A laboratory and glasshouse evaluation of chicken litter ash, wood ash, and iron smelting slag as liming agents and P fertilisers

CSIRO PUBLISHING

www.publish.csiro.au/journals/ajsr Australian Journal of Soil Research, 2007, 45, 374–389

A laboratory and glasshouse evaluation of chicken litter ash, wood ash,and iron smelting slag as liming agents and P fertilisers

B. E. YusiharniA, H. ZiadiA, and R. J. GilkesA,B

ASchool of Earth and Geographical Sciences, Faculty of Natural and Agricultural Sciences,The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.

BCorresponding author. Email: [email protected]

Abstract. Standard AOAC methods of chemical analysis have been used to characterise the industrial byproducts partlyburnt chicken litter ash (CLA), totally burnt chicken litter ash (CLAT), wood ash (WA), and iron smelting slag, for use asa combined liming agent and phosphate (P) fertiliser. These materials are effective liming agents with calcium carbonateequivalence of 93–99%. Total P concentrations of CLA (3.6% P), CLAT (4.75% P), slag (0.26% P), and WA (0.44% P)indicate that they would function as P fertilisers when applied at the high rates required for liming soils. The form of Pin slag is unknown; CLA and CLAT consist mostly of mixtures of the phosphate mineral apatite with calcite and quartz.WA consists mostly of calcite, quartz, and various salts. For long extraction times, total P dissolved increased in thesequence CA (citric acid) > NAC (neutral ammonium citrate) > AAC (alkaline ammonium citrate). Little apatite persistedin residues of CLA and CLAT after 120 h of CA extraction but considerable amounts of apatite remained in NAC and AACresidues. A glasshouse P-response experiment was carried out with ryegrass on an acid lateritic soil with the applicationof various levels of phosphate as chicken litter ash, iron smelting slag, and wood ash. Monocalcium phosphate (MCP),dicalcium phosphate (DCP), and rock phosphate (RP) were included for comparison purposes. Based on plant yield data,the relative agronomic effectiveness (RE) of DCP compared to MCP was 57%, 72%, 73%, and 94%, respectively, for 4successive harvests, for RP was 24%, 34%, 70%, and 56%, for chicken litter ash was 13%, 16%, 33%, and 39%, for slagwas 8%, 9%, 16%, and 10%, for WA was 6%, 9%, and was effectively zero for the final 2 harvests. For no extraction timewas the P soluble in the 3 citrate extractants a reliable predictor of the agronomic effectiveness of these materials as Pfertilisers established by plant growth measurements.

Additional keywords: byproducts, citrate extraction, electron microscopy, available P.

Introduction

Soil acidity is a major problem worldwide, as it decreasesplant growth by affecting the availability of nutrients andcauses various toxicities. Acid soils are commonly deficientin phosphate (P), so that both conditions require correction.This can be carried out by the application of a single mineralameliorant with appropriate properties. Some alkaline industrialbyproducts may be suitable as they contain P, which may beavailable to plants. These materials include iron smeltingslag, wood ash, and chicken litter ash but their liming valueand phosphate fertiliser effectiveness are poorly defined.Byproducts are commonly dumped in landfill; therefore,any use of byproducts to ameliorate land will contributeto the preservation of alternative resources and provide aneffective solution for the disposal of byproducts (Francis andYoussef 2004).

In order for a P fertiliser to be effective, substantial amountsof P should dissolve shortly after application to soils andall P should eventually dissolve (Hughes and Gilkes 1984).Conventional chemical P fertilisers (SP, DAP, MAP) are mostlysoluble in water and are highly effective. Rock phosphate

is almost insoluble in water as it relies on soil acidity andrhizosphere acidity to promote dissolution and, consequently, isoften much less effective than chemical fertilisers (Khasawnehand Doll 1978). The solubility of the above-mentioned industrialbyproducts in soil is not known.

Laboratory assessments of the potential agronomiceffectiveness of a material to be used as a P fertiliser aremade to determine appropriate rates of application in thefield. The effectiveness of poorly soluble phosphate fertiliserssuch as rock phosphate and phosphatic byproducts may beassessed by standard analytical procedures (AOAC 1975) thatdetermine the solubility of phosphate in water, citric acid,neutral ammonium citrate, and alkaline ammonium citrate.Depending on the composition of the fertiliser and its reactionsin soil, a particular extractant may provide the best predictionof fertiliser performance as determined by field or glasshouseexperiments (Colwell 1963). This paper investigates the natureof byproducts (chicken litter ash, wood ash, iron-smelting slag)that act as a combined liming agent and phosphate fertiliser andevaluates them using standard AOAC fertiliser analyses and aglasshouse experiment.

© CSIRO 2007 10.1071/SR06136 0004-9573/07/050374

Evaluation of liming agents and P fertilisers Australian Journal of Soil Research 375

Table 1. Nomenclature for calcined chicken litter samples produced bycalcination at various temperatures and for byproducts together with

their pH measured in water

Key Explanation pH H2O (1 : 5)

C500 Chicken litter burnt at 500◦C 10.18C550 Chicken litter burnt at 550◦C 10.27C600 Chicken litter burnt at 600◦C 10.29C650 Chicken litter burnt at 650◦C 10.33C700 Chicken litter burnt at 700◦C 10.37C750 Chicken litter burnt at 750◦C 10.38C800 Chicken litter burnt at 800◦C 10.52C850 Chicken litter burnt at 850◦C 10.55C900 Chicken litter burnt at 900◦C 10.56C950 Chicken litter burnt at 950◦C 10.59C1000 Chicken litter burnt at 1000◦C 10.62CLA Chicken litter partly burnt in 9.93

incinerator at 700◦C–800◦CCLAT CLA heated in furnace 11.31

at 700◦C overnightRP Sechura rock phosphate 7.96WA Wood ash 12.77Slag Iron smelting slag 10.59

