Gulf Coast GCSAA Presentation on MLSN

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Dr. Larry Stowell presented the new concept of Minimum Levels for Sustainable Nutrition to the Gulf Coast Golf Course Superintendent’s Association via webcast on December 11, 2012. The attached pdf file provides an edited version of the presentation that includes information requested during the question and answer period. The key change was the inclusion of information on nutrient requirements for bermudagrass that is overseeded with ryegrass compared to non-overseeded bermudagrass.

Here are some bottom-line tips on fertilization to target soil MLSN guidelines:

• Apply maintenance applications nitrogen (N), phosphrous (P) and potassium (K) in a ratio of 10:1:4 (N:P:K). To prevent leaching and runoff, never apply more than 0.5 lbs N/1000 sq ft in a single application. Lower rates of application and shorter frerquencies are recommended. Adjust nitrogen rates to produce turfgrass performance that grows and recovers adequately to meet golfer expectations.
• Test soils in the spring and fall and compare soil test results to MLSN guidelines
• If soil tests report nutrient levels lower than listed in the MLSN guidelines, increase the ratio of P and K in the maintenance fertilizer applications. For example change to a 6:1:4 (N:P:K) ratio. If nutrients other than P and K are low, for example calcium or magnesium are lower than MLSN guidelines, supply these nutrients as needed to adjust soil levels to exceed MLSN guidelines. Application of 1 lb element/1000 sq ft (about 5 g element/m^2) will increase soil levels by about 20 ppm per application.

Stowell, L. Minimum Levels for Sustainable Nutrition. Golf Coast GCSA Meeting Dec. 11, 2012

Research advances in soil management: The Bouyoucos Conference

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The Bouyoucos Conference on the Advances in Research on Soil Biological, Chemical and Physical Properties for Sustainable Constructed Rootzones recently brought together agronomists, plant and soil scientists from around the globe to share information on soil biopysical, biochemical and hydrological research that impacts constructed root zones, such as those on golf courses and sports fields.

PACE Turf's Larry Stowell was an invited speaker, where he shared the work he has been doing with Dr. Micah Woods on reduced fertilizer inputs, coined the Minimum Levels for Sustainable Nutrition (MLSN) Guidelines.

Stay tuned for Larry's reports on the most interesting research results from this meeting.

By the way, Dr. George Bouyoucos, for whom the conference is named, was an esteemed soil scientist whose work during the early part of the 20th century is still the basis for much of what we know about the physics of soils.

A new look at calculating calcium requirements

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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 43.65

   For example, (68 lb calcium/acre)/43.65 = 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

For example 40 ppm excess sodium x 0.04 = 1.6 lbs calcium needed/1000 sq ft

7. 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 330 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.