Modeling phosphorus in the environment - Chapter 13 pptx

Critical source areasare dependent on the coincidence of transport i.e., surface runoff, erosion, andsubsurface flow and source factors i.e., soil, fertilizer, manure as influenced bysit

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Phosphorus Indices, Best Management Practices, and Calibration Data

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Jennifer Weld

The Pennsylvania State University, University Park, PA

Andrew N Sharpley

U.S Department of Agriculture-Agricultural Research Service, University Park, PA

CONTENTS

13.1 History of Development 301

13.1.1 Background 301

13.1.2 Development 304

13.2 Index Framework 306

13.2.1 Parameters 306

13.2.2 Calculating a Phosphorus Index Value 322

13.3 Inclusion of Best Management Practices Factors 323

13.3.1 Examples of Index Site Assessment and Interpretation 323

13.4 Integration of P Indices into Existing Models or Nutrient Management Planning Software 325

13.5 Field Testing 326

13.6 Availability of P Indices 327

13.7 Conclusions 327

References 328

13.1 HISTORY OF DEVELOPMENT

In response to mounting water-quality concerns, many states have developed guidelines for land application of phosphorus (P) and watershed management based

on the potential for P loss in agricultural runoff (U.S Department of Agriculture and U.S Environmental Protection Agency 1999) These actions have been spurred,

in part, by a federal initiative in which the U.S Department of Agriculture (USDA) and U.S Environmental Protection Agency (USEPA) created a joint strategy to implement Comprehensive Nutrient Management Plans (CNMPs) on animal feeding operations with a national deadline of 2008

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Under the USDA–USEPA joint strategy, USDA’s Natural Resources vation Service (NRCS) is charged with implementing a new nutrient managementpolicy As a result, the NRCS planning standard addressing nutrient management(590 standard), which was based on nitrogen (N), has been rewritten to include aP-based planning standard In each state, NRCS state conservationists must decidewhich of three P-based approaches will be used in nutrient management planningpolicy These approaches are agronomic soil test P (STP) recommendations, envi-ronmental STP thresholds, or a P Index to rank fields according to their vulnera-bility to potential P loss States have already selected the P-based strategies fortheir 590 standard The P Index has been selected for most states’ 590 standards(Figure 13.1).

Conser-Reasons for widespread adoption of the P Index approach are that other Pmanagement options (i.e., agronomic and environmental STP) are inflexible, overlyrestrictive, and do not account for the critical role of transport mechanisms indetermining a site’s P loss potential Generally, most P exported from agriculturalwatersheds derives from only a small part of the landscape during a few relativelylarge storms, where hydrologically active areas of a watershed contributing surfacerunoff to stream flow are coincident with areas of high soil P or recent manureapplications Even in regions where subsurface flow pathways dominate P trans-port (e.g., some areas of the coastal plains), areas contributing P to drainage watersare localized to soils with high soil P saturation and hydrologic connectivity to thesurface drainage network

FIGURE 13.1 Summary of P management strategies adopted by state USDA-NRCS

agen-cies for revision of the 590 nutrient management practice standard (From Sharpley, A.N.

et al 2003 Journal of Soil and Water Conservation 58: 137–152 With permission)

Alaska and Hawaii

adopted the P Index

P Index

Soil test crop response

P Index and/or environmental P threshold or soil test crop response

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Phosphorus Indices 303

To be effective, risk assessment must consider critical source areas within awatershed that are most vulnerable to P loss in surface runoff Critical source areasare dependent on the coincidence of transport (i.e., surface runoff, erosion, andsubsurface flow) and source factors (i.e., soil, fertilizer, manure) as influenced bysite management (Table 13.1) Transport factors mobilize P sources, creating path-ways of P loss from a field or watershed Source and site management factors aretypically well defined and reflect land-use patterns related to soil P status, mineralfertilizer and manure P inputs, and tillage

TABLE 13.1

Factors Influencing P Loss from Agricultural Watersheds and Their Impact

on Surface Water Quality

Transport

Erosion Total P loss strongly related to erosion.

Surface runoff Can carry soluble P released from soil or other P sources.

