Effects of humic sustnces derived from orgnic wste enhncement on the growth nd minerl nutrition of mize Boris Eyherguiel, Jérôme Silvestre, Philippe Morrd To cite this version: Boris Eyherguiel, Jérôme Silvestre, Philippe Morrd. Effects of humic sustnces derived from orgnic wste enhncement on the growth nd minerl nutrition of mize. Bioresource Technology, Elsevier, 2008, vol. 99, pp. 4206-4212. <10.1016/j.iortech.2007.08.082>. <hl-00940093> HAL Id: hl-00940093 https://hl.rchives-ouvertes.fr/hl-00940093 Sumitted on 31 Jn 2014 HAL is multi-disciplinry open ccess rchive for the deposit nd dissemintion of scientific reserch documents, whether they re pulished or not. The documents my come from teching nd reserch institutions in Frnce or rod, or from pulic or privte reserch centers. L rchive ouverte pluridisciplinire HAL, est destinée u dépôt et à l diffusion de documents scientifiques de niveu recherche, puliés ou non, émnnt des étlissements d enseignement et de recherche frnçis ou étrngers, des lortoires pulics ou privés.
This is n uthor-deposited version pulished in : http://oto.univ-toulouse.fr/ Eprints ID : 10804 To link to this rticle : DOI: 10.1016/j.iortech.2007.08.082 http://dx.doi.org/10.1016/ j.iortech.2007.08.082 To cite this version: Eyherguiel, Boris nd Silvestre, Jérôme nd Morrd, Philippe Effects of humic sustnces derived from orgnic wste enhncement on the growth nd minerl nutrition of mize. (2008) Bioresource Technology, vol. 99 (n 10). pp. 4206-4212. ISSN 0960-8524 Any correspondnce concerning this service should e sent to the repository dministrtor: stff-oto@listes-diff.inp-toulouse.fr
Effects of humic sustnces derived from orgnic wste enhncement on the growth nd minerl nutrition of mize B. Eyherguiel *, J. Silvestre, P. Morrd Lortoire Agronomie Environnement Ecotoxicologie, Ecole Ntionle Supérieure d Agronomie de Toulouse, Av. de l Agroiopôle, 31326 Cstnet Tolosn Cedex, Frnce Astrct A physico-chemicl process hs een developed to trnsform nd enhnce lignocellulosic wste in liquid humic extrcts: humic-like sustnces (HLS). The im of this study ws to determine the effects of HLS on plnt physiology in order to consider their griculturl use s orgnic fertilizers. The effects of HLS were evluted on mize seed germintion, nd their impct on growth, development nd minerl nutrition ws studied on mize plnts cultivted under hydroponic conditions. The experimentl results showed tht HLS do not increse the percentge nd rte of germintion ut enhnce the root elongtion of seeds thus treted. Positive effects were lso oserved on the whole plnt growth s well s on root, shoot nd lef iomss. These effects cn e relted to the high wter nd minerl consumption of plnts undergoing this tretment. The high wter efficiency indicted tht such plnts produce more iomss thn non-treted plnts for the sme consumption of the nutrient solution. Furthermore, the use of HLS induced flowering precocity nd modified root development suggesting possile interction of HLS with developmentl processes. Considering the eneficil effect of HLS on different stges of plnt growth, their use my present vrious scientific nd economic dvntges. The physico-chemicl trnsformtion of swdust is n interesting wy of enhncing orgnic wste mterils. Keywords: Humic sustnces; Wste enhncement; Mize; Whole plnt growth; Hydroponic culture 1. Introduction It hs long een recognized tht humic sustnces (HS) hve mny eneficil effects on soil nd plnt growth. These heterogeneous nd complex molecules, uiquitous in the environment, cn produce vrious morphologicl, physiologicl nd iochemicl effects on higher plnts (Chen nd Avid, 1990; Vughn nd Mlcom, 1985). The influence of humic mteril on plnt growth, hve een investigted on iometric fctors nd numerous studies hve shown tht humic sustnces enhnce root, lef nd shoot growth ut lso stimulte the germintion of vrious crop species (Piccolo et l., 1993). These positive * Corresponding uthor. E-mil ddress: eyhergu@enst.fr (B. Eyherguiel). effects re explined y the direct interction of HS with physiologicl nd metolism processes (Nrdi et l., 2002). The ddition of HS increse nutrient uptke (Linehn, 1978), cell permeility (Vughn nd Ord, 1985) nd modify mechnisms involved in plnt growth stimultion (Lee nd Brtlett, 1976). Due to their properties, humic sustnces ply mjor role in soil fertiliztion. Mny products of different origins (pet, compost, leonrdite) re commonly used in griculture to develop orgnic fertiliztion methods (Ayuso et l., 1996; Myhew, 2004). For numer of yers, vrious products contining humic cids hve een commercilized for use on grss (Cooper et l., 1998), horticulturl plnts (Rieiro et l., 2000) or crop production (Lee nd Brtlett, 1976). In spite of positive influences on the plnt growth of sustnces such s leonrdite, (Brownell et l., 1987; Fernndez-Escor et l., 1996),
