A slow release nitrogen fertiliser produced by simultaneous granulation and superheated steam drying of urea with brown coal

Transcription

1 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 DOI /s RESEARCH Open Access A slow relese nitrogen fertiliser produced y simultneous grnultion nd superheted stem drying of ure with rown col Michel T. Rose 1,4, Emily L. Perkins 1,2, Biplo K. Sh 1, Evone C. W. Tng 2, Timothy R. Cvgnro 3, W. Roy Jckson 1, Kren P. Hpgood 2, Andrew F. A. Hodley 2 nd Antonio F. Ptti 1* Astrct Bckground: The inefficient use of nitrogen (N) fertiliser s consequence of N losses from soil is pressing issue in rod-cre griculturl systems. The reserch reported here tested the hypothesis tht grnultion of synthetic N fertiliser (ure) with nturl orgnic C resource (rown col) would reduce fertiliser N loss from the soil system. Results: Ure-enriched rown col grnules were simultneously formed nd dried within pilot-scle superheted stem dryer. After ppliction to unplnted soil columns, the ure-rown col grnules reduced nitrous oxide emission y up to 40 %, reduced minerl nitrogen leching nd mintined higher levels of N in topsoil when compred to conventionl ure lone. Reduced gseous N losses without reduction in plnt N uptke were lso oserved in plnted soil columns treted with ure-rown col grnules. Conclusions: Brown col-ure lended fertiliser showed potentil for more efficient use of N in the long term nd hs environmentl enefits in retining more N in the soil. Keywords: Superheted stem drying, Nitrous oxide, Greenhouse gs emissions, Soil enhncement, Controlledrelese fertiliser, Lignite Bckground Two mjor chllenges fcing frmers worldwide include improving nitrogen (N) fertiliser use efficiency, nd reversing the widespred loss of soil orgnic mtter. Nitrogen fertilisers re routinely pplied in mny cropping nd psture systems in order to increse yields nd grin or fodder protein content. However significnt proportion of pplied fertiliser N is often not used y the crop or psture nd the reminder is susceptile to loss through leching, runoff or denitrifiction [1]. This lost N represents oth n economic inefficiency nd n environmentl urden, s off-site N movement in wter pollutes quifers nd nturl wter courses, whilst nitrous *Correspondence: ntonio.ptti@monsh.edu Michel T. Rose nd Emily L. Perkins contriuted eqully to this work 1 School of Chemistry, Monsh University, Clyton, VIC 3800, Austrli Full list of uthor informtion is ville t the end of the rticle oxide contriutes to greenhouse gs ccumultion in the tmosphere [2]. The loss of soil orgnic mtter hs lso impcted on crop productivity. Soil orgnic mtter provides numerous eneficil functions to crop production, including high wter holding cpcity; the cpility to provide, retin nd recycle nutrients; nd the cpcity to uffer chnges in ph, slinity nd other chemicl stressors [3]. Soil cron lso contriutes to the retention of pplied N [4], suggesting tht mngement prctices tht increse soil C cn lso reduce fertiliser N loss. Indeed, Gentile et l. [5] found tht incorporting low qulity (i.e. low % N) mize residues could immoilise fertiliser N in field soil nd reduce N leching losses to greter extent thn high qulity (high % N) residues, without impcting on crop N uptke over the growing seson. A numer of studies hve lso shown tht iochrs cn reduce nitrte nd 2016 Rose et l. This rticle is distriuted under the terms of the Cretive Commons Attriution 4.0 Interntionl License ( which permits unrestricted use, distriution, nd reproduction in ny medium, provided you give pproprite credit to the originl uthor(s) nd the source, provide link to the Cretive Commons license, nd indicte if chnges were mde. The Cretive Commons Pulic Domin Dediction wiver ( pulicdomin/zero/1.0/) pplies to the dt mde ville in this rticle, unless otherwise stted.

