Recycling of biogas digestates in plant production: NPK fertilizer value and risk of leaching

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1 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7: ORIGINAL RESEARCH Reyling of iogs digesttes in plnt prodution: NPK fertilizer vlue nd risk of lehing Trine A. Sogn 1 Ivn Drgievi 1 Ror Linjordet 3 Tore Krogstd 1 Vinent G. H. Eijsink 2 Susnne Eih Gretorex 1 Reeived: 3 August 2017 / Aepted: 16 Deemer 2017 / Pulished online: 8 Jnury 2018 The Author(s) This rtile is n open ess pulition Astrt Purpose The min purposes of the study were to ssess the NPK fertilizer vlue of iogs digesttes in different soils nd to evlute the risk of unwnted nutrient lehing. Methods The fertilizer vlue of digesttes from neroi digesters ws investigted in greenhouse pot experiment with whet in three different soils; silt, lom nd snd. The digesttes were sed on different feedstok nd hd low, dry mtter ontent. The fertilizing effet of digesttes ws ompred to minerl fertilizer nd mnure. To investigte the fte of exess nutrients in soil fter the growing seson, the pots were lehed fter hrvest. A omplementry soil olumn lehing experiment without plnts ws rried out in the lortory. Results The onentrtion of mmonium in digesttes provided good inditor of the nitrogen fertilizer vlue of the digesttes. In the silt nd lom, the mmonium N frtion in digesttes hd fertilizer replement vlue equl to tht of minerl fertilizer N, wheres the replement vlue ws higher in the nutrient poor sndy soil. Digesttes often hve rtio etween nitrogen, phosphorus nd potssium whih is not fvourle for plnt growth. However, the suoptiml lne did not result in redued plnt growth or unwnted lehing from soil. Conlusions The results show tht digesttes from iogs prodution sed on fundmentlly different feedstok re promising s NPK fertilizers. The N fertiliztion n simply e sed on the digestte NH 4 + onentrtion nd, t lest for whet prodution, onsiderle vrition in the onentrtions of K nd P n e tolerted. Keywords Digesttes Fertilizer Nitrogen Phosphorus Potssium Introdution The ore of the ioeonomy is the hnge from use of fossil rw mterils to sustinle prodution, refinement nd utiliztion of renewle iomss. For instne, prodution of iogs using orgni wste s feedstok represents plusile tivity within the ioeonomy. Orgni wste eomes vlule resoure, nd ompred to fossil fuel utiliztion, use of iogs yields redued ron footprint * Trine A. Sogn trine.sogn@nmu.no 1 2 Fulty of Environmentl Sienes nd Nturl Resoure Mngement, Norwegin University of Life Sienes, Ås, Norwy Fulty of Chemistry, Biotehnology nd Food Siene, Norwegin University of Life Sienes, Ås, Norwy 3 Norwegin Institute of Bioeonomy Reserh, Ås, Norwy (Rehl nd Müller 2013; Uusitlo et l. 2014). Biogs prodution through neroi digestion leves orgni residues, digesttes, whih re rih in nutrients. If these digesttes re utilized in plnt prodution, nutrients lredy within the nutrient yle will e reyled nd the sustinility of the iogs prodution proess improves (Arthurson 2009; Ldni nd Vinteräk 2009; Vneekhute et l. 2013). In ddition, use of orgni fertilizers ontriutes to mintining nd/or improving soil qulity (Hti et l. 2006). Utiliztion of digesttes my reple or t lest redue the use of minerl fertilizer in gronomi plnt prodution. The liquid phse of digesttes is usully rih in plnt-ville nutrients suh s mmonium (NH 4 + ), phosphte nd potssium (K). Additionlly, more nitrogen (N) will e plnt ville y miroil deomposition nd minerliztion of the digesttes solid phse. As neroi digestion produes methne (CH 4 ) gs from the orgni feedstok, whih is susequently removed for use s iogs, the digesttes hve Vol.:( )

2 50 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7:49 58 lower ron to nitrogen rtio (C/N rtio) thn the feedstok (Möller nd Müller 2012). Although dependent on deomposition time, C/N rtio lower thn out 25 usully entils tht the orgni mtter hs surplus of N reltive to the N demnd of the soil miroil ommunity, whih then n e minerlized to NH 4 +, i.e. plnt-ville minerl N (Ferris et l. 1998). Sine frmers hve to se their N fertilizer strtegy on frm level N udgets with reltively high preision, the minerl N fertilizer equivlents or replement vlues of different digesttes re of importne. Studies with mnure hve shown low plnt vilility nd then little effet from the orgni N on plnt growth in the first yer of pplition due to slow minerliztion (Möller nd Müller 2012; We et l. 2013). On the other hnd, the NH 4 + in the liquid phse