How does the Hedley sequential phosphorus fractionation reflect impacts of land use and management on soil phosphorus: A review

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J. Plant Nutr. Soil Sci. 2009, 172, 305–325 DOI: 10.1002/jpln.200800223 305

Review Article

How does the Hedley sequential phosphorus fractionation reflect impactsof land use and management on soil phosphorus: A reviewWakene Negassa1 and Peter Leinweber1*

1 University of Rostock, Institute of Land Use, Justus-von-Liebig Weg 6, 18051 Rostock, Germany

AbstractThe Hedley sequential-phosphorus (P)-fractionation method has been used in many countriesto study the effects of land-use and management systems on soil P. Many data sets have beenobtained but collectively never have been considered or to goal topic reviewed. Therefore, theobjectives of this review were to compile and systematically evaluate these data. The data gen-erated over many years were grouped into temperate, and subtropical and tropical soils of differ-ent land use and duration of soil-management studies. In natural ecosystems, vegetation typesand composition and percent of vegetation covers substantially affected all P fractions with pro-nounced impacts on the labile and moderately labile P. In short-term studies (£ 10 y), changes inthe labile and moderately labile inorganic P (Pi) fractions were detected when more P (e.g., byfactor 5) was applied than commonly recommended for agricultural crops. However, without Papplication the changes in all P fractions were subtle in temperate soils, but declines were signif-icant in labile and moderately labile P in subtropical and tropical soils. In both temperate and tro-pical climates, medium (10–25 y) and long-term (>25 y) cultivation without P applicationdepleted all P fractions, whereas most of P fractions increased with continuous P application,regardless of the amount and source of P. Synthesis of data resulted in multiple-regression func-tions which described differences in labile and moderately labile P fractions as function of differ-ences in amount of P application and duration of the experiments. Moreover, the correlationanalysis also showed strong association among most of the P fractions. Current limitations indata interpretation of Hedley fractionation can be overcome by the application of 31P nuclear–-magnetic resonance (NMR) and X-ray absorption near-edge fine-structure (XANES) spectro-scopy.

Key words: soil phosphorus / P speciation / labile P / moderately labile P / stable P / temperate soils /tropical soils / 31P NMR / P XANES

Accepted November 9, 2009

1 Introduction

Soil P exists in inorganic and organic compounds that rangefrom ions in solution to very stable inorganic and organiccompounds. The inorganic P (Pi) compounds mainly couplewith amorphous and crystalline forms of Al, Fe, and Ca. Theorganic (Po) compounds are associated with rapidly to slowlydecomposable organic molecules such as nucleic acids,phospholipids, sugar phosphates, inositol phosphates, andrecalcitrant humic substances (Hedley et al., 1982; Tiessenand Moir, 1993; Reddy et al., 1999). Different sequential-P-fractionation schemes have been developed to quantify P inthe above described inorganic and organic forms, as sum-marized recently by Pierzynski et al. (2005). Among these dif-ferent sequential-P-fractionation schemes, the method devel-oped by Hedley et al. (1982), sometimes with slight modifica-tion, was widely applied in many countries. Cross andSchlesinger (1995) published a thorough review on applica-tions of the Hedley fractionation to characterize the biogeo-chemical P cycling in natural, unfertilized, and uncultivated

soils that were arranged according to the soil orders of theUSDA classification. Although a huge dataset on Hedley Pfractions in soils from different land-use and managementsystems of both temperate and tropical agroecosystems hasbeen accumulated over the past 25 y, a review comparable toCross and Schlesinger (1995) has not yet been published.

Therefore, the objectives of this review were to (1) compileand summarize the concentrations and proportions of P frac-tions obtained by the Hedley sequential P fractionation incontrasting land-use and management systems of temperate,subtropical, and tropical soils, and (2) to review results ofnew analytical approaches in P speciation which have poten-tial to improve the interpretation of the Hedley fractions. Wehypothesize that compiling many results from different geo-graphical areas could help to generalize probable effects ofland use and management on the Hedley fractions. Further-more, reviewing previous studies helps to identify gaps in

* Correspondence: Prof. Dr. P. Leinweber;e-mail: [email protected]

knowledge and propose new research approaches in study-ing the dynamics of P fractions for sustainable agriculturalproduction.

2 Methods of data mining and evaluation

More than 100 articles published in soil science and relatedjournals in the past 25 y were evaluated. As different studiesused different units, we normalized the concentrations intomg Pkg–1 for P fractions and the applied P into kg P ha–1.Approximate bulk densities of (1.0 to 1.4) � 103 kg m–3 wereused to convert the applied P from mg Pkg–1 into kg P ha–1

for some studies. The amounts of different applied organicwaste such as manure, biosolids, crop residues, and greenmanure were converted into their total P equivalent on dry-matter basis. The amounts of P applied with fertilizer andorganic materials in the reviewed studies ranged from 0 to921 kg ha–1 over the corresponding study period (0–111 y).Phosphorus sources, specific rate of P, and duration of thestudies are listed in Tab. 4 to 7 for temperate soils and in Tab.9 and 10 for subtropical and tropical soils. As many reviewswere published on the effects of organic materials on soil Pdynamics in both temperate and tropical ecosystems (Stew-art and Tiessen, 1987; Condron et al., 2005; Hedley andMcLaughlin, 2005; Singh and Lal, 2005; Oberson and Fros-sard, 2005; Mullins et al., 2005; Nziguheba and B�nemann,2005), we focused on studies in which the Hedley sequential-P-fractionation scheme was applied to different land-use andmanagement systems.

In most studies from temperate climates, the extracted Pfractions comprised resin-P, 0.5 M NaHCO3-Pi and Po, 0.1 MNaOH-Pi and Po, 1 M HCl-P or 1 M H2SO4-P, and residual-Pfractions. A few studies separately extracted P from internalsurfaces of soil aggregates by ultrasonication in 0.1 MNaOH-P and recalcitrant P fractions in concentrated HCl-Pwhich in the present review were summed to the NaOH- andresidual-P fractions, respectively. Similar sequential-P-frac-tionation procedure was applied to tropical soils except forresin-P fraction in most studies. However, the number of Pfractions extracted that ranged from 4 to 9, did not show con-sistency in both agroecosystems and it was usually lower forthe studies conducted on subtropical and tropical soils (Tab.1 and 2). Unless otherwise stated, the following terminologywas used throughout the text: labile P (resin-P, 0.5 MNaHCO3-Pi and Po), moderately labile P (0.1 M NaOH-Pi andPo), and stable P fractions (HCl-P and residual-P).

Since stages of soil development affect the distribution andtransformation of different P fractions (Cross and Schle-singer, 1995), we organized this review according to the SoilTaxonomy Classification System (Brady and Weil, 2008) andassigned to these units if classifications from other systemswere reported. Accordingly, this review summarized themajor effects of land-use and management systems on theupper soil horizons, mostly ranging from 0 to 20 cm depth.Furthermore, we considered only the extreme treatments incontrasting land-use and management systems because thedifferences in P fractions from the narrow-range treatmentswere small in most studies. The effects of land-use and man-agement systems on P fractions are affected by the intensity

and duration of the management. As a result, studies wereclassified into native vegetation covers, short-term (£10 y),medium-term (10–25 y), and long-term (>25 y) in temperate,subtropical, and tropical soils. These classifications helped toillustrate the impact of land-use and management systemsover time across different soil orders in all agroecosystems.

The effects of applying different P sources over various studyperiods on P fractions were analyzed by multiple regressionsfor absolute concentration of labile and moderately labile Pfractions in selected studies in temperate, subtropical, andtropical soils. Differences in labile and moderately labile Pwere computed as function of difference in P-applicationrates and duration of the studies. Land-use and managementsystems without P application were excluded from the multi-ple-regression analysis. Pearson correlation analyses werealso computed for absolute concentrations of all P fractionsexept those from natural ecosystems.

3 Effects of land use and management on Pfractions in temperate soils

3.1 Native vegetation covers

Impacts of native vegetation covers on P fractions in varioussoil types of temperate climates were reviewed (Tab. 3). Dif-ferent vegetation at the same soil orders altered both theabsolute concentrations and the proportions of different Pfractions. The major differences were observed mainly inlabile and moderately labile P fractions. For instance, theresin-P proportion was larger under coniferous than underbroadleaf forest. Furthermore, the proportion of Po undergrasses and pastures exceeded that under forest in most ofsoil orders. This is attributed to high organic-matter (OM)accumulation by fine roots of grasses particularly in the A hor-izon (Brady and Weil, 2008) that is usually proportional to theconcentration of Po (Tiessen et al., 1984). Although little infor-mation was available on the P species of forest and grass lit-ter, we hypothesize that forest litter contains relatively moreorthophosphate diesters than grassland (McDowell andStewart, 2006). Similarly, Leinweber et al. (1997a) and Tar-anto et al. (2000) reported that orthophosphate diesters weremore easily mineralized than orthophosphate monoesters. Inaddition to litter quality, associated microorganisms, vegeta-tion composition, soil moisture regime, and soil physicochem-ical and biological characteristics affected organic-P minerali-zation (Jones, 1998; Hinsinger, 2001; Nziguheba and B�ne-mann, 2005). The absolute concentration and proportion ofHCl-P fraction was higher under beech for the Inceptisols andgrasses for the Ultisol, but higher under forest covers for theMollisols and Spodosols.

Forest sites in the temperate climate are covered predomi-nantly by ectomycorrhizal tree species (e.g., Fagus or Piceaspp.), whereas grassland and pasture are covered predomi-nantly by arbuscular mycorrhizal plants. Arbuscular mycorrhi-zal fungi are especially effective in the uptake of P beyondthe rhizosphere (Zhu et al., 2001), which is reflected by arapid turnover in Po in soils under grass and a build-up of alarge, potentially labile, microbially derived Po pool (Guggen-


306 Negassa, Leinweber J. Plant Nutr. Soil Sci. 2009, 172, 305–325


Table 1: Overview on studies which used the Hedley sequential P fractionation to different land-use and management systems in temperate cli-mate and which were selected for the present review.

