pH is high but not crazy for grass.

The magnesium being out of balance is what's causing the hard soil and muck when wet. Morpheuspa or Yardtractor can help you with that.

The contractor was not clueless as to the proper way to prep for a lawn. Grading it is the proper way. Nothing needed to be amended before hand. You're going to do that now with organic fertilizer and chemistry customized according to the soil test.

You said you watered religiously. If that means you watered all day, every Sunday, that would be about perfect. If it means something else, then you likely overwatered it. That might be what you're seeing. Watering too often in the summer leads to more problems than it cures.

Can you post a picture or two? Pictures of gardens look much better when taken in the shade or on a cloudy day with no flash. You might take one at a level of 3 inches away from the grass where there is both green and brown grass. Then take another showing the big picture.

Let's start at the beginning. Sort of, I tend to bounce around a little bit.

pH 7.9: This is being set off by the high magnesium, but it's not out of bounds for an excellent lawn. More as we go below.

CEC 12.9: A nice soil that holds plenty of resources and doesn't drift terribly quickly. Once balanced, re-testing every two to four years will be sufficient.

Organic Matter 1.2%: Poor, but that's normal for new construction. Always mulch mow, mow all your fall leaves (if any), import neighbors' leaves who are discarding them at the roadside, and consider feeding organically for the little boost that'll give you. Raising your OM will make the pH matter a lot less as well, so while not critical with your high CEC, it's a help given your high pH.

Phosphorus 21: Pretty close to optimal. If you want to use some starter fertilizer once when you redo things, go ahead, but it's not necessary. I don't feel strongly about adding it or not adding it, this isn't a decision that has any long-term consequences. But once will be more than enough.

Calcium 1500: Fine! Next time, I'd like to see you get a Logan test so we can see how the calcium is competing with the magnesium, but you should be within spitting distance of Good to Very Good levels.

Magnesium 630: Very high, but not off the charts (although it's getting close). Again, Logan test next year as saturation percentages get hard to predict when you have an excess like this. It's likely making your soil sticky, cracked when dry, and generally hard to dig. While gypsum can help, I don't recommend that at this time as you already have optimal calcium levels and I'm not a fan of imbalancing one resource in favor of another unless I absolutely have to. In this case, I don't expect any issues with plants and the numbers aren't high enough to cause the magnesium to full-scale block other optimal resources. Raising OM will help with the tight soil and cracking issues as well.

Potassium 74: I'd really like to see this around 150 (bare minimum) at your pH and soil CEC, and knowing that magnesium is dominating the soil profile (while K can make your soil tight and make the problem worse in the presence of high magnesium, I'm balancing that against the excessive magnesium blocking the uptake of other cations, including potassium). The other thought here is the faint, probably vain hope, that the sulfates will bond with a bit of the Mg and wash out. But let's not count on that. To fix it, we use potassium sulfate, which you can sometimes get at garden or landscape stores, or some will order it for you. Online is another option, but it does tend to be a bit more expensive. Get the granular, it's much easier to apply. Recommendations below.

Minor Elements: Not tested.

Recommendations, General:

* In this case, to feed the lawn I'd be tempted to use urea or ammonium sulfate, both acidifying fertilizers (ammonium sulfate more than urea). With use, you'll see some lowering in the medium calcium levels, and a general slight lowering of the pH, at which point we can pour on the calcium sulfate (gypsum) to abolish a little magnesium and bring the calcium back up. Over the course of years, this soil could be rebalanced that way, although it will take some work and considerable attention. Most off the shelf synthetic fertilizers are urea-based.

* The potassium sulfate is a technical mistake, but this is a most unusual case where I feel more comfortable making the mistake than not making it. In any case, the mistake (slightly tighter soil than you already have) is fairly minor. I'm only adding about four pounds of available potassium per thousand square feet.

* I didn't mention it above, but even though not tested, at that pH your available iron levels are going to be low even if the soil iron levels are sky high. Any time you like, you can feed the lawn with Milorganite to slowly raise soil iron levels and provide the lawn with a small amount of immediately-available iron.

* The potassium application won't impact your seeding in September at all, but if the lawn is short and you're not comfortable walking on it yet, you can push it back to October 15th easily. Just so long as you have at least four weeks until ground freeze, you're fine.

Recommendations, Soil Balancing:

October 1: Apply 2 pounds per thousand square feet of potassium sulfate.

