MLSN Guidelines: what they are, and how to use them

The presentation explains the MLSN guidelines and answers questions about their development and use. The MLSN guidelines work like this.

1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below the MLSN guideline.

2. Estimate future use of those elements, and make sure that amount can be supplied by the soil, while still keeping the soil above the MLSN guideline.

3. If the soil doesn't have enough to do that, then apply enough of that element as fertilizer to keep the soil above the MLSN guideline.

Transcript

1. MLSN Guidelines
   What they are, and how to use them
   Micah Woods
   Chief Scientist
   Asian Turfgrass Center
   www.asianturfgrass.com
   6 May 2015
   a TurfNet webinar
   

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2. MLSN in 10 minutes
   MLSN is an acronym for
   Minimum Levels for Sustainable Nutrition. This is a method for the
   interpretation of soil nutrient analyses.
   

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3. MLSN answers the 2 questions of soil testing
   1. Is this element required as fertilizer?
   2. If it is required, how much?
   

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4. More specifically…
   One can express the quantity of an element required as fertilizer as
   Q.
   a + b − c = Q
   where,
   a is the quantity of the element used by the grass
   b is the quantity of the element required in the soil
   c is the quantity of the element present in the soil
   Q is the quantity of the element required as fertilizer
   

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5. MLSN is a value for b
   amount needed
   a + b −
   amount present
   c =
   fertilizer requirement
   Q
   a is a site-specific use estimate, b is the MLSN guideline, and c is the
   soil test result.
   

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6. a, www.paceturf.org/journal/climate
   

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7. b
   

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8. Using MLSN
   1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below
   the MLSN guideline.
   

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9. Using MLSN
   1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below
   the MLSN guideline.
   2. Estimate future use of those elements (a), and make sure that
   amount can be supplied by the soil, while still keeping the soil
   above the MLSN guideline (b).
   

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10. Using MLSN
    1. Keep the soil levels of K, P, Ca, Mg, and S from dropping below
    the MLSN guideline.
    2. Estimate future use of those elements (a), and make sure that
    amount can be supplied by the soil, while still keeping the soil
    above the MLSN guideline (b).
    3. If the soil (c) doesn’t have enough to do that, then apply
    enough of that element as fertilizer (Q) to keep the soil above
    the MLSN guideline.
    

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11. As an example for K
    a + b − c = Q
    

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12. As an example for K
    a + b − c = Q
    In ppm, a = 100, b = 37, c = 70.
    

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13. As an example for K
    a + b − c = Q
    In ppm, a = 100, b = 37, c = 70.
    amount needed
    100 + 37 −
    amount present
    70 =
    fertilizer requirement
    67
    

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14. As an example for K
    a + b − c = Q
    In ppm, a = 100, b = 37, c = 70.
    amount needed
    100 + 37 −
    amount present
    70 =
    fertilizer requirement
    67
    Convert between 3-dimensional (ppm) and 2-dimensional (ex. g m-2,
    or lb 1000 -2) based on rootzone depth and soil bulk density. For a
    10 cm deep rootzone with bulk density of 1.5 g cm-3, 1 g m-2 equals
    6.7 ppm, and 1 lb 1000 -2 equals 33.5 ppm. Using that conversion,
    Q of 67 ppm is a K requirement of 10 g m-2 or 2 lb 1000 -2.
    

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15. estions?
    

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16. Is there continued field sampling or any plans to be er
    regionalize the sampling for possibly di erent MLSN numbers
    for di erent regions or possibly between di erent soil types
    (ex. USGA vs. Native Soil)?
    MLSN is dynamic in that we systematically add data and review the
    guidelines. The Global Soil Survey is an ongoing project to gather
    more data. No immediate plans for regionalization, basically
    because of lack of data, and scope of project. Note, however, that
    while b is constant, a is infinitely site-specific and c is both soil and
    site-specific.
    

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17. What soil testing method(s) should we utilize to determine
    the nutrient levels in the bank prior to making fertilizer
    applications to correct deficiencies (if any)?
    We used the Mehlich 3 extraction for the development of the MLSN
    guidelines.
    

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18. What about the correlation with other testing methods. I have
    years of soil test data, but unfortunately these used a di erent
    extraction method (I believe ammonium acetate). Is there a
    reliable and accurate way to convert the values from other
    extraction methods to Melich 3?
    There are some conversion equations that can be used. Any
    conversion will introduce some error, but with a bit of e ort one can
    make useful estimates.
    

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19. Soil paste extracts? yes or no?
    No. Soil paste extracts, or saturated paste extracts – these are for
    assessing soil salinity. Not a good test for determining how much
    fertilizer should be applied.
    

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20. Why not regionalization? WOW‼ I simply CANNOT wrap my
    head around the thought of not considering soil types and or
    regionalization for nutrient recommendations‼ So are you
    saying that sand has the same nutrient holding ability as a
    rich sandy loam
    I agree that it seems counterintuitive to make nutrient
    recommendations with guidelines (b) that admi edly do not
    consider soil type or region. But by thinking about the a and c of the
    equation used to get Q, there is infinite regionalization. These are
    adjusted for:
    grass species
    desired growth rate
    site soil conditions
    time of year
    site climate
    

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21. I’ll ask myself a question. Can you explain how the guidelines
    were developed?
    Sure. I’ll use potassium (K) as an example.
    

