Final answer:
The primary cause of soil salinization in North Africa and Southwest Asia is the use of irrigation with salty water, leading to the accumulation of salt in the soil which reduces agricultural productivity.
Step-by-step explanation:
The primary cause of the salinization of soils in North Africa and Southwest Asia is D) Irrigation with salty water. In arid climates, like those in North Africa and Southwest Asia, salinization is a significant issue as it leads to reduced agricultural productivity. When fields are irrigated with water containing small quantities of salt, over time, these salts accumulate in the soil. To remediate salinization, fresh water is used to flush out the salts, thereby restoring the soil's productivity.
Salinization is exacerbated by factors such as the limitation of fresh water for flushing out the salts due to water scarcity and the high demands on agricultural production to feed growing populations. Notably, in places like Egypt, where agriculture plays a crucial role in the economy and supports a large rural population, the impact of soil salinization is of great concern.