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An Algorithm for Estimating Amounts of Rock Phosphate Needed to MeetCrop Phosphorus Requirements in West African SoilsAminata S. Diarraa; Russell S. Yostb; Mamadou D. Doumbiaa; Tasnee Attanandanac; Adama Bagayokoa;Aliou B. Kouyatea; Richard Kablanb; Xinmin Wangb

a LaboSEP, Institut d'Economie Rurale BP 262, Bamako, Mali b Department of Tropical Plants and SoilScience, University of Hawaii at Manoa, Honolulu, Hawaii, USA c Department of Soil Science, Facultyof Agriculture, Kasetsart University, Jatujak, Bangkok, Thailand

Online publication date: 18 March 2004

To cite this Article Diarra, Aminata S. , Yost, Russell S. , Doumbia, Mamadou D. , Attanandana, Tasnee , Bagayoko,Adama , Kouyate, Aliou B. , Kablan, Richard and Wang, Xinmin(2004) 'An Algorithm for Estimating Amounts of RockPhosphate Needed to Meet Crop Phosphorus Requirements in West African Soils', Communications in Soil Science andPlant Analysis, 35: 3, 385 — 397To link to this Article: DOI: 10.1081/CSS-120029720URL: http://dx.doi.org/10.1081/CSS-120029720

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COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS

Vol. 35, Nos. 3 & 4, pp. 385–397, 2004

An Algorithm for Estimating Amounts of Rock

Phosphate Needed to Meet Crop Phosphorus

Requirements in West African Soils

Aminata S. Diarra,1 Russell S. Yost,2,*Mamadou D. Doumbia,1

Tasnee Attanandana,3 Adama Bagayoko,1 Aliou B. Kouyate,1

Richard Kablan,2 and Xinmin Wang2

1LaboSEP, Institut d’Economie Rurale BP 262, Bamako, Mali2Department of Tropical Plants and Soil Science, University of

Hawaii at Manoa, Honolulu, Hawaii, USA3Department of Soil Science, Faculty of Agriculture, Kasetsart

University, Jatujak, Bangkok, Thailand

ABSTRACT

An incubation study was conducted (i) to investigate the influence of

soil properties on the dissolution of Tilemsi rock phosphate (PNT)

and extractability of phosphorus (P) after dissolution and (ii) to

develop an algorithm for estimating amounts of rock P needed tomeet

crop P requirements in West African soils. Subsequently, the amount

*Correspondence: Russell S. Yost, Department of Tropical Plants and Soil

Science, University of Hawaii at Monoa, 3190 Maile Way, Honolulu, HI 96822;

Fax: 808-956-3894; E-mail: rsyost@Hawaii.edu.

385

DOI: 10.1081/CSS-120029720 0010-3624 (Print); 1532-2416 (Online)

Copyright & 2004 by Marcel Dekker, Inc. www.dekker.com

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of phosphate rock (PR) that had dissolved and changes in Bray-P and

Olsen-P were respectively determined by measuring the increase in

extractable P (�NaOH-P) and changes in plant-available P (�Olsen-P

and� Bray-P). The extent of dissolution of PNT ranged from 3.3 and

38.2% of the total P added to the soils. The greatest PNT dissolution

was obtained in Niessumana and Longorola soils, which are acid

lowland soils. The highest amount of plant-available P was also

measured in these soils. Exchangeable acidity, calcium (Ca) satura-

tion, and effective cation exchange capacity appeared to be the factors

controlling the PNT dissolution. The amount of rock phosphate

dissolved in contrasting Malian soils could be predicted by a

modified MacKay’s equation of the form: Y¼Aþ (B � e�c � time),

where Y¼ amount of PNT dissolved, measured by NaOH extraction;

A¼ 78.1627þ 30.62149 acidity� 0.63335CaSat; B¼�16.58786�

21.74709 acidityþ 4.07675ECEC and c¼ curvature coefficient. The

amount of P to reach the optimal yield for a given crop, which is the

difference between P critical level andmeasured P in a given soil, could

be estimated using the plant available-P/NaOH-P ratio and the above

modified MacKay’s equation.

Key Words: Phosphate rocks; Tilemsi rock phosphate (PNT);

PR dissolution; NaOH-P and soils.

