Strathmere Farm Groundwater Nitrate Project

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Strathmere Farm Groundwater Nitrate Project
Cathy Ryan University of Calgary Nick
Stokman Middlesex County Soil Crop Improvement
Assn. Note This presentation is a modified
version of that presented at public open house
for Strathroy Groundwater Nitrate Study, Nov 18,
2000
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Study goals

• observe relative rates of N leaching from
  different crops and management practices
• develop management practices that will minimize
  nitrate leaching to groundwater
• develop useful groundwater monitoring strategy
  to assess management practices
• groundwater research

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Strathmere Farm

• 95 workable acres, mainly no-till since 1986
• 2600 ft (800 m) long x 1500 ft (450 m) wide
• four or five fields, 6 year crop rotation
  (below)

Possible sources of groundwater nitrate?? (in red)
100 kg N/ha per year commercial fertilizer
corn - soy - corn -soy - alfalfa - alfalfa
alfalfa burndown
natural N fixation
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Groundwater study established at Strathmere Farm
in 1996 because

• shallow surficial groundwater aquifer
  (vulnerable, short time for groundwater impacts)
• simple flow system
• outstanding cooperation from MCSCIA

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From Chapman and Putnam, 1984. Physiography
of Southern Ontario, 3rd Ed. ON Geol. Survey Map
2715.
Surficial Geology of Strathroy area
Strathmere Farm
- located on Caradoc sand plain - shallow
aquifer, vulnerable to groundwater
contamination - relatively simple flow
system
Seaforth Moraine
Sttrathmere Farm
Caradoc sand plain
site
Ekfrid clay plain
sand plain
clay plain
till moraine
till plain
till plain (drumlins)
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Strathmere Farm Groundwater
- water table 5 ft to 12 ft (1.5 to 4 m) deep -
groundwater flows 150 ft (50m) horizontally
and 1 to 2 ft (0.25 to 0.5 m) vertically in one
year - groundwater flow direction is SSE
(towards Sydenham River) - sampled by means of
four multi-level sampling (MLS) fences
(please see next slide for diagram of an MLS
fence) - MLS fences are located on downgradient
edge of fields
groundwater flow direction
MLS FENCE location
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GROUNDWATER SAMPLERS Multi Level Samplers
(MLSs)
cable ties
1/8 PE tubes
Individual groundwater sampling port with Nytex
screen
1/2 PVC centre-stalk
All 15 sampling tubes are sampled at once using a
custom-build manifold
View of MLS sticking up out of ground after
installation by drilling
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The MLSs are installed in a line of 7 or 15,
located perpendicular to groundwater flow and
known as a fence
ground surface
water table
Sampling of all points in this MLS fence will
provide a groundwater nitrate picture that is
about 3m deep and about 10m wide (see an example
on the next slide)
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Example of single MLS fence sampling event
Groundwater nitrate concentration (in milligrams
N per litre water)
Ground water table (5 to 12 feet deep)
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DEPTH (M) BELOW WATER TABLE
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10 mg N/L is the drinking water objective
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Q Is there a groundwater nitrate problem under
Strathmere Farm? A Yes. The average groundwater
nitrate concentration is 19 mg N/L (nearly 2x
the drinking water objective of 10 mg N/L). Q
Is this worse than surrounding farms on the sand
plain? A Probably not. Since Strathmere applies
conservative rates of fertilizer N, groundwater
impacts under other sand-plain farms are probably
more severe. Q Where is the nitrate coming
from? A Most of the groundwater nitrate is
leached from commercial fertilizer N applied to
corn. Evidence for this statement is provided
below.
Sampling point depth (m)
drinking water standard (10 mg N/L)
Average groundwater nitrate concentration at
Strathmere Farm is 19 mg N/L
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Tracer was dissolved in and co-applied with
commercial fertilizer applied in spring, 1997.
The similar groundwater distribution of nitrate
and tracer in the following spring shown below is
convincing evidence that the high nitrate
concentrations come from fertilizer.
West Field Fence, sampled June 8, 1998
Similar nitrate and tracer distribution indicates
nitrate came from fertilizer
Among the highest nitrate concentrations observed
The two profiles on the right are created by
conducting two analyses on the same set of
groundwater samples.
TRACER CONCENTRATION (milligrams Br per liter H2O)
Nitrate concentrations
Tracer concentrations
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Relatively low rates of nitrate leaching occur
under N-fixing crops. In essence groundwater
nitrate can be cleaned up by not applying
fertilizer nitrogen.
Jan , 1997
Groundwater nitrate in the main fence at the
beginning of the study
Nov, 1999
Groundwater above the dotted line infiltrated
under soy and alfalfa. This is the lowest
nitrate groundwater observed in the study.
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Higher rates of fertilizer application result in
increased rates of nitrate leaching to
groundwater
200 kg N/ha applied
100 kg N/ha applied
Mid fence, December 4, 1999
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Successive years of fertilizer application can be
seen an nitrate rich bands in groundwater
nitrate profiles.
Mid-field fence, May 20,1997
1997 soy (no fertilier applied)
1996 corn (fertilized)
1994 soy (no fertilier applied)
1995 corn (fertilized)
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Q if crop management can clean up groundwater at
Strathmere Farm,could it clean up groundwater
around municipal wells? A There is every reason
to think this is possible. The 2, 5 and 10 year
capture zones are being mapped by International
Water Supplys Strathroy Groundwater Nitrate
Study. The most effective place to begin would
be in these areas.
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Q How much would groundwater friendly farming
cost the farmer (in other words, what would it
cost the farmer to clean up groundwater)? A The
Middlesex Soil and Crop Improvement Association
has been conducting fertilizer trials for a
number of years. Using the current rotation at
Strathmere Farm, we calculate a net loss of about
11/ha to not apply any fertilizer N. This is
equivalent to about 20 of the farm profit.
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Proposed Phase II At Strathmere Farm test
rotations to minimize fertilizer N, maximize
profit continue groundwater research In 2 year
catchment zones around Strathroy well
heads work with farmers on voluntary program to
facilitate groundwater-friendly crop rotation
around municipal wells an application has been
made to the Ontario Stewardship Fund to
compensate farmers financially for lost yield due
to decreased fertilizer application. ideally
observed decreased nitrate concentrations in
municipal groundwater supply (this would be a
first!).
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This study has been supported by
University of Calgary Middlesex Soil and Crop
Improvement Association Ontario Ministry of
Agriculture, Food, and Rural Affairs Environmental
Farm Plan NSERC University of Waterloo Regional
Municipality of Waterloo
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