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Little River, TX | Goals for soil test results really vary according to you crop as well as the soil type.
First I only really look at calcareous and clay soils types and as you might expect only hay crops.
I have a note that Idaho has upped the desired Olsen soil test value for phosphate when growing alfalfa, from 15 ppm P to 20 ppm P. In other times I see 18 ppm P is the soil test level where only removal rates need to be applied.
In a wild theory 4.6 lbs of P2O5 = 1 ppm P. The best most will find is it takes ±18 lbs of P2O5 to change the soil test 1 ppm if the soil is something like 6.8 pH. For calcareous soils they add 10 lbs of P2O5 for each percent of free lime. From my experience ±71 lbs = 1 ppm P.
Phosphate has some funny tricks for us. Put a little on and nothing happens. Put a lot out and some times a little something happens, & sometimes big things happens. It appears there is a balance zone in phosphate, be below that zone and very little return for your phaophate dollar. Get where there is a slight surpluse and we get a large return on our dollar.
Add to the confusion, crops like corn are not so demanding, while wheat is almost as demanding as alfalfa.
Potash is a whole different deal here. Here what is excessive potash according to the soil test and conventional wisdom is really deficient, for here.
So as long as a plant analysis is reasonably normal than the soil test can be considered reasonably good, considering.
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Fertilizer removal rates...your thoughts?