INTRODUCTION

Many research programs have provided evidence that P is the mostdeficient and plant growth-limiting nutrient in West African soils.[1–5]

Phosphate rock (PR) materials from around the world have beenevaluated for their suitability as low-cost, direct application P fertilizers.However, many PRs have not proven to be sufficiently soluble for directapplication in intensive agricultural production.[6]

The PR dissolution depends on chemical and physical properties ofthe PR and the soil properties.[7] Several scientists[6,8,9] pointed out thatPR dissolution is highly related to PR reactivity. The reactivity dependson the isomorphous substitution of CO3/PO4 in the PR.[10] Mokwunye[9]

founded that West African PRs are not very reactive.Regarding soil properties that might be expected to affect the extent

of dissolution of rock phosphate in soils, Khasawneh and Doll[6] listedthe following:

1. Concentration of Hþ in the soil and the Hþ buffer capacity insoil: the dissolution of PR in soils is driven by the supply of Hþ,

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which is controlled by the initial soil pH and the pH buffercapacity of the soil. The presence of Hþ ions in the soil results inthe rapid conversion of the PO3�

4 to H2PO�4 and HPO2�

4 . Severalauthors[11–16] also found that the rate of dissolution of PRincreased with increasing pH buffer capacity of the soil. In anyevent, the ability of a soil to supply Hþ ions appears to be animportant factor controlling dissolution of PR.

2. Concentration of P in soil solution and P buffering capacity ofthe soil: PR dissolution increases as the P retention capacity ofsoil increases.[6]

3. Concentration of Ca2þ in soil solution and Ca2þ bufferingcapacity of the soil: PR dissolution increases with lower exchange-able Ca in soil. Robinson and Syers[17] found the Ca sink hada large influence on PR dissolution.

4. Organic matter content: organic matter is related to the bondingof Ca and provides an effective sink for Ca.[6]

5. Soil texture: coarse-textured soils and sands are, in general, notgood sinks for P and Ca.[6]

Wright et al.[14] reported a low dissolution of PR in soil with high pH,high Ca saturation and a low P retention capacity. Using 30 contrastingsoils MacKay et al.[18] found that percent Ca-saturation, P-sorptioncapacity, and Ca-exchange capacity of the soil were the three most impor-tant parameters influencing Sechura PR (from Peru) dissolution in soils.They found that the dissolution of Sechura PR increased as exchangeableCa decreased and as P-sorption capacity increased. Chu et al.,[19] Chienet al.,[20] and Smyth and Sanchez[21] also found that the dissolution of PRincreased as the P-sorption capacity of the soil increased. Bolland andBarrow[22] demonstrated that the capacity of the soil to adsorb P mightpotentially play amajor role in the dissolution of apatite rock phosphate insoil. In the computer simulationmodel of PR dissolution[18] the capacity ofthe soil to adsorb P was more important than the pH buffering capacity ofthe soil. Hammond et al.[7] and Wright et al.[14] suggested that dissolutionof PR depended on pH, Ca status in soil (exchangeable Ca and soil Casaturation), and P status of soil (soil solution P and P-sorption capacity).

Some of the early studies compared the effects of clay percentageon increasing rock phosphate dissolution and increasing P retention.[23]

The simulation results suggested that while increased clay percentageincreased rock phosphate dissolution, it increased P retention even more,resulting in reduced P availability (Wang 1997, personal communication).

The purpose of this study was to develop an algorithm (method)that would produce quantitative estimates of the amount of rock

Estimating Amounts of Rock Phosphate 387

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phosphate necessary to provide nutrient P for crops in West Africa.The indicator of adequate amounts of nutrient P can be extractable P suchas Bray 1 or Olsen methods. Other extractants could be used after alaboratory incubation and calibration with NaOH extractable P. Theexample developed in this article uses Tilemsi rock phosphate from Mali,West Africa.

