changes in some soil phosphorus availability parameters as induced by phosphorus addition and soil...

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Changes in some soilphosphorus availabilityparameters as induced byphosphorus addition andsoil sorption propertiesRoberto Indiati a & Andrew N. Sharpley ba Istituto Sperimentale per la Nutrizionedelle Piante , via della Navicella 2, Rome,00184, Italyb USDA‐ARS , Pasture Systems and WatershedManagement Research Laboratory , CurtinRoad, University Park, PAPublished online: 11 Nov 2008.

To cite this article: Roberto Indiati & Andrew N. Sharpley (1997) Changesin some soil phosphorus availability parameters as induced by phosphorusaddition and soil sorption properties, Communications in Soil Science andPlant Analysis, 28:17-18, 1565-1578, DOI: 10.1080/00103629709369897

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COMMUN. SOIL SCI. PLANT ANAL., 28(17&18), 1565-1578 (1997)

Changes in Some Soil PhosphorusAvailability Parameters as Induced byPhosphorus Addition and Soil SorptionProperties

Roberto Indiatia and Andrew N. Sharpleyb

aIstituto Sperimentale per la Nutrizione delle Piante, via della Navicella 2,00184 Rome, ItalybUSDA-ARS Pasture Systems and Watershed Management ResearchLaboratory, Curtin Road, University Park, PA

ABSTRACT

Changes in agronomic and environmental soil phosphorus (P) availabilityparameters, i.e., Mehlich- and Olsen-extractable P, reversibly-adsorbed P,soil-solution P, and equilibrium-P concentration were determined followingequilibration of 13 Italian soils with five rates of P application (0, 12.5, 25,50, and 100 mg P kg-1 soil). Soil P availability as determined by each parameterincreased with added P. The relative change in soil P availability with addedP was a function of soil sorption index silicon (SI), according to the equationDP=(Padded)

a*exp(b+g*SI). This equation accounted for 94 to 98% of thevariance in soil-P availability. The inclusion of SI in a soil testing programmay increase the reliability in assessing both soil-P fertilizer requirementsand the vulnerability of a soil to P loss in runoff following land application offertilizer or manure P.

1565

Copyright © 1997 by Marcel Dekker, Inc.

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1566 INDIATI AND SHARPLEY

INTRODUCTION

Traditionally, soil testing consists of chemical extractions to assess the plantavailable nutrient status of a soil. Through common usage, the term "soil testing"includes interpretations, evaluations, and fertilizer recommendations based onresults of the chemical extractions and on several other considerations, such ascrop yield goal, and soil management and physical conditions. It is well knownthat the amount of fertilizer P required to increase the extractable-P concentrationin soil is dependant on soil chemical and physical characteristics (principally,type and amount of clay, iron and aluminum oxides, calcium carbonates, andorganic matter), as these, in turn, are the determining factors of soil P availabilityand sorption properties (Barrow, 1980; Larsen et al., 1965; Lopez-Hernandez andBurnham, 1974).

Recently, several authors have attempted to relate soil characteristics to theeffectiveness or plant recovery of fertilizer P in soil. In an incubation study,Johnston et al. (1991) used clay content to predict the quantity of P fertilizernecessary to raise the soil test value in a variety of soils from South Africa. Cox(1994) determined the effect of P applied on extractable P with time on Ultisolsvarying in clay content in field experiments and calculated the change in soil testP per unit of applied P as a function of clay content. Moughli et al. (1993) includeda soil P buffer-capacity parameter with extractable P levels to improve the accuracyof fertilizer P recommendations for Mediterranean soils.

In the last 15 years, however, more agricultural soils have tested "high" or"excessive" in P in several areas of Europe and the United States (Breeuwsmaand Silva, 1992; Sharpley et al , 1994). This has stimulated interest in using soilP tests to quantify the potential for non-point source inputs of agricultural P tosurface waters and acceleration of freshwater eutrophication. In fact, there iswidespread belief that assessing the potential for P loss from an individual site isa prerequisite for efficient, prioritized nutrient management programs (Sims, 1993 ;Sharpley, 1995). In this context, concern about the relationship between soil Pand degradation of surface water quality has created a demand for soil testinglaboratories to expand beyond their traditional scope and begin offering"environmental P tests", soil tests that measure other pools of P or that offer anenvironmental interpretation of the analytical results (Gartley and Sims, 1994).The objective of these tests would be to develop a P indexing procedure that canidentify soils, landforms, and management practices that are vulnerable tomovement in runoff.

