Soil and Water growth and development after seeding plant

Soil and Water growth and development after seeding plant

1. Soil and Soil WaterSoil and Soil Water

2. What is soil?
Soil is the unconsolidated
cover on the surface of
the earth.
Soil is made up of
mineral particles,
organic particles,
air, and
water.
Soil is capable of
supporting plant growth.

3. Functions of agricultural soils
•Anchor plant roots
•Supply water to plant roots
•Provide air for plant roots
•Furnish nutrients for plant
growth
•Release water with low levels of
nutrients

4. Soil Components
The 4 parts of soil
Mineral
Matter
45%
Soil
Water
25%
Soil
Air
25%
Organic
Matter
5%
About ½ of the
soil volume is
solid particles
About ½ of the
soil volume is
pore space

5. Soil Physical Properties
•The mineral part of soil consists of sand, silt, and
clay particles
•The amounts of each size particle determines the
textural property of the soil
–Coarse textured, loose (more sand, less clay)
–Fine textured, heavy (more clay, less sand)
–Loamy (more even mix of sand, silt and clay
Sand
2 – 0.05 mm
Silt
0.05 - 0.002 mm
Clay
Less than 0.002 mm

7. Soil Structure
The arrangement of sand, silt, and clay particles
to form larger aggregates.
•Organic matter is the glue that
holds the aggregates together
•Large pores (spaces) between
aggregates are filled with air in a
moist soil.
•Small pores are filled with water in
a moist soil. Even smaller pores
inside the aggregates (not shown)
are also filled with water.
•If the individual particles are arranged
in small aggregates with rounded
edges, we speak granular structure.
This is very desirable for plant growth.
It provides both large and small pores
1/25 cm

8. •Unlike soil texture,
structure can be
changed by
mechanical
operations.
•A soil with good
structure has soil
pores that are
large enough to
transmit water and
air without
restriction.

9. •Bad Structure: soil compaction.

10. •Bad Structure: Soil crusting.

11. Chemical Properties of Soil
1.Cation exchange capacity (CEC) is the total amount of
cations that a soil can retain
–The higher the soil CEC the greater ability it has to store plant nutrients
2.Soil acidity and alkalinity.
–Acidity and alkalinity of the soil is defined by its pH.
•pH>7 is considwered alkaline
•pH<7 is considered acidic
–Plants differ in their pH tolerance
•Examples: pH 4.5-5.5: potato, pH 5.5-6.5: tomato, pH 6.5-7.5
onion.
–The availability of some plant nutrient is regulated by the
acidity or alkalinity of the soil.

12. Chemical Properties of Soil
3.Saline and Sodic Soil.
–Saline soils contain unusually large amounts of
soluble salts.
–Measured by electrical conductivity (EC)
–EC units:
•mmhos/cm or dS/m
•ppm. ppt or %.
–Sodic soils differ from saline soils in that a large
percentage (over 15%) of the total cation exchange
sites of the soils are occupied by Sodium ions (Na).

13. •Saline and/or sodic soils.

15. Soil Water
•Water makes up approximately 90 % of
a plant's mass and performs many
functions:
–Required for seed germination.
–Serves as part of the plant's structure.
–Carries minerals into and through the
plant.
–Transports photosynthates and other
biochemicals through the plant.
–Cools the plant by evaporation
(Transpiration).

16. Soil Water
•The pore spaces are always filled with water,
air, or a mixture of both.
–Saturated soil: pore spaces are filled with water
•unhealthy condition for plants if it lasts too long because
the oxygen needed for respiration is missing.
–Dry soil: pore spaces are filled mostly with air
–Water holding capacity: the ability of the soil to
retain water is called its.

17. Soil Water
•Clay soils have smaller but more numerous pores than
sandy soils.

18. Pure
water
Saline
water

19. Soil Water levels
•Saturation: all pores filled with water
–Ψw = 0 bar
•Field Capacity: saturation – gravitational water
–Water level is determined by soil type
–Ψw = -0.1 to -0.3 bar/atm
•Permanent wilting point: The soil moisture content at which
a plant wilts and cannot recover when placed in an
environment of 100 percent relative humidity is
–Ψw = -15 to -25 bar/atm
•Available water (AW) is defined as the soil moisture
between field capacity (FC) and the permanent wilting
point (PWP).

21. Plant Water

22. Plant Water
•Most of the absorbed water (95%) is lost from the
leaves by transpiration.
•Water loss in the plant is regulated to a certain extent
by the opening and closing of stomata on the leaf
surfaces.
•Not all water leaves the leaf:
–Some water is part of the plant's structures or held in the
cytoplasm.
–Some is used for biochemical processes,
–Some is stored in the tonoplast.
•The pressure of water inside a cell creates turgor
pressure, which gives plants rigidity. When there is
insufficient water to create turgor, the plant wilts.

23. Root water Absorption

24. Xylem Conducts water and minerals
from roots to plant
-composed of dead cells that
form water-pipe system
Water
movement in
Stems