MATERIALS AND METHODS

In developing the algorithm, it was recognized that factors thatincrease dissolution sometimes also increase P sorption or retention.Therefore, the two processes of dissolution and retention were separated.Dissolution processes include soil factors (soil pH, soil calcium status,etc.), type of rock phosphate, and many of the management factors suchas type of crop and weather conditions. The P retention process, however,seemed to be relatively unaffected by variable management factors, at leastas proposed by Cox.[24]

Incubation studies were carried out with five soils representative of thefood and fiber production agriculture in Mali. Selected properties of thesoils used in the investigation are shown in Table 1. The soils were air-driedand passed through a 2-mm sieve. The following chemical parameterswere determined: organic carbon by combustion,[25] pH in water at a soil:solution ratio 1:1, exchangeable cations by extraction with 1M NH4OAc(pH 7),[26–28] exchangeable acidity,[26] ECEC (effective cation exchange

Table 1. Soil properties of samples selected for rock phosphate study.

Soil

pH(H2O)

1:1

Clay

(%)

ECECa

(cmolc kg�1)

Exchangeable

(cmolc kg�1)

CaSat

(%)

5b 10b

Ca Acidity kg PNT/ha

Cinzana plateau 5.0 5 1.14 0.54 0.33 47 50 100

Cinzana valley 6.47 36 11.53 9.11 0 79 3568 7136

Cinzana slope 5.6 4 1.31 1.02 0 78 134 267

Niessumana 4.3 36.5 6.35 1.37 4.2 22 39 78

Longorola 4.9 36.5 7.34 2.08 3.83 28 72 143

aECEC¼ effective cation exchange capacity.bEstimates of amounts of rock phosphate (Tilemsi) to increase Bray 1 by 5 and

10mgP/kg, respectively.

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capacity) was estimated by summing the exchangeable cations and

exchangeable acidity, clay content by the pipette method,[29] and plant

available P by extraction with sodium bicarbonate[30] and Bray

1-extractable P (0.025M HClþ 0.03M NH4F).[31]

The rate of dissolution of Tilemsi PR over 60 days was investigated.

Tilemsi PR (PNT) was ground to pass a 250-mm sieve. The characteristics

of the PR material are given in Table 2.The PNT was added to the soils at a rate of 500mgkg�1 soil,

thoroughly mixed, moistened to field capacity with deionized water, and

incubated at 22–24�C. A control was included for each soil and was

similarly treated. Each treatment was in 3 replications. Soils were aerated

and the moisture content adjusted to field capacity every two days during

the incubation. Treated and untreated (control) soils were sampled after

0, 3, 7, 15, 30, and 60 days of incubation to estimate the rate of dissolution

of PNT. Extent of PR dissolution and available P (Olsen- and Bray

1-extractable P) were determined at each sampling time. The extent of

dissolution in the various soil samples was estimated by the 0.5M NaOH

method.[18] Soil samples were extracted for 16 h with 0.5MNaOH at a soil

to solution ratio of 1:100 following a prewash with 1M NaCl for 1 h.

Phosphorus in the extracts was determined colorimetrically by the method

of Murphy and Riley[33] and absorbance was measured at 880 nm. The

difference in P level (�P-NaOH) between treated and untreated samples

was used as an estimate of PR dissolution. The available P was determined

in treated and untreated soils at each sampling time. Extractable P was

estimated by the Olsen and Bray 1 methods. The difference in extractable

P (�P-Olsen and �P-Bray) between treated and untreated samples was

used as an estimate of P available for plants after PR dissolution and

subsequent reaction of the released P with soil. Data were statistically

analyzed using the General Linear Model procedure of SAS.[34]

Table 2. Selected chemical characteristics of Tilemsi PR.

Location Solubility

Total P

(%)

ApatiteCitrate

soluble P

(% of rock) CO3/PO4

Length of

a-axis A�

Empirical

formula

Tilemsi,

Mali

Medium 12.22 9.331 Ca9.63 Na0.27Mg0.10 (PO4)4.96(CO3)1.04 F2.41

1.65 0.210

Source: Truong et al.[32]

Estimating Amounts of Rock Phosphate 389

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RESULTS AND DISCUSSION

The influence of soil properties on the rate and extent of dissolution ofa PR can be seen clearly in Fig. 1. The increase in NaOH-extractable P in asoil, to which PNT has been added, relative to the control soil, can be takento represent the amount of P dissolved from the PR. The PNT dissolved toa differing extent in different soils. The rate of dissolution of PNT rangedfrom 3.3 to 38.2% of the total P added to the soils. The shapes of thedissolution curves were similar. The rate of dissolution rapidly slowedafter about 7–14 days incubation. In each case, the reaction reachedequilibrium after 40–50 days. Other authors[17,21,23,35,36] obtained similarshaped dissolution curves. The maximum PNT dissolution, in this study,followed the sequence: Niessumana>Longorola>Cinzana plateau>Cinzana slope>Cinzana valley, which is consistent with the decreasingCa-saturation of the soils. Dissolution of PNT has often been shown toincrease with decreasing Ca-saturation of soil.[17,18]

