The evaluation of stability and maturity during the composting of cattle manure

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1 Aville online t Chemosphere 70 (2008) The evlution of stility nd mturity during the omposting of ttle mnure Mrí Gómez-Brndón *, Cristin Lzno, Jorge Domínguez Deprtmento de Eologí y Biologí Animl, Universidd de Vigo, Vigo E-36310, Spin Reeived 27 Ferury 2007; reeived in revised form 22 June 2007; epted 26 June 2007 Aville online 8 August 2007 Astrt We exmined hemil, miroiologil nd iohemil prmeters in order to ssess their effetiveness s stility nd mturity inditors during the omposting proess of ttle mnure. The omposting mteril otined fter 15 d in trenhes nd t different times during the mturtion phse (i.e. 80, 180 nd 270 d) were nlyzed. We found tht the mteril olleted t the end of the tive phse ws indequte to e pplied to soil s orgni mendment due to its high ontent of NH þ 4, its high level of phytotoxiity nd the low degree of orgni mtter stility. After mturtion period of 80 d, the stility of the smple inresed. This ws shown y redution in the dissolved orgni ron (DOC) ontent nd NH þ 4 onentrtion nd lso y redution in the miroil tivity nd iomss; however, 180 d of omposting were not suffiient to redue the phytotoxiity to levels onsistent for sfe soil pplition. Among the vrious prmeters studied, the hnge in DOC with omposting time gve good indition of stility. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: DOC; Minerl N; Miroil iomss; Bsl respirtion; Enzymti tivities; Phytotoxiity 1. Introdution Cttle mnure is vlule resoure s soil fertilizer, providing high ontent of mro- nd mironutrients for rop growth, nd represents low-ost lterntive to minerl fertilizers (Shrpley nd Smith, 1995). However, the overprodution of orgni wstes y ttle reeding hs led to inpproprite disposl prties; for exmple, their indisriminte pplition to griulturl fields nd their improper timing of pplition, tht is, they re not pplied when it would e most enefiil for rops. These prties ould use serious environmentl prolems tht ould inlude n exessive input of potentilly hrmful tre metls, inorgni slts nd pthogens (Huthison et l., 2005); n inrese in nutrient loss from soils through lehing, erosion nd runoff due to not onsidering the nutrient requirements of rops (Vervoort et l., 1998); * Corresponding uthor. Tel.: ; fx: E-mil ddress: mrigomez@uvigo.es (M. Gómez-Brndón). nd the emission of hydrogen sulphide, mmoni nd other toxi gses (Slzr et l., 2005). The omposting proess my signifintly redue the environmentl prolems ssoited with the mngement of mnures y trnsforming them into sfer nd more stilized mteril for pplition to soil (Crr et l., 1995). To otin high qulity ompost it is neessry to understnd the hnges tht the mteril undergoes with the omposting proess. The stility nd mturity of the ompost re essentil for its suessful pplition, prtiulrly for omposts used in high vlue hortiulturl rops (Wng et l., 2004). The terms stility nd mturity re usully used interhngely to desrie the degree of deomposition nd trnsformtion of the orgni mtter in ompost (Zmor- Nhum et l., 2005), despite the ft they desrie different properties of the omposting sustrte. Stility is strongly relted to the rte of miroil tivity in ompost, nd is evluted y different respirometri mesurements (Lsridi nd Stentiford, 1998) nd/or y studying the trnsformtions in the hemil hrteristis of ompost orgni /$ - see front mtter Ó 2007 Elsevier Ltd. All rights reserved. doi: /j.hemosphere

