Biochar as a Substitute for Vermiculite in Potting Mix for Hybrid Poplar

Transcription

1 Bioenerg. Res. (1) 7:1 131 DOI 1.17/s y Biohr s Sustitute for Vermiulite in Potting Mix for Hyrid Poplr Willim L. Hedlee & Ctherine E. Brewer & Rihrd B. Hll Pulished online: 16 July 13 # Springer Siene+Business Medi New York 13 Astrt The purpose of this study ws to evlute iohr s sustitute for vermiulite in potting mixes for unrooted vegettive uttings of hyrid poplr s represented y the lone NM6 (Populus nigr L. Populus suveolens Fisher susp. mximowizii A. Henry). We ompred three tretments (pet moss (ontrol), pet moss mixed with vermiulite, nd pet moss mixed with iohr) t three times (pre-experiment, pre-fertilizer, nd post-fertilizer). The iohr nd vermiulite mixes hd signifintly higher tion exhnge pity (CEC) nd pre-experiment exhngele K thn the ontrol. Trees grown in the iohr nd vermiulite mixes hd signifintly higher shoot K thn the ontrol t pre-fertilizer nd post-fertilizer nd signifintly higher shoot nd totl iomss t post-fertilizer. The iohr mix ws lso ssoited with lower root iomss nd higher shoot/root iomss rtio thn the vermiulite mix t postfertilizer. Vetor nlysis indited tht ll tretments were defiient in N t pre-fertilizer, nd the ontrol ws lso defiient in K t pre-fertilizer nd post-fertilizer. Liner regression onfirmed tht shoot iomss ws strongly W. L. Hedlee (*) : R. B. Hll Deprtment of Nturl Resoure Eology nd Mngement, Iow Stte University, 339 Siene II, Ames, IA , USA e-mil: whedlee@istte.edu R. B. Hll e-mil: rhll@istte.edu C. E. Brewer Center for Sustinle Environmentl Tehnologies, Iow Stte University, Biorenewles Reserh Lortory, Ames, IA 511, USA Present Address: C. E. Brewer Deprtment of Chemil Engineering, New Mexio Stte University, P.O. Box 31, MSC 385, Ls Crues, NM 8833, USA e-mil: rewer@nmsu.edu orrelted (R =.97) with N nd K uptke (in ddition to initil utting dimeter), lso, root iomss ws strongly orrelted (R =.96) with potting mix CEC (in ddition to shoot iomss). Luxury onsumption of K t pre-fertilizer indites tht the inreses in shoot nd totl iomss oserved with the iohr nd vermiulite tretments rise from this nutrient eing pre-loded in oth mixes. We onlude tht iohr provides enefits equivlent to vermiulite in terms of key nutrient vilility nd totl iomss produtivity. Keywords Biohr. Biomss. Ction exhnge pity. Fertilizer. Populus. Pyrolysis Arevitions CEC Ction exhnge pity ECEC Effetive tion exhnge pity Introdution Biohr is high-ron, porous oprodut of iomss fst pyrolysis for the prodution of renewle io-oil [1, ]. Biohr s porosity results in high surfe res for iohr prtiles, whih n serve numer of funtions suh s dsoring nutrients nd inresing tion exhnge pity (CEC) in soils [3 5]. Other potentil enefits of dding iohr to the soil inlude inresed wter holding pity [6, 7], higher ph [8], inresed levels of ertin plnt nutrients [9, 1], nd redued nitrogen lehing nd/or voltiliztion [11 13]. While muh reserh to dte hs foused on pplying iohr to griulturl soils, iohr s propertieslsomkeit useful for greenhouse pplitions. For exmple, Dumroese et l. [1] found tht pet moss mended with iohr pellets showed improved hydruli wter ondutivity nd wter

2 Bioenerg. Res. (1) 7: vilility, nd Grer et l. [15] found tht potting mix mended with iohr enhned tomto nd pepper plnt growth. Moreover, greenhouse pplitions present importnt dvntges over field pplitions; for instne, voiding the issues of redued heriide effiy tht my our with field pplitions [16 18]. In ddition, dily greenhouse wtering my help to further pitlize on iohr s nutrient dsorption properties, s n environment of lternting sturted nd unsturted onditions hs een shown to enhne the CEC of wood-derived iohrs [19, ]. The purpose of this study ws to evlute iohr s sustitute for vermiulite, nonrenewle resoure used in greenhouses to improve the CEC of potting mixes, for growing hyrid poplr trees. Hyrid poplrs were seleted euse they hve rpid growth under greenhouse onditions, they re redily propgted from vegettive uttings whih redue the inherent vriility of the test plnts, nd they hve demonstrted potentil s short rottion woody rops for ioenergy prodution in the region [1, ]. The lone NM6 is fst-rooting hyrid whih is esy to lonlly propgte [3] nd is expeted to e representtive of hyrid poplrs utilized in the region. While unrooted uttings re typilly used for field plnting, greenhouse prodution of the loned plnts is often used in the initil phse of sling up new seletion for ommeril use; in ddition, poplrs serve s model plnts for woody speies in generl [, 5], mny of whih re rered in the greenhouse efore eing plnted in the field. The hypotheses tested were (1) hyrid poplr uttings grown in potting mix ontining iohr would hve similr produtivity s those grown in potting mix ontining vermiulite, () the uttings grown in these mixes would hve higher produtivity thn those grown in mix