is plnt-ville (Gutser et l. 2005) nd my e diretly omprle with minerl N fertilizer. Nevertheless, it is ommon prtie for frmers to estimte the fertiliztion vlue of mnure y onsidering smll prt of orgnilly ound N nd redued effetiveness of the minerl N (Kirhmnn 1985), the ltter in order to llow for gseous nd/or lehing losses t pplition nd during the growing seson. A mjor hllenge with ll orgni fertilizers is the preditility of the dditionl minerl N relese y deomposition of the orgni mtter. Assessments of the fertilizer potentil of digesttes hve een rried out (Alurquerque et l. 2012; Kuszel nd Lorenowiz 2015; Cvlli et l. 2016; Riv et l. 2016), ut due to the wide vriety of feedstok used for iogs prodution, the effiieny nd ext preditility of the fertilizer N vlue of digesttes is diffiult. Over time, orgni N in the solid phse of digesttes will e minerlized nd NH 4 + will e relesed. In prodution system with ontinuous plnt over, the residul effet due to minerliztion is positive s it ensures grdul supply of NH 4 + to the plnts. However, in erel prodution, the timing of the minerliztion is ruil. For exmple, relese of minerl N lte in the growing seson, when plnts hve less requirement for N, or in sesons without plnt over, will inrese the risk of nitrte (NO 3 ) lehing. In griulturl res with only one growing seson per yer nd then often months without plnt over, relese of minerl N from orgni mtter deomposition my inrese the risk of N lehing. Next to N, K nd phosphorus (P) re quntittively the most importnt plnt nutrients nd essentil to seure proper growth nd development. Phosphorus nd K in the feedstok re generlly retined during the neroi digestion proess (Zirkler et l. 2014). In ddition to dissolved inorgni phosphte in the liquid phse, the solid phse of the digesttes ontins oth inorgni nd orgni P (Ktki et l. 2017). As surplus of phosphte in soils my eventully led to eutrophition of freshwter resoures nd esturies, it is importnt to void overdosing of P, y lning the P nd N input. In plnts, K is not uilt into orgni omplexes ut retined in tioni form. Consequently, the K in digesttes derived from plnt mteril is diretly plnt-ville oth in the solid nd liquid phse. Some grss plnt speies re known to hve higher uptke of K thn required in the metolism t high K vilility (Øgrd et l. 2001). An exessive K uptke my e prolemti due to ntgonisms with mgnesium, resulting in nutrient imlnes with negtive onsequenes for growth nd qulity (e.g. digestiility) (Msters nd Thompson 2016). Thus, lso the mount of K reltive to N nd P is importnt for optimized fertiliztion. Orgni mteril in soil is not only importnt s soure of plnt nutrients, it is lso importnt for soil porosity nd struture, s well s the ility to store wter nd nutrients. Soils low in orgni mtter re often ompt, hve poor struture nd low nutrient inding pity, s well s low ility to store wter. This study ws imed t evluting the impt of widely different feedstoks for iogs prodution on the minerl N fertilizer replement vlues of the resulting digesttes, s well s the P nd K supply to grin rops nd potentil losses through lehing. To ssess these issues we hve rried out greenhouse experiment with whet, using five different digesttes derived from iogs retors running on different omintions of mnure, whey permete, fish silge, food wste nd sewge sludge, in three different soils. We hve ompred plnt growth s well s nutrient lehing in tretments with digesttes with dt otined from ontrol tretments, inluding no fertiliztion, pplition of minerl fertilizer nd fresh mnure. A supplementry soil olumn lehing experiment without plnts ws rried out in the lortory in order to study nutrient lehing from soils without plnts. Mterils nd methods The digesttes The experiments in this study inluded the following tretments: 1. Control without fertiliztion (C), 2. Minerl fertilizer (MF), 3. Fresh mnure (FM), 4. Digested mnure (EDM), 5. Whey permete o-digested with mnure (EWM), 6. Whey permete nd fish silge o-digested with mnure (EWMF), 7. Commeril digesttes from soure seprted orgni household wste (CF) nd 8. Commeril digesttes from soure seprted orgni wste mixed with sewge sludge (CFS). The first three were ontrols (no fertilizer, minerl fertilizer nd mnure, respetively); the next three were experimentl digesttes produed in the iogs lortory of the Norwegin University of Life Sienes nd the Norwegin Institute of Bioeonomy Reserh, loted 35 km south-est of the Norwegin pitl Oslo, wheres the finl two were digesttes from ommeril iogs plnts.

