Iowa Nutrient Reduction Strategy: Background Information Reid Christianson, P.E., Ph.D. Center for Watershed Protection Ellicott City, Maryland

Project Components Project Goal – 45% reduction in riverine N & P Baseline Development Best Management Practice performance Scenario Development Economic Assessment

Steps in Baseline Development Define Scale Determine Land Use Determine Yield Nitrogen – Fertilizer, manure, timing… Phosphorus – Application rate, soil test P, tillage…

Project Team Science Team – ~20 individuals – Representing 5 agencies or organizations – Three subgroups Nitrogen Phosphorus Hydrology

What scale should be used? Discussion on the appropriate scale of analysis – Field? – Township? – County? – Major Land Resource Area (MLRA)? Discussion on data sources available – USDA-NRCS Comprehensive Effects Assessment Project (CEAP)?

Iowa’s Major Land Resource Areas (MLRA)

Land Use Development NASS Cropland Data Layer for 2006 – 2010

NASS Cropland Data Layer

MLRACSCCEXTPH ac 102C 170,15150,07718,17938, ,737,1731,252,577190,573351, ,196,7481,031,193275,016402, ,386339,918201,090705, A 1,833,615208,44695,204118, B 2,938,063408,404280,603510, C 2,137,445479,204310,546855, D 960,32165,004199,602999, ,19763,872201,8161,564, C 127,77644,99620,18331,534 Iowa Total 17,064,8733,943,6941,792,8125,578,194 Resulting Crop Acres

Corn and Soybean Yields County averages – 2007 Census of Agriculture Harvested grain Harvested area Counties split between MLRAs – Partitioned based on area in MLRA

Continuous Corn and Corn-Soybean Corn Yield Adjustments Corn yields for continuous corn – ~8% lower than observed in a corn-soybean rotation (Erickson, 2008) Corn yields proportionally adjusted based on crop area – Up for corn in a corn soybean rotation – Down for continuous corn Overall corn yield matches MLRA average

Resulting Yields MLRA Corn Yield Corn-Soybean Corn Yield Continuous Corn Soybean Yield bu/ac 102C A B C D C

Water Yield and Tile Drainage Water Yield – Long term USGS measured flow and National Climatic Data Center daily precipitation Tile drainage based on the Iowa Drainage Guide – Soil series requiring drainage – Slopes less than or equal to 2%

MLRAWater Yield in/yr A B C D

Nitrogen Use This is where all the fun starts Point of substantial discussion – How to credit manure? – How to take into account the variability of N application? – Fertilization of pasture and hay? – What about urban turf grass? Significant time required to hash out these details

N Components What was the source? What type of crop was it applied to? When was the nitrogen being applied? What was the method of application? Was it applied with an inhibitor?

Nitrogen Application David et al., 2010 ManureFertilizer SwinePoultryCattle Subtracted N from cattle on pasture Adjusted for first year availability Subtracted turf grass Subtracted pasture Subtracted alfalfa Nitrogen applied to corn

Overall N Application Based on David et al. (2010) county estimates – Adjusted for cattle on pasture (2002 Ag Census) – Manure numbers adjusted for first year availability Subtracted 9% of statewide nitrogen sales for turf grass (Libra et al., 2004) Manure SourceAvailability (%) Cattle40 Broilers60 Layers60 Turkey60 Hog100 Sawyer and Mallarino (2008)

N to Pasture and Alfalfa Pasture N based on recommended application rate across state – 80 lb N/ac (Barnhart et al., 1997) Alfalfa N rate based on phosphorus use – 4 ton/ac/yr yield (Duffy, 2011) – 12.5 lb P 2 O 5 /ton (Sawyer et al., 2011) – Ratio of MAP to DAP sales (IDALS, 2011) = Ratio of MAP to DAP application – ~17 lb N/ac

MLRACommercial FertilizerManureTotal Applied to Corn lb N/ac 102C A B C D C Iowa Total

Adjustment for Continuous Corn Assume 50 lb/ac more N applied on continuous corn (Blackmer et al., 1997; Sawyer et al., 2011c) MLRA Total Applied to CornRate on CBRate on CC lb N/ac 102C A B C D C Iowa Total

Timing and Inhibitors Timing – Assumed 25% of fertilizer applied in fall (Randall and Sawyer, 2008) – Assumed all manure is applied in fall Inhibitor – Roughly 2 million acres treated with nitrapyrin (Dow AgroSciences, 2012) – Assumed applied with fall anhydrous

P Components How much P was applied? To which crop was it applied? When was P applied? How much P is in the soil? Was it incorporated into the soil? What is the distance to a stream?

P Application Based on Jacobson et al. (2011) county estimates – Adjusted for cattle on pasture (2002 Ag Census) Total P partitioned to corn, soybeans, and hay – Based on fraction of P used by each crop (Sawyer et al. (2002) P removal in soybean and corn grain was 0.8 lb P 2 O 5 /bu lb P 2 O 5 /bu, respectively P removal in alfalfa was 12.5 lb P 2 O 5 /ton

Resulting P Application MLRA Rate on Corn Rate on Soybean Rate on Alfalfa Hay lb P 2 O 5 /ac A B C D Iowa Total583738

Soil Test P Soil samples analyzed by the ISU Soil and Plant Analysis Laboratory (2006 to 2010) (Mallarino et al., 2011) – Highest county ppm – Optimum – 16 to 20 ppm MLRASoil-Test P (ppm) A32 107B28 108C27 108D

Tillage Estimates from the Conservation Technology Information Center (CTIC) – Conservation Tillage (>30% residue) No-till/Ridge-Till Mulch-Till No-TillMulch TillNo-TillMulch Till MLRA% of CC % of CS 102C A B C D C

Distance Classes & Soils Information Iowa P-Index Data Requirements – Distance from center of field to National Hydrography Dataset streams 7 distance classes ( 0-500, 500-1,000, 1,000-2,000, 2,000-4,000, 4,000-8,000, 8,000-16,000, and >16,000 feet ) – Representative soil type for each distance class Erodibility factor, saturated hydraulic conductivity, slope, slope length Zonal statistics to estimate mean values – Land cover determined RUSLE cover factor

Contour Farming and Terraces Available datasets are incomplete – mainly for farm programs – Used best professional judgment on MLRAs where practice would likely be prevalent Contour farming on 50% of land in MLRA 105 Combination of contour farming and terraces on 50% of land in MLRA 107B

Future Efforts – Data Collection Fertilizer sales by county – with intended county of application? Incentivized self reporting? – Could include information on N & P use, crop area, yield, etc. Poll Co-ops for anonymous pertinent information?

Summary ComponentSource Land UseNASS Cropland Data Layer Water YieldNational Climatic Data Center, USGS Water Watch Tile DrainageIowa Drainage Guide, Soil Survey Geographic (SSURGO) Database Nitrogen ApplicationDavid et al. (2010), USDA Census of Agriculture, Libra et al. (2004), Sawyer and Mallarino (2008), Barnhart et al. (1997), Duffy (2011), Sawyer et al. (2011), IDALS (2011) Phosphorus ApplicationJacobson et al. (2011), USDA Census of Agriculture, Sawyer et al. (2002) Soil Test PMallarino et al. (2011) TillageCTIC (2008) Iowa P-Index InputSoil Survey Geographic (SSURGO) Database, SCS-Iowa (1990), National Land Cover Database (NLCD), National Hydrography Dataset (NHD)