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2 Chpter 20 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves Betriz Gómez-Muñoz, Dvid J. Htch, Rolnd Bol nd Roerto Grcí-Ruiz Additionl informtion is ville t the end of the chpter 1. Introduction Olive oil frming is significnt feture of lnd use in Mediterrnen regions, covering over five million hectres in the EU Memer Sttes. The min res of olive oil production re in Spin (2.4 million h), followed y Itly (1.4 million h), Greece (1 million h) nd Portugl (0.5 million h) [1]. Whilst olive plnttions re found over most of the Mediterrnen region, round 65% of the Spnish olive oil re is locted in Andlusi (southern Spin), representing 30% of the totl EU olive oil production nd out 35% of the utilized griculturl re. Therefore, olive oil frming in Andlusi is of gret socil, economic nd environmentl significnce nd ny chnge in the olive oil industry in terms of mngement prctices nd post-processing options could e of wide importnce, t lest t the regionl scle. The olive oil industry genertes lrge quntities of y-products. Almost ll of the olive mills in Spin use the two phse centrifugtion system for oil extrction to reduce wstewter genertion nd lower the contminnt lod, compred with the three phse centrifugtion system [2] which is currently used y other Mediterrnen countries. The min y product of the two phse extrction system is olive mill pomce (OMP, herefter), which in Mediterrnen res is produced during short period over the winter, from Novemer to Ferury [3], the mount generted vrying etween 7 nd 30 million m 3 per yer [4-6]. Typiclly, OMP is semi solid to semi liquid y-product resulting from the mix of lpechin, the min y products resulting from the older three phse extrction procedure, nd orujo. This y-product is mde minly with wter, seed nd pulp nd is potentilly hrmful y product for the environment, ecuse of the phytotoxic nd ntimicroil properties, low ph, reltively high slinity nd orgnic lod, nd the phenolic 2012 Gómez-Muñoz et l., licensee InTech. This is n open ccess chpter distriuted under the terms of the Cretive Commons Attriution License ( which permits unrestricted use, distriution, nd reproduction in ny medium, provided the originl work is properly cited.

3 460 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement nd lipid constituents [7-11]. Direct ppliction to rivers or soil is not llowed under most of the ntionl regultions of the producer countries. The min physico chemicl chrcteriztion of OMP cn e found in other reports [10,12,13]. According to these studies, OMP is cidic, with very high content of orgnic mtter nd cron, rich in potssium (K), poor in phosphorus (P), with intermedite levels of nitrogen (N) nd my lso contin phenolic nd lipid compounds. Some economic (due to costs ssocited with disposl) nd environmentl prolems rise from the disposl of OMP. The vrious options for the fte of the lrge mounts of OMP which re produced nnully in Andlusi cn e very diverse: generl description of these cn e found in [14]. Briefly, one lterntive for the disposl of this lrge mount of OMP could e in evportive ponds, ut lrge res would e required for this option which might lso pose severl potentil environmentl prolems such s d odour, leching nd insect prolifertion. Another mjor preferred option would include the genertion of renewle energy tking dvntge of the reltively high clorific vlue of OMP. Other importnt uses include the trnsformtion of OMP into n orgnic fertiliser nd soil conditioner through composting. The process of composting OMP consists of mixing it with lend of nturl orgnic residues (e.g. olive leves nd twigs collected fter clening the olive fruit in the mill, nd/or strw, or mnures), which is then llowed to decompose in erted piles for 7 to 9 months. This mens of re-utiliztion cn help to improve soil fertility in olive oil frms which re chrcterized y low orgnic mtter, reduce the cost of inorgnic fertilisers or, for commercil enterprise, cn provide n dditionl source of revenue for the olive oil mill economy. The min resons for composting re tht OMP hs semi solid consistency which mkes it difficult to mnge, nd to eliminte ny phytotoxicl effects y composting for t lest 18 weeks [15]. Composting OMP enles it to e snitized; the mss nd volume of the product re reduced nd stilized prior to lnd spreding. As lredy mentioned, efore composting, OMP is mixed with ulking gents such s olive tree leves, which re gthered long with the olive fruit, twigs nd smll rnches, strw [16], cotton wste [17] nd mnure to increse the nutrient content, or ny other mterils of niml or plnt origin which re ville loclly. In Andlusi, composted olive mill pomce (COMP, herefter) production hs incresed exponentilly during the lst seven yers from 1000 tonnes in 2003 to in 2011 [18] nd there re out 14 olive mills which re producing COMP in this region. Despite this rpid increse, there re no pulished studies on the min grochemicl properties nd the effects of OMP ppliction to soil. Indeed, there re few studies on the min physico-chemicl chnges in OMP during composting [19-21], or on the chemicl chrcteristion of the finl OMP composted product [22]. Moreover, these studies hve een undertken using only limited numer of OMP composts, which were produced in only low experimentl quntities nd t smll experimentl scle. The min ims of this chpter re to review the informtion from other studies nd our own on the grochemicl chrcteriztion of COMP currently produced in Andlusi nd on the short- nd long-term effects of its ppliction on the soil physico-chemicl nd iologicl properties.