As we move from agronomic to environmental concerns with soils containingP levels in excess of crop requirements, will current soil test methods to assessplant availability of P be suitable for estimates of P forms important toeutrophication? If not, are appropriate methods available? Environmental soiltests for P must estimate the bioavailability of soil, sediment, or runoff P to aquatic

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SOIL PHOSPHORUS AVAILABILITY PARAMETERS 1567

organisms and the long-term capacity of a soil to retain P against leaching. Theamount of P in soil, sediment, or runoff that is potentially available for algaluptake can be quantified by algal assays which require up to 100-day incubation(Miller et al., 1978). Thus, more rapid chemical extradants, such as sodiumhydroxide (NaOH) (Dorich et al., 1980), ammonium fluoride (NH4F) (Porcella etal., 1970), and ion exchange resin (Huett et al., 1979) have been used. Morerecently, Sharpley (1993) showed that the amount of P removed from runoffsediment by iron oxide-impregnated filter paper (Fe-oxide strip) was related(r2=0.92 to 0.95) to the growth of several algal species incubated with runoff asthe sole source of P. As the strips act as a P-sink, they simulate P removal fromsoil or sediment-water samples by plant roots and algae.

Thus, the Fe-oxide strip method has a stronger theoretical justification for itsuse over chemical extradants to estimate bioavailable P. The method may havepotential use as an environmental soil P test to identify soils liable to enrich runoffwith sufficient P to accelerate eutrophication. In addition to bioavailable P,environmental soil tests will need to estimate the long-term capacity of a soil toretain P against leaching. For example, estimates of the P-loading capacity of asoils receiving continual applications of P in manure or waste water, will aiddevelopment of sustainable management systems. This capacity is commonlyestimated by sorption isotherms that can be used to derive sorption maxima andequilibrium-P concentrations (EPCo) for soil horizons. The EPCo is defined asthe soluble-P concentration that is supported by a soil sample at which not netsorption or desorption occurs. This parameter identifies the amount and directionof changes between soluble and particulate P that occur during transport ofsediment in stream flow. Thus, it is useful in predicting whether soils and sedimentswill gain or lose P when in contact with runoff waters or in streams or lakes (Wolfet al , 1985).

However, the isotherms require equilibration of soil with a series of P solutionsof increasing P concentration, normally for 24 hours and are not well adapted toroutine soil testing laboratories. Bache and Williams (1971), and more recentlyMozaffari and Sims ( 1991 ), however, suggested that a single-point isotherm couldbe used to estimate the P adsorption maxima of soils with reasonable accuracy.The objectives of this research were: i) to determine the variation in some soil Pparameters after addition of five different rates of P to 13 Italian soils and ii) toinvestigate the relationship between such a variation and the soil P sorption index,SI. The studied P parameters were: soil P extractable by Mehlich (Mehlich, 1984)and Olsen (Olsen 1954) solutions, reversibly adsorbed P (Qo), soil solution P(Psol and equilibrium P concentration (EPCo). The Qo represents the maximumdesorbable P (Van De Zee et al., 1987) and can be used to compare available Pcontents for different soils. Mehlich-3 and Olsen available P, and Qo are consideredsoil P quantity parameters, whereas Psol and EPCo represent soil P intensityparameters.

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TABLE 1. Selected soil properties. Soil classification units from the FAO World Map(FAO/UNESCO, 1975).