Material and methodsCalcination of chicken litterA bulk sample of chicken litter was supplied by Blair FoxGeneration, which is developing a power station to be firedby this material. Combustion temperatures and conditionsmay vary substantially during this process, so that diversecombustion products may be produced. Subsamples of 1 kgof the chicken litter were burnt in a ventilated electric mufflefurnace for 1 h at various temperatures (500◦, 550◦, 600◦, 650◦,700◦, 750◦, 800◦, 850◦, 900◦, 950◦, 1000◦C). A large amount(>100 kg) of chicken litter was burnt (CLA) in a commercialincinerator for 36 h at temperatures that ranged between 700◦C

Table 2. Properties of industrial byproducts

Properties CLA CLAT Slag WA RP

pH (1 : 5 H2O) 9.93 11.31 10.59 12.77 7.66EC (1 : 5 H2O) (Ds/m) 1.54 1.62 1.43 1.35 1.31CCE (%) 94 97 93 99 48Total phosphorus (%) 3.6 4.75 0.26 0.44 15.85P soluble in waterA (%) 6 6 15 13 2P soluble in citric acidA (%) 75 81 80 57 38P soluble in neutral 48 55 49 80 2

ammonium citrateA (%)P soluble in alkaline 34 39 40 67 1

ammonium citrateA (%)Total calcium (%) 16.62 18.02 27.82 22.23 19.27Total magnesium (%) 1.48 1.94 6.07 3.75 0.48Total potassium (%) 2.93 4.11 0.12 3.65 0.78Total sodium (%) 1.53 1.86 0.22 2.62 0.98Total Cd (mg/kg) 5.75 6.62 0.27 0.59 47.2Total Ni (mg/kg) 15.9 19.3 14.9 52.6 26.1Total As (mg/kg) 20.8 30.4 3.1 2.1 25.5Total Pb (mg/kg) 7.4 8.5 0.6 15.4 8Total Cu (mg/kg) 47.9 52.4 18.2 41.3 11Total Mn (g/kg) 1.8 1.4 11.2 4.2 1.7Total Zn (g/kg) 7.4 9.5 0.1 0.2 0.1

AExpressed as a percentage of total phosphorus.

and 800◦C. Combustion was only partial, as much carbonisedlitter (charcoal) remained. Totally burnt chicken litter (CLAT)was derived from CLA, by heating overnight in a fully oxidisingenvironment at 700◦C to remove residual charcoal from CLA. Akey to the materials investigated, abbreviations used to identifythese materials, and the pH of these materials, together withSechura rock phosphate, are given in Table 1.

Industrial byproductsIron smelting slag came from the HIsmelt KwinanaDemonstration Plant, Western Australia, which utilises iron ore,

Table 3. Percentages of total phosphorus, calcium, magnesium, potassium, and sodium dissolved after 1 h extraction in citrate solutions for chickenlitter calcined at various temperatures and for Sechura rock phosphate (RP), wood ash (WA), and slag

CA, Citric acid; NAC, neutral ammonium citrate; AAC, alkaline ammonium citrate

Samples Phosphorus Calcium Magnesium Potassium SodiumCA NAC AAC CA NAC AAC CA NAC AAC CA NAC AAC CA NAC AAC

C500 37 37 23 21 21 11 47 46 39 47 52 51 28 34 30C550 39 37 26 21 21 11 48 47 40 47 53 52 29 35 32C600 43 40 27 23 21 12 50 49 41 50 54 52 31 38 32C650 44 41 29 23 22 13 53 51 42 54 58 53 34 43 33C700 54 42 30 24 22 13 54 52 43 58 64 63 38 45 37C750 48 44 30 25 22 13 55 52 45 62 67 65 40 46 37C800 53 45 32 28 22 14 67 62 52 68 74 71 48 51 46C850 64 46 32 33 22 15 78 70 60 75 82 79 54 57 51C900 71 47 32 88 62 11 82 71 56 68 33 30 66 31 22C950 71 48 36 92 40 8 23 94 78 90 32 30 90 39 34C1000 96 53 48 50 23 20 91 99 85 79 83 79 72 74 69CLA 75 46 34 88 62 58 82 71 56 95 46 43 80 38 26CLAT 81 49 39 92 40 39 86 72 60 90 32 30 90 39 34RP 38 2 1 77 16 3 30 10 6 4 4 3 74 47 32WA 57 78 69 85 85 88 79 75 82 87 55 51 2 78 79Slag 80 18 40 40 24 22 55 26 18 6 5 5 30 25 18

376 Australian Journal of Soil Research B. E. Yusiharni et al.

lime, and coal. Wood ash was from eucalyptus (Mallee sp.)timber and litter, which is burnt in an experimental bioenergypower station at Narrogin, Western Australia. The chemicalcomposition of the byproducts and Sechura rock phosphate,which was included for comparative purposes, is givenin Table 2.

