In any case, moving on to the analysis of the actual numbers, it does at least seem that the 6/25/2020 and 10/5/2020 samples were taken from the same lawn. Most items are pretty similar. I speculate that if a soil remediation plan were suggested for each of these lawns, that the recommended course of action would be about the same for both.
Actually, that's a good question... What would be the recommended soil remediation plan for the most recent sample?
Seems to me the recommendations would be pretty much the same for both samples, with the possible exception that the October test would suggest that epsom salt is necessary to be applied every 60 days along with sulfate of potash, while the June test would be marginal for the application of epsom salt.
But, other than that, no phosphorus, no lime based on either test. Boron indicated from both tests. Spring test indicates manganese, while the autumn test doesn't.
Regarding how much salt should have been expected to leach out of the soil, I found
one article online talking about the subject which indicated that 6 inches of "good quality water" would give a 50% soluble salt reduction, 1 foot of water an 80% reduction, and 2 feet of water a 90% reduction. If the sodium in our soil were primarily from winter road salt, then it would be largely soluble, so one would expect to see leaching due to rainfall at a similar rate.
Our sample from June 17 measured a 5.24% sodium saturation level. Our Sept 24 test measured a 3.50% sodium saturation level. That's a 33.2% reduction. According to the weather station at our nearest airport in Manchester, NH (about 7 miles away), they received a total of 5.13" of rain between June 17 and Sept 24th (0.15" in the remainder of June, 3.02" in July, 1.22" in August, and 0.74" in the preceding portion of September). (Yes, it's been dry in NH, we normally average about 3.5" each month during those months.) A reduction of 33.2% from 5.13" of rain is in the same ballpark as 6" giving a 50% reduction, so that seems believable.
However, as to how the calcium went up, I don't have a great explanation. We haven't applied any lime this year. Sampling variation could be a cause. There is a little calcium (~2.0%) in Bay State Fertilizer, and we have applied it three times at a rate of about 16#/ksqft each time, but I don't think that would have made its way down to the 3-4 inch depth yet. I wonder if it's possible that calcium we applied the prior fall (9#/ksqft of calcitic lime on 9/19/2019) could have still been making its way down to the 3-4 inch depth?
Magnesium seemed to be the biggest mover. Sampling variation? Leaching out of the soil?
Sodium we already talked about. Changes in micronutrients don't seem particularly surprising. Manganese was the biggest mover; I did apply that twice this year.
In any case, I'm not sure that I have learned a whole lot from this test. We still need to keep applying potassium. Seems like epsom salt should also still be on our list of supplemental nutrients, and boron should still be in our plan. I haven't ever observed salt damage to the grass growing near the road in the spring, so maybe high sodium levels in our spring soil tests is just what we should expect?
I'm also wondering if we should bother with a spring soil test, or if we should just base our spring plan off this test, especially since we have a half-dozen years of history which basically all have a stabilized plan in the most recent few years?