2 M. Gómez-Brndón et l. / Chemosphere 70 (2008) mtter (Pihler nd Kögel-Knner, 2000). Respirometri tests hve een shown to e dequte for ssessing ompost stility euse they re le to mesure the extent of whih redily iodegrdle orgni mtter hs deomposed during the omposting proess (Adni et l., 2004). Compost mturity generlly refers to the degree of deomposition of phytotoxi orgni sustnes produed during the tive omposting phse nd to the sene of pthogens nd vile weed seeds (Wu et l., 2000). Both these properties re ritil for the qulity nd mrketility of the finl produt. The pplition of unstle ompost to soil my produe ompetition for oxygen etween miroil iomss nd plnt roots/seeds. This ft n deprive plnt roots/ seeds of oxygen, nd led to the prodution of H 2 S nd NO 2 (Mthur et l., 1993). Another prolem is nitrogen strvtion of plnts s miroorgnisms svenge soil N to mke up for the defiit resulting from the pplition of unstle ompost with high C to N rtio. The phytotoxiity of unstle omposts represents nother mjor prolem; this is due to the emission of mmoni nd the presene of other phytotoxi sustnes like phenoli ompounds nd ethylene oxide tht is synthesized during the deomposition of unstle ompost in soil. Low-moleulr weight orgni ids (i.e. eti, propioni nd utyri ids) produed y the neroi digestion of the orgni mtrix re lso responsile for ompost phytotoxiity (Fuhs, 2002). Mngement of the omposting proess must onsider the potentil gronomi vlue of the end produt nd its suitility for plnt rops y evluting its degree of mturity. Biologil methods involving seed germintion tests nd plnt growth iossys hve een used to evlute the mturity of ompost (Coopernd et l., 2003). This is tedious work nd there re disgreements regrding the ility of these tests to determine ompost mturity (Brewer nd Sullivn, 2003). A lrge vriety of tehniques hve een reported for the determintion of ompost stility (Wng et l., 2004). Chemil prmeters suh s ph, eletril ondutivity (EC), tion exhnge pity, dissolved orgni ron (DOC) nd the rtios of C to N nd NH þ 4 to NO 3 hve een pplied s inditors of stility. Sine stiliztion implies the formtion of humi-like sustnes, humifition indexes re generlly epted s riterion of stility, ut their solute vlues vry gretly mong omposts of different soure mterils. Moreover, their determintion requires proper seprtion of the non-humi frtion from the fulvi id frtion euse other ompounds with similr struture to humi sustnes ut different iologil mening (i.e. lignin residues, quinones, polyphenols, fts, et.) n e extrted (Sánhez-Monedero et l., 1999). Stility inditors sed on the study of miroil iomss nd its tivity hve lso een proposed. Mondini et l. (2006) reported tht miroil iomss n e used s stility prmeter in ligno-ellulosi wste omposts euse it lerly reflets the trnsformtion of orgni mtter during the omposting proess. Respirtion (CO 2 evolution rte nd/or O 2 uptke rte) is generl mesure of miroil tivity, nd it hs een widely used to evlute the stility of ompost (Gómez et l., 2006). The ATP ontent nd enzyme tivities re lso useful s inditors of ompost stility (Tiqui et l., 2002; Boulter-Bitzer et l., 2006). The use of different prmeters pproprite to determine the mturity nd/or stility of omposts will llow us to roden our knowledge out the omposting proess. Therefore, the two mjor ojetives of this study were () to desrie the hemil, miroiologil nd iohemil hnges during the industril omposting of ttle mnure nd () to ompre different prmeters with respet to their ility to evlute ompost stility nd mturity during the industril omposting of ttle mnure. 2. Mterils nd methods 2.1. Soure mterils nd omposting proess This study followed the omposting proess of fresh ttle mnure otined from the griulturl ttle omplex Energí Viv, S.A. in León, Spin. The reserhers did not ontrol the omposting opertion or ttempt to influene the ourse of the omposting proess, whih involved n tive phse of 15 d, followed y mturtion stge in piles for 270 d. Cttle mnure sujet to the tive phse in five trenhes with pproximte dimensions of 42 m long, 1.8 m wide nd 4.5 m high where eh ontined pproximtely 300 m 3 of mteril. Throughout the proess, these trenhes were erted from the ottom with fored ir through lower in order to indue ir onvetion movement into the mteril nd deliver oxygen to miroorgnisms. The funtioning of the ir lower vried s funtion of the temperture: (i) ontinuous ertion when the temperture of the omposting mss overme the vlue of 60 C; (ii) intermittent ertion ording to preset yle of 5 min ertion nd 5 min puse when the temperture ws found etween 55 C nd 60 C; nd (iii) intermittent ertion ording to preset yle of 5 min ertion followed y 10 min puse when the temperture ws elow 55 C. The fored ventiltion ws omined with dily turnings in order to homogenize the omposting mss nd to void the sustrte omption nd the susequent low porosity nd defiient ir distriution. The omposting mteril ws wtered with wter nd the moisture ontent ws ontrolled dily nd kept within the rnge of reommended vlues (45 65%; Miller, 1993). During the uring phse, the omposting mixture from eh trenh ws pilled up nd left to mture in mturtion piles (50 m long, 2 m wide nd 2 m high) up to 270 d in spe overed on top y eiling with the sides opened. These piles were turned for ertion twie month nd spordilly wtered with lehtes from the ttle frm. Smples were olleted t 10 rndom lotions t 15, 80,

3 438 M. Gómez-Brndón et l. / Chemosphere 70 (2008) nd 270 d nd thoroughly mixed to generte omposite smples. All the smples were stored in seled plsti ontiners tht were kept t 5 C until they were nlyzed. The initil fresh ttle mnure ws lso nlyzed for omprison Chemil nlyses EC nd ph were nlyzed in wter extrts (1:10, w/v). Totl C nd N ontents were nlyzed on Crlo Er 1500C/N nlyzer on dried smples. DOC ws determined in 0.5 M K 2 SO 4 extrts (1:50, w/v) y het digestion (150 C, 30 min) with sulphuri id nd potssium dihromte nd red in Bio-Rd Miroplte Reder 550 t 590 nm. Inorgni nitrogen (NH þ 4 nd NO 3 ) ws determined in 0.5 M K 2 SO 4 extrts (1:5, w/v) using the modified indophenol lue tehnique (Sims et l., 1995) with Bio-Rd Miroplte Reder 550. The ontent of P ws nlyzed in mmonium ironte-diethylenetriminepenteti id (AB-DTPA) extrts (1:6, w/v) y tomi sorption spetrophotometry (Soltnpour nd Shw, 1977) Miroiologil nd iohemil nlyses Miroil iomss ron (Cmi) ws determined y the hloroform fumigtion extrtion method (Vne et l., 1987) on moist smples (5 g fresh weight). The filtered extrts of oth fumigted nd non-fumigted smples were nlyzed for solule orgni C using Miroplte Reder (Bio-Rd Miroplte Reder 550, 590 nm). Cmi ws estimted s the differene etween the orgni C extrted from the fumigted nd the nonfumigted smple, multiplied y the K 2 SO 4 extrtion effiieny ftor for miroil C (K = 2.64). Ergosterol is memrne-ound moleule ommonly used s fungl iomrker (Bååth nd Anderson, 2003). The ergosterol ontent of the smples ws extrted y the mirowve ssisted extrtion method nd determined y HPLC nlysis (Young, 1995). Miroil tivity ws ssessed y mesuring the rte of CO 2 evolution from the smples (5 g fresh weight) fter 6 h of inution. The evolved CO 2 ws trpped in 0.02 M NOH nd then mesured y titrtion with HCl to phenolphthlein endpoint, fter dding exess BCl 2 (Anderson, 1982). Alkline phosphomonoesterse tivity ws estimted y determining the p-nitrophenol (PNP) relesed, fter inuting the smples (1 g fresh weight) with p-nitrophenyl phosphte (0.025 M) for 1 h t 37 C, in Bio-Rd Miroplte Reder 550 t 400 nm (Eivzi nd Tti, 1972). - gluosidse tivity ws ssessed y determining the PNP relesed, fter inuting the smples (1 g fresh weight) with -D-gluopyrnoside (0.025 M) for 1 h t 37 C, in Bio-Rd Miroplte Reder 550 t 400 nm (Eivzi nd Tti, 1988). Protese tivity ws mesured y determining the mino ids relesed, fter inuting the smples (1 g fresh weight) with sodium seinte (2%) for 2 h t 50 C, using Folin Ciolteu regent, in Bio-Rd Miroplte Reder 550 t 700 nm (Ldd nd Butler, 1972). Cellulse tivity ws estimted y determining the reduing sugrs relesed fter inuting the smples (5 g fresh weight) with roxymethyl ellulose sodium slt (0.7%) for 24 h t 50 C, in Bio-Rd Miroplte Reder t 690 nm (Shinner nd Von Mersi, 1990) Phytotoxiity ssy The phytotoxiity of the smples ws determined in distilled wter extrts (1:5, w/v) following the method of Zuoni nd de Bertoldi (1987). The extrts were gitted vigorously for 1 h nd then entrifuged for 15 min t rpm in order to seprte the phses. The superntnt ws olleted nd filtered through 0.45 lm memrne filter. The extrts were diluted to 30% nd used s germintion medi. One milliliter of the germintion solution ws pipetted