The dissolution curves obtained for 5 soils could be described by amodified MacKay’s equation of the form:

Y ¼ Aþ ðB � e�c�timeÞ ð1Þ

in which Y¼ amount of PNT dissolved, measured by NaOH extractionat time; A: asymptote; B: difference between the asymptote and theintercept; and c: curvature coefficient.

0

50

100

150

200

250

0 20 40 60 80

Incubation time, Days

NaO

H-P

, m

g/k

g

Cinzana plateau - pH 5.0

Cinzana Valley - pH 6.47

Cinzana slope - pH 5.6

Niessumana - pH 4.3

Longorola - pH 4.9

Figure 1. Predicted dissolution of Tilemsi rock phosphate in soils of varying

acidity, Ca saturation, and effective cation exchange capacity. Symbols-

experimental data, lines-model predictions. (View this art in color at www.

dekker.com.)

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When the Cinzana valley soil with pH 6.5, was excluded from theanalysis, the stepwise multiple linear regression gave the followingequations to predict A and B.

A ¼ 78:1627þ 30:62149 acidity� 0:63335CaSat (Residual

Mean Square ¼ 0:16132Þ ð2Þ

B ¼ �16:58786� 21:74709 acidityþ 4:07675 ECEC (Residual

Mean Square ¼ 0:01463Þ ð3Þ

where CaSat¼Ca-saturation, %. CaSat can be calculated from the datain Table 1. Acidity and ECEC are in cmolc kg

�1 as in Table 1.By using Eqs. (1)–(3) for acid soils (pH 5.6 or below), the rate and

extent of dissolution of PNT can be determined. However, the modelmust be evaluated under field conditions.

These equations relate the PR dissolution to the percent Ca satura-tion, effective cation exchangeable capacity and soil acidity. Khasawnehand Doll,[6] MacKay et al.,[18] and Robinson and Syers[17] demonstratedthat Ca saturation had a large influence on PR dissolution.

An Algorithm to Predict Amounts of Rock Phosphate

Necessary to Meet Plant Requirements

The proposed method begins with an analysis by the PDSS(Phosphorus Decision Support System), in which the user selects thecrop and indicates the soil test and soil test values of the field or land tobe managed (Fig. 2). If the soil test value is below the critical level then

PredictionNo P deficiency - EXIT

Yes P deficient

Rock P Rock P module

Recommendation

DiagnosisChoose P materiel

Soluble P (Treble Super)

Economic Analysis

Figure 2. Phosphorus decision support system and linkages of PR module.

Estimating Amounts of Rock Phosphate 391

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P is recommended. The amount of P must now be determined. As in thestandard PDSS format, the difference between the critical level and themeasured P is the amount of P that must be added in the form of eithersoluble or rock phosphate fertilizer. This value will be called the DeltaP(Pc-P0). Now the amount of rock phosphate that will provide thisamount of soluble P needs to be determined. This approach now con-tinues by converting the estimate of the extractable P needed to reach theP critical level into the amount of 0.5M NaOH-P that needs to be increased.This value is now a multiple variable function that can be predicted fromsoil and site properties using equations such as that proposed by MacKayet al.[18] and the revision to MacKay’s equation as proposed above(Eqs. (2) and (3)) (Table 1). As the factors in the equation indicated, thisequation will require the input of Ca saturation, effective cation exchangecapacity (ECEC), and soil acidity. Calcium saturation can be approxi-mated by measuring exchangeable Ca and ECEC.

Thus, it is hypothesized that the amount of rock phosphate can bepredicted by relating soil test P levels to changes in NaOH extractable P.The first predictions of this algorithm are given in Table 1 on the far rightcolumns of 5 and 10, indicating the predicted amounts of Tilemsi rockphosphate required to increase Bray 1 by 5 and 10mgP/kg, respectively,after 30 days of incubation. The modified MacKay’s equation can predictthe amount of dissolved PR. This equation needs testing in greenhouseand field conditions.

