Estimating Turfgrass Nutrient Use

Micah WoodsChief Scientist | Asian Turfgrass Centerseminar.asianturfgrass.com/20150128_ontario.html@asianturfgrass

Ontario GSA ConferenceNiagara Falls28 January 2015

First, do we need to add an element as fertilizer?

seashore paspalumLanai, 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 bentgrassShanghai, China

To answer those fundamental questions, we need to estimate 3 quantities

creeping bentgrassShanghai, China

To answer those fundamental questions, we need to estimate 3 quantities

creeping bentgrassShanghai, China

To answer those fundamental questions, we need to estimate 3 quantities

creeping bentgrassShanghai, China

To answer those fundamental questions, we need to estimate 3 quantities

creeping bentgrassShanghai, 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 paspalumMauritius

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 bentgrassChiba, 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 bentgrassHokkaido, 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 10P 74 11Ca 605 90Mg 87 13S 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) fertilizerK 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 bentgrassShimane, 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