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Department of Agricultural and Biosystems Engineering
Opportunities and Challenges to Implementing Non-Point Source Nutrient
Reduction Practices
Matthew HelmersDirector, Iowa Nutrient Research Center
Dean’s Professor, College of Ag. & Life Sciences Professor, Dept. of Ag. and Biosystems Eng.
Iowa State University
Department of Agricultural and Biosystems Engineering
Mississippi River System
Gulf of Mexico Hypoxia Goals
Hypoxia Action Plan Goal: Reduce the size of the zone to 5,000 km2
by 2015
EPA-SAB Recommendations: Reduce Total Riverine Nitrogen and Phosphorus Loads by 45%
Historic Changes
Soil Nitrate Production vs. Crop Nitrate Uptake
In the shaded areas, the soil produces nitrate, but there is no crop to use it. As a result,
some nitrate is lost to waterways.
March February
Rate of soil nitrate
production from
native soil organic
matter
Rate of corn or
soybean nitrate uptake
The majority of nitrate used by corn and soybean comes from soil nitrate production.
Corn gets the difference from fertilizer while soybean gets
the difference from legume fixation of atmospheric nitrogen.
Slide from M. Castellano - ISU
What Can We Do to Reach
These Goals?
Phosphorus Practice Performance
(Field to Stream Reduction)
Estimate Total Phosphorus Load Reduction (%)
0 20 40 60 80 100
Ph
osp
ho
rus R
ed
uctio
n P
ractice No phosphorus until STP drops to optimal level
No-till (70% residue) vs. conventional tillage (30% residue)
Cover Crops (Rye)
Perennial - Land retirement
Pasture
Buffers
Terraces
Error bars show standard deviation of practice performance
Nitrate-N Practice Performance
Estimate Nitrate-N Concentration Reduction (%)
-40 -20 0 20 40 60 80 100
Nitra
te-N
Re
du
ctio
n P
ractice
Moving from Fall to Spring N Application
Sidedress N Application
Reduce N rate to MRTN*
Nitrification Inhibitor
Cover Crop
Extended Rotations
Perennial Energy Crops
Pasture and Land Retirement
Controlled Drainage**
Shallow Drainage**
Wetlands
Bioreactors
Saturated Buffers**
*MRTN - Maximum Return to Nitrogen Application Rate from Corn Nitrogen Rate Calculator (http://cnrc.agron.iastate.edu/)** Load reduction Error bars show standard deviation of practice performance
Nitrate
Response to
Nitrogen
Estimated Nitrogen Application Rate –
Manure + Fertilizer (2008 Estimates)Rate on
CB
Rate on
CC
MLRA lb N/ac lb N/ac
102C 182 232
103 154 204
104 144 194
105 131 181
107A 184 234
107B 139 189
108C 163 213
108D 120 170
109 142 192
115C 146 196
Iowa Total 151 201
Nitrogen Application Rate Example
Existing Conditions – N Rate MRTN – N Rate
Soil Nitrate Production vs. Crop Nitrate Uptake
Addition of a Cover Crop
March February
Rate of soil nitrate
production from
native soil organic
matter
Rate of corn or
soybean nitrate uptake
Cover crops can use nitrate when corn and beans are not growing, thus reducing the
asynchrony between soil nitrate production and crop
nitrate uptake.
Cover crop
nitrate use
Cover crop
nitrate use
In the shaded areas, the soil produces nitrate, but there is no crop to use it. As a result,
some nitrate is lost to waterways.
Slide from M. Castellano - ISU
Winter Cereal Rye Cover Crops
Ames Gilmore City
Impacts of Cover Crops on Nitrate-N Load in
Drainage Water – Gilmore City
36% Reduction
34% Reduction
NWRF Drainage NERF Drainage
COBS
SERF Drainage
Replicated subsurface drainage plots to evaluate performance of various in-field management practices
Gilmore City DRF
Impact of Land Management
Drainage water management
From Christianson and Helmers, 2011
Illustration by John Petersen
(www.petersenart.com)
Subsurface Drainage Bioreactor
Saturated buffers
Corn
Soybean
1 km
Targeted Wetland Restoration
DD Tile
There is considerable interest in using wetlands to intercept and
reduce nitrogen loads in tile drained landscapes.
Nitrate Removal Wetland
Hydrologic and nutrient loading rates are
major drivers of wetland performance.
Wetlands occupying only 1% of landscape can reduce long term average nitrate loads about 52%.
