Which source irrigates the largest area in Uttar Pradesh?

The correct answer is B, tube wells. The alluvium of the Ganga plain holds water close to the surface, so a farmer can sink a tube well cheaply and pump whenever the crop needs water rather than waiting for a canal turn. As a result tube wells water more of the net irrigated area of Uttar Pradesh than any other source, and the state has more of them than any other in the country.

Option A, canals, come second and dominate only in the western Doab and the Sharda Sahayak command, where the old systems run. Option C, tanks, matter in the southern plateau districts of Bundelkhand and in parts of the east, but they cover a small area and dry up in a weak monsoon. Option D, lift irrigation from rivers, is used locally along the Ganga, Yamuna and Ghaghara and is again minor. The follow up question usually asks for the consequence, which is the falling water table in the heavily pumped western districts.