1. Ch. 4: Soil Water, Plant Nutrition, Soil Symbioses

2. Soil Supplies water and nutrients to plants
1) What influences soil water supply?
2) What nutrients do plants need, and what influences soil nutrient supply?

3. Soil water What determines water potential soil?g = +
total m p s
What determines water potential soil?
gravitational potential: unimportant
pressure potential: unimportant

4. Soil water solute potential: important saline soils g = + total m p s
Dauphin Island: salt marsh

5. Soil water g = +
total m p s
matric potential: #1 in importance

6. Soil water Matric potential determined by texture
Soils have pore space: air spaces
Clay most
Sandy least

7. Soil water Water added, pores fill
When pores filled, soil saturated: Saturation water content
Note sand<clay loam

8. Soil water Allow gravity drain water Gravitational water
Most coarse (sandy) soil, least fine (clay) soil
Soil at field capacity: fully charged with water
1.7 3

9. Soil water Plant uses water: becomes stressed
permanent wilting point (PWP): plant psi = soil psi, no water flows into plant
For mesophytes (“normal” plants), -1.5 MPa

10. Soil water Field Capacity - PWP: available water capacity
Greatest loam, less clay, least sandy soil
1.8 2 1

11. Soil water Unavailable water: water held too tightly
Greatest clay soil, least sandy soil

12. Soil water
Recap: coarse soil little field capacity, delivers little. Hold loose!
Fine soil lots field capacity, delivers good amount, retains PWP. Hold tight!
Loam (& silt loam soil): hold just right!
Fig.
4.9b

13. Soil water
Texture impacts infiltration: ability water to penetrate soil

14. Soil water Texture impacts infiltration: ability water penetrate soil
Coarse soil: high infiltration. Fine soil: low
Structure can impact infiltration

15. Soil water Vertical water movement in soil: not always “a downer!”
Hydraulic lift: movement water by plant roots from deep to shallow soil at night
Soil dry:
Low psi
water
Soil moist:
High psi

16. Soil water Ex, Acer saccharum (sugar maple) NY forest
Helps understory herbs
Herbs larger within 2 m tree (greater moisture).

17. Dew in soil
Soil distillation: movement water from deep to surface soil
May occur in deserts
hot
cold
med.
Day
med.
Nite
Water vapor
cold
warm
Relative temperatures in day and nite