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PERFORMANCE OF A RECIPROCAL SHAKER IN MECHANICAL DISPERSION OF SOIL... 1131

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PERFORMANCE OF A RECIPROCAL SHAKER INMECHANICAL DISPERSION OF SOIL SAMPLES FOR

PARTICLE-SIZE ANALYSIS(1)

Thayse Aparecida Dourado(2), Laura Fernanda Simões da Silva(3) & Mara de AndradeMarinho(4)

SUMMARY

The dispersion of the samples in soil particle-size analysis is a fundamentalstep, which is commonly achieved with a combination of chemical agents andmechanical agitation. The purpose of this study was to evaluate the efficiency of alow-speed reciprocal shaker for the mechanical dispersion of soil samples ofdifferent textural classes. The particle size of 61 soil samples was analyzed in fourreplications, using the pipette method to determine the clay fraction and sievingto determine coarse, fine and total sand fractions. The silt content was obtained bydifference. To evaluate the performance, the results of the reciprocal shaker (RSh)were compared with data of the same soil samples available in reports of theProficiency testing for Soil Analysis Laboratories of the Agronomic Institute ofCampinas (Prolab/IAC). The accuracy was analyzed based on the maximum andminimum values defining the confidence intervals for the particle-size fractionsof each soil sample. Graphical indicators were also used for data comparison, basedon dispersion and linear adjustment. The descriptive statistics indicatedpredominantly low variability in more than 90 % of the results for sand, medium-textured and clay samples, and for 68 % of the results for heavy clay samples,indicating satisfactory repeatability of measurements with the RSh. Mediumvariability was frequently associated with silt, followed by the fine sand fraction.The sensitivity analyses indicated an accuracy of 100 % for the three main separates

(1) Paper presented at the XXXII Brazilian Congress of Soil Science (Fortaleza, CE, 2-7/08/2009), during both oral and postersections. Received in August 15, 2012 and approved in May 18, 2012.

(2) Undergraduate student at State University of Campinas, College of Agricultural Engineering - UNICAMP/FEAGRI. Financialsupport: Scientific Initiation Fellowship from SAE/UNICAMP. Av. Cândido Rondon, 501, Bairro Barão Geraldo. CEP 13083-875 Campinas (SP). E-mail: [email protected]

(3) Substitute Professor at Universidade Estadual Paulista - UNESP - Campus Rio Claro, Dept. of Petrology and Metallogeny,Institute of Geosciences and Exact Sciences. Avenida 24-A, 1515. CEP 13506-900. E-mail: [email protected]

(4) Associate Professor at State University of Campinas, College of Agricultural Engineering - UNICAMP/ FEAGRI. E-mail:[email protected]

1132 Thayse Aparecida Dourado et al.

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(total sand, silt and clay), in all 52 samples of the textural classes heavy clay, clayand medium. For the nine sand soil samples, the average accuracy was 85.2 %;highest deviations were observed for the silt fraction. In relation to the linearadjustments, the correlation coefficients of 0.93 (silt) or > 0.93 (total sand andclay), as well as the differences between the angular coefficients and the unit <0.16, indicated a high correlation between the reference data (Prolab/IAC) andresults obtained with the RSh. In conclusion, the mechanical dispersion by thereciprocal shaker of soil samples of different textural classes was satisfactory.The results allowed recommending the use of the equipment at low agitation forparticle sizeanalysis. The advantages of this Brazilian apparatus are its low cost,the possibility to simultaneously analyze a great number of samples using ordinary,easily replaceable glass or plastic bottles.

Index terms: soil texture, pipette method, mechanical dispersion, accuracyanalysis.

RESUMO: AVALIAÇÃO DO DESEMPENHO DE MESA AGITADORARECIPROCANTE NA DISPERSÃO DE AMOSTRAS DE SOLOPARA FINS DE ANÁLISE GRANULOMÉTRICA