Subsurface flow In sandy, organic, or P-saturated soils, P can leach through the soil

Phosphorus can also move through the soil by preferential flow through macropores The presence of artificial drainage can capture this subsurface flow and move it directly to surface water Soil texture Influences relative amounts of surface and subsurface flow occurring Irrigation runoff Improper irrigation management can induce surface runoff and

erosion of P.

Connectivity to stream The closer the field to the stream, the greater the chance of P reaching it Channel effects Eroded material and associated P can be deposited or resuspended

with a change in stream flow Dissolved P can be sorbed or desorbed

by stream channel sediments and bank material and be taken up by

or mineralized from biota.

Proximity of P-sensitive water Some watersheds are closer to P-sensitive waters than others

(i.e., point of impact).

Sensitivity P input Shallow lakes with large surface area tend to be more vulnerable to

Application method P loss increases in the order: subsurface injection; plowed under; and

surface broadcast with no incorporation.

Application timing The sooner it rains after P is applied, the greater the risk for P loss.

Source: Adapted from A.N Sharpley, J.L Weld, D.B Beegle, P.J.A Kleinman, W.J Gburek, P.A Moore, and G Mullins, Journal of Soil and Water Conservation 58, 137–152, 2003.With permission

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The P Index was originally developed to identify the vulnerability of agriculturalfields to P loss (Lemunyon and Gilbert 1993) The original Index accounted for andranked transport and source factors controlling P loss in surface runoff from a givensite Each site factor affecting P loss was weighted, assuming that certain factorshave a different effect on P loss than others A P Index value, reflecting site vulner-ability to P loss, was determined by selecting the rating value for each site factor,multiplying that value by the appropriate weighting coefficient, and summing theweighted products of all factors.

Since its inception, three major changes have been introduced to many revisedversions of the P Index First, source and transport factors are related in a multipli-cative rather than additive fashion to better represent actual site vulnerability to Ploss (Gbuerk et al 2000) For example, if surface runoff does not occur at a particularsite, its vulnerability should be low regardless of the soil P content In the original

P Index, a site’s risk could be ranked as very high based on site-management factorsalone, even though no surface runoff or erosion occurred (Lemunyon and Gilbert1993) On the other hand, a site with a high potential for surface runoff, erosion, orsubsurface flow but with low soil P has a low risk for P loss, unless P as mineralfertilizer or manure is applied

Second, an additional transport factor reflecting distance from the stream hasbeen incorporated into the P Index The contributing distance categories in revised

P indices are based on hydrologic analysis that considers the probability, or risk,

of occurrence of a rainfall event of a given magnitude resulting in sufficient runoff

to potentially transport P offsite

The third major change in Index formulation has been the use of continuous,open-ended parameter scaling for erosion, STP, and P application rate, as eitherfertilizer or manure This enables indices to better address the effect of the very higherosion and STP values of the original P Index on P loss potential and to avoidhaving to subjectively quantify these categories Finally, the open-ended scaling oferosion, STP, and P rate avoided the unrealistic situation where a one- or two-unitincrease in any of these parameters could change risk category and dramaticallyalter P Index rating and its interpretation

Though the P Index concept has been broadly adopted, its development from aconcept into a field-assessment tool has followed several different trends throughoutthe United States The variations reflect not only regional differences in P transportbut also philosophical differences as to how P risk from a site should be assessedusing a P Indexing approach Current research and field evaluations play a significantrole in the continued modification of P indices to best fit and address regional andstate conditions This has resulted in many states incorporating unique factors thatextend beyond the scope of the three previously described P Index modificationsadopted by many revised P indices

As mentioned already, computation of final P Index values can be additive, asoriginally proposed by Lemunyon and Gilbert (1993), or multiplicative, as proposed

by Gburek et al (2000) (Table 13.2 and Table 13.3) Seventeen of the reviewedindices use the multiplicative approach, whereas 20 use the additive approach

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Phosphorus Indices 305

TABLE 13.2

The P Index Approach Using Pennsylvania’s Index Version 1 as an Example

PART A: SCREENING TOOL

Evaluation Category Soil Test P (Mehlich-3) > 200 mg P kg−1 If yes to either factor then proceed

to Part B Contributing Distance < 150 ft

PART B: SOURCE FACTORS Soil test (Mehlich-3P) Soil Test P (mg P kg−1)

