Plot‐Scale Monitoring to Determine Effectiveness of Individual Water Quality Practices

Matthew HelmersDean’s Professor, College of Ag. & Life Sciences Professor, Dept. of Ag. and Biosystems Eng.

Iowa State University

Department of Agricultural and Biosystems Engineering

NWRF DrainageGilmore City DRF

NERF Drainage

COBS

SERF Drainage

Replicated subsurface drainage plots to evaluate performance of various in-field management practices

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

Flow and sampling set-up at Gilmore City site

Timing of Subsurface Drainage (1990-2011)

Corn-Soybean Rotation 150/160 lb-N/acre Application Rate

Variability in Drainage, Nitrate Concentration and Nitrate Loss – Weather a Major Driver

Impact of Nitrogen Application Rate

Impact of Application Timing: 2006-14

140 kg-N/ha 168 kg-N/ha

Impact of Application Timing: 2006-14

140 kg-N/ha 168 kg-N/ha

Impact of Nitrogen Source – 168kg-N/ha

Impact of Nitrogen Source – 168 kg-N/ha

Impacts of Cover Crops on Nitrate-N Concentration in Drainage Water – Gilmore City

~25% Reduction in Nitrate-N Concentration With Annual Rye Cover Crop

Using Prairie Strips to Reduce Sediment and Nutrient Loss

prairiestrips.org

Watershed Experiment: NSNWR

Neal Smith Prairie Learning Center

Site 1

Site 2

Site 3

#S#S#S

#SSite 1

Site 2

Site 3Site 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 boundaryRefuge boundary

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

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%

Watershed CharacteristicsSize (acre)

Slope (%)

Location and percent of grass filters* 

Basswood‐1 1.3 7.5 10% at footslopeBasswood‐2 1.2 6.6 5% at footslope and 5% at upslopeBasswood‐3 1.2 6.4 10% at footslope and 10% upslopeBasswood‐4 1.4 8.2 10% at footslope and 10% upslopeBasswood‐5 3.1 8.9 5% at footslope and 5% upslopeBasswood‐6 2.1 10.5 All rowcropsInterim‐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 footslopeInterim‐3 1.8 9.3 All rowcropsOrbweaver‐1 2.9 10.3 10% at footslopeOrbweaver‐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

What is unique?

Natural Flow Conditions

Surface Runoff MonitoringH-flumes monitor movement of water, sediment, and nutrients

Precipitation (April‐November)

Surface Runoff 

Sediment Loss in Runoff (2007‐2012)

>95% Reduction in sediment export from watersheds with prairie filter strips

Phosphorus Loss in Runoff (2007‐2012)

Zhou et al., 2014

>90% Reduction in TP export from watersheds with prairie filter strips

Total Nitrogen Loss in Runoff (2007‐2011)

Zhou et al., 2014

>90% Reduction in TN export from watersheds with prairie filter strips

Nitrate‐N Loss in Runoff (2007‐2011)

Zhou et al., 2014

Visual Examples (4 inch rain in June 2008)

100% Crop 100% Prairie10% Prairie90% Crop

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