Soil order/country Land use (kg P ha–1 y–1)a Duration NPFb DTPc References

Native vegetation

Inceptisol/Denmark grass/beech 8 323 Magid (1993)

Spodosol/Denmark spruce 8 80 Magid (1993)

Inceptsol/New Zealandd grass/pinus 7 70 Condron et al. (1996)

Inceptisol/Chile conifer/broadleaf 9 128 Thomas et al. (1999)

Inceptisol/France above timberline 7 151 Cassagne et al. (2000)

Spodosol/France forest/timberline 7 366 Cassagne et al. (2000)

Inceptisol/New Zealandd forest/grass 8 86 Chen et al. (2000)

Mollisol/Khyrgzia forest/pasture 8 473 Turri�n et al. (2000)

Ultisol/New Zealand forest/pasture 9 1588 McDowell and Stewart (2006)

Histosol/USA marsh/forest 8 6 Levy and Schlesinger (1999)

Incubation studies (day)

Mollisol/Canada arable 0–324 270 9 95 Hedley et al. (1982)

Mollisol/Canada rotation 100–400 63 9 268 Wagar et al. (1986)

Mollisol/Canada arable 0–48 120 9 21 Qian and Schoenau (2000)

/Austeralia woodland 0–120 120 5 51 Taranto et al. (2000)

Alfisol/USA tillage systems – 8 9 0 Daroub et al. (2000)

Inceptisol/USA tillage systems – 7 9 79 Daroub et al. (2000)

Mollisol/Canada arable 0–737 120 7 305 Kashem et al. (2003)



Alfisol/USA tillage systems – 8 9 0 Daroub et al. (2000)

Inceptisol/USA tillage systems – 7 9 79 Daroub et al. (2000)

Short-term field studies (y)

Alfisol/Canada arable 0–90 10 9 79 Richards et al. (1995)

Inceptisol/Canada arable 0–90 10 9 236 Richards et al. (1995)

Inceptisol/Canada arable 0–44 6 9 145 Tran and N’dayegamiye (1995)

Inceptisol/Canada arable 0–33 8 7 28 Zheng et al. (2002)

Inceptisol/Canada arable 0–20 10 7 47 Zheng et al. (2004)

Alfisol/Switzerland arable 0–40 12/5 6 79 Oberson et al. (1993)

Mollisol/Canada arable 0–18 5 9 98 Qian et al. (2004)

Mollisol/USA poplar 0–271 6 7 2181 Sui et al. (1999)

Mollisol/USA grass 0–175 6 7 1315 Sui et al. (1999)

Medium-term studies

Alfisol/Germany arable/grass 25 5 378 Leinweber et al. (1997a)

Inceptisol/Germany arable/grass 25 5 4238 Leinweber et al. (1997a)

/Germany grass/arable 25–60 25 5 122 Leinweber et al. (1999)

/Germany fallow/grass 0–40 25 5 56 Leinweber et al. (1999)

Inceptisol/New Zealandd pasture 0–62 19 6 196 Condron and Goh (1989)

Inceptisol/USA pasture 0–75 25 7 1467 Sharpley et al. (2004)

Ultisol/USA grass 0–130 12 7 653 Sharpley et al. (2004)

Inceptisol/Canada arable 0–41 15 7 396 Ajmone-Marsan et al. (2006)

Inceptisol/Canada arable/pasture 7 881 Frossard et al. (1989)

Spodosol/Germany arable 5 1358 Leinweber (1996)

Inceptisol/USA pasture 0–75 25 7 1467 Sharpley et al. (2004)

Long-term studies

Alfisol/USA arable 0–26 111 8 523 Motavalli and Miles (2002)

Mollisol/Canada pasture/ arable 65 9 219 Hedley et al. (1982)

Mollisol/Canada virgin/arable 62 7 74 Tiessen et al. (1983)

Chernozem/Canada arable 0–32 36 9 60 Campbell et al. (1986)

a (kg P ha–1 y–1): The applied P was from different sources such cattle manure, swine manure, poultry manure, biosolids, and fertilizer P; bNPF:number of P fractions; c DTP: change in total P fractions between the highest and lowest P applied or between contrasting land uses in mgPkg–1.

J. Plant Nutr. Soil Sci. 2009, 172, 305–325 Hedley fractionation reflects impacts on soil phosphorus 307


Table 2: Overview on studies which used the Hedley sequential P fractionation to different land-use and management systems in subtropicaland tropical climate and which were selected for the present review.

Soil order/country Land use (kg P ha–1y–1)a Duration NPFb DTPc References

Native vegetation

Aridisol/USA grass/shrub 9 144 Cross and Schlesinger ( 2001)

Ulfisol/Ethiopia forest 7 419 Solomon et al. (2002)

Alfisol/Ethiopia forest 7 567 Solomon et al. (2002)

Oxisol/Brazil cerrado/pasture 6 45 Lilienfein et al. (2000)

Ardisol/Peru vegetation cover <3% to >60% 7 514 Fabre et al. (2006)

Inceptisol/Brazil vegetation lower /upper 9 1751 Agbenin and Tiessen (1994)

Oxisols/Venezuela forest Lower/upper 7 10 Tiessen et al. (1994)

Oxisol/Brazil caatinga Lower/upper 7 87 Araujo et al. (2004)

Alfisol/Brazil caatinga Lower/upper 7 92 Araujo et al. (2004)

Incubation studies (d)

Inceptisol/Mexico arable Non/incubated 66 7 7 Crews (1996)

Andisol/Mexico arable Non/incubated 66 7 53 Crews (1996)

Aridisol/Mexico arable Non/incubated 66 7 51 Crews (1996)

Ultisol/Rwanda grassland 0–353 28 5 131 Iyamuremye et al. (1996)

Ultisol/Rwanda homestead 0–353 28 5 136 Iyamuremye et al. (1996)

Inceptisol/Rwanda waterlogged 0–353 28 5 224 Iyamuremye et al. (1996)

Vertisol/India arable 0–234 64 5 167 Sammi Reddy et al. (1996)

Alfisol/Kenya arable 0–15 120 5 23 Nziguheba et al. (1998)

Vertisol/India arable 0–21 120 6 11 Damodar Reddy et al. (2001)

Oxisol/Colombia native/arable 0–60 14 7 189 Buehler et al. (2002)

Alfisol/India arable 0–18 120 6 11 Damodar Reddy et al. (2005)

Andosol/Argentine native 0–45 90 5 30 Zubillaga and Camelo (1998)

Vertisol/Argentine native 0–45 90 5 0 Zubillaga and Camelo (1998)

Ultisol/Argentine native 0–45 90 5 19 Zubillaga and Camelo (1998)

Alfisol/Nigeria arable 0–680 14 4 260 Agbenin and Igbokwe (2006)


Oxisol/Colombia native/arable 0–60 5 8 151 Oberson et al. (2001)

Ultisol/C�te d’Ivoire arable 0–180 5 5 84 Abekoe and Sahrawat (2003)

Vertisol/India arable 0–66 4 6 163 Damodar Reddy et al. (1999)

Alfisol/Nigeria fallow – 2 5 26 Kolawole et al. (2004)

Inceptisol/Costa Rd fallow – 3 7 73 Derry et al. (2005)

Ultisol/Philippine grass land 0–155 3 5 174 Dobermann et al. (2004)

Ultisol/Philippine arable-rotation 0–83 3 5 196 Dobermann et al. (2004)

Oxisol/Indonesia fallow 0–138 3 5 213 Dobermann et al. (2004)

Oxisol/Colombia native/arable 0–60 5 8 151 Oberson et al. (2001)

Ultisol/C�te d’Ivoire arable 0–180 5 5 84 Abekoe and Sahrawat (2003)

Inceptisol/Costa Rd alley cropping 0–39 10 7 31 Paniagua et al. (1995)

Oxisols/Brazil native/arable 10 4 139 Neufeldt et al. (2000)

Medium-term studies

Oxisol/ Brazil native/arable 12 7 30 Tiessen et al. (1992)

Ultisol/Peru arable 0–80 13 7 202 Beck and Sanchez (1996)

Alfisol/Tanzania woodland/arable 15 7 294 Solomon and Lehmann (2000)

Alfisol/Tanzania homestead/arable 15 7 510 Solomon and Lehmann (2000)

Ultisol/Cameroon arable/plantation 27–60 15 6 672 Techienkoua and Zech (2003)

Oxisol/Brazil tillage systems ZTe/CTf 5 25 Selles et al. (1997)

Oxisol/Brazil tillage systems ZTe/CTf 6 67 Lilienfein et al. (2000)

Oxisol/Peru native/arable 0/70 11 4 461 Neufeldt et al. (2000)

Long-term studies

Alfisol/Ethiopia native/arable 35 7 419 Solomon et al. (2002)

Alfisol/Nigeria arable 0/54 45 7 883 Agbenin and Goladi (1998)

a (kg P ha–1y–1): the applied P was from different sources such as cattle manure, green manure, crop residues, and fertilizer P; bNPF: number Pof fractions; c DTP: change in total P fractions between the highest and lowest applied P or between contrasting land uses in mg Pkg–1; d

Costa R.: Costa Rica; e ZT: zero tillage; f CT: conventional tillage.


berger et al., 1996). This could explain why labile Po predomi-nated under grasses and pasture while the labile Pi fractionswere more prominent in forest soils (Magid, 1993; Cassagneet al., 2000; Chen et al., 2000).

Moreover, the work of Thomas et al. (1999) confirmed thatforest composition had a major impact on P-fractiondynamics because samples from coniferous forest had morelabile P than samples from broadleaf forest. The concentra-tion of resin-P was correlated with the content of organic C(Thomas et al., 1999) which suggested that the resin-P wasmineralized from OM, perhaps more accumulated under coni-ferous than under broadleaf forest.

3.2 Effects of short-term land-use andmanagement systems

3.2.1 Incubation studies

Short-term incubation studies (1 to 16 weeks) were carriedout in Mollisols to measure changes in the labile and stable Pforms following various doses of P-fertilizer applications(Wagar et al., 1986). Furthermore, short-term manuringeffects on the P distribution were investigated by Qian andSchoenau (2000) and Kashem et al. (2004). Longer-termincubation studies (36 weeks) were carried out to examineseasonal P transformations (Hedley et al., 1982). The highestabsolute concentration and relative proportion of the appliedP from different sources was recovered in the labile Pi formsin these incubation studies (Tab. 4). The highest recovery ofthe applied P in the labile P fractions was not surprising asthe amount of applied P (up to 921 kg P ha–1) was severaltimes higher than the normal fertilizer P used in temperatesoils. Similar to the short-term field studies discussed below,the increases in labile P fractions were directly proportional tothe amount of applied P irrespectively of the P sources. Otherless soluble P fractions increased slightly (Tab. 4). Applica-tion of P with biosolids, hog manure, cattle manure, and fertili-zer P in the study by Kashem et al. (2004) increased theabsolute concentration of all P fractions by factor 2 or moreexcept HCl-P as compared with the treatment without P.However, the highest labile Pi fraction was extracted from thesoil that received cattle manure followed by the soil thatreceived hog manure. This shows that different types of ani-mal manure could vary in their effects on P distribution prob-ably due to variations in P concentrations and binding formsin animal feeds, differences in chemical composition, storagemethods, and stage of decomposition. The studies clearlypointed out that extraordinarily high application of P in theform of fertilizer P, manure, and biosolids amplified the con-centration of the labile Pi fractions in very short incubationperiods.