into sterilized Petri dish lined with Whtmn #1 filter pper. Ten seeds of grden ress (Lepidium stivum L.), whih is one of the most sensitive test speies for evluting the phytotoxiity (Gehringer et l., 2003), were evenly distriuted on the filter pper nd inuted 24 h t C in the drk. Then, the germintion ws stopped y dding 1 ml of ethnol. The seed germintion perentge nd root elongtion of L. stivum were lso mesured in distilled wter nd used s ontrol. Finlly, the germintion index (GI), expressed s perentge of ontrol, ws lulted sed on reltive seed germintion perentge nd reltive root elongtion Sttistil nlyses The sttistil nlysis of dt ws rried out using the SPSS 11.0 progrm for Windows. A normlity test ws mde for ll the prmeters prior to nlyzing the vrine. The results were sumitted to n ANOVA test in order to determine hnges in the vriles with the omposting time. A Tukey s test ws used for testing signifint sttistil differenes mong omposting times. The reltionships etween vriles were defined y regression nlysis. A prinipl omponents nlysis ws rried out to summrize the results otined with the hemil, iohemil nd miroiologil prmeters. Two prinipl omponents (PC1 nd PC2) were used for this nlysis. 3. Results nd disussion 3.1. Chemil hnges The min hemil properties of the initil ttle mnure nd the omposting mixture fter 15, 80, 180 nd 270 d re shown in Tle 1. An inrese in the ph vlues ws reorded during the tive phse, suggesting the lkliniztion of the mnure s onsequene of the relese of mmoni from the degrdtion nd minerliztion of

4 M. Gómez-Brndón et l. / Chemosphere 70 (2008) Tle 1 Vrition in the hemil properties of ttle mnure with omposting time Composting time (dys) Thermophili Mturtion EC (ms m 1 ) 1.30 ± ± ± ± ± 0.12 ph Totl C (%) ± ± ± ± ± 1.22 Totl N (%) 2.40 ± ± ± ± ± 0.13 C to N rtio 17 ± ± ± ± ± 0.12 DOC (mg kg 1 dw) 7000 ± ± ± ± ± 10 NH þ 4 (mg kg 1 w) 600 ± ± ± ± ± 30 NO 3 (mg kg 1 dw) 20 ± ± ± ± ± 10 NH þ 4 to NO 3 rtio 30 ± ± ± ± ± 0.89 Aville P (mg kg 1 ) 170 ± ± ± ± ± 10 Vlues re mens ± stndrd error (n = 5). Vlues within the sme row followed y the sme letter re not signifintly different ording to Tukey s test (P = 0.05). orgni ompounds. During the mturtion stge, ph rehed higher levels thn in the initil ttle mnure nd the smple olleted t the end of the tive phse. This inrese is not typil in the mturtion phse, where it is expeted tht the ph drops to neutrl vlues nd then stilizes. The wtering of the mturtion piles with the lehtes from the ttle frm, nd the turnings of these piles ould e responsile of these results. The ph vlues rehed during the mturtion re rther high nd this ft ould hve importnt implitions on the fertility nd produtivity of soils sujeted to ompost mendment, s well s on the development of ph-sensitive plnts (Boulter- Bitzer et l., 2000). Moreover, eptle ph rnges should e within tolerle levels to miroorgnisms, i.e. teri generlly need ph rnge of 6 7.5; fungi n tolerte wider rnge, ; nd tinomyetes Our omposting mteril olleted t different times during the mturtion phse presented ph rnges tht exeeded the previous ones; thus, the ddition of these mterils to soil my lso strongly influene the soil miroflor. The EC lso ffets the qulity of omposts in lrge wy euse it reflets their slinity nd suitility for rop growth. This prmeter inresed fter the tive phse proly due to the relese of solule slts like mmonium nd phosphte resulting from the deomposition of esily iodegrdle orgni sustrtes. As in the se of the ph, higher levels of EC were found during the mturtion stge. The ddition of liquid niml wstes to the mturtion piles nd the turning of these piles ould hve een responsile for the inrese in EC. In spite of this inrese, the EC of ompost otined fter 270 d of mturtion did not exeed the limit vlue of 3 ms m 1 inditing mteril tht ould e sfely pplied to soil (Soumré et l., 2002). When n orgni wste is omposted, the C to N rtio generlly dereses throughout the omposting proess due to the C losses s CO 2 nd then stilizes in the rnge of (Chefetz et l., 1996). As the totl N ontent