without iohr or vermiulite, nd (3) the differenes in produtivity mong the tretments would e explined y the ility of the potting mixes to dsor plnt nutrients from the soil solution (i.e., CEC). To test these hypotheses, three tretments were evluted: pet moss (ontrol), pet moss mixed with vermiulite, nd pet moss mixed with iohr. Chemil properties (ph, CEC, nd ECEC) nd nutrient ontent (totl N nd exhngele K, C, Mg, nd N) of the potting mixes were mesured t three times (pre-experiment, prefertilizer, nd post-fertilizer) to guge their inherent nutrient ontent nd their ility to dsor nutrients. Trees were destrutively smpled t pre-fertilizer nd post-fertilizer to determine the effets of tretment nd time on the mount of shoot (stem+leves), root, utting, nd totl (shoot+ root+utting) iomss produed, s well s shoot/root iomss rtio. In ddition, nutrient (N, K, C, Mg, nd N) onentrtions nd ontents were nlyzed for eh plnt tissue. The potting mix properties nd plnt nutrients responsile for tretment effets on iomss prmeters were identified nd evluted using three-step proess. In the first step, nlysis of vrine (ANOVA) ws used to identify signifint differenes in potting mix properties nd nutrients, the onentrtions nd ontents of nutrients in the plnts, nd iomss prodution. For the seond step, vetor nlysis ws used to identify the nutrients responsile for produing the oserved iomss responses. In vetor nlysis, folir prmeters (i.e., lest squres mens of shoot nutrient onentrtions, shoot nutrient ontents, nd shoot iomss derived from ANOVA) re simultneously grphed for eh tretment reltive to referene ondition (i.e., ontrol), wherey the diretion nd mgnitude of the differenes from the referene ondition indite the nture nd strength of nutrient responses. This method llows for the dignosis of plnt nutrient sttus nd hs een pplied to hyrid poplrs in previous studies [6, 7]. Vetor nlysis is lso ple of deteting the trnsfer of nutrients from the shoots to other tissues; in suh ses, possile nutrient trnsfer ws further investigted using ANOVA for root nd utting nutrients. In the third nd finl step, liner regression ws used to evlute the preditive power of the vriles identified y ANOVA nd/or vetor nlysis s hving signifint effets on iomss prodution. Mterils nd Methods Biohr Mteril The iohr ws produed t the Iow Stte University BioCentury Reserh Frm (Boone, IA) on pilot sle (8 kg hr 1 ) uling fluidized ed fst pyrolysis. The red ok feedstok ws ground to prtile size of <6 μm prior to fst pyrolysis t 5 C. The snd ed ws fluidized with N. Biohr ws olleted y ylone from the produt strem with n pproximte yield of 1 15 %. Greenhouse Experiment The experiment ws onduted t the Iow Stte University Forestry Greenhouse (Ames, IA) during the spring of 1. Three potting medi tretments were evluted s follows: pet (1 % pet moss; ontrol), vermiulite mix (75 % pet moss nd 5 % vermiulite y volume), nd iohr mix (75 % pet moss nd 5 % iohr y volume). A rndomized omplete lok design ws used. Tretments were rndomly ssigned to 36 m 3 Aelertor ontiners (Nursery Supplies In., Chmersurg, PA) in eh of three trys (loks). Eh try held 3 ontiners: 1 pet, 1 vermiulite mix, nd 1 iohr mix, for totl of 96 ontiners (eh of whih ws filled with 5 m 3 of the ssigned mix). Unrooted vegettive uttings (1 m long) of the hyrid poplr NM6 (Populus nigr L. Populus suveolens

3 1 Bioenerg. Res. (1) 7:1 131 Fisher susp. mximowizii A. Henry) were soked in wter for h, plnted in the ontiners (one tree per ontiner), nd initil utting dimeters were reorded. The trys were pled in enh-sle humidity tent (onsisting of opque plsti sheeting supported y PVC pipe) for the first 3 weeks nd then on open enhes for the reminder of the experiment. They were suirrigted ontinuously over the first weeks nd twie dily for 3 min t time over the reminder of the experiment. Hlf of the trees per tretment were destrutively smpled fter 6 weeks of growth (prior to fertiliztion; men height=7. m), nd the other hlf were destrutively smpled fter 8 weeks (following fertiliztion; men height= 38.1 m). Fertilizer solution ws prepred y dissolving dry fertilizer in wter (3.6 g L 1 ); the solution ws pplied t rte of 35 ml per tree t the strt of the seventh week nd 7 ml per tree t the strt of the eighth week. Destrutive smpling onsisted of seprting the tree tissues (shoots (stems+leves), roots, nd uttings) nd oven-drying the tissues t 5 C to otin the dry weights prior to tissue nutrient nlysis. Due to the smll mount of root mteril ville for most trees in the pre-fertilizer hrvest, root smples from up to five trees were ulked y tretment, resulting in totl of 18 root smples (rther thn 8) for the pre-fertilizer hrvest. For the potting medi, smples of the unused mixes were olleted to determine their pre-experiment hemil properties nd nutrient ontents. To determine the pre-fertilizer nd post-fertilizer effets, the medium from eh ontiner ws