A dispersão da amostra de solo é uma etapa fundamental da análise granulométrica,sendo realizada mediante o uso de dispersantes químicos e agitação mecânica. O objetivodeste trabalho foi avaliar a eficiência de mesa agitadora reciprocante de baixa rotação nadispersão mecânica de amostras de solos de diferentes classes texturais. Foram realizadasanálises granulométricas em 61 amostras com quatro repetições, empregando o método dapipeta para determinação da fração argila e tamisagem para determinação das fraçõesareia grossa, areia fina e areia total, sendo o silte determinado por diferença. Na avaliaçãode desempenho, os resultados obtidos com uso da mesa agitadora reciprocante (MAR) foramcomparados com dados disponíveis para as mesmas amostras oriundos de relatórios doEnsaio de Proficiência IAC para Laboratórios de Análises de Solos - Prolab/IAC. Análisesde acurácia foram realizadas com base nos valores dos intervalos de confiança definidospara cada fração granulométrica componente de cada amostra ensaiada. Indicadores gráficostambém foram utilizados na comparação de dados, por meio de dispersão e ajuste linear. Aestatística descritiva indicou preponderância de baixa variabilidade em mais de 90 % dosresultados obtidos para as amostras de texturas arenosa, média e argilosa e em 68 % dosobtidos para as amostras de textura muito argilosa, indicando boa repetibilidade dosresultados obtidos com a MAR. Média variabilidade foi mais frequentemente associada àfração silte, seguida da fração areia fina. Os resultados das análises de sensibilidade indicamacurácia de 100 % nas três frações granulométricas - areia total, silte e argila - para todas asamostras analisadas pertencentes às classes texturais muito argilosa, argilosa e média.Para as nove amostras de textura arenosa, a acurácia média foi de 85,2 %, e os maioresdesvios ocorreram em relação à fração silte. Nas aproximações lineares, coeficientes decorrelação igual (silte) ou superiores (areia total e argila) a 0,93, bem como diferençasmenores do que 0,16 entre os coeficientes angulares das retas e o valor unitário, indicam altacorrelação entre os resultados de referência (Prolab/IAC) e os obtidos nos ensaios com aMAR. Conclui-se pelo desempenho satisfatório da mesa agitadora reciprocante de baixarotação para dispersão mecânica de amostras de solo de diferentes classes texturais parafins de análise granulométrica, permitindo recomendar o uso alternativo do equipamentoquando se emprega agitação lenta. As vantagens do uso do equipamento nacional incluem obaixo custo, a possibilidade de análise simultânea de grande número de amostras e o uso defrascos comuns, de vidro ou de plástico, baratos e de fácil reposição.

Termos de indexação: granulometria, método da pipeta, dispersão mecânica, análise deacurácia.


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INTRODUCTION

Soil texture is based on different combinations ofsand, silt, and clay separates that define the particle-size distribution of a soil sample (Gee & Or, 2002).Particle-size distribution is a natural and permanentsoil property and one of the most frequently used forsoil characterization (Hillel, 1982). Because of thecorrelation between specific surface and particle size,the percentage distribution of the various sizes ofindividual particles within a soil is an important soilcharacteristic (Baver et al., 1972). The particle-sizedistribution of a soil is determined by particle-sizeanalysis. Particle-size analysis is defined as ameasurement of the size distribution of the individual(primary) particles in a soil sample, according totexture fractions in a given classification scheme(Baver et al., 1972; Gee & Or, 2002). The analysis ofparticle sizes is a common and essential physicalanalysis of the soil, for which conventionally “fineearth” is used, or the soil fraction that can be sievedthrough 2 mm mesh. The size limits of the three mainfractions of soil particles sand, silt and clay are givenby diameter ranges, according to different scales. Thesand fraction contains the largest particles, withdiameters between 2.0 and 0.02 mm (ISSS) or 2.0 and0.05 mm (USDA). Silt consists of medium-sizedparticles, with diameters from 0.02 to 0.002 mm (ISSS)or from 0.05 to 0.002 mm (USDA), and the clayfraction contains the smallest soil particles, withdiameters below 0,002 mm or 0,2 on both scales (Gee& Or, 2002).

Soil texture is widely recognized as beingfundamental for soil identification and classification.More recently, particle-size distribution has beenwidely used as an independent variable in pedotransferfunctions for the estimation of more complex soilphysical properties (Tomasella et al., 2000, Silva etal., 2008). In the soil, organic matter, iron oxides andcarbonates act as cementing agents, keeping theparticles together and forming aggregates. Thesuccess of particle-size analysis depends firstly on thesample preparation to ensure a complete dispersionof all aggregates into their individual primaryparticles without breaking up the particles themselvesand secondly, on the accurate fractionation of a sampleinto its different separates (Baver et al., 1972). Thus,the dispersion phase consists of the individualizationof the soil primary particles in aqueous suspension,by using chemical agents and physical methods (Gee& Or, 2002). The chemical agents are used toeliminate the flocculating ions, such as Al and Ca, toincrease the repulsion between the primary particles,and to stabilize the individual particles in thesuspension throughout the analysis (Gee & Or, 2002;Ruiz, 2005). In Brazil, the Brazilian AgriculturalResearch Corporation - Embrapa (1997) recommendsthe chemical agents Na-hydroxide (NaOH) or Na-hexametaphosphate buffered with Na-carbonate fornormal soils, the use of hydrogen chloride (HCl) at

