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
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
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%
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 Manure Fertilizer Swine Poultry Cattle Subtracted turf grass Subtracted N from cattle on pasture Subtracted pasture Adjusted for first year availability 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) 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/yryield (Duffy, 2011) • 12.5 lb P2O5/ton (Sawyer et al., 2011) • Ratio of MAP to DAP sales (IDALS, 2011) = Ratio of MAP to DAP application • ~17 lb N/ac
Adjustment for Continuous Corn • Assume 50 lb/ac more N applied on continuous corn (Blackmer et al., 1997; Sawyer et al., 2011c)
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 lbP2O5/bu 0.375 lb P2O5/bu, respectively • P removal in alfalfa was 12.5 lb P2O5/ton
Resulting P Application
Soil Test P • Soil samples analyzed by the ISU Soil and Plant Analysis Laboratory (2006 to 2010) (Mallarino et al., 2011) • Highest county - 131 ppm • Optimum – 16 to 20 ppm
Tillage • Estimates from the Conservation Technology Information Center (CTIC) • Conservation Tillage (>30% residue) • No-till/Ridge-Till • Mulch-Till
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