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22. Guideline development process: the raw data
    0
    100
    200
    300
    400
    500
    0 1000 2000 3000
    3721 soil samples from good turf
    K (ppm)
    

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23. Data organized into a histogram
    K (ppm)
    Frequency
    0 100 200 300 400 500
    0 100 300
    

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24. Remember, all the samples are from good turf, like this
    

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25. I am curious about the definition of good turf. What are the
    characteristics of good turf?
    For the MLSN samples, which all come from
    professionally-managed turf areas, the good turf is from areas that
    the professional turf manager identifies as performing well at the
    time the sample was collected. It is the inverse of bad turf or
    problem areas identified by a professional turf manager.
    

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26. With an overlay of probability density
    K (ppm)
    Frequency
    0 100 200 300 400 500
    0 100 300
    density
    

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27. A gaussian (normal) model doesn’t fit well
    K (ppm)
    Frequency
    0 100 200 300 400 500
    0 100 300
    density
    normal
    

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28. A log-logistic distribution fits the data much be er
    K (ppm)
    Frequency
    0 100 200 300 400 500
    0 100 300
    density
    normal
    log-logistic
    

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29. Probability of the sample being below x
    0 100 200 300 400 500
    0.0 0.4 0.8
    K (ppm)
    Cumulative probability
    data
    

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30. Model is very close to the data
    0 100 200 300 400 500
    0.0 0.4 0.8
    K (ppm)
    Cumulative probability
    data
    model
    

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31. Identify a MLSN for K at cumulative probability of 0.1
    0 100 200 300 400 500
    0.0 0.4 0.8
    K (ppm)
    Cumulative probability
    model
    

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32. Fertilizer is recommended to keep the soil above MLSN
    K (ppm)
    Frequency
    0 100 200 300 400 500
    0 100 300
    

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33. Would you elaborate on the potassium trial conducted by
    Rutgers where winterkill was more severe on poa plots that
    had less than 50 ppm of K?
    In the trial at Rutgers, there is a K deficiency in plots not supplied
    with K. Where K has been supplied, the winter damage was not
    evident, and anthracnose is reduced. If the MLSN approach were
    implemented on those trials, enough K would be supplied to
    eliminate the deficiency.
    

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34. How do you convert a soil report results from lbs/ acre to ppm
    to see if one’s numbers are above or below the MLSN
    requirements?
    You divide lbs/acre by 2 to get ppm, assuming the samples are from
    a 6” (15 cm) depth. You should be ge ing results in ppm which is
    what the lab machines measure. Any lb/acre or lb/1000 or kg/ha
    reporting is a calculated number from the ppm result.
    

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35. Can I also assume that you also do not consider that some
    irrigation water can act as a stripper?
    That’s correct. If there are no salts in the water, then there won’t be
    anything in the water to exchange with ions in the soil, and it won’t
    act as a stripper. And one would not be leaching the soil if the water
    doesn’t have salt in it. If the water does have salt in it, then the ions
    in the water will exchange with the ions on exchange sites in the
    soil, to some extent, with the tendency being more adsorption of
    divalent cations (Ca2+, Mg2+) in the soil and more monovalent
    cations (K+, Na+) in solution.
    

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36. What are your thoughts on nutrients being tied up in the
    soil
    This is an unnecessary complication. One measures nutrient
    availability by doing a soil test and interpreting the soil test to
    determine if a nutrient is required as fertilizer.
    

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37. Was the work done to develop the MLSN done at 4 or 6
    inches? Also, what if you have specified to your lab that the
    samples were taken at a 4” depth?
    The samples for the development of MLSN were from 4 inches (10
    cm). The lab should report ppm units back to you, which are
    independent of soil depth; if the lab reports lb/acre or kg/ha, they
    will have calculated that based on the sample depth you provided
    them.
    

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38. Once you are above those levels, you just need to maintain it
    to that point? The numbers that I have are well above those
    levels, therefore I would not need to apply Ca, P, Mg or K. Just
    a straight N product, since the other nutrients are not lacking
    in the soil makeup? How does one do that in a natural or
    organic program in which many products contain small
    amounts of P and K with the N application?
    That’s correct. And I would do that as best as I could, trying to use
    products with low amounts of P and K. Really I would try to avoid P
    completely if the soil had enough.
    

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39. I would like to see info included about soil health testing
    ...My thoughts are that we as turfgrass managers leave
    behind the biological leg of the stool and rely on the physical,
    and chemical legs exclusively and that the real MSLN could be
    improved upon and may be lowered based on soil health.
    Good point. There are some intriguing new tests for assessing soil
    biology or “soil health.” But these tests su er from the same
    problem as conventional soil chemical guidelines – how can one
    interpret the results for turfgrass? With tests of soil health, I’m
    optimistic about being able to make recommendations in the future,
    but at present it would just be guessing.
    

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40. More information available at:
    www.turfnet.com/topic/7024-mlsn-questions-for-upcoming-
    webinar/
    www.blog.asianturfgrass.com/fertilizer/
    www.paceturf.org
    www.gcsaa.org/gcm-magazine/2014/january/gcm-january-
    2014-just-what-the-grass-requires
    www.facebook.com/mlsnturf
    

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