April 1: Apply 2 pounds per thousand square feet of potassium sulfate.

May 1: Apply 2 pounds per thousand square feet of potassium sulfate.

June 1: Apply 2 pounds per thousand square feet of potassium sulfate.

Thank you for the great advice! Couple of questions, is potassium sulfate the same as potash? If potassium sulfate has an analysis of 0-0-50 and you say my first application is 2 pounds per thousand sf, does that mean it would actually take 4 lbs of the product per thousand sf? Sorry for my ignorance!

Also, my lab results gave the recommendation of sulfur, 10 lbs/1,000 sf annually. Any need for this application?

Morph, in regards to feeding the lawn, you mentioned using urea or ammonium sulfate fertilizers. When you say this, I am assuming this will cover my annual "N" requirement? Again, my results suggest 4 lbs of N per 1,000 sf, so am I just looking at a standard 28-0-3 mix and getting at that 4 lb annual limit? If I use Milo in addition to this, will I be getting too much nitrogen on an annual basis? Sorry for all the questions, just trying to get a handle on this!

I feel like I'm being "messed" with. I've been like, preempted. I totally agree with the analysis and recommendations and we DO post to give the OPs the best advice possible.

OP, you've got two issues, Mg, and a far second in importance, pH.

Mg:

In addition to current advice, you can create a series of miniature "dry wells" by implementing plug aeration and filing the holes with late stage organic matter (peat moss) or sand to help improve water and nutrient penetration. It helps but is not a panacea.

pH:

Sulfur was recommended to reduce your pH ( ideal pH would be 6.5-6.8ish). It should be applied in cooler temps to reduce adverse results to the turf. It works best when incorporated ( e,g, tilled in or aeration will help increase the soil profile affected). Much, much easier to apply ammonium sulfate fertilizers and probably just as effective in the end. The biggest issues with a higher pH is iron, phosphorous and boron availability. P and Iron has been addressed, boron was not measured.

>>Thank you for the great advice! Couple of questions, is potassium sulfate the same as potash?

Potassium sulfate is also called sulfate of potash. Sorry, I forgot to mention that! The word's actually a historic holdover.

Potash itself actually refers to another chemical, potassium carbonate, or potassium ash. It's what you get when you soak wood ash in water.

>>If potassium sulfate has an analysis of 0-0-50 and you say my first application is 2 pounds per thousand sf, does that mean it would actually take 4 lbs of the product per thousand sf? Sorry for my ignorance!

That's not ignorant! Use 2 pounds of potassium sulfate (the result being around 1 pound of potash equivalent, or 0.83 pounds of elemental potassium). I always adjust the numbers to match the product I'm recommending.

>>Also, my lab results gave the recommendation of sulfur, 10 lbs/1,000 sf annually. Any need for this application?

None. Surface applied sulfur occasionally has its uses, but this isn't one of them. You'll end up losing the vast majority of it to the atmosphere as sulfur dioxide (smog).

Sulfur wasn't tested here, but I'm going to guess it's adequate to maybe a little low but nothing to worry about. It's doubtful you need any, so there's no reason to add elemental S since its ability to change your pH is very low.

>>Morph, in regards to feeding the lawn, you mentioned using urea or ammonium sulfate fertilizers. When you say this, I am assuming this will cover my annual "N" requirement?

Yes! Normal apps would be Memorial Day, Labor Day, October 1, and whenever the lawn stops growing but is still green, for a target around 4 pounds per thousand of N per year.

>>Again, my results suggest 4 lbs of N per 1,000 sf, so am I just looking at a standard 28-0-3 mix and getting at that 4 lb annual limit? If I use Milo in addition to this, will I be getting too much nitrogen on an annual basis? Sorry for all the questions, just trying to get a handle on this!

Ask away!

Fortunately, organic nitrogen works much differently, requiring bacterial and fungal action to reach the plants. It's slower, more sustained, and rather difficult to overdo. My top flight year was a test--I added over 1,300 pound of organics to the soil per thousand square feet, for a grand total of 37 pounds of organic nitrogen.

If you did that synthetically, everything would die and stay dead until it washed out. Organically, growth rates were incredibly high, everything was dark green, and I was mowing a lot.

An extra kick or three or four of organics won't hurt. In fact, they'll tend to slow down and moderate the synthetics you add to the soil (you can look up "rhizosphere" and "soil food web" for some background on this).