3.2.2 Short-term field studies

Short-term field studies (0 to £ 10 y) were carried out to deter-mine the pathways of P transformation and identify P poolswhich were sinks or sources for P under contrasting croppingpractices (Zheng et al., 2002, 2004) and to evaluate therepeated application of fertilizer P on forms and distribution of


Table

3:Soilp

hosp

horusfrac

tions

unde

rdiffe

rent

vege

tatio

nsin

tempe

rate

clim

ate.

Soil

Res

in-P

NaH

CO

3-Pi

NaH

CO

3-Po

NaO

H-P

iNaO

H-P

oHCl-P

Res

idual-P

TP

Referen

ces

orde

rland

use

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(sum

)

broa

dlea

f67

1615

469

1727

612

129

92

108

2641

6Tho

mas

etal.(19

99)

conifer

9627

113

4613

113

9025

31

104

2936

1Tho

mas

etal.(19

99)

Ince

ptisol

gras

s26

264

517

413

521

3934

726

604

172

1313

50Mag

id(199

3),C

henet

al.(20

00),

Con

dron

etal.(19

96)

Ince

ptisol

forest

291

120

443

416

1354

5051

819

236

926

91Che

net

al.(20

00)

Ince

ptisol

beec

h12

514

728

303

354

101

133

1548

555

889

Mag

id(199

3)

Mollisols

pasture

312

282

129

946

342

231

146

1158

142

1366

Fross

ardet

al.(19

89),Turri�

net

al.

(200

0)

Mollisol

forest

333

575

303

275

2534

031

358

3310

93Turri�

net

al.(20

00)

Spo

doso

lab

ove

timbe

rline

424

283

146

1429

629

365

3674

776

710

27Cas

sagn

eet

al.(20

00)

Spo

doso

ltim

berline

667

778

105

1047

552

652

102

1081

810

04Cas

sagn

eet

al.(20

00)

Spo

doso

lforest

192

243

475

159

1739

542

219

2378

893

8Cas

sagn

eet

al.(20

00)

Ultiso

lgras

s44

552

645

527

229

311

3316

117

526

937

McD

owella

ndStewart(20

06)

Ultiso

lforest

396

467

406

190

2924

838

7011

284

661

McD

owella

ndStewart(20

06)


soil Pi and Po (Richard et al., 1995) in Inceptisols (Tab. 4).The absolute concentration of the resin-P was 41 mg Pkg–1

at the inception of the study and increased by 2.6 to 6.3 mgPkg–1 with continuous application of P for 8 y at the rate of 26to 42 kg P ha–1 y–1 either from fertilizer P or liquid dairy man-ure (Zheng et al., 2002). A similar study conducted by thesame authors also indicated the highest resin-P (103mgkg–1) at the inception of the study that was changed by 8and 12 mg Pkg–1 with continuous application of 20 kg P ha–1

y–1 for 10 y in the form of liquid dairy manure and fertilizer P,respectively (Zheng et al., 2004). The unusually high P con-centrations in the resin fraction at the beginning of the studiesby Zheng et al. (2002, 2004) could be attributed to the Paccumulation from previous fertilizer-P applications as thestudies were conducted on agricultural research farms. Con-tinuous application of 0 to 42 kg P ha–1 y–1 for 8 to 10 y didnot change the absolute concentrations and the relative pro-portions of different P fractions in Inceptisols of differentcountries irrespectively of the P sources (Tab. 4). However,application of 90 kg P ha–1 y–1 for 10 y substantially increasedthe labile and moderately labile Pi fractions (Tab. 4) (Richardset al., 1995).

Short-term studies conducted on Mollisols and Alfisols oftemperate climate also showed that changes in P fractionsdepended on the amount of applied P regardless of Psources. For instance, both the absolute concentrations andproportions of different P fractions were slightly increased bylow P fertilization (<46 kg ha–1 y–1) for 5 y and substantiallyincreased by high P fertilization (>90 kg ha–1 y–1) (Obersonet al., 1993; Richards et al., 1995) (Tab. 5). For instance,extraordinary large P applications with cattle manure (Qianet al., 2004) and biosolids (Sui et al., 1999) highly enrichedthe labile and moderately labile Pi fractions. However, theabsolute concentrations and proportions of stable P fractions,particularly in soils treated with biosolids, decreased. Prob-ably this can be explained by an increased solubility of previ-ously stable P fractions due to the decrease in soil pH from6.2 to 5 (Sui et al., 1999). Surprisingly, both the absolute con-centrations and the proportions of the different P fractionsremained almost constant during continuous cultivation with-out any P application for 10 y (Tab. 5). This confirms studiesthat reported the Hedley sequential-P-fractionation schemeas insensitive to detect small changes in P fractions followingwithout P or with low rate of P application to agricultural soilsover short periods (Qian and Schoenau, 2000; Hylander andSim�n, 2006).

3.2.3 Phosphorus losses

A few studies were carried out to explain P losses with leach-ing or preferential flow by Hedley fractions, which reflectedprevious P applications or imbalances. In a cracking clay soilof the Brimstone Experimental Farm (UK), the application of16 and 33 kg P ha–1 for two consecutive years did not affectboth the absolute concentration and the proportions of P frac-tions (Fig. 1). This was in line with the absence of any signifi-cant differences in the P losses with drainage water betweenthe fertilization treatments (Addiscott et al., 2000). However,in this experiment for the first time an unexpected but signifi-cant dependency of most P fractions on sampling date was

observed. Ranking of the dependent variables according toincreasing F probability indicated that sampling date influ-enced P fractions of lower solubility (NaOH-P, residual-P)more strongly than the more labile P (Olsen-P, resin-P, andH2O-P). The significant reduction in the proportions ofNaOH-P between March and November 1995 (Fig. 1) led todecreases in the concentrations of oxalate-extractable Alfrom approx. 90mmol kg–1 to approx. 60mmol kg–1 and to theincreased proportions of stable residual P. The latter could bean effect of shrinking of clay minerals that favor the formationof stable P–Al–organic matter bonds or inclusions. Further-more, some losses of NaOH-P were most probably con-nected with migrating of colloidal matter with fast preferential(by-pass) flows. Interestingly, P-fertilizer application in Sep-tember could not recover the previous proportions of labileand moderately labile P (Fig. 1).

Investigations on lysimeters filled with sand and loamy sandalso showed that soil texture determined P leaching fromsoils mainly because of hydraulic properties interacting withP binding (Leinweber et al., 1999). Among the sequential Pfractions, the P concentrations and leaching losses were sig-nificantly and positively correlated with NaHCO3-P but notwith resin-P. This indicated that not only phosphate ions butalso dissolved and colloidal matter contributes to P losses.This is in agreement with P losses greater for total P as deter-mined by IPC than for molybdenum-reactive P observed inthe Brimstone experimental field (Addiscott et al., 2000).

Susceptibility to runoff and distance to waterways are otherfactors that determined relationships between P fractions andeutrophication risk. Absolute concentrations and proportionsof different P fractions could be affected by slope position inspite of the same soil order, management, and weather con-dition (Wagar et al., 1986; Heilmann et al., 2005). After 5 y ofcropping, 15% of the applied P (160 kg ha–1) was taken up byplants, 60% remained in the top 15 cm, and 30% was recov-ered from below 15 cm (Wagar et al., 1986). According tothese authors, Po were the predominant P fractions below15 cm soil depth. This indicated that some Po fractions weremore mobile than Pi. Mobilization and downward movementof P was also increased by seasonal water ponding. Similarstudies also confirmed that pedogenesis and slope positionand resulting transport processes governed the distributionand forms of P and phosphatase activity at field scale (Heil-mann et al., 2005). These authors also stated that the con-centrations of labile and moderately labile Po and phospha-tase activity were highest in the lower slope positions whichwere sources of P losses. In general, the same soil orderunder different weather conditions, management history,slope position, and basic soil properties could differentlyaffect the distribution and losses of applied fertilizer P.

3.3 Effects of medium-term land-use andmanagement systems

A number of studies investigated the effects of medium-term(10–25 y) land-use and management systems in various soiltypes of temperate climate (Tab. 6). Application of 40 to130 kg P y–1 in form of manure and mineral fertilizer for



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Table 4: Effects of incubation and short-term management systems on P fractions of arable soils in temperate climate.

Soilorder

P source (kg P ha–1) Duration Resin-P NaHCO3-Pi NaHCO3-Po NaOH-Pi NaOH-Po HCl-P Residual-P TP References

(y–1) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) % (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (sum)

Incubation studiesa (d)

Mollisol 0 167 42 5 46 5 36 4 43 5 212 23 133 14 410 44 923 Hedley et al. (1982)

Mollisol SMb 15 112 35 5 25 4 5 1 32 5 116 17 190 27 292 42 695 Wagar et al. (1986)

Mollisol SMb 60 112 36 5 25 4 6 1 33 5 120 17 193 27 298 42 711 Qian and Schoenau(2000)

Mollisol Fert-Pc 396 141 124 11 127 11 44 4 87 8 200 17 209 18 365 32 1155 Kashem et al. (2004)

Mollisol BSd 921 120 87 4 319 16 156 8 82 4 466 24 87 4 749 38 1946

Mollisol HMe 921 120 138 7 383 19 107 5 70 3 447 22 138 7 742 37 2025

Mollisol CMf 921 120 167 8 310 15 95 5 114 6 396 20 167 8 756 38 2005


Inceptisol 0 0 41 5 27 3 25 3 59 7 104 12 90 11 493 59 839 Zheng et al. (2002)

Inceptisol Fert-Pc 27 8 46 5 30 3 24 3 67 8 111 13 94 11 493 57 865 Zheng et al. (2002)

Inceptisol LDMg 26 8 44 5 29 3 24 3 65 8 117 14 96 11 489 57 864 Zheng et al. (2002)



Inceptisol 0 0 6 1 14 3 16 3 20 4 16 3 220 47 179 38 471 Richards et al. (1995)


Inceptisol Fert-Pc 90 10 38 6 71 10 19 3 78 11 19 3 272 40 189 28 686 Richards et al. (1995)


Inceptisol 0 0 103 6 62 3 67 4 142 8 230 13 990 55 190 11 1784 Zheng et al. (2004)



a Incubation: data were means of similar studies; b SM: swine manure; c Fert-P: fertilizer P; d BS: biosolids; e HM: hog manure; f CM: cattle manure; g LDM: liquid dairy manure.