Characterisation of the materialsThe pH of the materials was determined in a 1 : 5 deionisedwater extract. Calcium carbonate equivalent (CCE) wasdetermined using the AOAC 1.005 procedure, (AOAC 1975).Major elements were determined by atomic absorptionspectrophotometry (AAS) (Perkin-Elmer, Analyst 300,Norwalk, CT, USA) and trace elements with a model PE ELAN600 inductively coupled plasma-mass spectrometry (ICPMS)instrument (Perkin-Elmer, Norwalk, CT, USA) after perchloricacid digestion. Total phosphorus in these digest was determinedcolourimetrically using the molybdovanadophosphate (yellow)method (Rayment and Higginson 1992). The compounds inbyproducts were identified by X-ray powder diffraction (XRD)

using a Philips PW3020 diffractometer. Samples for scanningelectron microscopy and energy dispersive X-ray spectrometry(EDS) using a JEOL 3600 instrument were placed onmetal stubs.

Chemical extraction of the materials (AOAC Method)The byproducts were analysed for available P using Associationof Official Analytical Chemistry (AOAC) standard methods

Table 4. Levels of P (mg/g) added to soil for the plant growthexperiment

MCP DCP RP CLA CLAT WA Slag

4.2 8.3 20.8 33.3 18.8 10.4 12.58.3 16.7 41.7 66.7 37.5 20.8 2516.7 33.3 83.3 133.3 75 41.7 5033.3 66.7 166.7 266.7 150 83.3 10066.7 133.3 333.3 533.3 300 166.7 200

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C500 C550 C600 C650 C700 C750 C800

C850 C900 C950 C1000

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Fig. 1. Percentages of total P extracted from chicken litter ash produced at various temperaturesfor various durations of extraction in (a) citric acid, (b) neutral ammonium citrate, and (c) alkalineammonium citrate.


(AOAC 1975) using water, citric acid (CA), neutral ammoniumcitrate (NAC), and alkaline ammonium citrate (AAC) extractions(Table 3). Gilkes and Palmer (1979) have shown that the standardAOAC extraction procedures may not be optimum for the bestprediction of the agronomic effectiveness of calcined phosphateminerals. They used various extraction times to evaluate thekinetics and congruency of dissolution of the phosphates todetermine optimum extraction times. The same procedure hasbeen followed here to determine an optimum procedure forbyproducts and for the rock phosphate that was included asa comparison material. Citric acid 2% (CA) was preparedby dissolving 100 g of citric acid in 5 L of deionised (DI)water. Neutral ammonium citrate (NAC) was prepared as inthe standard procedure, AOAC 2.036 (AOAC 1975). Alkaline

ammonium citrate (AAC) solution was prepared by dissolving865 g citric acid in 2 L of water to which 3 L of 5 M NH4OHwere added (Boxma 1977). The pH was adjusted to 9.35 and thespecific gravity to 1.08 by small additions of these reagents. Thesolid : solution ratio for each extractant was 1 : 100 w/v and thetemperature of extraction was 65◦C for NAC and AAC and 25◦Cfor CA.

The extractants were shaken in a temperature-controlledmechanical shaker with a vigorous action that kept particlesin suspension. Aliquots of the suspension were removed foranalysis at 7 times (0.5, 1, 2, 6, 24, 72, 120 h). Aliquotswere quenched with pure ice (NAC and AAC) and cold water(CA) to slow the reaction during filtering. The suspension wasimmediately filtered through 0.22-µm Millipore filter and the

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Fig. 2. XRD patterns of chicken litter calcined at various temperatures before (a) and after extraction for 120 h in citricacid (b), neutral ammonium citrate (c) and alkaline ammonium citrate (d ); Q, quartz (d = 3.43 A); A, apatite (d = 2.84 A),Cu Kα radiation.


filtrate analysed for phosphorus, calcium, magnesium, sodium,and potassium. The solid residue after 120 h extraction waswashed three times with DI water and then analysed by XRDand SEM.

Chemical analysis of the extractsPhosphate was determined in the extracts by spectrophotometry(molybdate blue method) (Rayment and Higginson 1992).The reagents were 0.02 M ammonium molybdate and 0.001 M

C500 C500 after CA extraction

C500 analysed grain C500 analysed grain after CA extraction

C500 after NAC extraction C500 after AAC extraction

C500 analysed grain after NAC extraction C500 analysed grain after AAC extraction

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Fig. 3. Scanning electron micrographs and spectra of the indicated particles for 500◦C calcined chicken litter (C500) before andafter extraction for 120 h in citrate solutions.


hydrazine sulfate solution; equal volumes were freshly mixedfor each batch of analyses. A 0.3-mL aliquot of the quenchedcitrate solution was added to 1 mL of hydrochloric acid anddiluted with DI water to fill a 10-mL volumetric flask. Next1 mL of the solution was mixed with 4 mL hydrazine solutionand 5 mL of molybdate solution in a flask. The solution wasshaken and placed in a boiling water bath for 10 min thencooled to room temperature in a water bath. The absorbancewas read at 820 nm on a Hitachi U-1100 spectrophotometerusing a bandwidth of 2 nm and 1 cm path length cell. Calcium,magnesium, sodium, and potassium were determined by AASafter dilution and addition of appropriate ionisation suppressants(Gilkes and Palmer 1979).

Glasshouse experimentThe <2-mm fraction of the topsoil (0–0.10 m) of a Yalanbeelateritic gravel soil from Bakers Hill, 73 km east of Perth,Western Australia, was used in this research. Soil propertiesare as follows: pH (1 : 5 H2O) 4.5, EC (1 : 5 H2O) 0.6 dS/m,total P 0.25%, bicarbonate-extractable P 0.49 µg/g (Colwell1963), clay, silt, and sand were 4%, 6%, and 90%,respectively.

