You talked about everything (thank you) except water. Have you had a lot of rain this year? Did the grass sit in standing water for any length of time?

The photo shows a diseased blade of grass. Question is how did it get that way?

Organics may seem expensive, but in the long run, you'll save because you won't have the issues other people have. The grass will not have problems with stress from summer heat, winter cold, insects, disease, and weeds. Are you trying to translate pounds of N from chemical to organics? You can't do that. NPK is completely irrelevant in an organic program. With organics you're interested in pounds of protein. Protein contains the nitrogen element which eventually (3 weeks after application) gets turned into plant food. The organic process is biological. Some of the bacteria and fungi involved in the transition to plant food involves absorbing N from the air and converting that into plant food, too. But if those microbes do not receive food (organic fertilizer), they cannot do their job. So there is no apples to apples comparison between organic and chemical ferts. They both work. I happen to believe it is much easier and less hassle to stick completely with organic fertilizers and organic insect control.

The organic solution to lawn disease is ordinary corn meal. Call your local feed stores to see if they have it. You want either whole ground or chopped corn. Whole corn (deer corn) will grow a field of corn, so that's not usually what people want. Apply corn meal at a rate of 20 pounds per 1,000 square feet. Apply now and again in a month. You don't have to water it in, but it helps if you moisten it right after you apply. Just wash it off the tops of the grass so it's sitting on the soil. Corn meal works by attracting a beneficial, predatory fungus to the corn. That fungus literally eats other fungi. The population builds up on the corn and then it launches off to kill the disease fungi in your lawn. Apply to the entire lawn so you don't miss any spots. If you miss any spots, you can always reapply. If you miss spots, they will show up as slightly yellow in about 3 weeks. That's because corn meal is also an organic fertilizer which greens up the grass.