nmrg-ppt-soil-ph - Agronomy - Kansas State University

73 Pages·2006·3.02 MB·English

by  Dale Leikam

Soil pH and Liming
What is pH?
• A measure of the relative acidity of a
substance, or
• The negative logarithm of the hydrogen
ion concentration
pH Range
< 7.0 Acid
>7.0 Alkaline
7 14
0
Notes on pH
• pH is a convenient notation
– (5.0 is easier to use than 0.00001 or 10-5)
• The H in pH stands for hydrogen ions
• A change in pH of one unit equals a 10 fold change in H+
concentration
• A change of pH 6.0 to 5.7 doubles the acidity
The Relationship Between pH and
Hydrogen Ion Concentration
pH H+Concentration
5.0 0.00001 or 10-5
6.0 0.000001 or 10-6
7.0 0.0000001 or 10-7
8.0 0.00000001 or 10-8
Typical pH Range of Soils
Neutrality
Acidity Alkalinity
Very Very
Strong Strong Moderate Slight Slight Moderate Strong Strong
3 4 5 6 7 8 9 10 11
Humid region mineral soils
Acid Alkali
peat Arid Region Mineral Soils mineral
soils Extreme range in pH for soils
most mineral soils
Typical pH Values
pH Scale
14 Lye Solution
13
12 Washing Soda
Alkaline
11
10 Milk of Magnesia
9
8 Hard Water
Neutral 7
Normal pH Range
6 Milk
5
4 Coffee
Acid
3 Coca Cola
2 Stomach Acid
1 Battery Acid
Sulfuric Acid
0
Importance of Soil pH
• Low pH dissolves Al+++
• (1000x more soluble at pH 4.5 than at 5.5
• Plant toxicity
• High pH and High pH: lower availability of some
nutrients
• P, Zn, Fe, etc.
• Low pH affects microbe activity which affects nutrient
cycles, legume nodulation, residue decomposition,
diseases, herbicide breakdown and carryover.
• Herbicide efficacy/carryover
Effect Of Lime Rate On Soil Acidity
Extractable Al and Wheat Yield
Kansas - 4 year average
Lime 0-6 Inch Depth Wheat
Rate Soil pH Extr. Al Yield
Lbs Ecc/A ppm Bu/A
0 4.6 102 15
3,000 5.1 26 39
6,000 5.9 0 38
12,000 6.4 0 36
Initial Soil pH = 4.7, Extr. Al = 94 ppm & Lime Rec = 12,000 Lbs Ecc/A

Effect of Soil pH on Nutrient Availability?