Topic 3 Agriculture Section 3.1 Soil

1. UNIT 3 – AGRICULTURE
AND THE
ENVIRONMENT

2. CONTENTS
 Soil composition
Soils for plant growth
Agriculture types

3. LEARNING OBJECTIVES
 Describe and explain the composition of soils
Describe soils as a medium for plant growth
 Describe the differences between sandy and clay soil
Describe the different types of agriculture

4. SOIL COMPOSITION
Mixture of:
 Mineral particles from weathering and erosion of rocks
 Organic matter of living plants, animals and microorganisms and decaying matter (humus)
 Water from precipitation
 Air (rich in carbon dioxide_
 40-45% inorganic; 5% organic; 25% water; 25% air
 Soil particles come in different sizes
 Small (0.002mm) = CLAY
 Medium (0.002 – 0.05) = SILT
 Big (0.05 – 2mm) = SANDY

5. CLAY VS SILT VS SAND
SIZE?
WATER RETENTION?
SPACES?
DRAINAGE?
TIME TO HEAT UP OR LOSE HEAT?
BUT WHAT IS SOIL IS A MIXTURE??
 = LOAM

6. SOILS FOR PLANT GROWTH
 REQUIRES MINERALS AND NUTRITIONAL ELEMENTS FOR HEALTHY GROWTH AND
REPRODUCTION
MINERALS (NOT SOIL) AND WATER FROM ROOT HAIRS IN FORM OF IONS (DISSOLVED IN SOIL
WATER)
MOST NB = NITROGEN, PHOSPHORUS, POTASSIUM, MAGNESIUM

7. MINERAL ION MINERAL ELEMENT HOW USED IN PLANTS
Nitrate NITROGEN (N) Combines with glucose to form
amino acids
Phosphate PHOSPHORUS (P) Important for DNA and cell
membranes; required for
respiration and growth
Potassium cation (K+) POTASSIUM (K) Must be present for
photosynthesis
Magnesium Mg²(+) MAGNESIUM (Mg) Used for manufacturing
chlorophyll– no Magnesium = no
photosynthesis = death

8. Organic matter
 Reservoir of nutrients
Improves water-holding capacity of soil
Helps to bind or clump soil into aggregates that improves soil structure and permeability
Important role in preventing soil erosion
Increases water filtration

9. SOIL pH
 Acidic
Neutral
Alkaline

11. AGRICULTURE TYPES
 Agriculture / farming = cultivation of the soil for the growing of crops and the rearing of animals
38% of land surface
1/3 of the world’s population obtain their livelihood from agriculture and associated food
processing industries
475 million farms = subsistence or semi-subsistence level and support 2 billion people on plots
of land smaller than 0.02 sq km
Subsistence farming = self-sufficiency farming
 Asia and Africa
 Undernourished people
 Poverty

12. 1. Subsistence
Slash and burn
 Subsistence farming
 Tropical regions
 Shifting cultivation
 Clear felling and burning forest and scrub to make room for crops and cattle
 Ash = fertility boost
 Rains – leach soils of nutrients
 Abandoned  new clearings made
 = unsustainable and damaging to forest ecosystems

13. 2. Commercial
Commercial farms are fewer than subsistence farms; they are larger and therefore account for
over 80% of the world’s agricultural land
= farming for profit
Almost all farming in MEDC’s (more economically developed countries) = commercial
Can be:
 Arable
 Pastoral
 Mixed
 Intensive operations; large investments of capital
 Modern machines and technologies