3 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7: The experimentl digesttes were produed on lortory sle in ontinuously stirred tnk retors (CSTR, Dolly, Belh Bioteknik, Stokholm, Sweden) operting t 37 C with working volume of 6 L, nd hydruli retention time of 20 dys. Tretment 4 used n experimentl digestte from retor fed with mnure only (EDM). The experimentl digesttes used in tretments 5 nd 6 were produed in retors fed with mixture of whey permete nd mnure in volume (ml) rtio of 70 to 230 (EWM) nd 180 to 120 (EWMF), respetively. The ltter digestte (EWMF) lso inluded 6 ml fish silge in the feedstok mixture, in order to redue the C/N rtio. Orgni loding rtes for EDM, EWM nd EWMF were 3.4, 4.3 nd 5.4 g voltile solids (VS) L 1 dy 1, respetively. The digesttes used in tretments 7 nd 8 were ommeril digesttes olleted from muniipl iogs plnts. The digestte in tretment 7 (CF) ws from ommeril iogs plnt where iogs is produed on soure seprted orgni household wste. The digestte in tretment 8 (CFS) ws from ommeril iogs plnt where iogs is produed sed on soure-seprted orgni household wste mixed with sewge sludge (50:50, sed on fresh weight). The pot experiment A pot experiment ws rried out in greenhouse with whet (Tritium estivum L.vr. Zer) s test rop. The pots hd soil volume of pproximtely 6.7 L. Assuming soil depth of 20 m, 300,000 pots orrespond to one hetre (h) of rle lnd. Three different soils: snd, silt nd lom (Tle 2), were used s growth medi. The pots were irrigted regulrly in order to keep the soil wter ontent t 60% of the soils wter holding pity (WHC) throughout the experiment. No wter ws lehed from the pots during the experiment. The experiment onsisted of the eight tretments s explined ove. The minerl fertilizer tretment (MF) orresponded to dose of pproximtely 120 kg N h 1, 20 kg P h 1 nd 180 kg K h 1. The NPK level ws sed on ommon fertilizer reommendtion for whet prodution in Norwy, ut djusted in order to give optiml whet growth in pots within greenhouse. Beuse relese of plnt-ville minerl N from the mnure nd the solid frtion of the digesttes usully is low during the first growing seson fter pplition due to slow minerliztion (Svensson et l. 2004), the mounts of mnure nd digesttes were djusted sed on their inorgni N ontent, i.e. NH 4 + onentrtion (Tles 1 nd 3) in wet smples only. Sine the tretments (1 8) vried in perent DM, the soil moisture ws djusted y pplition of deionised wter ording to weight fter the initil ddition of fertilizers in order to hieve soil moisture t 60% WHC. To redue plnt growth effets due to differenes in soil ph (Tle 2), 20 nd 10 g lium ronte (CCO 3 ) per pot were dded to the lom nd snd, respetively, ringing the ph up to pproximtely 6.2. Plnts were hrvested fter 14 weeks of growth y utting the whet strws one m ove the soil surfe, nd divided into erel grin nd strw fter drying t 60 C to onstnt weight. Lehing experiment fter hrvest In order to evlute the risk of nutrient lehing fter the growing seson, simple lehing study ws onduted fter the hrvest. For tht purpose, the pots were first irrigted to 100% WHC nd then lehed with 1 L deionized wter, dded in doses of 250 ml eh during the ourse of n hour. The lehte drined from the soil through tue t the se of the pots. Soil lehing experiment without plnts Another lehing experiment ws rried out with re soils in the lortory. This study ws intended to represent worst-se senrio with extremely hevy rinfll just fter Tle 1 Chemil hrteristis of the mnure nd the digesttes (tretments 3 to 8) used in the experiments Tretments DM % ph Tot C g kg 1 Tot N g kg 1 NH 4 N + NO 3 N g L 1 NH 4 N + NO 3 N P g kg 1 DM K g kg 1 DM g kg 1 3. FM EDM EWM EWMF CF CFS g per 100 g DM, i.e. mesured in smples dried t 55 C Mesured in fresh smples Clulted sed on the mesured onentrtion in fresh smples nd DM%

