Estimating Turfgrass Nutrient Use
Micah Woods
Chief Scientist | Asian Turfgrass Center
seminar.asianturfgrass.com/20150128_ontario.html
@asianturfgrass
Ontario GSA Conference
Niagara Falls
28 January 2015

First, do we need to add an element as
fertilizer?
seashore paspalum
Lanai, Hawaii

Second, how much do we need to add? creeping bentgrass
Hokkaido, Japan

To answer those fundamental questions, we
need to estimate 3 quantities
creeping bentgrass
Shanghai, China

To answer those fundamental questions, we
need to estimate 3 quantities
creeping bentgrass
Shanghai, China

To answer those fundamental questions, we
need to estimate 3 quantities
creeping bentgrass
Shanghai, China

To answer those fundamental questions, we
need to estimate 3 quantities
creeping bentgrass
Shanghai, China

To answer those fundamental questions, we
need to estimate 3 quantities
creeping bentgrass
Shanghai, China

These 3 quantities
simplify to 2 – the
amount we have, and
the amount we need
The amount the grass
uses + the amount
required (a + b) is the
amount we need
The amount in the soil (c)
is the amount we have
manilagrass (Zoysia matrella)
Chonburi, Thailand

If the amount we have
is more than the amount
we need, none of that
element is required as
fertilizer.
If the amount we have
is smaller than the
amount we need,
fertilizer must be supplied
to make up the difference.
a + b - c
seashore paspalum
Mauritius

Quantity a, the amount used
We can make a conservative estimate of this based on
nitrogen applied and turfgrass species.

1) the more nitrogen applied, the more
growth & 2) we always want healthy grass
creeping bentgrass
Chiba, Japan

Bentgrass leaves contain,
as % of dry weight, about:
N 4%
K 2%
P 0.5%
Ca 0.5%
Mg 0.2%
S 0.2%
Fe 0.01%
creeping bentgrass
Hokkaido, Japan

To estimate the amount used:
1. Known N supply
2. (N supply) / 0.04 = dry clipping yield
3. From that, use of any element can be estimated

Quantity b, the amount required in soil
We identify this as the lowest level we can safely let
the element decrease to in the soil. This is the basis of
the minimum levels for sustainable nutrition (MLSN).

http://www.paceturf.org/PTRI/Documents/1202_ref.pdf

Quantity c, the amount in the soil
We measure this by doing a soil test.

How to work out
a + b – c = fertilizer requirement
First, Toronto as an example

Using growth potential (GP) allows one to get an
estimate of the amount of nitrogen that may be used,
based on optimum growth temperatures and desired
growth rate.
For creeping bentgrass, I generally use a monthly
maximum of 3 g N/m2
.

These values of predicted use are quantity a

Useful conversion factors
5 g/m2
= 1 lb/1000 f2
1 g/m2
= 6.7 ppm in a 10 cm rootzone with bulk
density of 1.5

http://www.paceturf.org/index.php/public/ipm_planning_tools

element MLSN (ppm) MLSN (g/m2
)
K 37 5.5
P 21 3.1
Ca 331 49
Mg 47 7.0
S 7 1.0
Quantity b, the amount required in the soil,
we can take from the MLSN guidelines.

element M3 (ppm) M3 (g/m2
)
K 67 10
P 74 11
Ca 605 90
Mg 87 13
S 14 2.1
Quantity c, the amount we have in the soil,
we measure by a soil test.
I'll use here median values from Global Soil
Survey samples (n = 93).

The amount of an element required as fertilizer is the
amount we need minus the amount we have:
a + b – c
For the conditions described, using GP for Toronto
2014 weather, maximum monthly N of 3 g/m2
, and soil
data as the median of the GSS, we get .

element a (use) b (reserve) c (in soil) fertilizer
K 6.6 5.5 10 2.1
P 1.7 3.1 11 -6.2
Ca 1.7 49 90 -39
Mg 0.7 7.0 13 -5.3
S 0.7 1.0 2.1 -0.4

This answers the 2
questions we started
with. Is an element
required as fertilizer? If
so, how much?
In the process of
answering, we also
familiarize ourselves with
the useful quantities a, b,
and c.
creeping bentgrass
Shimane, Japan

https://www.facebook.com/mlsnturfhttp://www.blog.asianturfgrass.com/fertilizer/
http://www.paceturf.org/journal/global_soil_survey
http://www.paceturf.org/journal/minimum_level_for_sustainable_nutrition

Handout link
seminar.asianturfgrass.com/20150128_ontario.html