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

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 NRS 2013 by watershed 2007 1997 2017 1987 2002 2012 1982 1992 BMP Mapping & In-field survey 2006-10 Annual reports Model begin 2014 development period 1

9/28/2017 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 2

9/28/2017 Estimated Nitrogen Load State Average Nitrogen Load Nitrate ‐ N Load (tons) 1982 to 1997 Average 330,000 310,000 • 1982-1997 290,000 Nitrate Load (tons) Average Load – 270,000 292,000 tons 250,000 • NRS Load – 307,000 tons 230,000 • 5% increase 210,000 190,000 170,000 150,000 1982 1987 1992 1997 INRS ‐ NSSA Phosphorus Load State Average Phosphorus Load Phosphorus Load (tons) 1982 to 1997 Average 30,000 25,000 Phosphorus Load (tons) • 1982-1997 Average Load – 20,000 21,436 tons • NRS Load – 15,000 16,800 tons • 22% decrease 10,000 5,000 0 1982 1987 1992 1997 INRS ‐ NSSA 3

9/28/2017 Summary Nutrient 1980-96 INRS-NSSA % Change From Average Load Load (Tons) 1980-96 to INRS- (Tons) 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 4

9/28/2017 Land Use -Total agricultural acres including corn/soybean, continuous corn, extended rotation, and pasture/hay All Agricultural Land 30,000,000 25,000,000 20,000,000 Acres 15,000,000 10,000,000 5,000,000 0 1982 1987 1992 1997 INRS ‐ NSSA Land Use Corn/Soybean & Continuous Corn 25,000,000 20,000,000 15,000,000 Acres 10,000,000 5,000,000 0 1982 1987 1992 1997 INRS ‐ NSSA 5

9/28/2017 Nitrogen Application 1400000 1200000 Commercial Fertilizer Manure Nitrogen Application (lbs) 1000000 800000 600000 400000 200000 0 1982 1987 1992 1997 INRS-NSSA Nitrogen Application per Acre Nitrogen Application Rate to Corn in a Corn ‐ Soybean Rotation 180 160 140 Nitrogen Application Rate (lb/acre) 120 100 80 60 40 20 0 1982 1987 1992 1997 INRS ‐ NSSA 6

9/28/2017 Fraction of No ‐ till Acres 0.5 Tillage Fraction of Rowcrop Acres 0.4 0.3 0.2 0.1 0 Fraction of Intense Till Acres 0.5 Fraction of Rowcrop Acres 0.4 0.3 0.2 0.1 0 Soil Test Phosphorus Soil Test Phosphorus 34 33 Soil Test Phosphorus (mg/kg) 32 31 30 29 28 27 26 25 1982 1987 1992 1997 INRS ‐ NSSA 7

9/28/2017 Phosphorus Application Estimated P2O5 Application Rate 60 P2O5 Application Rate (lb/acre) 50 40 30 20 10 0 1982 1987 1992 1997 INRS ‐ NSSA Land Use Corn/Soybean 20,000,000 15,000,000 Acres 10,000,000 5,000,000 0 1982 1987 1992 1997 INRS ‐ NSSA 8

9/28/2017 Land Use Continuous Corn 6,000,000 4,000,000 Acres 2,000,000 0 1982 1987 1992 1997 INRS ‐ NSSA Corn Yields Corn Yield Corn/Soybean Rotation 180 160 140 120 Yield (bu/acre) 100 80 60 40 20 0 1982 1987 1992 1997 INRS ‐ NSSA 9