2 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 2 of 14 mmonium leching from pplied N fertilisers, ut the effectiveness depends on the chemicl chrcteristics of the iochrs nd their rte of ppliction [6 8]. There is therefore strong reson to hypothesise tht lending common minerl N fertilisers with orgnic mterils s orgno-minerl fertilisers could reduce offsite fertiliser N loss. To dte, most controlled-relese N fertilisers (CRFs) rely on polymer cotings tht dely fertiliser relese; higher-stility chemicl fertilisers tht tke more time to soluilise; or grnules coted or mixed with specific compounds tht inhiit N trnsformtion pthwys, such s urese or nitrifiction inhiitors [9, 10]. Of the few studies investigting controlled-relese orgno-minerl N fertilisers, Richrds et l. [11] showed tht lending of commercil mmonium nitrte fertiliser with sphgnum pet reduced fertiliser nitrte leching whilst still providing sufficient N for the growth of mize. More recently, Gonzlez et l. [12] found tht ure formulted together with iochr slowed down the relese of ure, ut none of the iochr CRFs performed s well s commercil CRF tht did not contin iochr. Brown col, lso known s lignite, is n lterntive mteril with properties tht mke it ppeling for use s N fertiliser crrier. Previous work found tht rown col incorportion into soil slightly reduced mmonium vilility in one soil, ut the study did not look t minerl N leching or nitrous oxide emissions [13]. One reson tht rown cols my differ in their N retention ehviour compred with iochrs tht unlike most iochrs, rown cols re generlly cidic rther thn lkline. Furthermore, wheres most iochrs re of limited vilility nd reltively high cost of $ per tonne [14, 15], rown col is redily ville in mny countries t lower cost, for exmple, pproximtely $50 per tonne in Austrli. A mjor drwck to the use of rown col s crrier mteril, however, is its high moisture content (typiclly % for rown cols mined in Victori, Austrli). This mkes trnsporttion of rown col prohiitively expensive nd thus mkes drying of the col n essentil process. Dried rown col is prone to crumle into fine dust when hndled, incresing its propensity to undergo spontneous comustion. This introduces further difficulties for hndling nd storge. Dried rown col grnules of suitle strength nd resistnce to ttrition my e vile solution to these issues. The grnultion process provides method for the ddition of N fertiliser in either liquid or solid form. Grnultion is size enlrgement process, where fine prticles re gglomerted into lrger grnules [16]. Methods of grnulting col dust hve een investigted s mens to reduce losses nd optimise the use of this resource nd more recently, the potentil of improving the hndling properties of rown col hs een investigted [17]. During the grnultion process inder is often required to enle the prticles to dhere nd form lrger prticles. In the cse of rown col, it hs een found tht the wter contined within the pores of the col structure provides most of the inder requirements for the grnultion process to occur. As the rown col prticles re sujected to mechnicl forces within the grnultor drum, the inherent wter is forced to the surfce of the prticle nd is ville s inder. Additionl inder my e required, depending on the rown col used nd the desired properties, such s prticle strength, of the finl grnules. After grnultion the rown col grnules still contin wter tht must e removed to reduce trnsporttion cost, lthough the loction of some of the inherent wter hs moved from the interior of the col prticle to the surfce of the col grnules. A suitle drying method is required tht oth decreses the risk of spontneous comustion occurring during the drying process nd is economiclly vile. Mny dewtering methods hve een studied; oth evportive techniques tht require the ltent het of vporistion of wter, nd non-evportive techniques tht remove the wter under pressure or using mechnicl mnipultion of the col structure hve een identified [18]. In the 1980s superheted stem drying of rown col ws suggested s n lterntive [19], providing n oxygen deficient tmosphere for drying tht removes the risk of spontneous comustion nd mens of recpturing much of the ltent het required for drying y utilising the stem fter the drying process. The im of this work ws to evlute the use of ure lended with rown col s fertiliser. We first sought to optimise the grnultion nd superheted stem drying of the ure-rown col lend, efore undertking series of soil-sed experiments to compre the leching, nitrous oxide emissions nd plnt uptke of N from urerown col grnules versus conventionl ure fertiliser. This reserch provides proof of concept for further optimistion of orgno-minerl fertiliser mnufcture using redily ville lignite resources. Methods L grnultion Run-of-mine rown col (BC) from Loy Yng, Austrli, ws used for these experiments. The col hd moisture content of 50 % (wet sis) nd ws milled to <3 mm prticle size. For l trils, powdered ure (Sigm) ws used. Grnulr ure (Richgro, Austrli) of 2 4 mm in dimeter ws used for stem drying trils. Drum grnultion of three different formultions for pot trils were crried out. Ure ws ground into powder nd hnd-mixed in weight rtios ure to wet col of

3 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 3 of 14 1:3 (i.e. high N ure-rown col lend, herefter referred to s UBC-H) nd 1:10 (low N ure-rown col lend, UBC-L). A third formultion contined no ure. Some dditionl wter ws used s inder in the grnultion process. For tches mde with ure, 500 g of wet col ws used with the pproprite ddition of ure. The col only tch used 1500 g of wet col nd dditionl wter. The grnultion ws crried out in stinless steel drum grnultor with n internl dimeter of 37 cm. The drum speed ws set t 34 rpm. Grnultion of col with ure occurred very quickly, in less thn 10 min; the product grnules ppered very wet on the surfce. Grnultion of col lone typiclly took min. Grnules were ir dried for t lest 72 h t mient conditions. Product grnules with typicl size of 4 mm were used for further pot trils. Pilot scle trils of comined grnultion nd superheted stem (SHS) drying Wet Loy Yng run-of-mine BC ws milled to 3 mm nd pre-mixed with grnulr ure for 2.5 dys t mss rtio ure to wet col of 1:6 (medium ure-rown col lend, UBC-M). After this time the ure grnules were nolonger visile nd ssumed to hve dissolved into the inherent wter contined within the rown col prticles. Additionl wter (180 ml to 1 kg pre-mixed col nd ure) ws mixed with the col/ure lend s the feed stock for the grnultion nd drying tril. This dditionl wter ws required to ssist the grnultion process tht occurs t the strt of the drum nd to prevent excessive dust production, which could negtively impct on the grnultion process. The feed formultion ws dded into the feed hopper t the strt of the drum nd then fed into the drum vi screw feeder (Fig. 1). In the first section of the drum (pproximtely ¼ of the drum length), the internl flights hd een reduced in height to increse the residence time in this section during which the grnule growth could occur. Once the col progressed further down the drum the incresed height of the flights ssisted the col grnules to move more quickly long the drum, reducing the residence time in which grnule rekge could occur. At the end of the drum nother screw feeder removed the grnules from the drum nd out to the product exit chute. Product smples were collected nd the prticle size distriution nd moisture content were mesured. This pilot-scle rig hs cpcity to hndle up to 50 kg/hr of col. Drum operting prmeters of drum speed, fn speed (stem velocity) nd stem temperture were djusted to optimise the prticle size distriution nd finl moisture content of the product. After the initil strt-up period, the conditions were chnged s shown in Tle 1. Ech condition ws mintined for 1 h. Grnule chrcteristion The mss medin prticle size, d50, ws mesured y sieving the smple nd determining the prticle dimeter for which 50 % of the distriution is elow tht prticle size. Similrly the d10 nd d90 represent the prticle Fig. 1 Schemtic of the pilot-scle superheted stem drum dryer

