The answer to 'lawn fertilization yellowing' is that lawn fertilizer can sometimes cause temporary yellowing or discoloration of the grass. This is usually due to the nitrogen content in the fertilizer, which can temporarily stress the grass and cause it to yellow before the nutrients are fully absorbed and the grass recovers.
Yellowing after fertilizing is a common occurrence and is not necessarily a sign of a serious problem. However, if the yellowing persists for more than a few weeks or spreads across a large area of the lawn, it could indicate an underlying issue that may require professional diagnosis and treatment.