Why test for Potassium?
Answer: Because plants need it and soil may lack it.
Potassium is one of the three main soil elements added by farmers and gardeners to boost and sustain plant growth over multiple growing seasons. The phosphorus in commercial fertilizers comes from phosphate rock. Nitrogen, Phosphorus and Potassium, denoted as (N-P-K) ratio notation on fertilizers you an buy, are the “Big 3” primary nutrients. Each plays a key role in plant nutrition. As most plants grow, they take these nutrients up and use them, depleting the soil.
Why Do Plants Need Potassium?
Phosphorus helps plants use and store energy, including that produced by photosynthesis. Specifically, phosphorus is a component of ATP (adenosine triphosphate) and of NADPH (nicotinamide adenine dinucleotide phosphate), which are essential energy-carrying molecules used in various stages of photosynthesis which plants use to turn sunlight into chemical energy. Phosphorus in the right range is needed to help plants grow and develop normally.
Step-by-step Guide for Measuring Potassium in Your Soil
Step 1: Gather the necessary equipment and materials:
– Soil sampling container or scoop
– Clean plastic bucket or container
– Clean water
– pH testing kit
– Potassium testing kit
Step 2: Choose the location to take the soil sample. It should be representative of the area you want to measure potassium levels in.
Step 3: Collect soil samples – Gather soil samples from various areas of your garden, making sure to avoid areas with obvious differences in soil conditions. Use a clean gardening trowel or shovel to collect samples at a depth of 4-6 inches (10-15 cm). Combine these samples into a clean bucket and mix thoroughly.
Step 4: Remove any stones, roots, or other debris from the soil sample. Ensure that you have about 1 cup of soil for testing purposes.
Step 5: Drying – Spread the mixed soil on a clean plastic sheet or tray and let it air dry for a few days in a cool, shaded area. Alternately, you can use an oven to dry it at a low heat setting (around 200 degrees Fahrenheit) until it is completely dry. This drying step, however it is done, is crucial to prevent any water interference during testing. Ensure the soil is completely dry before continuing to the next step.
Step 6: Once the sample is dry, crush the soil into a fine powder using a mortar and pestle or a clean, hard surface and rolling pin.
Step 7: Sieving – Once the soil is dry, remove any rocks, debris, or plant material. Then, use a sieve or mesh with a mesh size of approximately 2 mm to sieve the soil. This will help separate any larger particles from the fine soil material.
Step 8: Soil to water ratio – The next step involves creating a soil sample solution by mixing the sieved soil with distilled water in a specific ratio. Follow the instructions provided in the potassium testing kit for the appropriate ratio of soil to water. If a guide is not provided, for every 1 part of soil, add 5 parts of distilled water. For example, if you have 100 grams of sieved soil, mix it with 500 grams (or milliliters) of distilled water.
Step 9: Use the pH testing kit to measure and record the pH level of the soil slurry. This step helps to ensure the accuracy of potassium testing, as pH affects potassium availability to plants.
Step 10: After noting the pH level, proceed with the potassium testing according to the instructions provided in the testing kit. Different kits may have varying procedures, but generally, you’ll add a specific chemical or reagent, followed by shaking or stirring the mixture and observing any color changes.
Step 11: Shaking and settling – Place the soil and water mixture in a clean jar or container with a tight-fitting lid. Shake the jar vigorously for a few minutes to ensure the soil particles are dispersed into the water. Allow the solution to settle for approximately 30 minutes.
Step 12: Filtering – After settling, pour the liquid portion of the sample into another clean container, leaving behind the settled soil particles. This liquid, called the “soil extract,” contains soluble nutrients that can be analyzed.
Step 13: Compare the color of the soil slurry to the color chart provided with the potassium testing kit to determine the potassium level in your soil. Different color intensities will correspond to different potassium concentrations, allowing you to quantify the amount of potassium present in your soil sample.
Step 14: Record the potassium measurement for future reference or further analysis. Note the date, time, reading and locations sampled as well as drying method. This information will help you later compare measurements and to determine whether your soil requires potassium supplementation for optimum plant growth.
Note: Testing for nitrogen and phosphorus: This is generally done at the same time, however, unlike potassium, home-based DIY tests are less accurate in providing nitrogen and phosphorus measurements. Consider utilizing professional lab testing to obtain more precise results for these nutrients.