4 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 4 of 14 Tle 1 Operting conditions for pilot-scle comined grnultion nd drying tril Condition no. Temperture ( C) Fn speed (m/s) Drum speed Comments Mximum Strt-up, previous col only conditions used Mximum Mximum Mximum dimeter for which 10 nd 90 % of the distriution hve prticle dimeter elow this vlue. The moisture content of the product ws clculted on wet sis using the product mss efore nd fter oven drying t 105 C for 4 h. Single prticle compressive crush strength tests were crried out on product grnules using ench-top scle Instron testing mchine. The mximum force pplied to rek the prticle ws mesured. A minimum of 10 prticles from ech condition were tested nd the verge nd stndrd devition of the crush strength were determined. The cron, hydrogen nd nitrogen content of the smples were determined y comustion using PerkinElmer 2400 series II CHNS/O nlyser, operted in CHN mode. Oxygen contents of the smples were determined y difference. Smples were nlysed in triplicte nd smple mss of pproximtely 2 mg ws used. The grnule surfce morphology nd cross-sectionl re morphology were exmined y opticl microscopy (Motic SMZ-168 microscope with universl stnd). Individul grnules from oth l nd pilot-scle trils were exmined. The cross-sectionl re of the grnules ws exposed y frcturing the grnules with sclpel. Comprison of stem drying versus ir drying Although stem drying ws considered the techniclly fvourle technique for drying the ure-bc grnules in terms of lrge-scle process sfety nd energy efficiency, the effect of the stem drying on the retention of the ure within the formultion ws uncler. Lortorysed drying trils were conducted on l grnulted tch of 1:6 rtio ure-bc grnules, grnultion method used s descried erlier. Smples (50 g) of grnules from this tch were dried under the conditions outlined in Tle 2. The CHN nlyses of grnules from these dried smples nd those of tches used in the pot trils were then crried out using the method descried ove. Leching experiment A 6-week column experiment ws conducted to determine the leching nd denitrifiction potentil of ure-rown col (ure-bc) lended fertilisers versus Tle 2 Conditions used for stem drying versus ir drying comprison Drying method Grnultion method Ure-BC nitrogen content Air, mient temperture L grnultion UBC-L Air, mient temperture L grnultion UBC-H Air, mient temperture L grnultion UBC-M Air 105 C 1 h L grnultion UBC-M Air 130 C 1 h L grnultion UBC-M Stem 105 C 60 %RH 1 h L grnultion UBC-M Stem 130 C 60 %RH 1 h L grnultion UBC-M Stem 105 C 100 %RH 1 h L grnultion UBC-M Stem 130 C 100 %RH 1 h L grnultion UBC-M SHS drum pilot tril SHS drum pilot tril UBC-M UBC ure-rown col grnule t low N (L), high N (H) or medium N (M) content; SHS superheted stem conventionl ure fertiliser. Twenty polycronte columns (18 mm dimeter, 250 mm height) were covered t one end with nylon mesh nd then pcked with 1 cm of wshed snd nd 88 g of soil (lomy snd). The soil occupied volume of 60 cm 3, giving ulk density of 1.4 g cm 3. Soil columns were sturted with 50 ml of wter in order to determine field cpcity nd ed volume. Columns were susequently llowed to equilirte for 10 dys under free-drining conditions. After this, soils were mended with either conventionl ure, UBC-H or UBC-L t depth of 20 mm, to give finl nominl delivery of 18.4 mg of ure N per column. This ws equivlent to 230 mg N kg 1 soil if evenly distriuted throughout the entire profile. Two controls were lso included: one contined rw rown col t rte equivlent to the UBC-L, nd n unfertilized control. All tretments were replicted four times. After tretment pplictions, soils were wet to field cpcity nd incuted t 24 C for 42 dys. During this time three leching events were conducted: t dys 7, 21 nd 35 fter tretment ppliction. At ech leching event, soils were djusted to field cpcity moisture nd then eluted with hlf ed volume (pproximtely

