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Bray-1 Method
Plant-available phosphorus is extracted with a solution consisting of 0.025 N HCl and 0.03 N NH4F, referred to as Bray-1 extractant. A 1-gram scoop of air-dried soil and 10 milliliters of extractant are shaken for 5 minutes. The amount of phosphorus extracted is determined by measuring the intensity of the blue color developed via the Murphy-Riley Method. The color is measured with a Brinkman PC 900 probe colorimeter at 880 nm. The result is reported in parts per million (ppm) phosphorus (P) in the soil. The upper reporting limit for this test is 100 ppm. For situations in which an exact value above the typical range is needed, see the Nutrient Management P test under "Tests available upon request".
Olsen Method
For highly calcareous soils (pH greater than 7.4), the Olsen sodium bicarbonate method is used. A 1-gram scoop of air-dried soil and 20 milliliters of 0.5 M sodium bicarbonate (NaHCO3) solution are shaken for 30 minutes. Blue color in the filtered extract is developed with molybdate-ascorbic acid reagent and measured with the Brinkman PC 900 probe colorimeter at 880 nm. Results are reported as parts per million (ppm) phosphorus (P) in the soil. As with the Bray P-1 test, potentially available organic P is not measured. The upper reporting limit for this test is 50 ppm. For situations in which an exact value above the typical range is needed, see the Nutrient Management P test under "Tests available upon request".