MLSN Cheat Sheet
U.S. customary units

Deﬁnition
MLSN is an initialism for minimum levels for sustainable nutrition.
This is a method for soil test interpretation and fertilizer
recommendations.

MLSN really quick start
If you have Mehlich 3 soil test data, you can directly compare yourtest results (in ppm) to the MLSN guideline levels. If your soil isabove the guideline, then you don’t need to add that element –today. You can be conﬁdent that high quality turfgrass can beproduced in soils with that quantity of the element. If your soil isbelow the guideline, you can have high quality turfgrass too. But
you should be aware that there are few soils producing highquality turfgrass with nutrient levels that low. You’ll probably wantto add enough of the element to raise it above the MLSN guideline.
That’s only the situation for today. Is your grass alive? We hope so!
If it is, then it is using nutrients. The nutrient content in the soil isgoing to be lower tomorrow than it was today – unless your grass isdead or dormant – because the grass uses nutrients. To really usethe MLSN guidelines, you need to look not at today, but into thefuture. This cheat sheet is meant to provide all the explanations
and calculations you’ll require.

MLSN quick start
These are the steps to take to get started using MLSN – in thestandard way – immediately. If you don’t know how to get thesequantities, don’t worry. The other sections of this cheat sheet
show how to ﬁnd these quantities, and how to make more
modiﬁcations to ﬁt your site.
1. Soil test Take soil samples to a depth of 4 inches. Then use theMehlich 3 extractant to ﬁnd soil test K, P, Ca, Mg, and S. Lookat the results in parts per million (ppm). Express the results
as mass per area. Call this quantity c.
2. Estimate grass use Find grass use of those elements over atime duration (t). Express those use estimates as mass perarea. Call this quantity a.
3. Check the MLSN guideline Express the value for each element
as mass per area. Call this quantity b. The MLSN minimum
levels for each element are given in this table.
ElementppmKPCaMgS3721331476

4. Calculate fertilizer requirement The fertilizer amount to apply
over time t is a + b − c.
5. Repeat for each element This process gives a fertilizer
requirement for time t for K, P, Ca, Mg, and S.

Estimating grass use

The soil test amountThe value a is the expected grass use for time t. Here are three
ways to get that value.

The soil test amount c is the amount from a Mehlich 3 soil test.
Note that conversion of soil test results from concentration units(ppm) to mass of nutrients per area, depends on the rootzone
depth and on the soil’s bulk density. You can either customize thisfor your location, or use the standard conversions.

Estimate from growth One can collect the clippings, express themas a mass, and calculate the quantity of nutrients in thatmass of clippings. Clipping volume is a rapid way toestimate the mass. For every 25 gallons (or 100 quarts) ofclippings 1000 ft-2 , expect a dry mass of 13 lbs 1000 ft-2 .
Then, calculate nutrient content by considering theelements in healthy turf. I typically use these numbers.

Agrostis & Poa

CynodonPaspalum

We recommend Mehlich 3 soil testing (Mehlich, 1984) when using
MLSN. If you use a different soil testing method, but want to use
the MLSN guidelines, you will have to convert the test results totheir expected values in Mehlich 3 – or convert the MLSN guidelines
to expected values in the other extractant. This conversion process
Festuca introduces an unknown amount of error into the calculation.

42
0.5
0.5
0.2
0.2

32
0.5
0.5
0.2
0.2

3
3
0.5
0.5
0.2
0.2

3
1.5
0.50.50.2
0.2

ElementNKPCaMg
S

Soil tests other than Mehlich 3% in dry leaves

If you know that your turf contains different concentrationsof nutrients than shown in this table, please make theadjustments to ﬁt your site.
Estimate based on N supply The grass cannot grow more than theN supply. Dividing the N supply by the percentage N in theleaves gives the maximum clipping yield. One can thenwork out the maximum use of all the elements. Forexample, Cynodon supplied with 3 lbs N 1000 ft-2 has a3= 100 lbs. To account for N
maximum clipping yield of 0.03
mineralization, I make an estimate based on soil organic
matter being 5% N and 2.5% of that N mineralized in oneyear (Havlin et al., 1998, p. 109).
Predict based on GP If one doesn’t know clippings or N supply,
the temperature-based growth potential (GP) provides a
straightforward way to get an estimate of N use, andconsequently, of maximum possibly growth. One sets a
maximum N rate for any duration (d) of the year, calculates
GP for time intervals of length d, and multiplying maximum
N by GP gives the expected N use (Woods, 2013).

The MLSN guidelines
The MLSN guidelines are given in units of ppm. This is mg ofelement per kg of soil. In the calculation of a fertilizer requirement,
I express the MLSN guideline amount as b. This amount is added tothe amount the grass uses. This ensures that 100% of grass use,plus the MLSN minimum amount in the soil, are present in any
fertilizer recommendation.

