Soil Chemistry

1. Soil Chemistry

2. Soil Chemistry • Mineral salts • From weathered rocks • Break down of Organic Matter (OM) • Addition of fertilizer

3. Soil Chemistry • Salt dissolves in soil solution (H2O) as ionic forms • Ion: +/- charged particle • Ex: table salt = NaCl = Na+ and Cl- Cations H+ Ca2+ Mg2+ NH4+ K+ Anions OH- Cl- CO32- SO42-

4. Soil Chemistry • Colloids: particles of clay and O.M. suspended in solution • These attract and exchange cations! • Cation Exchange Capacity (CEC) = the soil fertility • CEC: O.M. > Clay > Silt > Sand

5. Soil Chemistry • Plants absorb nutrients as ions! • Sandy soils have a low CEC and therefore cannot hold on to ions well • These soils require frequent, light applications of fertilizer

6. Soil Chemistry • Soil pH • Relationship of H+ ions to OH- ions Acid H+ > OH- Neutral H+ = OH- Basic H+ < OH- (also called, “alkaline”)

7. Soil Chemistry H+ and Al3+ produce acidic soils Ca2+ and Mg2+ produce basic soils High rainfall areas are acidic soils Low rainfall areas are generally basic or neutral soils

8. Soil Chemistry Salt build-up in low-rainfall location damages crops

9. Fungi most active if pH<5.5 • Bacteria most active if pH>5.5 Properly nodulated legumes add 55 to 300 pounds of nitrogen per acre to soil.

12. pH of various liquids household ammonia 11.9 sea water 8.5 human blood 7.4 milk 6.4 orange juice 3.5 lemon juice 2.3 vinegar 2.8

14. Plants which like acidic conditions • Ericaceous plants (blueberry, cranberry, azalea, rhododendron)

15. Plants which like acidic conditions • Ericaceous plants (blueberry, cranberry, azalea, rhododendron)

16. Plants which like acidic conditions • Ericaceous plants (blueberry, cranberry, azalea, rhododendron)

17. Plants which like acidic conditions • Ericaceous plants (blueberry, cranberry, azalea, rhododendron)

18. Plants which like acidic conditions • Ericaceous plants (blueberry, cranberry, azalea, rhododendron)

19. Soil Chemistry • If pH very low or very high, soil nutrients become unavailable to the plant • Liming - raises the pH (makes the soil more basic) and is used on acidic soils. • CaCO3 • MgCO3 • Most of Vermont’s soils are acidic • Most tropical soils are acidic due to high rainfall

20. Liming DON’TS • You should NOT lime your lawn after having applied a fertilizer that contains ammonium nitrate. The ammonium is converted to ammonia gas which can cause burning on the foliage of the grass and surrounding trees and shrubs!

21. Cliff of limestone

23. 2H+ + 2OH- 2H2O (water)

24. Soil Chemistry • Acidifying the soil or lowering the pH • Elemental sulfur (effect is temporary) • Ammonium sulfate (effect is temporary) • Aluminum sulfate is also used but not recommended as aluminum is a heavy metal!

25. Soil Chemistry • Basic soils often can cause iron chlorosis in plants • This can be corrected by acidifying the soil • or choosing a plant which is tolerant of • alkaline soils! • Intervienal chlorosis: often on • acid-loving plants like roses, fruit trees, • azaleas and rhododendrons

29. Blue in acidic soils <5.5 with available aluminum Pink in neutral soils near pH of 7