4 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves Agrochemicl chrcteriztion of composted olive mill pomce The reltively high diversity of the ulking gents used (such s olive mill pomce, olive lefy mteril (OLM), mnure or strw) s well s the vrile proportion in which they re mixed is responsile for the highly heterogeneous nture nd vriility of the qulity of the COMP Composition of commercilly produced composted olive mill pomce As fr s we know, there re no studies on the chrcteriztion of currently commercilly produced COMP. In one of our own study, seven redy to pply OMP composts were collected from different olive mills locted in severl provinces of Andlusi. COMP smples differed in composition nd in the proportions of primry mterils such s OMP, OLM, mnure nd strw, s shown in Tle 1 nd Picture 1. Composted olive mill pomce OMP OLM Mnure Strw COMP1 80% 7% Sheep M 13% COMP2 75% 12% Poultry M 13% COMP3 60% Sheep M 40% COMP4 70% 8% Sheep M 12% 10% COMP5 85% 5% 10% COMP6 80% 20% COMP7 80% 13% Poultry M 7% Tle 1. Composition of different composted olive mill pomces descried in this chpter. OMP nd OLM refer to olive mill pomce nd olive lefy mterils, respectively. Picture 1. Visul ppernce of the composted olive mill pomce used in this study. COMP ph rnged 7.45 to 8.34 nd were dequte for most griculturl purposes. Those COMPs mde of mnure tended to hve higher ph. Men COMP ph ws 8.03, vlue

5 462 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement similr to those reported y [20,23] for other experimentlly produced composts mde of OMP, nd is within the ph rnge considered s optiml for the ctivity of microorgnisms nd plnt growth [24,25]. In ll cses, electric conductivity ws lower thn the 10 ds m 1, threshold estlished s indictor of possile phytotoxic/phyto inhiitory effects on plnts or in soil [26]. COMP hs high content of orgnic mtter (60.5%, on verge) nd cron (30.7%, on verge) (Tle 2). These vlues re higher thn those reported for cow, sheep nd poultry mnures nd similr to those found for horse, pig nd rit [27]. The highest vlues were found in those composts which included OLM nd strw with little or no mnure (COMP4 through to COMP7) nd my e due to incomplete orgnic mtter degrdtion of the lrger prticle sizes nd the higher lignin content of OLM. A low orgnic mtter degrdtion rte during composting hs een reported [20], minly ecuse the high lignin content of the OMP nd the high moisture of the initil mixture which limits sufficient ertion. For these COMPs, ppliction to soil could e good strtegy to increse the orgnic mtter content of soils of olive oil frms which in the Mediterrnen sin re usully depleted in orgnic mtter nd re exposed to progressive degrdtion processes. Furthermore, the content of lile cron in the COMPs re reltively low, indicting tht respired cron derived from compost fter ppliction to soil would e expected to e low. Therefore, COMP ppliction to soil could increse C storge due to the high totl cron content nd expected low rte of C minerlistion (see elow). Totl nitrogen (TN) verged 1.5%, nd ws higher for those COMP which included reltively high mounts of mnure during composting (Tle 2). This vlues is within the rnge of tht found for compost mde from plnt residues [28,29] nd similr to tht reported for compost produced experimentlly with OMP plus rit or sheep mnure, nd rice strw or lmond shells [22]. The C:N rtio rnged from 27.2 to 35.8 for COMP4, COMP5 nd COMP6, which did not include, or contined only limited mounts of mnure, while the rtio ws much lower (t ) for COMP1, COMP2, COMP3 nd COMP7, which included sheep or poultry mnures (Tle 2). The totl K (TK) in the composts verged 1.7% nd ws highest for COMP2, which included high proportion of poultry mnure nd lowest for COMP4 nd COMP5, oth of which included strw (Tle 2). These vlues were within the rnge of vlues reported y other uthors [20,23] for experimentlly produced compost nd lso similr to those of OMP [13]. This indictes tht K ws not lost through leching during the composting process. The totl P of the composts verged 0.41% nd ws highest for those mended with mnure (COMP1, COMP2 nd COMP3) nd lowest for those which included only OLM or strw (Tle 2). TP vlues were lower thn those of municipl solid wstes nd sewge sludge, lthough similr to other vegetle wstes nd mnures [30]. Those COMPs with high percentge of mnure hd lower lignin contents, ut lignin content tended to increse in those COMPs with higher proportion of OLM nd strw. Polyphenol contents of the COMPs were less thn 2%, even though OMP is usully chrcterized y high levels of polyphenols (Tle 2). Polyphenols from olive oil mill wste

6 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 463 wter hve een found to e toxic for some soil microorgnisms [31], nd this is one of the min resons why direct ppliction to soil cnnot e recommended. The low polyphenol contents in the composts gree with vlues found y other reserchers [32], who showed tht the polyphenol content decreses during composting. In ll cses, the polyphenol contents were lower thn 4%: the limit which hs een estlished where there is shift etween net N minerliztion nd immoiliztion during decomposition [33]. Those composts which re currently produced in Andlusi nd which included mnure showed typicl lignin nd polyphenol contents lower tht 20% nd 2%, respectively nd therefore re suitle s orgnic fertilisers. Lignin nd polyphenol contents of residues hve een shown to e roust indices for the prediction of N minerlistion from residue N fter incorportion in soil [34,35], with typicl thresholds for immedite net N minerlistion eing < 15% lignin nd < 3 4% totl extrctle polyphenol contents [36-38]. COMPs phytotoxicities (Zuconni test) were typiclly higher thn 50%, except for COMP3 nd COMP5, suggesting tht reltively high percentge of the currently produced COMPs re mture enough to e pplied in the field. COMP commercilly produced (min men- mx) Others uthors 1 Orgnic mtter (LOI) (g kg -1 ) Totl C (g kg -1 ) Totl N (g kg -1 ) C:N Totl P (%) Totl K (%) Lignin (g kg -1 ) Polyphenols (%) Lile orgnic C (g kg -1 ) Tle 2. Min physico-chemicl properties of seven commercilly produced composted olive mill pomces (Tle 1) nd results from iliogrphic review of different uthors for composted olive mill pomce. Vlues re men of four replictes. 1Other uthors [19,20,21,22,23] for experimentlly produced COMPs Nutrient distriution in different prticle size frctions of composted olive mill pomce The seprtion nd ppliction of different COMP prticle sizes could provide for etter optimiztion of COMP mngement, ecuse firly cler reltionship etween prticle size distriution of n exogenous source of orgnic mtter nd the C nd N dynmics in soils for sludge compost [39] (mong others) hs een demonstrted. Similrly, C minerlistion nd turnover ws seen to differ ccording to the prticle size frction in cttle slurry compost [40,41], lso from sludge strw mixture [42] nd in n eroiclly digested sewge sludge composted long with screened green wste compost, stored yrd