5 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 5 of ml) of distilled wter. Lechte ws collected in 20 ml scintilltion vils for 2 h post-leching nd then frozen for future nlysis of minerl N. Greenhouse gs smpling occurred on 1, 3, 8, 10, 13, 17, 22, 24, 27, 31, 36, 38 nd 41 dys fter tretment ppliction, y plcing ruer septum over the top of the columns nd smpling gs (20 ml) with gs-tight syringe immeditely fter cpping nd 1 h lter. Gs smples were injected into pre-evcuted 12 ml Exetiner vils (Lco, Englnd) for future nlysis. Hedspce volumes for ech column were mesured independently. At the end of the experiment (dy 42) columns were dissected into three 8 cm sections. Soil ws removed from ech section nd frozen until nlysis for KClextrctle minerl N (nitrte + nitrite, mmonium) nd totl N. Plnt growth experiment A 6-week glsshouse experiment ws conducted to determine the potentil of ure-bc lended fertilisers versus conventionl ure fertiliser to supply N to whet. Whet ws grown in 1.5 kg of soil in pots of 10 cm dimeter nd 20 cm height in the glsshouse for durtion of 42 d. Fertiliser ws pplied t sowing y plcing fertiliser grnules t depth of 4 cm elow the soil surfce (2 cm elow the seed). Fertiliser tretments were the sme s in the column experiment descried ove, i.e. ure, UBC-H, UBC-L, rown col grnule control nd no fertiliser control, such tht ech tretment received the sme mount of N. Plnts were wtered weekly to 60 % field cpcity, with single leching event t 20 dys fter sowing. At this time, soil ws wtered to field cpcity nd then n dditionl 50 ml of wter ws pplied to simulte hevy rinfll event. Lechte ws collected from holes in the ottom of the pots nd nlysed for nitrte nd mmonium. Greenhouse gs emissions were mesured weekly t 7, 14, 21 nd 35 dys fter sowing, y connecting 15 cm height PVC cover with septum nd smpling gs (20 ml) with gs-tight syringe immeditely fter covering nd 1 h lter. Gs smples were injected into pre-evcuted 12 ml Exetiner vils for future nlysis. Hedspce volumes for ech pot were mesured independently. After 42 dys of growth, ll pots were destructively hrvested y removing whet shoot nd roots nd prtitioning the soil profile into three sections: 0 6, 6 12 nd cm. Soil ws nlysed for nitrte nd mmonium. Plnt shoots were oven dried t 70 C, ground nd nlysed for N content y dry comustion. Greenhouse gs nlysis Gs smples were nlysed for CO 2 nd N 2 O using n Agilent 7890A greenhouse gs nlyser. This system seprtes gses on HyeSep Q 80/100 columns followed y detection of CO 2 y flme ionistion nd N 2 O y electron cpture. Gs flux over the 60 min smpling durtion ws checked for linerity periodiclly throughout oth column nd glsshouse experiments y mesuring t 0, 20, 40 nd 60 min. The flux of N 2 O-N ws clculted y converting volumetric gs chromtogrphy dt (ppm) to molr equivlents using the idel gs eqution, corrected for temperture nd pressure, nd ccounting for the volume of the smpling hedspce nd re of surfce flux. For the column leching study, hourly flux dt were integrted over time y tking n verge of two consecutive mesurements nd multiplying y the time intervl, in order to clculte cumultive emissions. Becuse only four smpling N 2 O smpling events were tken for the plnt growth experiments, dt re reported s the hourly flux for ech event. Grnule, soil, plnt tissue nd lechte nlysis Totl C nd N in fertiliser grnules, soils nd plnt tissues were mesured using high-frequency induction furnce (LECO Pty Ltd). All mterils were finely ground using stinless steel ll mill prior to nlysis. Minerl N ws extrcted from soils (homogenised nd sieved to <2 mm) with 2 M KCl using 1:4 soil:extrctnt rtio. Lechtes nd soil extrcts were filtered through 0.2 micrometre cellulose cette prior to nlysis for minerl N species y spectrophotometry in microplte formts. NH 4 + ws quntified fter recting with slicylte nd hypochlorite in uffered lkline solution contining sodium nitroprusside s reductnt [20]. NO 3 ws determined y reduction of nitrte using vndium (III) comined with detection y cidic Griess regent [21]. Sttisticl nlysis Leching nd plnt experiments were estlished s rndomised lock designs. Minerl N concentrtions in soil nd lechte; nitrous oxide fluxes nd plnt growth nd N content were nlysed using one-wy ANOVA with 5 levels (Ure, UBC-H, UBC-L, BC control, no tretment control). Position in the glsshouse/lortory ws used s lock fctor. Post-hoc testing y lest significnt difference (P < 0.05) ws used to seprte mens. All nlyses were conducted with SPSS. Results L grnultion L grnultion experiments produced tches of ure- BC nd BC grnules for pot trils, leching experiments nd the drying method comprison study. Initil oservtions suggested tht grnules with higher ure content showed signs of ure re-crystllistion on the surfce

6 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 6 of 14 of the grnules, s indicted y smll white crystls on the exterior of the col grnules (Fig. 3c). Comined grnultion nd stem drying pilot scle trils The results of the superheted stem drying trils re shown in Fig. 2. The strt-up conditions were mintined for 3 h, with product smples tken every 20 min strting t 100 min, denoted s time 0 for the experiment. The dry mss output ws initilly ffected y chnges in the fn speed, ut returned to n equilirium level of round 80 ± 15 g/min fter 20 min (not shown). The men prticle size, d50, ws lso initilly ffected y oth the chnge in fn speed nd chnge in temperture, ut returned to mm fter 20 min. The error rs displyed in Fig. 2 show the d10 nd d90, thus represent the width of 80 % of the prticle size distriution. For this tril, the d50 rnged from 1.5 to 3.5 mm. The product moisture content ws reltively stle t % moisture fter the initil strt-up phse. The clculted product moisture content rnged from 15 to 27 % for the conditions used in this tril. The initil feed moisture content ws 58 %. At round 240 min there ws n unexpected 8 min power outge fter which the drum ws restrted. Very little chnge ws oserved in the medin prticle size or prticle size distriution, lthough noted decrese in the product moisture content ws oserved nd likely Fig. 2 Results of superheted stem drum trils, drum inlet temperture nd set conditions on upper grph, d50 nd product moisture contenton lower grph. Error rs show the width of 80 % of the prticle size distriution

