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

MLRA CS CC EXT PH ac ac ac ac102C 170,151 50,077 18,179 38,866103 4,737,173 1,252,577 190,573 351,362104 3,196,748 1,031,193 275,016 402,026105 381,386 339,918 201,090 705,142107A 1,833,615 208,446 95,204 118,910107B 2,938,063 408,404 280,603 510,586108C 2,137,445 479,204 310,546 855,004108D 960,321 65,004 199,602 999,998109 582,197 63,872 201,816 1,564,762115C 127,776 44,996 20,183 31,534Iowa Total 17,064,873 3,943,694 1,792,812 5,578,194

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

MLRACorn Yield

Corn-SoybeanCorn Yield

Continuous CornSoybean

Yield bu/ac bu/ac bu/ac

102C 163 150 53103 175 161 50104 176 162 51105 179 165 50

107A 161 148 51107B 156 143 49108C 177 163 51108D 151 139 49109 155 143 47

115C 181 167 49

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%

MLRA Water Yield in/yr

103 10.4104 11.9105 11.3

107A 7.1107B 8.2108C 11.2108D 9.8109 12.0

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 N fromcattle 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 Source Availability (%)Cattle 40Broilers 60Layers 60Turkey 60Hog 100

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 P2O5/ton (Sawyer et al., 2011)– Ratio of MAP to DAP sales (IDALS, 2011) = Ratio of

MAP to DAP application– ~17 lb N/ac

MLRA Commercial Fertilizer Manure Total Applied to Corn lb N/ac lb N/ac lb N/ac

102C 117 84 201103 136 35 171104 134 29 163105 130 33 163

107A 129 64 193107B 128 22 149108C 148 30 178108D 108 18 126109 123 28 151

115C 144 22 166Iowa Total 133 33 166

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 Corn Rate on CB Rate on CClb N/ac lb N/ac lb N/ac

102C 201 182 232103 171 154 204104 163 144 194105 163 131 181

107A 193 184 234107B 149 139 189108C 178 163 213108D 126 120 170109 151 142 192

115C 166 146 196Iowa Total 166 151 201

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 P2O5/bu

0.375 lb P2O5/bu, respectively

• P removal in alfalfa was 12.5 lb P2O5/ton

Resulting P Application

MLRA Rate on Corn Rate on Soybean

Rate on Alfalfa Hay

lb P2O5/ac lb P2O5/ac lb P2O5/ac103 59 35 34104 56 35 40105 64 42 51

107A 81 53 55107B 48 31 32108C 58 38 39108D 44 29 28109 54 36 32

Iowa Total 58 37 38

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

MLRA Soil-Test P (ppm)103 30104 27105 27

107A 32107B 28108C 27108D 19109 11

Tillage

• Estimates from the Conservation Technology Information Center (CTIC)– Conservation Tillage (>30% residue)• No-till/Ridge-Till• Mulch-Till

No-Till Mulch Till No-Till Mulch TillMLRA % of CC % of CC % of CS % of CS102C 4 16 11 25103 4 34 9 49104 11 37 24 38105 11 30 31 37107A 8 21 14 40107B 39 24 53 21108C 15 31 36 28108D 28 28 45 24109 11 21 34 24115C 9 37 33 29

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?

SummaryComponent Source

Land Use NASS Cropland Data Layer

Water Yield National Climatic Data Center, USGS Water Watch

Tile Drainage Iowa Drainage Guide, Soil Survey Geographic (SSURGO) Database

Nitrogen Application David 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 Application Jacobson et al. (2011), USDA Census of Agriculture, Sawyer et al. (2002)

Soil Test P Mallarino et al. (2011)

Tillage CTIC (2008)

Iowa P-Index Input Soil Survey Geographic (SSURGO) Database, SCS-Iowa (1990), National Land Cover Database (NLCD), National Hydrography Dataset (NHD)