7 464 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement trimmings nd crushed wood pllets [39]. Moreover, the nitrogen vilility in compost hs lso een shown to e relted to prticle size, incresing s prticle size decresed in sludge compost [43]. Generlly, N minerlistion is greter in the fine nd wter solule frctions thn in corser frctions, t lest for mnure nd city refuse composts [44] nd composted sewge sludge [39]. These results suggest tht the size of frctions in compost contriute sustntilly to the totl C nd N dynmics of minerlistion fter compost is incorported into soil. This is of prticulr interest, ecuse depending on the rnge in prticle sizes, composts could therefore provide mens for storge of C in soil (i.e. from the lrger sized compost frctions), or source of ville N (i.e. from the finer compost frctions). The diversity nd vrile mount of rw mterils used to otin COMP mke the finl products very heterogeneous nd therefore, it is expected tht the nutrients nd the min physico-chemicl properties lso differ in the prticle size frctions of COMP. However, no studies existed to corroorte this, therefore in seprte study we exmined whether or not this expecttion out COMP ws correct. To estimte the nutrient distriution in prticle size frction of COMP, seven commercilly produced COMPs were studied (Tle 1) y sieving successively through to otin 3 different sized frctions: <0.212, nd mm. Aout 52% of COMP prticles were lrger thn 1mm for those COMPs with high content of mnure, wheres, in contrst for COMPs without mnure nd with strw the consisted for 80% of these lrger prticle sizes.. The percentge of fine prticles (<0.212 mm) douled for COMPs with mnure. These COMPs showed similr percentges of prticle size frctions reported for duck mnure [45], suggesting tht during composting, mnures generte reltively high content of finer frctions. In generl, the content of different compounds rich in orgnic C, such s orgnic mtter, totl cron nd lignin incresed with prticle size, eing significntly higher for frctions etween 1 to 6 mm. In sewge sludge compost mde with screened refuse, yrd trimmings nd pllets [39], nd for two types of diry slurries others found [41], s in this study, n increse in the totl C content with lrger prticles, lthough these differences were less distinct. In contrst, nutrients contents including totl N, minerl N, totl P or totl K were significntly higher in the fine frctions (<0.212 mm). More thn 40% of the totl N, P nd K found in the originl COMPs were in the <1 mm prticle frctions in COMPs which included sheep or poultry mnure during composting, wheres for COMP5, 6 nd 7, the contriution of <1 mm frctions ws lower thn 30%. This finding grees with those for mnure nd city refuse composts [44], niml slurry [41,45-47] nd sludge compost [39], from workers who oserved tht most of the totl N nd vrious forms of N ville in the short-term were mostly in the finer nd wter solule frctions. As result of lower N, ut higher C, the C:N rtio decresed s prticle size incresed (Figure 1). Similr reltionships etween C:N rtio nd prticle size frctions were otined for cttle slurry [46,47] nd for sludge compost [39]. Typiclly, the C:N rtio for prticles finer thn 1 mm ws lower thn 18.2 in ll COMPs, except those which included strw (COMP4 nd COMP5), suggesting higher N vilility of the orgnic N from these

8 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 465 prticles. During decomposition, mnures with C:N rtios elow 15 re likely to result in positive (net) N minerlistion fter ppliction to soil [48]. Overll, the germintion index ws higher thn 80% in the <1 mm frctions, wheres it ws lower thn 50% (e.g. with some degree of phytotoxicity) for frctions mm, lthough this ws not true for COMPs mde without mnure (COMP5 nd 6 mixtures) (Figure 1). Thus, the frctiontion of the compost produced in olive mills contining <1 mm phytotoxicity free frctions is highly recommended for commercil purposes. C/N COMP2&COMP7 COMP3 COMP1&COMP4 COMP5&COMP6 c PNM (% of TN dded) < < < < c C minerlized (% of TC dded) IG (%) < < < < c < < < < COMP2& COMP7 COMP3 COMP1& COMP4 COMP5& COMP6 c < < < < Figure 1. Box plot of C:N, potentil minerlisle N (PNM), minerlisle C nd germintion index of prticle size frctions of comintions of COMPs ccording to the Principl Component Anlysis. Different letters stnd for significnt differences (P <0.05) mong prticle size frctions.

9 466 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement The min differences mong seven COMP tested ccording their qulity ws shown in the Principl Component Anlysis (Figure 2). First principl component (PC1), which ws negtively correlted with COMP qulity indictors (e.g. totl nd ville nutrients, C:N rtio, ), ctegorized the COMPs ccording to the pool of nutrients nd orgnic mtter nd C, showing the high influence of rw mterils in the qulity of individul COMPs. Those COMPs mde with poultry mnure resulted in high qulity product, followed y COMPs mde with sheep mnure, wheres the qulity of those COMPs mde with high proportion of OLM nd strw ut no mnure ws low. In ddition, there ws trend for the qulity to increse in reltion to the content of finer frctions. This highlighted the lrge influence of the rw mterils in the finl composition nd qulity of COMP product; high proportion of mnure incresed the undnce of finer prticles with high nutrients contents, wheres the ddition of lrge mounts of OLM cused n increse in the content of lrger prticles with high content of C compounds. Overll, the seprtion nd ppliction of different COMP prticle sizes could e useful for etter optimiztion of COMP mngement, considering tht the smllest prticles (<1 mm) hve much higher germintion index vlue, totl N, P nd K nd higher potentil to minerlise N, providing more homogeneous, high qulity compost. On the other hnd, lrger prticles (>1 mm) hd higher contents of orgnic mtter nd C nd tended to hve the lowest C minerlistion nd thus, on ppliction to the soil in olive groves s soil conditioner, could improve the structure nd increse the orgnic mtter of the poorer soils nd increse the storge of soil orgnic C. Figure 2. Scores of the whole nd the prticle size frctions of the COMPs in the spce defined y PC1 nd PC2.

