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 – = 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 (CaCO3)
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 [(NH4)2SO4]
Ammonium Nitrate (NH4NO3)
Ferrous Sulfate (FeSO4)

22. Changing the pH level of an alkaline soil
Acid-forming chemicals such as:
Ferrous Sulfate (FeSO4)
Calcium Sulfate (CaSO4) 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 (H2SO4) 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 (NaNO3)
Potassium Nitrate (KNO3)
Calcium Nitrate [Ca(NO3)2]
Calcium Carbonate (CaCO3)

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++ NH4++ 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)