Soil Test P Rating = 0.20 a Soil Test P (mg P kg−1)

Fertilizer P rate Fertilizer P (lb P2O5/acre)

Manure P rate Manure P (lb P2O5/acre)

P source

application

method

0.2 Placed or

injected 2"

or more

deep

0.4 Incorporated

<1 week

0.6 Incorporated > 1 week or not incorporated April to October

0.8 Incorporated >1 week

or not incorporated November to March

1.0 Surface applied

to frozen or snow covered soil

Fertilizer Rating = Rate × Method

Manure P

availability

0.5 Treated manure/Biosolids

0.8 Dairy

1.0 Swine

Manure Rating = Rate × Method × Availability Source Factor = Soil Test P Rating + Fertilizer Rating + Manure Rating PART C: TRANSPORT FACTORS

Runoff

potential

0 Very low

2 Low

4 Medium

6 High

8 Very high Subsurface

drainage

0 None

1 Some

2 a Patterned Contributing

applies to distance

< 150 ft

1.0 Grassed waterway or none

1.1 Direct connection: applies to distance

> 150 ft

Transport Factor = Modified Connectivity × (Transport Sum/22)

Phosphorus Index Value = 2 × Source Factor × Transport Factor

a Or rapid permeability soil near a stream.

Source: Adapted from J.L Weld, D Beegle, W.J Gburek, P.J Kleinman, and A.N Sharpley 2003 The Pennsylvania Phosphorus Index: Version 1, Extension PUBLICATIONS.CAT US 180 5m3/03ps

4591 With permission.

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In addition to using the multiplicative approach, the Pennsylvania P Index variesthe transport factor from 0 to 1 (Table 13.2)

The original P Index outlined an approach to identify sites with a high ability to P loss based on evaluation of a variety of P source and transport factors.Most states (44 of 47) (Table 13.4) have maintained this original approach and haveexamined site vulnerability to P loss However, in response to questions regardingthe relationship between P Index values and actual P loadings, several states havetaken a different approach This approach adopted by Arkansas, Georgia, and Iowauses source, transport, and management factors common to most other indices,but instead of estimating a vulnerability to or potential for P loss, calculates anestimated P loss that is used either directly or converted to a relative PI Indexvalue (Table 13.4)

vulner-13.2 INDEX FRAMEWORK

P indices include assessments of both source management and transport factors tofacilitate the assessment and identification of critical source areas These factorshave been chosen because they determine P loss in most cases (Table 13.1)

TABLE 13.3

General Interpretations and Management Guidance Using Pennsylvania’s

P Index

P Index Value Rating General Interpretation Management Guidance

< 59 Low If current farming practices are

maintained, there is a low risk of adverse impacts on surface waters.

N-based applications

60 –79 Medium Chance for adverse impacts on surface

waters exists, and some remediation should be taken to minimize P loss.

N-based applications

80 –100 High Adverse impact on surface waters

Conservation measures and P management plan are needed to minimize P loss.

P application limited

to crop removal of P

> 100 Very high Adverse impact on surface waters All

necessary conservation measures and P management plan must be implemented

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Phosphorus Indices

TABLE 13.4

P Index Approaches and Modifications

FIV based on Mehlich-3 P

FIV based on Mehlich-1 P Application

rate

Waste water volume Application

Injection Incorporation Surface applied

Incorporation Surface applied

Irrigation Incorporation Surface applied

Time to incorporation

Season applied Time to incorporation

surface waters

feeding management

Organic P source availability Grazing intensity

Polyacrylamides Cover crops

Organic P source availability

(continued)

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Modeling Phosphorus in the Environment

Water (RUSLE) Wind (WEQ) Irrigation (QS value)

Soil permeability class

Field slope

Curve number Field slope Precipitation

Field slope

Hydrologic soil group Field slope Artificial drainage Subsurface

drainage/

flooding

Underground outlet

systems

Water table depth Leaching rating

Leaching potential Soil properties

Contour buffer strips

Vegetated buffer width

Wetlands Buffer strip Detention/treatment area

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Phosphorus Indices Receiving

Determination Additive Risk assessment Additive Risk assessment AdditiveRisk assessment MultiplicativeLoss assessment Additive Risk assessment MultiplicativeRisk assessment Multiplicative Risk assessment

Reference

Cabrera et al

(2002)

NRCS (2002a)

NRCS (2004a)

Davis et al.