Table 5: Short-term effects of land-use and management systems on P fractions in temperate Mollisols and Alfisols.

Soilorder

Land use Psource

P-applica-tion rate

Duration Resin-P NaHCO3-Pi NaHCO3-Po NaOH-Pi NaOH-Po HCl-P Residual-P TP References

(kg ha–1 y–1) (y) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (mg kg–1) (%) (sum)

Mollisol cultivated 0 5 12 2 8 2 6 1 21 4 109 21 174 33 198 38 528 Qian et al. (2004)

Mollisol cultivated SMa 18 5 9 2 8 2 7 1 16 3 95 18 158 30 239 45 532 Qian et al. (2004)

Mollisol cultivated CMb 0 5 16 3 12 2 7 1 14 3 103 20 149 29 212 41 513 Qian et al. (2004)

Mollisol cultivated CMb 124 5 67 10 27 4 9 1 22 3 84 13 216 34 218 34 643 Qian et al. (2004)

Mollisol poplar 0 6 21 3 91 14 23 3 104 16 124 19 157 24 146 22 666 Sui et al. (1999)

Mollisol poplar BSc 271 6 165 6 479 17 47 2 928 33 483 17 530 19 216 8 2848 Sui et al. (1999)

Mollisol switchgrass 0 6 9 1 50 7 19 3 84 12 98 14 189 26 274 38 723 Sui et al. (1999)

Mollisol switchgrass BSc 175 6 76 4 295 14 52 3 595 29 209 10 429 21 382 19 2038 Sui et al. (1999)

Alfisol cultivated 0 0 20 4 29 6 17 3 57 12 69 14 107 22 192 39 491 Richards et al. (1995)

Alfisol cultivated 0 10 21 4 59 9 31 5 105 17 91 14 102 16 197 31 628 Richards et al. (1995)

Alfisol cultivated Fert-Pd 46 5 38 5 12 2 100 14 132 18 172 23 282 38 736 Oberson et al. (1993)

a SM: swine manure; b CM: cattle manure; c BS: biosolids; d Fert-P: fertilizer-P.

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12–25 y affected the absolute concentration and proportionof all P fractions in Inceptisols and Ultisols (Tran and N’daye-gamiye, 1995; Sharpley et al., 2004; Condron and Goh,1989) (Tab. 6). Major changes following continuous applica-tion of 75 kg P ha–1 y–1 on pasture for 25 y in the form of dairymanure increased the absolute concentrations of labile andtotal P by factors of 4 to 6 (Sharpley et al., 2004). Similarly,the application of 62 kg P ha–1 y–1 for 19 y doubled the abso-lute concentration of the labile and moderately labile Pi frac-tions and increased the proportions of these fractions as well(Condron and Goh, 1989) (Tab. 6). Moreover, application ofmanure and fertilizer P maintained the concentration of Poand slightly affected the stable P fraction (Tran and N’daye-gamiye, 1995). Surprisingly, minor changes were observedafter 19 y in both the absolute concentrations (Condron andGoh, 1989) and proportions of different P fractions in unferti-lized pasture soils used for grazing (Tab. 6). This is attributedto minimum soil disturbance and potential losses by erosion,internal recycling, and small net export of P.

The absolute and relative concentration of P depends onsource of manure, environmental condition, feed type, sto-rage method and duration, state of the applied manure (solidor liquid form) (Kleinman et al., 2005). For instance, enrichinganimal feeds with extra P contributes to P-rich excrement,and high stocking densities are major reasons for regional Pimbalances in developed countries (Toor et al., 2005). There-fore, controlling P concentration in animal feeds and stockingdensity could help to reduce P load on soils and water bodies.Moreover, basic soil properties also highly influenced the rateof mineralization and transformation of the applied manureeither directly or indirectly. For instance, increasing soil pH byliming enhanced the mineralization of Po and the transforma-tion of labile and moderately labile P forms into more stableHCl-P (Condron and Goh, 1989). Applications of different ani-mal manure continuously at 40–200 kg P ha–1 y–1 for 10–25 yshifted high proportion of P fractions into HCl-P (Sharpleyet al., 2004). According to these authors, this could reduce

the fear of potential losses of P to surface water in heavilymanured soils. But under such high–P loading conditions, theentrance of P to aquatic ecosystems is inevitable. Moreover,under poorly drained soils and shallow water tables, repeatedapplications of manure in excess of plant requirement couldshift P from resilient to more labile forms that eventually in-creased the potential for P loss (Ajmone-Marsan et al.,2006). The labile P fractions exist in equilibrium with moder-ately labile P fractions, and these two P pools are also sensi-tive to change because of fertilizer application or nutrientdepletion (Schmidt et al., 1997). Path analyses showed thattransformations between P fractions depended on the stageof soil development, type of P sources, and soil properties(Tiessen et al., 1984; Zheng et al., 2002). For instance, inmoderately weathered soils, approx. 86% of resin-P origi-nated from NaHCO3-Pi and NaOH-Pi, and in highly weath-ered soil, 80% of resin-P derived from labile and moderatelylabile Po (Tiessen et al., 1984). In a dairy manure system, aswell approx. 86% of resin-P originated from applied fertilizerPi but added manure Po was transformed into labile andmoderately labile Po (Zheng et al., 2002). As a number of fac-tors contribute to transformations of P fractions, it is difficultto exactly determine the kinetics of exchange reactions. A con-ceptualized model based on P cycles categorized soil P trans-formation into three components such as slow Pi, rapid Pi andPo, and slow Po (Tiessen et al., 1984). Moreover, the role of soilmicrobial activities (Jackobsen et al., 2005), P uptake by plants(Kovar and Classen, 2005), root exudation, and other rhizo-sphere processes (Jones, 1998; Hinsinger, 2001) have para-mount importance on soil-P transformations.

At the landscape scale, the absolute concentrations of thelabile P fractions are very important for immediate agriculturalproductivity and risk of P losses to waterways. For instance,in some soils in NW Germany concentrations of labile P frac-tions in the range of 93–500 mg Pkg–1 were by far above theplant requirements (Leinweber, 1996; Leinweber et al.,1997a), although residual-P predominated among the P frac-


0

10

20

30

40

50

60

70

80

90

100

P fertilization (kg ha-1)

Sampling month

P application month

16 33 16 33Aug. 1994 Mar. 1995 Nov. 1995 Jan. 1996 Mar. 1996

Pho

spho

rus

fract

ions

(%TP

)

Resin-P NaOH-P Residual-PNaHCO3-P H2SO4-P

Dec.1994 Sept.1995

Figure 1: Effects of P fertilization on Pfractions in a temperate cracking claysoil (plots of the Brimstone Farm Experi-ment, UK; data modified from Leinwe-ber, 1998, unpublished).


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Table 6: Effects of medium-term land-use and management systems on P fractions in temperate soils.

Soilorder

Land use Psource

P-applica-tion rate

Duration Resin-P NaHCO3-Pi NaHCO3-Po NaOH-Pi NaOH-Po HCl-P Residual-P TP References

(kg ha–1

y–1)(y) (mg

kg–1)(%) (mg

kg–1)(%) (mg

kg–1)(%) (mg

kg–1)(%) (mg

kg–1)(%) (mg

kg–1)(%) (mg

kg–1)(%) (sum)

Inceptisol pasture 0 25 12 3 28 6 48 10 97 20 119 25 72 15 104 22 480 Sharpley et al. (2004)

Inceptisol pasture DMa 75 25 229 12 232 12 82 4 286 15 228 12 550 28 340 17 1947 Sharpley et al. (2004)

Inceptisol pasture 0 0 20 4 40 8 113 24 206 44 27 6 67 14 473 Condron and Goh (1989)

Inceptisol pasture 0 19 19 5 39 10 91 22 162 40 32 8 65 16 408 Condron and Goh (1989

Inceptisol pasture Fert-Pb 62 19 49 7 69 10 187 28 197 29 98 15 69 10 669 Condron and Goh (1989

Inceptisol cultivated 0 15 8 1 41 6 51 8 115 18 97 15 80 12 263 40 655 Ajmone-Marsan et al.(2006)

Inceptisol cultivated LHMc 41 15 42 4 130 12 50 5 231 22 268 25 57 5 273 26 1051 Ajmone-Marsan et al.(2006)

Mollisol cultivate Fert-Pb 44 13 66 9 43 6 29 4 202 27 124 17 117 16 158 21 739 Tran and N’dayegamiye(1995)

Mollisol cultivated CMd 40 13 46 6 34 5 35 5 174 24 154 21 113 15 182 25 738 Tran and N’dayegamiye(1995)

Mollisol cultivated Mixe 84 13 105 14 58 8 35 5 152 20 159 21 101 13 160 21 770 Tran and N’dayegamiye(1995)

Alfisol cultivated 0 12 19 3 12 2 73 11 123 19 162 25 269 41 658 Oberson et al. (1993)

Ultisol pasture 0 12 8 5 10 6 12 8 21 13 44 28 7 4 57 36 159 Sharpley et al. (2004)

Ultisol pasture PMf 130 12 67 7 53 6 68 7 77 8 216 23 256 28 189 20 926 Sharpley et al. (2004)

NaHCO3-P NaOH-P H2SO4-P

Inceptisol cultivated MDAg 25 117 8 154 10 595 39 141 9 508 34 1515 Leinweber (1996)

Inceptisol cultivated MDAg 25 225 5 139 3 537 11 299 6 3786 76 4986 Leinweber et al. (1997)

Inceptisol grass MDAg 25 23 2 70 7 43 4 7 1 820 85 963 Leinweber et al. (1997)

Alfisol cultivated MDAg 25 160 9 340 18 554 30 138 7 671 36 1863 Leinweber et al. (1997)




Alfisol grass MDAg 25 108 4 179 7 334 12 70 3 2002 74 2693 Leinweber (1996)

Spodosol cultivate MDAg 25 131 10 237 18 382 29 152 11 432 32 1334 Leinweber (1996)

a DM: dairymanure; b Fert-P: fertilizer P; c LHM: liquid hogmanure; d CM: cattlemanure; eMix:mixture of fertilizer P and cattlemanure; f PM: poultrymanure; gMDA:manures of different animals.

