Nutrient Reduction Strategy Phosphorus Science Team

Iowa Science Assessment of Nonpoint Source Practices to

Reduce Phosphorus to the Mississippi River Basin

Nutrient Reduction StrategyPhosphorus Science Team

Nutrient Reduction StrategyPhosphorus Science Team• Jim Baker – IDALS/ISU• Reid Christianson – ISU• Rick Cruse – ISU• John Kovar – USDA-ARS• Matt Helmers – ISU• Tom Isenhart – ISU• Antonio Mallarino – ISU• Keith Schilling – IDNR• Calvin Wolter – IDNR• Dave Webber - ISU

Approach1. Establish baseline – existing conditions

– Major Land Resource Areas used to aggregate conditions

2. Extensive literature review to assess potential performance of practices– Outside peer review of science team documents (practice

performance and baseline conditions)

3. Estimate potential load reductions of implementing nutrient reduction practices (scenarios)– “Full implementation” and “Combined” scenarios

4. Estimate cost of implementation and cost per pound of nitrogen and phosphorus reduction

Approach• The P evaluation primarily focused on practices that

limit or control P losses from agricultural land.• Does not include known sources of P such as point

sources, leaking rural septic systems, and stream bank erosion.

ISU NREM USDA NRCS

Approach• Stream banks are known to be a potentially large source of

suspended and bedded sediments.• Estimated contributions ranging from 40 to 80% of annual

sediment loads in Midwestern streams.• Accurate accounting is difficult.

Isenhart et al.Unpublished

Practice Review Process • Established an overall list of potential practices

based on input of overall science team• Shortened the list to those expected to have

greatest potential for nutrient reduction through detailed discussion of P team – reviewed by overall science team

• New and emerging practices could be added in future

Practice Review Process Phosphorus Reduction Strategies Excluded Due to Very Limited Impact or Not Information at this Point

•Timing of phosphorus application•Living mulches (e.g. kura clover)•Green manure•No continuous soybean•Shallow drainage •Drainage water management•Bioreactors•Two-stage ditches

Practice Review ProcessP reduction practices fall into three main groups

1. P Management Practices• Application• Source (commercial fertilizer, manure)• Placement• Cover crops• Tillage

2. Land use change• Crop choice• Perennial vegetation

3. Erosion Control and Edge of Field Practices• Terraces• Wetlands• Buffers• Other erosion control

Practice Review Process• Extensive review of literature from Iowa and

surrounding states – Used Iowa and surrounding states to try to

have similar soils and climatic conditions– Reviewed and compiled impacts phosphorus

concentrations and loads– Reviewed and compiled impacts on corn yield

• Summarized expected practice performance

Nitrogen or Phosphorus?

Nitrogen moves primarily as nitrate-N with water

Phosphorus moves primarily with eroded soil

• Practices were compared with a corn-soybean rotation– P needed by the two crops surface-applied once

after soybean harvest in the fall before soils freeze

– Tillage includes chisel plowing cornstalks after harvest and disking/field cultivating in the spring before planting soybeans

– Before planting corn the normal practice is disking/field cultivating in the spring

Phosphorus Reduction Practices

Phosphorus Application Rate• P rate is less important than N rate as it affects water quality• P rate affects the STP level, so historical P application rates and current STP level are important for impacts on water quality• Application rate is of great concern when any manure type is applied at N-based rates• Load reduction was estimated using Iowa P Index comparing rates of 200 kg P2O5 ha-1 (max), and 125 kg P2O5 ha-1 (avg.) compared to the average

annual removal for a corn-soybean rotation of 62 kg P2O5 ha-1.• Estimates in bracket are “worst case scenarios” in which a rainfall occurs within 24 hours of P application

Phosphorus Management Practices

Practice Comments % P Load ReductionMin Avg.

(SD)Max

Phosphorus Application

Applying P based on crop removal – Assuming optimal STP level and P

incorporation

0[0]

0.6[70]

1.3[83]

Soil Test Phosphorus Level• Phosphorus loss can be reduced by decreasing total soil P concentration• This practice assumes limiting or stopping P application to high-testing soils until STP is lowered to agronomically optimum concentrations of 20 ppm for corn and

soybean production• Load reduction was estimated using Iowa P Index for a 5 Mg ha-1 erosion rate • Maximum load reduction was estimated by comparing P loss with an STP of the two highest counties in IA (125 ppm) to the optimum (20 ppm) STP level• Average load reduction was estimated based on reducing the average STP of all counties in IA (40 ppm) to the optimum STP level• Estimates in brackets are from unpublished work by Mallarino (2011)



