1. Ch. 4: Soils, Nutrition etc.

2. Soil Definition: Natural body with layers (horizons)
Mineral + organic matter (OM)
Differs from parent material: substance from which soil derived

3. Weathering Factors
Mineral component: generated by weathering rock

4. Soil Texture
A: Sand & silt
Major particle sizes (know these)
B: clays

5. Textural triangle Distribution particles by size class: texture
Loam: mix sand, silt, clay
Texture important: fertility, water availability

6. Soil Structure Particles form peds (visible when soil dry)
Affect water + root penetration
How important??

7. Organic matter (OM) Humus: partly decomposed OM
Usually negatively charged:
carboxyl groups (-COOH)
phenols

8. Soil Fertility Defn: Ability soil hold & deliver nutrients
Determined by texture, organic matter, pH
Holding soil….

9. Soil Fertility Texture: clays important Huge surface area
Negatively charged: hold cations useful for plants (Ca++, K+, Mg++, Zn++)
Huge surface area
Surface of clay in top 10 cm 0.5 ha soil would cover continental U.S.!!

10. Soil Fertility
Humus has negative charge: clay & humus hold cations

11. Soil Fertility
Cation Exchange Capacity: amount negative charge per unit soil
Units? centimoles (+) charge/kg dry soil (cmolc/kg)
Represents “potential fertility”

12. Soil Fertility Examples: Great Plains prairie soil: 30 cmolc/kg
NE US conifer forest soil: 2 cmolc/kg

13. Soil Fertility H+ (and Al+++) also attracted to negative charge.
Take up space: not useful to plants.
Base saturation (BS): % exchange sites occupied by “good” cations (bases: Ca++, Mg++, K+) plus Na+

14. Soil Fertility BS, pH & CEC determine “actual fertility”
1) High CEC + high BS: more fertile
2) If BS low: pH low (lots H+)

15. Soil pH Measure H+ ion concentration
Most AL soils: (strongly acid)
Black Belt soils: (alkaline)

16. Soil pH pH effects: 1) H+ damages roots (@ extreme pH values)
2) soil microflora
Acid favors fungi (incl. mycorrhizal)
Alkaline favors bacteria
3) soil structure (sometimes)

17. Soil pH 4) nutrient availability. Major pH influence!
Nutrient deficiency:
Acid: N, P, Ca, Mg, K, S
Alkaline: Fe, Mn, Zn, Cu, Co, B

18. Soil pH 4) nutrient availability. Major pH influence!
Nutrient toxicity:
Acid: Fe, Mn, Zn, Cu, Co
Alkaline: Mo

19. Soil pH Plant sensitivity & nutrient needs matter Black Belt lab (#4):
Black Belt soil: no pines
Fe deficiency likely