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313

tions (Tab. 6). These extraordinary high P concentrations inlabile forms are explained by excrement inputs from a largenumber of pigs, poultry, and cattle productions that couldthreaten water quality due to eutrophication. Although the ex-tent of labile P builds-up differed with soil types, land use,and livestock density, the highest degree of P saturation(139%) as compared with elsewhere in Europe was reportedfrom this region (Leinweber et al., 1997b).

3.4 Effects of long-term land-use and managementsystems

Several studies investigated the impact of long-term differentland-use and management systems on P fractions in tempe-rate soils (Tiessen et al., 1983; Campbell et al., 1986; Mota-valli and Miles, 2002). These studies showed that cultivationwithout fertilizer-P input for long time depleted most of the Pfractions and vice versa with P input regardless of the amountof applied P (Tab. 7). Long-term applications of manure andfertilizer P increased all P fractions irrespectively of theamount of applied P as compared with native prairie and con-tinuous cropping without P input (Motavalli and Miles, 2002).The studies showed that continuous monoculture and croprotation without P application depleted all P fractions. How-ever, residual-P was enriched in the continuous monocultureand highly depleted in the crop rotation. McKenzie et al.(1992) also indicated that the intensity of P depletion variedwith cropping systems. The depletion of different P fractionswas higher in monocultures (continuous wheat) than in croprotations if other conditions were comparable. The soilsunder crop rotations had higher proportions and concentra-tion of Po fractions than similar soils under monoculture(Motavalli and Miles, 2002). This difference between thecropping systems in concentration of different P fractionscould be caused by variation in crop types, crop-residue man-agement systems, climatic condition, and temporal P fluctua-tions among seasons (Oberson et al., 1996) and associatedmicroorganisms in the rhizosphere. The long-term influenceof P applications on Po fractions generally was minimal irre-spectively of the sources and amount of applied P (Campbellet al., 1986;Motavalli and Miles, 2002).

Continuous cultivation for 65 y without P input considerablydepleted the concentration of all P fractions except the HCl-Pfraction in Mollisols as compared with the adjacent unculti-vated prairie (Tiessen et al., 1983). Disproportional depletionof moderately labile P increased the proportion of HCl-Pwhich was the dominant P form in moderately weatheredsoils (Schoenau et al., 1989; Cross and Schlesinger, 1995).However, a Mollisol which received approx. 32 kg P ha–1 y–1

for 36 y had increased concentrations of the labile Pi fractionby 38% as compared with the untreated plot of the samecropping system (Campbell et al., 1986). Continuous long-term P applications at low rate could increase the concentra-tion of labile and moderately labile P fractions. As crops andpastures removed certain amounts of the applied P throughharvesting, the major portions returned to the soils in the formof above- and belowground residues. Therefore, special pre-cautions are required in managing soils subjected to continu-ous long-term P applications even if the P dose is low.

In summary, loading temperate soils with large amounts of Pfrom different sources resulted in large increases in the mostlabile P fractions regardless of the period of applications.Moreover, continuous applications of low doses of fertilizer P(11 to 32 kg P ha–1 y–1) for 36–111 y increased almost all Pfractions. Soil-textural classes, slope position, and seasonalwater ponding were found to affect leaching losses of labile Pfractions with pronounced mobility in Po forms. Therefore,either high P loading within a short-term or low fertilizer-Papplication surplus to removal in the long-term is potentiallyrisky for the nutrient status of aquatic ecosystems. On theother hand, continuous cultivation without P input highlydepleted the labile and moderately labile P fractions, whereasit moderately depleted the stable P fractions. Although cropproduction without P application is not a common practice ontemperate soils, judicious application of different P sourceson agricultural lands are required. This entails consideringthe P uptake and efficiency of the crop in balance with P addi-tion, using residual-P from previously applied P for crop pro-duction, and appropriate animal-waste management for sus-tainable production and productivity of both conventional andorganic farming.

4 Effects of land use and management on Pfractions in subtropical and tropical soils

4.1 Native vegetation covers and toposequence

Many studies in tropical regions investigated P fractionsunder native vegetation covers (Lilienfein et al., 2000; Crossand Schlesinger, 2001; Solomon et al., 2002; Fabre et al.,2006) and/or toposequence effects on the distribution of Pfractions (Agbenin and Tiessen, 1994; Araujo et al., 2004).Some studies also compared anthropogenic disturbed agroe-cosystems to native vegetation cover (Tiessen et al., 1992;Beck and Sanchez, 1996; Neufeldt et al., 2000; Obersonet al., 2001; Abekoe and Sahrawat, 2003). The general orderof different P fractions was based on the stage of soil devel-opment and percent of vegetation cover. Accordingly, the Ari-disols were highly dominated by HCl-P fractions, whereas theUltisols and Oxisols were dominated by residual-P (Tab. 8).Residual-P in Aridisols and moderately labile Po in moder-ately and highly weathered tropical soils were the secondhigher concentration and proportion of P fractions (Tab. 8).Increasing percent of vegetation cover on Aridsols largelyaugmented the labile and moderately labile P fractions at theexpense of the stable P fraction. This clearly shows that notonly the stage of soil development (Cross and Schlesinger,1995) but also percent and type of vegetation cover (Crossand Schlesinger, 2001; Fabre et al., 2006) govern the con-centrations and proportions of biogeochemical P forms in sur-face soils.

Table 8 also shows the influence of toposequence on P formsand distribution in tropical soils. The differences in both abso-lute concentration and proportion of different P fractions weremore pronounced when the soils and vegetation differedacross the toposequence. In a toposequence with associatedEntisols and Inceptisols, the absolute concentration of almostall P fractions decreased from the upper to the lower slope



position (Agbenin and Tiessen, 1994). This was attributed toP leaching and runoff losses from the middle and lowerslopes. However, in Oxisols the proportions of labile Pi andmoderately labile Po and Pi increased from the upper to thelower slope positions. Microclimate effects such as moistureand temperature variations across the toposequence mayhave favored soil organic matter (SOM) accumulation in mid-dle and lower slope resulting in elevated proportions of labileand moderately labile P (Tiessen et al., 1994; Ara�jo et al.,2004).

4.2 Effects of short-term land use andmanagement systems

4.2.1 Incubation studies

A number of incubation and fractionation studies were carriedout to understand short-term transformations of the applied Pin tropical soils (Iyamuremye et al., 1996; Crews, 1996;Sammmi Reddy et al., 1996; Nziguheba et al., 1998; Damo-dar Reddy et al., 2001, 2005; Agbenin and Igbokwe, 2006).Incubating Alfisols soils with 15 kg P ha–1 slightly increasedthe absolute concentration and relative proportions of labileand moderately labile P fractions (Tab. 9). Increasing the rateof P application increased the absolute concentration andproportion of labile and moderately labile Pi, but had onlyweak effects on the concentration of Po (Iyamuremye et al.,1996; Sammi Reddy et al., 1996; Damodar Reddy et al.,2001; Agbenin and Igbokwe, 2006) particularly in Oxisols(Tab. 9). Studies conducted with 33P labeling also confirmedthat the application of mineral fertilizer on highly weatheredlow-P soils (Buehler et al., 2002) and moderately weatheredhigh-P soils (Daroub et al., 2000) did affect neither the Po northe stable P fractions. Lack of increment in Po concentrationin tropical soils is attributed to the rapid mineralization of Po inthe tropics, regardless of P fertilization. Moreover, a declinein Po was also reported by Agbenin and Goladi (1998) for atropical Alfisol with continuous application of cow dung. How-ever, as the incubation was prolonged particularly in highlyweathered tropical soils, up to 90% of the applied P wastransformed into moderately labile Pi within 60 d (Abekoe andTiessen, 1998; Ochwoh et al., 2005).

Most of the studies used large amounts of inorganic- andorganic-fertilizer P which are usually not available for most ofsmall-scale farmers in the tropics. Therefore, studies con-ducted with realistic rate of fertilizer P or with integrated appli-cation of different organic amendments are crucial in solvingP-fertility problems in the subtropics and tropics. Accordingly,Nziguheba et al. (1998) and Damodar Reddy et al. (2005)reported studies with P amounts usually recommended fortropical soils to get optimum crop yields. On the other hand,incubation studies conducted with high P load up to 680 kgha–1 highly increased the labile and slightly the stable P frac-tions (Iyamuremye et al., 1996; Agbenin and Igbokwe, 2006).This shows the potential for P loss and water pollution frominappropriate waste management in the tropics. In summary,the effects of incubation on the absolute concentration andproportions of different P fractions mainly depend on theamount of applied P and stage of soil development. In moder-ately weathered Vertisols and Alfisols, the labile P fractions


Table

7:Effe

ctsof

long

-term

land

-use

andman

agem

ents

ystemson

Pfrac

tions

intempe

rate

soils.

Soil

order

Lan

duse

Pso

urce

P-applic

a-tionrate

Duration

Res

in-P

NaH

CO

3-Pi

NaH

CO

3-Po

NaO

H-P

iNaO

H-P

oHCl-P

Res

idual-P

TP

Referen

ces

(kgha

–1

y–1 )

(y)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(mg

kg–1)

(%)

(sum

)

Mollisols

gras

s0

6543

626

334

435

512

116

174

2333

744

769

Hed

leyet

al.(19

82)

Mollisols

FW

a0

6519

311

218

325

483

1317

829

326

5262

3Ties

senet

al.(19

83)

Mollisols

FWW

b0

3625

313

210

115

258

827

235

375

4976

8Cam

pbelle

tal.(198

6)

Mollisols

FWW

bFYM

e32

3640

521

312

121

363

828

034

391

4782

8Cam

pbelle

tal.(198

6)

Alfiso

lgras

s0

111

41

72

6018

227

177

547

252

1632

9Motav

allian

dMiles(200

2)

Alfiso

lCCM

c0

111

31

188

2310

198

3114

10

133

5822

8Motav

allian

dMiles(200

2)

Alfiso

lCCM

cFert-Pf

26111

5410

5510

377

7614

104

1925

519

135

542

Motav

allian

dMiles(200

2)

Alfiso

lCCM

cFYM

e11

111

567

181

2223

314

918

149

1823

323

629

817

Motav

allian

dMiles(200

2)

Alfiso

lCWRCd

0111

52

63

3014

157

6933

94

7335

207

Motav

allian

dMiles(200

2)

Alfiso

lCWRCd

Fert-Pf

21111

276

399

369

4511

6816

8821

113

2741

6Motav

allian

dMiles(200

2)

Alfiso

lCWRCd

FYM

e11

111

214

418

6011

448

8215

167

3112

223

537

Motav

allian

dMiles(200

2)

aFW:fallow–w

heatrotatio

n;bFWW:fallow–w

heat–w

heatrotatio

n;cCCM:con

tinuo

usco

rnmon

ocropp

ing;

dCWRC:corn–

whe

at–red

clov

errotatio

n;eFYM:farmya

rdman

ure;

f Fert-P:fertilizer

P.