Soil

code

2093852870281374965263363345122259

Soil

unit

RegosolFluvisolFluvisol

Regosol

LuvisolLuvisolRegosolLuvisol

CambisolFluvisolFluvisolLithosolRegosol

PH

(H2O)

6.77.56.67.06.77.76.67.77.86.16.27.16.8

Clay

%

920910163118243023355167

Organ.C%

1.042.305.83

3.460.201.262.620.981.341.281.082.320.55

CDB-AI2O3"

%

0.050.140.38

0.28

0.380.470.430.330.360.901.130.821.14

CDB-Fe2Os*

%

0.570.890.79

0.54

1.031.611.101.802.162.863.293.835.19

TotalCaCOj

%

0.015.50.00.00.02.20.04.326.20.00.00.00.0

Slb

2.13.56.68.09.013.115.819.623.428.036.044.250.0

Olsen-P

mg kg'1

11.512.321.010.15.67.612.04.85.66.510.511.935.3

•Iron and aluminum oxides extracted with citrate-bicarbonate-dithionite solution.bSoil sorption index.

MATERIALS AND METHODS

Thirteen soils (surface horizons) representing a wide range in physical andchemical properties and P-adsorption capacity were selected from several locationsin the Southern Latium area of Italy, air dried, and screened through a 2-mm sieve(Table 1). Soil pH was determined by using a glass electrode at a 2.5:1 water tosoil ratio (v/w); particle size analysis following dispersion with hexametaphosphate(Day, 1965); carbonate content by a Dietrich-Frhulig calcimeter; and organiccarbon by the wet oxidation procedure (Raveh and Avnimelech, 1972). Free iron(Fe) and aluminum (Al) oxides were extracted with the citrate-dithionite-bicarbonate solution, the Fe and Al in solution determined by atomic absorptionspectrometry (Mehra and Jackson, 1960).

Soil Phosphorus Incubation

Soils were incubated with and without P [0, 12.5, 25, 50, and 100 mg P aspotassium dihydrogen phosphate (KH2PO4) kg1 of soil] for 90 days at roomtemperature (20±2°C) in PVC capsules open to the air. Soils were rewetted tofield capacity twice a week. Soils were then air dried, sieved (2-mm), and analyzed

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for Mehlich (M3)-extractable P and Olsen-extractable P, reversibly-adsorbed P,soil solution P, and equilibrium P concentration.

Soil Phosphorus Availability

Extractable P was determined by: i) Mehlich 3 extraction (mixture of 0.2MCHjCOOH, 0.25MNH4NO3,0.015M NH4F, 0.013M HNO,, and 0.001M EDTA),for five minutes at a soil to solution ratio of 1:10 (w/v) (Mehlich, 1984) and ii)Olsen solution (0.5M NaHCO3 solution at pH=8.5) with 30 minutes extraction ata soil to solution ratio of 1:20 (W/v) (Olsen et al., 1954). For the soil solution P(Psol), one gram of soil was shaken with 5 mL distilled water for 15 minutes,allowed to stand for one hour, and shaken again for five minutes. Aftercentrifugation and filtration through ashless filter paper, the solution was analyzedfor P(Wolt, 1994).

Iron Oxide-impregnated Strip Phosphorus Extraction

For the determination of readily reversible P (Qo), one g of soil, 40 mL 0.01MCaClj solution and four Fe-oxide strips were shaken for 20 hours (Van der Zee,1987). At the end of the extraction, the strips were removed, rinsed free foradhering soil particles, and air dried. Phosphorus retained on the strips wasremoved by shaking the strip with 40 mL 0.1M sulfuric acid (H2SO4) for one hour(Menon et al., 1989) and analyzed.

Iron-oxide impregnated strips were prepared by immersing filter paper circles(15-cm diameter, Whatman No. 541) in a 10% (w/v) solution of ferric chloride(FeCl36H2O). The paper circles were then air dried and immersed in 2.7Mammonium hydroxided (NH4OH) solution to convert FeCl3 to Fe-oxide. Immersionin NH4OH was carried out as rapidly as possible to avoid uneven oxide depositionon the paper (Lin et al., 1991). After the paper circles were air dried, they werecut into strips 10 cm by 2 cm and stored for later use.