(SD)Max


Soil-test P – No P applied until STP drops to optimum

0[35]

17[40]

52[50]

Site-Specific P Management• Site-specific management that considers the P loss risk from different areas of a field could be a beneficial practice to reduce P loss• Not well studied, but research in IA has found variable-rate fertilizer and manure P application to be effective in reducing within field

variability of STP levels• The approach used to estimate P load reduction was the same as for the STP practice and used mean values from a recent

unpublished study by Mallarino that included the mean proportion of IA STP classes for each field



(SD)Max


Site-specific P management 0 14

Source of Phosphorus• There is little evidence of P source (i.e. fertilizer compared to manure P) effects short-term delivery from fields if the P

is incorporated into the soil• In the long term, manure can reduce runoff compared to inorganic P forms by increasing soil organic carbon• If runoff-producing rainfall events occur immediately after application, less P loss occurs with solid beef and poultry

manure compared with commercial fertilizer



(SD)Max

Source of Phosphorus

Liquid swine, dairy, and poultry manure compared to commercial fertilizer –

Runoff shortly after application

-64 46(45)

90

Beef manure compared to commercial fertilizer – Runoff shortly after application

-133 46(96)

98

Placement of Phosphorus• Subsurface banding of P or incorporation of surface-applied P fertilizer or manure on sloping ground

reduces P loss significantly compared with surface application when runoff-producing precipitation occurs shortly after application

• Estimates in brackets are from a report by Dinnes (2004) and are the author’s best professional judgment



(SD)Max

Placement of Phosphorus

Broadcast incorporated within 1 week compared to no incorporation, same

tillage

4 36(27)

86

With seed or knifed bands compared to surface application, no incorporation

-50

[-20]

24(46)[35]

95

[70]

Cover Crops• Cover crops reduce erosion by improving soil structure and providing ground cover as

a physical barrier between raindrops and the soil surface



(SD)Max

Cover Crops Winter Rye -39 29(37)

68

Tillage• Tillage practices affect soil erosion, the primary process for P delivery in IA• Tillage effects on P loss are site specific, but less P loss generally occurs with minimum or no tillage

compared with conventional tillage• No-till can increase the proportion of total P lost as dissolved P, especially in tile-drained areas



(SD)Max

Tillage Conservation till – chisel compared to moldboard plowing

-47 33(49)

100

No-till compared to chisel plowing 27 90(17)

100

Crop Choice• There is very little P loss data for specific extended rotations compared to a corn-soybean rotation in IA

Perennial Vegetation• Perennial vegetation established as energy crops or land retirement would significantly reduce soil erosion and P loss• Delivery of P to water bodies is highly affected by pasture management

Land Use Change


(SD)Max

Crop Choice Extended Rotation -

Perennial Vegetation

Energy Crops -13 34(34)

79

Land retirement (CRP) 75

Grazed Pastures 2 59(42)

85

Buffers• Designed to reduce P delivery by removing particulate P from runoff through filtration and sedimentation and reducing dissolved P by plant uptake or soil

binding• Riparian buffers can also stabilize stream banks

Erosion Control• Designed to reduce sediment delivery • Includes sedimentation basins, drop structures, ponds, etc.

Erosion Control and Edge-of-Field Practices


(SD)Max

Terraces 51 77(19)

98

Buffers -10 58(32)

98

Erosion Control Sedimentation basins or ponds 75 85 95

Phosphorus Reduction Practices

Practice% Phosphorus-P Reduction [Average (Std. Dev.)]

Phosphorus Management

Producer does not apply phosphorus until STP drops to

optimal level17 (40)

Source (Liquid swine compared to commercial)

46 (45)

Incorporation 36 (27)

No-till (70% residue) vs. conventional tillage (30%

residue)90 (17)

Land UsePerennial – Land retirement 75 (-)

Cover Crops (Rye) 29 (37)Pasture 59 (42)

Edge-of-Field Buffers 58 (32)

*Load reduction not concentration reduction

P-Index Model

P-Index Inputs for Erosion Component

• Gross Erosion rate (tons/acre/yr)• Landform Region (Sediment Delivery ratio)• Distance from Stream• Buffer Distance• Enrichment Factor (Tillage/No till)• Soil Test Phosphorus content (ppm P)