Predicting Amounts of Dissolved P That Is Plant Available

As well documented in the literature, estimates of the amounts ofNaOH-extractable P are not usually sufficient to estimate plantavailability. For PR to be viable alternative fertilizer, it should dissolvein soil. The second requirement is that the P released remains available toplants. Syers and Mackay[35] pointed out that the soil properties thatincrease the extent of PR dissolution in soil may not necessarily result inan increase in the amount of plant available P.

In this study, Olsen- and Bray1-P were used as the indicators of plantavailable P. Levels of Olsen-P and Bray1-P varied with soils and time ofincubation (Fig. 3). The change in available P (� Olsen- and � Bray-P)ranges from 1.09 to 59.3mg kg�1 and 0.5 to 65.6mg kg�1, respectively.The � Olsen- and � Bray-P in soil where PNT was added generallyincreased as � NaOH-P increased (Figs. 1 and 3).

It is proposed to measure one of the extractable P methods such asBray 1 or Olsen P to establish the relationship between extractable P pools

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of these methods with the pools of NaOH. This proposed relationshipmay not be as highly affected by management factors, as is the rockphosphate dissolution. It may also, after an initial period, assume somenearly constant value, which occurred in the incubation study after about30 days (Fig. 4). It is noted that for these soils, the ratios of Bray 1 andOlsen P to NaOH were quite different among soils, suggesting that thebuffering of these extractable P measured may differ substantially. Thisalso needs testing in field conditions.

Delta Olsen-P.

0

10

20

30

40

50

60

70(a)

(b)

0 10 20 30 40 50 60 70

Time, days

De

lta

Ols

en

-P,

mg

kg

-1

Cinzana platea

Cinzana slope

Cinzana valley

Niessumana

Longorola

Delta Bray-P.

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Time, days

De

lta

Bra

y-P

, m

g/k

g

Cinzana plateau

Cinzana slope

Cinzana valley

Niessumana

Longorola

Figure 3. Changes in extractable P in soil over 60 days following PNT addition

at 500mgPkg�1 of soil.

Estimating Amounts of Rock Phosphate 393

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Perhaps this relationship will be sufficiently constant that it needs tobe estimated only once for a particular soil or perhaps it can be predictedfrom other soil properties such as those used to predict buffer coefficientsuch as percent clay. The relationship between Olsen P/NaOH-P ratioand clay content in soils could be described by the following equation:Olsen P/NaOH-P¼ 0.58� 0.0095 �Clay (R2

¼ 0.69).

CONCLUSIONS

In summary, results from this study demonstrated that thedissolution rate of PR varied from soil to soil but was fairly rapid overfirst 7–14 days of incubation until a steady state was reached afterapproximately 50 days. The incomplete dissolution of PNT is probablydue to the saturation of the Ca and P sinks in the conditions of closed,nonleached system.

The extent of PNT dissolution in 5 Malian soils after 60 daysincubation ranged from 3.3 to 38% of the total P added. Exchangeableacidity, calcium saturation and the effective cation exchange capacitywere the most important factors influencing the PNT dissolution. Nosingle soil property was responsible for promoting the dissolution of PRover all soils investigated. Limited solubility of Tilemsi phosphate rock

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 10 20 30 40 50 60 70

Time, days

Delt

a B

ray-P

/Delt

aN

aO

H

b) Delta Olsen/Delta NaOH

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80

Time, days

Delt

a O

lsen

/delt

aN

aO

H

Cinzana plateau

Cinzana valley

Cinzana slope

Niessumana

Longorola

a) Delta Bray-P/Delta NaOH

Figure 4. Variation of delta available-P/deltaNaOHduring 60 days of incubation

period.

394 Diarra et al.

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occurred in soil with combinations of low exchangeable acidity, high soilpH, and high Ca saturation.

Bray1 and Olsen extractable-P were used as estimates of P availablefor plant after dissolution of PR. The general pattern of available P overtime was similar to that of PR dissolution. Soils with the greatest extentof PR dissolution had the highest levels of extractable P.

The algorithm can be used to predict the amount of PR that shouldbe applied in order to supply nutrient P required to meet croprequirements except in soil with pH 6.4.

