Among the following, which one is the least water-efficient crop?

The correct option is Sugarcane.

Explanation:

Water Use Efficiency (WUE) of a crop is defined as the amount of yield or biomass produced per unit of water used (evapotranspired). Crops with lower water use efficiency require significantly higher volumes of water to produce a given amount of dry matter or economic yield.

Let's analyze the given options in terms of their water requirements and water efficiency:

1. Sugarcane: Sugarcane is a long-duration, high water-consuming crop. It requires about 1500 to 2500 mm of water throughout its growing cycle. Although it is a C4 plant, its overall biomass production requires enormous amounts of water, making it the least water-efficient crop among the given choices, especially in terms of water consumed per crop season.

2. Pearl millet (Bajra): Pearl millet is a highly drought-tolerant C4 cereal crop widely grown in arid and semi-arid regions. It has very high water-use efficiency and low total water requirements (around 250 to 450 mm).

3. Red gram (Pigeon pea): Red gram is a rainfed legume crop with a deep root system that helps it withstand drought stress, giving it relatively good water-use efficiency under rainfed conditions.

4. Sunflower: Sunflower is an oilseed crop with moderate water requirements (around 500 to 600 mm) and high water productivity under controlled irrigation.

Therefore, Sugarcane consumes the largest volume of water per unit area and is considered the least water-efficient crop among the listed options.