their use remins controversil ecuse of their heterogeneity (Mlcolm nd McCrthy, 1986). Nowdys, enhncement nd recycling of orgnic wste y composting processes cn e considered s the most efficient wy to produce orgnic soil conditioners. Compost (Lulkis nd Petss, 1995; Rviv, 1998; Senesi, 1989), s well s vermicompost (Atiyeh et l., 2002; Atiyeh et l., 2001), re suitle nd widely used in griculture to enhnce plnt growth. However the composting process tkes long time to generte stle nd mture products. To reduce composting time nd to limit the heterogeneity of humic products, physico-chemicl process hs een developed to enhnce lignocellulosic wste nd to produce liquid orgnic fertilizer. The degrdtion nd oxidtion of wood wste ws mnged through fst, controlled nd reproducile steps. The end product termed humic-like sustnces (HLS) presents similrity in composition, structure nd properties with nturl humic sustnces coming from soil nd compost (Eyherguiel et l., 2002; Richrd, 2002). The ojective of this work ws to determine the physiologicl effects of HLS on mize seed germintion nd on vegettive growth nd the development of mize plnts cultivted under hydroponic conditions. 2. Methods 2.1. Humic-like sustnce extrction Humic-like sustnces were otined from the physicochemicl degrdtion of homogeneous lignocellulosic rw mterils. Poplr swdust ws heted under oxidizing lkline conditions s descried in Morrd et l. (2005). Humic-like sustnces were extrcted from swdust with potssium hydroxide (1N) for the durtion of n hour. After centrifugtion, rown liquid extrct ws collected nd djusted to ph 7 with nitric cid (1N). This process voids the complex mechnisms of nturl humic sustnce genesis nd leds to the production of reproducile nd stle humic products (Tle 1). The chemicl nlysis of humic nd fulvic cid proportion, totl orgnic cron content nd ville nutrients were used to chrcterize the humic extrct (Eyherguiel, 2004). Humic cids Tle 1 Properties of humic like sustnces HLS ph 6.8 Totl orgnic cron (g l 1 ) 9.36 Humic Acids (%) 56.4 Fulvic Acids (%) 43.6 E 465 /E 665 8.2 Minerl content (g l 1 ) Potssium 38.4 Nitrte 40.2 Phosphte 0.4 Sulphte 0.18 Clcium 0.04 Mgnesium 0.005 (HA) were precipitted y the cidifiction of the HLS extrct to ph 1.0 with concentrted HCl. Precipitted HAs were seprted from fulvic cids (FA) y centrifugtion t 4000 rpm for 20 min nd redissolved in sodium hydroxide solution (0.1 M). Fulvic cids were otined from the superntnt solution recovered fter the precipittion of the humic cids. The totl orgnic cron content of HA nd FA solutions ws mesured y the dichromte oxidtion method (Wlkley nd Blck, 1934). Spectrophotometric mesurements were crried out with Perkin Elmer Lmd 20 spectrometer using qurtz cells. The E 4 /E 6 rtios were clculted s the rtio of sornce t 465 nd t 665 nm ccording to Schnitzer nd Khn (1972). 2.2. Germintion test To test the cpcity of HLS to enhnce germintion, mize seeds (20 per ppliction) were germinted on filter pper moistened y 10 ml of humic solution (50 mg of cron per liter (mg C l 1 ) dissolved in nutrient solution; ph 5.0) or clssicl nutrient solution s reference solution. The nutrient solution ws prepred in deionized wter s follows: 4 mm C (NO 3 ) 2 ; 2 mm KH 2 PO 4 ; 3 mm MgSO 4, 11 mm KNO 3 ; 15 ml l 1 FeEDTA; 0.52 ml l 1 H 3 BO 4 ; 0.49 ml l 1 MnCl 2 ; 0.11 ml l 1 ZnCl 2 ; 0.06 ml l 1 CuCl 2 ; 0.01 ml l 1 NMoO 4 (Morrd, 1995). HLS were pplied y the ddition of the initil humic liquid extrct (9.36 g C l 1 ) in nutritive solution to rte of 0 nd 50 mg C l 1. The HLS solution ws formulted ccording to nutrients supplied y undiluted HLS, so tht oth