hnged slightly with the omposting time, in the present study, signifint redution of this rtio during the mturtion phse ws minly due to the depletion of esily degrdle ron ompounds s outlined y DOC dynmis (Tle 1). The rte of derese in DOC onentrtion depends on the soure mteril nd the omposting tehnique utilized. The mount of DOC during the omposting proess is relted to the equilirium etween vrious retions whih inrese or derese its onentrtion. The degrdtion of solid polymeri mteril in the omposting sustrte my led to the formtion of solule orgni mtter, whih would inrese the DOC onentrtion. On the other hnd, the redution in DOC depends on the ontinuous minerliztion of solule orgni ompounds, nd the repolymeriztion nd ondenstion pthwys tht led to the formtion of omplex orgni sustrtes with low soluility in wter whih tend to floulte out the solution (Sid-Pulliino nd Gigliotti, 2007). Minerl N (NH þ 4 nd NO 3 ) inresed signifintly during the tive phse whih indites n intense minerliztion. On the ontrry, t mturtion stge, the onentrtion of NH þ 4 gretly deresed due to its voltilistion s NH 3 s result of the high ph oserved during this phse nd most likely euse of the frequent turning. Low levels of NO 3 were lso found during the mturtion phse. This ft my hve een the result of lehing of NO 3 with the wtering of the mturtion piles. Brewer nd Sullivn (2003) reported derese in NO 3 in yrd trimmings ompost otined fter 133 d of mturtion proly due to the lehing from sturted ompost or denitrifition. Compred to the initil ttle mnure, the NH þ 4 to NO 3 rtio gretly deresed during the tive phse due to the high levels of NO 3 deteted in this stge. After 80 d of mturtion, this rtio inresed with respet to the smple olleted t the end of the tive phse. However, lower vlues of this rtio were reported in the smples olleted fter 180 nd 270 d of mturtion minly due to the low ontent of NH þ Miroiologil nd iohemil hnges The deresing trend of miroil iomss throughout the omposting proess (Fig. 1) ws in greement with

5 440 M. Gómez-Brndón et l. / Chemosphere 70 (2008) Cmi (mg kg -1 dw) Ergosterol ontent (mg kg -1 OM) Bsl respirtion (mg CO 2 kg -1 OM) other works (Grí et l., 1992; Insm et l., 1996; Klmer nd Bååth, 1998), reporting results otined with different iomss quntifition methods (fumigtion extrtion, sustrte-indued respirtion, ATP ontent, totl phospholipid ftty ids ontent). The fungl iomss mesured s ergosterol ontent lso deresed during the tive phse nd mturtion stge ompred to the initil ttle mnure (Fig. 1). The miroil tivity mesured s sl respirtion rehed mximum vlue of 5000 mg CO 2 kg 1 orgni mtter during the tive phse, whih ould e ttriuted to the presene of esily degrdle mterils tht stimulte the miroil ommunity of the initil ttle mnure. Moreover, the relese of lile ompounds resulting from the oxidtive iodegrdtion of the mtrix during the omposting proess ould lso explin the higher vlue otined on dy 15 with respet to the initil feedstok (Sid-Pulliino et l., 2007). However, lower rtes of respirtion inditive of minor miroil tivity were reorded Time (dys) Fig. 1. Chnges in () Cmi, () ergosterol ontent nd () sl respirtion of the initil ttle mnure (t = 0) nd the omposting mteril olleted t the end of the tive phse nd t different times during the mturtion stge (i.e. 80, 180 nd 270 d). Vlues re mens ± stndrd error (n = 5). Different letters indite signifint differenes t P < 0.05 (Tukey HSD). fter the mturtion period of 80 d (Fig. 1). The derese of miroil tivity ws orroorted y the redution in the miroil iomss s indited y the low levels of Cmi during the mturtion period. Enzymti prmeters lso reflet the tivity of the miroil ommunity nd indite the ility of omposting to degrde wide rnge of ommon orgni sustrtes (Mondini et l., 2004). Importnt enzymes involved in the omposting proess inlude ellulses, whih depolymerise ellulose; -gluosidses whih hydrolyse gluosides; midohydrolses, proteses nd ureses involved in N minerliztion; nd phosphomonoesterses nd rylsulphtses tht remove phosphte nd sulphte groups from orgni