Testing the Soil for Phosphorus & Potassium in My Front Yard

Selecting a Test Kit

• Several home soil test kits are available. Some use capsules and some use liquid solutions. All test kits rely on color comparisons to determine nutrient levels. If you know you have difficulty with color discrimination, have someone help you interpret the test results.

Collecting the Soil Sample

• Select eight to 10 spots for sampling. Scrape aside mulch and leaf litter or remove a patch of sod. With a core sampler or clean spade, remove a uniform width slice of soil about 6 inches deep from each collection site. Mix the samples in a clean bucket. If there are bare spots and spots where plants grow well in the yard, sample each area separately. Wait at least six weeks after applying fertilizer or lime before taking the samples.

Phosphorus Test

• Fill the test tube to the appropriate level with phosphorus extracting solution or water and add soil according to the directions with your kit. Cap and shake the tube to dissolve the soil. If your kit contains capsules, add the phosphorus capsule and shake to dissolve. If you are using reagents, which are liquid solutions that cause reactions, transfer the settled liquid to a clean test tube, add the phosphorus indicator reagent, mix and add a phosphorus tablet. Compare the color to the chart that came with your kit. An ideal available phosphorus level is 30 to 37 ppm.

Potassium Test

• Mix soil with water or potassium extracting solution according to the directions provided with your kit. Add the potassium capsule if you are using capsules, shake to dissolve and let settle. Transfer the liquid to a clean test tube if you are using reagents. Drop in a potassium test tablet. Add color indicator one drop at a time, counting the drops until the solution turns blue. Compare the blue shade to the color chart. Potassium levels should be 90 to 240 ppm, depending on the soil type.