How do chemical fertilizers
affect the pH of soil?
Erin Flynn
EDTEP 586
December 11, 2003
Initial Model
Miracle-Gro®
Soil
Bacteria
BAD for plants!
3H+
pH
Background Information
o
o
o
o
Liquid Miracle-Gro® plant food is a source of
ammonium and nitrate, essential nutrients for plant
growth.
Bacteria in the soil convert ammonium (NH3) to nitrate
(NO3).
Excess H+ ions in soil cause a decrease in pH.
Changes in pH of the soil can adversely affect the
plants that grow in it.
Assumptions
o
o
o
o
The bacteria responsible for the conversion of NH3 to NO3 are
present and active in all of my soil samples.
The amount of ammonium that was added to the soil samples is
enough to disturb the system (i.e. not all H+ released in the conversion
of NH3 to NO3 will be bound to negatively charged organic matter in
the soil).
The buffering capacity of the soil samples is negligible.
The amount of time that elapsed through the course of this
experiment (3 weeks) is enough time to see a change in pH.
Methods
November 19, 2003
o Collected soil samples from four Seattle area parks, in areas where plant life
tended to be “wild” (i.e. not landscaped, such as wooded areas).
o Samples were taken from 6” below the ground surface.
o Plants within a 20 ft radius of the dig site were surveyed and catalogued.
o Samples were split into 3: first sample was tested for pH immediately; the
second and third were incubated at 68°F for three weeks.
o 100 ml of sterile water was added to the control sample, and 100 ml of Liquid
Miracle-Gro® was added to the experimental sample at a 1:1000 dilution.
November 24 & December 2, 2003
o 20 ml of sterile water was added to all samples.
December 9, 2003
o pH was tested for all experimental and control samples.
How did I test the soil pH?
o
o
o
o
o
o
o
Used “color pHast® pH 0-14” strips (EM-Reagents).
Placed a pH strip on the bottom of a 5” plastic pot.
Covered the strip with a 5” diameter filter paper.
Added the soil into the pot.
Poured 100 mL of pre-boiled, room temperature, filtered
H2O and mixed.
Allowed the water to drain out of the pot.
Inverted the pot, and read the pH strip while still moist.
Soil Samples
1: Southwest
County Park,
Edmonds WA
1
2
3
4
2: Lincoln Park,
West Seattle
3: Carkeek Park,
Seattle
4: Discovery Park,
Seattle
Data Table
Date
Site #1
Site #2
Site #3
Site #4
11/19 C
4.0
5.0
5.0
5.5
Water
Control
5.0
12/9 C
4.0
5.0
5.0
5.5
5.0
12/9 E
3.0
5.0
3.0
5.0
5.0
pH values of the soil samples at two timepoints. C = control sample
(water only added), E = experiment sample (Miracle-Gro added).
®
pH change of soil samples
6
5
4
pH
0 days
20 days C
20 days E
3
2
1
0
sample #1 sample #2 sample #3 sample #4
water
control
This chart shows the change in pH values of the four soil samples
plus water control over the three week period. E= ammonium added,
C = water only added.
Why does pH change when ammonium
fertilizer is added to the soil?
o
o
o
The conversion of ammonium to nitrate releases three H+
ions.
If there is no buffering agent in the soil to bind to the free
H+, it results in a decrease in pH (increase in acidity) of the
soil; if there is, the pH will remain unchanged.
If soil is already acidic when ammonium fertilizer is added,
denoting a lack of binding materials for free H+, the pH of
the soil will only continue to decrease.
What is the effect on the plants
living in this soil?
o
o
When soil is strongly acidic, the bacteria and
other microbes that are responsible for the
breakdown of organic material in the soil into
useful nutrients for the plant are inhibited.
If the pH of the soil is too low, nutrients within
the soil may become insoluble, rendering them
useless to plants.
Plants found at sample sites 1 & 2
Site 1: Southwest County Park,
Edmonds, WA
o Sword Fern*
o Bracken*
o Salmonberry*
o Red Huckleberry*
o Western Hemlock
o English Elm*
o English Holly
Site 2: Lincoln Park,
West Seattle, WA
o Big Leaf Maple
o Low Oregon-Grape
o Western Red Cedar
o Bracken
o Western Hemlock
* Denotes species that would be at risk
of failure at pH = 3.0 found in experiment
Plants found at sample sites 3 & 4
Site 3: Carkeek Park, Seattle, WA
o
o
o
o
o
o
o
o
Big Leaf Maple*
Trailing Blackberry*
Salal*
Sword Fern*
Western Red Cedar*
Atlantic Ivy
Low Oregon-Grape*
Red Huckleberry*
Site 4: Discovery Park, Seattle, WA
o Big Leaf Maple
o Lady Fern
o Sword Fern
o Trailing Blackberry
o Atlantic Ivy
o Western Red Cedar
o Low Oregon-Grape
o Western Hemlock
* Denotes species that would be at risk
of failure at pH = 3.0 found in experiment
The Survivors
English Holly
NON-NATIVE
Atlantic Ivy
NON-NATIVE
Western Hemlock
NATIVE
Revised Model
Miracle-Gro®
temperature
soil
horizon
NH3
Bacteria
NO3
soil type
3H+
in health of plants
living in this soil
soil pH
soil texture
Soil organic matter
rainfall
Fertilizers should be applied with
extreme caution!!!
o
o
o
Make sure you test the pH of your soil before
adding ANY commercial fertilizer.
Carefully check to see what types of chemicals
and nutrients your particular plant food
contains.
Do not over-fertilize … more is definitely not
better.
THANK YOU!
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
Websites:
http://www.sciam.com/article.cfm?articleID=0009D21B-BDB0-1C729EB7809EC588F2D7&catID=2
http://www.sciam.com/article.cfm?articleID=00029C3D-E295-1CCEB4A8809EC588EEDF&catID=1
http://bordeaux.uwaterloo.ca/biology447/modules/module8/soil/chap2f.htm
http://www.extension.iastate.edu/carroll/crops/fertilizer_and_soil_ph.htm
http://www.soils.wisc.edu/~bleam/SS230_FAQ98C.html
http://www.rook.org/earl/bwca/nature/ferns/pteridiumaqui.html
http://www.laspilitas.com/plants/526.htm
http://rcgardens.ca/factsheets/factsheets/fernfacts.html
http://www.laspilitas.com/plants/676.htm
http://www.laspilitas.com/plants/1095.htm
http://www.extension.umn.edu/distribution/horticulture/components/1731-29.html
http://www.na.fs.fed.us/spfo/pubs/silvics_manual/Volume_1/tsuga/heterophylla.htm
http://eesc.orst.edu/agcomwebfile/edmat/html/ec/ec1303/ec1303.html
http://reference.allrefer.com/wildlife-plants-animals/plants/shrub/vacpar/botanical-ecologicalcharacteristics.html
http://www.biodiversity.org.uk/ibs/envmath/resources/year3/env324/moffatt/HTMLfiles/i_aquifolium.h
tm
http://www.crescentbloom.com/Plants/Specimen/GA/Gaultheria%20shallon.htm