olleted during destrutive smpling of the trees nd ulked y try for eh tretment. The medi ws then ovendried t 5 C prior to nlysis of hemil properties nd nutrient ontents. Beuse the potting mixes were ulked y try, the dt were evluted s ompletely rndomized design, with the three trys serving s replites (3 tretments 3 smple times 3 replites=7 totl smples). Lortory Anlyses Plnt tissues nd potting mixes were sent to the US Forest Servie Institute for Applied Eosystem Studies in Rhinelnder, WI, where they were ground through.5 mm sreen prior to nlysis. For oth the plnt tissues nd the potting mixes, totl N ontent ws determined with Flsh EA111 N-C nlyzer with model MAS utosmpler (Thermo Eletron, vi CE Elnteh, In., Lkewood, NJ). For the remining plnt tissue nutrients, tomi emission spetrosopy (AES) ws onduted using Vrin Agilent model FS tomi sorption spetrophotometer (Agilent Tehnologies, Englewood, CO) following nitri id digestion. For the potting mixes, exhngele se tions (K, C, Mg, nd N) were extrted with hexmmine olt (Co) hloride nd nlyzed vi AES. The se tions were summed to determine CEC (dsorption of se tions), nd ECEC (dsorption of ll tions) ws determined from the differene of the Co level mesured ompred to the initil Co level, s desried y Ciesielski nd Sterkemn [8]. Potting mix ph ws mesured y dding potting mix (1 g) to 5 ml of dilute CCl solution (.1 mol L 1 ), shking for 1 h, then mesuring with n AuCp omintion ph eletrode nd Aumet model no. XL5 ph meter (Fisher Sientifi, Wlthm, MA, USA). Anlysis of Vrine All dt were evluted s two-wy ftoril (tretment time) with ANOVA using PROC GLM in SAS (SAS Institute In., Cry, NC). Whenever tretment, time, or tretment time intertions were found to e signifint (P<.5), multiple omprisons nlyses (with Tukey s djustment) were onduted to identify sttistilly signifint differenes etween the djusted lest squres mens. Eh tree tissue ws evluted for differenes in iomss (i.e., dry weight) nd nutrient onentrtions, with initil utting dimeter s ovrite sed on previous reserh showing the influene of utting size on erly growth nd survivl of poplr lones [9]. In ddition, the nutrient ontent of eh tissue (determined y multiplying the mesured nutrient onentrtion y the dry weight of the tissue) nd totl iomss (determined y summing the dry weights of the tissues) were similrly evluted, gin with initil utting dimeter s ovrite. For shoot/root iomss rtio, shoot iomss ws used s the ovrite sed on previous reserh showing the influene of tree development on iomss llotion [3]. The potting mixes were tested for differenes in ph, CEC, ECEC, nd nutrient onentrtions nd ontents. Nutrient ontents (in milligrms per ontiner) were lulted y multiplying the mesured nutrient onentrtions (in milligrm per kilogrm) y the ulk density (in kilogrms per ontiner) of the mix; CEC nd ECEC (in milliequivlent per ontiner) were similrly lulted y multiplying the mesured vlue (in milliequivlent per kilogrms) y the potting medi ulk density (in kilogrms per ontiner). Vetor Anlysis Vetor nlysis ws onduted using the djusted lest squres mens of the shoot prmeters (speifilly shoot iomss, nutrient onentrtions, nd nutrient ontents). The pre-fertilizer pet tretment ws used s the referene ondition (reltive vlue=1 for ll shoot prmeters), nd the reltive vlues for ll other tretment time omintions were lulted y dividing the mesured vlue y tht of the referene ondition nd multiplying y 1. These reltive vlues were grphed for eh nutrient to ompre tretment effets on nutrient sttus sed on the typil interprettions of

4 Bioenerg. Res. (1) 7: vetor nlysis digrms (Fig. 1, dpted from Lteif et l. [7]). The interprettions reflet the nutrient sttus of the tretment plnts nd n e summrized s follows: (A) inresed iomss with inresed nutrient ontent nd deresed nutrient onentrtion (growth dilution), (B) inresed iomss with inresed nutrient ontent nd no hnge in nutrient onentrtion (suffiieny), (C) inresed iomss with inresed nutrient ontent nd onentrtion (defiieny), (D) no hnge in iomss with inresed nutrient ontent nd onentrtion (luxury onsumption), (E) deresed iomss with inresed nutrient onentrtion nd inresed or deresed nutrient ontent (toxiity), (F) deresed iomss with deresed nutrient onentrtion nd ontent (ntgonism), nd (G) little or no inrese in iomss with deresed nutrient onentrtion nd ontent (retrnslotion). For more thorough desription of vetor nlysis nd its potentil pplitions, see Hse nd Rose [31] nd Imo nd Timmer [3]. Liner Regression To evlute the preditive power of vriles identified y ANOVA nd/or vetor nlysis s hving signifint effets on iomss prmeters, liner regression ws onduted using PROC GLM in SAS. Speifilly, oeffiients of determintion (R ) vlues were determined for iomss prmeter Reltive Nutrient Conentrtion () F R Reltive Shoot Mss (m) G E D Reltive Nutrient Amount () A B C models whih used the identified vriles, nd the sttistil signifine of