AGRI 0110: Introductory Soil Science

• AGRI 0110 is an introductory soil science course for 3 credits
• Ravindra Ramnarine, Ph.D. teaches AGRI 0110

Contact Information:

• Office: Department of Food Production, Sir Frank Stockdale Building, Room #207A (Upstairs)
• Phone: 662-2002 Ext. 82578
• Email: [email protected]
• Students need to email for an appointment for office hours

Learning Outcomes:

• Upon completion of this course students will be able to:
• Describe the multiple roles of soils in our daily lives
• Identify soil chemical, physical, and biological characteristics
• Relate the properties of soil to their behaviour
• Describe the relationships among soil properties
• Solve basic quantitative problems involving soil properties
• Summarise the key soil properties affecting agriculture

Course Reference Text:

• Weil, R. and N. Brady, "The nature and properties of soils," 15th ed. (2016) or 14th ed. (2008), Pearson, Columbus, Ohio
• Required reading materials will be uploaded on myeLearning or provided in class, and can be tested
• “The nature and properties of soils,” 15th edition – 4 copies are available in Reserve at the library
• “The nature and properties of soils,” 14th edition - 6 copies available in the General Collection at the library

Module 1: Soil as a Resource, Functions, and Components Learning Objectives:

• Understand that Soil Science consists of a wide variety of disciplines
• Define soil and explain why it is an important natural resource
• Describe functions of soil in the ecosystem
• Identify the components of a typical soil

What is Soil Science?

• Soil Science deals with soil as a natural resource on the surface of the earth
• Soil Science includes Soil Biology, Soil Chemistry, Soil Physics, Soil Mineralogy, Pedology, Soil Fertility, Soil Management, and Soil Conservation

Disciplines of Soil Science:

• Soil Biology: the macro- and microorganism population of the soil, its role in various transformation processes, and its importance in plant nutrition and crop production
• Soil Chemistry: the chemical constitution, the chemical properties, and the chemical reactions in soil
• Soil Physics: the physical properties and physical behavior of soil
• Soil Mineralogy: the solid inorganic phases (minerals) affecting the physical and chemical properties of the soil
• Pedology: the study of the genesis (formation), morphology, and classification of soils
• Soil Fertility: the ability of the soil to provide the essential nutrients required for plant growth
• Soil Management: application of operations, practices, and treatments to protect soil and enhance its performance
• Soil Conservation: the protection of soil against physical loss by erosion or against chemical deterioration (degradation)

What is Soil?

• Weil & Brady define soil in "The Nature and Properties of Soil (Glossary)" as a dynamic natural body composed of mineral and organic solids, gases, liquids, and living organisms which can serve as a medium for plant growth
• Soil is also the collection of natural bodies occupying parts of Earth's surface that is capable of supporting plant growth and that has properties resulting from the integrated effects of climate and living organisms acting upon parent material, conditioned by topography over time

Soil as a Resource:

• Soils are an important natural resource crucial to life on Earth
• Soils continue to supply food
• Plant biomass (e.g. crops) grown on soils may become an increasingly important feedstock for fuels and manufacturing as the world's petroleum supplies dwindle
• Soil is essential for food production
• Without soil, there will be No Crops or Livestock

Soil as a Non-Renewable Resource

• Soil acts as the basis for food, feed, medicines, ecosystem services, and fuel
• Global population will exceed 9 billion by 2050
• There will be an increased demand for healthier and nutritious food
• Agricultural production increases 60% globally with a ~100% increase in developing countries
• Soils are under pressure from intensification and competing uses of forestry, cropping, pasture & urbanization

Our Soils Today:

• 33% of global soil is moderately to highly degraded through erosion, salinization, compaction, acidification, chemical pollution & nutrient depletion, hampering soils functions and affecting food production
• 83% of rural people in Sub-Saharan Africa depend on their land for livelihood
• 40% of Africa's soils are currently degraded
• In most countries, there is little opportunity for expansion of arable land