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Table 8: Effects of different vegetations and toposequence on P fractions in subtropical and tropical soils.

Soil order Land use Slope NaHCO3-Pi NaHCO3-Po NaOH-Pi NaOH-Po HCl-P Residual-P TP References

(mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (sum)

Native vegetations

Aridisol grass 17 9 1 1 11 6 4 2 79 41 79 41 191 Cross and Schlesinger (2001)

Aridisol shrub 17 5 3 1 10 3 3 1 196 58 108 32 337 Cross and Schlesinger (2001)

Aridisol <3% VGa 68 15 10 2 33 7 22 5 267 60 47 11 447 Fabre et al. (2006)

Aridisol >60% VGa 197 20 122 13 125 13 139 14 136 14 242 25 961 Fabre et al. (2006)

Alfisol forest 24 2 96 7 72 5 405 30 24 2 734 54 1355 Solomon et al. (2002)

Ultisol forest 12 1 131 9 96 7 478 34 36 3 657 47 1410 Solomon et al. (2002)

Oxisol cerrado 7 2 11 3 42 11 101 26 0 228 59 388 Lilienfein et al. (2000)

Oxisol d. pastureb 6 2 11 3 40 12 89 26 0 197 57 343 Lilienfein et al. (2000)

Ultisol forest 11 7 33 21 27 17 2 1 84 54 157 Abekoe and Sahrawat (2003)

Ultisol forest 17 24 29 78 2 81 231 Beck and Sanchez (1996)

Oxisol cerado 15 13 39 34 41 35 21 18 116 Neufeldt et al. (2000)

Oxisol savanna 7 3 11 5 27 13 45 21 121 57 211 Oberson et al. (2001)

Oxisol caatinga 7 5 5 4 13 11 22 18 2 1 76 61 124 Tiessen et al. (1992)

Toposequence

Entisol caatinga upperc 25 2 9 0 38 12 70 7 59 49 146 29 347 Agbenin and Tiessen (1994)

Inceptisols mixed forest midd 28 3 11 0 36 13 60 2 69 37 130 44 334 Agbenin and Tiessen (1994)

Inceptisols mixed forest lowere 26 5 13 0 38 13 83 4 80 18 147 59 387 Agbenin and Tiessen (1994)

Alfisol caatinga upperc 72 7 0 3 376 11 232 20 1560 17 937 42 3177 Araffljo et al. (2004)

Alfisol caatinga midd 80 8 2 3 302 11 53 18 850 21 1027 39 2314 Araffljo et al. (2004)

Alfisol caatinga lowere 77 7 6 3 191 10 51 21 260 21 854 38 1439 Araffljo et al. (2004)

Oxisols caatinga upperc 19 5 7 2 48 12 58 15 40 10 224 57 396 Araffljo et al. (2004)

Oxisols caatinga midd 21 8 6 2 37 14 60 23 32 12 109 41 265 Araffljo et al. (2004)

Oxisols caatinga lowere 18 6 6 2 45 15 78 25 32 10 128 42 307 Araffljo et al. (2004)

a VG: vegetation cover; b d. pasture: degraded pasture; c upper: upper slope; d mid: mid slope; e lower: lower slope.

316Negassa,Leinw

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highly enriched, whereas in highly weathered Oxisols, thelabile and moderately labile Pi fractions were significantly in-creased over those in the respective control treatments.Regardless of duration of incubation, and sources of appliedP, the absolute concentration and proportion of Po wereslightly affected in incubated tropical soils except under highP loading.

4.2.2 Pot experiments

Continuous cropping of maize (Zea mays L.) and soybean(Glycine max [L.] Merr) on different tropical soils loaded withhigh dose of fertilizer P highly depleted the labile and moder-ately labile Pi fractions (Guo et al., 2000). These authors alsostated that the Po and stable P fractions remained almostconstant at the end of 14 crop harvests except the labile Po ina Mollisol that was highly depleted. Similarly, growing alfalfa(Medicago sativa L.) for 66 d highly depleted the native labilePi in the rhizosphere of different soil orders without affectingthe Po fractions (Crews, 1996). This clearly showed that soilPo has minor contribution to plant nutrition under high dose offertilizer P but is a major source of plant-available P in low-input tropical agriculture (Adepetu and Corey, 1976; Tiessenet al., 1992; Nziguheba and B�nemann, 2005). Althoughsuch a high dose of fertilizer-P application practically doesnot exist elsewhere, supporting the P-fraction data by plant-biomass yields could help to understand the efficiency of resi-dual-P fertilizers for plant growth that usually advocated as astrategy for P capitalization in low-P subtropical and tropicalsoils.

4.2.3 Short-term field studies

Table 9 also compiles a number of studies on short-termland-use and management effects on P fractions. Forinstance, short fallow periods decreased the absolute con-centration of Po fractions by 35% in the third year as compar-ed with the first year and increased the concentration ofHCl-P by 48% (Derry et al., 2005). This indicates the minerali-zation of Po fractions and transformation into either plant-available P or HCl-P fractions or losses by erosion dependingon prevailing soil properties, land-management systems, andclimatic elements. Total P content also declined over yearswhich masked most of the change in relative proportions ofdifferent P fractions (Tab. 9). Moreover, continuous applica-tion of fertilizer P to the strongly weathered tropical soils sub-stantially increased both the absolute concentration and rela-tive proportions of the labile and moderately labile Pi, and ofthe HCl-P fractions (Dobermann et al., 2002) (Tab. 9). Theamorphous and crystalline sesquioxides were important indetermining the distribution and transformation of the appliedP in these soils (Dobermann et al., 2002). As the amounts ofcrystalline and amorphous Ca compounds are very low in tro-pical Ultisols and Oxisols, an increment in the HCl-P fractioncould be attributed to the presence of Po, which is usually notdetermined in this fraction. Although no information exists onPo status of 1 M HCl–extracted P fraction in tropical soils, astudy conducted on temperate soils indicated high concentra-tion of Po in the HCl-P fraction in some soils (He et al., 2006).

Phosphorus fractions were investigated in various land-useand management systems in different tropical soils (Tiessenet al., 1992; Paniagua et al., 1995; Damodar Reddy et al.,1999; Oberson et al., 2001; Abekoe and Sahrawat, 2003).Continuous application of 23 to 62 kg P ha–1 y–1 for 10 y in-creased the proportion of labile Pi in Inceptisols (Tab. 9).However, application of organic amendments without fertilizerP decreased both the labile Pi and Po fractions (Paniaguaet al., 1995). This could be explained by the low P content ofthe organic amendments. Correspondingly, continuous appli-cation of integrated manure and fertilizer P for 4 y increasedthe absolute concentration of labile and moderately labile Pfractions. Among the labile fractions, the Pi increased by fac-tor 4 in plots receiving the highest P dose as compared withPi in the control (Damodar Reddy et al., 1999) (Tab. 9). Thisclearly indicated that continuous application of P at leastthree times greater than the normal plant requirement isrequired to detect changes in labile P fractions by Hedleysequential-P-fractionation method within a short-term study.However, on highly weathered tropical soils like Oxisols,mineralization of Po fractions and subsequent transformationinto plant-available P or stable P fractions contributed to Podepletion in Oxisols (Tiessen et al., 1992). As a result, fertili-zer-P application to highly weathered tropical soils scarcelyenriched any of the Po fractions (Tiessen et al., 1984; Friesenet al., 1997; Oberson et al., 2001).

Crop production without fertilizer-P application decreased themoderately labile Po fraction by 42% in an Ultisol within a dec-ade confirming that moderately labile Po fractions weresources of plant-available P in tropical low-input agriculture(Beck and Sanchez, 1996). The residuals of high doses offertilizer P in highly weathered tropical soils were not suffi-cient for successive plant growth without P input. Thisencourages applying low rate of P at each cropping seasonfrequently (Nziguheba et al., 2002; Abekoe and Sahrawat,2003). This contradicts the recommendations of manyresearchers who suggested high doses of fertilizer P to satu-rate P-sorption sites in P-fixing tropical soils (Buresh et al.,1997; Sanchez et al., 1997). An economic constraint alsodoes not allow small-scale farmers to apply even optimumfertilizer-P rate for crop production in most countries of sub-tropical and tropical climates.

4.3 Effects of medium- and long-term land-useand management systems

Many studies were conducted in tropical agroecosystems tounderstand the impact of medium-term (10–25 y) land-useand management systems on P fractions (Solomon and Leh-mann, 2000; Solomon et al., 2002; Techienkoua and Zech,2003; Tiessen et al., 1992). Continuous cultivation of differenttropical soils with little input of P drastically decreased theabsolute concentration of all P fractions as compared withtheir respective uncultivated soils (Tab. 10). Conversely, theabsolute concentration of labile P fraction was increased byfactor 2 to 6 in homesteads (Iyamuremye et al., 1996; Solo-mon and Lehmann, 2000). This is attributed to continuousapplication of organic materials in the homestead, which is atypical soil-fertility management system in small-scale farms



ª2009

WILE

Y-VCHVerlag

GmbH

&Co.K

GaA

,Weinheim

www.plant-soil.com

Table 9: Phosphorus distribution in tropical soils subjected to incubation, short-term fallows, and continuous P application.