eh vrile within the model ws lso determined using Type III sums of squres. As previously noted, potting mixes were ulked y try; thus, when potting mix vriles were used in liner regression, the iomss prmeters were verged y try to mintin onsisteny with the potting mix dt. Results Potting Mix Properties nd Nutrients Anlyses of the potting mixes hemil properties nd nutrient ontents indited signifint tretment nd time effets for severl of the prmeters, with signifint intertions for ph s well s exhngele K nd N (Tle 1). Regrding tretment effets, the iohr nd vermiulite mixes hd signifintly higher CEC nd exhngele Mg thn the pet (Tle ). Also, the iohr mix hd signifintly higher ECEC nd exhngele C thn oth the pet nd the vermiulite. The vermiulite mix hd signifintly lower totl N thn oth the iohr mix nd the pet. For the time effets, CEC inresed signifintly from pre-experiment to pre-fertilizer, long with exhngele C (whih ws likely introdued vi the tp wter used for irrigtion). ECEC showed similr trend s CEC, ut the differenes were not sttistilly signifint; similrly, time effets were not signifint for totl N or exhngele Mg. As noted ove, signifint tretment time intertions were found for ph nd exhngele K nd N. The pet showed no signifint hnge in ph over time, wheres the other two tretments oth showed signifint inreses from pre-experiment to pre-fertilizer nd signifint dereses from pre-fertilizer to post-fertilizer (Fig. ). The pet ws signifintly lower in K thn the other two tretments t preexperiment nd did not hnge signifintly t pre-fertilizer, ut inresed signifintly t post-fertilizer; onversely, K deresed signifintly for the other two tretments from preexperiment to pre-fertilizer nd did not hnge signifintly from pre-fertilizer to post-fertilizer (Fig. ). All tretments inresed signifintly in N from pre-experiment to prefertilizer, with the pet eing signifintly lower thn the other two tretments t pre-fertilizer; in ddition, the iohr mix inresed signifintly from pre-fertilizer to postfertilizer, wheres the other two tretments did not hnge signifintly (Fig. ). Shoot Nutrient Conentrtions nd Contents Fig. 1 Exmple of vetor nlysis digrm nd the interprettions ssoited with shifts in shoot iomss (m), shoot nutrient onentrtion (), nd shoot nutrient mount (), for eh vetor (A G) reltive to the referene ondition (R); dpted from Lteif et l. [7] Shoot nutrient onentrtions showed minly tretment nd/or time effets, with only shoot K onentrtion showing signifint tretment time intertion (Tle 3). Conversely,

5 1 Bioenerg. Res. (1) 7:1 131 Tle 1 P vlues from ANOVA of potting mix hemil properties (ph, CEC, ECEC) nd nutrient ontent (totl N nd exhngele K, C, Mg, N). Sttistilly signifint effets (P<.5) re itliized Effet ph CEC ECEC N K C Mg N Tretment <.1 <.1 <.1.8 <.1 <.1 <.1 <.1 Time <.1 < <.1 Trt Time <.1 shoot nutrient ontents showed signifint tretment time intertions for ll nutrients evluted. Shoot N onentrtion ws signifintly higher with the pet thn with the other two tretments (Tle ). Shoot C onentrtion ws signifintly lower with the vermiulite tretment thn with the others. Shoot Mg onentrtion for the pet ws signifintly lower thn the vermiulite ut signifintly higher thn the iohr. No signifint tretment differenes were oserved for shoot N onentrtion. The tretment time intertion for shoot K onentrtion (Fig. 3) shows tht the iohr nd vermiulite tretments were signifintly higher thn the pet oth pre-fertilizer nd post-fertilizer; lso, the pet tretment showed signifint inrese from pre-fertilizer to post-fertilizer, wheres the other two tretments did not hnge signifintly. Tretment time intertions for shoot nutrient ontents re illustrted in Fig.. For shoot N, Mg, nd N ontent, no signifint differenes etween tretments were oserved t pre-fertilizer, nd ll tretments inresed from pre-fertilizer to post-fertilizer, ut t post-fertilizer, the iohr nd vermiulite were signifintly higher thn pet. For shoot C ontent, no signifint differenes etween tretments were oserved t pre-fertilizer, nd ll tretments inresed from pre-fertilizer to post-fertilizer, ut t post-fertilizer, the iohr ws signifintly higher thn the other two tretments. For Tle Adjusted lest squres mens for potting mix hemil properties nd nutrients y tretment nd time. Signifint differenes etween mens (P<.5) re indited with different letters within the olumn. Units of mesure for the prmeters re: CEC nd ECEC (meq ontiner 1 ); totl N nd exhngele C nd Mg (mg ontiner 1 ). Results for ph nd exhngele K nd N re not shown here due to signifint tretment time intertions Effet CEC ECEC N C Mg Tretment Vermiulite Biohr Time Pre-experiment Pre-fertilizer Post-fertilizer shoot K ontent, the iohr nd vermiulite tretments were signifintly higher thn pet oth pre-fertilizer nd post-fertilizer, with the solute differene eing lrger t post-fertilizer. Tree Biomss Produtivity The iomss produtivity dt showed signifint