Interpreting Soil Tests
This page is designed to help you dive further into the results from your soil tests. You will find information on each section of the report as well as additional resources on better lawn care, pest management, and soil health.
Step One: Get a Soil Test
The first step is taking a soil sample. Learn more about taking a proper soil sample in this MU Extension guide and through this Missouri Department of Conservation guide to taking a soil sample.
It is recommended that you retest your soil every 3 years to see if your nutrient needs have changed. Samples can be dropped off at the Greene County Extension office located inside the Springfield-Greene County Botanical Center at 2400 S. Scenic Ave, Springfield, MO 65807, or with your local extension office.
Once you have your soil test, let’s break down each part of the soil test. Pictured is an example of a soil test. Under “Soil Test Information” you can find your rating of various soil nutrients. In the next section, “Nutrient and Lime Requirements” you will find recommendations for soil additives. The box at the bottom includes personalized recommendations for lawn care.
Soil Test Information
pH
Soil pH measures the hydrogen within the soil. Soil pH plays an important role in how much nutrients are available to plants. If your soil pH is too low, you may need to add limestone to increase the pH so that more nutrients are available.
More information: MU Extension Guide (page 2); MU Guide Soil Testing for Lawns (page 1)
Phosphorus
Phosphorus works to store and transfer energy in plants. This is used for growth, reproduction, root growth, and the plants’ ability to withstand harsh conditions. Too much phosphorus can be detrimental to local water quality.
More information: MU Extension Guide (page 2); MU Plant Diagnostic Clinic; Managing Lawns and Turfgrass; MU Extension Phosphorus in Missouri Soils; MU Guide Soil Testing for Lawns (page 2)
Potassium
Potassium helps plants use water and resist droughts.
More information: MU Extension Guide (page 2); MU Soil and Plant Testing Laboratory; Drought Resources; MU Extension Potassium; MU Guide Soil Testing for Lawns (page 3)
Calcium
Calcium helps the soil structure and aeration of the soil. This allows for plants to have better access within the soil as they grow more roots.
More information: MU Extension Guide (page 2); MU Guide Soil Testing for Lawns (page 3); MU Soil and Plant Testing Laboratory; The ABCs of Soil Health (arcgis.com); Managing Lawns and Turfgrass; Overseeding a Lawn; Overseeding a Thin Lawn
Magnesium
Magnesium helps the plants to complete photosynthesis by being the central molecule in chlorophyll.
More information: MU Extension Guide; MU Guide Soil Testing for Lawns (page 3); MU Soil and Plant Testing Laboratory; Weed Science
Organic matter
Organic matter affects many properties of soil including physical, chemical, and biological. Organic matter influences soil structure and erosion. Organic matter is a source of nutrients for plants. Microorganisms that live within the soil breakdown the organic matter into minerals that are then available for plants to use at nutrients. Typically, organic matter can be increased with compost or fertilizers. A basic rule of thumb for urban lawns is to “strive for 5%” organic matter. Soils with higher levels of organic matter do a better job retaining water and contribute to soil fertility. You can increase organic matter by avoiding bagging your grass clippings and/or applying a light topdressing of compost.
More information:
Nutrient and Lime Requirements
Based on these results, the soil appears to be low on Phosphorus (P) but contains adequate amounts of Calcium (Ca), potassium (K), and Magnesium (Mg). As the soil test indicates in the “Nutrient and Lime Requirements” box, this lawn will likely benefit from an application of 1lb. of nitrogen and .5lbs. of phosphorus per 1000 sq. ft. to maintain and improve sustained plant growth. To apply a fertilizer to this lawn, one will need to pay attention to the fertilizer ratios listed on the bag. The three numbers listed represent the amount of Nitrogen-Phosphorus-Potassium (N-P-K) found within that specific fertilizer blend. An example of a locally available blend is 24-22-4. Once a fertilizer blend has been selected, there is a simple equation that will determine the application rate. An example is provided below.
Let’s say the chosen fertilizer has a 24-22-4 ratio. The soil test recommends adding 1 pound of nitrogen and one-half pound of phosphorus per 1,000 square feet. Since excess phosphorus can be detrimental to local water quality, we will calculate to the phosphorus recommendations. To calculate the application rate, simply divide the amount of phosphorus needed per 1,000 square feet by the percentage of the phosphorus in the bag. If the soil test calls for 0.5 pounds of phosphorus per 1,000 square feet, your equation would look like this: 0.5/0.22=2.27 pounds of 24-22-4 per 1,000 square feet. So, for a 3,500 square feet lawn one would need a total of 8 pounds (2.27lbs x 3.5 = 7.95) of 24-22-4 fertilizer.
