Getting a Good Soil Sample – Step By Step

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Carol A. Crotta

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A lawn reflects the quality of the soil underneath. If the soil is deficient in major nutrients, compacted so that water can’t penetrate properly or so sandy that it can’t hold onto water for long, you’ll see it in your grass. You’ll have sparse, patchy growth or weak, yellowed blades. On the other hand, a deep green, thick, thriving lawn is a testament to a healthy soil base below. It’s likely filled with nutrients, has the right texture and contains a flourishing microbe and earthworm population generating rich organic matter. Good lawn soil is fertile with humus, holds water, yet drains well, and isn’t too sandy or claylike.

Soil test kits measure the levels of the three major nutrients in your soil – nitrogen, potassium and phosphorus – as well as its pH.

The truth, however, is that few gardeners are blessed with this type of soil – loam – the best of all possible soils. But no matter what kind of soil base you’ve got, you can bring it close to that ideal texture, pH level and nutrient content with some amending. But you have to figure out what your soil needs first – which you can determine with a simple soil test.

There are a couple of ways to get your soil tested. One is to use a home test kit; the other is to send off a soil sample to a lab recommended by your local agricultural Extension Office or garden retailer. Both methods produce equally reliable test results, provided you take care to acquire a good sample. (Follow the procedure shown in the pictures and described in their captions for best results.)

No matter how your soil is tested (by lab or by you through a home test kit), the result will be a breakdown of the three key nutrients (nitrogen, potassium and phosphorus) and the minor or trace nutrients (like manganese, copper, zinc and iron) in your soil. For the major nutrients, a good test kit will not only tell you the reading, but also indicate the measured level of each compared with an ideal standard. For example, if the test results indicate that your soil’s nitrogen level is 0.2, with 1.0 being the optimum amount of nitrogen the soil should contain, you’ll know that your soil has only 20 percent of the nitrogen content needed to support your lawn. This means you’ll need to supplement with a high-nitrogen amendment.

The results also reveal the pH level of your soil – that is, the acid to alkaline balance, which is as critical a soil component as the nutrient level. Most turfgrasses prefer a slightly acidic level between 6.5 and 7.0 pH to flourish. If your soil pH is below 6.5, the soil is too acid. If it’s above 7.0, the soil is too alkaline for good grass growth. Your pH result may indicate that you need to add sulfur to acidify the soil or lime to de-acidify it.

The pH analysis also may indicate the amount of lime in the soil. Too much lime can restrict your attempts to acidify a soil’s pH balance because it absorbs sulfur, so you’ll need to add more than normal to achieve the desired result. The analysis also might indicate that your soil has too much sodium, or salt buildup, which can be caused naturally by soil minerals, your local water supply or excess use of salt-based fertilizers. Too much salinity can cause leaf burn and kill your grass before it has a chance to grow. To cure this condition, you may need to add gypsum followed by a thorough watering to leach out the salts.

Once you’ve got the soil test results, you’ll be ready to amend properly.

Soil Test - Step 1

Dig a hole at least 16 inches wide and deep in the area to be tested. If the area is large, dig test holes in several different locations.

Soil Test - Step 2

Using a clean trowel and disposable cup, take the sample from the side of the hole to avoid collecting surface soil that may have fallen into the hole.

Soil Test - Step 3

Repeat the collection process with a new, clean cup for each of the test holes.

Soil Test - Step 4

On a clean sheet of paper, combine and thoroughly mix the samples from each cup to make one uniformly mixed sample.

Soil Test - Step 5

Place the sample in a clean, sealable plastic bag for transport to either a laboratory or to the site where you’ll perform the analysis from a home test kit.

Facts

Water should penetrate your soil readily. For any lawn, claylike soil needs to be lightened with sand, gypsum and ample organic humus to improve drainage. Sandy soil needs to be amended with organic matter or water-absorbing polymers to improve water retention.
Application rates for most soil amendments are measured in terms of quantity per 1,000 square feet of lawn, and tools like spreaders have application settings to match.

Tips

Make sure your inground irrigation system is designed to match your soil, water pressure and slope. Choose approved backflow prevention valves, and comply with all local code requirements. If you live in a climate with freezing winter temperatures, be sure to protect your watering system from expansive leaks and breakage by including a drainout fitting situated at the lowest point in the system. (Such fittings allow you to empty the pipes and spray-heads in fall.)
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