Converting from ppm to lbs 1000 ft-2 , and vice versa
1000 ft2 to a depth of 4 inches has a mass of 13,395 kg when thebulk density is 1.5 g cm-3 . 1 lb (454,000 mg) distributed through13,395 kg is thus 454000= 34 mg kg-1 . One can ﬁnd the conversion
13395
factor for any rootzone depth and any bulk density using this sameprocess.

P We’ve calculated an MLSN for the Bray-2 (30 ppm) and Olsen (6ppm) extractants. We don’t have information on otherextraction methods for P.
K, Ca, Mg When using 1 N ammonium acetate, or the Morgan
extractant, the approximate MLSN guidelines convert to 30ppm for K, 265 ppm for Ca, and 38 ppm for Mg. Alternatively,multiply the ammonium acetate or Morgan test results by
1.2 and then use the unmodiﬁed MLSN guideline.
S No known conversion.

How and why MLSN works
It works by ensuring the grass is supplied with all the nutrients it
can use while keeping a safe amount of each nutrient untouchedin the soil as a reserve. The MLSN calculation identiﬁes the amountof nutrients the grass uses at a particular site. It then ensures thegrass is either supplied with 100% of those nutrients from fertilizer,
from soil, or from a combination of soil and fertilizer (Woods et al.,2014).
This approach recognizes that grass uses nutrients. Rather thantrying to maintain all the nutrients the grass could ever use, andthen some, in a hypothetical optimum soil that doesn’t exist, theMLSN approach makes a careful estimate of plant use and makes
sure the grass is supplied with that much while still keeping a safe
amount in reserve, untouched, in the soil. This approach puts theturfgrass manager in control.
“The fundamental principle of successful
greenkeeping is the recognition of the fact that theﬁnest golﬁng grasses ﬂourish on poor soil and that
more harm is done by over-, rather thanunderfertilizing” (MacKenzie, 1998).

Why MLSN is needed
Conventional soil test interpretation is based on guidelines thatare higher than required to produce high quality turf. Turner andWaddington (1978) described this problem 40 years ago:
“Unfortunately, turfgrass recommendations appear
to be based on research done with other crops, suchas forages, results from turfgrass fertility studies notdesigned to relate to soil testing, and the best
judgement of the agronomist making therecommendations.”

Carrow et al. (2001, p. 164) wrote about this problem in their
Turfgrass Soil Fertility book:The quantile function for a log-logistic distribution is given by Eq. 2.
F −1 (p) = α“In some cases, turfgrasses have been placed in a‘high’ P and K requirement category, while pasturegrasses were in a ‘low’ category. This decision wasbased on economics, not agronomics. The cost offertilization was not considered of primary
importance for turf.”(p1−p)1/β,p ∈ [0, 1)(2)What about micronutrients?
I don’t worry about them. They are used in tiny amounts by thegrass. The grass uses about 400 times ( 40000) as much N as it does100
the most used micronutrient. The grass probably can get all themicronutrients it needs from the soil, because it uses such small
quantities of them. And because it uses such small quantities ofthem, if you are worried about it, apply micronutrients. It doesn’t
cost much and is easy to do.

The MLSN approach to soil test interpretation is designed to makea fertilizer recommendation that is based on supplying the grass
all the nutrients that it can use, while ensuring a safe amountremains in the soil. This solves – or more precisely, avoids – manyof the problems of conventional soil test interpretation.

The MLSN guideline was selected as the value at which theprobability of a random variable (X) drawn from this distribution
having a value less than or equal to the MLSN guideline is 0.1. Thatis, the MLSN guideline is the value of x where P (X ≤ x) = 0.1,
obtained by evaluating the quantile function (Eq. 2) at p = 0.1.
You can work through these, using your soil test values as x in Eq. 1,
or choosing any quantile you want between 0 and 1 as p in Eq. 2.
Or let the sustainability index (SI) calculator make the calculation
for you: https://asianturfgrass.shinyapps.io/turfsi/.

How MLSN was developed

Frequently asked questions

Salinity can kill the grass. That’s a major problem. To keep thegrass from getting killed by high salinity, one needs to leach thesalts from the soil. I wouldn’t worry much about soil nutrient levels
or MLSN if I have a salinity problem. I would leach the salts, and I
would supply 100% or a little more than the grass can use.

We studied the nutrient content of thousands of turfgrass soils inwhich good turf was growing at the time the sample was collected.
The details of this process are described in Woods et al. (2016).
After removing samples with pH < 5.5 and pH > 8.5, and selecting
those soils that have nutrient holding capacities similar to putting
green soils, we looked at the distribution of nutrients in thesamples. This is K, as an example.

How do I know the nutrients are available?