The industrial byproducts used in the glasshouse study werepartly burnt chicken litter ash (CLA), totally burnt chickenlitter ash (CLAT), iron smelting slag, and wood ash (WA).CLA was derived from chicken litter burnt in an incineratorfor 36 h at temperatures between 700◦C and 800◦C. CLAT wasderived from CLA, by heating overnight at 700◦C in an oxidisingenvironment to remove residual charcoal from CLA. Propertiesof these materials are given in Table 2.

The treatments consisted of various rates of application tothe lateritic soil of the byproducts and monocalcium phosphate(MCP), dicalcium phosphate (DCP) and rock phosphate fromSechura (RP). Levels of phosphate for all sources including acontrol (zero rate) are listed in Table 4.

An amount of 1.5 kg of <2 mm soil was placed in a plasticbag. The basal fertiliser contained all nutrient elements except P(Palmer and Gilkes 1982) was applied with P fertilisers and thesoil was then mixed thoroughly and incubated at field capacityfor 4 days before seeding. Fifty pre-germinated seeds of annualryegrass (Lolium rigidum Gaud) were placed in the pots at5 cm depth and thinned to 20 plants per pot after the plants hadreached 2-leaf stage. The treatments were replicated 2 times andplaced in a completely randomised block design. The pots werererandomised each 7 days and maintained at constant weightwith deionised water. Ryegrass was harvested after 8 weeksand at 4-week intervals thereafter. The plants were harvestedby cutting the tops at about 1 cm above the soil surface at eachharvest and dried at 60◦C until constant weight occurred.

The harvested plant tops were then ground and analysed forP, Ca, Mg, K, Na, S, and trace elements by X-ray fluorescencespectrometry of pressed powder (Rayment and Higginson 1992).Soil samples were analysed for pH and EC (1 : 5 H2O), andavailable P (Colwell 1963) before planting and after the lastharvest.

The agronomic effectiveness (RE) of the materials asphosphate fertilisers was calculated for each of the 4 harvests,using the yield data. The ratio of the linear initial slope of theresponse curve for fertiliser relative to the slope for monocalcium

phosphate was calculated and it is the value of RE (Bolland andGilkes 1990). The same procedure was used to calculate REvalues based on plant P content and soil Bic-P values.

Results and discussion

Calcination of chicken litter

Chicken litter calcined at various temperatures had pH valuesthat increased from 10.18 (C500) to 10.62 (C1000) (Table 1).For the calcined chicken litter ash samples, the solubility ofphosphorus in AOAC citrate extractants varied with periodof extraction and the type of extractant. The percentages oftotal P extracted from chicken litter ash calcined at varioustemperatures and for various extraction times are shown inFig. 1. The major trend is that phosphorus solubility in all3 extractants increased as calcination temperature increasedup to the maximum calcination temperature of 1000◦C. Mostdissolution of P in citric acid (CA) occurred within 0.5 h,whereas dissolution continued for approximately 6 h in neutralammonium citrate (NAC) and 72 h in alkaline ammoniumcitrate (AAC). For all 3 extractants, considerable P had notdissolved after 120 h of extraction and this is likely to bepresent in refractory inorganic or residual organic compounds.Doak et al. (1965) have demonstrated that the solubility ofcalcined Christmas Island rock phosphate in the same citrateextractants increased to a maximum solubility of nearly 100%

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Fig. 4. Percentage of P extracted from 5 phosphatic byproducts by 3 citrateextractants for various durations of extraction: (a) citric acid, (b) neutralammonium citrate, (c) alkaline ammonium citrate. � CLA, � CLAT, N RP,× WA, ∗ Slag.


after calcination at temperatures between 500◦C and 650◦C anddecreased for higher calcination temperatures. The proportionof total P that had dissolved after 120 h was similar for all3 extractants but increased in the sequence CA > NAC > AACfor shorter periods of extraction. In contrast, Gilkes and Palmer(1979) observed that the dissolution of calcined iron–aluminiumphosphate in CA and NAC was less than in AAC. The solubilityof apatitic rock phosphate fertilisers in these reagents follows thesame trend as for litter ash (CA > NAC > AAC) (Lehr 1980).

The percentage dissolution of the major cations in calcinedchicken litter in CA, NAC, and AAC after a 1-h extractionis shown in Table 3. Dissolution was not congruent for any

extractant or material as indicated by the different percentagedissolution values for each element. Dissolution of calcium inCA increased from C500 to C950 and decreased at C1000. ForNAC and AAC the percentages of calcium dissolved were lessthan for CA. Higher proportions of magnesium, potassium, andsodium dissolved compared to calcium for all 3 extractants.CA, NAC, and AAC dissolved most magnesium for calcinationtemperatures between 800◦C and 1000◦C. In contrast, there wereno systematic trends for potassium and sodium. These diversedissolution behaviours for the 4 cations indicate that they do notcoexist in the byproducts in a single compound, thus dissolutionis incongruent.

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Fig. 5. XRD patterns of (a) byproducts and their residues after extraction for 120 h in (b) citric acid, (c) neutral ammoniumcitrate, and (d ) alkaline ammonium citrate; Q, quartz (d = 3.43 A); A, apatite (d = 2.84 A); C, calcite (d = 3.04 A); Ak, akermanite(d = 2.85 A); and G, gehlenite (d = 3.71 A), Cu Kα radiation.


