Theory question 101
Soil(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 soil
(c) (i) State the characteristics of sandy and loamy soils (ii) What type of vegetation does each support?
Show the model answer
(a) Dry equal masses of sand, loam and clay; place cotton wool in three funnels on measuring cylinders; put each soil in a funnel; pour the same volume of water (e.g. 100 cm³) on each; leave until dripping stops; measure the water collected
Water retained = water added − water collected; clay retains most, then loam, sand least
(b) Any three: particle size/texture; humus/organic matter content; soil structure (crumbs); amount of clay; pore spaces; compaction
(c)(i) Sandy: large coarse particles; large air spaces; well drained and aerated; holds little water; low in nutrients; warms quickly
Loamy: mixture of sand, silt and clay with humus; good crumb structure; moderate drainage and water retention; well aerated; fertile
(ii) Sandy soil – sparse vegetation (grasses, shrubs, drought-tolerant plants); loamy soil – luxuriant vegetation, good for most crops and forest
State that equal masses of soil and equal volumes of water must be used.