More research will be required, especially under field conditions tomodify and validate the algorithm of the PR dissolution in the presenceof the plant and Ca and P removal.

REFERENCES

1. Enwezor, W.O.; Moore, A.W. Phosphorus status of some Nigeriansoils. Soil Sci. 1966, 102, 322–328.

2. Jones,M.;Wild,A.Soils of theWestAfricanSavanna:TheMaintenanceand Improvement of Their Fertility; Tech. Commun. No. 55, CommonWealth Agricultural Bureaux: Farnham Royal, UK, 1975.

3. Poulain, J.F. Amelioration de la fertilite des sols agricoles du Mali.Bilan de treize annees de travaux (1962–1974). Agron. Tropicale1976, 31, 402–416.

4. Pieri, C. Fertilite des cultures vivrieres et fertilite des sols en agriculturepaysanne subsaharienne. Agron. Tropicale. 1986, 41, 1–20.

5. Manu, A.; Bationo, A.; Geiger, S.C. Fertility status of selected milletproducing soils of West Africa with emphasis on phosphorus. SoilSci. 1991, 152, 315–320.

6. Khasawneh, F.E.; Doll, E.L. The use of phosphate rock for directapplication to soils. Adv. Agron. 1978, 30, 159–206.

7. Hammond, L.L.; Chien, S.H.; Mokwunye, A.U. Agronomic value ofunacidulated and partially acidulated phosphate rocks indigenous tothe tropics. Adv. Agron. 1986, 40, 89–140.

8. Hughes, J.C.; Gilkes, R.J. The effect of rock phosphate properties onthe extent of fertilizer dissolution in soils. Aust. J. Soil Res. 1986, 24,209–217.

9. Mokwunye, A.U. Reaction in soils involving phosphate rocks, InProceedings of Seminar on Use of Local Mineral Resources ofSustainable Agriculture in West Africa; Misc. Fertilizer Studies No.11, 1994; Gerner, H., Mokwunye, A.U., Eds.; IFDC-Africa: Lome,Togo, Africa, 1994.

Estimating Amounts of Rock Phosphate 395

Downloaded By: [University of Hawaii] At: 01:09 31 October 2010

ORDER REPRINTS

10. Easterwood, G.W.; Sartain, J.B.; Street, J.J. Fertilizer effectivenessof three carbonate apatites on an acid Ultisol. Commun. Soil Sci.Plant Anal. 1989, 20, 789–800.

11. Anderson, L.; Kussov, W.R.; Corey, R.B. Phosphate rock dissolu-tion in soil: Indications from plant growth studies. Soil Sci. Soc.Am. J. 1985, 49, 918–925.

12. Bolan, N.S.; Hedley, M.J. Dissolution of phosphate rock in soils. 2.Effect of pH on the dissolution and plant available of phosphaterock in soil with pH dependent charge. Fert. Res. 1990, 24, 125–34.

13. Rajan, S.S.S.; Fox, R.L.; Saunders, W.M.H.; Upsdell, M. Influenceof pH, time and rate of application on phosphate rock dissolutionand availability to pastures. Fert. Res. 1991, 28, 85–93.

14. Wright, R.J.; Baligar, V.C.; Belesky, D.P. Dissolution of NorthCarolina phosphate rock in soils of the Appalachian region. Soil Sci.1992, 153, 25–36.

15. Hughes, J.C.; Gilkes, R.J. Rock phosphate dissolution andbicarbonate-soluble P in some soils from South-WesternAustralia. Aust. J. Soil Res. 1994, 32, 767–779.

16. Babare, A.M.; Gilkes, R.J.; Sale, P.W.G. The effect of phosphatebuffering capacity and other soil properties on North Carolinaphosphate rock dissolution, availability of dissolved P and relativeagronomic effectiveness. Australian J. Exp. Agric. 1994, 37, 1037–1049.

17. Robinson, J.S.; Syers, J.K. A critical evaluation of the factorsinfluencing the dissolution of Gafsa phosphate rock. J. Soil Sci.1990, 41, 597–605.

18. Mackay, A.D.; Syers, J.K.; Tillman, R.W.; Gregg, P.E.H. A simplemodel to describe the dissolution of phosphate in soils. Soil Sci. Soc.Am. J. 1986, 50, 291–296.

