soil and plant growth 12423241.ppt

soil and plant

1. Soil and Plant Growth
What is soil?
–As a medium for plant growth, soil can be described
as a complex natural material derived from
disintegrated and decomposed rocks, and organic
materials, which provides nutrients, moisture,and
anchorage for land plants

2. Four principal components of soil
1. 45% Minerals (clay, sand, or silt particles)
2. 25% Air
3. 25% Water
4. 5% Organic matter (living & dead)

3. How soils are formed?
This is a long term process that involves both
physical & chemical weathering, along with
biological activity.
It can take 100+ years to form 1” of topsoil

4. Characteristics involved in forming soil.
Parent Material –material from which soils are
formed.
Climate –Temperature and moisture.
Living Organisms –microscopic & macroscopic
plants and animals.
Topography –shape & position of the land
surface.
Time –period during which parent material has
been subjected to soil formation.

5. Plants and Soil
Nutrients are
released by
decomposers
Productive soil is a
dynamic process
Nutrient cycling is
key to
understanding

6. Soil profile
Organized into horizons
O-Organic ( A-Topsoil)
A-Topsoil
B-Subsoil
C-Parent material

7. Soil Texture
Clay is the smallest
Silt
Sand the largest
Loam a mixture

8. Spheroidal
Granular & Crumb
(organic matter content is high)

9. Prism-Like
Prismatic & Columnar
(found in subsoils and common in arid &
semiarid regions)

10. Plate-Like
Platy
(can occur in any part of the profile)

11. Block-Like
Blocky
(most common in subsoils, particularly those in
humid regions)

12. others
Massive & single grain

13. Soil structures influence?
Soil moisture relationship
Aeration
Heat transfer
Root growth

14. Soil Reaction (pH)
Soil reaction (acidic, neutral, alkaline) refers to
the relative concentration of hydrogen ions (H
+
)
and hydroxyl ions (OH
-
) in the soil

15. Soil & Plants
Nutrient-Holding
Capacity
Water Holding
Capacity
(permeability)
Aeration ( porosity)
pH

16. pH
The acidity or alkalinity of the soil
pH is not a fixed characteristic of the soil and,
depending on a number of conditions, varies over time.
Soils in climates with high rainfall & humidity generally
tend to be acid. (This is due to the leaching of base
elements as well as by harvested crops usage of
sodium, potassium, calcium, & magnesium)
Soils in arid climates tend to be alkaline.

17. pH Range
0 -4.0 = extremely acid
4.1 –5.0 = strongly acid
5.1 –6.0 = moderately acid
6.1 –6.9 = slightly acid
7.0 = neutral
7.1 –8.0 = slightly alkaline
8.1 –9.0 = moderately alkaline
9.1 –10 .0 = strongly alkaline
10.1 –14 = extremely alkaline

18. pH Range
The pH for most agriculture soils lies between 5
and 8.5

19. Changing the pH level
of an acid soil
1. The pH of an acid soil can be increased by
adding amendments or fertilizers containing
such elements as:
•Calcium
•Potassium
•Sodium
•Magnesium

20. Changing the pH level
of an acid soil
Calcium Carbonate (CaCO
3)
Also known as agricultural lime
This is finely ground limestone
This is effective due to its ability to provide
calcium (Ca
++
) and hyfroxyl (OH
-
) ions

21. Changing the pH level
of an acid soil
The prolonged use of chemical fertilizers that are
residually acid tend to make the soil acid.
Examples are:
Ammonium Sulfate [(NH
4)
2SO
4]
Ammonium Nitrate (NH
4NO
3)
Ferrous Sulfate (FeSO
4)

22. Changing the pH level
of an alkaline soil
Acid-forming chemicals such as:
Ferrous Sulfate (FeSO
4)
Calcium Sulfate (CaSO
4) in some irrigation areas, a
saturated solution of calcium sulfate is allowed to
drip into the irrigation water or spread as a powder.
Elemental Sulfar (S) through the process of
oxidation produces sulfuric acid (H
2SO
4) and acidify
the soil

23. Changing the pH level
of an alkaline soil
The prolonged use of chemical fertilizers that
are residually alkaline tend to make the soil
more alkaline. Examples are:
Sodium Nitrate (NaNO
3)
Potassium Nitrate (KNO
3)
Calcium Nitrate [Ca(NO
3)
2]
Calcium Carbonate (CaCO
3)

24. pH and Plant Nutrients
The availability of certain plant nutrients is
regulated by the acidity or alkalinity of the soil.
Examples:
Iron and Zinc become less available to plants as
the pH increases
Phosphorus is more available at a soil pH of 6.5
–7 than at either higher or lower values.

25. pH and Plant Nutrients
Calcium availability decreases with increased
acidity.

26. Cation Exchange Capacity
CEC is an important measure of the fertility and
potential productivity of a soil
Clay and organic matter have a net negative
charge which attract the positively charged
cations. (se figure 1-9)
Ca
++
, Mg
++
K
++
NH
4
++
are plant nutrients
Na
++
& H
++
effect soil chemical & physical
characteristics

27. Soil Organic Matter
Helps strengthen soil aggregates
Improves aeration and water infiltration
Increases water-holding capacity
Provides significant amounts of CEC
Provides buffering against rapid change in soil
reaction acid 0r alkaline forming materials are
added to soil

28. Form stable organic compounds that can
increase the availability of micronutrients.
Provides a source of many plant nutrients.
Provides a food source for soil microorganisms.

29. Types of organic matter
Green manure crops
Crop residues
Animal manures
Compost
Look at Table 1-3

30. Soil Organisms

31. Soil Organisms
Micro flora
Bacteria
Fungi
Algae
You tell me what they do?

32. Soil Management
1. Tillage (Primary & Secondary)
2. No-Till or Minimal till
3. Conservation (National Resources
Conservation Service NRCS –2 billion tons of
topsoil lost per year)
Best Management Practices (BMP, crop,
fertilizer, pesticide, & water management)