the reference nd HLS solutions presented the sme mcronutrient input. The optimum dose of HLS (50 mg C l 1 ) ws previously determined y screening test using 25, 50, 100, 200, 500 mg C l 1 (Eyherguiel, 2004). The experiment ws crried out in drkness t 25 C in growth chmer for period of two weeks. From the 3rd to the 6th dy of incution, the germintion rte ws clculted s descried in Piccolo et l. (1993). The numer of seeds in ech dish showing rdicle emergence were counted. The dily count ws used to clculte the men germintion rte (MGR) s Ni/Ti where Ni is the numer of germinted seeds on the ith dy nd Ti is the ith counting dy. The root elongtion ws mesured dily for period of 2 weeks. Then plnts were wshed with distilled wter nd hrvested. Roots nd shoots were seprted for totl fresh weight determintion. The dry weight of seedlings ws recorded fter 48 h of drying in n oven t 70 C. 2.3. Growth test In order to ssess the effect of HLS on rooting, plnt growth nd development, hydroponic culture of mize seedling ws crried out. The experiment took plce in greenhouse using mize seeds (Ze mys L.) pre-germinted for 72 h on filter pper moistened with distilled wter. Forty mize seedlings (three dys old) with uniform
size nd shpe nd helthy spect were selected nd trnsferred into 42 L culture tnk contining n erted stndrd solution to cclimtize the seedlings to hydroponic conditions. After 10 dys, 20 mize seedlings of similr weight nd height were trnsplnted, t the 2 3 lef stge, into n opque plstic continer (15 L) contining n erted tretment solution (one plnt per continer sumerged in the nutrient solution). The nutrient solution ws prepred s descried previously for the germintion test. The HLS ws pplied t the rte of 0 nd 50 mg C l 1 y the ddition of n initil humic liquid extrct (9.36 g C l 1 ) in nutritive solution. The solution ws formulted ccording to the nutrients supplied y undiluted HLS to otin reference nd tretment solution with n equl composition. The optimum dose of HLS (50 mg C l 1 ) ws previously determined y screening test (Eyherguiel, 2004). The ph of the HLS solution ws djusted to 6.0 ± 0.5 with smll mount of nitric cid (0.1N) inducing negligile effects on nutrient content. The electricl conductivity ws 2.45 ms/cm. The experiment ws crried out in greenhouse, during two months, for 16-h period of light (25 C) nd n 8-h period of drkness (16 C). Nutrient solutions were continuously erted nd filled weekly to quntity of 15 L with distilled wter in order to record wter consumption nd to monitor ph nd electricl conductivity to monitor culture conditions. After 2 months of ppliction, plnt heights (roots nd stems) were mesured from the 5th node to the plnt tip nd the totl lef numer ws recorded. The hrvest dte ws determined s is usully done in griculturl prctice, t green mturity in the erly stge of co filling. Plnts were hrvested nd seprted into leves, stems nd roots for fresh weight determintion of ech orgn. The smples were dried for 48 h in n oven t 70 C for dry weight determintion. 2.4. Minerl nutrient nlysis To determine if HLS enhnced nutrient uptke, the nutrient depletion from solutions ws mesured t the end of the two-month experimenttion period. Plnt smples were ground in Wiley mill to prticle size of 1 mm nd then nlyzed for their minerl content following dry shing. Mcronutrient (P, K, C, S) content were determined y HPLC (DionexÒDX100) except for nitrogen which ws determined using Leco CHN elementl nlyzer. Microelements were nlyzed y tomic sorption spectrometry (Perkin Elmer). The minerl nlysis results re given in tissue concentrtions (tissue content s percentge of dry weight) nd quntities (the consumption of nutrient elements in mg) of ech element in order to present oth physiologicl nd gronomicl dt. 2.5. Sttisticl nlysis The experimentl designs were rndomized complete lock with 20 repetitions for the germintion test nd 10 repetitions for plnt experiments. All dt ws nlyzed sttisticlly y one-wy ANOVA method using the SigmSttÓ softwre pckge nd considering the tretment s the independent vrile. The men (of ech prmeter mesured) ws evluted sttisticlly y Tuckey s test considering significnce level of P P 0.05 throughout the study. 