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Soil Testing

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objective

Obtain soil tests to determine the chemical and physical condition of the soil and to ascertain recommendations for adjustments.

Test soil to obtain necessary information for sound management decisions.

  • An uninformed approach to soil and nutrient management is not economically or environmentally responsible.
  • Soil test results can dictate approaches for management of soil, for assessment of overall plant health, for refinement of a fertility program, for the prevention of nutrient losses to the environment, and for other aspects of management.
  • Conduct chemical (nutrients, heavy metals, pH, CEC, exchangeable acidity, base saturation) and physical (texture, percent organic matter) soils analyses prior to establishment, renovation, or at the beginning of assuming management responsibility for a site where limited history is available.

Soil Chemical Properties 

Soil Physical Properties 

Ex. pH, fertility, nutrient reserves, heavy metals, salinity 

Ex. texture, particle size distribution, percent organic matter 

  • Provides information about growing conditions of soil
  • Informs additions of fertilizer and liming materials
  • Provides information about behavior of soil
  • Helps in assessment of drainage characteristics and compatibility of amendments with existing soil

For established, healthy turf, conduct soil chemical analyses at least every three years and monitor pH annually. 

  • Have soil tested at a laboratory offering the modified Morgan extraction method for nutrients. Over fifty years of research indicates that this is the most appropriate nutrient extraction method for New England soils and is used by the University of Massachusetts Soil & Plant Tissue Testing Laboratory. Different analytical procedures can yield vastly different results.
  • Test soil conditioners, topdressing materials, composts and other turf amendments separately to ensure suitability for use.

Learn how to correctly interpret soil test results.

  • Soil test results are of little value without an appropriate interpretation.
  • Research data about the relationship between soil test values and the need for amendments form the foundation of soil test interpretation.
  • As the soil test level for a nutrient increases, plant growth increases until a point where the nutrient is no longer limiting; this point is known as the critical soil test level. The critical soil test level is defined as the extractable nutrient concentration in soil above which plant growth (or performance) response to added nutrient is unlikely.
  • Nutrient levels are considered sufficient when the concentration is just above the critical soil test level. This is known as the Optimum soil test range.
  • When levels are below the Optimum range (Very Low or Low), the addition of more of the nutrient will usually improve turf performance.
  • Nutrient recommendations provided by the soil testing lab are intended to meet short- term turf nutritional needs and provide enough to slowly (over several years) build soil test levels to the Optimum range.
  • When soil test levels are in the Optimum range turf response to application of that nutrient is unlikely, but some amount may be recommended to maintain soil levels over time.
  • It is important to keep in mind that factors other than nutrients may limit turfgrass growth, and simply adding more nutrients may not improve turf performance. To optimize turf performance and maximize response to fertilizer nutrients, sound management practices must be used (e.g., cultivar selection, establishment, irrigation management, and pest and stress management).

Categories

Interpretation 

Table 8. Interpretation of soil test categories

Very Low 

Soil test level is well below optimum. Very high probability of plant response to additional nutrients.

Substantial amounts of additional nutrients required to achieve optimum growth. Fertilizer rates based on plant response and are designed to gradually increase soil nutrient levels to the optimum range over a period of several years. 

Low 

Soil test level is below optimum. High probability of plant response to addition of nutrients.

Moderate amounts of additional nutrients needed to achieve optimum growth. Recommendations based on plant response and are intended to gradually increase soil nutrient levels to the optimum range. 

Optimum 

For most plants, low probability of response to addition of nutrient. Most desirable soil test range on economic and environmental basis.

To maintain this range for successive years, nutrients must be retained in the system, or those nutrients removed by plants or lost to the environment must be replaced. 

Above Optimum 

The nutrient is considered more than adequate and will not limit plant performance or quality. At the top end of this range, there is the possibility of a negative impact on the turf if nutrients are added.

Additional nutrient applications are not recommended. 

Excessive 

This soil test level is independent of plant response and, due to environmental concerns, is only defined for soil test phosphorus (P). This P concentration is associated with elevated risk of P loss in leachate and runoff at concentrations high enough to impair surface water quality.

No P should be applied and steps should be taken to minimize losses from leaching and runoff. 

The modified Morgan extractable nutrient values associated with each of the soil test categories for Massachusetts are summarized in Table 7. These values, derived from the results of regional soil test calibration research, are used to determine fertilizer needs for turfgrass. Notice that N is not included in Table 7. Soil testing is of limited value for determining N needs due to the dynamic behavior of soil nitrogen (N) in the humid Northeastern US. Soil testing is most useful for determining fertilizer phosphorus (P) and potassium (K) needs. 

  Very Low Low Optimum Above optimum Excessive
Table 9. UMass soil test categories for modified Morgan extractable nutrients.
P, ppma 0 - 1.9 2 - 3.9 4 - 14 14 - 40 >40
K, ppm 0 - 49 50 - 99 100 - 160 >160 -
Ca, ppm 0 - 499 500 - 999 1000 - 1500 >1500 -
Mg, ppm 0 - 24 25 - 49 50 - 120 >120 -
a. ppm = parts per million