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. .... _.. _.___ ~___-r.. _~___ <br />Available Phosphorus in Mine Soils - Continued <br />8. Prepare a 10 ml blank with 10 ml NaHC03 and dilute to 25 ml. <br />Run as a sample. <br />9. Obtain P concentration from standard curve prepared as follows: <br />a) Pipette aliquots, containing from 2 to 25 micrograms of P, <br />of the dilute P solution into 25 ml volumetric flasks and <br />add 10 ml of the NaHCO extracting solution to each flask. <br />Dilute to volume and transfer to test tubes. <br />b) Develop color with 5 ml of Ammonium Molybdate solution <br />and 1 ml of SnC12 solution. Run with samples and blank. <br />c) Plot absorbance vs. P concentration on linear graph paper. <br />Calculations: <br />ppm available P in the soil = (total ug P in sample, taken <br />from standard curve) x 2 <br />• <br /> <br />6-93 <br />