This document summarizes research on using various agricultural management practices to improve water quality. It describes studies that used replicated subsurface drainage plots to evaluate the impact of nitrogen application rate, timing, and source on nitrate levels in drainage water. Cover crops were found to reduce nitrate concentrations by 25%. It also describes a watershed experiment showing that strategically placed prairie strips reduced sediment and nutrient losses in surface runoff by over 90% compared to watersheds without prairie strips. The research demonstrated the potential for cover crops and prairie strips to help protect water quality.

1. Plot‐Scale Monitoring to Determine Effectiveness
of Individual Water Quality Practices
Matthew Helmers
Dean’s Professor, College of Ag. & Life Sciences
Professor, Dept. of Ag. and Biosystems Eng.
Iowa State University
Department of Agricultural and Biosystems Engineering

2. NWRF Drainage
Gilmore City DRF
NERF Drainage
COBS
SERF Drainage
Replicated subsurface drainage plots to evaluate performance
of various in-field management practices

3. Department of Agricultural and
Biosystems Engineering
Plot Sampling Layout
125 ft
50 ft
Perforated border tile -
drains to remote outlet
Flow monitoring sump
(three drain lines in each sump)
Treatment plot
125 ft
50 ft
Perforated border tile -
drains to remote outlet
Flow monitoring sump
(three drain lines in each sump)
Treatment plot

4. Flow and sampling set-up at Gilmore City site

5. Timing of Subsurface Drainage
(1990-2011)

6. Corn-Soybean Rotation 150/160 lb-N/acre Application Rate
Variability in Drainage, Nitrate Concentration
and Nitrate Loss – Weather a Major Driver

7. Impact of Nitrogen Application Rate

8. Impact of Application Timing: 2006-14
140 kg-N/ha 168 kg-N/ha

9. Impact of Application Timing: 2006-14
140 kg-N/ha 168 kg-N/ha

10. Impact of Nitrogen Source – 168kg-N/ha

11. Impact of Nitrogen Source – 168 kg-N/ha

12. Impacts of Cover Crops on Nitrate-N
Concentration in Drainage Water – Gilmore City
~25% Reduction in Nitrate-N Concentration
With Annual Rye Cover Crop

13. Using Prairie
Strips to Reduce
Sediment and
Nutrient Loss
prairiestrips.org

14. Watershed Experiment: NSNWR
Neal Smith Prairie
Learning Center
Site 1
Site 2
Site 3
#S
#S
#S
#S
Site 1
Site 2
Site 3
Site 0
%U
Neal Smith
Prairie Learning Center
0 2 4 6 8 10 12 Kilometers
N
EW
S
300 0 300 600 Meters
Walnut Creek Watershed boundary
Refuge boundary

15. Site History
• Watersheds under primarily bromegrass cover until fall
2006
• Watershed instrumentation: spring 2005
• Pre‐treatment data collection: 2005 – 2006 field
seasons
• Treatment establishment: fall 2006 & spring 2007
– Soybean planted in 2007
– Prairie strips sown in July 2007
• No‐till corn‐soybean rotation in cropped areas

16. reconstructed prairie
corn - soybean row crops, ZERO TILLAGE
Experimental Watershed Treatments
12 watersheds:
Balanced Incomplete Block Design:
3 reps X 4 treatments X 3 blocks
0% 10% 10% 20%

17. Watershed Characteristics
Size
(acre)
Slope
(%)
Location and percent of grass filters*
Basswood‐1 1.3 7.5 10% at footslope
Basswood‐2 1.2 6.6 5% at footslope and 5% at upslope
Basswood‐3 1.2 6.4 10% at footslope and 10% upslope
Basswood‐4 1.4 8.2 10% at footslope and 10% upslope
Basswood‐5 3.1 8.9 5% at footslope and 5% upslope
Basswood‐6 2.1 10.5 All rowcrops
Interim‐1 7.4 7.7 3.3% at footslope, 3.3% at sideslope, and
3.3% at upslope
Interim‐2 7.9 6.1 10% at footslope
Interim‐3 1.8 9.3 All rowcrops
Orbweaver‐1 2.9 10.3 10% at footslope
Orbweaver‐2 5.9 6.7 6.7% at footslope, 6.7% at sideslope, and
6.7% at upslope
Orbweaver‐3 3.1 6.6 All rowcrops
*Percent of grass filters = area of filters / area of watershed

18. What is unique?
Natural Flow Conditions

19. Surface Runoff
Monitoring
H-flumes monitor movement of
water, sediment, and nutrients

20. Precipitation (April‐November)

21. Surface Runoff

22. Sediment Loss in Runoff (2007‐2012)
>95% Reduction
in sediment
export from
watersheds with
prairie filter strips

23. Phosphorus Loss in Runoff (2007‐2012)
Zhou et al., 2014
>90% Reduction
in TP export from
watersheds with
prairie filter strips

24. Total Nitrogen Loss in Runoff (2007‐2011)
Zhou et al., 2014
>90% Reduction
in TN export from
watersheds with
prairie filter strips

25. Nitrate‐N Loss in Runoff (2007‐2011)
Zhou et al., 2014

26. Visual Examples (4 inch rain in June 2008)
100% Crop 100% Prairie
10% Prairie
90% Crop

27. Summary
• In Iowa, on average the majority of drainage
and nitrate-N loss occurs in April-June
• Timing of nitrogen application (fall or early
season sidedress) had little impact on nitrate-N
concentrations in drainage
• In north-central Iowa, winter cereal rye cover
crops reduced nitrate-N concentration in
subsurface drainage by ~25%
• Strategically sited prairie strips hold potential for
reducing surface runoff and loss of sediment
and nutrients with surface runoff