4 52 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7:49 58 Tle 2 Chrteristis of the soils used in the pot nd lehing experiments ph L ph N mg kg 1 P-AL mg kg 1 K-AL mg kg 1 CEC mol kg 1 Snd (%) Silt (%) Cly (%) Tot. C g kg 1 Tot. N g kg 1 NO 3 N NH 4 N mg kg 1 Lom Snd Silt Prior to CCO3 ddition After CCO3 ddition P-AL nd K-AL denote plnt-ville frtions nd were mesured in soil extrts with n mmonium ette ltte solution (0.1 M mmonium ltte nd 0.4 M eti id, ph 3.75) dding the different fertilizers. Plexiglss olumns of 24 mm in dimeter nd 30 m in length were filled with 15 m of the sme three soils s in the greenhouse pot experiment, i.e. snd, silt nd lom (Tle 2). In order to prevent soil loss during the lehing experiment, plsti filter overed with PVC pellets (2 mm dimeter) ws pled t the ottom of the olumns. The top of eh olumn ws lso overed with PVC pellets in order to seure effetive distriution of the dded wter. Eh olumn ws overed with tinfoil in order to prevent light exposure nd therey minimize lge growth within the olumns. The tretments were the sme s in the growth experiment (Tle 3) nd mounts of fertilizer dded per volume of soil (ml per L soil) orresponded to those in the growth experiment. Prior to lehing, the soil olumns were sturted with deionized wter. The olumns were then irrigted with deionized wter t flow rte of 1.3 ml h 1 orresponding to 500 mm of preipittion during 7 dys period. The lehtes were olleted t the se of the olumn every dy during the 7 dys nd filtered prior to nlysis. Chemil nlysis Chemil hrteristis of the different digesttes, s well s of the mnure used in the experiments, re given in Tle 1. Totl C nd N in mnure nd digesttes were mesured in dried nd rushed smples y dry omustion (Nelson nd Sommers 1982) t 1050 C, using Leo CHN instrument (St. Joseph, Mihign, USA) ording to the Dums method (Bremner nd Mulvney 1982). NH 4 + in fresh digesttes nd mnures ws mesured y flow injetion nlysis (FIA) fter extrtion with 2 M potssium hloride (KCl) s desried in Bremner (1965). For the determintion of the totl onentrtions of P nd K, the mnure nd digesttes were digested in onentrted ultrpure nitri id for 90 min y stepwise heting up to 250 C using Milestone Ultrlve nd nlysed using Indutively Coupled Plsm Mss Spetrometry (Agilent ICP-MS 8800 TripleQ). The soil ph ws mesured in deionised wter, with soil to liquid rtio equl to 1:2.5. The totl C nd N in the soil ws determined in dried nd rushed smples y dry omustion (Nelson nd Sommers 1982) t 1050 C, using Leo CHN-1000 instrument (St. Joseph, Mihign, USA) s desried ove for mnure nd digesttes. The soil ontent of NH 4 + nd NO 3 ws mesured y flow injetion nlysis (FIAstr 5000, sed on ISO nd EN ISO 11732:1997) fter extrtion with 2 M KCl. Plnt-ville P (P-AL) nd K (K-AL) were estimted y extrtion with n mmonium ette ltte solution (0.1 M mmonium ltte nd 0.4-M eti id, ph 3.75) (Egnér et l. 1960), followed y indutively oupled plsm optil emission spetrometry (ICP-OES, Perkin Elmer Optim 5300 DV).