ompounds. In our study, the lkline phosphomonoesterse tivity gretly deresed during the tive phse proly due to the feedk inhiition of this enzyme y inorgni phosphte (Ayuso et l., 1996). The high levels of extrtle P found in the smple olleted t the end of the tive phse support this hypothesis (Tle 1). However, ompred to this smple, this enzyme tivity ws signifintly higher fter 180 nd 270 d of mturtion (Fig. 2). This ould e due to the derese in extrtle P ontent during this period, s well s due to the formtion of n enzyme humus omplex, whih would mke this enzyme more resistnt to denturtion (Mondini et l., 2004). Protese tivity deresed throughout the proess (Fig. 2), whih is inditive of redution in the sustrte for protese ple of tivting the synthesis of this enzyme (Diz Burgos nd Polo, 1991). Compred to the initil ttle mnure, lower levels of ellulse tivity were reported during the tive nd mturtion stges (Fig. 2). On the other hnd there were no signifint differenes in -gluosidse tivity with the omposting time (Fig. 2d). It is ssumed tht soil ellulses nd -gluosidses re minly produed y fungi (Hyno, 1986). In the present study, redution in the fungl iomrker ergosterol ws oserved during the tive phse nd the mturtion stge (Fig. 1). We found signifint orreltion etween ergosterol nd ellulse tivity (R 2 = 0.50, P = ), ut not with the -gluosidse tivity (R 2 = 0.05, P = 0.164). One possile explntion is the protetion of -gluosidse through the formtion of omplexes with the humi sustnes, whih mde the enzyme more resistnt to physil nd miroil degrdtion Summry of hemil, miroiologil nd iohemil hnges using prinipl omponents nlysis PC1 explined 60% of the vrine nd PC2 22% for totl explined vrine of 82%. The vriles responsile for the hnges long PC1 inluded ph, EC, totl C nd N, C to N rtio, DOC, NH þ 4, NO 3, NHþ 4 to NO 3 rtio, extrtle P, Cmi, sl respirtion nd protese tivity. All of them were positively orrelted with this funtion, exept ph, EC nd totl N. The vriles responsile for the hnges long PC2 inluded the

6 M. Gómez-Brndón et l. / Chemosphere 70 (2008) Protese tivity Phosphomonoesterse (mg tyrosine kg -1 dw) tivity (mg PNP kg -1 dw) dys dys dys PC2 (22%) Initil feedstok PC1 (60%) dys Cellulse tivity β-gluosidse tivity (mg eq gluose kg -1 dw) d (mg PNP kg -1 dw) phosphomonoesterse nd ellulse tivities nd ergosterol, whih were positively orrelted with this funtion. The smple olleted t the end of the tive phse seprted from the initil ttle mnure long PC2 (Fig. 3). This hnge ws highlighted y derese in the onentrtion of ergosterol nd phosphomonoesterse nd ellulse tivities during the tive phse. However, the omposting Time (dys) Fig. 2. Chnges in () lkline phosphomonoesterse, () protese, () ellulse nd (d) -gluosidse tivities of the initil ttle mnure (t = 0) nd the omposting mteril olleted t the end of the tive phse nd t different times during the mturtion stge (i.e. 80, 180 nd 270 d). Vlues re mens ± stndrd error (n = 5). Different letters indite signifint differenes t P < 0.05 (Tukey HSD) Fig. 3. Prinipl omponents nlysis of the hemil, miroiologil nd iohemil prmeters of the initil ttle mnure (t = 0) nd the omposting mteril olleted t the end of the tive phse nd t different times during the mturtion stge (i.e. 80, 180 nd 270 d). mteril olleted t different times during the mturtion phse seprted from the initil ttle mnure nd the smple olleted t the end of the tive phse minly long PC1. In this se, the hnge ws hrterized y n inrese in the ph, EC nd totl N nd derese in the totl C, C to N rtio, DOC, NH þ 4,NO 3, extrtle P, Cmi, sl respirtion nd protese tivity during the mturtion period Phytotoxiity iossy The germintion index ws 0% in the initil ttle mnure, nd rehed vlue of 24% during the tive phse. Then, t mturtion stge, GI of 87% ws reorded fter 270 d of mturtion (Fig. 4). Thus, more thn 180 d were needed to overome the threshold limit of 60% stted y Zuoni nd de Bertoldi (1987) to redue the phytotoxiity to levels onsistent for sfe soil pplition Evlution of stility nd mturity prmeters The gretest onern regrding the evlution of mturity is tht this prmeter does not only depend on the type of mteril nd omposting proess utilized ut lso on the trget use of the finl produt. As the omposting of niml mnures inreses, due to its prtil hrteristi s method of reyling, it eomes more nd more importnt to determine the pproprite use of eh method for the evlution of the stility nd mturity of the ompost. The pplition of hemil prmeters to ssess the stility of ompost is ommon prtise in the reserh on

