Soil sample Sand (%) Silt (%) Clay (%) Organic matter (%) A 82 8 5 5 B 15 25 55 5 C 40 35 18 7 D 10 20 65 5 2 Table 2.1 shows the percentage composition of ...

(a) Soil sample with the highest proportion of sand [1]

Sample A, with 82% sand. [1] This is overwhelmingly sandy and would feel very gritty, drain rapidly, and have poor nutrient retention.

(b) Best soil sample for growing most crops, and why [2]

Sample C (a loam). [1] It has a balanced mixture of sand (40%), silt (35%), and clay (18%) with the highest organic matter (7%). This balance gives it good drainage (from the sand), good water retention (from the silt and clay), easy workability, and reasonable nutrient-holding capacity - making it suitable for the widest range of crops. [1]

(c) Why sample D is difficult to plough when dry [2]

1. Sample D has 65% clay. When clay soil dries out, the very small particles pack tightly together and the soil becomes extremely hard and compact. [1]
2. This hardness makes it highly resistant to the plough, requiring much more force to break up. The plough blade cannot penetrate easily, and large, hard clods form rather than a fine tilth. [1]

(d) Two problems growing maize in sample A [2]

Any two of:

1. Sandy soil does not retain water well, so maize plants may suffer drought stress between rainfalls or irrigations, since water drains away rapidly through the large pore spaces. [1]
2. Sandy soil has low nutrient-holding capacity (low cation exchange capacity), so applied fertiliser is quickly leached below the root zone by drainage water, leaving the maize short of nutrients. [1]
3. Sandy soil warms up quickly in the sun and can dry out the surface layer, damaging shallow-rooted seedlings.

(e) Meaning of soil composition [2]

1. Soil composition refers to the different materials that together make up the soil. [1]
2. These include mineral particles (sand, silt, clay), organic matter (humus from decomposed plant and animal material), water, air, and living organisms (earthworms, bacteria, fungi). [1]