tretment effets for shoot/root iomss rtio nd signifint time effets for utting iomss nd shoot/root iomss rtio (Tle 5). Signifint tretment time intertions were oserved for shoot, root, nd totl iomss. Regrding tretment effets, the iohr tretment produed signifintly higher shoot/root iomss rtio thn the vermiulite nd pet tretments, with vermiulite lso eing signifintly higher thn pet (Tle 6). For time effets, the shoot/root iomss rtio deresed from pre-fertilizer to post-fertilizer, wheres utting iomss inresed from pre-fertilizer to post-fertilizer. Tretment time intertions for shoot, root, nd totl iomss re illustrted in Fig. 5. While the tretments did not differ signifintly in shoot or totl iomss pre-fertilizer, nd ll tretments inresed signifintly from pre-fertilizer to post-fertilizer, the iohr nd vermiulite tretments hd signifintly higher shoot nd totl iomss post-fertilizer thn the pet (Fig. 5, d). Root iomss lso did not differ signifintly etween tretments pre-fertilizer, nd inresed for ll tretments from pre-fertilizer to post-fertilizer, ut t post-fertilizer, the vermiulite tretment hd signifintly higher root iomss thn iohr, while pet ws intermedite (Fig. 5). No signifint intertions were deteted for utting iomss (Fig. 5); the dt re inluded here to illustrte the ontriution of uttings to totl iomss. Also, the ovrite of initil utting dimeter hd signifint influene (P<.1) on the iomss of ll tissues, nd the ovrite of shoot iomss hd signifint influene (P=.) on shoot/root iomss rtio (not shown). Vetor Anlysis The vetor nlysis digrms (Fig. 6) illustrte the reltive shoot nutrient onentrtions, shoot nutrient ontents, nd shoot iomss for eh tretment pre-fertilizer (smll symols) nd post-fertilizer (lrge symols), reltive to the prefertilizer ontrol (pet). Vetors show the differenes etween

6 Bioenerg. Res. (1) 7: () ph () Exhngele K (mg ontiner -1 ) () Exhngele N (mg ontiner -1 ) Vermiulite Biohr e de de de Pre-Experiment e e de d d Vermiulite Biohr Pre-Experiment Vermiulite Biohr e e e d Pre-Experiment Fig. Adjusted lest squres mens (±1 stndrd error) from tretment time intertions for potting mix ph, exhngele K, nd exhngele N. Sttistilly signifint differenes (P<.5) re indited with different letters ove the rs d d tretments pre-fertilizer (dotted lines) nd the hnges for eh tretment from pre-fertilizer to post-fertilizer (dshed lines). For N (Fig. 6), the pre-fertilizer iohr nd vermiulite vetors showed shift towrds lower N onentrtion nd slightly lower N ontent long with slightly higher mss, whih is inditive of possile trnsfer (e.g., retrnslotion) from the shoots to other tissues. However, sttistil nlyses of uttings nd roots did not reflet nutrient trnsfer within the plnt, in tht N levels were lso lower in the uttings nd roots for these tretments, reltive to pet (not shown). At post-fertilizer, ll tretments shifted towrds higher N onentrtion, N ontent, nd shoot mss; this indites tht ll tretments were defiient in N prior to fertiliztion. Beuse the iohr nd vermiulite were ssoited with higher mss ut similr N onentrtions s pet t post-fertilizer, it n lso e onluded tht pet ws suffiient in N reltive to the other two tretments. Thus, the higher shoot produtivity for iohr nd vermiulite likely is not ttriutle to differene in N vilility. The pre-fertilizer iohr nd vermiulite vetors showed shift towrds higher K onentrtion nd higher K ontent long with only slightly higher shoot mss, whih is inditive of luxury onsumption (Fig. 6). At post-fertilizer, the iohr nd vermiulite tretments shifted towrds higher totl K ontent nd shoot mss with little hnge in K onentrtion, while with pet, ll three of these inresed; this indites tht the iohr nd vermiulite were suffiient in K prior to fertiliztion, wheres the pet ws defiient. In ddition, the lower K onentrtion, K ontent, nd shoot mss for pet t post-fertilizer (reltive to the other two tretments) suggests tht the trees growing in pet were lso K-limited t post-fertilizer. Thus, the higher shoot produtivity for iohr nd vermiulite is likely relted to superior vilility of K. With C (Fig. 6), the pre-fertilizer vermiulite vetor showed shift towrds lower C onentrtion nd slightly lower C ontent long with slightly higher mss; this indites possile trnsfer (e.g., retrnslotion) of C from the shoots to other tissues. However, sttistil nlyses of uttings nd roots did not reflet nutrient trnsfer within the plnt, in tht C levels were lso lower in the uttings nd Tle 3 P vlues from ANOVA of shoot nutrient (N, K, C, Mg, nd N) onentrtions nd ontent. Sttistilly signifint effets (P<.5) re itliized Shoot onentrtion Shoot ontent Effet N K C Mg N N K C Mg N Tretment.11 <.1 <.1 < <.1 <.1 <.1 <.1 <.1 Time <.1.19 <.1.79 <.1 <.1 <.1 <.1 <.1 <.1 Trt Time.551 < <.1 <.1. <.1.1

