Lawns, Lakes, and Laws
Lawns, Lakes, and Laws

Phosphorus the element
 Phosphorus and plants and soil
 Phosphorus and lakes
 Sources of urban phosphorus runoff
 Controlling phosphorus runoff
Issue: Over-enrichment of lakes and rivers
Phosphorus
“P”
• Needed plant nutrient
• Most rare of the major
“life building blocks” (C, H, O, N, P, S)
• 75% of nation’s use is mined in Florida
Phosphate
PO4
• Phosphorus is highly reactive
• Does not exist as an element in nature
• Combines with oxygen to form
phosphate
Phosphorus
and plants
• Function: Energy transfer and cell division
• Deficiency: Stunted growth
• Deficiency: Purple or yellow leaves
• Deficiency: More common in cool spring
Phosphorus
and plants
• Function: Energy transfer and cell division
• Deficiency: Stunted growth
• Deficiency: Purple or yellow leaves
• Deficiency: More common in cool spring
Phosphorus in soil
Soil
Solution
P
Active
Soil
P
< 1 lbs/acre
< 10 to > 300
lbs/acre
“Pools” of phosphorus storage in soil
Phosphorus in soil
Soil
Solution
P
Active
Soil
P
• Soil solution phosphorus (H2PO4-)
– Form taken up by plants
– Mobile form
– Small fraction of total soil P (< 1 lb/acre)
Phosphorus in soil
Soil
Solution
P
Active
Soil
P
• Active soil phosphorus
– In equilibrium with solution P
– < 10 lbs/acre to > 300 lbs/acre
– Tightly adhered to soil particles
Phosphorus and soil pH
6.0 pH
7.0 pH
Availability of phosphorus vs. soil pH
Phosphorus
fertilization
• Recommended on turf when:
Solution P + Soil P < 25 ppm*
* Bray P1 test
Phosphorus
and lakes
• Most limiting plant nutrient in lakes
• Algae “blooms” = low oxygen and smell
• 1 lbs P = 300 lbs to 500 lbs algae
Impacts of phosphorus
High growth
Low light
Low oxygen
Speeding aging of lakes
10,000’s YEARS IN NATURAL CONDITIONS
10’s to 100’s YEARS UNDER HUMAN INFLUENCE
Tropic State
(ppb)
A factor of 1,000 less!
60 parts per
BILLION
30 parts per
MILLION
It takes a 1,000 times less phosphorus to
turn a lake green than keep a lawn healthy
As phosphorus goes up, algae goes
up, and water clarity goes down
Secchi Disk
Secchi disk is a
low-tech way to
measure water
clarity and
determine a lake’s
tropic state
Experimental
Lake Area Study
(Fisheries and Oceans Canada)
• Top-to-bottom curtain divides lake in two
• Carbon and nitrogen added to one side
• Carbon, nitrogen and phosphorus added
to other – effect is clear to see
Sources of phosphorus
“When it rains, it pollutes”
Think watersheds!
Types
of runoff
pollution
•
•
•
•
•
Sediment – soil erosion, street grit
Nutrients – nitrogen and phosphorus
Bacteria - wildlife, pets, sewage
Organics – manure, leaves, grass
Toxics – lead, zinc, copper, pesticides
Impervious
surfaces
Residential Areas =
50% Impervious
Every city lot is waterfront property!
Sources of phosphorus runoff
Bannerman - Wisconsin DNR
Roofs
Sidewalks
Driveways
Streets
Lawns
0%
10%
20%
30%
40%
50%
Sources of phosphorus runoff from lawns
Soluble plant P
Soil solution P
Soil particle P
Product
Sources of phosphorus
runoff from lawns
LIKELYHOOD
• Runoff from plant material (dissolved)
• Misapplied fertilizer (dissolved)
• Runoff from soil solution (dissolved)
• Attached to eroded soil (particulate)
Sources of phosphorus
runoff from lawns
LIKELYHOOD
• Runoff from plant material (dissolved)
• Misapplied fertilizer (dissolved)
• Runoff from soil solution (dissolved)
• Attached to eroded soil (particulate)
Phosphorus runoff by land use
Lbs./Acre/Year
SOIL EROSION
Source
Bare cropland
Plowed corn
No-till corn
Hayland
Lawns
Soluble P
0.10
0.27
0.98
0.39
0.36
Particulate P
33.20
13.50
1.90
0.02
0.00
Sources: Sharpley and Menzel 1987; Rehm, 1997, Kussow, 2000.