Phosphorus Sorption Studies

Equilibrium P concentration was determined by shaking one gram of soil in 20mL 0.02M potassium chloride (KC1) solution containing from 0 to 10 mg P L1

for 24 hours at 25°C. Two drops of toluene were added to minimize microbialactivity. After centrifugation and filtration, P concentration in solution wasdetermined and the amount of P sorbed was calculated as the difference betweenadded and solution P. The EPCo was calculated as the intercept P versus solutionP relationship (White and Beckett, 1964; Taylor and Kunishi, 1971). The amountof P sorbed, X (mg-100 g1), from one addition of 1.5 g P kg"1 of soil in a 0.02MKC1 solution was determined after shaking for 24 hours at a solution to soil ratioof 20:1 (Bache and Williams, 1971). The P sorption index (SI) was calculatedusing the quotient XlogC1, where C is the solution P concentration expressed as

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TABLE 2. Regression equation constants for the relationships' of Mehlich3 extractable-P (M3-P), Olsen-P, reversibly-adsorbed P(Qo), soil P solution (PÍO/) and equilibrium P concentration (EPCo) versus added P.

soil

code

209

385

28

70

281

374

96

526

336

33

45

122

259

M3-P(mgkg-1)

a

9.5

25.6

40.8

18.2

8.9

12.1

11.6

1.6

2.1

3.4

4.2

4.5

12.2

b

0.72

0.62

0.61

0.56

0.34

0.39

0.29

0.22

0.17

0.12

0.09

0.07

0.10

R2

0.999

0.998

0.999

0.998

0.998

0.993

0.987

0.983

0.986

0.974

0.999

0.979

0.988

Olsen-P (mg kg1 )

a

11.4

11.6

23.1

8.8

9.9

25.5

11.8

5.7

4.8

6.8

10.6

10.8

36.4

b

0.47

0.44

0.29

0.33

0.34

0.29

0.26

0.22

0.21

0.21

0.17

0.15

0.15

R2

0.994

0.993

0.982

0.987

0.998

0.996

0.999

0.990

0.985

0.998

0.967

0.952

0.982

Qo (mg kg'1

a

29.6

21.9

35.7

15.4

4.3

8.3

27.4

10.9

13.1

25.3

15.3

23.4

46.0

b

0.53

0.51

0.46

0.40

0.28

0.29

0.26

0.28

0.21

0.17

0.15

0.18

0.14

)

R2

0.997

0.995

0.999

0.997

0.983

0.985

0.990

0.996

0.992

0.996

0.996

0.997

0.995

Psol(mgL-1)

a

0.109

0.019

0.237

0.021

0.084

0.045

0.026

0.010

0.011

0.018

0.014

0.007

0.025

b

0.0220

0.0160

0.0096

0.0045

0.0024

0.0019

0.0021

0.0012

0.0006

0.0007

0.0003

0.0002

0.0001

R2

0.982

0.970

0.976

0.913

0.967

0.938

0.880

0.979

0.927

0.996

0.987

0.991

0.995

EPCo(mgL-')

a

-0.016

0.018

0.094

-0.012

0.003

0.016

0.035

0.010

0.005

0.002

0.021

0.024

0.034

b

0.0150

0.0140

0.0071

0.0037

0.0015

0.0012

0.0004

0.0004

0.0004

0.0002

0.0001

0.0001

0.0000

R2

0.970

0.979

0.978

0.891

0.852

0.939

0.996

0.979

0.879

0.996

0.871

0.991

0.986

'Equation is: P = a + bX, where X is the amount of added P. tfl

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HmolesL1. The concentration of P in solution was measured by the ammoniummolybdate method with ascorbic acid as the reducing agent (Murphy and Riley,1962). All determinations were made in duplicate and results given as means.Data processing and statistical analyses were performed with the aid of theStatgraphycs Statistics Package software.

RESULTS AND DISCUSSION

Some physical and chemical characteristics of the studied soils are reported inTable 1. The selected soils ranged widely in their physico-chemical parameterswhich is reflected in the variation in SI. Data of the studied soil P parametersfollowing the equilibration with the five rates of fertilizer P are shown for all soilsin Table 2. Data are expressed in terms of the coefficients of fitted regressionequations for the change with P addition.