7 16 Bioenerg. Res. (1) 7:1 131 Tle Adjusted lest squres mens for shoot nutrient onentrtions (N, C, Mg, nd N; %), y tretment nd time. Signifint differenes etween mens (P<.5) re indited with different letters within the olumn for given effet. Results for shoot K onentrtion nd shoot nutrient ontents (N, K, C, Mg, nd N) re not shown here due to signifint tretment time intertions Effet N C Mg N Tretment Vermiulite Biohr Time Pre-fertilizer Post-fertilizer roots for the vermiulite tretment, reltive to iohr nd pet (not shown). At post-fertilizer, ll three tretments inresed slightly in C onentrtion, with reltively lrger inreses in C ontent nd shoot mss; this is inditive of slight defiieny for ll tretments. As shown in Fig. 6d, the pre-fertilizer iohr vetor showed shift towrds lower Mg onentrtion ut slightly higher Mg ontent nd shoot mss, wheres the vermiulite vetor showed shift towrds higher Mg onentrtion long with slightly higher Mg ontent nd shoot mss; this is inditive of growth dilution for iohr nd luxury onsumption for vermiulite. At post-fertilizer, ll three tretments shifted towrds higher Mg ontent nd shoot mss with little hnge in Mg onentrtion; this indites the tretments were suffiient in Mg. The pre-fertilizer iohr nd vermiulite vetors showed shift towrd slightly lower N onentrtion long with slightly higher N ontent nd shoot mss, whih indites slight growth dilution for iohr nd vermiulite (Fig. 6e). At postfertilizer, ll three tretments inresed slightly in N onentrtion, with reltively lrger inreses in totl N nd shoot mss; this is inditive of slight defiieny for ll tretments. Shoot K (% plnt -1 ) 3 1 Vermiulite Biohr Fig. 3 Adjusted lest squres mens (±1 stndrd error) from tretment time intertion for shoot K onentrtion. Sttistilly signifint differenes (P<.5) re indited with different letters ove the rs Liner Regression The ANOVA nd vetor nlysis results suggest tht shoot iomss produtivity ws influened y N nd K uptke, nd tht initil utting dimeter lso hd signifint effet. Thus, shoot iomss ws modeled with the vriles of shoot N ontent, shoot K ontent, nd initil utting dimeter. The overll model fit ws strong (R =.97; Fig. 7), with eh of the three vriles eing sttistilly signifint (P<.1) preditors of shoot iomss. The resulting eqution is: B S ¼ :863D i þ :9N S þ :11K S :315 ð1þ Where B S is the shoot iomss (in grms per tree), D i is the initil dimeter of the utting (in millimeters), N S is the shoot nitrogen ontent (in milligrms per tree), nd K S is the shoot potssium ontent (in milligrms per tree). The signifine of shoot iomss s ovrite in the ANOVA for shoot/root iomss rtio indites tht iomss llotion to the roots ws influened y shoot size. In ddition, previous reserh suggests tht inresed nutrient vilility dereses root iomss llotion (therey inresing shoot/root rtio) in poplrs [33], whih in this study is supported y the oserved inreses in shoot/root rtio for the tretments hving higher CEC (i.e., iohr nd vermiulite) reltive to the ontrol. Bsed on these oservtions, root iomss ws modeled with the vriles of shoot iomss nd potting mix CEC. The overll model fit ws strong (R =.96; Fig. 7), with oth vriles eing sttistilly signifint (P.) preditors of root iomss. The resulting eqution is: B R ¼ :665B S :85M CEC þ :1561 ðþ Where B R is the root iomss (in grms per tree), B S is the shoot iomss (in grms per tree), nd M CEC is the CEC (in milliequivlents per ontiner) of the medi. Preditly, the ANOVA results indite tht initil utting dimeter hd signifint effet on utting iomss. Also, the signifint inrese in utting iomss over time demonstrtes tht portion of the photosynthte produed y the shoot ws lloted to utting growth. Thus, utting iomss ws modeled with the vriles of initil utting dimeter nd shoot iomss. The overll model fit ws strong (R =.9; Fig. 7), with oth vriles eing sttistilly signifint (P<.1) preditors of utting iomss. The resulting eqution is: B C ¼ :585D i þ :1397B S 3:7 ð3þ Where B C is utting iomss, D i is the initil dimeter of the utting (in millimeters), nd B S is shoot iomss (in grms per tree). Liner regression ws not onduted for the remining iomss prmeters, s they n e determined

8 Bioenerg. Res. (1) 7: () Shoot N (mg plnt -1 ) Vermiulite Biohr (d) Shoot Mg (mg plnt -1 ) Vermiulite Biohr d d d () Shoot K (mg plnt -1 ) Vermiulite Biohr d (e) Shoot N (mg plnt -1 ) Vermiulite Biohr () Shoot C (mg plnt -1 ) 3 1 Vermiulite Biohr Fig. Adjusted lest squres mens (±1 stndrd error) from tretment time intertions for totl shoot ontent of N, K, C, d Mg, nd e N. Sttistilly signifint differenes (P<.5) re indited with different letters ove the rs y summing equtions 1 3 (totl iomss) or dividing eqution 1 y eqution (shoot/root iomss rtio). Disussion The results of this study demonstrte tht iohr is suitle replement for vermiulite in potting mix in terms of key nutrient vilility nd totl iomss prodution. The iohr nd vermiulite mixes hd signifintly higher tion exhnge pity (CEC) nd pre-experiment exhngele K thn the pet ontrol (see Tle nd Fig. ) nd were similr to one