10 % for calcareous soils, and Na-hexametaphosphatefor saline soils. In São Paulo State, the AgronomicInstitute of Campinas (IAC) recommends the use of amixture of Na-hydroxide and Na-hexametaphosphate(Camargo et al., 1986). Sodium can adsorb highquantities of water and when the Na ion is adsorbedon the surface of soil particles it induces repulsionbetween them, which in turn facilitates thestabilization of the individual particles in suspension.In recent research, Neto et al. (2009) evaluated theeffectiveness of different chemical agents for thedispersion of a Rhodic Hapludox irrigated withcalcium-rich water. They concluded that thecombination of hydrogen chloride (HCl) with Na-hydroxide (NaOH) was the most efficient way ofrecovering the clay fraction. Classical physicalmethods of soil dispersion include fast or slowshaking or rolling of the soil suspension. In the past20 years, electronic dispersion, primarily by the useof sonication, has become increasingly popular (Gee& Or, 2002). In Brazil, Embrapa (1997) recommendsthe use of electric stirrers at high speed (10,000 to12,000 rpm) for a short stirring time, varying from5 min (for sandy soils) to 15 min (for clayey soils). InSão Paulo, Grohmann & Raij (1977) demonstratedthe superiority of slow shaking for a more efficientsoil dispersion and clay determination for soilparticle-size analysis performed in the IAClaboratories. Later , Camargo et al. (1986)recommended the use of low-speed stirrers (30 rpm),for example the Wiegner shaker, with longer stirringtime, of about 16 h. According to Gee & Or (2002),not only a standardization of the treatments but alsothe testing of specific methodologies are needed, sincethe mechanical techniques can result in thefragmentation of the primary particles. The reciprocalshaker evaluated here belongs to the category of slow-speed shakers, for which there are no comparativeperformance studies based on the results obtainedwith methodologies and agitators commonly used inthe laboratories. The advantages of this reciprocalshaker include its relatively low cost, the capacityto shake a large number (40) of samplessimultaneously, and the possibility of using cheapand easy replaceable glass or plastic pots. Given theabove, our objective was to evaluate the efficiency ofa slow reciprocal shaker for the dispersion of soilsamples of different textural classes for particle-sizeanalysis.

MATERIAL AND METHODS

Experimental location and characterizationof the soil samples

The experiment was conducted at the SoilLaboratory (Labsol) of the College of AgriculturalEngineering, State University of Campinas,Campinas, SP.


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The tests were conducted with 61 soil samples ofdifferent textural classes. According to the texturalgroups defined by Embrapa (2006), the texture of nineof the soil samples was sandy (containing <150 g kg-1

clay and > 700 g kg-1 sand), of 22 medium (with claycontents < 350 g kg-1 and > 150 g kg-1), of 20 samplesclayey (with clay contents > 350 g kg-1 and < 600 gkg-1), and of the last 10 samples the texture was HeavyClay (with clay contents > 600 g kg-1).

The samples were selected from a soil bank of theLabsol, due to its participation in the IAC ProficiencyTesting for Soil Analyses Laboratories - Prolab/IAC.The choice of this soil sample bank was due to theavailability of results of particle-size analysesperformed by more than 80 laboratories participatingin the program. The data were used as references inthe performance evaluation of the reciprocatingshaker. The statistical procedures used in the Prolab/IAC define the average value and the acceptable rangeof results obtained for each particle-size fraction (coarsesand, fine sand, total sand, silt and clay) for each soilsample (Quaggio et al., 1994). The acceptable rangedepends on the coefficient of variation (CV) of theresults for each particle-size fraction for each soilsample, according to the following criteria: a) forCV 40 %, the acceptable range is the average ± 1.0standard deviation (s) calculated from the resultsobtained by all laboratories; b) for CV between 20 and40 %, the acceptable range is the average ± 1.5 s, andc) for CV < 20 %, the acceptable range of results is theaverage ± 2.0 s. These data sets of particle-size analysesdetermined independently and as a part of a soil analysisquality program, were considered appropriate to drawconclusions not only about the accuracy but also onthe precision of the results obtained by mechanicaldispersion with a reciprocal shaker (RSh).

Analysis methodsThe particle-size analyses were carried out by the

Pipette Method described by Day (1965) for claydetermination, by sieving for separation of the sandsand by the difference between the former to obtainsilt, according to the procedures described by Embrapa(1997) and Camargo et al. (1986).

