Test Garden Soil for Phosphorous: DIY?

[optimizer]

Hi, I was wanting to test garden soil for its phosphorous content. I've seen test kits and electric/chemical kits and the like, but is it possible to do this DIY? I'd need to create a solution and have a scale to determine results. Thanks for your help.

 

[chemisttree]

Yes, if you are prepared to do this:

Nutrient Management P
For situations involving soil phosphorus and nutrient management decisions where extractable P is likely to exceed 100 ppm on the Bray test and 50 ppm on the Olsen test. The range for the nutrient management P test is 20-250 ppm. This test is basically the same as the Olsen P test, but with a dilution of the extract before colorimetric analysis. In detail: A 1 gram scoop of soil and 20 milliliters of 0.5 molar sodium bicarbonate (NaHCO3) solution are shaken for 30 minutes. The mixture is filtered and the filtrate is diluted 5 X with sodium bicarbonate. A blue color is developed with successive additions of 1) ammonium molybdate-sulfuric acid solution and then 2) ascorbic acid solution. The intensity of blue color, corresponding to the amount of P in the extract, is measured with a fiberoptic probe colorimeter at 882 nm. Results are reported as parts per million (ppm) extractable phosphorus (P) in the soil.

or this (for low levels):

Extractable Phosphorus
Bray-1 Method
The soil phosphorus measured is that which is extracted by a solution consisting of 0.025 normal HCl and 0.03 normal NH4F, referred to as Bray-1 extractant. A 1 gram scoop of 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 in the filtrate when treated with ammonium molybdate-hydrochloric acid solution and then aminonaphthol-sulfonic acid solution. The color is measured by an absorption spectrophotometer at 640 nm. The result is reported in parts per million (ppm) phosphorus (P) in the soil. The phosphorus measured does not represent all of the phosphorus that may be available for plant growth; e.g., some fraction of the organic phosphorus not measured may become available upon mineralization. The upper reporting limit for this test is 100 ppm. For situations such as nutrient management decisions where a higher value is needed, see the nutrient management test below.

Olsen Method
For highly calcareous soils (pH greater than 7.4), the Olsen sodium bicarbonate method is used. A 1 gram scoop of soil and 20 milliliters of 0.5 molar sodium bicarbonate (NaHCO3) solution are shaken for 30 minutes. Blue color in the filtered extract is developed with successive additions of an ammonium molybdate-sulfuric acid solution and then an ascorbic acid solution and measured with a fiberoptic probe colorimeter at 882 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 by the test. The upper reporting limit for this test is 50 ppm. For situations such as nutrient management decisions where a higher value is needed, see the nutrient management test below.

 

[ravenprp]

Yes, it is possible to test garden soil for phosphorous content using a DIY method. One option is to create a solution using a mixture of water and a phosphorous extractant, such as ammonium acetate or citric acid. The soil is then added to the solution and shaken to extract the phosphorous. The solution is then filtered and the concentration of phosphorous is measured using a colorimetric test or a spectrophotometer. This method requires some knowledge of chemistry and access to the necessary materials and equipment.

Another DIY option is to use a home soil test kit specifically designed for phosphorous. These kits typically use a chemical reaction to determine the phosphorous levels in the soil. They can be purchased at gardening stores or online and come with instructions on how to use them.

Whichever DIY method you choose, it is important to follow the instructions carefully and to calibrate any equipment used to ensure accurate results. It may also be helpful to compare your DIY results with a professional soil test for validation. Ultimately, testing your garden soil for phosphorous is a great way to determine if your plants are getting the necessary nutrients for healthy growth.