Grass clippings
• Contain 0.13 lbs P / 1000 sq. ft. / year
• That’s 0.65 lbs P / ave. yard / year
Controlling
“P” runoff is
package deal
Phosphorus
fertilization
•
•
•
•
MN law restricts P lawn fertilizer use
Rarely needed on established lawns
Important when seeding or sodding
Apply according to soil test
Reading the bag
Look for the middle
number!
N-P-K
• Given in % phosphate by weight
• Phosphate (P2O5) not phosphorus (P)!
• P = P2O5 ÷ 2.29
Reading the bag
Look for “the zero in
middle” for
phosphorus-free
Taking
a soil test
•
•
•
•
The best way to determine P need
Rare as meteor hits in the metro
Poor sample technique gives poor results
Recommended when “troubleshooting”
Application
challenges
•
•
•
•
Selecting fert. with needed N-P-K balance
1,000 sq. ft.??? How big is my lawn?
Setting spreader application rate
Soil test? Calibrate? Get a life!!!
The law
and the lawn
• State phosphorus lawn fertilizer law
• Local fertilizer ordinances
• “Use” vs. “Sale” regulation
Minnesota phosphorus
lawn fertilizer law
• First law passed 2002; revised 2004
• Zero P rule goes statewide Jan. 1, 2005
• Concerns phosphorus lawn fertilizer
• Involves use, not sale, of fertilizer
• First in nation - has drawn attention
MN lawn fertilizer law
A restriction, not a ban:
• 0% P2O5 fertilizer required, unless:
- Newly seeded or sodded lawn
- Soil test shows need
- Applied by trained golf course staff
MN lawn fertilizer law
• When there is need to apply phosphorus,
University of MN recommendations are
to be followed
• Law administered by the Minnesota
Department of Agriculture
• Enforcement by local units of
government as a petty misdemeanor
MN lawn fertilizer law
Prohibited to apply
fertilizer (any type) to
impervious surfaces.
Examples: Streets,
sidewalks, driveways.
Sweep up over-spread
material.
MN lawn fertilizer law
• Preempts local ordinances on fertilizer
use
• Law does not restrict what stores can
sell or what customers can buy
• Allows pre-2002 local ordinances on
fertilizer sales to stand
City of Burnsville
ordinance - before state law
• No application between Nov 15 - April 1
• Clean fertilizer from impervious surfaces
• Keep outside 20 foot buffer around water
• Apply no greater than 0% P2O5 fertilizer
unless new lawn or soil test shows need
• Notice of law needs to be posted in stores
City of Burnsville
ordinance - after state law
• No application between Nov 15 - April 1
• Clean fertilizer from impervious surfaces
• Keep outside 20 foot buffer around water
• Apply no greater than 0% P2O5 fertilizer
unless new lawn or soil test shows need
• Notice of law needs to be posted in stores
Publication on
the new law
800-877-6300
to place orders
0% P2O5 fertilizers becoming
widely available . . .
What to advise . . .
• On existing lawns
- Use 0% P2O5 fertilizer unless a need
for phosphorus is shown (soil test)
- Soil test if lawn if failing to thrive
- Apply to UM recommendations when
phosphorus is used
What to advise . . .
• On new lawns
- Soil test to 6” depth
- No test? Apply 2 lbs. P2O5/1,000 sq. ft.
- Mix fertilizer well into top 6” of soil
What to advise . . .
• Leftover phosphorus lawn fertilizer
- In Greater MN, leftover phosphorus
lawn fertilizer can be used up on lawns
- In Twin Cities Metro, leftover
phosphorus lawn fertilizer can be used
on non-lawn applications (garden)
- If a lawn fertilizer contains a pesticide,
it cannot be used for non-lawn use –
dispose as household hazardous waste
What to advise . . .
• All lawns
- Sweep up, rake up, pick up
- Soil test if interested in “baseline”
What to advise . . .
• Future? – practices to increase infiltration
Rain garden in
Burnsville, MN
www.cleanwatermn.org
• Spring / Fall messages in the media
• Website with resources for citizens,
cities, and teachers/students
• TV weather broadcast / clean water
feature
Ron Struss
Extension Educator
University of Minnesota Extension Service
651-480-7708
rstruss@umn.edu