Soil Chemistry

Mineral saltsMineral salts –From weathered rocks –Break down of Organic Matter (OM) –Addition of fertilizer

Soil Chemistry Salt dissolves in soil solution (H 2 O) as ionic formsSalt dissolves in soil solution (H 2 O) as ionic forms Ion: +/- charged particleIon: +/- charged particle Ex: table salt = NaCl = Na + and Cl -Ex: table salt = NaCl = Na + and Cl - Cations H + Ca 2+ Mg 2+ NH 4 + K + Anions OH - Cl - CO 3 2- SO 4 2-

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

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

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

Soil Chemistry H + and Al 3+ produce acidic soils Ca 2+ and Mg 2+ produce basic soils High rainfall areas are acidic soils Low rainfall areas are generally basic or neutral soils

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

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

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

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

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

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

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

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

Soil Chemistry If pH very low or very high, soil nutrients become unavailable to the plantIf 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.Liming - raises the pH (makes the soil more basic) and is used on acidic soils. –CaCO 3 –MgCO 3 Most of Vermont’s soils are acidicMost of Vermont’s soils are acidic Most tropical soils are acidic due to high rainfallMost tropical soils are acidic due to high rainfall

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!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!

Cliff of limestone

2H + + 2OH - 2H 2 O (water)

Soil Chemistry Acidifying the soil or lowering the pHAcidifying 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!

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

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