10 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves Effects of composted olive mill pomce on nitrogen vilility Although it is expected tht the ppliction of COMP-orgnic N would lso supply some ville N for the plnt, there is little informtion on the decomposition rte of COMP nd the impct this my hve on the N ville for the growth nd productivity of olive trees. Previous work [49] showed reltively low net N minerlistion in soil fter ppliction of compost otined from olive mill wstewter tken from n evportive pond nd other griculturl y products, suggesting tht during decomposition of composted OMP, N immoiliztion could tke plce. More detiled knowledge of the min soil N trnsformtions nd dynmics, following COMP ppliction to soil, could e the key to regulting soil fertility through n improved cpility to predict crop ville N nd orgnic mtter sequestrtion nd losses Nitrogen supply fter the ppliction of composted olive mill pomce Aville nitrogen supply throughout net N minerlistion (NM) nd nitrifiction ws studied for commercilly produced COMPs differing in the rw mterils co-composted with OMP (Tle 1) in n eroic incution experiment under controlled conditions over two yers. The highest rtes of NM for the control soil nd COMP smples were found during the first week of incution. This positive net N minerlistion ws proly from the N nd C contined in the lile components of the COMP, which cn e used directly y microes s n energy source. After the initil stge of minerl N relese, net N immoiliztion during COMP decomposition ws found. Proly ecuse the microorgnisms egn to decomposed the more reclcitrnt compounds (with higher C:N rtio) nd this plced demnd on ville soil N resulting in net N immoiliztion, which cn ultimtely e re minerlised over time. Similr rtes of minerlistion were found with mture composted mterils [50,51]. This result ws unexpected since, ccording to the TN contents, C:N rtios nd lignin contents of the different COMPs, net N minerlistion would e expected ccording to the view tht the ddition of orgnic mtter generlly cuses N minerlistion [52-54]. Rw mterils co-composted with OMP hd effects on net N minerliztion. During the first yer of incution, N immoiliztion ws found in ll COMPs, except for COMPs mde chiefly from OMP nd OLM. After two yers, decomposition of COMP resulted in positive net N minerliztion (i.e. net minerl N supply) for ll COMPs (Figure 3), with vlues s high s 95% of tht dded s COMP-N. These results demonstrte tht the orgnic N contined in the COMPs is not redily ville over short to medium timescles, nd suggests tht most of the orgnic N my e in reltively reclcitrnt forms. Indeed, during the composting process, N is immoilised in condensed romtic compounds which might contriute to the reduced vilility of N [55]. Therefore, the ppliction of COMP my result in short term declines in N vilility in griculturl soils: it is therefore recommended tht during the first yer, the ppliction of COMP should e comined with some other N-rich source of fertilizer. On the other hnd, utumn COMP ppliction could e useful pproch to lowering soil inorgnic N levels, therey reducing potentil N losses y leching.

11 468 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement 3.2. Appliction of composted olive mill pomce to soil reduce nitrogen losses y leching Plnt nitrogen use efficiency is usully lower thn 50%, though highly dependent on crop type nd environmentl conditions. There re different wys y which the N is lost nd no longer ville for crop uptke, such s denitrifiction, mmoni voltiliztion nd leching, which might lso e ssocited with environmentl prolems. N leching cn contminte groundwter or surfce wters through runoff. Indeed, lthough N contmintion of groundwter rises from severl sources, such s industril wste, municipl lndfills, mining, or septic systems, griculturl prctices remin mjor source [56-58]. Aout 15 55% of N pplied to crops cn e lost y leching every yer [59,60]. This is prticulrly importnt in olive oil groves s mny olive crops re on res vulnerle to nitrte pollution. g IN cumultive g COMP1 COMP2 COMP3 COMP4 COMP5 COMP6 COMP Time(d) 150 g IN cumultive g COMP1 COMP2 COMP3 COMP4 COMP5 COMP6 COMP7 Figure 3. () Cumultive mounts of COMP mended inorgnic N (IN) for ech smpling period nd () t the end of incution (365 d) for COMP mended soils. Brs for ech smpling represent the men of the stndrd devitions of the whole set of COMP smples.

12 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 469 Tking into ccount tht N contined in COMP is not redily ville in the short-term, N lost y leching is expected to e low fter ppliction of COMP to soils. Indeed, short-term (51 dys) leching losses of N fter ppliction of COMP were similr or even lower (etween -5 to 10% of the dded N) thn the unmended control soils in n experiment crried out under lortory conditions. These vlues were much lower thn those found for commercil orgnic fertilizer (up to 30% of the dded) nd ure or sodium nitrte (up to 80% of the dded) for the sme mount of totl N dded (Figure 4) c c N loss y leching (%) COMP O COMP CT08 CPR Ure NNO 3 - Orgnic Inorgnic Figure 4. Percentge of N lost s nitrte y leching of the totl N dded (equivlent to 100 µg N g -1 ) fter 51 d nd three precipittion events (totl precipittion equivlent to 80 l m -2 ). Vlues re the men of 4 replictes. Br denotes stndrd devition. Different letters denote significnt differences etween tretments (P<0.05). Similr results were found in n experiment under outdoor conditions fter one yer. Nitrte leching in soils mended with COMP ws compred with soils mended with sheep mnure (sheep M), commercil orgnic fertilizer (CPR), or inorgnic fertiliser. Fertilisers were pplied t two different rtes (equivlent to 100 nd 200 g N g -1 ) comined with two modes of ppliction (on the soil surfce or mixed with soil) nd simulting utumn conditions. The lowest losses were for COMP mended soils (up to 7% of tht pplied) nd the method of ppliction hd significnt effects on minerl N leching (Figure 5). In generl, those soils which received COMP on the soil surfce verged negtive minerl N losses (i.e. lower or similr losses to the control soil). N ppliction rtes hd no effect on COMP IN leching, regrdless of the wy the COMP ws pplied. Overll, inorgnic N leching for those tretments which received either Sheep M or CPR did not differ significntly, lthough leching fter surfce ppliction of CPR ws higher thn sheep M. Up to 37% of the fertiliser derived N ws leched for the doule surfce ppliction of CPR. No effects of rte or methods of ppliction on IN leching were found for CPR. However, for sheep M, leching ws higher t the doule rte nd lower for the surfce, compred with the mixed in ppliction. The highest IN leching reched 58% of the dded N for inorgnic fertiliser ppliction (Figure 5). Results from the lortory nd outdoor experiment clerly showed