Spring (April-May) and fall (September-October) are the best times to apply conventional chemical fertilizers to your lawn. Spring fertilization helps to jump-start plant growth while supplying nutrients to maintain your lawn throughout the growing season. Fall fertilization will help to prepare your lawn for winter dormancy and strengthen the plant’s root system, allowing your lawn to thrive next spring. Apply the fertilizer evenly throughout lawn. Ensure that any fertilizer that lands on your driveway or sidewalk gets swept into your lawn to prevent excess nutrients from making their way into our local waterways. It’s best to apply fertilizers before a light rain to help quickly dissolve the fertilizer granules and work the nutrients into the soil. Fertilizing before a large rain event can wash away your fertilizer, wasting your time and money and harming our local water ways. If rain is not in the forecast, “water in” your fertilizer using a sprinkler or in-ground irrigation system.
Spreaders are available via the Springfield Tool Library, and compost is available at the Yardwaste Recycling Center in Springfield, A standard pickup truck can hold approximately 1-2 cubic yards of compost. Ask an employee how much they typically load into a vehicle of your load rating. If in doubt, play it safe and go with a lighter load.
Regardless of the type of spreader you plan to use, it must be adjusted to ensure even distribution of fertilizer and other materials. Recalibration may be necessary when using the spreader for other tasks such as overseeding or application of pelletized lime due to the different shapes and sizes of granules or seeds. The easiest way to apply is to set your spreader on the lowest setting and make multiple passes.
Place your rotary spreader inside a container or on a tarp to catch any spills that may occur while filling. This prevents waste and eliminates the risk of excess materials being added to your lawn. Store leftover fertilizer and pelletized lime in watertight containers to avoid clumping and spills. Five-gallon buckets with lids are a sturdy, cheap, and reusable option.
More information: Natural Lawn Care; Soil Health | NRCS (usda.gov); Compost Builds Healthy Soils ILSR 02-11-16; How to Convert an Inorganic Fertilizer Recommendation to an Organic One | UGA Cooperative Extension; Calibrating Your Fertilizer Spreader (psu.edu); Home — Beyond Pesticides; A Homeowner's Guide to Fertilizer (ncagr.gov); Fertilizer Numbers: What They Mean and How to Use Them to Grow Better (savvygardening.com)
Other General Lawn Care
Compaction
Soil compaction can affect permeability and water percolation. Driving or parking vehicles, building structures, or concrete and other impermeable surfaces can all cause your soil to become compacted. This may result in poor nutrient uptake or large pools of water to form after rain. Soil compaction can be prevented by avoiding parking or driving vehicles over areas that are already prone to erosion or compaction.
Soil compaction can be remedied by core aeration or tine aeration. Core aeration is most commonly used and is easy to do on your own. It is recommended to core aerate your lawn at least once every 2-3 years to break up compaction, increase water infiltration, and allow organic matter to be quickly incorporated into the soil. Core aerators can be borrowed from several local rental companies at hourly and daily rates. Spring and fall are popular times to aerate cool season lawns, so be sure to call ahead to check on equipment availability.
More information: Improve Your Property MDC; Managing Lawns and Turfgrass
Overseeding
If you’ve observed thinning or bare patches in your lawn, it’s probably time to consider overseeding. Fall is the best time to overseed cool-season lawns because there are fewer weeds to compete with your newly planted grass. Following core aeration and compost application will allow for better seed to soil contact and improved germination rates. Be sure to follow up overseeding with frequent watering (2-3 times per week) until established.
More information: Overseeding a Thin Lawn
Shade & Tree Canopy
Shade and tree canopy is a major factor of whether or not vegetation will be successful in your yard. It’s important to note problem areas and trim trees as needed. Root placement of trees can also affect the success of other vegetation or other trees. Some trees, like the black walnut tree, create an allelopathic barrier that prevents other plants from growing around it. With this information, you can better understand the natural competition that is taking place within your yard to better plan, seed, and manage vegetation and trees on your property.
More information: MU Guide on Tree Pests; MU Guide on House Bugs; MU Extension Weed Science; Invasive Nuisance Species MDC