a) PrinciplesThe pipette method is a direct sampling procedure

based on the particle settling speed in an aqueoussuspension according to Stokes’ law (Equation 1). Thebasic assumptions to apply Stokes’ law to soilsuspensions are: a) the terminal velocity is reachedas soon as settling begins; b) resistance to settling isentirely due to the viscosity of the fluid; c) particlesare smooth and spherical; d) there is no interactionbetween individual particles in the suspension (Gee& Or, 2002). Since the soil particles are not smoothand spherical, d must be regarded as equivalent ratherthan actual diameters. The methods of particle-sizeanalysis based on the settling velocity determine thesoil particles more precisely according to the settling

time, as defined by equation 2. For clay fractiondetermination, after the dispersion of the soil sample,the time and the distance of vertical displacement ofthe particles through the aqueous suspension are fixed,so that only the clay particles remain in suspensionat that depth. At the time t, a small subsample istaken from the suspension at depth h, according toequation 2. After oven-drying and subtracting thedispersant weight (blank test), the clay mass of thesoil sample is determined. To determine the sandfraction, the soil suspension is passed either througha set of two sieves, to separate the coarse from thefine sand fractions (ISSS), or through a set of fivesieves, to separate the sand in very coarse, coarse,medium, fine and very fine (USDA). Then, the sandfractions are oven-dried and weighed for contentdeterminations. After determining the sand and theclay fractions, the silt fraction is calculated by thedifference (Camargo et al., 1986; Embrapa, 1997). Thepipette method is often used as a standard methodand the results of the particle-size analysis areexpressed in g kg-1 by the International System.

Eq. 1

Eq. 2

b) Analytical procedureFor soils with less than 5 % of organic matter (OM)

(< 50 g kg-1), 10 g of the < 2mm fraction of air-driedsoil was weighed and transferred to a 500 mL glasspot with 50 mL of dispersant solution* (a mixture of20 g of Na-hydroxide PA and 50 g of Na-hexametaphosphate in 5 L of distilled water, stirredwith magnetic stirrer until the reagents weredissolved). After closing, the glass pot was placed onthe low-speed reciprocal shaker (RSh) for mechanicalstirring at 130 rpm for 14-16 h (Figure 1).

The stirring velocity was determined based onpreliminary tests at different speeds, whichdemonstrated that 130 rpm was the ideal rotationspeed to promote an effective movement of thesuspension within the glass pot. For soils containingmore than 5 % of organic matter (> 50 g kg-1), a pre-treatment was required to eliminate OM as follows:fill 10 g of the < 2mm fraction of air-dried fine earthinto a 800 mL beaker, add 200 mL of Na-pyrophosphate 0.1 mol L-1 and 50 mL of hydrogenperoxide (H2O2 ~30 %), and let it stand overnight.The next day, maintain at 40 oC in water bath for 8h, and stir with a glass rod every 2 h. To remove theexcess of H2O2, raise the temperature to 80 °C, untilalmost dry. Wash the sample, centrifuge it twice withdistilled water, and remove the supernatant. Air-drythe sample, grind and weigh the quantity requiredfor the particle-size analysis.


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After the stirring period, the suspension was sievedthrough a 0.053 mm (270 mesh) into a 0.5 Lsedimentation cylinder for sand separation. Thematerial retained on the sieve (sand) was transferredto a 0.4 L beaker, and oven-dried at 105 °C. Then thedried sands were transferred to a set of two sieves:0.21 mm (coarse sand) and 0.05 mm (fine sand), andshaken for 30 min on a sieve vibrator. The masses ofthe coarse sand and of the fine sand were weighed(precision 0.01 g).

The volume of the suspended material wascompleted to 0.5 L and the test tube placed in a waterbath. The suspension was stirred for 30 s with aglass rod with a plunger slightly smaller than thecylinder diameter attached to its lower end. Thesettling time was defined according to the suspensiontemperature.

After the sedimentation period required for clayrecovery only, 10 mL of the suspension were pipettedfrom a depth of 5 cm, transferred to a tared beaker(precision 0.0001 g), and dried at 105 0C for 24 h.After drying, the beaker was placed in a desiccatoruntil reaching room temperature, then weighed(precision 0.0001 g) and the weight of the clay +dispersing agents determined.

A blank test was performed to determine theweight of the dispersing agents by preparing a solutionwith the same concentration used in the analysis (50mL of dispersing solution* in a sedimentation cylinder+ water to complete 0.5 L). A 10 mL aliquot of thesolution was transferred to a beaker and oven-driedat 105 0C for 24 h. After drying, the beaker was placedin a desiccator until reaching room temperature; thenit was weighed (precision 0.0001 g) to determine themass of the dispersing agents contained in the 10 mLaliquot. This value was subtracted from the weight ofclay + dispersing agents to determine the clay contentonly.

The silt fraction was calculated by the differencebetween the sum of the sand and the clay fractions inrelation to 1000g, since the results should be expressedin g kg-1 (Camargo et al., 1986; Embrapa, 1997). Foreach soil sample, particle-size analysis was performedin four replications.

c) Statistical analysis of the particle-sizeanalysis results and performance evaluationof the reciprocal low speed shaker (RSh)

The results were subjected to descriptive analysisto determine the following values: mean, standarddeviation, and the maximum, minimum andcoefficient of variation, using the SAS statisticalprogram. The data variability, expressed by thecoefficient of variation (CV %), was evaluated accordingto the Warrick & Nielsen (1980) criteria, by whichcoefficients below 12 % indicate low variability; thecoefficients varying between 12 and 60 % mediumvariability; and the coefficients > 60 % high variability.