The XRD patterns of samples of chicken litter ash that hadbeen calcined at various temperatures are shown in Fig. 2a.The major crystalline compounds present are apatite andquartz. Calcined chicken litter ash contains abundant amorphous

CLA CLA after CA extraction

CLA analysed grain CLA analysed grain after CA extraction

CLA after NAC extraction CLA after AAC extraction

CLA analysed grain after NAC extraction CLA analysed grain after AAC extraction

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Fig. 6. Scanning electron micrographs and spectra of indicated particles for original CLA and residues after extraction for 120 hin 3 citrate solutions.

material (mostly charcoal) as indicated by broad backgroundscatter centred at 25◦ 2θ. As calcination temperature increased,the intensity and sharpness of apatite peaks increased, whichis due to loss of charcoal and the increased abundance, greater


structural order, and larger crystal size of the apatite that formedduring calcination (Klug and Alexander 1974).

The XRD patterns for the residues of calcined chickenlitter ash samples after CA extraction (Fig. 2b) show strongerquartz peaks and a stronger amorphous carbon band than forCLA, as these insoluble compounds have been concentratedby dissolution of apatite. All the apatite had been dissolved inCA for each calcination temperature. Broad reflections due toprecipitated citrate salts are present for some CA residues.

These XRD results may be compared with the dissolution datashown in Fig. 1a, which indicate that for the higher calcinationtemperatures (≥850◦C) most P had dissolved in CA after 120 hof extraction. Much smaller amounts of P had dissolved forlower calcination temperatures and a similar trend occurredfor Ca, Mg, K, and Na (Table 3). It is suggested that CAcompletely dissolved the inorganic apatite, which is the mainform of P for high temperature calcines, but did not dissolve theorganic forms of P that persist in the lower temperature calcines.For NAC extraction, a comparison of Figs 1b and 2c showsthat some apatite did not dissolve for the highest temperature(≥850◦C) calcines, which is consistent with less P beingextracted (maximum 70%) than for CA, the organic P once againbeing insoluble. For the AAC extraction (Figs 1c and 2d) evenless apatite and P (maximum 58%) dissolved.

The SEM micrographs and EDS spectra of C500 and theresidue of C500 after the 3 citrate extractions show the diverseparticle sizes, shapes, and compositions present in this material(Fig. 3). Similar observation were made for the other calcinedmaterials and their residues. Most grains seen in the micrographsconsist mostly of carbon and contain only a little P andcations. The P-enriched grains in C500 have complex anddiverse chemical compositions. The grain in C500 indicatedin Fig. 3 contains much Ca and P, which could be present inapatite together with minor K, Mg, and Na, which may alsobe present within apatite (Lindsay et al. 1989) or possibly inseparate compounds such as carbonates or oxides, as indicatedby the dissolution data in Table 3 that describe incongruentdissolution. After CA extraction of C500, few Ca- and P-richgrains remained, as they had mostly dissolved, but only 40% oftotal P had dissolved, as much of the remaining P is presentin organic form in carbon grains. The rare P-enriched grainindicated in Fig. 3 for CA residue is probably a mixture of apatiteand a calcium silicate mineral. Figure 3 shows that some Ca-and P-rich apatite grains remain after NAC and AAC extraction,which is consistent with XRD and chemical extraction results. Inall 3 types of citrate residue some of the P is associated with thecharcoal, where it is present at the low concentration (Codlinget al. 2002) that was determined by EDS (<1%). The majority ofthe non-carbon grains were silicate minerals and represent sandthat had been incorporated into the litter.

Dissolution of industrial byproducts

The chemical compositions of the byproducts are given inTable 2 and indicate that these materials will provide severalplant nutrient elements in addition to P. Indeed at the rates ofapplication of byproducts used to lime soils (t/ha) large amountof Ca, Mg, K, and trace elements (Cu, Zn, Mn, etc.) wouldbe provided by the ash materials. Slag will provide much Ca

and Mg, little K, and some trace elements. The concentrationsof the heavy metals Cd, Ni, As, and Pb in the byproductsare insufficient to generate an environmental hazard at normalapplication rates for lime (Alloway and Ayres 1993). All of thebyproducts are likely to be effective liming agents as they havecalcium carbonate equivalent (CCE) values ranging from 93 to99%, whereas RP had much smaller CCE (48%) (Table 2).

The effects of extraction time and extractant type ondissolution of P from byproducts are illustrated in Fig. 4. Thesolubility of the P in RP was small in NAC and AAC, andhigher in CA, reflecting the presence of well-ordered apatite.Apatite is almost insoluble in water so that when apatite RPis applied to soil, any dissolution that occurs is the result of achemical reaction between soil acidity and RP, hence the use ofan acidic extractant (CA) to predict likely dissolution in acid soils(Khasawneh and Doll 1978). Lim and Gilkes (2001) showed thatthe equilibrium solubility of various RPs in CA was reached afterdifferent durations of extraction but that was generally attainedwithin 24 h, whereas minor additional dissolution of RP after24 h occurred in the present research.

Products CLAT and CLA showed similar and considerableamounts of dissolution in each extractant, with amounts ofsoluble P being in the sequence CA > NAC > AAC for shorterextraction times. For all 3 extractants there was little or noadditional dissolution after about 6 h of extraction. Much of the Pin WA rapidly dissolved in all 3 extractants, with relatively littleadditional dissolution occurring for longer extraction periods.The P in slag dissolved more slowly in NAC and AAC than inCA but essentially all P had dissolved after 6 h. Only a minor

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Fig. 7. X-ray spectrum of a carbon grain in partly burnt chicken litter ashshowing that it contains minor amounts of Si, P, S, Cl, K, and Ca (a) and asilicate grain (feldspars) in totally burnt chicken litter ash containing muchSi, Al, K, and Ca (b).


proportion of P in RP had dissolved in NAC and AAC after 120 h.Much more of the P in RP dissolved in CA and most dissolutionhad occurred within a short time.