5 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7: Tle 3 Tretments 1 8 expressed s element ddition (mg) per pot Tretments Mnure/digestte ml N :P:K rtio N P K pot 1 mg pot 1 1. C 2. MF 4:1: FM 286 4:1: EDM 422 4:2: EWM 294 4:1: EWMF 540 4:4: CF 349 4:1: CFS 441 4:1: Inorgni N only The doses multiplied with 0.3 orrespond to kg per hetre. The doses divided y 100 orrespond to mg per soil olumn in the soil olumn experiment The prtile size distriution (i.e. perent of snd, silt nd ly in the soil, Tle 2) ws determined y the pipette method (Elonen 1971). The lehtes from the pots fter hrvest nd from the soil olumn experiment were nlysed for mmonium (NH 4 N) nd nitrte (NO 3 N) y flow injetion nlysis (FIAstr 5000, sed on ISO nd EN ISO 11732:1997) nd for other nutrients y ICP-OES (Perkin Elmer Optim 5300 DV). Clultions nd sttistil nlysis The minerl N fertilizer replement vlue is the rtio etween the grin yield otined in the digesttes or mnure tretments (tretments 3 8) nd the grin yield otined in the minerl N fertilizer tretment. The totl iomss nd grin yield figures in t h 1 re lulted y multiplying the mounts mesured in g DM pot 1 with ftor 0.3. The ftor is generted ssuming soil depth of 20 m nd thus 300,000 pots of 6.7 L orrespond to one hetre (h) rle lnd. The 300,000 h re divided y 10 6 to onvert from grm to tons of iomss or grin yield. Eh tretment, oth in the olumn nd pot experiments, ws replited three times for eh soil. Tretment nd soil effets were tested sttistilly y nlysis of vrine nd multiple testing using the GLM nd Student Neumn Keul s test (SNK) ville in the SAS omputer work pkge (SAS v.9.4). Differenes were onsidered signifint t p < Results nd disussion Biomss nd yield Digesttes generlly hd the sme fertilizing effet on totl iomss nd grin yields s mnure, with mnure eing g DM/pot g DM/pot g DM/pot d e Lom d Snd d similr to or etter thn minerl fertilizer (Fig. 1. Multiplying the figures (g DM pot 1 ) with ftor 0.3 gives totl iomss nd grin yield in t h 1 ). Totl iomss nd grin yields were generlly lower in snd nd lom ompred to silt, with n verge grin yield ross the tretments C MF FM EDM EWM EWMF CF CFS Grin yield Silt Totl iomss Fig. 1 Totl iomss (g DM pot 1 ) nd grin yield (g DM pot 1 ) in lom, snd nd silt. The stndrd devition within eh tretment (n = 3) is indited y the line extending the olumn. Within eh soil, signifint differenes re indited y letters d

6 54 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7:49 58 orresponding to 1.7 t h 1 in the lom, 2.1 t h 1 in the snd nd 3.2 t h 1 in the silt. The orgni fertilizers showed signifintly positive iomss effet (not signifint for the CFS tretment) reltive to the minerl fertilizer in the snd only. The vrition in grin yield oinided generlly with the vrition in totl iomss prodution. Figure 1 shows tht in the silt nd lom, the nitrogen fertilizer replement vlue (NFRV) (We et l. 2013) for mnure nd digesttes is pproximtely 1, when sed on the NH 4 + onentrtion mesured in the fresh smples of the digesttes (Tle 1). In the snd, the NFRVs of mnure nd digesttes seem to e higher thn 1 (signifint only for the EDM nd CF tretments). The poor growth of whet plnts reeiving minerl fertilizer my e onneted to the high moility of minerl N in snd. Due to their ontent of orgni mteril, mnure nd digesttes my ontriute to keeping plnt-ville N in the top lyer of the soil t the eginning of the growing seson, thus ensuring suffiient supply while the root systems is not yet well developed. Minerl fertilizer-sed N will esily e wshed down in the sndy soil due to lk of inding sites. The snd is soil poor in nutrients nd with low ontent of orgni mtter (Tle 2) nd s suh growth medium in whih positive effets of digesttes re expeted. In ddition to the effet of the orgni mtter ddition on improving nutrient vilility, other plnt growth onditions, suh s wter-holding pity re likely to improve. Sine the mnure nd digesttes vried in nutrient onentrtions (Tle 1), nd the mount of mnure nd digesttes pplied to the pots in the different tretments ws djusted to give the sme minerl N input, the input of P nd K vried in the different tretments (Tle 3). No dditionl fertilizer ws pplied in order to ompenste for these differenes. In the minerl fertilizer tretment, the rtio etween N, P nd K ws 4:1:6. The ommeril digestte sed on food wste (CF) hd lmost the sme lne etween N, P nd K s the minerl fertilizer, while the experimentl digestte sed on whey permete, mnure nd fish silge (EWMF) represented the highest input of oth P nd K reltive to the minerl fertilizer (4:4:24; Tle 3). Although the minerl fertilizer tretment represents n dequte lne etween the mronutrients N, P nd K for whet, it is still possile tht growth in snd, whih