For a performance analysis and to validate theresults obtained with the RSh, the data accuracy wasanalyzed (Fletcher et al., 1986), based on confidenceintervals (IC) as the criteria of acceptance, as definedby the particle-size data of the analysis performed withthe same samples by the laboratories of the Prolab/IAC program (Tables 1 and 2). Graphic indicators werealso used to compare the results, using theORIGINPROR 7.5 software, which visualized datadispersion and the linear fit between the averagecontent of a given particle-size fraction (sand, silt orclay) for each soil sample (reference data obtained fromthe Prolab/IAC program) and the value obtained usingthe RSh.

RESULTS AND DISCUSSION

The results of the descriptive analysis for coarsesand, fine sand, total sand, clay and silt fractions fornine sandy soil samples (containing < 150 g kg-1 clayand > 700 g kg-1 sand) are shown in Table 3. For allsandy samples (9), the coefficients of variation (CV) ofthe results for fine sand, total sand and clay werelower than 12 %, indicating low variability. Thevariability in the results for coarse sand was also low,except for sample 2, for which the CV of 13.95 %indicated medium variability, according to the criteriaof Warrick & Nielsen (1980). For silt, mediumvariability was observed for three samples (2, 4 and6); however, for the remaining six samples, variabilitywas also low. In general, low variability wascharacterized for 91 % of the results obtained for thesandy soil samples.

The results shown in table 4 were obtained from21 medium-textured soil samples. For almost 92 % ofthe data, including coarse sand, total sand and clayfractions of all tested samples, variability was low

Figure 1. A view of the reciprocal shaker (RSh) asused for the mechanical dispersion of the soilsamples using common glass pots.


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(CV 12 %); medium variability (12 CV 60 %)was only observed for fine sand (samples 22, 23 and27) and silt (samples 12, 16, 17, 27 and 30).

For the set of 20 clayey soil samples, variabilitywas low in 93 % of the results; for 15 samples,variability was low for all fractions: coarse sand, fine

SampleSand

Clay SiltCoarse Fine Total

g kg-1

Sandy soil samples1 188 to 458 297 to 568 710 to 807 83 to 177 68 to 1522 289 to 561 271 to 573 781 to 910 51 to 110 44 to 863 232 to 501 337 to 606 787 to 885 64 to 123 38 to 884 324 to 668 294 to 555 897 to 949 35 to 77 11 to 315 323 to 553 282 to 540 784 to 929 44 to 82 41 to 1006 273 to 595 308 to 644 875 to 955 38 to 76 15 to 357 259 to 496 307 to 635 806 to 894 56 to 108 44 to 898 251 to 525 272 to 599 795 to 875 66 to 131 39 to 879 241 to 527 295 to 596 802 to 867 63 to 130 46 to 92

Medium textured soil samples10 352 to 497 141 to 283 606 to 665 235 to 359 47 to 9511 385 to 452 84 to 151 474 to 600 235 to 391 101 to 19612 300 to 457 140 to 291 543 to 634 268 to 388 59 to 11613 391 to 466 88 to 135 501 to 578 254 to 369 99 to 18314 387 to 449 94 to 144 501 to 571 267 to 369 98 to 18615 242 to 413 166 to 323 528 to 612 272 to 402 55 to 12816 409 to 534 69 to 116 530 to 614 244 to 373 83 to 16717 285 to 461 158 to 288 559 to 625 286 to 395 31 to 10618 267 to 394 181 to 304 545 to 602 303 to 375 58 to 11819 299 to 446 165 to 260 564 to 624 297 to 386 43 to 9520 305 to 419 182 to 269 564 to 618 299 to 374 51 to 9721 276 to 386 193 to 291 553 to 594 301 to 371 66 to 11722 287 to 418 157 to 275 540 to 599 286 to 382 62 to 13323 412 to 559 118 to 223 620 to 707 173 to 268 79 to 14924 356 to 464 69 to 143 476 to 564 279 to 392 107 to 18025 255 to 380 197 to 334 538 to 644 250 to 371 63 to 14226 373 to 467 82 to 124 491 to 558 266 to 397 98 to 17927 385 to 456 83 to 128 477 to 567 285 to 380 103 to 18328 298 to 431 162 to 298 548 to 634 241 to 349 80 to 16029 321 to 425 173 to 263 553 to 628 257 to 335 71 to 15630 507 to 615 62 to 138 583 to 734 197 to 283 60 to 12931 296 to 431 196 to 327 581 to 680 225 to 306 64 to 146

Table 1. Confidence intervals for coarse, fine and total sand, and silt and Clay contents for nine sandy and 22medium textured soil samples

Source: Values extracted from the Prolab/IAC reports.

sand, total sand, silt, and clay (Table 5). Mediumvariability was only inferred for fine sand (samples37, 39 and 45), coarse sand (sample 43) and silt(samples 37, 41 and 45).

