Correct Option (a):
Water-use efficiency (WUE) is defined as the amount of crop yield produced per unit of water consumed. Sugarcane is considered a highly water-intensive crop due to its long growing period, typically 10-12 months, and substantial water requirement, ranging from 1500 to 2500 mm. This high water demand relative to its productivity per unit of water makes it one of the least water-efficient crops among the given options.
Incorrect Options:
- Sunflower (b): This crop has a moderate water requirement, typically needing 600-1000 mm of water during its growth cycle. It is significantly more water-efficient than sugarcane.
- Pearl millet (c): Known for its drought resistance, pearl millet requires considerably less water, usually between 450-650 mm. It is well-suited for arid and semi-arid regions, indicating high water efficiency.
- Red gram (d): Also known as pigeon pea, red gram is a relatively water-efficient legume, requiring approximately 350-500 mm of water. It is commonly cultivated in rainfed areas, demonstrating its lower water dependency compared to sugarcane.