7 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 7 of 14 result of the incresed residence time of the product t elevted temperture during the power outge. Grnule chrcteristion The composite grnules t ll ure-bc rtios nd for oth grnultion methods significntly incresed in nitrogen content compred to the rw col (Tle 3). During grnultion of rown col, the wet rown col lredy contins lrge reservoir of wter within the porous structure of the col. As the col is consolidted within the drum, the wter is forced out of the pore structure nd on to the surfce of the col prticles, which llows the wter to ct s inder in the grnultion process. The surfce wter on the col prticle forms inding gent when the prticles collide, nd the prticles colesce. In the cse of ure ddition, the ure is thought to dissolve into the inherent wter within the col due to its high soluility nd is therefore eluted towrds the surfce of the prticles s the consolidtion process occurs. The grnule crush strength ws mesured for ure- BC grnules tht were grnulted nd dried in the pilotscle superheted stem drum dryer. Both tches hd ure to wet col rtio of 1:6 (UBC-M). The verge crush strength of 10 grnules for ech tch is presented (Tle 3). The grnule crush strength is comprtively low t 2.2 nd 2.9 N, respectively for the two test tches. For hndling purposes the grnules crush strength should e t lest N, crush strength of N or greter eing highly desirle [22]. Surfce morphology At lower N content, UBC-M nd UBC-L, no significnt ure crystls re oserved on the grnule surfce or within the cross-sectionl re (Fig. 3, ). This ws true for ll drying methods. With the highest N content UBC- H, ure crystls were oserved on the surfce of the grnule, ut not throughout the interior s seen in the imge of the cross-sectionl re (Fig. 3c). Tle 3 CHN nd crush strength nlysis for rw col nd comined col nd ure grnules, percentges on dry sis Ure: wet col rtio C % H % N % Crush strength (N) Typicl victorin BC ND UBC-H (l grnultion) ND UBC-M (pilot grnultion) ± ± 0.5 UBC-L (l grnultion) ND Note tht two crush strengths re given for UBC-M, representing two different tch runs of the pilot-scle grnultion UBC ure-rown col grnule t low N (L), high N (H) or medium N (M) content; ND not determined Comprison of drying methods on nitrogen content of formultion To compre the effects of stem nd ir drying on the N content of the dried grnules, single tch of UBC-M grnules ws mde in the lortory drum grnultor nd dried y different methods (Tle 4). The low cron percentges oserved for stem dried smples t 105 C for 60 nd 100 % RH were likely ecuse the smples were not s dry s the other smples, nd this is lso inferred y the higher hydrogen nd oxygen content. The cron to nitrogen rtio (C:N) ws clculted to compre the smples without the effect of moisture. The theoreticl C:N rtio ws clculted from mss lnce tht ssumed no loss of mteril during the grnultion nd drying process. The mesured vlues were in close greement with the theoreticl vlues for ll drying methods nd for the different formultions (Fig. 4). Leching experiment The ddition of ure fertilisers, s either stright ure or grnulted ure-bc, significntly incresed the concentrtion of oth minerl N species in wter leching from the soil column compred with columns not receiving N fertiliser (Fig. 5). Grnultion of ure with rown col significntly reduced the mount of oth nitrte nd mmonium leched out of the soil profile. Incresing the rtio of BC to N (i.e. the UBC-L grnule) reduced the mount of mmonium lost through leching y over 40 %, whilst the mount of nitrte lost vi leching ws reduced y lmost 20 %. As expected, the ddition of ure fertilisers, s either stright ure or grnulted ure-bc, significntly incresed the concentrtion of oth minerl N species in the soil column compred with columns not receiving N fertiliser (Fig. 6). Grnultion of ure with rown col significntly incresed the mount of mmonium residing in the top soil (0 8 cm), nd reduced the mount of mmonium in middle lyer (6 12 cm). The top soil of ure-bc grnules contined lmost doule the mount of mmonium thn tht of the soil treted with stright ure. Grnulting ure with BC did not significntly lter the mount of nitrte in topsoil compred with stright ure, ut soil treted with the low N ure-bc grnules hd significntly less nitrte in the lower lyers thn the other two N tretments. Grnultion of ure with BC, in prticulr the low N ure-bc grnultion, lso mintined higher level of totl N in the topsoil s compred with stright ure (Tle 5). Appliction of N fertilisers (either stright ure or ure-bc grnules) significntly incresed the emissions of N 2 O from soil (Tle 6). The high N ure-bc grnules did not reduce the loss of N 2 O compred with stright ure. However, the low N ure-bc grnules

8 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 8 of 14 Fig. 3 Opticl microscopy imges of rown col nd ure whole grnules (left hnd column) nd internl cross section (right hnd column) for UBC-L, UBC-M nd c UBC-H reduced N 2 O emissions y pproximtely 35 % over the durtion of the experiment, compred with oth other N fertilisers. Plnt growth experiment No significnt differences in plnt growth were oserved etween ny of the tretments, ut some minor differences were oserved in terms of N content (Fig. 7). Whet growing in pots treted with rown col control lone (no ure) hd significntly lower N content thn pots receiving ure or the low ure-bc lend. Greenhouse gs mesurements over the growth durtion of the experiment showed higher emissions of N 2 O from pots fertilised with stright ure s compred with

9 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 9 of 14 Tle 4 CHN nlysis for col-ure (UBC-M) grnules dried under different conditions Drying conditions C % H % N % O % Air dried, mient, 5 dys Air dried, oven 105 C, 1 h Air dried, oven 130 C, 1 h Stem dried, oven 105 C, 60 % RH, 1 h Stem dried, oven 130 C, 60 % RH, 1 h Stem dried, oven 105 C, 100 % RH, 1 h Stem dried, oven 130 C, 100 % RH, 1 h Oxygen ws clculted y difference ure-bc lends nd non-fertilised pots (Fig. 8). This ws prticulrly evident fter the sturtion event on dy 21, where N 2 O emissions from ure-fertilised plots were more thn doule tht of non-fertilised pots nd the high ure-bc lend. At the end of the experiment, significnt differences in the concentrtion of nitrte were oserved in the different tretments (Fig. 9). Unfertilised pots (control nd BC control) contined very low concentrtions of nitrte throughout the soil profile, wheres ll soils receiving N-contining fertilisers contined significntly (P < 0.05) higher levels. The high N ure-bc tretment contined significntly (P < 0.05) higher levels of nitrte in topsoil thn the low N ure-bc lend, ut oth were not significntly different from the stright ure tretment. Discussion Grnultion Ure-enriched BC grnules were successfully mde t oth lortory nd pilot scle. The pilot-scle grnultion ws chieved within the drum of superheted stem dryer, thus enling the simultneous grnultion nd drying of the grnulr product. Superheted stem drying provides n intrinsiclly sfe method for drying BC which hs propensity to undergo spontneous comustion. The tmospheric pressure of the superheted stem reduces the cost nd energy requirement for the drying process nd provides the option to recpture the ltent het required to dry the col [23]. The N content of the dried products t ll C:N rtios ws close to the theoreticl N content determined from the initil mount of ure ddition to the wet col. This ws true for ll of the drying methods tested here nd despite the oservtion of crystlline ure on the surfce of the high N formultion, which my hve resulted in lost ure. The role of the ure within the grnultion process should lso e considered. This highly solule fertiliser Fig. 4 C:N for ure-bc grnules of different lends nd dried y different methods

