Nutrient Reduction Strategy and Best

Management PracticesMatthew Helmers

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

Iowa State University

Situation• Increasing concern for local and regional waters• Substantial demand for agricultural products• Hypoxia Action Plan in 2008 called for

development and implementation of comprehensive N and P reduction strategies for states in the Mississippi/Atchafalaya River Basin

• Increasing concern about phosphorus loading to Lake Erie and the role of drainage in this loading

Gulf of Mexico Hypoxia Goals

Hypoxia Action Plan Goal: Reduce the size of the zone to 5,000 km2

by 2015

EPA-SAB Recommendations: Reduce Total Riverine Nitrogen and Phosphorus Loads by 45%

Current and Pending Programs• States in the Mississippi River Basin are

implementing state nutrient reduction strategies

• These strategies are a voluntary approach to reducing nutrient loading to downstream waters

• Increasing demand to document water quality improvements and increasing demand for accountability

• Increasing discussion about regulation

Timing of Subsurface Drainage (1990-2011)

Soil Nitrate Production vs. Crop Nitrate Uptake

In the shaded areas, the soil produces nitrate, but there is no crop to use it. As a result, somenitrate is lost to waterways.

March February

Rate of soil nitrate production from native soil organic matter

Rate of corn or soybean nitrate uptake

The majority of nitrate used by corn and soybean comes from soil nitrate production. Corn gets the difference from fertilizer while soybean gets the difference from legume fixation of atmospheric nitrogen.

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Water Flow Pathways

Land management and land use impacts ET and infiltration which in turn impact surface runoff, subsurface drainage, deep percolation

Naturally Well-Drained Soils Soils with Poor Natural Drainage

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 (MRTN rate 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)**

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

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)

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

Soil Nitrate Production vs. Crop Nitrate UptakeAddition of a Cover Crop

March February

Rate of soil nitrate production from native soil organic matter

Rate of corn or soybean nitrate uptake

Cover crops can use nitrate when corn and beans are not growing, thus reducing the asynchrony between soil nitrate production and crop nitrate uptake.

Cover crop nitrate use

Cover crop nitrate use

In the shaded areas, the soil produces nitrate, but there is no crop to use it. As a result, some nitrate is lost to waterways.

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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 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)

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

Nitrate Removal Wetlands

Cover Crops

Subsurface Drainage Bioreactors

Saturated Buffers

Prairie Strips

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 ++

What Might it Take to Reach our Goals?

Nitrate-N Reduction

Practice/Scenario % (from baseline)

N management - Maximum Return to Nitrogen Application Rate and 60% of all Corn-Bean and Continuous Corn Acres with Cover CropEdge-of-Field - 27% of all ag land treated with wetland and 60% of all subsurface drained land with bioreactor

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Example: Combination Scenarios that Achieves N Goal From Non-Point Sources for Nutrient Reduction Strategy

What Might it Take to Reach our Goals?

Nitrate-N Reduction

Practice/Scenario % (from baseline)

N management - Maximum Return to Nitrogen Application Rate and 25% of all Corn-Bean and Continuous Corn Acres with Cover CropLand Use - 25% of acreage with Extended RotationsEdge-of-Field - 27% of all ag land treated with wetland and 60% of all subsurface drained land with bioreactor

42

Example: Combination Scenarios that Achieves N Goal From Non-Point Sources for Nutrient Reduction Strategy

Summary• The Iowa Nutrient Reduction Strategy is a

statewide effort to reduce nutrient loading• To reach the goals will take broad

implementation of multiple practices• Are there opportunities to implement practices

that enhance or protect long-term value of the land?