Different types of plants have different types of roots. There are some plants that have fibrous roots and these roots spread out and absorb water near the surface of the soil. Another type of root is called a tap root. In this case tap roots anchor plants firmly and can absorb water from deep beneath the ground. Each type of root serves a purpose to bring the plant the nutrients it needs.
Nature knows best and each type of plant will come naturally equipped with whatever root best serves that plant. Some platns that typically have tap roots include beets, carrots, and parsnip. Plants that have fibrous roots include onions, rice, and millet.