nother in shoot N nd K onentrtion nd ontent (see Figs. 3 nd, nd Tle ), whih resulted in signifintly higher shoot nd totl iomss produtivity thn the ontrol (see Fig. 5). Vetor nlysis suggests tht the trees growing in the iohr nd vermiulite mixes were limited primrily y N, wheres the trees growing in pet were limited y oth N nd K (see Fig. 6, ); thus, the improved iomss produtivity of the trees grown with iohr nd vermiulite ppers to e ttriutle to higher K vilility. The elevted levels of exhngele K for the iohr nd vermiulite tretments reltive to pet t pre-experiment nd pre-fertilizer (see Fig. ), long with the luxury onsumption of K ssoited with these tretments t pre-fertilizer (see Fig. 6), indite tht the inresed vilility of K ws due Tle 5 P vlues from ANOVA of tree iomss (shoot, B S ; root, B R ; utting, B C ; nd totl, B T ) nd shoot/root rtio (B S /B R ). Sttistilly signifint effets (P<.5) re itliized Effet B S B R B C B T B S :B R Tretment < <.1 <.1 Time <.1 <.1.5 <.1 <.1 Trt time <

9 18 Bioenerg. Res. (1) 7:1 131 Tle 6 Adjusted lest squres mens for utting iomss (B C ) nd shoot/root iomss rtio (B S /B R ) y tretment nd time. Signifint differenes etween mens (P<.5) re indited with different letters within the olumn for given effet. Results for shoot, root, nd totl iomss re not shown here due to signifint tretment time intertions Effet B C B S :B R Tretment Vermiulite Biohr.87.9 Time Pre-fertilizer Post-fertilizer t lest in prt to the nutrient eing preloded in the mixes rther thn simply their ility to dsor K from the soil solution. However, the higher CEC vlues for oth tretments reltive to pet (s well s higher ECEC for iohr) suggest tht superior vilility of K nd/or other tions my e sustined over longer periods. Additionl reserh to test this hypothesis is therefore reommended. Differenes etween the iohr nd vermiulite mixes were lso oserved, ut did not pper to e signifint ftors in shoot or totl iomss produtivity. For exmple, totl N ws higher in the iohr mix thn the vermiulite mix (see Tle ), nd exhngele K ws higher in the vermiulite mix thn the iohr mix (see Fig. ); however, these differenes did not trnslte to differenes in shoot or totl produtivity or even to differenes in onentrtions or ontents of the nutrients within the plnts. In the se of N, the higher levels for iohr my represent differene in fixed N rther thn ville N. Regrding K, it ppers tht the higher exhngele K for vermiulite represents surplus supply. In ddition, the iohr mix hd signifintly higher exhngele C nd post-fertilizer N thn the vermiulite mix (see Tle nd Fig. ). This orresponded with higher shoot nutrient onentrtion nd ontent of C for the iohr tretment ompred to vermiulite, ut no signifint differenes etween the two with regrd to N (see Tle nd Fig. ). Although these differenes did not pper to signifintly impt hyrid poplr growth in this study (see Fig. 5), they my e importnt for other speies whih re prone to speifi nutrient defiienies (e.g., C in tomtoes) or sensitivities (e.g., N in ens), nd therefore dditionl reserh with wider vriety of poplr lones nd other rops is reommended. Suh studies should ount for the initil utting dimeter nd hnges in iomss llotion ssoited with plnt development, whih were found to hve signifint influenes on tree growth in this study nd re onsistent with previous reserh [9, 3]. () Shoot Biomss (g plnt -1 ) () Root Biomss (g plnt -1 ) () Cutting Biomss (g plnt -1 ) (d) Totl Biomss (g plnt -1 ) Vermiulite Biohr Vermiulite Biohr Vermiulite Biohr Vermiulite Biohr Fig. 5 Adjusted lest squres mens (±1 stndrd error) from tretment time intertions for shoot, root, utting, nd d totl (shoot+root+utting) iomss. Sttistilly signifint differenes (P<.5) re indited with different letters ove the rs. Though nonsignifint, the intertion for uttings is shown here to demonstrte the ontriution to totl iomss

10 Bioenerg. Res. (1) 7: () Reltive N Conentrtion 15 1 Reltive Shoot Mss Vermiulite Vermiulite Biohr Biohr Reltive N Content (d) Reltive Mg Conentrtion 15 1 Reltive Shoot Mss Reltive Mg Content () Reltive K Conentrtion 15 1 Reltive Shoot Mss Vermiulite Biohr (e) Reltive N Conentrtion 15 1 Reltive Shoot Mss Vermiulite Biohr Reltive K Content Reltive N Content () Reltive C Conentrtion 15 1 Reltive Shoot Mss Vermiulite Biohr Reltive C Content Fig. 6 Vetor digrms showing reltive shifts ssoited with iohr (dimond), vermiulite (tringle), nd pet (white squre) tretments pre-fertilizer (smll symols) nd post-fertilizer (lrge symols) for N, K, C, d Mg, nd e N. In ll ses the initil referene ondition (shoot mss, nutrient onentrtion, nd nutrient ontent=1) is the pet tretment t pre-fertilizer While vetor nlysis suggested possile pre-fertilizer trnsfer of N (iohr nd vermiulite tretments) nd C (vermiulite tretment) from the shoots to other tissues (see Fig. 6, ), sttistil nlyses indited tht the levels of these nutrients were similrly lower