Desertification

In an area rich in plantlife, you can touch the ground and start a life draining effect. On the start of each of your turns, for as long as you focus on the spell using an action, you extend the spell's radius by 5 feet. The spell effect is a cylinder with a height of 100ft, that can reach a maximum radius of 50ft provided you concentrate on the spell for the full duration. All nonmagical plants in the area are enveloped in a dull grey glow and start to dust. At the end of the spell, all soil is rendered magically infertile and turned to sand, while all nonmagical  plantlife withers away to dust. The spell does not affect magical plantlife, creatures or stuctures.

When the spell ends, you regain hit points equal to a number of d10 equal to the number of rounds you concentrated on the spell, to a maximum of 10d10 hitpoints. 

The lingering magical infertileness of the land is tethered to the innate life energy of the area and therefore cannot be dispelled using Dispel Magic. It can only be dispelled by a Wish spell; or a Plant Growth spell cast at equal or higher level.