19. Chu, C.R.; Moschler, W.W.; Thomas, G.W. Rock phosphatetransformations in acid soils. Soil Sci. Soc. Am. J. 1962, 26, 476–478.

20. Chien, S.H.; Clayton, W.R.; McClellan, G.H. Kinetics of dissolu-tion of phosphate rocks in soils. Soil Sci. Soc. Am. J. 1980, 44,260–264.

21. Smyth, T.J.; Sanchez, P.A. Phosphate rock dissolution andavailability in Cerrado soils as affected by phosphorus sorptioncapacity. Soil Sci. Soc. Am. J. 1982, 46, 339–345.

22. Bolland, M.D.A.; Barrow, N.J. Effect of level of application on therelative effectiveness of rock phosphate. Fert. Res. 1988, 15,181–192.

23. Novais, R.F.; Smyth, T.J. Fosforo em Solo e Planta em CondicoesTropicais; Fedeal University of Vicosa: Vicosa, Minas Gerais,Brasil, 1999 (in Portuguese).

396 Diarra et al.

Downloaded By: [University of Hawaii] At: 01:09 31 October 2010

ORDER REPRINTS

24. Cox, F.R. Predicting increases in extractable P from fertilizing soilsof varying clay content. Soil Sci. Soc. Am. J. 1994, 58, 1249–1253.

25. Nelson, D.W.; Sommers, L.E. Total carbon, organic carbon, andorganic matter. Methods of Soil Analysis, Part 2, 2nd Ed.; Page,A.L., Miller, R.H., Keeney, D.R., Eds.; American Society ofAgronomy: Madison, WI, 1982; Agron. No. 9, 539–579.

26. Thomas, G.W. Exchangeable cations. Methods of Soil Analysis,Part 2, 2nd Ed.; Page, A.L., Miller, R.H., Keeney, D.R., Eds.;American Society of Agronomy: Madison, WI, 1982; Agron. No. 9,159–164.

27. Knudsen, D.; Peterson, G.A.; Pratt, P.F. Lithium, sodium, andpotassium. Methods of Soil Analysis, Part 2, 2nd Ed.; Page, A.L.,Miller, R.H., Keeney, D.R., Eds.; American Society of Agronomy:Madison, WI, 1982; Agron. No. 9, 225–245.

28. Lanyon, L.E.; Heald, W.R. Magnesium, calcium, strontium, andbarium. Methods of Soil Analysis, Part 2, 2nd Ed.; Page, A.L.,Miller, R.H., Keeney, D.R., Eds.; American Society of Agronomy:Madison, WI, 1982; Agron. No. 9, 247–260.

29. Gee, G.P.; Bauder, J.W. Particle size analysis. Methods of SoilAnalysis. Part 1, 2nd Ed.; Agron. Monogr. 9., ASA and SSSA,Madison, WI, 1986; Agron. No. 9, 383–411.

30. Olsen, R.; Sommers, L.E. Phosphorus. Methods of Soil Analysis,Part 2, 2nd Ed.; Page, A.L., Miller, R.H., Keeney, D.R., Eds.;American Society of Agronomy: Madison, WI, 1982; Agron. No. 9,403–430.

31. Bray, R.H.; Kurtz, L.T. Determination of total, organic andavailable forms of P in soil. Soil Sci. 1945, 59, 39–45.

32. Truong, G.W.; Pichot, J.; Bernard, B. Caracterisation etcomparaison des phosphates tricalciques d’Afrique de l’Ouest envue de leur utilisation directe en agriculture. Agron. Trop. (France)1978, 33 (2), 136–145.

33. Murphy, J.; Riley, J.P. A modified single solution method for thedetermination of phosphate in natural waters. Anal. Chem. Acta.1962, 27, 31–36.

34. SAS. SAS User’s Guide: Statistics, Version 5; SAS Institute: Cary,NC, 1985.

35. Syers, J.K.; Mackay, A.D. Reaction of Sechura phosphate rock andsingle superphosphate in soil. Soil Sci. Soc. Am. J. 1986, 50,480–485.

36. Kanabo, I.A.K.; Gilkes, R.J. The influence of the addition ofgoethite to the soil on the dissolution of North Carolina phosphaterock. Aust. J. Soil Res. 1987, 25, 313–322.

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