From: W.G. Crumpton
Drainage water recycling
Science-based Trials of Row-crops
Integrated with Prairie Strips
www.prairiestrips.org
Photo: Jasper Co., Matt Helmers• Watershed-based scientific monitoring
• Comparing prairie strip treatments to 100% corn-soy crop control
Science-based Trials of Row-crops
Integrated with Prairie Strips
www.prairiestrips.org
Strategically adding ~10% prairie to crop fields:
• 44% reduction in water runoff
• 95% reduction in soil loss
• 90% reduction in P runoff
• 84% reduction in N runoff
• 70% reduction in subsurface NO3-N concentrations (not tiled)
• Potentially improves beneficial insects and wildlife
• Doesn’t reduce per acre yields
• Doesn’t create a weed problem
• Cheaper than installing terraces; cost comparable to cover
crops
Source: Data collected between 2007-2014 at Neal Smith National Wildlife Refuge
Imag
es: J
ose
Gu
tier
rez
These flumes measure surface water movement and soil, nitrogen and phosphorus export from the STRIPS experiment sites at the Neal Smith National Wildlife Refuge. Compare the transport of these resources from: 1) a 100% no-till, corn crop field, 2) a 90% corn crop field treated with a 10% prairie strip, and 3) a 100% prairie. These pictures were all taken after the same 4” rain event in June, 2008.
1 2 3
Phosphorus Loss in Runoff (2007-2012)
Zhou et al., 2014
>90% Reduction in TP export from watersheds with prairie filter strips
Nitrate-N Concentrations in Groundwater at the Footslope of Each Watershed
Example: Combination Scenarios that Achieve N and P Goal From Non-Point Sources
From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction on
Nitrogen and 29% reduction on Phosphorus
Nitrate-N
Reduction
Phosphorus
Reduction
Initial
Investment
Total Equal
Annualized
Cost
Statewide
Average EAC
Costs
Practice/Scenario% (from
baseline)
% (from
baseline)(million $)
(million
$/yr)($/acre)
MRTN Rate, 60% Acreage with
Cover Crop, 27% of ag land treated
with wetland and 60% of drained land
has bioreactor
42 30 3,218 756 36
MRTN Rate, 95% of acreage in
Cover Crops, 34% of ag land in
heavily tile drained land treated with
wetland, and 5% land retirement
42 50 1,222 1,214 58
Level of Implementation Needed for
one Nitrate-N Reduction Scenario
To Reach our Goals
• WE NEED IT ALL!!
– N Management
– Cropping practices/landuse
– Edge-of-Field Practices
Potential Impacts of Pursuing
These Strategies?• Economic Evaluation of Governor
Bradstad’sWater Quality Initiative
(https://governor.iowa.gov/sites/default/file
s/documents/ISU%20CARD%20Economic
%20Evaluation.pdf)
Projected Annual Costs for NCS1NCS1 Mil of Ac Estimated
N Tons
Reduced
(1000)
Initial
Investment
($/ac
Treated)
Initial
Investment
($Million)
Equal
Annual
Cost ($/ac)
Equal
Annual
Cost
($Million)
Nitrogen
Optimized
18.9 25 -2 -38
Cover
Crops: 60%
12.6 47 25 315
Wetlands:
27 of Ag
Land
7.7 42 316 2427 10 80
Bioreactors:
60% of
drained
land
5.9 33 133 790 8 50
Total 3217 407
Per Acre 19
Projected Annual Benefits for NCS1NCS1 Source Low ($Million) High ($Million)
Reduced Soil
Erosion
Wetland 40 72
Cover Crops 22 32
Recreation/Wildlife
Wetland 3 7
Water Based
Recreation
5 22
Residential
Amenity
17 35
Drinking Water
Purification
0 13
Total 87 183
Average 135
Total Economic Impact of NCS1
Direct Total
Total Economic Impact Under NCS1
Output ($) 445,000,000 691,000,241
Value Added ($) 155,202,063 296,359,597
Labor Income ($) 173,429,609 250,678,858
Employment 1149 2801
$445 million in spending would create $691 million in total economic activity
What is the Payoff?
• Improved local water
• Protection of our soil resources
• Employment opportunities to implement
these practices
• More diverse landscape
Summary
• To reach the goals will take broad
implementation of multiple practices
• Are there opportunities to implement practices
that enhance or protect long-term value of the
land?
• Are there rural economic benefits?
Discussion
mhelmers@iastate.edu
Twitter: @ISUAgWaterMgmt
Website: http://agwatermgmt.ae.iastate.edu/
Department of Agricultural and Biosystems Engineering
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