Final answer:
A farmer cannot predict or prevent weather changes such as drought, which have a significant impact on agricultural production. Measures can be taken against other issues such as pest infestations and soil erosion, but weather events remain largely beyond a farmer's control.
Step-by-step explanation:
Among the options provided, a farmer cannot predict or effectively prevent weather changes. Weather events, such as drought, excessive rainfall, floods, and other extreme conditions, greatly impact crop yields, soil health, and the overall agricultural environment. A severe drought, for example, can drastically decrease the supply of agricultural products, leading to a lower quantity available at any given price. On the other hand, especially favorable weather can lead to increased production and a shift in the supply curve to the right.
Soil erosion and desertification are also major concerns that can be influenced by weather and climate, though to some extent, they can be mitigated by careful land management practices. Agricultural production can be affected not just by the quantity, but also the quality of crop yields, which might be linked to a variety of factors including pest infestations, soil salinity, and nutrient-poor soils. However, these factors can sometimes be controlled or improved by the farmer, unlike unpredictable weather changes.