Finally, low variability was observed in 68 % ofthe results obtained for 10 Heavy Clay soil samples,


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SampleSand

Clay SiltCoarse Fine Total

g kg-1

Clayey soil samples32 183 to 264 105 to 159 307 to 417 401 to 568 94 to 20333 271 to 361 79 to 141 379 to 479 322 to 466 109 to 24234 122 to 180 92 to 148 216 to 329 457 to 622 116 to 26135 118 to 188 89 to 150 215 to 333 459 to 603 133 to 24836 196 to 268 104 to 163 327 to 403 404 to 570 102 to 19537 215 to 336 71 to 147 308 to 483 310 to 509 126 to 24838 138 to 171 99 to 143 229 to 322 472 to 638 101 to 21539 188 to 264 103 to 173 325 to 400 434 to 542 95 to 20040 126 to 178 96 to 143 242 to 304 480 to 604 116 to 25141 239 to 341 145 to 235 454 to 506 365 to 478 62 to 12842 30 to 62 69 to 134 103 to 194 406 to 603 240 to 45643 27 to 60 52 to 103 76 to 160 421 to 623 251 to 44844 252 to 347 147 to 223 461 to 506 373 to 460 71 to 13145 24 to 53 46 to 100 76 to 148 436 to 694 194 to 42346 237 to 340 154 to 227 455 to 507 380 to 452 72 to 13547 227 to 314 151 to 225 431 to 485 391 to 492 63 to 13648 242 to 322 92 to 168 374 to 451 353 to 518 100 to 20549 231 to 340 74 to 134 361 to 426 411 to 502 105 to 20050 124 to 287 71 to 136 205 to 408 332 to 574 176 to 30851 85 to 128 145 to 226 250 to 338 482 to 610 101 to 219

Heavy Clay Soil Samples52 40 to 77 60 to 110 100 to 214 526 to 737 122 to 28353 11 to 32 7 to 27 16 to 75 578 to 735 220 to 38154 40 to 76 65 to 108 113 to 181 520 to 741 142 to 28055 40 to 77 69 to 102 106 to 186 560 to 720 133 to 28356 48 to 83 97 to 139 147 to 214 508 to 698 136 to 28257 43 to 89 96 to 142 153 to 215 541 to 683 124 to 27958 42 to 85 99 to 139 147 to 218 542 to 677 135 to 27259 44 to 91 103 to 142 156 to 226 543 to 677 125 to 28260 52 to 86 101 to 146 159 to 229 554 to 677 131 to 25361 49 to 88 104 to 146 167 to 223 559 to 673 128 to 241

Table 2. Confidence intervals for coarse sand, fine sand, total sand, silt and clay contents for 20 Clayey soilsamples and for 10 Heavy Clay soil samples

Source: Values extracted from the Prolab/IAC reports.

including the clay fraction (all samples), coarse sand(samples 54, 55, 56, 57), fine sand (samples 52, 54,55, 56, 57, 58, 59, 61), total sand (samples 52, 54, 55,56, 57, 58) and silt (samples 53, 54, 56, 57, 58).Medium variability was inferred for coarse sand(samples 52, 53, 58, 59, 60, 61), fine sand (sample

53), total sand (samples 53, 59, 60, 61), and silt(samples 52, 55, 59, 60, 61).

The prevalence of low variability for various datasets indicates a good repeatability of the results ofthe analysis using the low speed reciprocal shaker(RSh). Medium variability was characterized


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Sample Textural fraction Mean Standard deviation Maximum Minimum CV

g kg-1 %

1 Coarse Sand 269 9.12 283 242 7.12Fine Sand 475 18.92 500 458 3.98Total Sand 744 3.00 746 740 0.4Clay 117 3.37 122 115 2.88Silt 140 2.87 144 138 2.06









Table 3. Descriptive statistics of the results from particle-size analyses of nine Sandy soil samples (n= 4replications)


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g kg-1 %











Table 4. Descriptive statistics of the results from particle-size analyses of 21 Medium textured soil samples(n = 4 replications)

Continue...


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g kg-1 %












Table 4. Cont.


