ refers to the extent of acidity or alkalinity of the soil. A pH of 7.0 is neutral, while above 7.0 is alkaline, sweet, or basic. Soil with a pH of 6.9 or below is acidic or sour. Measuring pH is vital as plants rely on the correct pH to absorb the nutrients to survive and thrive, making it essential to maintaining a healthy crop.
To successfully grow plants, testing with a digital soil pH tester in the USA will help you understand the current pH levels and whether you need to make any changes. If you need to increase or decrease pH in the soil, there are several common compounds you can add to it. Once the correct pH is met, you can have healthy and productive plants.
Why Is the Soil pH So Important?
The acidity or alkalinity of soil will determine whether plants from the soil may absorb nutrients. For instance, as soil becomes increasingly acidic (pH of 5.5 and below), the nutrients, phosphorus, potassium, and others become tightly bound to the soil and are not absorbed by plant roots.
Most plants thrive best in soils with a pH of 6.0 or 6.5 to 7.4. Many needled evergreens, such as pine, spruce, and fir, will tolerate a slightly acidic soil pH of 5.5 to 6.0. Broadleaved evergreens and acid-loving plants such as rhododendron, azalea, mountain laurel, heath, heather, and blueberry prefer a pH range of 4.5-6.0.
Most native Rockland soils are acidic (pH of 4.8-5.5). For lawns, vegetables, flowers, and some trees and shrubs, the addition of powdered agricultural limestone may raise the pH above 6.0.
The pH value of soil is mostly impacted by the parent materials of the soil when it is formed. Soils developed from basic/alkaline rocks usually have a higher pH value than the soils formed from acidic rocks. The soil pH is also influenced by rainfall when water percolates through the soil layers, usually turning the soil more acidic due to the acidic elements replacing leached alkaline nutrients like the calcium and magnesium.
Source: Freepik
Factors Affecting Soil Ph/Acidity:
Rainfall:
Rainfall contributes to a soil’s acidity levels. Water (H₂O) combines with the carbon dioxide (CO₂) to form a weak acid, the carbonic acid (H₂CO₃). The weaker acid ionizes releasing hydrogen (H⁺) as well as bicarbonate (HCO₃). The released hydrogen ions then replace the calcium ions by soil colloids, causing the soil layer to become acidic. The displaced calcium (Ca⁺⁺) ions combine with bicarbonate ions to form the calcium bicarbonate, which, being soluble, is leached out from the soil. The net effect is increased soil acidity.
Nitrogen Fertilizers:
Nitrogen levels affect soil pH. Nitrogen sources—fertilizers, manures, legumes—contain or form ammonium, which increases soil acidity unless the plant absorbs the ammonium ions directly. The greater the nitrogen fertilization rate, the greater is the soil acidification. As ammonium gets converted to nitrate in the soil called nitrification, H ions are released.
For each pound of nitrogen as ammonium, approximately 1.8 pounds of pure calcium carbonate is needed to neutralize the residual acidity. The nitrate provided or formed can combine with the basic cations like calcium, magnesium, and potassium and leach out from the topsoil into the subsoil. As these bases are eliminated and replaced by H ions, soils become more acidic.
Plants:
Legumes like soybeans, alfalfa, and clovers take up more cations than anions. This causes the H ions to be released from the plant roots to maintain the electro-chemical balance within their tissues. The result is net soil acidification.
Subsoil Acidity:
The subsoil may be highly acidic even if the top 6-inches of soil show a pH above 6.0. When subsoil pH drops below 5.0, aluminum and manganese in the soil become highly soluble and, in some soils, may be even toxic to plant growth. Cotton and, to some extent, soybeans are the examples of crops that are sensitive to the highly soluble aluminum levels in the subsoil layer, and crop yields may also be reduced under conditions of low subsoil pH.
If you’ve observed areas of stunted plant growths in your field, take a subsoil sample in such areas. If the soil pH is highly acidic (below 5.2), lime should be applied very early in the fall and turned as profoundly as possible.
Liming:
Correcting soil acidity using lime is the foundation of a good soil fertility program. Liming does more than just correct soil acidity. It also:
- Supplies the essential plant nutrients, Ca and Mg, if dolomitic lime is used
- It makes other essential nutrients more available
- It prevents elements such as Mn and Al from being toxic to plant growth.
What Can be Done to Correct the Poor Soil pH?
Limestone (available at garden centers) neutralizes overly acidic soil. Powdered or pelleted agricultural limestone is very commonly used. Don’t overdo the lime—raising the pH is much easier than lowering it. Alkaline soils are neutralized with elemental sulfur, iron sulfate, or aluminum sulfate.
Summing Up:
Soils require a specific pH to grow plants successfully.
If you wish to adjust the soil’s pH, start by measuring its current pH and understanding the target pH for your plants. The best way to increase the soil’s pH is by using a lime-based compound such as dolomite lime or agricultural lime.
If you have any questions about soil pH or are unsure which pH probe will best suit your needs, contact our team at SoilOptix®.
