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Watershed Management: Education

Soil Testing


Soil Testing

shovel in soil

A soil test is the process of sampling and evaluating a soil to measure the fertility of a field, lawn, or garden. The results are used to make recommendations on fertilizer use. Some tests can also determine if other treatments are needed to remedy poor soil conditions.

Why should I do a soil test?

Take the guesswork out of caring for your lawn. If your lawn seems unhealthy, get your soil tested to determine what your lawn needs. In many cases, the problem is not a lack of nutrients within the soil. Knowing the organic matter content and pH is the best place to start for proper soil preparation and lawn maintenance. Then follow up with effectively applying nutrients and water to yield a more drought and pest resistant lawn.

Where Can I Get A Soil Test?

The following businesses provide soil testing or kits:

Or ask your lawn care professional.

Note: Most kits sold at hardware stores do not test for organic matter content. However, they tend to be less expensive and they provide immediate test results. Laboratories provide professional analysis, providing more accurate test results. They typically charge $15 to $25 for their services and will often provide customized recommendations for amending your soil.

soil

How do I take a sample?

Using a shovel, trowel, or other clean tool made of stainless steel, dig a hole about 6" deep in your lawn or garden. If the area is large, take multiple samples and mix them together in a clean bucket. Samples should be placed in designated containers and labeled. While soil samples can be taken year-round, it is recommended to do soil amending and fertilizer applications in the fall to allow time for changes to occur before the next growing season.

What information should I include with my sample?

If you are sending your soil sample to a lab for testing, it is helpful to include information about the sampling site. Note any nearby structures or activities that may produce unusual test results. For more personalized fertilizer application recommendations, noting the type of grass you have is also helpful.

What do the soil test results mean?

Organic Matter Content

You cannot have a healthy lawn without the proper foundation. Many homeowners in the Lincoln area find that they have low organic matter content in their soil. This is especially true in newer neighborhoods, where topsoil was removed during construction. Organic matter is important for a healthy lawn because it helps the soil retain nutrients and moisture. When soils contain little to no organic matter, lawns require more time and money to maintain.

compost
Add compost to replenish organic matter in your soil

For a healthy lawn, the soil should contain at least 5 percent organic matter. If your soil test results indicate low organic matter content, consider amending your soil with compost. Making the investment in healthier soil now means less time and money spent on fertilizer and maintenance later.

To gradually add organic matter to an existing lawn, a thin layer of compost may be spread over the area as needed. One cubic yard of compost will cover approximately 1500 to 2000 ft2. Keep in mind that compost being applied to an existing lawn should not exceed 0.5 inches in depth. Therefore, more than one application may be required to reach the desired organic matter content.

If you are planting a new lawn, compost may be tilled into the soil prior to seeding. The general recommendation is to till 2 inches of compost into 8 inches of soil. However, this may vary depending on the quality of the soil.

pH

What are your weeds telling you? Many common lawn weeds thrive in acidic soil conditions, while most turfgrasses often fail to grow.

For a healthy lawn, near neutral soil conditions are ideal. Acidic or alkaline soils, however, are not harmful in and of themselves. The problem has more to do with the way soil pH affects the availability of different nutrients within the soil. Most nutrients are readily available for plant use in neutral soils, while some nutrients become less available in acidic and alkaline soils. Soil pH also affects the population and activity of microorganisms that benefit plants through nitrogen-fixation and other processes.

pH range

For existing lawns, changing soil pH can be difficult. Consider natural alternatives before turning to traditional methods of raising or lowering pH. For example, using compost to increase organic matter content can also help balance soil pH over time. In cases of very acidic or alkaline soils, traditional methods such as dolomite lime (raises pH) and elemental sulfur (lowers pH) may be used. Always seek professional advice before using these products to ensure proper application.

If you are planting a new lawn, changing soil pH is somewhat easier. Soil amendments such as compost, lime, or sulfur may be tilled into the soil prior to seeding.

Know when the battle is not worth fighting. If the area in question continues to have acidic or alkaline soil after amendments have been made, then it may be time to give up on the idea of having turfgrass grow there. Consider planting ground cover that will tolerate poor soil conditions instead.

Nutrients

Nitrogen, phosphorus and potassium are essential to plant growth. Therefore, they are the three nutrients most commonly found in fertilizers. However, most soils in the Lincoln area already contain more than enough of these nutrients to support a healthy lawn. Knowing the nutrient profile of your soil can help determine what type of fertilizer to apply and how much is needed in each application. It can also help you determine proper timing of applications to benefit your lawn or garden plants. Not only will you improve the overall health of your lawn, you will save time and money as well.

Nitrogen
lawn mower
Use a mulching lawnmower to return nitrogen to the soil
Nitrogen is a building block of plant proteins, making it a key nutrient for plant growth. If your soil test results indicate a slight to moderate deficiency, look for natural ways to gradually return nitrogen to the soil. For example, grass clippings left on the lawn return nitrogen to the soil as they decompose. Using a mulching mower adds 1 lb of nitrogen per 1000 ft2 annually.
Avoid applying nitrogen during the spring and summer months. This promotes excessive growth, which means more watering and maintenance for you. Applying too much nitrogen can weaken grass roots, alter soil pH, promote disease, and contribute to thatch build-up. If you must apply nitrogen, do it in the fall when the grass is still growing. This helps strengthen root structure and promotes a healthier lawn over the long run.
Phosphorus
Through its role in the division and organization of cells, phosphorus is a key player in early plant growth and root formation. Plants also use phosphorus to form hereditary material and to store and transfer energy.
Most soils in the Lincoln area are naturally high in phosphorus, so any excess will quickly wash off your lawn when it rains. Only apply phosphorus if your soil test results indicate a deficiency. If you must apply phosphorus, wait until early summer when uptake is most rapid. Use your soil test results to determine how much to apply.
Potassium
Plants use potassium for opening and closing stomata (tiny pores) on the surface of their leaves, allowing them to conserve water. Potassium also increases resistance to diseases and aids in photosynthesis.
Most soils in the Lincoln area are naturally high in potassium, so any excess will quickly wash off your lawn when it rains. Only apply potassium if your soil test results indicate a deficiency. The best time to apply potassium is in the fall. Use your soil test results to determine how much to apply.

Additional Resources

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Watershed Management: Education