7 442 M. Gómez-Brndón et l. / Chemosphere 70 (2008) Germintion index (%) Time (dys) Fig. 4. Chnges in the germintion index of the initil ttle mnure (t = 0) nd the omposting mteril olleted t the end of the tive phse nd t different times during the mturtion stge (i.e. 80, 180 nd 270 d). Vlues re mens ± stndrd error (n = 5). Different letters indite signifint differenes t P < 0.05 (Tukey HSD). omposting. To e good inditor, hemil prmeter should fulfil the following requirements: () follow onsistent trend during the omposting proess; () provide referene, ritil or threshold vlues; () require reltively rpid nd hep nlytil proedures nd (d) e esily interpretle. Some of the prmeters frequently referred to in the literture regrding the evlution of ompost stility re disussed in this study. C to N rtio my not e good inditor of ompost stility euse it n level off efore the ompost stilizes (Nmkoong et l., 1999). For exmple, when wstes rih in nitrogen re used s soure mteril for omposting, like sewge sledges or mnures, the C to N rtio n e within the vlues of stle ompost even though it my still e unstle. Zmor-Nhum et l. (2005) reported C to N rtio lower thn the utoff vlue of 15 very erly during the omposting of ttle mnure, while importnt stiliztion proesses were still tking ple. DOC generlly ontins orgni ompounds hving different suseptiilities to miroil degrdtion nd different phytotoxi properties. For this reson DOC omposition my hve n importnt role in determining the stiliztion proess. In the present study, DOC onentrtions during the mturtion phse were lower thn the threshold vlue of 4000 mg kg 1 suggested y Zmor- Nhum et l. (2005) for stle ompost showing tht the omposting mteril ws stilized fter 80 d from the point of view of DOC ontent (Tle 1). In ddition, we found signifint orreltion etween DOC nd respirtion (R 2 = 0.60, P = ). Chi et l. (2003) lso showed DOC to e highly orrelted to respirtion. Compost stility n e determined in terms of nitrifition, whih minly tkes ple during the mturtion stge when tempertures re lose to the mient. At the end of the omposting proess the ontent of NO 3 should e higher thn tht of NH þ 4, inditing tht the proess hs een performed under dequte ertion onditions (Bernl et l., 1998). Our omposting mteril olleted t different times during the mturtion phse did not exeed the limit vlue of 400 mg kg 1 suggested y Zuoni nd de Bertoldi (1987) for the onentrtion of NH þ 4 in stle omposts; ut, the levels of NO 3 were lower thn expeted during the mturtion phse (Tle 1). The NH þ 4 to NO 3 rtio hs lso een used to estimte the ompost stility (Bernl et l., 1998), giving limit vlue of 0.16 for stle omposts. In our se, this vlue ws exeeded during the mturtion phse due to the low ontent of NO 3 deteted during this stge (Tle 1). As minerl nitrogen forms hnged irregulrly with the omposting time, they nnot e relile inditors. After mturtion period of 80 d, similrly to DOC, the stility ssessed y the rte of miroil respirtion inresed, euse lower rtes of respirtion were reported in the omposting mteril olleted t different times during the mturtion stge (Fig. 1). Wng et l. (2004) lso reported low rtes of respirtion, inditive of highly stilized omposts, towrds the end of the omposting of diry nd pig mnures. Adni et l. (2004) proposed dynmi respirtion index s n urte inditor to mesure the stility of omposts resulting from different strting mterils. They reported threshold vlues of 1000 nd 500 mg O 2 kg 1 orgni mtter h 1 to indite medium nd high stility, respetively. Other studies hve estlished tht the mesurements