(a) Describe an experiment to compare the... | WAEC SSCE - Biology - 1997 (Essay)

Question 1 Report

(a) Describe an experiment to compare the water-holding capacity of sandy, loamy and clayey soils.

(b) List three factors that may affect the water-holding capacity of soils.

Answer

(a) Experiment to compare the water-holding capacity of sandy, loamy and clayey soils

Materials: three identical filter funnels, three filter papers, three measuring cylinders, equal known masses (or volumes) of dry sandy, loamy and clayey soil, and a fixed volume of water.
Method: Line each funnel with a filter paper and place each over a measuring cylinder. Put an equal amount of each dried soil into its own funnel. Pour the same measured volume of water (for example 100 cm³) into each funnel at the same time. Allow the water to drain until dripping stops.
Measure the volume of water that collects (the filtrate) in each measuring cylinder.
Water retained = volume poured in minus volume drained out.
Observation/Result: most water drains through the sandy soil (little retained); least water drains through the clayey soil (most retained); loamy soil is intermediate.
Conclusion: water-holding capacity is highest in clayey soil, intermediate in loamy soil and lowest in sandy soil.

(b) Three factors affecting water-holding capacity of soil

The size of the soil particles (fine particles hold more water than coarse ones).
The amount of humus (organic matter) present (humus absorbs and holds water).
The degree of compaction and the pore spaces (porosity) of the soil.

(c)(i) Characteristics

Sandy soil: made of large particles; well aerated; drains quickly and holds little water; light and easy to work; low in humus and mineral nutrients; warms up quickly.
Loamy soil: a balanced mixture of sand, silt and clay; well aerated and drained yet holds enough water; rich in humus and nutrients; the most fertile soil.

(c)(ii) Vegetation supported

Sandy soil supports desert or savanna vegetation such as cactus, grasses and drought-resistant shrubs.
Loamy soil supports rich crop plants and dense vegetation (rainforest/farm crops) such as maize, yam, vegetables and most food crops.

Answer Details

(a) Experiment to compare the water-holding capacity of sandy, loamy and clayey soils

Materials: three identical filter funnels, three filter papers, three measuring cylinders, equal known masses (or volumes) of dry sandy, loamy and clayey soil, and a fixed volume of water.
Method: Line each funnel with a filter paper and place each over a measuring cylinder. Put an equal amount of each dried soil into its own funnel. Pour the same measured volume of water (for example 100 cm³) into each funnel at the same time. Allow the water to drain until dripping stops.
Measure the volume of water that collects (the filtrate) in each measuring cylinder.
Water retained = volume poured in minus volume drained out.
Observation/Result: most water drains through the sandy soil (little retained); least water drains through the clayey soil (most retained); loamy soil is intermediate.
Conclusion: water-holding capacity is highest in clayey soil, intermediate in loamy soil and lowest in sandy soil.

(b) Three factors affecting water-holding capacity of soil

The size of the soil particles (fine particles hold more water than coarse ones).
The amount of humus (organic matter) present (humus absorbs and holds water).
The degree of compaction and the pore spaces (porosity) of the soil.

(c)(i) Characteristics

Sandy soil: made of large particles; well aerated; drains quickly and holds little water; light and easy to work; low in humus and mineral nutrients; warms up quickly.
Loamy soil: a balanced mixture of sand, silt and clay; well aerated and drained yet holds enough water; rich in humus and nutrients; the most fertile soil.

(c)(ii) Vegetation supported

Sandy soil supports desert or savanna vegetation such as cactus, grasses and drought-resistant shrubs.
Loamy soil supports rich crop plants and dense vegetation (rainforest/farm crops) such as maize, yam, vegetables and most food crops.

(a) Describe an experiment to compare the water-holding capacity of sandy, loamy and clayey soils. (b) List three factors that may affect the water-holding ...