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