helmers soil health - iowa state university...edge‐of‐ field controlled drainage 33 (32)* 1.29...

Department of Agricultural and Biosystems Engineering

The Value of Improving Soil Health on Water Quality

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

Water Quality Situation

• Increasing concern for local and regional waters

• States in Mississippi River Basin have developed state nutrient reduction strategies

Nitrate-N Reduction PracticesPractice

% Nitrate‐N Reduction [Avg. (Std. Dev.)]

Cost of N Reduction ($/lb)

N‐Mgt

Timing (Fall to spring) 6 (25) ‐283Nitrogen Application Rate (MRTN 

rate MRTN)10 ‐0.6

Nitrification Inhibitor (nitrapyrin) 9 (19) ‐1.53Cover Crops (Rye) 31 (29) 5.96

Land Use

Perennial – Pasture/Land retirement 85 (9) 9.12

Perennial – Energy Crops 72 (23) 21.46

Extended Rotations 42 (12) 2.7

Edge‐of‐Field

Controlled Drainage 33 (32)* 1.29

Shallow Drainage 32 (15)*

Wetlands 52 1.38

Bioreactors 43 (21) 0.92

Buffers 91 (20)** 1.91

Saturated Buffers 50 (13) 

*Load reduction not concentration reduction **Concentration reduction of that water interacts with active zone below the buffer

Nitrate-N Reduction PracticesPractice

% Nitrate‐N Reduction [Avg. (Std. Dev.)]

Cost of N Reduction ($/lb)

N‐Mgt

Timing (Fall to spring) 6 (25) ‐283Nitrogen Application Rate (MRTN 

rate MRTN)10 ‐0.6

Nitrification Inhibitor (nitrapyrin) 9 (19) ‐1.53Cover Crops (Rye) 31 (29) 5.96

Land Use

Perennial – Pasture/Land retirement

85 (9) 9.12

Perennial – Energy Crops 72 (23) 21.46

Extended Rotations 42 (12) 2.7

Edge‐of‐Field

Controlled Drainage 33 (32)* 1.29

Shallow Drainage 32 (15)*

Wetlands 52 1.38

Bioreactors 43 (21) 0.92

Buffers 91 (20)** 1.91

Saturated Buffers 50 (13) *Load reduction not concentration reduction **Concentration reduction of that water interacts with active zone below the buffer

Phosphorus Reduction Practices

Practice% Phosphorus‐P 

Reduction [Average (Std. Dev.)]

% Corn Yield Change 

Phosphorus Management

Producer does not apply phosphorus until STP drops 

to optimal level17 (40) 0

No‐till (70% residue) vs. conventional tillage (30% 

residue)90 (17) ‐6 (8)

Cover Crops (Rye) 29 (37) ‐6 (7)

Land UsePerennial – Land retirement 75 (‐)

Pasture 59 (42)

Edge‐of‐FieldBuffers 58 (32)

Terraces 77 (19)Assessment did not include stream bed and bank contributions although recognized as significant

Phosphorus Reduction Practices

Practice% Phosphorus‐P 

Reduction [Average (Std. Dev.)]

% Corn Yield Change 

Phosphorus Management

Producer does not apply phosphorus until STP drops 

to optimal level17 (40) 0

No‐till (70% residue) vs. conventional tillage (30% 

residue)90 (17) ‐6 (8)

Cover Crops (Rye) 29 (37) ‐6 (7)

Land UsePerennial – Land retirement 75 (‐)

Pasture 59 (42)

Edge‐of‐FieldBuffers 58 (32)

Terraces 77 (19)Assessment did not include stream bed and bank contributions although recognized as significant

How Does Nitrate Leaching Vary from Year to Year?

Twenty-Five Year Summary of Nitrate-N Concentration

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014Avg

.Nitr

ate-

nitro

gen

Con

cent

ratio

n (p

pm)

0

5

10

15

20

25

30Nitrate-N Concentration

What is Different over this Period?

Twenty-Five Year Summary of Nitrate-N Concentration

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014Avg

.Nitr

ate-

nitro

gen

Con

cent

ratio

n (p

pm)

0

5

10

15

20

25

30Nitrate-N Concentration

Combined Corn-Soybean System – Same N management – Early Spring Sidedress at 150-160 lb-N/acre

Twenty-Five Year Summary

Combined Corn-Soybean System – Same N management – Early Spring Sidedress at 150-160 lb-N/acre

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014Avg

.

Dra

inag

e (in

)

0

5

10

15

20

25

30

Nitr

ate-

nitro

gen

Con

cent

ratio

n (p

pm)

0

5

10

15

20

25

30

Nitr

ate-

nitro

gen

Loss

(lb-

N/a

c)

0

20

40

60

80

100

120Leaching VolumeNitrate-N ConcentrationNitrate-N Loss

Nitrate Response to

Nitrogen

Do Practices that Improve Soil Health Also Improve Water Quality?

