Water diversion and pumping has allowed humans to grow crops in areas where natural supplies have been limited. A major challenge that exists in these regions due to over irrigation has been

a. High pesticide use
b. Low crop diversity
c. Salinization of soils
d. Soil erosion

The correct answer is D. Water diversion and pumping has allowed humans to grow crops in areas where natural supplies have been limited. A major challenge that exists in these regions due to over irrigation has been  soil erosion.

Explanation:

Soil erosion is a phenomenon of displacement of materials on the surface of the outermost layer of the earth's crust. It is one of the forms of regression and degradation of the soil. Protection against this erosion is an issue for the preservation of the agronomic quality of agricultural soils, the quality of surface water and the security of dwellings and infrastructure (covering of roads, appearance of muddy flows, clogging or filling of networks rainwater collection).