The best method of applying water to sandy undulating area is :

The correct answer is D, sprinkler irrigation. Sandy soil drinks water too fast for any surface method, and an uneven surface cannot be flooded evenly without heavy levelling. A sprinkler throws measured water through the air like rain, so it does not need level land, it can be matched to the rate at which the soil takes water, and very little is lost in field channels. This is the reason sprinkler sets have spread so widely in the sandy districts of western Rajasthan.

Option A, free flooding, wastes water on sand and leaves the high patches dry. Option B, subirrigation, works only where an impervious layer holds water within reach of the roots, which sandy undulating land does not have. Option C, the furrow method, suits row crops on fairly level ground with soils that hold water, and on a sandy slope the furrows would either wash out or drain away before the water spread.