David I can show you almost identical soil samples from just down the road in Fairfield County. Here are a few thoughts based on what I've learned over the last 8-10 years along with advice I have gotten from these boards and how it has turned out.
First off, you have to remember what we are working with here. The red clay we have is not really topsoil, it was the subsoil that was buried under 6-12" of topsoil before colonization. It is a kaolin clay which is different from clays found in other parts of the country. The bedrock under the clay is granite. So we end up with some situations that are somewhat unique when compared to other parts of the country. I say that, because some of the recommendations that are very much appropriate in other areas are not necessarily what will bring about better production from our soils.
Second, it would be helpful to see the next block down on your soil test. Click on the LabNum and it will take you to a full printout of your soil test. It should have your base saturation. That will include your CEC and also what the total saturation is. That is where you are going to be able to see the biggest change in your soil as you go forward. Also, spring for the organic matter in your test. It's an extra $5 but will help you see what goes on over a few years.
It is interesting to me that your pH, Ca and Mg dropped from 2016 - 2017. I wonder if you did some deep tillage soon after your 2016 samples or if you maybe pulled samples from a deeper soil horizon in 2017. When did you apply your lime and what was the tillage regime since applying the lime? What type of lime did you apply?
Irregardless of all of that - here is what I know about working in our red clay. It actually can be pretty dang good ground, but it takes a lot of amendment and it takes time. Make sure you are using calcium carbonate (ag lime). Don't focus just on the pH. You need to also be looking at raising the CEC and the base saturation. Remember, CEC is the soils ability to retain nutrients, so a low CEC with a great pH isn't going to retain nutrients the way a higher CEC soil with great pH will.
How do you help CEC? Organic matter my friend. That is why you want to be getting OM in your soil tests. Manure works great on our soils (cow and poultry). If you can get it - choose manure over synthetic fertilizers. You'll raise your P levels, and help your OM. Also, don't sweat the high K levels. That is a nuance of our kaolin clay soils and I still think you need to add a little bit of K in your fertilizer to be taken up by your next crop.
Aside from manure; take advantage of our long growing season and grow grasses. I would forget buckwheat. It comes up quick, looks great and then gets absolutely smoked in our summers. I know they say it mellows the soil, but there just isn't much to a buckwheat plant and when it is wilted down to nothing and gets rendered back to the soil you can't even tell there was anything grown there. Plus you are going to find that we have quite a few weeds that do well in our soil over the summer, and they have no problem pushing buckwheat out of the way and making a good run for it over the summer.
What I have found works best is to spend the summer growing a grass/grain crop like sorghum, pearl millet, or sudangrass. It isn't the most fun thing to grow over the summer, but it handles our summers very well and produces a lot of biomass. One thing I have learned through all of this, biomass above ground is good, but biomass (roots) below ground is great. I also think it helps control weeds because it shades the ground pretty well.
I don't do a whole lot of tillage, but I find that I have to do some because of how our soils crust. The way I follow the LC rotations I use my brassica planting as the primary opportunity to apply amendments. I put down 200#/acre of pelletized lime along with the full recommendation from the soil test for brassicas. The summer grain crop and the fall cereal grain / clover get minimal fertilizer applications and minimal tillage.
Since sticking to a routine of building organic matter by growing a high biomass grass crop during the summer, I've seen the best improvements in my soil tests across the board. pH is still hovering in the 6.5 range, but my CEC's have gotten up in the double digits and I can definitely see an improvement in the quality of crops.
The last thing I'll mention for now - regarding the size of the brassicas and the discrepancy across the field - there are a lot of other possible issues. What is moisture like across the field, or soil depth? What time of year were the brassicas planted? One thing that stands out when I look at your map, the area that does the best, also receives the most shade from the afternoon sun - again, heat and moisture stress?
