CARA'S TIPSRocks, soil formation, soil properties, nutrients and fertilisers
JAMBWAECNECO
What the syllabus asks
JAMB: B1 Rocks and soil formation, B2 Soil water and conservation, B3 Soil fertility (macro- and micronutrients, deficiency symptoms, cycles, fertilisers, organic manures)
WAEC: B6 Rock formation; B7 Soil formation and profile development; B8 Types, composition and properties of soil (nutrients, water, organisms, air, pH, texture, structure); B9 Plant nutrients and nutrient cycles, replenishing lost nutrients, fertilisers, organic agriculture; Practical A1–A5 (soil texture, profile, rocks, physical and chemical laboratory work, fertilisers and manures)
NECO: B6 Rock formation; B7 Soil formation and profile development; B8 Types, composition and properties of soil (nutrients, water, organisms, air, pH, texture, structure); B9 Plant nutrients and nutrient cycles, replenishing lost nutrients, fertilisers, organic agriculture; Practical A1–A5 (soil texture, profile, rocks, physical and chemical laboratory work, fertilisers and manures)
What you will learn
- Classify rocks and explain how each type forms.
- Explain the factors and processes of soil formation.
- Describe a soil profile and the features of each horizon.
- State the composition of soil and the roles of water, air and organisms.
- Distinguish sandy, clay and loamy soils and explain texture and structure.
- Carry out and interpret simple soil laboratory tests.
- Explain soil pH and how to correct acidity and alkalinity.
- State the functions and deficiency symptoms of major and minor nutrients.
- Describe the nitrogen, carbon, water and phosphorus cycles.
- Classify fertilisers and manures, calculate fertiliser rates, and explain organic agriculture.
Key points
- Rocks: igneous (magma), sedimentary (layers, fossils), metamorphic (heat/pressure: marble, slate, quartzite, gneiss).
- Weathering: physical, chemical (solution, hydrolysis, oxidation, hydration), biological.
- Soil-forming factors: climate, organisms, relief, parent material, time (CLORPT).
- Profile: O (litter), A (topsoil, eluviation), B (subsoil, illuviation), C (weathered rock), R (bedrock).
- Ideal loam (textbook): 45% mineral, 5% organic, 25% water, 25% air.
- Capillary water is the main water available to plants.
- Texture = sand/silt/clay proportions; structure = arrangement into aggregates; loam is best.
- Lab: sedimentation, water retention, moisture content, bulk density, porosity, capillarity.
- pH 6–7 suits most crops; lime corrects acidity; sulphur/gypsum/organic matter for alkalinity.
- N leaves/chlorophyll; P roots/seeds; K strength/quality/disease resistance.
- Nitrogen cycle: fixation, ammonification, nitrification (Nitrosomonas, Nitrobacter), denitrification.
- Fertility maintained by rotation, manures, fertilisers, fallowing, liming, cover crops.
- Fertilisers: urea 46% N, ammonium sulphate 21% N, SSP ~18% P₂O₅, MOP 60% K₂O; NPK compounds.
- Fertiliser needed = nutrient required ÷ fraction in fertiliser × area.
- Organic agriculture avoids synthetic inputs; erosion is controlled by cover, contours, terraces, windbreaks.
Start here: Rocks: types and formation
All soils begin as rock. On the Jos Plateau you can see bare granite hills; at Ewekoro in Ogun State limestone is quarried for cement; at Ikpeshi in Edo State marble is mined. Each of these is a different rock type.
| Type | How formed | Features | Examples |
|---|---|---|---|
| Igneous | Molten magma cools and solidifies, either inside the earth (intrusive, e.g. granite) or on the surface after volcanic eruption (extrusive, e.g. basalt) | Crystalline, hard, no layers, no fossils | Granite, basalt, gabbro, dolerite |
| Sedimentary | Fragments of older rock, shells and plant remains are deposited in layers (usually under water), then compacted and cemented | Layered (stratified), may contain fossils, often softer | Sandstone, limestone, shale, clay, coal, conglomerate |
| Metamorphic | Existing igneous or sedimentary rocks are changed by great heat and/or pressure without melting | Very hard, often banded or foliated, crystals realigned | Marble (from limestone), slate (from shale), quartzite (from sandstone), gneiss (from granite) |
Identifying rocks in the practical
- Granite: speckled grey/pink with visible crystals of quartz, feldspar and mica.
- Limestone: grey/white; fizzes with dilute hydrochloric acid (releases CO₂), because it is calcium carbonate.
- Sandstone: gritty, sand grains visible.
- Marble: crystalline, often white, also fizzes with acid.
- Shale: fine-grained, splits into thin layers.
A student drops dilute HCl on rock specimen X and it effervesces. X has visible layers and a shell fossil. Identify X and its rock type.
Effervescence shows carbonate; layers and fossils show sedimentary origin. X is limestone, a sedimentary rock.
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Practice questions
- residual (sedentary) soil
- alluvial soil
- colluvial soil
- loess
Show answer
A: residual (sedentary) soil
Transported soils are moved by water, wind or gravity.
- B horizon
- C horizon
- R horizon
- A horizon
Show answer
D: A horizon
Topsoil is richest in organic matter.
- silty soil
- loamy clay
- sandy soil
- clay soil
Show answer
C: sandy soil
Sand particles are about 0.05–2 mm across; clay particles are below 0.002 mm.
- gravel
- loam
- clay
- sand
Show answer
B: loam
Loam is ideal for most crops.
- hygroscopic water
- capillary water
- gravitational water
- free water
Show answer
A: hygroscopic water
Capillary water is the main available water.
Key words
- Rock
- A naturally occurring solid mass of one or more minerals.
- Igneous rock
- Rock formed from cooling and solidification of molten magma, e.g. granite, basalt.
- Sedimentary rock
- Rock formed from layers of deposited sediments that are compacted and cemented, e.g. sandstone, limestone, shale.
- Metamorphic rock
- Rock formed when existing rock is changed by heat and pressure, e.g. marble, slate, quartzite, gneiss.
- Weathering
- The breakdown of rocks in place by physical, chemical or biological processes.
- Parent material
- The rock or deposit from which a soil develops.
- Soil profile
- A vertical section of soil showing its layers (horizons) down to the parent rock.
- Horizon
- A distinct layer of a soil profile.
- Humus
- Dark, decomposed organic matter in soil.
- Soil texture
- The relative proportion of sand, silt and clay particles in a soil.
- Soil structure
- The arrangement of soil particles into aggregates (peds).
- Porosity
- The proportion of soil volume made up of pore spaces.
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