Soil order Landuse

Psource

P appli-cation

Dura-tion

NaHCO3-Pi NaHCO3-Po NaOH-Pi NaOH-Po HCl-P Residual-P TP References

(kg ha–1) (d) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (mgkg–1)

(%) (sum)

Incubation studiesa

Vertisols cultivated 0 92 5 2 7 2 44 11 85 21 139 34 97 24 406 Damodar Reddy et al. (2001)

Alfisols cultivated 0 120 12 5 20 8 45 17 114 43 18 7 54 21 263 Nziguheba et al. (1998)

Alfisols cultivated CRGMc 15 120 19 7 23 8 43 16 115 42 17 6 55 20 271 Damodar Reddy et al. (2005)

Oxisols cultivated 0 10 6 4 6 4 20 13 42 27 36 23 45 29 155 Buehler et al. (2002)

Oxisols cultivated Fert-Pb 40 10 35 11 14 4 104 32 51 16 61 19 62 19 325

Short-term fallow (y–1) (y)

Inceptisol fallow 0 1 2 0 32 4 58 7 244 28 31 4 503 58 870 Derry et al. (2005)



Ultisol fallow 0 3 2 0 0 52 10 164 33 29 6 253 51 500 Dobermann et al. (2004)

Ultisol fallow Fert-Pb 155 3 26 4 0 154 21 200 27 70 10 285 39 735 Dobermann et al. (2004)

Oxisol fallow 0 2 2 0 0 43 11 121 30 19 5 217 54 402 Dobermann et al. (2004)

Oxisol fallow Fert-Pb 207 2 39 6 0 163 27 129 21 49 8 235 38 615 Dobermann et al. (2004)

Short-term field studies

Inceptisol cultivated Fert-Pb 39 10 144 6 52 2 698 31 570 25 13 1 770 34 2247 Paniagua et al. (1995)

Inceptisol cultivated mulch 23 10 104 5 52 2 793 36 420 19 15 1 826 37 2210 Paniagua et al. (1995)

Inceptisol cultivated MULFPd 62 10 146 7 48 2 716 34 532 25 14 1 679 32 2135 Paniagua et al. (1995)

Vertisol cultivated 0 4 11 2 14 3 43 9 62 13 159 33 196 40 484 Damodar Reddy et al. (1999)

Vertisol cultivated FMYFPf 66 4 49 8 27 4 69 11 113 17 167 26 223 34 647 Damodar Reddy et al. (1999)

Ultisol cultivated 0 5 8 6 25 18 25 18 0 0 84 59 142 Abekoe and Sahrawat (2003)

Ultisol cultivated Fert-Pb 180 5 14 6 46 19 61 26 1 0 115 49 237 Abekoe and Sahrawat (2003)

Oxisol pasture Fert-Pb 16 5 12 5 15 6 46 17 51 19 139 53 263 Oberson et al. (2001)

Oxisol cultivated Fert-Pb 60 5 34 9 17 5 111 31 43 12 156 43 361 Oberson et al. (2001)

Oxisol fallow 10 5 4 5 3 19 13 24 16 3 2 93 62 149 Tiessen et al. (1992)

a incubation: data were means of similar studies; b Fert-P: fertilizer P; c CRGM: crop residues plus green manure; d MULFP: mulch plus fertilizer P; e FYMFP: farmyard manure plus fertilizer P.

318Negassa,Leinw

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in the subtropics and tropics. Continuous application of P tohighly weathered tropical soils increased the concentration ofdifferent Pi fractions with prominent effects on the moderatelylabile Pi fractions. This showed that the moderately labile Pifractions were both sources and sinks of plant-available P intropical soils (Cross and Schlesinger, 1995; Lilienfein et al.,2000; Techienkoua and Zech, 2003).

Similar to the findings for soils in temperate climates, continu-ous cultivation without P application considerably depletedthe labile and moderately labile P fractions in tropical soils(Solomon et al., 2002; Nwoke et al., 2003). However, thedepletion in subtropical and tropical soils was faster than intemperate soils mainly because of variations in basic soilproperties that emanated from soil-weathering stages, cli-matic elements, and management systems. High tempera-tures in the humid tropics accelerate the development of Ulti-sols and Oxisols with low soil pH and enrichments in variablycharged pedogenic oxides. Under such circumstances, thetransformations of labile and moderately labile Pi fractionsfrom native P and fertilizer-P application into stable P werefast.

A few studies investigated the impact of long-term (>25 y)land-use and management systems in subtropical and tropi-cal soils, and the data confirmed that P fractions weredepleted significantly without P input (Solomon et al., 2002).The application of organic materials did not stop the reductionof Po and residual-P fractions (Agbenin and Goladi, 1998).According to this study, however, application of either fertili-zer P or farmyard manure or a combination of them signifi-cantly increased labile to moderately labile Pi fractions.

In summary, agricultural practices with low P input to differenttropical soils depleted labile and moderately labile P fractions.However, the intensity of depletion depended on basic soilproperties such as soil texture, soil pH, SOM, native concen-tration of total P, and amount of applied P (Duffera andRobarge, 1996, 1999). Activities of soil organisms, types ofplants grown, and management systems could also affect theinternal transformation and cycle of both native and appliedP. As a result, the Hedley sequential P fractionation couldclearly sort out the fate of applied P in tropical soils if thedose of applied P was higher or the duration of managementwith low P input relatively longer.

5 Synthesis: Effect of P application and timeon labile and moderately labile P fractions

Results of studies selected according to variation in time andrate of P application were subjected to multiple-regressionanalyses to test the contribution of these factors on the varia-bility in concentrations of P fractions. Table 11 shows the var-iation in P application and duration of the studies on labileand moderately labile P fractions in soils of temperate, andsubtropical and tropical climate. The variations due to appli-cation of P and duration of studies were 46% in labile and18% in moderately labile P in soils of temperate climate. Thenegative coefficient for time in the data set of moderatelylabile P indicated that P from this fraction can be either trans-


Table

10:E

ffectsof

med

ium-an

dlong

-termsland

-use

andman

agem

ents

ystemson

Pfrac

tions

insu

btropica

land

trop

ical

soils.

Soilorder

Lan

duse

Pso

urce

Pap

plic

ation

Duration

NaH

CO

3-Pi

NaH

CO

3-Po

NaO

H-P

iNaO

H-P

oHCl-P

Res

idual-P

TP

Referen

ces

(kgha

–1)

(d)

(mgkg

–1)

(%)

(mgkg

–1)

(%)

(mgkg

–1)

(%)

(mgkg

–1)

(%)

(mgkg

–1)

(%)

(mgkg

–1)

(%)

(sum

)

Med

ium-term

studies

Alfiso

lscu

ltiva

ted

015

184

164

7717

5613

8820

189

4344

4Solom

onan

dLe

hman

n(200

0)

Alfiso

lho

mes

tead

man

ures

0>10

121

1370

713

814

9310

207

2232

734

956

Solom

onan

dLe

hman

n(200

0)

Alfiso

lcu

ltiva

ted

025

51

364

485

227

2410

160

965

935

Solom

onet

al.(20

02)

Ultiso

lE.plan

ta0

1559

52

043

735

137

1119

716

399

3212

31Te

chienk

ouaan

dZec

h(200

3

Ultiso

lcu

ltiva

ted

fertilize

rP

67>15

677

222

279

2720

120

198

1925

825

1025

Tech

ienk

ouaan

dZec

h(200

3

Ultiso

lT.

Plant

bfertilize

rP

150

1579

513

160

135

235

1424

915

521

3116

98Te

chienk

ouaan

dZec

h(200

3

Ultiso

lcu

ltiva

ted

013

83

136

3314

4620

21

132

5623

4Bec

kan

dSan

chez

(199

6)

Ultiso

lcu

ltiva

ted

fertilize

rP

8013

5713

4410

126

2976

1729

710

424

436

Bec

kan

dSan

chez

(199

6)

Oxiso

lcu

ltiva

ted

fertilize

rP

7011

132

2396

1715

827

191

3357

7Neu

feldte

tal.(200

0)

Oxiso

lRefores

ted

1333

2350

3539

2819

1314

1Neu

feldte

tal.(200

0)

Oxiso

lRefores

ted

fertilize

rP

3420

6916

102

2489

2115

938

419

Neu

feldte

tal.(200

0)

Oxiso

lcu

ltiva

ted

fertilize

rP

129

64

324

1620

134

393

6015

4Ties

senet

al.(19

92)

Long-term

studies

Alfiso

lT.

plan

tfertilize

rP

1035

121

485

485

227

2310

163

365

978

Solom

onet

al.(20

02)

Alfiso

lcu

ltiva

ted

045

170

1747

513

013

146

1511

011

397

4010

00Agb

enin

andGolad

i(19

98)

Alfiso

lcu

ltiva

ted

fertilize

rP

3645

697

2310

13

320

1035

712

338

1112

7941

3092

Agb

enin

andGolad

i(19

98)

Alfiso

lcu

ltiva

ted

mixture

5445

527

2811

06

393

2127

014

313

1727

014

1883

Agb

enin

andGolad

i(19

98)

aE.plan

t:eu

calyptus

plan

tatio

n;bT.

plan

t:teaplan

tatio

n.


formed into labile or stable P over time. The coefficients forannual P application (0.15) and intercepts (18.2) were smallerin the equations for the subtropical and tropical soils compar-ed to that for temperate soils, indicating the generally lowerlevel of labile P in the former soils. However, the coefficient of6.32 for the duration of experiment indicated that the factor“time” had a stronger influence on labile P in the subtropicaland tropical soils than in the temperate soils. This means thatP remains in a labile form for only short periods in the subtro-pics and tropics. Furthermore, the lower values for R2, whichwas not significant (p > 0.05) for moderately labile P, couldbe attributed to a stronger influence of soil-weathering stagesand resulting effects of soil physico-chemical properties onlabile and moderately labile P in subtropical and tropical thanin the temperate soils (Tiessen et al., 1984).

We also calculated multiple-regression equations using thedifferences for P concentrations (DPlabile) and P applications(DPapplied) for labile P in subtropical and tropical soils:

DPlabile [mg kg–1] = 0.1 � DPapplied [kg ha–1 y–1] + 3.8 � time[y] + 18.2; R2 = 0.50***.

The standard error of labile-P analyses in tropical soils was onaverage 6 mgkg–1 (Negassa, unpublished). An experimentwith, e.g., 20 kg annual P application should then have run for>2 y before a significant increase (e.g., by 18 mg Plabile kg–1)can be expected. In other words, this above equation andthose in Table 11 can be used to calculate the concentrationsof P fractions and their possible changes from the data of fieldexperiments. This avoids running the time- and labor-con-suming Hedley sequential P fractionation where no changesin P fractions are expected.

