6 Fig. 6.1 shows a diagram of the three main types of weathering that contribute to soil formation. (a) Name the three types of weathering shown in Fig. 6.1...

Labelled answer diagram:

(a) The three types of weathering:

1. Physical weathering (also called mechanical weathering) [1].
2. Chemical weathering [1].
3. Biological weathering [1].

(b) One example of each type:

1. Physical weathering: frost action (freeze-thaw), where water expands in rock crevices upon freezing, splitting the rock apart [1]. Other examples: exfoliation (thermal expansion and contraction), abrasion by wind-blown particles.
2. Chemical weathering: dissolving of limestone by carbonic acid in rainwater [1]. Other examples: oxidation of iron-bearing minerals (rusting), hydrolysis of feldspar.
3. Biological weathering: root growth widening cracks in rocks as plants establish themselves on rock surfaces [1]. Other examples: burrowing by earthworms or termites, acids produced by lichen or moss.

(c) Weathering alone does not produce fertile agricultural soil because:

1. Weathered rock particles are purely mineral fragments and lack organic matter (humus), which is essential for soil structure and nutrient supply [1].
2. The nutrients present in rock fragments are not in forms that plant roots can readily absorb; biological decomposition is needed to convert them to available forms [1].
3. Without soil organisms to decompose dead material and recycle nutrients, there is no nutrient cycling, and the soil structure remains poor because there are no organic binding agents to create soil aggregates [1].

(d) Before weathered rock particles can support healthy crop growth, the following must be added:

1. Organic matter (humus) from decomposed plant and animal remains, which improves soil structure, water retention, and nutrient supply [1].
2. Soil organisms such as bacteria, fungi, and earthworms that decompose organic material and recycle nutrients into plant-available forms [1].