10 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 10 of 14 Ammonium (mg/l) c d d c c c c Totl U UBC-H UBC-L BC Control Ammonium (mg/kg) c c c c Top Middle Bo om U UBC-H UBC-L BC Control Nitrte (mg/l) c c c c Totl Time of leching event (d) c c U UBC-H UBC-L BC Control Fig. 5 Ammonium nd nitrte concentrtion in lechtes t ech leching event. The column to the fr right shows the totl N leched. Tretment revitions re: U ure, UBC-H ure-rown col grnule (17 % N), UBC-L ure-rown col grnule (8.7 % N), BC rown col grnule, control no N or C ddition. Within specified time, letters ove column re different if the vlue is significntly different (P < 0.05) Nitrte (mg/kg) Top Middle Bo om c c Soil profile c c U UBC-H UBC-L BC Control Fig. 6 Ammonium nd nitrte remining in soil t 42 dys, fter three leching events. The depth of the different soil profile lyers re top (0 8 cm), middle (8 16 cm) nd ottom (18 25 cm). Tretment revitions re: U ure, UBC-H ure-rown col grnule (17 % N), UBC-L ure-rown col grnule (8.7 % N), BC rown col grnule, control no N or C ddition. Within profile depth, letters ove column re different if the vlue is significntly different (P < 0.05) dissolves into the inherent wter within the rw BC, which is prtilly drwn to the surfce of the col prticles, reducing the consolidtion time required within the grnultion process. This ws oserved in the significntly reduced grnultion time for the lortory tches of ure-bc compred to the grnultion of BC lone. This prtil extrction of the inherent wter lso reduced the requirement for dditionl wter to ct s inder within the grnultion process. The tumling motion nd impct forces on the col prticle during the consolidtion process drive the inherent wter to the surfce of the col prticle where it cts s inder etween col prticles to egin the grnultion process. As the grnules continue to form, the impct forces on the grnules drives more wter to the surfce llowing the grnule to grow further. This my lso effect the finl distriution of the N within the wet grnules. The difference in the drying mechnism etween ir dried grnules (surfce drying) nd stem dried grnules (internl removl of wter vpour), my lso hve n impct on the finl distriution of the N within the dried grnules. Further investigtion would determine if Tle 5 Totl N nd C in the topsoil t the end of the 42 dys incution Tretment Topsoil (0 8 cm) N content (%) Topsoil (0 8 cm) C content (%) U 0.43 ± ± 0.05 UBC-H 0.46 ± ± 0.35 UBC-L 0.50 ± 0.03 c 2.21 ± 0.69 c BC 0.03 ± 0.01 d 2.17 ± 0.14 c Control 0.02 ± 0.01 d 1.17 ± 0.2 Tretment revitions re: U ure; UBC-H ure-rown col grnule (17 % N); UBC-L ure-rown col grnule (8.7 % N); BC rown col grnule; control no N or C ddition Errors re 95 % confidence levels. Within column, letters djcent to vlues re different if the vlues within column re significntly different (P < 0.05) this effect is significnt with respect to the finl use of the ure-bc grnules. The finl strength of the dried grnules is significntly less thn tht of other fertiliser grnules currently used in griculture. To enle the ure-bc grnules to e fesile lterntive, further work on the formultion is

11 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 11 of 14 Tle 6 Cumultive emissions of N 2 O-N (µg per column) from the surfce of the soil columns over the durtion of the experiment Tretment Cumultive N 2 O-N (µg) emissions t 21 d U 28 ± ± 20 UBC-H 33 ± ± 36 UBC-L 11 ± 4 76 ± 9 BC 0.4 ± 0.1 c 1.9 ± 0.3 c Control 1.4 ± 2.2 c 1.6 ± 2.2 c Cumultive N 2 O-N (µg) emissions t 42 d Tretment revitions re: U ure; UBC-H ure-rown col grnule (17 % N); UBC-L ure-rown col grnule (8.7 % N); BC rown col grnule; control no N or C ddition Errors re 95 % confidence levels. Within column, letters djcent to vlues re different if the vlues within column re significntly different (P < 0.05) required to increse the grnule strength. An dditive to either the inder or the ure-bc solid lend my provide the required strength for the dried grnules. N dynmics in unplnted soil treted with ure fertilisers Grnultion of ure with BC hd strong effect on the ehviour of the fertiliser N in the soil system. Both high N nd low N ure-bc grnules mintined higher totl N nd mmonium concentrtions in unplnted topsoil, suggesting mechnism y which the BC either slows the rte of ure hydrolysis or inds to mmonium, mking it less moile. This is supported y the lechte dt from unplnted soil, which showed tht y grnulting the ure with BC, less minerl N (oth mmonium nd nitrte) ws leched from the soil profile s compred with stright ure. It is importnt to note tht the high N grnules did not retin s much N in the top soil. This is similr to the findings of Gentile et l. [5], who demonstrted tht fertiliser N retention ws higher in soil mended with low qulity (i.e. low N) residue thn high N residues, due to net N immoilistion. However, in their cse, it ws postulted tht immoilistion ws primrily consequence of incresed microil demnd to mtch the higher vilility of cron-rich growth sustrte. In our cse, we elieve tht microil immoilistion due to higher C vilility is unlikely, since previous studies hve shown rown col to e poor C source over short-time periods [13]. Insted, it is likely tht dsorption of ure nd/ or minerlised mmonium to the lignite mtrix is the min mechnism responsile for immoilistion, s hs een oserved for high C:N iochrs [8, 24]. The lower retention of N in topsoil y the high N grnules ppers to e consequence of oversturtion of sorption sites within the rown col mtrix, s shown y the presence of ure crystls throughout the grnules (Fig. 3). This effectively increses the surfce re of the crystlline ure nd would promote fster dissolution nd ssocited leching. The low N ure-bc grnules were lso superior to the high N grnules in terms of N 2 O losses: emissions were significntly reduced y incorporting more BC in the N fertiliser grnules. The fct tht there ws no significnt difference in N 2 O emissions etween ure nd high N rown col grnules suggests tht the vilility of nitrte for denitrifiction over the durtion of the experiment ws similr in these two tretments. In contrst, the reduction in N 2 O emissions from the low N ure-bc grnules tretment suggests lower nitrte vilility LSD = LSD = Dry weight (g) N content (%) Control Ure BC BC-Ure (low) BC-Ure (high) Tretment Fig. 7 Effect of different N fertilisers on erly whet growth nd lef tissue N ccumultion 0.0 Control Ure BC BC-Ure (low) BC-Ure (high)