13 470 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement the reclcitrnt nture of the COMP-N (i.e. high degree of N retention) despite the reltively low C:N rtio, confirming previous results on COMP-derived negtive net N minerlistion nd nitrifiction. Thus, ppliction of COMP on olive oil frms distriuted in the nitrte vulnerle res might e suitle strtegy to diminish nitrte contminted groundwter. This strtegy grees with [61] who reported tht composted mteril cn considerly lower the risk of groundwter contmintion. Slow relese, controlled relese nd stilized fertilisers, such s composted OMP re recommended for severl gro environmentl situtions to improve nutrient use efficiency y reducing nutrient losses from the soil. Results from our studies clerly demonstrted the high efficiency of composted OMP to retin N nd the eneficil reduction of nitrte leching elicited y this compost f mg N-IN lechte y COMP S1 COMP S2 COMP M1 COMPM2 Sheep M S1 d Sheep M S2 Sheep M M1 Sheep M M2 CPR S1 CPR S2 CPR M1 CPR M2 Inor Figure 5. Cumultive fertiliser derived minerl N (nitrte + mmonium) leching fter one yer under nturl rinfll nd temperture in outdoor conditions for soils which received: i) composted olive mill pomce (COMP), ii) sheep mnure (Sheep M), iii) commercil orgnic fertilisers (CPR), or iv) NNO3 (Inor) t 1 (250 µg N g -1 ) or 2 (500 µg N g -1 ) doses. M nd S, stnd for soil in which the fertilisers were mixed (M) with the soil or pplied to the soil surfce (S). Vlues re mens of 4 replictes nd rs denote stndrd devitions. Different letters denote significnt differences (P<0.05). c ce c cde c e 3.3. N2O emission derived of ppliction of composted olive mill pomce Agriculturl soils re significnt source of tmospheric N2O which is of concern ecuse of the role this gs hs in glol wrming [62]. Emissions of N2O from soil hve een shown to increse fter the ddition of plnt residues [63] nd orgnic fertilisers [64], the iochemicl composition (or qulity) eing n importnt determinnt of the mgnitude of N2O emissions [65]. N2O emissions in soil mended with COMP (100 µg N g 1 ) were determined under eroic incution over 51 dys. Soil N2O N fluxes were constnt nd reltively low (2.71 ng N2O N g 1 d 1 ), nd did not vry significntly etween COMP-mended nd the control soils, except

14 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 471 for the COMP which ws mde with moderte levels of sheep mnure (COMP1) (Figure 6). The cumultive N-N2O emissions fter 51-dys were only 0.23% of the dded COMP-N. This result ws not in greement with the well documented increse in N2O emissions fter plnt residue ddition to soils s reported in other studies [63,65]. The very low increse in N2O emissions fter COMP ppliction suggests tht N losses vi denitrifiction fter the nnul ppliction of COMP to olive oil groves re expected to e very low, nd thus ppliction of COMP could provide orgnic N without incresing the emissions of N2O Figure 6. Time course of () N-N2O emission rte nd () cumultive N-N2O emission in soil mended with COMP during 51 dys of l incution under eroic conditions. Brs denote the men stndrd devitions for ech tretment nd smpling point. 4. COMP-cron minerliztion As shown ove, composted olive mill pomce (COMP) hs high content of totl cron, most of which of reclcitrnt nture (e.g. expected low C decomposition) such s lignin or fire. Therefore, COMP ppliction in soil cn e good strtegy to increse the orgnic mtter content in soil, s well s the orgnic C. This prctice could reduce CO2 emission to the tmosphere incresing C storge in soil Cron minerliztion Mesurements of soil CO2 emissions cn provide useful insights into soil C cycling, nd provide sis for evluting soil C dynmics nd potentil C sequestrtion in different griculturl systems [66], prticulrly in intensive production systems ffected y the different cropping prctices nd residue mngement [67]. Soil C cn only e ssimilted, nd recycled through the microil iomss, or respired [68]. Soil respirtion nd minerlistion re generlly thought to e relted to the composition of the microil iomss, which in soils, tends to vry oth cross sustrte qulities [69] nd in time [70]. Low C minerlistion mesured s CO2 C fluxes fter mture COMP ppliction hve een shown [71]. However, the COMP used in this study ws n experimentlly produced COMP. The mount of COMP-C minerlized fter 8 months of incution fter COMP

