Department of Agricultural and Biosystems Engineering

Iowa Nutrient Reduction Strategy Science

AssessmentMatthew 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

Iowa Nutrient Reduction Strategy – Science Team• Matt Helmers – ISU – N Team

Lead• Tom Isenhart – ISU – P Team Lead• John Lawrence – ISU• John Sawyer – ISU• Antonio Mallarino – ISU• William Crumpton – ISU• Rick Cruse – ISU• Mike Duffy – ISU• Reid Christianson – ISU• Phil Gassman – ISU• Dean Lemke – IDALS• Shawn Richmond – IDALS

• Jim Baker – IDALS/ISU• Keith Schilling – IDNR• Calvin Wolter – IDNR• Dan Jaynes – USDA-ARS• Mark Tomer – USDA-ARS• John Kovar – USDA-ARS• David James – USDA-ARS• Eric Hurley – USDA-NRCS• Mark David – Univ. of Illinois• Gyles Randall – Univ. of Mn• Katie Flahive - USEPA

Department of Agricultural and Biosystems Engineering

Approach1. Establish baseline – existing conditions2. Conduct an extensive literature review to assess

potential performance of practices• Outside peer review of science team documents (practice

performance and baseline conditions)3. Estimate potential load reductions of

implementing nutrient reduction practices (scenarios)• “Full implementation” and “Combined” scenarios

4. Estimate cost of implementation and cost per pound of nitrogen and phosphorus reduction

Estimated Nitrogen Application Rate –Manure + Fertilizer

Rate on CB Rate on CC

MLRA lb N/ac lb N/ac102C 182 232103 154 204104 144 194105 131 181107A 184 234107B 139 189108C 163 213108D 120 170109 142 192115C 146 196

Iowa Total 151 201

Maximum Return to Nitrogen from corn following soybean with $5/bushel corn and $0.5/lb of N = 133 lb-N/acre for CB (profitable range of 121-146 lb/acre) and 190 lb-N/acre for CC (profitable range of 177-202 lb-N/acre)

MLRAAverage STP of each 

MLRAmg P/kg soil

103 30104 27105 27107A 32107B 28108C 27108D 19109 11

Soil Test Phosphorous Concentrations

Optimum STP = 20 mg P/kg soil

Practice Review Process• Extensive review of literature from Iowa and

surrounding states – Used Iowa and surrounding states to try to

have similar soils and climatic conditions– Reviewed and compiled impacts on nitrogen

and phosphorus concentrations and loads– Reviewed and compiled impacts on corn yield

• Summarized expected practice performance

Nitrate-N Reduction PracticesPractice

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

% Corn Yield Change 

Nitrogen Management

Timing (Fall to spring) 6 (25) 4 (16)

Nitrogen Application Rate (Reduce rate to MRTN)

10 ‐1

Nitrification Inhibitor (nitrapyrin) 9 (19) 6 (22)

Cover Crops (Rye) 31 (29) ‐6 (7)

Land Use

Perennial – Pasture/Land retirement 85 (9)

Perennial – Energy Crops 72 (23)

Extended Rotations 42 (12) 7 (7)

Edge‐of‐Field

Controlled Drainage 33 (32)*

Shallow Drainage 32 (15)*

Wetlands 52

Bioreactors 43 (21)

Buffers 91 (20)***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

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Reducing nitrogen application rate from background to the MRTN 133 lbN/ac on CB and to 190 lb N/ac on CC

9 -0.58 -32

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Cover crops (rye) on ALL CS and CC acres 28 5.96 50 60 1,025

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Install Wetlands to treat 45% of the ag acres 22 1.38 191

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

1 km

Targeted Wetland Restoration

Iowa Conservation Reserve Enhancement Program (CREP)

0 0.1 0.2 0.3 0.4Average hydraulic loading rate (m day-1)

0

20

40

60

80

100Pe

rcen

t nitr

ate

mas

s rem

oved

Modeled nitrate removal2004-2011 observed wetlands2012 observed wetlands

Source: W. Crumpton

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Install Denitrification Bioreactors on all tile drained acres 18 0.92 101

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Install Buffers on all applicable lands (30 ft. on each side of stream) 7 1.91 18 14 88

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction on Nitrogen and 29% reduction on Phosphorus

100% Crop 100% Prairie10% Prairie ‐ 90% Crop

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Install Controlled Drainage on all applicable acres 2 1.29 18

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Perennial crops (energy crops) on ~6.5 million acres 18 21.46 29 238 2,318

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

Nutrient Load Reduction Scenarios

Nitrate-N Reduction

Cost of N Reduction

Phosphorus Reduction

Cost of P Reduction

Total Equal Annualized

Cost

Practice/Scenario % (from baseline) ($/lb) % (from

baseline) ($/lb) (million $/yr)

Convert all tillage to no-till 39 14 186.4

From Iowa Nutrient Reduction Strategy: Goals for Nonpoint Sources is 41% reduction in Nitrogen and 29% reduction in Phosphorus

Overall Comparison of Nitrate-N PracticesNitrate-N

ReductionCost of N Reduction

OtherBenefits

(Ecosystem Services)

Practice/Scenario % (from baseline) ($/lb)

Reducing nitrogen application rate from background to the MRTN 9 -0.58

Cover crops (rye) on ALL CS and CC acres 28 5.96 ++

Install Wetlands to treat 45% of the ag acres 22 1.38 ++

Install Denitrification Bioreactors on all tile drained acres 18 0.92

Install Buffers on all applicable lands 7 1.91 ++

Installing Controlled Drainage on all applicable acres 2 1.29

Perennial crops (energy crops) on ~6.5 million acres 18 21.46 ++

Overall Comparison of Phosphorus Practices

PReduction

Cost of P Reduction

OtherBenefits

(Ecosystem Services)

Practice/Scenario % (from baseline) ($/lb)

Cover crops (rye) on ALL CS and CC acres 50 60 ++

Convert all tillage to no-till 39 14 ++

P rate reduction in MLRA’s that have high to very high soil test P 7 -110

Establish streamside buffers (35ft) on all crop land 18 14 ++

Perennial crops (energy crops) equal to pasture/hay acreage from 1987 29 238 ++

Pasture and Land Retirement to equal acreage of Pasture/Hay and CRP from 1987 9 120 ++

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

Department of Agricultural and Biosystems Engineering

Summary• To achieve goals will require a combination of

practices – conservation systems approach• N versus P may require different practices• Multiple benefits and costs of practices need

to be considered• Iowa has initiated the Iowa Water Quality

Initiative as part of the Nutrient Reduction Strategy and has implemented a number of watershed demonstration practices

Department of Agricultural and Biosystems Engineering