Can We Look to the Past?

• Present Day • 1930’s

Impacts of Land Management Practices

• Used WEPP to simulate water flow and sediment delivery using 100 yrs of weather

• Land use and management derived from census of agriculture information, old publications, and personal communication with a landowner

• Mean census of Ag data for Osceola County being applied to this 1200 acre watershed 

Land‐use Change in Osceola County

1930's

1950's1970'sPresent…

0102030405060708090

100

Row CropSmall Grains Pasture Hay

Other

Percen

t of Lan

d‐Use 

Predicted ET, Runoff, and Sediment Delivery

0.00

5.00

10.00

15.00

20.00

25.00

30.00

Pre-Agriculture 1930's1950's

1970'sPresent Day

Fate of Precipitation and Sediment Delivery to Watershed Outlet

Runoff (in)Calc ET (in)Sediment Delivery (tons/ac/yr)

Estimated Nitrate-N Loss

Time Period

1930's 1950's 1970's Present

Nitr

ate-

N L

oss

(lb/a

cre)

0

5

10

15

20

Tillage

Water Quality Modeling

Used a field‐scale model, WEPP, to evaluate potential performance of practices on runoff and sediment loss

Why field‐scale scenarios and not watershed‐scale? Develop a database of 

potential field‐scale performance

Scale at which farmers and ag. professionals can easily relate

(Source: Chris Renschler)

Location of Sites Simulated

Site Characteristics

Site Area (ha) Mean Slope (%)

Primary Soil

Northwest Iowa 44.9 2.1 Galva silty clay loam

Loess Hills 39.6 10.8 Ida silt loamDes Moines Lobe 45.7 1.0 Nicollet loamWestern Deep Loess and Drift 35.9 7.1 Sharpsburg silty

clay loamEastern Deep Loess and Drift 77.5 0.9 Nira silty clay loamEastern Till Prairie 79.6 3.2 Kenyon loamNortheast Iowa 122.1 9.5 Fayette silt loamSouthern Thin Loess and Till Plain 22.8 7.5 Grundy silt loam

Simulated Soil Loss

Northw

est Io

wa Lo

ess H

ills

Des M

oines

Lobe

Wes

tern D

eep L

oess

and D

rift

Easter

n Dee

p Loe

ss an

d Drift

Easter

n Till P

rairie

Nort

heas

t Iowa

Southe

rn Thin

Loes

s and

Till Plai

n

Annu

al a

vera

ge s

oil

loss

(ton

s/ac

re)

0

5

10

15

20

Chisel plow tillageNo-till

Tillage and Nitrate-N Loss

Impacts of Tillage on Nitrate-N Loss (Nashua)Cumulative NO3-N losses in corn-soybean systems 2008-2015

Year

08 09 10 11 12 13 14 15 16

kg N

ha

-1

0

50

100

150

200

2502 Fall manure on corn CP6 Fall manure on corn NT

Impacts of Tillage on Nitrate-N Loss (Gilmore City)

1/1/11

4/1

/11

7/1/11

10

/1/11

1/1

/12

4/1/12

7/1

/12

10/1/

12

1/1/13

4/1

/13

7/1/13

10

/1/13

1/1

/14

4/1/14

7/1

/14

10/1/

14

1/1/15

4/1

/15

7/1/15

10

/1/15

1/1

/16

Cum

ulat

ive

Nitr

ate

Loss

(kg/

ha)

0

50

100

150

200

250

Conventional TillageNo Tillage

Cover Crops and Landuse

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

Impacts of Land Use Change

1/1/10

1/1/11

1/1/12

1/1/13

1/1/14

1/1/15

1/1/16

NO

3-N

Loa

d (k

g N

/ha)

0

20

40

60

80

100

120

140

160

180

Corn/SoybeanContinuous CornContinuous Corn with Cover CropPrairieFertilized Prairie

Gilmore City – Converted from Corn-Soybean to Orchard Grass/Clover in 2005

2006 2007 2008 2009 2010 2011 2012 2013 2014

Flow

-wei

ghte

d N

itrat

e-N

C

once

ntra

tion

(mg/

L)

0

2

4

6

8

10

In-field and Edge of Field Land Management Practices

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

What is unique?

Natural Flow Conditions

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%

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

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

Visual Examples (4 inch rain in June 2008)

100% Crop 100% Prairie10% Prairie90% Crop

Nitrate‐N Concentrations in Groundwater at the Footslope of Each Watershed

Dissolved Phosphorus Concentrations in Groundwater at the Footslope of Each Watershed

Soil Carbon and Nitrogen

Summary• Practices that have potential to

improve soil health have potential for water quality improvement – Some practices have less impact under

certain conditions

Contact

• mhelmers@iastate.edu• Twitter: @ISUAgWaterMgmt• Website: http://agwatermgmt.ae.iastate.edu/