15 472 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement ppliction in eight soils differing in soil orgnic cron (SOC) is shown in Figure 7. For ll cses, the COMP-C minerlized (e.g. emitted s C-CO2) ws less thn 10% of tht dded (4 g COMP-C g -1 ), nd this ws true, independently of soil texture or SOC contents. This result suggests tht C compounds in COMP re complex nd refrctory, resulting in high residence time in the soil. Moreover, the percentge of COMP-C minerlistion tended to e lower t higher rtes of COMP ppliction, which indictes higher potentil for COMP-C to ccumulte in the soils t higher rtes of ppliction (Figure 8). % Cumultive C of TC dded S1; SOC: 74.1 g kg -1 S2; SOC: 37.2 g kg -1 S3; SOC: 44.8 g kg -1 S4; SOC: 27.1 g kg -1 S5; SOC: 35.8 g kg -1 S6; SOC: 34.5 g kg -1 S7; SOC: 21.8 g kg -1 S8; SOC: 17.3 g kg Time (d) C storge in soil Figure 7. Percentge of C emitted s CO2 during COMP decomposition for eight types of soil fter 240 dys of incution. Brs denote stndrds devitions. 12 % Cumultive COMP-C emmited s CO 2 of TC dded COMP-C rte of ppliction (mg C dded g -1 ) High SOC Low SOC Figure 8. Effects of incresing the rte of COMP-C ppliction to two soils differing in soil orgnic cron (SOC) on cumultive COMP-C derived C-CO2 emissions fter 8 months of incution. Brs denote stndrds devitions of three replictes.

16 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves Long-term effects of composted olive mill pomce ppliction in olive groves The mjority of the olive grove soils of Andlusi re chrcterised y low levels of orgnic mtter, nd re exposed to progressive degrdtion processes. Thus, orgnic mtter ppliction is required to compenste for orgnic cron deficiency nd to improve soil fertility. As consequence, the use of trnsformed gro-industril wste for griculturl use, such s composted olive mill pomce, might represent relistic solution to overcome oth the soil degrdtion of olive oil groves nd sustinle disposl of OMP, thus incresing the sustinility of olive groves. Regionl uthorities, hve recognised the potentil use of COMP in griculture, nd hve promoted composting which hs resulted in n exponentil increse in the production of COMP during the lst 5 yers, with production of out tonnes in the hrvest cmpign [18]. However, the long-term effects of nnul ppliction of COMP on the soil fertility of olive oil groves should e evluted to promote more olive mill pomce composting. Soil smples were tken from four olive oil frms; Olver (O), Rej (R), Tozo (T) nd Andújr (A), which nnully received pplictions of COMP during 3, 4, 9 nd 16 yers, respectively (COMP olive oil frms, herefter). Soil smples were lso tken from comprle olive oil frms locted in the vicinity (<20 m) of ech of the COMP frms tht never received composted olive mill pomce (NCOMP, herefter). These NCOMP frms hve similr environmentl conditions, topogrphy nd soil texture to the COMP frms. Soil smples were chrcterized for physico-chemicl nd iologicl vriles to determine the fertility nd functionlity of soil fter COMP ppliction. In generl, soil ph in the 4, 9 nd 16 yers COMP sites ws 0.31, 0.23 nd 1.47 units lower thn the comprle NCOMP olive frming, respectively, wheres no differences were chieved in the site fter 3 yers of COMP ppliction. Moreover, the soil wter holding cpcity (WHC) ws significntly higher in the COMP treted soils, with increses of 2 4% with respect to NCOMP soils. The higher (WHC) in the soils under COMP frming ws expected (Tle 3), due to the reltively higher levels of orgnic mtter in these soils: the effect of orgnic mtter on the incresed potentil for soils to retin wter ws descried previously for 77 soil profiles [72]. Moreover, soil wter ggregte stility ws lso significntly higher fter COMP ppliction for ll treted soils: up to times greter for COMP compred with NCOMP treted soils (Tle 3). The higher soil ggregte stility in the COMP soils grees with the findings of [73], who showed tht the ppliction OMP to soils incresed this soil property from 64 to 73% fter 5 yers. The ction exchnge cpcity of soils treted with COMP ws lso significntly higher thn in the reltive NCOMP soils, independently of the site (e.g. numer of yers since COMP ws first pplied) (Tle 3). Overll, COMP ppliction significntly incresed oth orgnic mtter nd cron contents, compred with the NCOMP soil, except t the site tht received COMP for only three yers. The soil orgnic mtter content in soils treted for 4, 9 nd 16 yers with COMP (i.e. R, T nd A sites), ws from 2.1 to 8.5 times greter thn the respective NCOMP treted soil (Tle 3). Our

