PACE Turf - Turfgrass Information Center

Soil

A new look at calculating calcium requirements

We are continuing our efforts to refine the new Minimum Levels for Sustainable Nutrition (MLSN) guidelines in cooperation with Dr. Micah Woods at the Asian Turfgrass Center. In the process, we have received some questions about managing sodium.

The MLSN guideline identifies 110 ppm (milligrams/kilogram, mg/kg) sodium as the maximum threshold for cool season grasses. To maintain sodium below 110 ppm in the soil, supplemental calcium is sometimes needed. To determine how much calcium needs to be applied to reduce sodium if levels exceed 110 ppm, follow the calculations below. For a similar method using metric units, refer to the Asian Turfgrass Center calcium requirements in metric units:

  1. Determine how much excess sodium is present in your soil by subtracting 110 ppm (mg/kg) sodium (Na) from the value on your soil report.
    For example, if your soil contains 150 mg/kg sodium, your soil contains 40 mg/kg more (150 mg/kg - 110 mg/kg) sodium than is desired.
  2. To compute how much calcium is needed to displace the sodium, we need to convert sodium units from mass into units of positive charge. To make the calculations easier, we use millimoles (mmol) of charge.
    For example, (40 mg sodium/kg)/(23 mmol sodium charge/mg) = 1.7 mmol sodium charge/kg soil
  3. To displace 1.7 mmol sodium charge/kg with calcium, we will need 1.7 mmol calcium charge/kg soil
    For example, (1.7 mmol calcium charge/kg) X (20 mmol calcium charge/mg) = 34 mg calcium/kg (ppm) are needed to displace the sodium
  4. To convert this value to pounds per acre, multiply by 2
    For example, 34 ppm calcium X 2 = 68 lbs calcium/acre are needed to displace sodium
  5. To convert pounds per acre to pounds per 1000 sq ft, divide by 43.56
    For example, (68 lb calcium/acre)/43.56 = 1.6 lbs calcium/1000 sq ft needed to displace 40 ppm sodium
  6. A shortcut to steps 2 - 5 is to multiply the excess sodium ppm value by 0.04 to obtain pounds calcium/1000 sq ft needed to displace excess sodium
  7. For example 40 ppm excess sodium x 0.04 = 1.6 lbs calcium needed/1000 sq ft
  8. To determine how much of a calcium amendment is needed to provide the desired amount of calcium, divide by the proportion composition of the product.
    For example, gypsum typically contains about 23% calcium. Therefore a requirement for 1.66 lbs calcium/1000 sq ft will require: (1.6 lb calcium/1000 sq ft)/0.23 = 7 lbs gypsum/1000 sq ft required to displace 40 ppm sodium

It is important to remember that calcium is also required as a plant nutrient (at levels of 360 ppm in the soil), in addition to its value as a tool for managing sodium. When calculating calcium requirements, you will need to keep both the sodium management and plant nutrition requirements in mind.

Minimum Levels for Sustainable Nutrition Soil Guidelines (MLSN)

Increased economic and environmental pressures have caused many turfgrass managers to re–assess the way you manage turf. With fertilizers as one of the bigger inputs, we felt that it was time to review and revise our current soil guidelines to reflect these changes. The result is the "Minimum Level for Sustainable Nutrition" (MLSN) soil guidelines, a new, more sustainable approach to managing soil nutrient levels that can help you to decrease inputs and costs, while still maintaining desired turf quality and playability levels. Used in conjunction with Climate Appraisals and Growth Potential, annual fertilizer needs can be estimated. 

Working together with Dr. Micah Woods of the Asian Turfgrass Center, the guidelines were produced through review of key soil nutrient data from thousands of turf soil samples. Based on our evaluations, we determined that in many cases, guidelines could be safely lowered without a dramatic impact on turf quality or playability.

Since their introduction in 2012, the MLSN guidelines have been adopted by turf managers around the world, who have been surprised to find just how "low they can go" as they more precisely target the nutrient levels that the turf needs.

Scientific basis for the MLSN Guidelines:

Turf management articles about the MLSN Guidelines:

Websites with more information about the MLSN Guidelines:

Rainfall impact on sodium leaching at Denver Country Club

In the July 13, 2011 Super Journal report, "Rainfall impact on sodium leaching at Denver Country Club" (1.3 MB pdf document), we show the dramatic and positive impact that spring rainfall can have on reducing soil sodium and salinity.

In short, we saw that a 2.5 inch rainfall, which occurred over a 36 hour period during the spring of 2011, resulted in a 41% reduction in sodium, and a 19% reduction in overall soil salts.

In addition to causing general stress to turf and potential issues with soil physical properties, high sodium and high salts are also associated with rapid blight, a disease caused by Labyrinthula terrestris. In years when winter and spring rainfall is low, it may therefore be necessary to leach greens with good quality domestic water in order to avoid reaching the maximum levels of 110 ppm sodium that can result in rapid blight infestation.

Project title: Rainfall impact on sodium leaching at Denver Country Club

Principal investigator: Doug Brooks, Denver Country Club and Larry Stowell, Ph.D., CPAg, PACE Turf LLC

Further reading:

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