Turfgrass Establishment Series - Soil Testing
Turfgrasses, like all plants, require nutrients to grow and develop. These nutrients are held in the soil and taken up by turfgrass roots. Before planting turfgrass, it’s helpful to better understand the chemical components of the rootzone material to determine if adjustment is necessary. Soil testing is the process of collecting soil samples and analyzing those samples for pH, cation exchange capacity, and concentrations of essential plant elements.
When it comes to soil testing, a three-step process exists:
- Soil sample collection
- Laboratory analysis
- Soil test interpretation and fertilizer recommendation
1. Soil sample collection
Ohio State University Extension has a useful fact sheet outlining the steps to collect a soil sample, including methods for sampling when using a soil probe, garden spade, knife, or hand trowel. A point to include is that we recommend sampling at a 4-inch depth. It is helpful to mark your soil sampling tool at 4 inches to ensure consistency. Variation in sampling depth will affect the validity of the soil test report.
2. Laboratory analysis
Even with the same exact soil sample, different laboratories can yield different results. This is due to varying extractant methods. For Ohio soils, a laboratory that uses the Mehlich 3 extractant is recommended. This method will yield results and subsequent fertilizer recommendations most suitable for turfgrass grown in Ohio. Many private and public soil testing laboratories are available for Ohio residents. OSU Extension utilizes the Agricultural Analytical Services Lab at Penn State University, with each sampling kit costing $11 (plus shipping).
3. Soil test interpretation and fertilizer recommendation
The results from a soil test are rather useless without proper interpretation and a recommendation for fertilizer application. The Sufficiency Level of Available Nutrient (SLAN) is based on the likelihood of a turf response following an application of a specific nutrient and is the most common interpretation philosophy at land-grant university labs. SLAN provides recommendations for phosphorus (P) and potassium (K) in addition to other macronutrients (Ca, Mg, S), if needed. Another philosophy, Minimum Levels of Sustainable Nutrition (MLSN), has gained popularity as an option resulting in good quality turf under reduced fertilizer inputs relative to SLAN. However, soil testing labs do not provide MLSN recommendations on their reports, requiring the end-user to determine those fertilizer needs on their own (https://www.asianturfgrass.com/mlsn/).
It should be noted that soil testing does not provide a valuable assessment of nitrogen (N) status in the soil. Due to the many loss mechanisms of N in the soil (i.e., leeching, denitrification, volatilization), N recommendations provided on a soil test report are derived from turfgrass species performance data. Current research at OSU by Tyler Van Landingham is fine-tuning N fertilizer recommendations for turfgrass species common on Ohio lawns.
Additionally, a soil test will determine if lime is needed to raise pH. The optimal pH for lawns in Ohio is between 6 and 7, so lime additions may be required if pH is below 6. Check out the OSU Extension Fact Sheet “Lime and the Home Lawn” for more information about when to apply lime, how much to apply, and what lime source to apply.