is poor in nutrients (Tle 1), ws stimulted y the extr supply of P nd K in the mnure nd some of the digesttes. However, lso the digesttes not prtiulrly rih in P nd K resulted in good yields on the sndy soil (Fig. 1) nd the differenes mong the mnure nd digesttes were not signifint. There ws no ler overll trend. The N to P rtio in the orgni mendments ws never lower thn in the minerl fertilizer tretment, i.e. 4 to 1, ut the supply of K ws lower in tretments with ommeril digesttes (CF nd CFS). No symptoms relted to K defiieny were seen on the whet plnts in ny of the soils nd tretments. Thus, ll in ll it seems tht ll digestte tretments (Tle 3) provided P nd K in mounts nd rtios whih n e regrded dequte, i.e. within rnge suitle for whet prodution. This is in line with Tmone et l. (2010) who, sed simply on hemil, spetrosopi nd iologil hrteristis of severl digesttes pprised digesttes to hve good fertilizing properties just due to high ontent of N, P nd K in esily ville form. However, no plnt growth experiments were onduted in tht study. In the silt nd lom, pplition of mnure nd digesttes resulted in the sme iomss prodution nd grin yield s pplition of minerl fertilizer. Independent of tretment, the lowest iomss nd grin yields were oserved in the lom (Fig. 1). This ws most likely due to limited ir supply (Currie 1962) sine the sieved lom provides dense growth medium upon irrigtion. Notly, in this study the dense lom ws not improved y pplition of orgni mtter. Lehing Nitrogen Nitrogen pplied to soil s NH 4 + will rpidly nitrify to NO 3 if not tken up y plnts. Both NH 4 + nd NO 3 re plnt-ville, ut erels in generl prefer NO 3 (Crmer nd Lewis 1993). A surplus of NO 3 in soil reltive to the plnt requirement will e lehed fter hrvest or denitrified. Generlly, the NO 3 lehing from the pots fter hrvest A NO3-N [mg/pot] BP [mg/pot] C K [mg/pot] d d d d d C MF FM EDM EWM EWMF CF CFS Lom Snd Silt Fig. 2 Lehing of NO 3 N (), totl P () nd totl K () (mg pot 1 ) mesured fter hrvest in the pot experiment. The stndrd devition within eh tretment (n = 3) is indited y the line extending the olumn. Within eh soil, signifint differenes re indited y letters

7 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7: (Fig. 2) ws negtively relted to the iomss growth, i.e. high iomss growth resulted in low NO 3 lehing. Thus, ross the fertilizer tretments, NO 3 lehing ws generlly highest from the lom. Both in the snd nd lom, high NO 3 lehing ws seen in the minerl fertilizer tretment (Fig. 2). In these soils, the N given s NO 3 (lium nitrte) ws not utilized y the plnts. In the snd, the NO 3 seemed to e lehed towrds the ottom of the pot efore n effetive root system hd een developed. In the lom, root development might hve een restrited y omptness, nd thus, roots my physilly not hve een le to reh ll the fertilizer NO 3. The omptness of the lom my restrit oxygen vilility s well s root development, using redued uptke of minerl N during the period of vegettive growth when the plnt N demnd is t the highest. In the lom, NO 3 lehing ws redued when mnure nd experimentl digesttes were pplied (Fig. 2), ut the ommeril digestte tretments (CF nd CFS) showed the sme high NO 3 lehing s the MF tretment. Thus, the pplition of orgni mtter did not improve the N utiliztion in the ompt lom in generl. In the snd, rpid wter flow towrds the ottom of the pot my hve limited the plnts ility to svenge the nutrients. The NO 3 lehing from pots treted with the mnure or digesttes ws signifintly lower ompred to the MF tretment (Fig. 2). This ltter oservtion is in ordne with dt from Svood et l. (2013) who, in field experiments with mize prodution in sndy lom nd snd, found tht NO 3 lehing ws lower upon tretment with digesttes or mnure, ompred to tretment with minerl fertilizer. Interestingly in our experiments, NO 3 lehing from snd reeiving mnure or digesttes ws mostly lower (signifint for the EWMF nd ommeril digesttes) thn from snd not reeiving ny fertilizer. A similr inhiitory effet of orgni fertilizer on NO 3 lehing ws found y Krmer et l. (2006) sed on studies in n orgni frming system. They suggested tht the redued NO 3 lehing ould e due to positive effet of orgni mtter on the tivity of the denitrifying miroil ommunities. In the soil olumn lehing experiment, the mount of elements not retrieved in the lehte must e onsidered dsored in the soil or, in the se of N, possily lso lost s gseous N speies. Generlly only 50% or less of the minerl N dded ws lehed (Tle 4) despite the very high irrigtion rte equivlent to 500 mm of preipittion during 7 dys. When pplied on griulturl lnd, mnure is usully mehnilly inorported into the top soil to void mmoni (NH 3 ) losses. In the olumn experiment, Tle 4 Totl mounts (mg) of N, P nd K pplied (in) nd lehed (out) within 7 dys in the soil olumn experiment Soil Tretments N mg olumn 1 P mg olumn 1 K mg olumn 1 N in NO 3 N out NH4 N out P in P out K in K out Lom 1. C MF FM EDM EWM EWMF CF CFS Snd 1. C MF FM EDM EWM EWMF CF CFS Silt 1. C MF FM EDM EWM EWMF CF CFS