The diffraction patterns of CLA, CLAT, slag, WA, and RPbefore and after extraction for 120 h are shown in Fig. 5. As

for the laboratory calcined chicken litter, the major compoundspresent in the CLA and CLAT heated in an incinerator areapatite and quartz with calcite being present in CLA. Thebroad background for CLA is higher than for CLAT due to thecarbon having been removed from CLAT by prolonged oxidative

CLAT CLAT after CA extraction

CLAT analysed grain CLAT analysed grain after CA extraction

CLAT after NAC extraction CLAT after AAC extraction

CLAT analysed grain after NAC extraction CLAT analysed grain after AAC extraction

00 2 4 6 8 10

1000

2000

3000

4000

5000

6000

7000


cps

Mg P

Si

K

Ca

00 5 10 15

500100015002000250030003500400045005000

cps

Na

Mg

Si

Cl

K

Ca

00 2 4 6 8 10

100200300400500600700800900

cps

Na

Al

Si

K

Ca

P

00 5 10 15

200400600800

100012001400


cps

Mg

P

Cl

Ca

Si

Fig. 8. Scanning electron micrographs and spectra of indicated grains for CLAT and residues after extraction for 120 hin 3 citrate solutions.


calcination. The sharp XRD reflections indicate that CLA andCLAT contain well ordered apatite of large crystal size. Based onspacing data, the apatite in CLA and CLAT is carbonate apatite(Lehr 1980). Much apatite remained in CLA and CLAT after120 h extraction in all 3 extractants, which is consistent withthe P dissolution data (Fig. 4). Oxalate salts precipitated fromsolution for CLA and CLAT extracted by CA.

The minerals present in Sechura RP are apatite and quartz(Fig. 5) (Lim and Gilkes 2001). Much apatite remains in theresidues for all 3 extractants, which is consistent with the lowextent of dissolution of RP in citrate extractants shown in Fig. 4.Slag consists of calcium magnesium silicate (akermanite) andcalcium aluminium silicate (gehlenite) (Li and Gilkes 2002).The residue of slag after CA extraction contains little akermaniteand much gehlenite. The residues after NAC and AAC extractioncontain abundant akermanite and gehlenite. It appears that thereis no relationship between the extent of dissolution of these

compounds and the dissolution of P, which was approximately100% in all 3 extractants. We conclude that P is not containedwithin these silicates but is present in slag as a discrete, readilysoluble compound.

The WA consists mostly of calcite, quartz, and several saltsbut apatite was not identified, although it has been observed insome plant ashes (Harper et al. 1982). Humphreys et al. (1987)also found that wood ash mainly consisted of calcite; however,Etiegni et al. (1991) observed that quicklime (CaO) and calciumsilicate (Ca2SiO4) could be present. All of the calcite dissolvedin CA but NAC and AAC residues contain calcite together withminor amounts of unidentified compounds.

The SEM image of CLA shows abundant charcoal particlesand an apatite grain (Fig. 6), consisting mostly of Ca andP with a little Mg, an element that can substitute for Ca inthe apatite structure (White 1971). After CA, NAC, and AACextractions, all calcite had been removed from CLA, some

Soil EC

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

)m/

Sd( lioS

CE

Soil EC

Soil Bic P

0

2

4

6

8

10

12

1 10 100 1000

Log P applied (mg/kg)

)gk/gm( lio

S P ci

B

Soil Bic P

Soil pH

1

2

3

4

5

6

7

8

lioS

Hp

Soil pH

Fig. 9. Plots of log P applied (mg/kg) v. pH, EC, and Bic-P for soil samples taken after the last harvest: � MCP,� DCP, N RP, × Slag, ∗ WA,• CLA, + CLAT.


Harvest I

0

0.5

1.0

1.5

2.0

2.5

Harvest II

0

0.5

1.0

1.5

2.0

2.5

Harvest III

0

0.5

1.0

1.5

2.0

2.5

Yie

ld (

g/po

t)

Harvest IV

0

0.5

1.0

1.5

2.0

2.5

3.0

1 10 100 1000


Fig. 10. Yield (g/pot) v. log rate of P applied (mg/kg) for each harvest forthe 7 fertilisers: � MCP, � DCP, N RP, × Slag, ∗ WA,• CLA, + CLAT.

apatite grains persisted and these were often associated withsilicate minerals as indicated by the EDS spectra of grains inFig. 6. The ash of plant materials commonly contains organiccompounds and particularly carbon resulting from incompletecombustion (Sander and Andren 1997). Many particles of carbonare present in CLA and these contain minor amounts of P, Ca,and other elements (Fig. 7a). The SEM image for the completelycombusted CLAT (Fig. 8) is quite different from that of CLAas no carbon particles are present. Much Ca and P is presentin compound particles, variously containing Si, Al, Mg, andK. These compound particles persisted to some extent in all3 extractant residues (Fig. 7) so that the P (as apatite) in theseparticles may have been partly protected from dissolution bysurrounding insoluble silicate compounds.

