Current Science of Nutrient
Flows and Conservation
Actions in Iowa: Guiding
Principles
Matt Helmers
Iowa State University
Agricultural and Biosystems Engineering
Guiding Principles
• Reduce nutrient export
• Slow the flow – restore some of
the natural hydrology
Ways to Achieve This
•S
Synchronize
h i nutrient
t i t supply
l with
ith
nutrient demand
• Increase continuous living cover
• Optimize drainage design and
management
• Exploit the interface between land
and water
Synchronize Nutrient Supply with
N i
Nutrient
N
Needs
d
• Utili
Utilize
e nutrient
n trient management strategies that match
nutrient needs of crops both in rate and timing
• Benefits
– Reduce risk of losses
– Potentially reduce overall application rates
• Disadvantage
– Potential management challenges
• Need for better documentation of current
conditions
Annual Nitrate Concentrations from Waseca, MN
Nitrate-nittrogen
-1
co
oncentration (mg L )
40
Corn Phase
*
30
Fall application
Spring application
*
*
20
*
10
~21% increase with fall application
*
*
40
Soybean Phase
30
20
10
1987‐94: 135 lb‐N/acre
1995‐99: 120 lb‐N/acre
Fall application
Spring application
*
~10% decrease with fall application
*
0
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
Av 0
er 0
ag
e
Nitrate-n
nitrogen
-1
concentration (mg L )
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
1
Av 99
er 9
ag
e
0
Randall et al., 2003 and Randall et al., 2005
Monthly Nitrate Concentrations from Gilmore City, IA
-1
1
Nitrrate-N concen
ntration (mg L )
25
20
Corn
Corn
Soybean
15
10
Fall 125 - Corn (06)-Soybean (07)-Corn (08)
Spring
p g 125 - Corn ((06)-Soybean
)
y
((07)-Corn
)
((08))
5
0
4-06
5-06
7-06
3-07
4-07
6-07
9-07 10-07 4-08
5-08
Corn
--1
20
8-07
Month
25
Nittrate-N concen
ntration (mg L )
5-07
*
Soybean
*
Soybean
15
10
Fall 125 - Soybean (06)-Corn (07)-Soybean (08)
Spring 125 - Soybean (06)-Corn (07)-Soybean (08)
5
0
*
4-06
Statistical significant difference at P=0.10
5-06
7-06
3-07
4-07
5-07
6-07
Month
8-07
9-07 10-07 4-08
5-08
30
Nitrate-nitrogen cconcentrattion (mg/L)
Annual flow-weighted concentration
N-Concentration=5.72+1.33*exp(0.0116*(application rate)), R2=0.65
25
20
15
20% Reduction in Concentration
by reducing application rate
from 150 to 120 lb/acre
10
5
10% Reduction in Concentration
by reducing application rate
from 120 to 100 lb/acre
0
0
50
100
150
200
250
Nitrogen application rate (lb/acre)
Overall Nitrogen Application Rate Effect on Nitrate-Nitrogen Concentration
Corn/Soybean Rotation
Increase Continuous Living Cover
• Utili
Utilize
e cropping ssystems
stems that protect soil ssurface
rface
and reduce risk of leaching losses
• Benefits
– Reduced soil erosion and losses of contaminants
associated with surface runoff
– Recycle soil nutrients and reduce risk of nutrient losses
(e.g. loss of nitrates through drainage systems)
– Provide soil quality benefits
– Increased water use during susceptible periods
Increase Continuous Living Cover
• Disadvantage
Disad antage
– Potential management challenges
– Increased cost and potential impacts on yield
– Perennial land uses may result in reduced downstream
water flow
• Need for further documentation of practice
performance, management recommendations,
and further review of suitable cultivars and
species
Optimize Drainage Design and
Management
• Consider impacts of drainage design and
management on contaminant transport and
hydrology
• Drainage can impact both surface runoff and
subsurface drainage
• Balance surface runoff and subsurface drainage
implications
p
Drainage Design
• To p
protect crops,
p , the subsurface drainage
g system
y
must
be able to remove excess water from the active root
zone within 24 to 48 hours after a heavy rain
• Drainage coefficient is the depth of water to be removed
from the drainage area in 24 hours
• Modern drainage systems would be designed with a
drainage coefficient of 0.5-1.0 in/day
• From surveys performed in 1980’s many drainage
systems have a drainage coefficient of <0.25 in/day
(some <0
<0.10
10 in/day)
Impacts
p
of Drainage
g Design
g
Annual av
verage disc
charge (in)
10
8
6
Subsurface drainage
Surface water runoff
4
2
0
0.0
0.2
0.4
0.6
Drainage Coefficient (in/day)
0.8
1.0
Daily Discharge (cm)
5
5
DC = 0.05 in/day
DC = 0.10 in/day
DC = 0.37 in/day
DC = 0.50 in/day
4
3
10
2
15
1
0
Daily P
Precipitation
n (cm)
0
6
1
6/
1
4/
9
91
6/
7/
1
1/
9
5/
3
5/
24
/9
1
1
7/
9
5/
1
5/
1
0/
9
1
20
Date
DC = 0.05 in/day
DC = 0.10 in/day
DC = 0.37 in/day
DC = 0.50 in/day
4
3
5
10
2
15
1
Date
/8
2
6/
5
2
9/
8
5/
2
22
/8
2
5/
15
/8
2
5/
8/
82
20
5/
/8
2
0
Daily Prec
cipitation (cm
m)
0
5
5/
1
Daily Disc
charge (cm))
6
Impacts of
Drainage
Design on
Daily
Di h
Discharges
Subssurface d
drainage and
su
urface runoff (cm
m)
Impacts of Controlled Drainage
25
20
Subsurface drainage
15
10
Surface runoff
5
0
0.10
0.35
0.60
0.85
1.10
1.35
1.60
1.85
2.10
2.35
D i
Drainage
intensity
i
i ((cm d
day-11)
Impact of Controlled drainage (to maintain water table depth at 60cm) on average relative
yields,
ld subsurface
b f
d
drainage and
d surface
f
runoff
ff off WEBS_CC tile
l llandscape
d
simulated
l d over the
h
60 years (1945-2004) .