8 56 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7:49 58 however, mnure nd digesttes were pplied on the top of the soil nd wshed into the soil with the wterfront. The ir temperture in the lortory ws 20 C. Although the soil surfes were kept moist nd lso overed with pellets, the soil ph ws 6 nd slightly ove (Tle 2) fter the liming nd some N my hve een voltilized s NH 3. In the lom, N ws minly lehed s NO 3, in the snd minly s NH 4 +, while in the silt, oth forms ourred in the lehte with the mjor prt eing NO 3 (Tle 4). Although the lom is reltively ompt nd likely not rih in oxygen, the lehing dt show tht NH 4 + must hve een nitrified to NO 3 efore lehing, n oservtion tht proly reflets omintion of high miroil tivity nd high retention. N lehing from the snd treted with orgni fertilizers ourred minly s NH 4 + (Tle 4), whih is likely due to short retention times of non-dsored nitrogen in this porous soil. Still, N lehing in snd ws generlly less thn 20% of the minerl N dded. The tion exhnge pity of the snd is low, ut might hve een slightly improved y the orgni mtter ddition. Thus, dsorption of NH 4 + to negtive surfe hrges my our in the orgni fertilizer tretments. The ft tht NO 3 lehing ws found in the minerl fertilizer tretment, ut not in snd reeiving digesttes or mnure suggests lso positive effet of orgni mtter on the tivity of denitrifying miroil ommunities (Krmer et l. 2006). In the silt, the soil with the highest nturl ontent of NO 3 (Tle 2), N lehing ws generlly higher thn in the snd, ut t the sme level s in the lom. In the silt, the min prt of the N lehed ws s NO 3, ut notiele mount lso s NH 4 +. Thus, in this simple nd well-ontrolled soil system, N speies nd mounts lehed following ddition of orgni fertilizer depended on the soil type. Phosphorus The doses of totl P in the digesttes nd mnure tretments were equl to or higher thn the mount of phosphte pplied in the minerl fertilizer tretment (Tle 3). The lehing of P in the pot experiment ws generlly very low (Fig. 2). For ll the three soils, P lehing from the minerl fertilizer tretment ws s low s in the pots with no fertiliztion. Though very low, P lehing for the orgni fertilizer tretments in the snd ws signifintly higher ompred to the no fertilizer nd minerl fertilizer tretments. It is interesting to note tht the EWMF digestte hd more thn 4 times higher P ontent thn the minerl fertilizer nd tht this ws not refleted in the mounts of lehed P in ny of the soils. This result is in ontrst to findings y Lu nd O Connor (2001) who found onsiderle lehing of P from orgni wstes when pplied to ourse texture soils with low P-dsorption pity. However, the low lehing of P from digesttes found in our experiment orresponds somewht etter to the findings y Hrldsen et l. (2011) who investigted the fte of P from different orgni wste produts in similr greenhouse pot experiment with rley growing in snd. They found low P lehing in generl, ut somewht higher P lehing from the digesttes ompred to other orgni wste produts. In review y Lu et l. (2012) it is desried tht sine most of the P in iosolids is in relitrnt form, iosolids P my generlly e less sujeted to runoff loss ompred to other mendments when pplied to griulturl lnds. Results from the olumn experiment lso showed very low levels of lehed P for ll soils nd tretments (Tle 4). As the soil ph fter liming ws pproximtely 6 in ll the three soils (ph L, Tle 2), neither sorption to Al- nd Feoxides or preipittion with rontes were proesses expeted to redue the P lehing. At soil ph of out 6, the P dded in ll tretments seems to e effetively hemisored y lignd exhnge on the soil minerls even in the short time-spn onsidered in this study. Independent of the nturl plnt-ville P sttus of the soils (P-AL, Tle 2), whih ws low in the snd nd higher in the lom nd silt, the dded P ws effetively retined within the soils. In olumn lehing study inluding soils with different texture, P-sttus nd ph rnging from 5.8 to 7.9, Grí- Alete et l. (2014) found the potentil P losses onneted to digestte pplition not to e signifintly dependent on soil type, ut more relted to digestte hrteristis. The inrese of the soils P reserves my e positive for soils nturlly low in P. In long-term field study y Bedd et l. (2016), uild-up of the soil P sttus y ddition of ompost ompred to minerl fertilizer ws emphsised. However, in res prone to erosion, P supplies exeeding plnt requirements