Characterisation of byproducts used in glasshouseexperiment

Some characteristics of the industrial byproducts used in theglasshouse study are provided in Table 2. The pH ranged from9.9 to 12.8 and the CCE values of all the byproducts were >90%,indicating that their liming capacity is high (Cregan et al. 1989).Total P concentrations of CLA, CLAT, slag, and WA were 3.6%,4.75%, 0.26%, and 0.44%, respectively, indicating their value

as P fertilisers at the large rates of application that are used forliming agents. The water-soluble phosphorus concentration inthe materials was very low to low due to the nature of the Pcompounds and to the alkaline pH of the byproducts (Lindsay1979). The P solubility of byproducts was much higher incitric acid compared to neutral ammonium citrate and alkalineammonium citrate. The higher concentration of phosphorus inCLAT relative to CLA is due to removal of charcoal from CLA(Codling et al. 2002). Other major plant nutrients present inthese byproducts include Ca, Mg, Na, and K. Concentrations ofCd, As, and Cu in CLA and CLAT were moderately elevated,while the value of Cd/P ratios for all of the byproducts was low,ranging from 0.00010 to 0.00016. The concentrations of othertrace elements were within the normal range for soils in Australia(ANZECC/NHMRC 1992), so there is no contamination hazard.

Soil pH, EC, and bicarbonate-soluble P of soils from theglasshouse experiment

The effects of the addition of industrial byproducts on pH, EC,and Bic-P values of the soil after the last harvest are presented inFig. 9. MCP, DCP, and RP did not have a liming effect, whereasCLA, CLAT, WA, and slag increased soil pH. WA was the mosteffective liming agent and it increased soil pH by ∼2.3 units.However, for all the treatments soil pH was in the range 5.5–7.0depending on the rates of application of the byproducts, thesepH values are suitable for ryegrass (Slattery et al. 1999). The ECvalues were low for all the soils, with the highest EC value of1.40 dS/m at 533 mg/kg rate of CLA being insufficient to affectthe growth of ryegrass (Moore 1998). The EC values decreasedwith increasing application rate of MCP, DCP, and RP, whichmay have been due to the greater uptake of salts by the muchlarger plants produced by the higher levels of application of Pfertilisers.

The amount of Bic-P in the treated soil increasedsystematically with the increasing rate of fertiliser for all Psources. The effectiveness of compounds (DCP, RP, slag, WA,CLA, and CLAT) relative to MCP were 59%, 40% 19%, 29%,39%, and 45%, respectively.

Analyses of the plant tops indicate that the application ofbyproducts affected the concentrations of most plant nutrientelements (Na, Mg, K, Ca, Si, P, S, Cl, Mn, Cu, and Zn).However, nutrient concentrations were within the normal rangefor ryegrass so that it is likely that no element toxicity ordeficiency other than P occurred during the experiment (Reuterand Robinson 1997).

For each harvest dry matter yield generally increased with theamount of P applied, indicating the P-deficient nature of the soiland the influence of the P fertilisers (Fig. 10). Dry matter yield ofryegrass ranged from 0.03 g to 2.37 g/pot, 0.06 g to 2.38 g/pot,0.12 g to 2.28 g/pot, and 0.08 g to 2.81 g/pot, respectively, forthe 4 harvests. For harvest III and IV some plants died due toP deficiency for the low P application rates and for the leasteffective fertilisers.

The P concentration in the plants ranged from 0.01% to 0.1%and according to the critical values of Reuter and Robinson(1997) this entire range represents deficiency, even for the highrates of P application. However, this particular ryegrass cultivar,which is commonly grown on highly P-deficient Western


Australian soils, has a low demand for P so that the publishedcritical levels (for other cultivars) are inappropriate. Snars et al.(2004) found that concentrations of P in this ryegrass cultivarat sufficiency were much lower than the published values forryegrass of Reuter and Robinson (1997).

The internal efficiency of P utilisation is indicated by plots ofplant dry matter v. the P content of plants (Snars et al. 2004). Foreach harvest the existence of a single internal efficiency curvefor all P sources (Fig. 11) indicates that differences in yield weredue predominantly to differences in plant P content as was alsoobserved by Snars et al. (2004) with this ryegrass cultivar.

Figure 12 show the response curves for P content v. P appliedfor all the harvests. There was a large response in P contentto MCP, DCP, and RP application for all harvests. For thebyproducts there was a much smaller response for harvest I

Harvest I

y = 1.25x + 0.090

R 2 = 0.9977

0

0.5

1.0

1.5

2.0

2.5

Harvest II

y = 1.69x – 0.14

R 2 = 0.9964

0

0.5

1.0

1.5

2.0

2.5

Harvest III

y = 1.39x + 0.03

R2 = 0.9928

0

0.5

1.0

1.5

2.0

2.5

Yie

ld (

g/po

t)

Harvest IV

R2 = 0.9954

0

0.5

1.0

1.5

2.0

2.5

3.0

P content (mg P/pot)

y = 1.61x + 0.02

0 0.5 1.0 1.5 2.0

Fig. 11. Internal efficiency of P utilisation curves for each harvest:� MCP,� DCP, N RP, × Slag, ∗ WA,• CLA, + CLAT.

and II; for harvest III and IV there was no systematic trend inresponse for the byproducts. For slag and WA many plants diedbefore the third harvest. The growth response and P contentof ryegrass for soil amended with slag and WA may not simplyreflect a response to the applied P. For instance the liming effect ofthese materials (Turner 1993) may have affected the availabilityof P and other nutrients but this not evident in plant analyses.

Relative effectiveness (RE)

The agronomic RE of the phosphate fertilisers based on plantdata was derived by comparing the initial slope of responsecurves for plant yield and P content for the various materialswith MCP as the reference (Fig. 13).