17 474 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement dt confirmed previous results which indicted tht soil orgnic mtter incresed fter mendment with OMP during the first weeks fter ppliction [74] or fter severl yers [73,75]. Our results lso showed tht orgnic cron ws higher in the COMP tretment compred with the NCOMP tretment. The increse in orgnic cron fter COMP ppliction indictes tht the decomposition rtes of COMP C were reltively low, nd lower thn the rtes of nnul COMP C ppliction. These reclcitrnt compounds might contriute to the reduced rte of C decomposition. Soil orgnic cron ws higher in the soils treted with COMP, eing up to eight times higher in soil where COMP ws pplied during the lst 16 yers in comprison with NCOMP frming. When extrpolting to hectre scle, these results show tht soil orgnic C incresed up to 30 tonnes per h -1 y -1 in soil fter COMP ppliction. The low decomposition rte of COMP nd high orgnic C content in COMPmended soil indictes tht ppliction of COMP in olive oil groves is n pproprite strtegy to sequester orgnic cron into the soil nd should e evluted further. Overll, the totl N content ws higher in the COMP thn in the NCOMP soils lthough this depended on the site. At O nd R sites, which received three nd four yers of COMP ppliction respectively, differences with the comprle NCOMP soils were not significnt. However, totl N ws 1.3 nd 14.8 times higher in soil with 9 nd 16 yers of COMP ppliction (sites T nd A) thn in the comprle NCOMP treted soils (Tle 3). The higher TN in COMP soils ws expected, since ppliction of orgnic residues normlly results in n increse in the soil content of N [49,73,76]. They showed significnt increse in the TN fter two to three yers of ppliction of OMP or COMP, indicting tht COMP N is very resistnt to minerlistion, nd therefore is retined in the soil. Generlly, soil lile phosphorus (P) in the mended COMP soils ws higher thn the unmended soil. In the O, R nd A sites, soil ville P t the COMP soils ws 13.9, nd 1607 % higher thn the NCOMP soil, wheres no significnt difference ws found t T site (Tle 3). At ll sites, soil exchngele potssium ws significntly higher in the COMP treted soils thn in the unmended soils. Site WHC (%) SA (%) CEC (meq100 g 1 ) LOI (%) TC (%) TN (%) Aville P (µg P g 1 ) O COMP 26.3± ± ±1.22ª 3.95± ± ± ±0.04ª NCOMP 22.3± ± ± ± ± ± ±0.03ª R COMP 21.8± ±1.8ª 25.3±3.83ª 8.34± ± ± ±0.03ª NCOMP 20.5± ± ± ± ± ± ±0.02 T COMP 23.6± ±0.2ª 21.1±3.46ª 6.31± ± ± ±0.01ª NCOMP 20.5± ± ± ± ± ± ±0.02ª A COMP 30.2± ± ±6.9ª 16.1± ± ± ±0.33ª NCOMP 28.7± ±1.5ª 10.6± ± ± ± ±0.02 Tle 3. Wter holding cpcity (WHC), soil stles ggregtes (SA), ction exchngele cpcity (CEC), orgnic mtter (LOI), totl C (TC), totl N (TN) nd ville P of olive oil frming which received (COMP) or not (NCOMP) composted olive mill pomce t Olver (O), Rej (R), Tozo (T) nd Andújr (A). Dt re the men of five replictes ± stndrd devition. Different superscript letters for ech site denote significnt differences etween COMP nd NCOMP frming (one wy ANOVA; P< 0.05).

18 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 475 Figure 9. Soil cid phosphtse (), -glucosidse (), protese (c), invertse (d), nd dehydrogense (e) ctivities, potentil nitrifiction rte (f) nd geometric men of the ssyed soil enzyme in olive oil frms which received (lck) or not (white) COMP t Olver (O), Rej (R), Tozo (T) nd Andújr (A). The numer of yers since composted olive mill pomce hs een pplied to COMP frming is lso indicted. Different suscript letters stnd for significnt differences (P < 0.05) etween COMP nd NCOMP frming of ech site. Soil enzyme ctivities relted to cron, nitrogen nd phosphorus cycling hve een proposed s tool to ssess soil qulity/helth nd functioning [77]. Enzymes ctivities

19 476 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement relted to the C, N nd P cycles were ll significntly higher in soils mended with COMP thn in NCOMP soils (Figure 9). Others uthors [78,79] hve found similr results fter ppliction of mnures of different origin. When pooling ll the nlysed vriles in Principl Component Anlysis it ws found tht the first principl component (PC1) ws negtively correlted with soil orgnic mtter, totl N, ville P, soil ggregte stility nd soil enzyme ctivities nd therefore, PC1 is strongly relted to soil functioning. PC2, on the other hnd, ws positively correlted with cly content, WHC nd ction exchnge cpcity. COMP-treted soils shifted upwrds (higher WHC nd CEC) nd towrds the left (higher soil functioning) with respect to their NCOMP soils in the PC1 PC2 spce (Figure 10). Therefore PCA, which included ll the nlysed vriles, clerly seprted pired plots ccording to the COMP ppliction, supporting the hypothesis tht COMP ppliction improves overll soil functioning. 2 O COMP R COMP T COMP A COMP O NCOMP 1 R NCOMP T NCOMP A NCOMP PC PC2 Figure 10. Ordintion of the COMP nd NCOMP frms t Olver (O), Rej (R), Tozo (T) nd Andújr (A) in the spce defined y the PC1 nd PC2 xis resulting from the PCA nlysis crried out with physico chemicl nd iochemicl soil properties. Coordintes re the mens of t five replictes nd rs represent the stndrd devitions of the men. Arrows illustrte the differences in the position of the COMP nd NCOMP frming t ech site. Finlly, the vectoril distnce etween comprle COMP nd NCOMP frms (e.g. differences in soil functioning) tended to increse with the period of COMP ppliction, suggesting tht there is potentil for further increses in soil fertility nd functioning fter long-term ppliction of COMP. 6. Ecologicl services ssocited with the use of composted olive mill pomce s orgnic fertiliser There is glol trend towrds developing griculturl production systems which re sustinle. This involves the more efficient utilistion of inputs nd the reduction of wste products. Idelly, orgnic y-products should e trnsformed into useful products y

20 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 477 processes such s nutrient recycling, replenishment of soil orgnic mtter or genertion of energy. In this context, the cost of wste disposl would e voided nd environmentl pollution reduced. This fct hs led y to widespred increse in the vlue of y-products of the griculturl industry. This is lso now the cse for OMP. Recycling of OMP through composting (reltively esy-to-use nd low costing methodology) could e sound strtegy to provide some ecologicl services to olive oil groves (Figure 11). Firstly, composting OMP reduces most of the potentil environmentl pollution prolems linked with the disposl of pproximtely 4 million of tonnes of OMP produced in Andlusi over reltively short-time spn (3 months). On the other hnd, most of the nutrients (especilly nitrogen, phosphorus nd potssium) hrvested with the yield, re contined in the OMP, nd therefore fter composting nd ppliction to olive oil groves helps to recycle these nutrients, reducing the need for chemicl fertilisers. Our estimtes show tht etween one to two-thirds of the Andlusin olive oil groves could e fertilised nnully with the OMP produced in Andlusi fter composting, with susequent reduction of out 25 60% in chemicl fertilisers. In ddition, the min eneficiry of the economic nd environmentl profits of composting OMP nd ppliction to olive oil groves is the frmer. Figure 11. Fte of C, N nd P of the fruit hrvested in the olive oil frming when olive mill pomce (min y-product of the olive oil mill industry) is composted nd pplied to the olive oil groves. Some of the environmentl services linked to the recycling of olive mill pomce throughout composting, re lso indicted.

