EC Nebraska | Fast 18 - 1/7/2014 08:30
in the soil sample it is telling me that you only have 4ppm Phos correct? then in the recommendation it is asking you to apply 80 units of P2O5. how can the sample ask for P2O5 when it doesn't initially test for it in the first place. this is just how I read the sample not looking for an argument. so next question, how does one know to apply 80 units of P2O5 when the soil test on tests for P....?
Soil tests are just relative measurements. They have to be calibrated for a specific geography to have much real meaning. To do that, you need soils with different test levels. You then lay out replicated plots with different rates of fertilizer, grow your crops, and see which levels of fertilizer gave a yield response. You do that several different times, different soil test levels, three year studies, and you have a data set. You take that data set, fit a curve to it, and that's your calibration curve that says X lbs of fertilizer on Y testing ground will give your maximum yield response.
As you might guess, such tests are expensive, tedious, and lose validity the farther away you get in distance and time from the actual tests.
But they're the best we have. So that's what we use. |
Phosphorus in High PH soils
