Soil and Plant Growth

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

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 levelof 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 levelof 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 levelof 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 levelof 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 levelof 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)