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Understanding Soil pH and Its Impact on Agriculture

Soil pH is a measure of soil acidity or alkalinity, affecting nutrient availability for crops. Learn how pH levels influence plant growth, which crops prefer acidic or alkaline soils, and how to adjust pH using lime or sulfur. Discover the importance of pH in agriculture.

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Understanding Soil pH and Its Impact on Agriculture

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  1. SOIL CHEMISTRY

  2. SOIL pH A measure of the degree to which the soil is Acidic or Basic; also known as . . . Soil Reaction

  3. SOIL pH Technically: expressed as the negative logarithm of the hydrogen ion (H+) concentration

  4. SOIL pH At pH 7: - neutral pH - indicates H+ concentration of . . . 10-7 mol/L

  5. SOIL pH Since the product of normalities of H+ and OH- ions is always 10-14, OH- is also 10-7 mol/L mathematically . . . (10-7)(10-7) = 10-14

  6. SOIL pH therefore . . . at neutral pH (pH 7 on a scale from 0 to 14) amount of H+ ions = amount of OH- ions solution is neither acidic nor basic

  7. SOIL pH Most agricultural soils pH range from 4 to 9 . . . common productive agriculture soils fall between pH 5 to 8

  8. SOIL pH 2 factors affecting pH are: 1) Amount of precipitation 2) Type of vegetation

  9. SOIL pH AMOUNT OF PRECIPITATION – HUMID AREAS (heavy rainfall)  ACID SOILS Ca+, Mg+, and Na+ are leached downward and replaced by H+ ions

  10. SOIL pH TYPE OF VEGETATION – Vegetation affects pH over period of years: grasslands – higher pH forests – lower pH

  11. SOIL pH The most critical effects of soil pH are indirect . . . the availability (unavailability) of certain nutrients is greatly influenced by soil pH

  12. SOIL pH Nutrients UNAVAILABLE at higher pH: Cu – Copper Fe – Iron Mn – Manganese Zn – Zinc

  13. SOIL pH additionally . . . nitrogen-fixing bacteria associated with legumes are seriously hindered in acid soils Critical with beans and peas

  14. SOIL pH ADJUSTING SOIL pH - Crops vary considerably regarding soil pH preferences

  15. SOIL pH AZALEA BLUEBERRY RHODODENDRON ACID SOILS

  16. SOIL pH Mildly Acid Soils: Wheat Corn Soybean Apple Tomato

  17. SOIL pH Neutral to Slightly Acid Soils: Alfalfa Lettuce Muskmelon

  18. SOIL pH RAISING Soil pH: ADD LIME Factors to consider before applying - soil type - how much to raise the pH - fineness of lime - type of lime

  19. SOIL pH AMOUNT OF LIME NEEDED TO RAISE pH: Sandy Loam < Clay Loam WHY? Cation Exchange Capacity (CEC) of clay particles

  20. SOIL pH LOWERING Soil pH: AddSulfur - May be necessary for acid-loving crops - May also benefit potato production by reducing potato scab

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