3. Results 3.1. Humic-like sustnce chrcteriztion The generl properties of humic-like sustnces re shown in Tle 1. The HLS end-product is lck liquid presenting high orgnic cron content (9.36 g C l 1 ). The product is constituted y humic cids (56.4%) nd high level of fulvic cid (43.6%) confirmed y high E 465 /E 665 rtio chrcteristic of low moleculr weight content (Chen et l., 1977) (Tle 1). As demonstrted y Richrd (2002), HLS properties nd ehviour re similr to nturl humic sustnce properties extrcted from soil or compost. Elementl nlysis nd infrred spectroscopy indicte similrities in the composition nd structure of humic molecules. Gel filtrtion dt nd spectrophotometric nlysis confirmed the presence of high nd low moleculr weight prticles (Richrd, 2002). 3.2. Effects of HLS on germintion seeds The effects of HLS on seed germintion nd root elongtion re presented in Fig. 1 nd Tle 2. No increse ws oserved in the numer of germinted seed. The germintion strted 3 dys fter sowing nd the first dily count of germinted seed showed more rdicle emergence for the non-treted seed. However the men germintion rte Lenght (cm) 25 20 15 10 5 0 Control HLS 50 70 90 110 130 150 170 190 210 230 250 Time (h) Fig. 1. Kinetic of roots elongtion. Tle 2 The effect of humic-like sustnces on germintion Tretment Germintion rte (%) MGR 1 3 dys fter sowing 6 dys fter sowing Control 95 5.6 4.51 HLS 90 5.0 4.58 1 MGR: Men germintion rte.
fter 6 dys of incution ws not significntly different from the control plnts nd monitoring y Piccolo et l. (1993), the humic ppliction seemed to slow down the rte of germintion. During the first four dys fter germintion there ws no significnt difference etween root elongtion of treted nd non-treted seeds. The root length of treted seeds incresed progressively nd significntly (+18%) fter 5 dys of germintion (120 h) nd incresed up to 25% more fter 10 dys (240 h) of tretment (Fig. 1). 3.3. Effects of HLS on plnt growth The positive effects of HLS were lso oserved on the whole plnt growth. The iometric fctors of hrvested mize re presented in Tle 3. After two months of experiments, treted plnts exhiited significnt increse in totl iomss, out 66% more fresh weight nd 85% more dry weight. These effects were relted to the increse of the fresh nd dry weight of ech plnt orgn. HLS primrily enhnce the production of shoot, then lef nd root iomss. The most significnt growth ws recorded for shoot dry weight nd corresponded to twofold increse in plnt shoot iomss. The formtion of flowers ws noticed only in treted plnts. Furthermore, the humic tretment presented positive effect on shoot nd root length with significnt increse of 72% nd 25%, respectively. 3.4. Effects of HLS on development stges Tle 3 Effect of humic-like sustnces on iometric fctors Control HLS % of control Fresh weight (g) Roots 94 139.9 48.8 Shoots 297 475 60 Leves 98 154.2 57.3 Flowers 1 0 44.6 Totl 489 813.8 65.8 Humic tretment improved not only growth fctors ut lso my influence the development of mize plnts. Significnt differences in the numer of leves nd flowers occurred t the end of the experiment. HLS incresed the numer of leves up to 12%. The numer of stmintes (mle flowers) of treted plnts ws 25% higher thn those plnts grown in the reference solution. HLS ppliction enhnced flowering during plnt development s well s t hrvest time only treted plnts present cos (Tle 3). Furthermore, plnts cultivted with the HLS solution produced more thn one co per plnt. This enhncement in orgn production underlines the effects of HLS on the precocity of some developmentl processes. Moreover, in the presence of humic frction, the plnt root development ws modified (Fig. 2). Treted plnts exhiited high prolifertion of lterl roots compred to plnts grown in the reference solution which presented less importnt initition of dventive roots. In greement with O Donnell (1972) roots grown in the reference solution were long nd unrnched wheres those grown in the humic solution present profusion of smll lterl roots. Similrly, Cnells et l. (2002) reported tht humic tretment produced hyperinduction of lterl root site emergence on mize plnts. The elongtion nd prolifertion of these secondry roots induce n increse of totl rdiculr length nd root surfce re. 3.5. Effects