12 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 12 of 14 N 2 O Flux (µg N m -2 h -1 ) Time of irrig on event (d) U UBC-H UBC-L Fig. 8 Effect of different N fertilisers on N 2 O emissions (µg m 2 h 1 ) t different irrigtion events. Note tht dy 7, 14 nd 35 irrigtions were to 60 % soil wter holding cpcity; wheres the dy 21 irrigtion represented leching event in which soil ws sturted. Within specified time, letters ove column re different if the vlue is significntly different (P < 0.05) Nitrte concentr on (mg/kg) c Control Ure BC BC-Ure (low) c BC-Ure (high) Fig. 9 Effect of different N fertilisers on nitrte concentrtions through the soil profile t hrvest (42 DAS) BC C 0-6 cm 6-12 cm cm over the durtion of the incution, or, lterntively, tht the nitrte ws retined in zone where the ctivity of denitrifying orgnisms ws inhiited. There is lso specultion tht low N (high C:N) iochrs cn reduce N 2 O emissions y ctlysing the further reduction of N 2 O to N 2 [25, 26], which could represent n dditionl mechnism y which rown col lends cn reduce N 2 O emissions. Further reserch is needed to elucidte the primry mechnisms responsile for ltering N 2 O dynmics. N dynmics in plnted soil treted with ure fertilisers In contrst to unplnted soil columns suject to leching, grnultion of ure with rown col did not drsticlly lter the movement of N compred with stright ure in the plnted soil columns. Prt of the reson for this is likely due to the less severe irrigtion regime, since plnted soil columns were wtered to 60 % field cpcity three times with only one complete sturtion event (representing hevy rinfll) t dy 25. Nevertheless, there ws still evidence tht incorportion of rown col reduced nitrous oxide emissions, compred with conventionl ure, especilly under sturted conditions (Fig. 8). Importntly, the grnultion of ure with rown col did not reduce plnt growth or the cquisition of N y plnts in this limited six-week growth study (Fig. 7). In similr study evluting orgno-minerl N fertilisers, Richrds et l. [11] found tht lending ure or mmonium nitrte fertiliser with pet reduced totl N uptke y 9.1 % in three successive, 6-week corn crops grown under glsshouse conditions. However, under field conditions they found no significnt differences in yield or N uptke y corn grown with conventionl mmonium nitrte fertiliser or pet-lended mmonium nitrte. In our study, the short-time frme of the tril proly msked ny potentil effects, s evidenced y the minor differences etween N-fertilised tretments nd controls not receiving N fertiliser. In ddition, we did not mesure mmoni voltilistion during these experiments. Ammoni voltilistion cn represent significnt N loss pthwy from the plnt/soil system, prticulrly in lkline soils [1]. More work is therefore needed to extend the durtion nd scle of the plnt growth experiments, together with dditionl mesurements of potentil N loss through mmoni voltilistion. Overll our results suggest tht grnultion of ure with BC cn strongly reduce N losses from topsoil, y decresing N leching nd gseous emissions. In doing so, it is nticipted tht greter mount of fertiliser N will e ville to crops over longer time period, incresing the efficiency of fertiliser N use, ut this remins to e vlidted. Furthermore, our results show

