SOIL FERTILTY and pH
Transcript of SOIL FERTILTY and pH
SOIL pH SOIL REACTION is the relative ACIDITY or
ALKALINITY of the SOIL
In WATER molecules are in constant FLUX
H2O →→←← H+ + OH- (hydrogen ion) (hydroxyl ion)
pH scale MEASURES the concentration of H+ ions 0 – 1 – 2 – 3 – 4 – 5 – 6 – 7 – 8 – 9 – 10 – 11 – 12 – 13 – 14
Acidic Neutral Alkaline (Basic)
LOGARITHMIC SCALE
Typical solutions
SOIL pH
TYPICAL SOILS - 5.0 - 8.0 pH
0 – 1 – 2 – 3 – 4 – 5 – 6 – 7 – 8 – 9 – 10 – 11 – 12 – 13 – 14
Acidic Neutral Alkaline (Basic)
The most ACIDIC soils ?
The most ALKALINE soils ?
CAUSES of ACIDITY / ALKALINITY
PARENT MATERIAL
YOUNG SOILS retain the pH of the parent material
ACIDIC pH - Granite, Sandstone, Shale, Basalt (slightly acidic)
ALKALINE pH – Limestone CALCAREOUS soils typically have pH of 8.0 – 8.5
As SOILS AGE the pH can CHANGE due to other factors
CAUSES of ACIDITY / ALKALINITY PERCOLATION of RAINFALL
RAINWATER - 5.6 pH (slightly acidic) LEACHES away BASES (Ca+2, etc) and REPLACES with H+ and
Al+3 ions (both acidifiers)
As pH < 6.0 Al+3 HYDROLYSIS occurs which LOWERS pH to ~ 4.0
Al+3 + 2 H2O →→→→ Al (OH-)2+ + 2H+
(hydrolysis)
SEMI-ARID and ARID soils have little or no precipitation, more EVAPORATION means SALTS can accumulate and tend to have ALKALINE soils
CAUSES of ACIDITY / ALKALINITY RESPIRATION (by plant roots and biology)
SUGARS + O2 →→→→ CO2 + H2O
(respiration)
CO2 + H2O →→→→ H2CO3
(Carbonic acid)
H2CO3 →→→→ H+ + HCO3- (acidifiers)
Same thing happens with CO2 and WATER passing through the ATMOSPHERE causing acidic rainwater
CAUSES of ACIDITY / ALKALINITY EXCHANGE of NUTRIENTS by ROOTS
Take in BASE CATIONS (Ca+2, etc) and EXCHANGE with H+ ions (acidifier)
NITRIFICATION (bacteria)
2NH4+ + 3O2 →→→→ 2NO3
- + 8H+
(ammonium) (nitrate)
EFFECTS of pH PLANTS have pH preferences depending on their NATIVE
ENVIRONMENT and what they have EVOLVED with
EFFECTS of pH NUTRIENT
AVAILABILITY
TOXICITIES
SOIL BIOLOGY
Best GROWTH for all organisms near NEUTRAL pH
LIMING SOIL LIMING soil raises pH and
makes NUTRIENTS more available
UPTAKE of nutrients is
INCREASED Effectiveness of FERTILIZER
is ENHANCED Promotes greater
MICROBIAL GROWTH SUPPLIES Ca and/or Mg
LIMING SOIL LIMING MATERIALS
CALCITIC lime - CaCO3 DOLOMITIC lime - CaCO3 + MgCO3 BURNED lime – CaO HYDRATED lime – Ca(OH)2
WOOD ASHES
HOW LIME WORKS LIME interacts with soils in 2 WAYS
Replaces Al+3 + H+ IONS on EXCHANGE sites by MASS ACTION (high concentration)
CaCO3 + 2H2O →→→→ Ca+2 + H2CO3 + 2OH- (hydrolysis)
CONVERTS H+ ions to H2O taking H+ ions out of solution becoming more NEUTRAL pH
2OH- + 2H+ →→→→ 2H2O
APPLICATION of LIME
4 FACTORS effect APPLICATION RATE
PRESENT pH (from soil TEST)
ACTIVE ACIDITY is the pH of the SOIL SOLUTION or how many H+ ions in solution
MEASURED by pH METERS and STRIPS Tells you whether you NEED to LIME
DESIRED pH – depends on CROP grown
APPLICATION of LIME CEC - GREATER the
CEC the MORE LIME is NEEDED to raise pH – called BUFFERING CAPACITY
RESERVE ACIDITY - how many H+ IONS are on the exchange sites
Measured by SMP BUFFER TEST
Tells you HOW MUCH LIME to apply
APPLICATION of LIME LIME MATERIAL USED (See Handout)
TYPE of LIME USED
CALCIUM CARBONATE EQUIVALENT measures the neutralizing power in comparison to pure Calcium Carbonate
PURITY of mined limestone
The FINER it’s ground, the FASTER WORKING it is