in the uttings nd roots (not shown), nd thus reflet lower levels of these nutrients for the entire plnt. Suh inreses in the rtio of iomss produed per unit of nutrient in the plnt re often interpreted s n inrese in nutrient use effiieny [3]. As previous desriptions of vetor nlysis [6, 7, 31, 3] do not pper to ddress this potentil outome, we reommend the inlusion of inresed nutrient use effiieny s possile dignosis for the nutritionl effet of depletion desried in Fig. 1. Liner regression supported the results of the vetor nlysis, speifilly, tht shoot iomss produtivity ws lrgely funtion of N nd K uptke (in ddition to initil utting dimeter, s indited y ANOVA). This demonstrtes the utility of vetor nlysis (in onjuntion with ANOVA) for identifying the speifi vrile(s) responsile for tretmentrelted plnt growth responses, whih, onsidering the numer of vriles t ply (e.g., onentrtion nd ontent of eh nutrient s well s possile intertions etween them), might otherwise only e omplished with inresingly omplex sttistil models. Liner regression lso showed tht root iomss ws lrgely funtion of shoot iomss produtivity nd potting mix CEC, nd tht utting iomss ws lrgely funtion of shoot iomss produtivity nd initil utting

11 13 Bioenerg. Res. (1) 7:1 131 () Oserved B C (g plnt -1 ) Oserved B R (g plnt -1 ) Oserved B S (g plnt -1 ) () () Vermiulite Biohr R² = Vermiulite Biohr R² =.96 Vermiulite Biohr R² =.9 Predited B S (g plnt -1 ).1..3 Predited B R (g plnt -1 ) 6 Predited B C (g plnt -1 ) Fig. 7 Oserved versus predited vlues for shoot iomss, B S, root iomss, B R, nd utting iomss, B C. Individul plnts were used for shoots nd uttings (n=96); for roots, plnts were verged y tretments within trys t eh time (pre-fertilizer nd post-fertilizer) to mintin onsisteny with potting mix dt (n=18; see text). Dshed lines represent perfet 1:1 reltionships dimeter. Thus, the iomss produtivity of eh tissue ws influened y the potting mix, whether diretly vi K vilility (shoots) nd CEC (roots) or indiretly vi the influene of the potting mix on shoot iomss (roots nd uttings). Previous reserh y Grer et l. [15] showed tht pepper nd tomto plnt growth were signifintly enhned y the ddition of iohr to their potting mix. They onluded tht this ws not due to improved nutrient vilility (sed on lk of signifint differenes in lef nutrient onentrtions), nd hypothesized insted tht the iohr my hve stimulted enefiil soil miroes nd/or ontined nonnutrient hemils tht diretly stimulted plnt growth. However, their fertilizer regime (fertigtion pplied 3 times dily throughout the experiment) my hve supplied suffiient nutrients to the plnts diretly, negting ny differenes in the ility of the growing medi to supply nutrients. Our study, on the other hnd, purposefully indued suoptiml nutrient onditions to test for differenes in nutrient vilility nd uptke y the plnts. As suh, our study demonstrtes tht iohr my enhne plnt growth vi improved nutrient vilility under suoptiml nutrient onditions. Oxygen vilility is lso n importnt onsidertion in potting mixes, s limited oxygen hs een shown to derese shoot nd root growth in poplrs [35]. Though we did not evlute oxygen vilility in this study, we did oserve tht the ulk density of the iohr mix ws pproximtely 5 % greter thn tht of the other mixes, whih we expet would derese oxygen vilility. Indeed, previous reserh hs shown tht pelleted iohr mixed with pet t the sme rtio used in our study (5 % iohr nd 75 % pet y volume) redued ir-filled porosity from 7 to 38 % nd lowered reltive oxygen diffusivity y pproximtely hlf ompred to pet lone [1]. Thus, dditionl reserh on the effets of iohr on oxygen vilility (prtiulrly over longer time periods) is reommended. Finlly, it hs een estlished tht iohrs derived from different feedstoks nd under different pyrolysis onditions hve unique physil nd hemil properties [36, 37]. As suh, dditionl testing with vriety of iohrs is needed to ompre how the seletion of feedstoks nd proesses ffet the ility of different iohrs to serve s renewle sustitute for vermiulite. The osts ssoited with different feedstoks nd proesses will lso e importnt in determining the most eonomil sustitute for vermiulite, whih in the greenhouse industry ommnds prie of US$135 to 155 m 3 (pproximtely US$1,5 Mg 1 ) sed on supplier tlog priing (BFG Supply Co., Burton, OH). Aknowledgments The uthors would like to thnk the US Forest Servie Northern Reserh Sttion Institute for Applied Eosystem Studies (IAES) for supporting this projet. They would lso like to thnk Ronld Zlesny, Jr., Adm Wiese, Ed Buer, nd Brue Birr from IAES for produing the mini-uttings nd onduting the nutrient nlyses nd the Iow Stte University Center for Sustinle Environmentl Tehnologies for providing the iohr. One of the uthors (CB) would like to knowledge support from Ntionl Siene Foundtion Grdute Reserh Fellowship.

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