Saving Our Soils:

• Implement inclusive policies and governance, targeted soil research, and effective education & extension programmes
• Invest in sustainable soil management, stop soil degradation & restore degraded soils through soil information systems
• Sustainable soil management increases soil organic matter content and keeps soil surfaces vegetated
• Soil management wisely uses nutrients and promotes crop rotations which reduces erosion can lead to an average crop yield increase of 58%

Ecological Functions of Soil:

• Medium for plant growth
• Recycling system for nutrients and organic wastes
• Modifier of the atmosphere
• Habitat for soil organisms
• Engineering medium
• System for water supply and purification

1. Medium for Plant Growth:

• Plants obtain physical support, air, water, nutrient elements, temperature moderation, and protection from toxins
• Soil is the foundation for agriculture, the medium in which nearly all food-producing plants grow, and produces about 95% of food
• Healthy soils supply the essential nutrients, water, oxygen, and root support

1. Medium for Plant Growth: 17 Elements Essential for Plant Growth and Their Sources

• Macronutrients are used in relatively large amounts (> 0.1% of dry plant tissue)

• Micronutrients are used in relatively small amounts (< 0.1% of dry plant tissue)

• From air and water: Carbon (CO2), Hydrogen (H2O), and Oxygen (O2)

• Macronutrients from soil: Nitrogen (NO3–, NH4+), Phosphorus (HPO42-), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+), and Sulphur (SO42-)

• Micronutrients from soil: Iron (Fe2+), Manganese (Mn2+), Boron (H4BO4–), Molybdenum (MoO42-), Copper (Cu2+), Zinc (Zn2+), Nickel (Ni2+), and Chlorine (CI-)

• Note: The chemical (ionic) forms most commonly taken up by plants are shown in parentheses, with the chemical symbol for the element in bold

2. Recycling System for Nutrients & Organic Waste:

• Nutrient recycling, e.g., Nitrogen cycle
• Organic waste recycling

3. Modifier of the atmosphere:

• Examples of modifying the atmosphere include the ability to store carbon or release CO2
• Over farming and overgrazing can release dust particles in air (Dustbowl)
• A dust storm approaches Stratford, Texas, in 1935

4. Habitat for Organisms:

• One handful of soil contains more individual microbes than the total number of people who have ever lived on earth

5. Engineering Medium:

• Used for highways and runways, foundation for buildings, landfill & disposal sites, and parks & recreation grounds
• Princes Town, Trinidad is prone to landslides

6. System for Water Supply and Purification:

• Example of regulating water supplies includes the hydrological cycle

Soil in the Ecosphere:

• The soil or pedosphere is where the worlds of rock (the lithosphere), air (the atmosphere), water (the hydrosphere), and life (the biosphere) all meet
• The Ecosphere is the planet when we think of it as an ecosystem

Components of Soil:

• Minerals (Inorganic)
• Organic matter
• Water
• Air
• Mineral Particles: sand, silt and clay

Mineral Particles:

• Particles differ in size:
• Sand = 0.05 – 2.0 mm
• Silt = 0.002 – 0.05 mm
• Clay = < 0.002 mm

General Properties of Inorganic Soil Particles:

Other Components of the Soil:

• Organic Matter (SOM): the organic fraction of the soil that includes plant, animal and microbial residues in various stages of decomposition, biomass of soil microorganisms, and substances produced by plant roots and other soil organisms
• Water: water is contained in the soil pores, contains dissolved substances (the soil solution), and needed for an optimum soil water content for growth
• Air: found in the pore spaces, Air (O2) is required for root and microbial respiration, concentration of gases in soil air (variable): O2 = 20.6% and CO2 = 0.25%

Volume Composition:

• The volume composition of a loam surface soil: Mineral (45%), Air (20-30%), Water (20-30%), Organic (5%)
• A nearly equal proportion of air and water is generally ideal for plant growth
• The proportions of these two components fluctuate as the soil becomes wetter or drier