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g kg-1 %











Table 5. Descriptive statistics of the results from particle-size analysis of 20 Clay soil samples (n = 4replications)

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Table 5. Cont.


g kg-1 %












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g kg-1 %






57 Coarse Sand 66 5.32 71 60 8.12Fine Sand 120 3.55 124 117 2.96Total Sand 186 6.02 191 177 3.24Clay 641 15.35 652 618 2.39Silt 174 11.51 191 166 6.61Coarse Sand 61 8.18 68 52 13.52Fine Sand 114 8.18 122 103 7.15

58 Total Sand 175 4.34 181 171 2.48Clay 645 6.78 650 635 1.05Silt 180 10.30 194 169 5.71Coarse Sand 84 32.46 131 58 38.87Fine Sand 127 4.20 131 122 3.32



61 Total Sand 216 34.61 166 192 16.06Clay 633 14.01 642 612 2.21Silt 152 43.19 194 92 28.41

Table 6. Descriptive statistics of the results from particle-size analyses of 10 Heavy clay soil samples (n = 4replications)


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primarily for silt fraction, followed by fine sand, andalso for the results for the Heavy Clay soil samples.

The accuracy analysis for nine sandy soil samplesshowed that the estimations of sand and clay fractionsusing the RSh were 100 % accurate, once all obtainedresults were within the confidence intervals definedin table 1 and figure 2. For the silt fraction, theaccuracy of the estimations dropped to 55.6 %, becausethe estimated values of four out of nine samples werenot within the predefined confidence interval.However, the overall sensitivity or accuracy of theparticle-size analysis using the RSh in the dispersionof the sandy soil samples was high, reaching 85.2 %.For the medium-textured soil samples, all valuesobtained using the RSh were within the confidenceintervals defined in table 2, with 100 % accuracy forthe three particle size fractions sand, clay and silt(Figure 3). The estimations of the three main texturalfractions, sand, clay, and silt were also found to be100 % accurate for the clayey soil samples (Figure 4)and for the Heavy Clay soil samples (Figure 5). Insummary, considering all 61 soil samples of thedifferent textural classes, the mean accuracy of theestimations using the RSh was approximately 96 %,a high value.

The dispersion charts for mean values of sand,clay and silt extracted from the reports of Prolab/IAC (X axis) and those determined using the RSh (Yaxis) are illustrated (Figure 6: Sandy and Mediumtextured soil samples; Figure 7: Clayey and HeavyClay soil samples). The linear approximationsindicate similarities between the two data sources,as evidenced by the proximity of the angularcoefficient values (0.84 < m < 1.5) to the unit, whichcharacterizes the straight line of perfect correlation.The values of the correlation coefficients were alwaysgreater than 0.93, thus confirming the highcorrelation between the Prolab/IAC values (reference)and the results obtained with RSh. Of the texturalclasses, total sand and clay provided the best results,with correlation coefficients greater than 0.98 anddifferences between the angular coefficients of thestraight line and the unit value less than 0.16.Considering all textural classes tested, the largestdiscrepancies, not only in relation to the correlationcoefficient values (> 0.93), but also to the deviationsof the angular coefficients from unit (<0.5), wereobserved for the silt fraction estimations. This canbe explained by the fact that the silt fraction wasdetermined by difference, leading to cumulativeerrors in the estimations of this fraction. Ruiz (2005)

Figure 2. Accuracy analysis of nine sandy soil samples: representation of the minimum and maximumvalues of the confidence intervals (CI), means and average standard errors (bars) for total sand, silt andclay contents as determined by particle-size analysis using the reciprocal shaker (RSh).


R. Bras. Ci. Solo, 36:1131-1148

Figure 3. Accuracy analysis of 22 Medium-textured soil samples: representation of the minimum andmaximum values of the confidence intervals (CI), means and average standard errors (bars) for totalsand, silt and clay contents as determined by particle-size analysis using the reciprocal shaker (RSh).

Figure 4. Accuracy analysis for 21 Clayey soil samples: representation of the minimum and maximum valuesof the confidence intervals (CI), means and average standard errors (bars) for total sand, silt and claycontents as determined by particle-size analysis using the reciprocal shaker (RSh).

Silt

, g k

g-1

Cal

y, g

kg-

1To

tal s

and,

g k

g-1

Maximum value of CI Minimum value of CI Result from MAR

Silt

, g k

g-1

Cal

y, g

kg-

1To

tal s

and,

g k

g-1



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Figure 5. Accuracy analysis for 11 soil samples of the Heavy clay soil textural class: representation of the minimumand maximum values of the confidence intervals (CI), means and average standard errors (bars) for totalsand, silt and clay contents as determined by particle-size analysis using the reciprocal shaker (RSh).

Figure 6. Dispersion charts for mean values of total sand, clay and silt extracted from the data of the Prolab/IAC and results determined using the RSh for 9 Sandy soil samples (a, b and c) and for 21 Medium-textured soil samples (d, e and f).