Due to death after the second harvest of some plants fertilisedwith WA and CLAT, no RE values could be calculated for these Psources for the later harvests. Furthermore for the last 2 harvests,application of WA and CLAT as phosphorus fertilisers producedonly small responses in yield and P content, so that responsecurves were poorly defined (low R2 values).

The effectiveness of all the P sources relative to MCP showedan increasing trend with harvest number. There was a systematicincrease in RE values for the first 3 harvests for the byproductsDCP and RP. It should be noted that values of RE are relative

Harvest I

0

0.5

1.0

1.5

2.0

Harvest II

0

0.5

1.0

1.5

2.0

Harvest III

0

0.5

1.0

1.5

2.0

P c

onte

nt (

mg/

pot)

Harvest IV

0

0.5

1.0

1.5

2.0

1 10 100 1000


Fig. 12. P content v. log P applied for all harvests: � MCP, � DCP, N RP,× Slag, ∗ WA,• CLA, + CLAT.


Plant yield

0

20

40

60

80

100

120

P content

0

20

40

60

80

100

120

Harvest

RE

(%

)

MCP DCP RP Slag WA CLA CLAT

1 2 3 4

Fig. 13. RE values based on yield and P content for the 4 harvests.

to MCP for which absolute effectiveness decreases with time(Bolland and Gilkes 1990); thus, the absolute effectiveness of theother P fertilisers may not have increased with time. However,it is evident that chicken litter ash has appreciable value as aphosphate fertiliser (Codling et al. 2002), whereas wood ashand slag are relatively ineffective.

The CLA, CLAT, slag, and WA have a liming action andwould be applied at much higher rate than are used for fertilisers,so that it is likely that all 4 materials will provide additional P toplants.

Relationships of the relative agronomic effectiveness ofbyproducts with P availability determined by chemicalextraction

As discussed earlier, the solubility of P in bypoducts inAOAC extractants differs for the 3 extractants and the durationof extraction. Consequently, there is uncertainty over whichcombination of extractant and extraction time will be mostpredictive of the agronomic effectiveness of byproducts. Acomparison of these chemical results with values of agronomicRE obtained in a glasshouse study was done to determine the

most suitable extraction procedure for these P fertilisers (Gilkesand Palmer 1979).

No chemical measure of available P (no combination ofextractant type and time) was systematically and positivelyrelated to RE values obtained from the plant experiment, andin most instances there was a negative relationship between REand the P soluble in extractants. This situation is illustrated bythe relationship between RE and the solubility of P in CA fora 6-h extraction (Fig. 14). The lack of a systematic positiverelationship may be a consequence of the high pH of WA, CLA,and CLAT raising soil pH, so that the dissolution of these Psources in soil and the consequent availability of P to plants isreduced and is not simply related to the solubility of P in citratereagents. Where soil pH becomes elevated due to high rates ofapplication of these alkaline materials as liming agents, apatitein the fertilisers will not dissolve to the same extent as in an acidsoil (Anderson et al. 1985). Furthermore the high concentrationof Ca in soil solution due to the dissolution of Ca compoundsin the byproducts will also reduce dissolution of apatite inthe soil due to the common ion effect (Lindsay et al. 1989).Under these circumstances, CA, NAC, and AAC extractions


r = –0.90

0

5

10

15

20

25

30

0 20 40 60 80 100 120

% P soluble in CA for 6 h

RE

(%

)

WA

CLATSlag

CLA

RP

Fig. 14. The relationship of relative agronomic effectiveness (RE) and thesolubility of P in CA for 6-h extraction.

are unable to predict the agronomic effectiveness of this typeof fertiliser. Chien (1993) has proposed a sequential citrateextraction procedure for fertilisers to remove the confoundingeffect of calcite on the evaluation of RP fertilisers.

Conclusion

This research has shown that the combustion of chicken littersuch as occurs in a thermal power station produces a multi-element fertiliser where much of the phosphorus is soluble incitrate extractants. In general, phosphorus solubility followedthe sequence CA > NAC > AAC for short periods of extraction.Much of the P in CLA and CLAT was present as the mineralapatite, with the abundance, crystal order, and crystal size of theapatite increasing with calcination temperature. The forms of Pin WA and slag are unknown but are mostly soluble in citrateextractants, whereas much of the P present as apatite in rockphosphate is not soluble.

The high value of the correlation coefficient (0.90) in Fig. 14might encourage the view that P soluble in citric acid is highlypredictive of RE, but the relationship is negative and the datapoints are not sufficiently dispersed for the regression line to bereliable. Thus, it is not possible to predict the relative agronomiceffectiveness of these materials using citrate extractants, whichmay be a consequence of the high pH of these materials andthe presence of calcium carbonate. A similar situation exists forcarbonate-rich rock phosphate fertiliser (Chien 1993). Chickenlitter ash, wood ash, and slag have important liming values andtheir application to acid soils at normal rates for liming will notincrease soil pH to levels that prevent the apatite from eventuallydissolving and providing substantial P to plants.

Acknowledgments

We would like to thank HISmelt for providing slag and Terry Packard forsupplying chicken litter. Thanks to Michael Smirk for his assistance insolving chemical analysis problems and to Gary Cass and Elizabeth Halladin.

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Manuscript received 3 October 2006, accepted 2 July 2007

http://www.publish.csiro.au/journals/ajsr

Documents

A laboratory and glasshouse evaluation of chicken litter ash, wood ash, and iron smelting slag as liming agents and P fertilisers