of HLS on minerl nutrition The nutrient solution consumption of mize plnts treted with HLS ws higher thn tht of plnts grown in the reference solution (Tle 4). The men quntity of wter consumption ws 23.7 L per plnt with the HLS tretment versus 16.2 L for the reference solution. On the other hnd the wter efficiency of these plnts (clculted y dividing Dry weight (g) Roots 15.9 21.6 35.8 Shoots 54.5 109.1 100.2 Leves 25.2 38.6 53.2 Flowers 1 0 6.8 Totl 95.6 176.1 84.2 Length (cm) Roots 63.1 77.6 23 Shoots 102 176 72.5 Numer of leves nd flowers Leves 13.4 15.1 12.7 Cos ($ flower) 0 1.6 Stmintes (# flower) 0.8 1 25 Men in the sme line followed y the sme letter re not significnt (P = 0.05). 1 Represent totl of mle nd femle flower. Fig. 2. Effect of HLS (left) on lterl root emergence in comprison with control (right). Tle 4 Effects of HLS on wter consumption nd wter efficiency Wter consumption (l) Control 16.2 5.9 HLS 23.7 7.4 Gin (% of control) 46.5 25.4 Wter efficiency (g dry weight /l wter)
ph 9 8 7 6 5 4 Ec ns ph Control HLS 0 0 3 5 7 9 weeks Fig. 3. Evolution of ph nd electricl conductivity of nutrients solutions. grms of the finl plnt dry weight per liter of wter uptke during experiments) ws significntly incresed. This indictes tht for the sme wter consumption, treted plnts produced 25% more of iomss thn control plnts (Tle 4). The evolution of the electricl conductivity (EC) is relted to totl ion concentrtion. The EC of solution contining HLS ws reduced compred to the reference solution (Fig. 3). The lower EC of the humic solution indicted tht the ppliction of the humic extrct induced n Tle 5 Depletion of nutrient solutions nd nutrient uptke during mize growth Finl nutrient solution composition (mg l 1 ) ns 3 2 1 Electricl Conductivity Plnt uptke (mg) Control HLS Control HLS Mcroelements K 347.05 225.21 3710 4410 C 140.00 137.00 670 1190 Mg 31.56 27.77 130 120 N 94.48 65.02 1930 4000 S 184.87 153.03 540 570 P 15.19 11.96 970 1080 Microelements Cu 0.034 0.037 0.38 0.62 Mn 0.105 0.088 2.96 4.3 Zn 0.263 0.148 0.86 1.53 Fe 12.56 10.25 23.08 28.51 increse in the nutrient uptke. This result ws confirmed y the determintion of the nutrient element depletion of the reference nd HLS solutions which ws estimted y the mesurement of the finl contents of ech solution (Tle 5). Mcroelements (K, N, P, Mg nd S) nd microelements (Mn, Zn nd Fe) of the humic solution decresed from 15% to 30% ccording to the element. This result cn e relted to the gretest solution consumption of treted plnts. Conversely, plnt smple nlysis indictes the uptke of nutrient elements. Except for mgnesium, the minerl nutrition showed generl increse in the mcro nd microelement sorption tht could e relted to plnt growth stimultion. The ppliction of the humic extrct enhnced the plnt uptke of potssium, clcium, phosphorus nd incresed significntly the plnt uptke of nitrogen, mngnese nd iron. The gretest nutrient concentrtion of treted plnt tissues ws oserved in roots, proly ecuse of their direct contct with the nutrient solution (Tle 6). Significnt increses were oserved in copper, mgnesium nd sulphur content in treted compred to control plnts. 4. Discussion The process developed to trnsform orgnic wste, genertes humic-like sustnces under controlled nd precise conditions (Morrd et l., 2005; Richrd, 2002). Its reproduciility ttests the homogeneity of end products. According to the results reported in reserch literture (Chen nd Avid, 1990; Fgenro nd Agool, 1993; Vughn nd Mlcom, 1985), the positive effects of HLS were first oserved on iometric fctors reflecting plnt growth such s the mesurement of shoot nd root length or fresh nd dry weights for ech mize orgn. However, most of the studies re focused on the growth of young seedlings, nd little informtion is ville on the effect of HS on whole mture plnts (the dvnced development stges, i.e. flowering). Our study focuses on the effects of humic sustnces on whole plnt development from seed to seed. In ddition, few studies mentioned the impct of humic sustnces on Tle 6 Nutrient concentrtion in different plnt orgns Roots Shoots Leves Flowers Totl Control HLS Control HLS Control HLS Control HLS Control HLS Mcroelements (%) K 3.19 2.99 3.34 2.55 3.76 3.17 1.57 3.61 2.75 C 1.68 2.89 0.18 0.32 0.92 0.80 0.18 0.66 0.69 Mg 0.08 0.14 0.07 0.04 0.24 0.14 0.06 0.12 0.08 N 2.35 3.12 1.43 2.27 2.38 3.03 1.82 1.93 2.36 S 0.98 1.51 0.25 0.08 0.74 0.33 0.11 0.53 0.35 P 1.73 1.95 0.66 0.40 0.90 0.75 0.18 0.95 0.68 Microelements (mg l 1 ) Cu 78.7 90.2 19.2 21.3 42.5 43.2 29.3 37 37 Mn 421.7 451.7 60.0 56.7 658.3 511.7 67.5 290 286 Zn 165.0 200.0 63.3 51.7 61.7 115.0 67.5 84 91 Fe 9320 10726 680.0 215.0 870.0 870.0 387.5 2280 1896
