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DESCRIPTION
4. DESCRIPTION
4.1. SIGNIFICANCE OF USE
pH in agriculture
pH affects the ability of plant roots to absorb nutrients. Calcium, phosphorus, potassium and
magnesium are likely to be unavailable to plants in acidic soils. Plants have difficulty absorbing
copper, zinc, boron, manganese and iron in basic soils. By managing pH, you can create an ideal
environment for plants and often discourage plant pests at the same time.
pH is measured on a scale of 0‑14. A pH reading below 7 is considered acidic, while a pH reading
above 7 is basic. A pH reading of 7 is neutral, and is ideal for many plants and spray materials.
The pH scale is logarithmic, which means that a pH reading of 6 is 10 times more acidic than a
reading of 7.
You can measure the pH of your spray tank water, or your irrigation/fertigation water.
If spray tank water is too acidic (low pH) or too basic (high pH), the pesticides mixed in can be
deactivated and may even burn the plants.
The pH of water applied to the plants should match desired soil pH. Otherwise it will gradually
change the soil pH. Acidic fertilizers can be used to lower pH. Limestone is often used to raise pH.
The type of limestone applied and your soil type can make a difference in how quickly and how much
the pH will change. Most of the nitrogen and phosphorus fertilizers used today are acid forming.
For example, about 1.5 pounds of lime is required to neutralize the effect of applying 1 pound of
anhydrous ammonia to the soil.
Some irrigation water contains substantial quantities of calcium and magnesium bicarbonates
(lime) which help neutralize the acidifying effects. Thus, soils (without free lime) under production
become increasingly acidic unless lime is artificially applied or is present in the irrigation water.
This means farmers need to frequently check soil pH to determine whether they are maintaining a
proper soil acidity level.