Effect of Added Phosphorus on the Soil Phosphorus Parameters

The relationship between added P and M3-P, Olsen-P, Qo, Psol, and EPCo waslinear for all soils, indicating that for the P applications used (0 to 100 mg-kg1

soil), the proportion of added P remaining extractable was quite independent ofrate of P added (Figure 1 and Table 2). Therefore, the change in soil P parameterswith P addition could be described for each soil by: P.=aX + b., where P. representsthe Pi studied parameter and X the amount of added P, and ai (the level of Piparameter when no P was added) and b. (fractional amount of added P remainingin the extractable P. form) are constants for each parameter. The determinationcoefficients (R2) for the linear regression equation ranged from 0.97 to 1.00 forM3-P, from 0.95 to 1.00 for Olsen-P, from 0.98 to 1.00 for Qo, from 0.88 to 1.00for Psol, and from 0.87 to 1.00 for EPCo (PO.001). A slight deviation fromlinearity, especially for Psol and EPCo, was shown by the lowest adsorptioncapacity soils when P was added at the maximum level (100 mg P kg"1 soil).

The results are very similar to those described by Kovar and Barber (1988) ina study of the effect of P addition on anion-exchangeable P and soil-solution P for33 soils as a function of the P sorption characteristics. They found a curvilinearrelation between soil-solution P and P added (P = aXc *d; where X was the amountof added P and c was a constant indicating the degree of curvilinearity for eachsoil). However, Kovar and Barber (1988) equilibrated soils with higher rates of P(0 to 655 mg P kg1 soil) than were used in this study.

Effect of Silicon on the Change in Soil Phosphorus Parameters FollowingPhosphorus Addition

After soil P equilibration, soil P availability increased for all soils. At themaximum P rate (100 mg P kg"1 soil), M3-P increased in a range varying from 7.4to 71.6 mg P kg1, Olsen-P increased from 15.0 to 47.0 mg P kg1, Qo increased

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20 40 60

Padded (mgkg-1)20 40 60 80 100

Padded (mgkg-1)

0.043

0.036

0.000

, _ 0.025i

O.CED

0.015

0.010

0.005

Q003

-»-Psol-»-EPCo

Soil 259

20 40 80 80

Padded (mgkg-1)

2D 4) 80 80 10O

Padded (mgkg-1)

FIGURE 1. Changes in Mehlich-3 extractable P (M3-P), Olsen-P, reversibly-adsorbed P(Qo), soil P solution (Psol), and equilibrium P concentration (EPCo), with added P for twosoils contrasting in P retention power.

from 13.7 to 53.6 mg P kg1, whereas DPsol ranged from 0.010 to 2.207 mg P I/1,and DEPCo ranged from 0.004 to 1.450 mg P L1. However, the effectiveness ofapplied P to that change was different and specific for each soil, being dependenton the soil P adsorption properties. This is shown in Figure 1 for two soilscontrasting in P retention power: soil 209 with an SI value of 2 and soil 259 withan SI of 50. For all soils, soil SI influenced the change in P availability withadded P (Figure 2). The effect of buffering of soil P availability by soil sorptioncapacity with added P is evident. For the same level of added P, P availabilitychanges were larger for low SI soils and became negligible for high SI soils (Figure2).

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o.o

0.700

0.600a.

lit o

f add

edp

p

3 0.300I^ 0.200

0.100

0.000

*

*

.... M3-P

••- Olsen-P

- ^ Q o

A -

i i i i

10.0 20.0 30.0Soil SI

40.0 50.0

Q.

s

o,

0.01 SX

o.oieoo

0.01400

0.01200

0.010X

0.00800

0.006X

0.004X

0.002X

0.000000.0 10.0 20.0 30.0

Soil SI40.0

1

- - Psol

—EPCo

50.0

FIGURE 2. Changes per unit of added P in Mehlich-3 extractable P (M3-P), Olsen-P,reversibly-adsorbed P (Qo), soil P solution (PÍO/), and equilibrium P concentration (EPCo),as a function of soil sorption index (SI).