Gross Erosion Estimate• RUSLE model• A = R * K * LS * C * P• A = annual soil loss (tons/yr)• R = rainfall erosivity factor• K = soil erodibility factor• LS = length slope factor• C = cover factor• P = practice factor

County Data from NRCS

Distance Categories to NHD Stream Network

• 0 – 500 ft• 500 – 1,000 ft• 1,000 – 2,000 ft• 2,000 – 4,000 ft• 4,000 – 8,000 ft• 8,000 – 16,000 ft• > 16,000 ft

Data from SSURGO

• K Factor (soil erodibility factor)• Slope• Slope Length

Cover Factor

• Use Crop Rotation information from NASS CDL

• Use Tillage Practice information from CTIC• 7-8 combinations for each MLRA• Use Section I-C-1 from SCS-Iowa 1990 to

obtain Cover Factor and LS Factor

Practice Factor

• Contour Strip Cropping• Terraces• Contour Strip Cropping and Terraces• Use Section I-C-1 from SCS-Iowa 1990 to

obtain Practice Factor

Gross Erosion Calculation

• A = R * K * LS * C * P• Perform RUSLE calculation for each

cropping rotation/tillage combination in each distance class in MLRA

P-Index Model

• Landcover condition (crop and residue)• Dominant Soil type• Soil Test Phosphorus content (ppm P)• Fertilizer Application Rate (lb P2O5/acre)• Fertilizer Application Method

P-Index Inputs for Runoff Component

Dominant Soil Type in MLRA Distance Classes

• K Factor• KSat Factor (Saturated Conductivity)• Slope• Slope Length• Find Soil Type that matches all factors the

closest

P-Index Input for Drainage Component

• Tile Drained soil• Well Drained soil

Result of P-Index Model

• Phosphorus loss in lbs/ac/year for each crop rotation/tillage/buffer distance combination

• Sum up all combinations for MLRA to obtain total Phosphorus Loss for MLRA

• Perform for each individual management practice and combinations

Phosphorus Practices – Potential Load Reduction

Target Load Reduction from NPS for Hypoxia Goal ~29%

Scenario: Not applying P on acres with high or very high Soil-Test P (RR)•This practice involves not applying P on fields where STP values exceed the upper boundary of the optimum level for corn and soybean in Iowa (20 ppm, Bray-1 or Mehlich-3 tests, 6-inch sampling depth). This practice would be employed until the STP level reaches the optimum level.•Practice limitations, concerns, or considerations

• Limitation to utilization of manure-N. When manure is applied, use of the P Index (which considers STP together with other source and transport factors) to assess potential impact of N-based manure on P loss is a reasonable option considering farm economics and other issues.

• Landlord/tenant contracts often require maintaining STP levels, even if higher than optimum.

Phosphorus Reduction Scenarios

ScenarioPhosphorus Reduction

(% from baseline)

Potential Area(million acres)


P rate reduction in MLRAs that have high to very high soil test P

7 25.8

Scenario: Inject/Band P in All No-Till Acres (IN)•This practice involves injecting liquid P sources (fertilizer or manure) and banding solid inorganic fertilizers within all current no-till acres.•Practice limitations, concerns, or considerations

• For inorganic P fertilizers, it adds to the costs and does not increase (nor reduce) yield in Iowa. • Possible benefits of injecting or banding inorganic P fertilizer containing N by improving N use efficiency. • For liquid manure, this is a good practice to use manure-N efficiently.• For solid manure, there is no practical way to do it yet, but engineering advances for prototypes being evaluated could make it practical in the future.



(% from baseline)


Phosphorus Management Injection/band within no-till acres 0.3 4.8

Scenario: Convert All Intensive Tillage to Conservation Tillage (Tct)•This practice involves the conversion of all tillage acres to conservation tillage that covers 30 percent or more of the soil surface with crop residue, after planting, to reduce soil erosion by water.•Practice limitations, concerns, or considerations

• No clear data concerning impacts of this type of conservation tillage on possible corn yield reduction compared with moldboard plowing. However, data suggests the yield reduction is minimal in most conditions.

• These reduced tillage practices are significantly less efficient than no-till at controlling soil erosion and surface runoff.



(% from baseline)



Convert all intensive tillage to conservation tillage

11 8.6

Scenario: Convert All Tilled Area to No-Till (Tnt)•This practice involves the conversion of all tillage to no-till, whereby the soil is left undisturbed from harvest to planting except for strips up to 1/3 of the row width made with the planter (strips may involve only residue disturbance or may include soil disturbance). This practice assumes approximately 70 percent or more of the soil surface is covered with crop residue, after planting, to reduce soil erosion by water.•Practice limitations, concerns, or considerations

• No-till results in lower corn yield than with moldboard or chisel-plow tillage. However, the yield reduction is less or none for other minimum tillage options that, on the other hand, are less efficient at controlling soil erosion and surface runoff.