Additional resources

All the soils are producing good turf, but the soils contain a wide
range of K. If the soils with relatively low levels of an element are
producing good turf, then logic tells us that such an amount must
be enough to produce good turf. Having high K in the soil doesn’t
make the grass any better. It does, however, mean that less K
fertilizer is required.
We then used the VGAM package (Yee, 2016) in R (R Core Team,2017) to identify the scale (α) and shape (β) parameters for thelog-logistic distribution of each of the elements. These are theparameters of the log-logistic distributions of the MLSN data.
ElementScale (α)

Shape (β)

KPCaMg
S

73.48
55.07
548.13
83.17
19.37

3.20
2.23
4.85
3.83
2.30xβ,αβ + xβx ∈ [0, ∞)(1)• MLSN newsletter, www.subscribepage.com/mlsn• PACE Turf MLSN page, & the current guidelines,
www.paceturf.org/journal/minimum_level_for_sustainable_nutrition• Asian Turfgrass Center, www.asianturfgrass.com• MLSN on Facebook, www.facebook.com/mlsnturf• The #MLSN hashtag on Twitter

MLSN guideline, target level or minimum level?

References

Conventional soil test interpretation may give the impression that
there are target or optimum levels in the soil. The MLSN guideline
is a minimum value – minimum is the M in MLSN so we haven’t
always repeated that – that one doesn’t want to drop below. It’s
not a level below which one will have deﬁciency. It’s not a target
level that one ideally will have the soil at. What the MLSN guideline
represents is a level in the soil with enough of that element toproduce high quality turf. There is high quality turf in soils withless of that element too, and that’s why we are conﬁdent the MLSN
guideline is a safe level. But there aren’t a lot of soils with less, sowe suggest keeping the soil from dropping below the MLSN
guideline.

Carrow, R. N., Stowell, L. J., Gelernter, W. D., Davis, S., Duncan, R. R.,and Skorulski, J. (2004). Clarifying soil testing: III. SLAN
sufﬁciency ranges and recommendations. Golf Course Mgmt.,
72(1):194–198.
Carrow, R. N., Waddington, D. V., and Rieke, P. E. (2001). Turfgrasssoil fertility and chemical problems. John Wiley and Sons.
Havlin, J. L., Tisdale, S. L., Nelson, W. L., and Beaton, J. D. (1998). Soil
fertility and fertilizers: an introduction to nutrient management(6th Ed.). Prentice Hall, 6th edition.
MacKenzie, A. (1998). The Spirit of St. Andrews. Three Rivers Press.
Mehlich, A. (1984). Mehlich 3 soil test extractant: a modiﬁcation ofMehlich 2 extractant. Comm. Soil Sci. Plant Anal., 15:1409–1416.
R Core Team (2017). R: A Language and Environment for StatisticalComputing. R Foundation for Statistical Computing, Vienna,Austria.
Turner, T. R. and Waddington, D. V. (1978). Survey of soil testing
programs for turfgrasses. Comm. Soil Sci. Plant Anal., 9(1):71–87.
Woods, M. S. (2013). Using temperature to predict turfgrass growthpotential (GP) and to estimate turfgrass nitrogen use. Technicalreport, Asian Turfgrass Center.
Woods, M. S., Stowell, L. J., and Gelernter, W. D. (2014). Just what thegrass requires: using minimum levels for sustainable nutrition.
Golf Course Mgmt., pages 132–138.
Woods, M. S., Stowell, L. J., and Gelernter, W. D. (2016). Minimum soil
nutrient guidelines for turfgrass developed from Mehlich 3 soil
test results. PeerJ Preprints.
Yee, T. W. (2016). VGAM: vector generalized linear and additivemodels. R package version 1.0-1.

Seriously, the same minimum for every grass, soil, andlocation? No regional customization?
We are conﬁdent that the MLSN guideline is enough to produce
high quality turf for every grass, everywhere. MLSN has the ultimate
customization, however, because the grass use of elements isentirely site speciﬁc. In order to ensure the soil doesn’t drop below
the MLSN guideline, one has to estimate a, the expected plant use
over time. That’s where the customization comes in.

How is this different than conventional soil test
interpretation?

Once α and β are known, one can calculate the cumulative
distribution function (cdf) for any soil test value. The cdf for alog-logistic distribution is given by Eq. 1.
F (x) =You know the nutrients are available because you’ve done a soiltest. That’s what a soil test is – by deﬁnition it produces a nutrient
availability index. If you don’t trust the soil tests, then I suggest
skipping them altogether. Instead, assume the soil can supply
nothing, and supply to the grass 100% (or a little more) of its
possible use of each element. This isn’t the most efﬁcient way to
do it, but you won’t need to worry about availability, and it isguaranteed to supply all that the grass can use.

What about salinity?

The focus of MLSN is on keeping the soil from dropping below aknown safe level. To do this, one must account for how much thegrass uses over time. The MLSN approach explicitly calculates thegrass use. The conventional interpretation (Carrow et al., 2004) isabout classifying based on soil levels.

Prepared by Micah Woods on February 1, 2018, based on the latexsheet
template of Winston Chang.