Correct Option
The correct option isSevere winters restrict the growing season.
Explanation
Commercial grain farming is predominantly practiced in the interior parts of semi-arid lands of the mid-latitudes. Major areas include the Prairies of North America, the Pampas of Argentina, the Velds of South Africa, the Downs of Australia, and the Steppes of Eurasia. This type of agriculture is specialized and highly mechanized.
Detailed Analysis
- Lack of fertile soil. is incorrect: The soil in temperate grasslands (often Chernozem or prairie soils) is typically deep, rich in humus, and highly fertile. The limitation on cropping intensity is not due to soil quality.
- Severe winters restrict the growing season. is correct: These mid-latitude regions experience a continental climate with extreme temperature variations. The winters are severe and prolonged, which significantly restricts the duration of the growing season. This short climatic window allows for the cultivation and maturation of only a single crop per year.
- Lack of mechanization. is incorrect: Commercial grain farming is characterized by extensive mechanization. All agricultural operations, from ploughing to harvesting, are performed using heavy machinery to manage large farm sizes with low labor density.
- Government restrictions on multiple cropping. is incorrect: The restriction to a single crop is a result of climatic constraints (environmental factors), not government regulations or policy interventions.
Key Takeaway: The primary factor limiting commercial grain farming in temperate grasslands to a single crop is the short growing season caused by severe winters.