• No-till or conservation tillage does not affect soybean yield significantly.



(% from baseline)


Phosphorus Management Convert all tillage to no-till 39 16.1

Scenarios: Plant a rye cover crop on all corn-soybean and continuous corn acres (CCa)Plant a rye cover crop on all no-till acres (CCnt)

• The cover crop in this practice/scenario is late summer or early fall seeded winter cereal rye. • Practice limitations, concerns, or considerations

• Impact on seed industry due to increased demand for rye seed.• Row crops out of production to meet rye seed demand.• New markets for cover crop seed production and establishment.• Livestock grazing.• Corn and soybean planting equipment designed to manage cover crops in no-till.• Negative impact on corn grain yield for species with spring growth.


Scenario

Phosphorus Reduction

(% from baseline)



Cover crops (rye) on all CS and CC acres

50 21.0

Cover crops on all no-till acres 4 4.8

Scenario: Establishing 35 foot buffers on all crop land (BF)• Buffers have the potential to be implemented adjacent to streams to intercept

overland flow and reduce P transport to receiving waters.



(% from baseline)


Edge-of-Field Establish streamside buffers (35 ft.) on all crop land

18 0.4

Scenario: Perennial Crops (Energy Crops) Replacing Row Crops (EC)•This scenario switches corn and soybean row crop land to energy crops at the amount equivalent to reach the total number of acres in pasture/hay in 1987 for each MLRA. Row crop acres were reduced proportionally for the corn-soybean rotation and continuous corn.•Practice limitations, concerns, or considerations

• Immediate limited market for perennials as energy crops.• Market shifts in crop prices and demand.



(% from baseline)


Land Use Change

Perennial crops (Energy crops) equal to pasture/hay acreage from 1987. Take acres proportionally from all row crop. This is in addition to current pasture.

29 5.9

Scenario: Grazed Pasture and Land Retirement Replacing Row Crops (P/LR)•This scenario increases the acreage of pasture and retired land to equal the pasture/hay and retired land acreage in 1987, which was the first time land was enrolled in the Conservation Reserve Program (CRP). Row crop acres were reduced proportionally for corn-soybean rotation and continuous corn.•Practice limitations, concerns, or considerations

• Market and price shifts due to reduced row crop production.• New markets for grass-fed beef.


Scenario


(% from baseline)


Land Use Change

Pasture and Land Retirement to equal acreage of Pasture/Hay and CRP from 1987 (in MLRAs where 1987 was higher than now). Take acres from row crops proportionally.

9 1.8

Scenario: Extended Rotation (corn-soybean-alfalfa-alfalfa-alfalfa) (EXT)•This scenario Increases the acreage of extended rotations by doubling the current amount of extended rotations (and reducing proportionally the corn-soybean rotation and continuous corn) in each MLRA.•Practice limitations, concerns, or considerations

• Reduce the amount of corn and soybean produced in Iowa.• Market shift in product production (more alfalfa) and associated price for crops produced.• Increased livestock production to feed alfalfa.• Market shift as little fertilizer N is needed for corn following alfalfa.


Scenario


(% from baseline)


Land Use Change

Doubling the amount of extended rotation acreage (removing from CS and CC proportionally)

3 1.8



(% from baseline)



Cover crops (rye) on all CS and CC acres

50 21.0

Convert all tillage to no-till 39 16.1

Convert all intensive tillage to conservation tillage

11 8.6

Cover crop (rye) on all no-till acres 4 4.8

Phosphorus rate reduction in those MLRAs that have high to very high soil test phosphorus

7 25.8

Injection within no-till acres 0.3 4.8



Scenario

Phosphorus Reduction(% from baseline)


Edge of Field Buffers (35 feet) on all crop land 18 0.4

Land Use Change

Perennial crops (Energy crops) equal to pasture/hay acreage from 1987. Take acres proportionally from all row crop. This is in addition to current pasture.

29 5.9

Pasture and land retirement to equal pasture/hay, and CRP acreage from 1987 (in MLRAs where 1987 was higher than now). Take acres from row crops proportionally.

9 1.9

Doubling the amount of extended rotation acreage (removing from CS and CC proportionally).