of miroil respirtion n e prolemti s they re very sensitive to hnges of moisture, temperture, nd oxygen nd nitrogen vilility (Herrmnn nd Shnn, 1993). Wu et l. (2000) reported tht the low CO 2 evolution is not lwys n inditor of non-phytotoxi ompost. Therefore, the evlution of ompost stility sed on CO 2 evolution, nd the mturity sed on seed germintion, re two different prmeters of ompost qulity. In our study, despite of the ft tht low rtes of respirtion, inditive of highly stilized mterils, were reported fter 80 d of mturtion, more thn 180 d were needed to overome the threshold limit of 60% stted y Zuoni nd de Bertoldi (1987) for ompost to e onsidered phytotoxinfree (Fig. 4). The soure mteril nd the omposting ondition s well s the wtering of the mturtion piles with lehtes from the ttle frm ould hve required more time to rek down the phytotoxi sustnes. Considering the key roles of miroorgnisms in the omposting proess, the use of miroiologil properties s stility inditors is not surprising. Enzymti tivities ply n importnt role during the omposting proess, s they re implited in the iologil nd iohemil proesses through whih the initil orgni sustrtes re trnsformed into the end produt (Tiqui, 2002). As

8 M. Gómez-Brndón et l. / Chemosphere 70 (2008) onsequene, speifi enzymti tivities ould provide wy of hrterizing the omposting proess with reltion to the rte of trnsformtion of orgni residues nd the stility of the end produt. Mondini et l. (2004) reported tht the hnge in the lotion of enzymes throughout the omposting proess, i.e. from extrellulr to omplexed with humi-like sustnes, might e useful t the moment of evluting ompost stility, tking into ount tht not ll enzymes will e s eqully relile s stility index. Despite of the ft tht the mesurement of enzymti tivities is esy, quik nd inexpensive, it is diffiult to estlish generl threshold vlues to pply enzymti tivities s inditors of ompost stility due to the widely different orgni sustrtes involved in the omposting proesses. Thus, for ompost hrteriztion, it is neessry to follow the dynmis of enzymti tivities over time. Hving disussed the previous prmeters, determining the hnge in DOC ontent with omposting time seems to e the most suitle mesurement to evlute the stility of the omposting mteril. It fulfilled the lrgest numer of requirements, it followed onsistent trend nd rehed ritil vlue; moreover, it ws neither time-onsuming nor expensive nd ws esy to interpret. However, this does not men tht this mesurement is eqully urte to evlute the stility of ll soure mterils nd full omposting filities. The retion of dtses, showing whih protools re most effetive tking into ount the soure mteril, the omposting onditions nd if the experiment ws done in lortory or t full sle will help us to hose orretly the different prmeters for the evlution of ompost qulity. 4. Conlusions The tive phse ws ompnied y signifint inrese in EC, minerl N, extrtle P nd sl respirtion. However, lower levels of ergosterol nd phosphomonoesterse, protese nd ellulse tivities were found during this phse. The mturtion period ws hrterized y n inrese in ph, EC nd phosphomonoesterse tivity nd derese in C to N rtio, DOC, minerl N, extrtle P, sl respirtion nd protese tivity. The turning of mturtion piles nd the spordi ddition of lehtes from the ttle frm to these piles influened severl prmeters suh s the ph nd NO 3 ontent resulting in vlues tht re not typil from the mturtion stge. Moreover, mturtion phse of 80 d ws enough to otin stle ompost s outlined y severl prmeters, ut not to otin mture ompost (i.e. with low degree of phytotoxiity). Aknowledgements Mrí Gómez Brndón is finnilly supported y FPU fellowship from Ministerio de Eduión. The uthors thnk the personnel of Energí Viv, S.A. for hving let us follow the omposting proess in their fility. The uthors thnk Pul Friz for hving revised the English in this rtile. The uthors lso thnk the editor nd the two nonymous reviewers for helping us to improve the qulity of this work. 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