will inrese the risk of eutrophition of wter odies through trnsport of prtile-ound P (Shrpley et l. 2001). Potssium Among the three soils, the silt hd the highest nturl K ontent (Tle 2) nd, when no fertilizer ws dded, higher mounts of K lehed from the silt fter hrvest ompred to lom nd snd (Fig. 2). Among the fertilizer tretments, the ommeril digesttes (CF nd CFS) represented the lowest K input (Tle 3), nd K lehing from the pots reeiving these digesttes did not differ from the ontrol without ny fertilizer ddition. As plnt growth did not pper to e K-limited in the CF nd CFS tretments (Fig. 1) nd the lehing of K ws equl to the ontrol with no fertilizer ddition (Fig. 2), the low K onentrtion in the CF nd CFS tretments pprently still met the whet plnt requirements even in the K-poor snd. The tretments with experimentl digesttes EWMF nd EDM represented the highest K input (Tle 3), i.e. 2.6 nd

9 Interntionl Journl of Reyling of Orgni Wste in Agriulture (2018) 7: times, respetively, higher thn for MF. The mount of K lehed from lom nd silt treted with EWMF nd EDM ws similr to the minerl fertilizer tretment, suggesting higher plnt uptke nd/or umultion of K in the soil. For the snd, lehed mounts of K were higher from the tretments with K-rih digesttes nd neither plnt uptke nor umultion in the soil seems to hve plyed mjor role. The ddition of orgni mtter in the orgni fertilizers hs thus not improved K inding pity in the snd. In the snd, whih is nturlly low in K (Tle 2) nd ould thus hve profited from n umultion of K, most of the extr K ws lehed. In ordne with the dt from the pot experiments, the soil olumn lehing experiments showed generlly strong K dsorption in the lom (Tle 4). For the other two soils, vrying degrees of lehing were oserved (Tle 4). Also in the soil olumn experiment, the nturlly higher K ontent in the silt ompred to the snd ws refleted in the mount of K lehed. In the snd % of the K dded in the different fertilizer tretments ws lehed, nd lehing ws highest for the tretments with the highest K input, i.e. the EWMF nd the EDM tretments. In the silt, K lehing ws high for EDM, ut for the other tretments generlly lower ompred to snd. Fertilizer K input in exess of plnt requirements often hs een found to persist in soil for yers fter pplition, improving the soil K sttus (Yu et l. 2009; Zhng et l. 2011). Considering oth the results from the soil olumn experiment nd the fter hrvest lehing study, the effet of K input in exess of plnt requirements pprently vries dependent of soil type. In the silt, whih in generl hd the highest iomss prodution, the high mount of K dded ws to lrge extent tken up y the plnts. In the lom with lower iomss prodution, the extr K ws primrily dsored y the ly minerls, while exess K in the snd ws predominntly lehed from the system. Conlusion The present study provides n overview of how wide vriety of digesttes ffets plnt prodution nd lehing of nutrients. The results show tht the onentrtion of NH 4 + in digesttes (DM < 6%) provides good inditor of the N fertilizer vlue of the digesttes. Additionlly, in the snd, digestte pplition redued NO 3 lehing. In longer-term pplitions of digesttes in the field, dditionl N supply from minerliztion of the orgni mteril my enefit iomss prodution lso in following growing sesons. Prtiulrly in the nutrient poor snd, the orgni fertilizers hd positive effet on erel yields. The positive effet my e relted to n improved ility to keep plnt nutrients within the root zone t n erly stge of plnt development. Although most digesttes hd rtios etween the plnt mronutrients N, P nd K tht were not optiml for whet growth, the vrition in P nd K ontent seemed to e within rnge suitle for whet prodution. The risk of P lehing ws low, even in the sndy soil or t P input tht ws up to 4 times higher ompred to dequte minerl fertilizer dditions. The vrition in K input did not influene yield. In the snd, K from digesttes in exess of plnt requirements ws lehed from the soil, in the lom ssimilted in the soil leding to soil K-reserve uild-up, while in the silt, the higher K vilility ws met y higher iomss prodution nd/or soil umultion. Overll, the dt show tht digesttes from iogs prodution sed on fundmentlly different feedstoks re promising s fertilizers. The N fertiliztion n e sed only on the NH 4 + onentrtion of digesttes nd, t lest for whet prodution, onsiderle vrition in the onentrtions of K nd P n e tolerted. Aknowledgements We would like to thnk Kurt R. Johnsen for his help with the pot experiments, nd Dr. Vlentin Zivnovi, for her work with the soil nd soil wter nlyses. This work ws funded y the Norwegin Reserh Counil (Projet no /I10). 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