3 1.8


Combined Phosphorus Reduction ScenariosExamples!

Combined Nitrogen and PhosphorusReduction Scenarios

Examples!

Nitrate-N Phosphorus

Practice/Scenario % Reduction from baseline

NCS1Combined Scenario (MRTN Rate, 60% Acreage with Cover Crop, 27% of ag land treated with wetland and 60% of drained land has bioreactor)

42 30

NCS3Combined Scenario (MRTN Rate, 95% of acreage in all MLRAs with Cover Crops, 34% of ag land in MLRA 103 and 104 treated with wetland, and 5% land retirement in all MLRAs)

42 50

NCS8

Combined Scenario (MRTN Rate, Inhibitor with all Fall Commercial N, Sidedress All Spring N, 70% of all tile drained acres treated with bioreactor, 70% of all applicable land has controlled drainage, 31.5% of ag land treated with a wetland, and 70% of all agricultural streams have a buffer) - Phosphorus reduction practices (phosphorus rate reduction on all ag land, Convert 90% of Conventional Tillage CS & CC acres to Conservation Till and Convert 10% of Non-No-till CS & CC ground to No-Till)

42 29

Future NeedsPhosphorus management•Impacts on water quality of variable-rate fertilizer and manure P application technology•Development of commercially viable inorganic P fertilizer materials without N, so N and P management can be handled separately if needed•Field research based on large plots or catchments to study the impacts on P loss of alternative P management practices •Validation of the Iowa P index as an edge-of-field and watershed scale assessment tool

Future NeedsIn-field and edge-of-field soil and water conservation practices• An efficient method to estimate ephemeral gully erosion and delivery of sediment• Water quality data comparing extended rotations, pastures, and land retirement to a corn-soybean rotation• Cover crop management techniques adapted to Iowa to limit the risk to corn yield reduction including development of new cover crop species and varieties• Direct measurement of P loss from field edge and to surface water systems• Development and evaluation of management practices to reduce stream bank erosion and sediment delivery

Notes• Phosphorus assessment does not include stream

bed and bank contribution• It appears that nutrient strategy reduction goals

for P would be achieved under most scenarios meeting the goal for N

• If considered independently from N, P goals could be achieved at lower total cost with practices implemented on an MLRA basis

Summary• Process has identified practices that have greatest potential

for nutrient load reduction • Process has estimated potential field-level costs associated

with practice implementation and is also considering larger-scale economic impacts of practice implementation

• To achieve goals will require a combination of practices• N versus P requires different practices• Multiple benefits of practices will need to be considered• Knowing the starting point is still a challenge and knowing

what is being done on the land could (would) improve estimates of progress that can be made

Combined Phosphorus Reduction ScenariosScenario PCS11.Phosphorus is not applied to all agricultural acres (CS, CC, EXT, and pasture) where STP values exceed the optimum level (20 ppm). This practice would be used until the STP level reaches the optimum level.2.Conservation tillage is used on all CS and CC acres3.Streamside buffers are established on CS and CC acres.

Scenario PCS21.Phosphorus is not applied to 56% of agricultural acres (CS, CC, EXT, and pasture) where STP values exceed the optimum level (20 ppm). This practice would be used until the STP level reaches the optimum level.2.No-till is used on 56% of tilled CS and CC acres.3.Streamside buffers are established on 56% of CS and CC acres.

Scenario PCS31.Phosphorus is not applied to 53% of agricultural acres (CS, CC, EXT, and pasture) where STP values exceed the optimum level (20 ppm). This practice would be used until the STP level reaches the optimum level.2.No-till is used on 53% of tilled CS and CC acres.3.Cover crops are used on all no-till CS and CC acres.

Scenario PCS41.Phosphorus is not applied to 63% of agricultural acres (CS, CC, EXT, and pasture) where STP values exceed the optimum level (20 ppm). This practice would be used until the STP level reaches the optimum level.2.No-till is used on 63% of tilled CS and CC acres and cover crops established on no-till acres, except for MLRA 103 and 104.

Scenario PCS51.Phosphorus is not applied to 48% of agricultural acres (CS, CC, EXT, and pasture) where STP values exceed the optimum level (20 ppm). This practice would be used until the STP level reaches the optimum level.2.No-till is used on 48% of tilled CS and CC acres and cover crops established on no-till acres. 3.Streamside buffers are established on 48% of CS and CC acres

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Nutrient Reduction Strategy Phosphorus Science Team

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