Front Yard

Backyard

Front Yard

I would take a good, in depth, look at the areas of concern to see what is different there then the rest of the yard.
1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

I have completed those tests many times. No real difference. The jar test doesn't work too well tho, but I know based on drainage, they are the same composition.
After much research I believe the real problem is too high of magnesium is locking up the soil and causing the surface tension issue. I used dolomit lime to raise my pH a few years ago...foolish, because it spike the magnesium level. My ratio is between 3 & 4. Way too low. I know some papers suggest this ratio doesn't matter, but I highly disagree.

The pH in the back is 6.1, so I'm going to drop some MAG-I-CAL calcite lime to bring up my calcium level and improve the ratio. Next spring I plan to use gypsum to lower the magnesium & further increase calcium. I have high confidence that this will resolve the compaction issue.

Here is a link that might be useful: Safe Lawns Calcium

Have you tried aerating the lawn?

Personally, I dislike throwing a lot of stuff at a lawn and try to make any improvements via cultural means. Usually works well up here with our soils and cool season grasses -- not sure about all other parts of the country.

@gardengal48 - Yes, I core aerate every other year for the past 6 years. While the cores are open I then apply heavy applications of organic fertilizers. One year I even went around in that problem area and literally packed the core hole with compost to try and fix the problem.

I agree, I typically wouldn't just throw stuff down, but I am very certain that the compaction I am experiencing is due to my poor calcium to magnesium ratio. Magnesium binds soil together, while calcium naturally aerates it. If you look at the soil tests of my front yard vs. back yard, you will notice the biggest difference is my calcium saturation level in the back is 43, while it is 62 in the front. Even in the front yard my ratio is less than 4:1, but the back is worse at 3:1.

The best organic lawns I have seen all show this ratio closer to 8:1 or even higher. I think this is a critical, and often overlooked metric. Additionally, my front yard gets virtually no weeds, while the back and sides have a lot of dandelions. I hand pick all of them, before they go to seed...but the weeds usually have a story to tell. In this case, it seems to be indicating that my calcium levels are too low, which is favorable for dandelions to grow.

I will provide an update next fall with updated soil tests and observations of this problem area.

This is the results of water replacing air in the soil structures.
There is shade in the back yard so it needs a lot less water than the front lawn.
Soils need a chance to dry out in order to maintain good tilth then soak in water slowly like a sponge.
Of course heavy traffic on wet soil is an obvious cause for what your lawn is displaying.

For shade I would monitor when water is needed then only apply 1/4 inch in one day and if it didn't soak in deep enough with that application, then add the second 1/4 inch the following day. Then let it dry out before applying more. :)

SC77,
In your post, you state that the back yard, where you have a problem with your grass, receives dappled shade.
From what?
Is there a tree there? How close?
What kind of tree is it?
VERY important.
Trees steal water from grass, and the tree roots will move to where you are watering, and putting all that delicious compost and tea.