Table 12 shows the Pearson correlation coefficients among Pfractions in temperate, subtropical, and tropical soils. Theresults revealed strong associations among most of P frac-tions in temperate soils and among some P fractions in sub-tropical and tropical soils. The Pearson correlation coeffi-cients in Tab. 12 were stronger than those reported by Ties-sen et al. (1984), but were comparable with those reported byZheng et al. (2002). This general agreement clearly showsthat the concentrations of different P fractions depend oneach other, although other external factors such as P fertiliza-tion, OM decomposition, plant uptake of P, and associated

soil properties determined transformations among soil Ppools.

6 Phosphorus speciation by 31P NMR andX-ray absorption near-edge structurespectroscopy

The Hedley fractionation assigned P fractions on the basis oftheir different solubility in extractants of increasing strength;in other words, these P fractions are “operationally defined”.Although NaHCO3-P was tentatively assigned to Pi sorbed oncrystalline Al and Fe oxides and easily mineralized Po,NaOH-P to Pi sorbed to amorphous Al and Fe oxides andstable Po, and HCl-P to Ca-P-compounds (Tiessen et al.,1984), an unequivocal confirmation that the above extrac-tants solubilized exclusively the target P fraction is still lack-ing (Toor et al., 2006). Consequently, the value of the Hedleyfractionation in providing information about the biogeo-chemical behavior of P is limited (Hinsinger, 2001) because itdoes not give a P speciation in the different fractions.

Recent advances in soil-P speciation were achieved by theapplication of 31P nuclear–magnetic resonance (NMR) spec-troscopy in the liquid and solid state and by X-ray absorptionnear-edge structure (XANES) spectroscopy (e.g., Newmanand Tate, 1980; Condron et al., 1997, 2005; Hesterberg et al.,1999; Khare et al., 2004; Lombi et al., 2006). The liquid-state31P NMR was widely used to investigate effects of land-useand management systems on P speciation as recentlyreviewed by Condron et al. (2005). A few reports on combin-ed application of 31P NMR and Hedley fractionation in tempe-rate and tropical soils appeared (Leinweber et al., 1997a;Solomon and Lehmann, 2000; Taranto et al., 2000; Solomonet al., 2002; McDowell et al., 2005). Although these studiesdid not always derive relationships of the data generated bythe two methods, orthophosphate diesters and monoesterswere observed as main groups of Po and paralleled with theHedley fractions. The orthophosphate diesters could rep-resent the easily mineralized Po, extracted by 0.5M NaHCO3,whereas the orthophosphate monoesters were assigned tomore stable Po extracted by 0.1 M NaOH-P. Moreover, thehighest concentration of Pi (36% to 89%) was observed byliquid-state 31P NMR in excessively manured temperate soilsas the NaOH extracted most of the labile and moderately


Table 11: Multiple-linear-regression equations (y [mg kg–1] = a � x + b � z + c) showing the dependency of labile and moderately labile P frac-tions on the annual P application and duration of the studies in temperate, subtropical, and tropical soils. (a: slope of P application, b: slopeof time)

Soil origin and P fraction a = P (kg ha–1 y–1) b = Time (y) c = Intercept R2 n

Temperate soils

Labile P 0.66 – 0.11 0.14 – 0.63 102.7 – 21.5 0.46** 46

Moderately labile P 0.69 – 0.21 –0.64 – 1.29 224.3 – 43.6 0.18* 46

Subtropical and tropical soils

Labile P 0.15 – 0.04 6.32 – 3.00 18.2 – 18.9 0.34** 23

Moderately labile P 0.22 – 0.31 48.69 – 21.68 107.1 – 136.4 0.12ns 23

* significant at 0.05; ns: nonsignificant at 0.05 level; **: multiple regression is significant at 0.01 level.


labile Pi (Leinweber et al., 1997a). Similarly, 50% to 70% of Piwas observed in various land-use systems of tropical soilswith liquid-state 31P NMR (Solomon and Lehmann, 2000).However, the efficiency of 31P NMR in determining native Piwas small, but 20% to 50% of Po extracted by the Hedleysequential P fraction could be assigned by 31P NMR (Tarantoet al., 2000). This clearly shows that land-use and manage-ment systems governed the P species, and that these effectscould be determined in good agreement with the Hedley Pfractions and with liquid-state 31P NMR.

The application of solid-state 31P NMR spectroscopy to soilsis limited to a minimum concentration of 1 mg P g–1 requiredfor signal detection (Condron et al., 1997; Toor et al., 2006).Moreover, high concentrations of paramagnetics also nega-tively affected the spectra quality by decreasing signal-to-noise ratio and by increasing intensity of spinning side bands(Cade-Menun et al., 2002; Condron et al., 2005). Further-more, the association of different cations with P ions andocclusion of P species within the structure of organic phasesmade spectral resolution poor (Frossard et al., 1994; Shandet al., 1999). This may be one reason why solid-state 31PNMR was not used in combination with the Hedley P fraction.

Synchrotron-based P K-edge XANES is a new analyticaltechnique that advanced the knowledge of P species inminerals and soils (Hesterberg et al., 1999; Beaucheminet al., 2003; Sato et al., 2005) and organic wastes (Shoberet al., 2006; Toor et al., 2006). Moreover, the P K-edgeXANES was used to study P speciation and distribution incalcareous soils (Lombi et al., 2006) and to investigateadsorbed phosphate distribution in ferrihydrite and boehmite(Khare et al., 2004). However, as far as we know, only twostudies supported the Hedley sequential P fractions with P K-

edge XANES data (Beauchemin et al., 2003; Kruse and Lein-weber, 2008). According to these authors, the K-edgeXANES directly identified some forms of Pi in the soil, where-as the Hedley sequential P fractionation provided indirectsupporting data. However, the K-edge XANES in its presentresolution failed to identify Po compounds because the spec-tral features of Po were scarcely different from Pi regardlessof slight differences in the intensity of the white-line peak andshape of the oxygen oscillation (Beauchemin et al., 2003;Toor et al., 2006).

In a recent study on different types of manure, Ajiboye et al.(2007) clearly showed the advantages of the combination ofsequential P fractionation, solution 31P NMR, and P K-edgeXANES in P speciation. They emphasized that the combina-tion of any two of these techniques could not provide enoughinformation about P chemistry, but all three can. In summary,the specific advantages and disadvantages of both the clas-sic Hedley sequential P fractionation and the advanced P-speciation techniques strongly call for a combined applicationto increase our understanding of P chemistry in soils andrelated materials.

7 Conclusions

(1) The Hedley sequential P fractionation was suited to detectchanges in concentrations of different P fractions, dependingon the amount of P applied or severity of P depletion, and theduration of land-use and management impacts on P turnoverin soils. Therefore, this fractionation is a useful approach toinvestigate the fate of native and applied P in agroecosys-tems to adopt appropriate use and management concepts.


Table 12: Pearson correlation coefficients among concentrations of P fractions in temperate, subtropical, and tropical soils.

P fraction Resin-P NaHCO3-Pi NaHCO3-Po NaOH-Pi NaOH-Po HCl-P

(mg kg–1)

Temperate soils (n = 55)

Resin-P

NaHCO3-Pi 0.74**

NaHCO3-Po 0.57** 0.65**

NaOH-Pi 0.51** 0.70** 0.26 ns

NaOH-Po 0.69** 0.83** 0.79** 0.55*

HCl-P 0.54** 0.24 ns 0.23 ns 0.37** 0.32*

Residual-P 0.45** 0.50** 0.43** 0.00 0.47** 0.00

Subtropical and tropical soils (n = 28 to 32)

NaHCO3-Pi

NaHCO3-Po 0.85**

NaOH-Pi 0.41* 0.38*

NaOH-Po 0.45* 0.57** 0.81**

HCl-P 0.69** 0.46* 0.25 ns 0.07 ns

Residual-P 0.58** 0.62** 0.81** 0.81 0.16 ns

* significant at 0.05; ns: nonsignificant level; **: correlation is significant at 0.01 level.


(2) In natural ecosystems, the concentration of total P wassimilar in temperate, subtropical, and tropical soils regardlessof soil orders. However, subjecting the soils to different land-use and management systems radically shifted the concen-trations and distribution of P fractions. Loading soils with Pgreatly increased the labile Pi fraction in temperate climatesand the moderately labile Pi fraction in the subtropics and tro-pics. Therefore, excess labile Pi may be subject to runoff andleaching losses in temperate soils. The role of enriched mod-erately labile Pi in subtropical and tropical soils, either assource for plant nutrition or as potential contaminant of fresh-water, is less clear. Irrespectively of climatic zone, manage-ment could scarcely enrich Po in the short term, but the Pofractions were strongly depleted in tropical soils under low Pinput. Therefore, management of tropical soils should bedirected to maintain a Po level sufficient for the nutrition ofarable crops.

(3) The review of P in soil orders by Cross and Schlesinger(1995) and the present review strongly suggest that the Hed-ley fractions may have different meanings in both chemicalspecies and pedoecological functions in temperate comparedwith those in subtropical and tropical soils. Therefore, metho-dological approaches to improve the interpretation basis ofthe Hedley fractionation and derived consequences for soilmanagement must consider the soil mineralogical and phy-sico-chemical properties. Furthermore, relationships shouldbe established between labile and moderately labile P frac-tions and crop yields in different climates.

(4) The complementary application of advanced analyticaltechniques such as 31P NMR and synchrotron-basedP XANES will reveal more detailed insights into the chemicalspecies behind the sequential Hedley fractions and nonex-tractable residues. Success in the broad application of thesecomplementary analytical approaches will depend onimprovements in spectral resolution and P-detection limits,developments of new techniques and databases of referencecompounds, e.g., for XANES at the P L-edge (Kruse et al.,2009), and last but not least from broad access of researchersto the relevant techniques and facilities.

Acknowledgments

This research was supported by the German AcademicExchange Service (DAAD) project A/05/33320 who provideda fellowship for the first author. We thank Elena Heilmann,Institute for Land Use, University of Rostock, for assisting usin literature searches. The two anonymous reviewers arehighly acknowledged for their constructive comments andsuggestions that improved the quality of the manuscript.

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How does the Hedley sequential phosphorus fractionation reflect impacts of land use and management on soil phosphorus: A review

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