The relationship between the changes of the soil P parameters per unit of addedP and soil SI can be conveniently expressed by the following equations:

DM3-P = -0.429 * exp(-0.048*SI)DOlsen-P = -0.948 * exp(-0.021 * SI)Dqo = -0.743 * exp(-0.028*SI)Dpsol = -4.432 * exp(-0.l00*SI)DEPCo = -4.882 * exp(-0.l 12* SI)

R2 = 0.88(P<0.00l)R2 = 0.89R2 = 0.87R2 = 0.90R2 = 0.84

Cox (1994) found for 14 soils sampled from North Carolina and Brazil anexponential decrease [Y=exp(-aX)] in the change per unit of added P in M3-Pfrom 0.83 at 8% clay to <0.2 at 68% clay. The observed coefficient (a=-0.040)expressing the change in M3-P with clay is similar to the coefficient (a=-0.048)calculated for the change in M3-P per unit of P applied and soil SI which impliesa relationship between clay and SI for a wide range of soils.

Effect of Soil Silicon and Added Phosphorus on the Change in Soil PhosphorusParameters

Changes in soil P parameters as induced by several rates of fertilizer P and soilSI are shown in Figure 3, relative to M3-P and Psol. The effect of soil SI andadded P on the variation in P availability are accounted for by a mathematicalmodel of the type:

[1]

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9319 ana

FIGURE 3. Changes in Mehlich-3 extractable P (AM3-P), and soil P solution (ARso/) asa function of soil sorption index (SI), and added P.

where: P¡ is the soil P parameter considered for a given added P, P¡ 0 is thecorresponding value of the parameter when no P is added, X is the amount ofadded P expressed as mg P kg1 soil, Y is the soil sorption index, SI, and a, b, andg are constants specific for each soil P parameter. For M3-P, Olsen-P, and Qo thechanges are expressed in mg P kg1 soil, whereas for Psol and EPCo the dimensionunits are mg P I/1. The constant values and coefficient of determination of Equation[1] are given in Table 3.

TABLE 3. Constant values and determination coefficients for the equation relatingchanges in Mehlich-3 extractable P (M3-P), Olsen-P, reversibly-adsorbed P (Qo), soil Psolution (Psol), and equilibrium P concentration (EPCo), with added P and soil sorptionindex (SI): [AP = (P addedyV*"*5"] (Equationl).

Soil P parameter

M3-P

Olsen-P

Qo

Psol

EPCo

a

1.087

1.014

1.057

1.327

1.477

P

-0.604

-0.911

-0.861

-4.800

-5.881

Y

-0.064

-0.028

-0.038

-0.224

-0.224

R2

0.97

0.94

0.96

0.98

0.96

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TABLE 4. Absolute and percentage decrease in soilsorption index (SI), following P addition of 100 mgP kg"1 soil.

soil

2093852870281374965263363345122259

SI

2.13.56.68.09.013.115.819.623.428.036.044.250.0

ASI

1.00.92.41.42.31.91.61.51.20.53.52.51.9

A SI/SI *100

482636182615108521064

The constant a is related to the degree of linearity for the relationship betweenthe variation in the soil P parameters and added P, whereas the constant b and gare related to the rate of decrease of such changes with soil SI. From 94 to 98% ofthe variance of the model was accounted for by the variance in the independentvariables. Soil SI is a not time consuming determined index and can be determinedunder routine soil analyses, and in addition, it is an inherent soil property. Changesin the SI with added P are negligible and not significant up to rates of 50 mg P kg-1

soil. For a P application of 100 mg P kg"1 soil (equivalent to about 550 kg P2O5

ha1, considering a soil bulk density of 1.2 g cm3 and a broadcast P fertilizerincorporation to 20 cm of soil depth), a significant (P<5%) decrease in the soil SIwas observed. Such a decrease ranged from 0.5 to 3.5 mgkg1 , with percentagevariations between 2 and 48%, the highest changes being for the lowest SI soils(Table 4). The inclusion of a soil sorption index, SI, in soil testing programs mayimprove the prediction both of soil P fertilizer requirement and soil vulnerabilityto P movement during runoff as well as the potential risk for P pollution of surfacewaters following a P addition to these soils.

ACKNOWLEDGMENTS

The assistance of Dr. U. Neri in the statistical and mathematical computations isgratefully appreciated. This research was partially supported by the Italian Ministryof Agricultural, Food and Forestry Resources (PANDA Project Subproject 3, Seriesl,No. 15).

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changes in some soil phosphorus availability parameters as induced by phosphorus addition and soil...

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