4 Wind erosion is a serious problem in semi-arid farming regions. (a) State three conditions that make wind erosion more likely to occur. [3] (b) Describe h...

(a) Three conditions that make wind erosion more likely [3]:

1. Dry, loose or sandy soil with little organic matter. Organic matter acts as a binding agent between particles; without it, individual grains are easily lifted by wind. [1]
2. Flat, open landscape with no barriers. Wind accelerates across unobstructed terrain, building up enough force to detach and transport soil. [1]
3. Bare soil surface with no crop cover or stubble. Vegetation and residue shield the soil from direct wind contact and reduce wind speed at ground level. [1]

Also acceptable: strong or persistent winds; soil that has been finely cultivated (fine tilth is more vulnerable than cloddy soil).

(b) How a windbreak reduces wind erosion [3]:

1. The row of trees reduces wind speed on the sheltered (leeward) side. Air hitting the windbreak is forced up and over, creating a zone of calmer air downwind. [1]
2. Slower wind has less energy to lift and carry soil particles. The critical threshold wind speed for detaching particles is no longer reached in the sheltered zone. [1]
3. The windbreak also traps airborne soil particles that are already in suspension, preventing them from being transported further across the field. [1]

(c)(i) Distance protected by the windbreak [1]:

\[ 10 \times 8 = 80 \text{ m} \] [1]

(c)(ii) Whether the single windbreak adequately protects the entire field [2]:

No, the windbreak protects only 80 m, but the field is 200 m wide. [1] The far side of the field (200 - 80 = 120 m from the windbreak) remains exposed to wind erosion. A second windbreak approximately 80 m from the first, or additional protective measures such as cover crops or mulching, would be needed to protect the entire field. [1]