The answer to 'sod yellowing' is that there are several common causes, including improper watering, nutrient deficiencies, disease, and insect damage. Symptoms include the grass turning yellow or brown in patches, and the blades becoming thin and brittle. Solutions may include adjusting watering schedules, applying fertilizer, treating for pests or disease, or in some cases, replacing the affected sod.
If the yellowing is widespread or the cause is unclear, it's best to call a professional landscaper to diagnose and treat the issue properly. They can assess the underlying problem and recommend the most effective solution to restore your lawn.