A yellowing lawn looks hungry, so people feed it. In Central Texas that reflex frequently makes the problem worse, because the cause is usually not a shortage of what you are adding.
Alkaline soil locks up iron
Soils across most of this region are alkaline, and at high pH iron becomes chemically unavailable to plants even when it is present in the ground. The result is iron chlorosis: yellowing blades with veins that stay noticeably greener.
That vein pattern is the tell. Nitrogen deficiency yellows the whole blade fairly uniformly and shows in older growth first. Iron chlorosis shows in new growth and leaves the veins green.
Why more nitrogen backfires
Nitrogen pushes new growth. New growth demands iron. If iron is already unavailable, you have increased demand for something the plant cannot access, and the yellowing intensifies.
Meanwhile the excess nitrogen encourages disease. Take-all root rot on St. Augustine is made worse by high nitrogen, so a lawn treated for the wrong problem can end up with two.
What to do instead
A soil test is worth doing once. It costs little and tells you pH and what is actually present, which ends the guessing permanently.
For iron chlorosis, chelated iron works because it stays available at high pH, unlike ordinary iron sulfate. Compost top-dressing helps over time by improving soil biology around the roots. And check the obvious first: yellowing from compacted soil, poor drainage or a sprinkler zone that misses that area looks similar and is fixed by aeration or irrigation work rather than by any product.
The other causes of yellow that get misdiagnosed
Not every yellow lawn is iron. Nitrogen deficiency yellows uniformly and appears first in older growth, the reverse of iron chlorosis. Overwatering produces yellowing because roots lack oxygen, and the ground feels spongy. Compacted soil produces the same symptom by preventing roots from working at all.
Take-all root rot yellows in patches during spring, and the roots pull up easily and look dark rather than white. Chinch bugs produce yellowing that turns brown and does not recover with watering.
The diagnostic habit worth building: look at the pattern and the roots before reaching for a product. Uniform versus patchy, new growth versus old, and what the roots look like when you pull a plug will separate most of these in five minutes.
Soil testing and long-term correction
A soil test through your county extension office is inexpensive and ends the guessing. It reports pH and nutrient levels, which tells you whether you are dealing with an availability problem or an actual shortage. Doing it once is worth more than years of guessing from a bag label.
You cannot meaningfully change the pH of an alkaline soil across a whole yard, and attempts to do so with sulfur are temporary and expensive at that scale. The realistic strategy is to work with it: use chelated iron, which stays available at high pH, and build soil biology with compost so nutrients cycle better around the roots.
In planting beds, choosing species adapted to alkaline soil solves the problem permanently rather than treating it every season. Many of the plants that struggle here are simply acid-lovers in the wrong region.
Feeding the lawn and it keeps yellowing?
It is usually iron availability, not a fertilizer shortage.