21 478 Sustinle Development Authorittive nd Leding Edge Content for Environmentl Mngement Some of the environmentl services restored fter ppliction of COMP nd shown in this chpter include: i) Incresed soil orgnic mtter nd cron. Indeed our dt showed tht oth incresed significntly fter regulr pplictions of COMP nd there ws trend for incresed differences in SOM nd SOC etween soils mended or unmended with COMP ccording to the numer of yers when COMP ws pplied. Other vriles relted directly or indirectly with the increse in SOM include i) n increse in soil microil ctivity relted to nutrient recycling (e.g. soil enzyme ctivities), ction exchnge cpcity, soil ggregte stility nd ville P nd K, ii) increse in soil cron sequestrtion. COMP-C derived minerliztion is rther low (< 10% over one yer t optiml conditions) nd thus, regulr pplictions of COMP could contriute to soil C sequestrtion nd help llevite the soil C- CO2 emissions linked to olive oil cultivtion, iii) reduction of the potentil nitrte leching nd N2O emissions. Our dt on seven currently produced COMPs hve demonstrted tht during decomposition of OMP, soil minerl N is retined (i.e. net N immoiliztion) reducing not only nitrte leching, ut lso N2O emissions. 7. Conclusions The recycling of nutrient nd orgnic mtter of the olive mill pomce fter its composting nd ppliction to the soil of olive oil frming is worthwhile strtegy to void the potentil environmentl hrm of olive mill wste disposl nd could led to incresed soil fertility nd functionlity. The chrcteristics of the COMP currently produced re dequte for griculturl purposes (high orgnic mtter nd cron, high level of potssium nd from low to medium levels of N nd P, nd lck of phytotoxicity) nd the qulity ws highly dependent on the proportion of mnure co-composted with olive mill pomce. COMP-N is well humified nd during decomposition soil minerl N cn e immoilised depending on the proportion of rw mterils co-composted, nd therefore it is recommended to comine N rich fertiliser with COMP during the first yers of COMP ppliction. COMP-nitrte leching (t temporl scle of months to yer) nd nitrous oxide emissions were negligile fter COMP ppliction to soils. COMP-C minerliztion ws very low (< 10% of tht dded fter one yer) nd, therefore, COMP ppliction to soils could enhnce C sequestrtion in olive oil frming. Soil fertility nd functioning ws improved fter three yers of regulr pplictions of COMP to soils of olive oil groves there ws cler trend for further increse over longer periods of ppliction. Overll, composted olive mill pomce is worthwhile strtegy to reduce the environmentl prolems ssocited with the disposl of OLM, nd increses the sustinility nd ecologicl services of olive oil cultivtion. Author detils Betriz Gómez-Muñoz Corresponding Author Ecology Section, University of Jén, Cmpus Ls Lgunills s/n, Jén, Spin

22 The Compost of Olive Mill Pomce: From Wste to Resource Environmentl Benefits of Its Appliction in Olive Oil Groves 479 Dvid J. Htch Sustinle Soils nd Grsslnd Systems Deprtment, Rothmsted Reserch, North Wyke, Okehmpton, Devon, UK Rolnd Bol Institute of Bio-nd Geosciences, Agrosphere (IBG-3), Forschungszentrum Jülich GmH, Jülich, Germny Roerto Grcí-Ruiz Ecology Section, University of Jén, Cmpus Ls Lgunills s/n, Jén, Spin Acknowledgement This reserch ws crried out in the frmework of the Olive grove project of the Generl Secretry for Rurl Development nd orgnic production of the Junt de Andlucí, nd with the economic help of the Minister of Science nd Technology of Spin throughout the project referenced CGL We would like to thnks to Jose Mrí Álvrez nd the vrious olive oil frmers nd olive oil mills from which soil nd composted olive mill pomce smples were tken. 8. References [1] Beufoy G, Pienkowski M (2000) The environmentl impct of olive oil production in the Europen Union: prcticl options for improving the environmentl impct. Europen Forum on Nture Conservtion nd Pstorlism. Europen Commission, Brussels. [2] Dios Plomres R, Hros Giménez D, Montes Tuio F (2005) Estudio estructurl del sector oleícol de Andlucí. Nivel de clidd y respecto mediomientl de ls industris lmzrs. Comunicciones EXPOLIVA. [3] Moretis D, Stmti FE, Nikolidis NP, Klogerkis N (2011) Olive mill wstewter irrigtion of mize: impcts on soil nd groundwter. Agr. Wter Mnge. 98: [4] Crer F, López R, Mrtinez-Bordiú A, Dupuy de Lome E, Murillo JM (1996) Lnd tretment of olive oil mill wstewter. Int. Biodeter. Biodegr. 38: [5] Kvvdis V, Doul MK, Komnitss K, Likopoulou N (2010) Disposl of olive oil mill wstes in evportion ponds: effects on soil properties. J. Hzrd. Mter. 182: [6] López-Piñeiro A, Crer D, Alrrán Á, Peñ D (2011) Influence of two-phse olive mill wste ppliction to soil on teruthylzine ehviour nd persistence under controlled nd field conditions. J. Soil Sediment. 11: [7] Predes MJ, Moreno E, Rmos Cormenzn A, Mrtinez J (1987) Chrcteriztion of soil fter pollution with wste wters from olive oil extrction plnts. Chemosphere. 16: [8] Pérez J, de l Rui T, Moreno J, Mrtinez J (1992) Phenolic content nd nticteril ctivity of olive mill wstewter. Environ. Toxicol. Chem. 11:

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