(2004b)

NRCS (2001c)

NRCS (2000b) Source Factors

Mehlich-3

Bray P-1 Mehlich-3 P Olsen P

recommended rate

Application

method

Injection Incorporation Sprinkler application Surface applied

Injection Incorporation Surface applied Application

timing

Incorporation before or after a runoff event

Time to planting Time to incorporation

Season applied Cover at application

sources

practices Tillage

factors for organic P sources

(continued)

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Reference

Cabrera et al

(2002)

NRCS (2002a)

NRCS (2004a)

Davis et al.

(2004b)

NRCS (2001c)

NRCS (2000b) Transport Factors

Bioavailability factor

Ephemeral Classic gully

Water (RUSLE) Sprinkler Furrow irrigation

Land cover percent

Water (RUSLE)

Surface runoff

class

Curve number Location

Hydrologic soil group

Curve number Precipitation

Soil permeability class Field slope

Hydrologic soil group Field slope

Subsurface

drainage/flooding

Leaching curve number Percolation index Depth to water table

Discharge into a tile inlet

Tile drainage Field slope Soil texture Precipitation

Depth to water table Artificial drainage

Edge of field distance

to surface water

waterway or surface drain outlet

Buffer presence and width

width

Vegetative buffer width

Receiving water

priority

watershed County location

Ranked very low to very high

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Phosphorus Indices

Index Value

Determination

Multiplicative Soluble, runoff, particulate, and leachate assessment

No average PI value Individual risk factors evaluated

by field

Additive Erosion, runoff, and subsurface drainage assessments

Multiplicative Risk assessment

Additive Risk assesssment

Reference

NRCS (2001d)

Coale (2000)

Grigar and Lemunyon (1998)

NRCS (2001e)

NRCS (2000c)

Fasching (2001) Source Factors

Mehlich-1 P

Olsen P

Mississippi soil test P method

Olsen-P (High pH) Bray P-1 (Low pH)

Application

method

Injection Incorporation Surface applied Application

timing

Time to planting

handle manure nutrients

Organic P source availability

Manure N lb/ac/yr

N leaching index Soil management group

(continued)

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Reference

NRCS (2001d)

Coale (2000)

Grigar et al.

(1998)

NRCS (2001e)

NRCS (2000c)

Fasching (2001) Transport Factors

class

class Field slope

Subsurface

drainage/flooding

Depth to water table

Presence of surface water

Distance to surface water

concentrated surface water flow

width

Vegetated buffer width Application setbacks

Presence of a 100-ft filter strip

Maryland Clean Water Action Plan classification

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Field decision matrix with no PI value

Reference

Kucera (2000)

NRCS (2001f)

NRCS (2001g)

Bray P-1 (Low pH)

based on Mehlich-3 P

Olsen-P (High pH) Bray P-1 (Low pH)

Fe-P soil fraction Field slope

(continued )

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Reference

Kucera (2000)

NRCS (2001f)

NRCS (2001g)

Curve number Field slope

Presence of concentrated flow

Estimated runoff (in.yr)

Subsurface

drainage/flooding

Flooding frequency

Impact of artificial drainage Estimated subsurface flow (in./yr)

Watershed

Contributing

distance

Distance to concentrated surface water flow

application to surface water

Edge of field distance

to a stream or lake

Flow distance to a blue line stream

Particulate and dissolved P risk assessments

Particulate, soluble, leachate, and source

P risk assessment

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Phosphorus Indices

Reference

NRCS (2002b)

NRCS (2002c)

NRCS (2001h)

NRCS (2001i)

Weld et al.

(2003)

NRCS (2001j) Source Factors

Bray P-1 (Low pH) Mehlich-3 P

Bray P-1 (W Oregon)

Application

method

Incorporation Surface applied Application

timing

Cover at application Time to incorporation

no-till; contour buffer strips

Water (RUSLE) Soil surface loss potential

Water (RUSLE), sprinkler irrigation, furrow irrigation, wind

Field slope Depth of soil Rock size and cover

Field slope

Field slope Presence of surface runoff

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