A student studying environmental management investigated three soil samples collected from different locations: a sandy beach margin, a clay riverbank, and ...

(a) The soil type with the smallest particle size is clay soil, with particles less than 0.002 mm in diameter. [1]

(b) Why sandy soil drains quickly and holds few nutrients: [2]

• Sandy soil has large particles (0.05-2 mm) with large air spaces (pores) between them. Water drains rapidly through these large pores under the force of gravity because there is little resistance to flow. [1]
• As water moves quickly through the soil, it carries dissolved mineral nutrients (nitrates, potassium, phosphates) downward and out of the root zone. This process is called leaching. Because the water does not remain in contact with the soil particles long enough for roots to absorb nutrients, sandy soils are nutrient-poor for plant growth. [1]

(c) Why loam soil is considered the best soil for growing most crops: [4]

• Loam is a mixture of sand, silt and clay particles in roughly balanced proportions. This combination gives it the beneficial properties of each without their extremes. [1]
• Moderate drainage: Loam drains well enough to prevent waterlogging (unlike clay), but retains enough water for plants to absorb between rainfall events (unlike sand). This balance ensures a reliable water supply to roots. [1]
• Good aeration: The mixture of particle sizes creates pore spaces of varying dimensions. Larger pores allow air to reach roots, which need oxygen for aerobic respiration. This supports healthy root growth and the activity of beneficial soil organisms. [1]
• Nutrient retention and workability: Loam retains nutrients at a moderate-to-high level because the clay and silt fractions hold mineral ions on their surfaces. At the same time, it is easy to plough, dig and cultivate because it is not as heavy or sticky as pure clay. [1]

(d) How a farmer could improve a clay soil: [3]

• Adding organic matter (compost, well-rotted manure, leaf mould) improves soil structure by binding the tiny clay particles into larger aggregates (crumbs). This creates bigger air spaces between aggregates, improving both drainage and aeration while also adding nutrients. [1]
• Adding lime (calcium carbonate, CaCO₃) causes clay particles to clump together in a process called flocculation. This reduces the soil's stickiness, makes it easier to work and improves drainage. Lime also raises the pH if the soil is too acidic. [1]
• Practising crop rotation with deep-rooted plants (such as certain legumes or root vegetables) physically breaks up compacted clay layers, creating channels that improve water drainage and air penetration. The decaying roots also add organic matter to the soil. [1]