Silt

, g k

g-1

Cal

y, g

kg-

1To

tal s

and,

g k

g-1



R. Bras. Ci. Solo, 36:1131-1148

Figure 7. Dispersion charts for mean values of total sand, clay and silt extracted from the data of Prolab/IACand results determined using the RSh for 20 clayey soil samples (a, b and c) and for 10 heavy clay soilsamples (d, e and f).

demonstrated that the value of the silt fractioncalculated by subtracting the other fractions isoverestimated. To minimize this problem andpossibly increase the accuracy of the determination,the author suggested that an additional volume ofthe silt and clay suspension should be sampled toestimate silt. However, the effect of this procedureon the accuracy of determinations was not discussedhere.

In conclusion, the performance of the reciprocalshaker (RSh) was satisfactory enough to allow itsrecommendation as a suitable alternative to theconventional devices used for mechanical soil sampledispersion in particle-size analysis. Additionaladvantages of the equipment are its low cost, thepossibility of simultaneous dispersion of up to 40 soilsamples, and the option of using ordinary, cheap andeasily replaceable glass pots.

CONCLUSIONS

1. The mechanical dispersion of soil samples fromdifferent textural classes, even of the Heavy Clay classby the reciprocal shaker was satisfactory.

2. The tested equipment is a viable alternativefor the mechanical dispersion of soil samples forparticle-size analysis.

LITERATURE CITED

BAVER, L.D.; GARDNER, W.H. & GARDNER, W.R. Soilphysics. New York, John Wiley & Sons, 1972. p.1-53.

CAMARGO, O.A; MONIZ, A.C.; JORGE, J.A. & VALADARES,J.M.A.S. Métodos de análise química, mineralógica e físicade solos do Instituto Agronômico de Campinas. Campinas,Instituto Agronômico de Campinas, 1986. 57p. (BoletimTécnico, 106).

DAY, P.R. Particle fractionation and particle-size analysis. In:BLACK, C.A. ed. Methods of soil analysis. Madison, ASA/SSSA, 1965. Part 1. p.545-567. (Agronomy Monograph,9)

EMPRESA BRASILEIRA DE PESQUISA AGROPECUÁRIA -EMBRAPA. Sistema Brasileiro de Classificação de Solos.2.ed. Rio de Janeiro, EMBRAPA SOLOS, 2006. 306p.

EMPRESA BRASILEIRA DE PESQUISA AGROPECUÁRIA -EMBRAPA. Manual de métodos de análise de solo. 2.ed.Rio de Janeiro, Centro Nacional de Pesquisa de Solos,1997. p.27-34.

FLETCHER, G.J.O.; DANILOVICS, P.; FERNANDEZ, G.;PETERSON, D. & REEDER, G.D. Attributionalcomplexity: An individual diûerences measure. J.Personal. Soc. Psychol., 51:875-884, 1986.

GEE, G.W. & OR, D. Particle size analysis. In: DANE, J.H. &TOPP, G.C. Methods of soil analysis. Physical methods.Madison, Soil Science Society of America, 2002. Part 4.p.255-293.


R. Bras. Ci. Solo, 36:1131-1148

GROHMANN, F. & RAIJ, B. van. Dispersão mecânica e pré-tratamento para análise granulométrica de Latossolosargilosos. R. Bras. Ci. Solo, 1:52-53, 1977.

QUAGGIO, J.A.; CANTARELLA, H. & RAIJ, B. van. Evolutionof the analytical quality of soil testing laboratoriesintegrated in a sample exchange program. Commun. SoilSci. Plant Anal., 25:1007-1014, 1994.

HILLEL, D. Introduction to soil physics. San Diego, AcademicPress, 1982. p.21-39.

NETO, E. L. DE S.; FIGUEIREDO, L. H. A. & BEUTLER, A. N.Dispersão da fração argila de um Latossolo sob diferentessistemas de uso e dispersantes. R. Bras. Ci. Solo, 33:723-728, 2009.

RUIZ, H.A. Incremento da exatidão da análise granulométricado solo por meio da coleta da suspensão (silte + argila).R. Bras. Ci. Solo, 29:297-300, 2005.

SILVA, A.P.; TORMENA, C.A.; FIDALSKI, J. & IMHOFF, S.Funções de pedotransferência para as curvas de retençãode água e de resistência do solo à penetração. R. Bras. Ci.Solo, 32:1-10, 2008.

TOMASELLA, J.; HODNETT, M.G. & ROSSATO, L. Pedotransferfunctions for the estimation of soil water retention inBrazilian soils. Soil Sci. Soc. Am. J., 64:327-338, 2000.

WARRICK, A.W. & NIELSEN, D.R. Spatial variability of soilphysical properties in the field. In: HILLEL, D., ed. Applicationsof soil physics. New York, Academia Press, 1980. 385p.

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