Assessment of the Estimated Non- Point Source Nitrogen and - - PDF document

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9/28/2017 Assessment of the Estimated Non- Point Source Nitrogen and Phosphorus Loading from Agricultural Sources from Iowa During the 1980-96 Hypoxia Task Force Baseline Period Hypoxia Task Force Launch Farmer survey Action Plan baseline

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Assessment of the Estimated Non- Point Source Nitrogen and Phosphorus Loading from Agricultural Sources from Iowa During the 1980-96 Hypoxia Task Force Baseline Period

2006-10 Model development period 1982 1987 1992 1997 2002 Hypoxia Task Force Action Plan baseline 2012 2017 2007 Launch NRS 2013 Annual reports begin 2014 Farmer survey by watershed BMP Mapping & In-field survey

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Background

Followed similar procedures as Iowa Nutrient

Reduction Strategy Non-point Source Science Assessment (INRS-NSSA)

– Same estimated water yield as in Science Assessment

Commercial fertilizer based on sales numbers
Manure based on census of ag
Land use based on census of ag
Tillage based on CTIC and extrapolation to period

before CTIC estimates

STP based on lab measured values in a couple

periods and then changes based on P balance

MLRAs

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Estimated Nitrogen Load

1982-1997

Average Load – 292,000 tons

NRS Load –

307,000 tons

5% increase

150,000 170,000 190,000 210,000 230,000 250,000 270,000 290,000 310,000 330,000 1982 1987 1992 1997 INRS‐NSSA Nitrate Load (tons)

State Average Nitrogen Load

Nitrate‐N Load (tons) 1982 to 1997 Average

Phosphorus Load

1982-1997

Average Load – 21,436 tons

NRS Load –

16,800 tons

22% decrease

5,000 10,000 15,000 20,000 25,000 30,000 1982 1987 1992 1997 INRS‐NSSA Phosphorus Load (tons)

State Average Phosphorus Load

Phosphorus Load (tons) 1982 to 1997 Average

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Summary

Nutrient 1980-96 Average Load (Tons) INRS-NSSA Load (Tons) % Change From 1980-96 to INRS- NSSA Nitrate-N 292,022 307,449 5% Increase Phosphorus 21,436 16,800 22% Decrease

Limitation and Future Needs

Did not include stream bank contribution to

phosphorus

Assumed same level of structural practice

implementation as INRS-NSSA

– Future BMP mapping projects may impact P load estimation

Assumed uniform N application rate
Assumed constant weather conditions

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Land Use -Total agricultural acres including corn/soybean, continuous corn, extended rotation, and pasture/hay

5,000,000 10,000,000 15,000,000 20,000,000 25,000,000 30,000,000 1982 1987 1992 1997 INRS‐NSSA Acres

All Agricultural Land

Land Use

5,000,000 10,000,000 15,000,000 20,000,000 25,000,000 1982 1987 1992 1997 INRS‐NSSA Acres

Corn/Soybean & Continuous Corn

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Nitrogen Application

1982 1987 1992 1997 INRS-NSSA

Nitrogen Application (lbs)

200000 400000 600000 800000 1000000 1200000 1400000 Commercial Fertilizer Manure

Nitrogen Application per Acre

20 40 60 80 100 120 140 160 180 1982 1987 1992 1997 INRS‐NSSA Nitrogen Application Rate (lb/acre)

Nitrogen Application Rate to Corn in a Corn‐Soybean Rotation

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Tillage

0.1 0.2 0.3 0.4 0.5 Fraction of Rowcrop Acres

Fraction of No‐till Acres

0.1 0.2 0.3 0.4 0.5 Fraction of Rowcrop Acres

Fraction of Intense Till Acres

Soil Test Phosphorus

25 26 27 28 29 30 31 32 33 34 1982 1987 1992 1997 INRS‐NSSA Soil Test Phosphorus (mg/kg)

Soil Test Phosphorus

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Phosphorus Application

10 20 30 40 50 60 1982 1987 1992 1997 INRS‐NSSA P2O5 Application Rate (lb/acre)

Estimated P2O5 Application Rate

Land Use

5,000,000 10,000,000 15,000,000 20,000,000 1982 1987 1992 1997 INRS‐NSSA Acres

Corn/Soybean

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Land Use

2,000,000 4,000,000 6,000,000 1982 1987 1992 1997 INRS‐NSSA Acres

Continuous Corn

Corn Yields

20 40 60 80 100 120 140 160 180 1982 1987 1992 1997 INRS‐NSSA Yield (bu/acre)

Corn Yield Corn/Soybean Rotation