13 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 13 of 14 tht vrying the C:N rtio of the lended fertilisers hs significnt impct on the N dynmics, suggesting tht there is further opportunity to optimise the rtio of C:N to minimise N loss from soil whilst mximising crop uptke. Conclusions Ure nd BC ws successfully lended, grnulted nd dried on pilot scle. The grnules formed were of n pproprite size for griculturl use, lthough the current formultion produces grnules tht re not strong enough for the hndling requirements of fertiliser. The N retention in the grnules is close to tht clculted theoreticlly for the formultion nd is consistent for ll the ir drying nd stem drying methods tested. The ure-bc grnules significntly reduced the mount of nitrte nd mmonium lost though leching nd lso reduced the emission of nitrous oxides from the soil, whilst not reducing the plnt ville N. N losses were lower for the low N ure-bc formultion thn for the high N formultion, emphsising the significnt role of the rown col in the N retention. This work provides proof of concept for the pilot-scle production nd use of BC lended orgno-minerl fertiliser grnules. Additionl work is now necessry to chrcterise ure-bc grnule ehviour in vrious soil types nd under field conditions. Authors contriutions MTR nd ELP conceived experiments, conducted experiments, nlysed dt nd drfted the mnuscript. BKS nd ECWT conducted experiments nd ssisted in drfting the mnuscript. TRC, WRJ nd KPH ssisted in interprettion of dt nd writing of the mnuscript. AFAH nd AFP helped design nd conduct experiments, interpret dt nd write the mnuscript. All uthors red nd pproved the finl mnuscript. Author detils 1 School of Chemistry, Monsh University, Clyton, VIC 3800, Austrli. 2 Deprtment of Chemicl Engineering, Monsh University, Clyton, VIC 3800, Austrli. 3 Wite Reserch Institute nd School of Agriculture, Food nd Wine, University of Adelide, Adelide, SA 5005, Austrli. 4 Present Address: NSW Deprtment of Primry Industries, Wollongr, NSW 2480, Austrli. Acknowledgements We wish to cknowledge Pinches consolidted industries (Keith Engineering) for use of the pilot-scle superheted stem drum dryer, nd funding from Brown Col Innovtion Austrli under the projects: Improved hndling of lignite nd lignite derived products nd Col-derived dditives: A green option for improving soil cron, soil fertility nd griculturl productivity?. BKS ws the recipient of Monsh Grdute Scholrship. Thnk you to Ross Ellinghm for col preprtion nd ssistnce to run pilot equipment nd to Monsh Undergrdute students Nick Reid nd Benjmin Hrris who ssisted with dt collection from the soil studies. Competing interests This work ws funded y Brown Col Innovtion Austrli. Received: 12 Novemer 2015 Accepted: 4 April 2016 References 1. Cmeron KC, Di HJ, Moir JL. Nitrogen losses from the soil/plnt system: review. Ann Appl Biol. 2013;162: Vitousek PM, Aer JD, Howrth RW, Likens GE, Mtson PA, Schindler DW, et l. Humn ltertion of the glol nitrogen cycle: sources nd consequences. Ecol Appl. 1997;7: Allison FE. Soil orgnic mtter nd its role in crop production. London: Elsevier Scientific Pulishing Compny; Accoe F, Boeckx P, Busschert J, Hofmn G, Vn Cleemput O. Gross N trnsformtion rtes nd net N minerlistion rtes relted to the C nd N contents of soil orgnic mtter frctions in grsslnd soils of different ge. Soil Biol Biochem. 2004;36: Gentile R, Vnluwe B, Vn Kessel C, Six J. Mnging N vilility nd losses y comining fertilizer-n with different qulity residues in Keny. Agric Ecosyst Environ. 2009;131: Ding Y, Liu Y-X, Wu W-X, Shi D-Z, Yng M, Zhong Z-K. Evlution of iochr effects on nitrogen retention nd leching in multi-lyered soil columns. Wter Air Soil Pollut. 2010;213: Zheng H, Wng Z, Deng X, Herert S, Xing B. Impcts of dding iochr on nitrogen retention nd iovilility in griculturl soil. Geoderm. 2013;206: Yo Y, Go B, Zhng M, Inyng M, Zimmermn AR. Effect of iochr mendment on sorption nd leching of nitrte, mmonium, nd phosphte in sndy soil. Chemosphere. 2012;89: Dvidson D, Gu FX. Mterils for sustined nd controlled relese of nutrients nd molecules to support plnt growth. J Agric Food Chem. 2012;60: Chen D, Suter H, Islm A, Edis R, Freney JR, Wlker CN. Prospects of improving efficiency of fertiliser nitrogen in Austrlin griculture: review of enhnced efficiency fertilisers. Soil Res. 2008;46: Richrds JE, Digle J-Y, LeBlnc P, Pulin R, Ghnem I. Nitrogen vilility nd nitrte leching from orgno-minerl fertilizers. Cn J Soil Sci. 1993;73: González ME, Ce M, Medin J, González A, Diez MC, Crtes P, et l. Evlution of iodegrdle polymers s encpsulting gents for the development of ure controlled-relese fertilizer using iochr s support mteril. Sci Totl Environ. 2015;505: Trn CKT, Rose MT, Cvgnro TR, Ptti AF. Lignite mendment hs limited impcts on soil microil communities nd minerl nitrogen vilility. Appl Soil Ecol. 2015;95: Singh B, Mcdonld LM, Kookn RS, vn Zwieten L, Butler G, Joseph S, et l. Opportunities nd constrints for iochr technology in Austrlin griculture: looking eyond cron sequestrtion. Soil Res. 2014;52: Jirk S, Tomlinson T. Stte of the iochr industry survey of commercil ctivity in the iochr field. sites/defult/files/stte_of_the_biochr_industry_2013.pdf. 16. Ennis BJ, Lister JD. Prticle size enlrgement. In: Perry R, Green D, Mloney J, editors. Perry s chemicl engineers hndook. New York: McGrw-Hill; p Tng ECW, Perkins E, Hodley AFA, Hpgood KP. Development of lignite grnultion regime mp. In Chemec 2012: qulity of life through chemicl engineering: Septemer 2012, Wellington, New Zelnd. Engineers Austrli, Brton, A.C.T, p Bergins C. Kinetics nd mechnism during mechnicl/therml dewtering of lignite. Fuel. 2003;82: Potter OE, Beey CJ, Fernndo WJN, Ho P. Drying rown col in stemheted, stem-fluidized eds. Dry Technol. 1983;2: Forster JC. JC: 3-Soil smpling, hndling, storge nd nlysis. In: Kssem A, Nnnipieri P, editors. Methods in pplied soil microiology nd iochemistry. London: Acdemic Press; p Mirnd KM, Espey MG, Wink DA. A rpid, simple spectrophotometric method for simultneous detection of nitrte nd nitrite. Nitric Oxide. 2001;5: Hignett TP. Physicl nd chemicl properties of fertilizers nd methods for their determintion. In: Hignett TP, editor. Fertilizer mnul. Dordrecht: Springer; p Mujumdr AS. Superheted stem drying. Hnd Ind Dry. 1995;2:

14 Rose et l. Chem. Biol. Technol. Agric. (2016) 3:10 Pge 14 of DeLuc TH, Gundle MJ, McKenzie MD, Jones DL. Biochr effects on soil nutrient trnsformtions. In: Lehmnn J, Joseph S, editors. Biochr for environmentl mngement: science nd technology. London: Erthscn Pulictions Ltd; p Cyuel ML, Vn Zwieten L, Singh BP, Jeffery S, Roig A, Sánchez-Monedero MA. Biochr s role in mitigting soil nitrous oxide emissions: review nd met-nlysis. Agric Ecosyst Environ. 2014;191: Vn Zwieten L, Singh BP, Kimer SWL, Murphy DV, Mcdonld LM, Rust J, et l. An incution study investigting the mechnisms tht impct N 2 O flux from soil following iochr ppliction. Agric Ecosyst Environ. 2014;191:53 62.