wter consumption nd efficiency. HLS ppliction resulted in significntly higher wter consumption, confirming etter glol plnt growth. Moreover, the higher wter efficiency indicted tht the high wter consumption ws ssocited with n improved efficiency of the iomss synthesis. These oservtions suggest tht the plnt hydrous flow is incresed in the presence of the humic extrct. Furthermore, the wter consumption cn e relted to the increse of the nutrient uptke which is known to e involved in plnt growth (Lulkis nd Petss, 1995; Ruthn nd Schnitzer, 1981; Tn nd Nopmornodi, 1979). This hypothesis ws confirmed y significnt increse in nitrogen, mngnese nd iron uptke in treted plnts. According to Pinton et l. (1999) the eneficil effects of humic sustnces on plnt nutrition hs een ttriuted to the promotion of root development. Our results gree with this oservtion, showing higher increse in fresh nd dry weight nd the root elongtion of treted compred to control plnts. Moreover, HLS increse the lterl root emergence nd induce the production of smller ut more rmified secondry roots. Similr results were noticed y other uthors (Cnells et l., 2002; Hrtwigsen nd Evns, 2000). Tken together iometric nd development fctors indicte tht root development induces n increse in totl rdiculr length nd enhnce root surfce resulting in etter minerl nutrition. The modifiction of the root structure underlines the eneficil effects of HLS on severl stges of plnt development. Mny studies del with seed germintion ut few results re ville on the flowering or dvnced vegettive stge. Concerning the effects of HLS on orgn development, our results suggest n ccelertion of the flowering initition. At hrvest time, only treted plnts hve produced mle nd femle inflorescences nd most of these plnts present two cos indicting the flowering precocity. The seed germintion results emphsize lso tht HLS my ply n importnt role in seed germintion nd root elongtion which cn e considered s the erlier stimultion induced y the humic molecules. The difference in growth oserved etween treted nd control plnts might e due to different development speed. HLS seem to ccelerte plnt development. The numer of leves nd the presence of flowers on treted plnts confirm the end of the vegettive stge nd the initition of the reproductive stge. On the contrry, control plnts hve no flowers nd limited numer of leves indicting n erlier development stge. In the sme wy, the nutrient uptke does not reflect the nutrient concentrtion in plnts. The greter nutrient sorption y treted plnts cn e relted to their dvnced development stge ut this uptke does not induce significnt differences in the plnt nutrient concentrtion. Our results suggest tht HLS ct on plnt development y incresing the precocity ut lso on plnt growth y improving iomss synthesis efficiency. The effects on plnt development considertions suggest possile interction (direct or indirect) with plnt growth regultors. To explin these phenomen, humic molecules hve previously een reported for their uxin-like ctivities (Bottomley, 1917; Muscolo et l., 1999; O Donnell, 1972). O Donnell (1972) showed tht different humic extrcts produce similr effects to IAA on root elongtion. The understnding of the interction etween plnt hormones nd humic sustnces my e key to understnding the effects of humic molecules on plnt growth nd development. 5. Conclusion Within the experimentl conditions studied, we show tht HLS, s nturl humic sustnces, demonstrte positive effects on plnt growth. These results suggest tht the use of HLS my generte vrious scientific nd economic dvntges. The production of HLS from the physicochemicl trnsformtion of swdust is n interesting wy of enhncing orgnic wste mterils. 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