Exploit the Interface Between Land
and
dW
Water
• Benefits
– Prevent off-site transport of contaminants
– Treat water before entering downstream
waterbodies
– Maximize efficiency of practices
– Protect areas from future degradation
• Disadvantage
– May take some land out of production
Examples
• Incorporate
p
systems
y
that p
provide p
protection or
treatment of water at the land-water interface
• Practices
–
–
–
–
–
–
Tillage
Vegetative systems
Water storage features (e.g., terraces)
Stabilization of streams
W tl d
Wetlands
Riparian buffers
Various Buffer/Vegetative Systems
Photo Courtesy of USDA-NRCS
Performance for Buffer Systems
with
ith U
Unsubmerged
b
d Fl
Flow C
Conditions
diti
• Surface runoff where unsubmerged flow
conditions occur:
–
–
–
–
Sediment trapping
pp g efficiency
y – 41 to 100%
Infiltration efficiency – 9 to100%
Total phosphorus trapping efficiency – 27 to 96%
Nitrate-nitrogen trapping efficiency – 7 to 100%
• Treatment of subsurface flow minimal
where primary transport to stream is
through drainage systems
Grassed Waterway Performance
• Do they improve water
quality?
y
• Reduced gulley erosion:
USDA (1996) reports that
b
based
d on recentt studies
t di iin
19 states, ephemeral gully
erosion as a percentage of
sheet and rill erosion ranged
from 21% to 275%.
• Deposition of particulates as
water enters edge of
grassed waterways
Downstream Considerations
• Even if field-to-stream
field to stream transport of
contaminants are reduced in-stream
sources may contribute significant loading
to downstream waterbodies
Sediment Source Tracking Using Naturally Occurring
Radionuclides (7Be and 210Pb) as Tracers
USDA-NRCS
24%
ISU NREM
76%
Slide courtesy of Dr. Tom Isenhart
Stream Bank Stabilization
ISU - NREM
Slide courtesy of Dr. Tom Isenhart
ISU - NREM
Nitrate Removal Wetlands
• Wetlands have been shown to be effective in reducing
nutrient export particularly nitrate export
– Performance dependent on magnitude and timing of
nitrate loads along and capacity of wetland to remove
nitrate
• Research is needed to better p
predict nutrient load
reductions and determine the effectiveness under
different patters of precipitation and timing of loading to
the wetlands
• Siting of wetlands to intercept tile drainage is critical
Wetland Siting and Design for
Watershed Scale Endpoints
W.G. Crumpton, Iowa State University
Annual Nitrate Budget
\
Exported
E
t d
48.4 metric tons
Loss in Ditch and Stream
1.6 metric tons
W.G. Crumpton, Iowa State University
Annual Nitrate Budget
\
Conventional
approach
Exported
E
t d
48.4 metric tons
Loss in Ditch and Stream
1.6 metric tons
W.G. Crumpton, Iowa State University
Annual Nitrate Budget
\
Conventional
approach
Exported
E
t d
46.5 metric tons
Loss in Wetlands
1.9 metric tons
Loss in Ditch and Stream
1.6 metric tons
W.G. Crumpton, Iowa State University
Annual Nitrate Budget
Watershed
approach
\
Conventional
approach
Exported
E
t d
46.5 metric tons
Loss in Wetlands
1.9 metric tons
Loss in Ditch and Stream
1.6 metric tons
W.G. Crumpton, Iowa State University
Annual Nitrate Budget
Watershed
approach
Exported
29 8 metric tons
29.8
Loss in Wetlands
17 metric tons
Loss in Ditch and Stream
1.6 metric tons
\
Conventional
approach
Exported
E
t d
46.5 metric tons
Loss in Wetlands
1.9 metric tons
Loss in Ditch and Stream
1.6 metric tons
W.G. Crumpton, Iowa State University
Summary
• Water quality improvements that can be gained
by
y just
j
improved in-field nutrient management
g
may be limited
• Continuous living cover through cover crops or
increased perennial vegetation has potential to
reduce nutrient losses, increase water use, and
increase infiltration
• Drainage systems should be designed and
managed to minimize nutrient export factoring
surface and subsurface flow
Summary
• Practices that slow the flow of water
should be implemented and placed
strategically to intercept flowing water
• Practices should be targeted to the land
landwater interface to provide water quality
treatment before water enters downstream
water bodies – these practices may also
attenuate discharge hydrographs
• Practices need to be suited for the
contaminant
t i
t off concern
Panel
•
•
•
•
•
Dr. William Crumpton
Dr
Dr. Thomas Isenhart
Dr. Tom Kaspar
Dr Dan Jaynes
Dr.
Dr. Matt Helmers
Panel Discussion