I'll take a stab at it. As you may know 80% of phosphorus adheres to soil particles that's why you see silt fence used in construction projects. It lets the water through but catches the soil particles which contains most of the phosphorus. It has been shown that phosphorus is the main cause of algae growth in water.
This algae eventually dies and settles on the bottom of ponds and lakes. Bacteria that eat the algae will use up all the oxygen in the bottom of the lake. Cold water fish such as trout cannot survive in water that has less than 15 PPM of oxygen and will also die in about 24 hours in water warmer than 65 Deg. F, so they must leave the pond or die in such cases.
The reason this is true is because ponds and lakes set up what they call a hydrotherm where the water near the surface is warm and the bottom is very cold. This hydrotherm will not let oxygen defuse from the top into the bottom of the lake. So all the oxygen in the bottom of a lake (except for springs in the bottom) is put there when the water flips top to bottom which happens once in the spring and once in the fall (at least in northern parts of the U.S.). That is because water is most dense (heaviest) at around 40 deg. F.
Getting back to your low P reading. I think that the reason you are getting a low reading on the bray scale is because it's just not reading it. This is because you have a good amount of lime in your soil. The bray scale works best in soil with a PH of 6.8 or less and in silt clay soils. If you have clover growing it likes sweat ground. My suggestion is to write down what you have for plants growing especially plants that have come up on their own that you did not seed, then check to see what they most prefer for growing conditions. That most likely is what you have in your soil.
As far as the wide range of values you are seeing is soils tests. Do you have a large range of plants growing in different spots on you land? If not then I would not worry about what the tests say.
