Aged biochar affects gross nitrogen mineralisation and nitrogen recovery: a 15 N study in two contrasting soils

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1 Aged biohr ffets gross nitrogen minerlistion nd nitrogen reovery: 15 N study in two ontrsting soils Shmim Mi 1, Feike A. Dijkstr 1 nd Blwnt Singh 1 1 Center for Crbon, Wter nd Food, Fulty of Agriulture nd Environment, Shool of Life nd Environmentl Sienes, The University of Sydney, Cmden, NSW, 2570, Austrli. Corresponding uthor: Shmim Mi, emil: shmim.mi@sydney.edu.u Abstrt Biohr is pyrolysed biomss nd omprtively more resistnt to biodegrdtion thn to its originl biomss. When pplied to soils, it ould inrese griulturl produtivity through inresed nutrient retention. Here, we exmined the effets of biohr fter 21 months of pplition (20 t/h) in two soil types, i.e., nd, on gross nitrogen (N) minerlistion (GNM) nd 15 N reovery in grsslnd field experiment using 15 N-lbelled mmonium sulphte. The experiment lso inluded phosphorus (P) ddition tretment (1 kg h -1 ). The Demosol is lyey (52% snd nd 29% ly) while the is sndy (82% snd nd 8% ly). We only found n inresed GNM in the, when it reeived both biohr nd P. Biohr long with P ddition possibly enhned mirobil tivity in the nutrient limited. Biohr signifintly inresed totl 15 N reovery in the (on verge by 12%) nd redued lehing to sub-surfe soil lyers (on verge by 52%). Overll 15 N reovery ws greter in the, but ws not ffeted by biohr or P tretment. The inresed N retention with biohr ddition in the sndy my be due to NH 4 + -N retention t tion exhnge sites on ged biohr in the soil. Our results suggest tht ged biohr my inrese N use effiieny through redued lehing or gseous losses in sndy soils. Key Words: Aged biohr, soil types, P fertilistion, N minerlistion, N use effiieny Introdution Biohr is pyrolysed biomss rih in relitrnt rbon (C), nd when pplied to soils, it n potentilly inrese soil fertility nd griulturl produtivity through inresed nutrient retention (Jeffery et l. 2011). Ageing my inrese its potentility further s geing uses formtion of surfe negtive hrge nd CEC (Cheng et l. 2008; Mi et l., submitted), whih however, my tke severl yers to dedes depending on the soil nd biohr properties. Biohr geing in the soil my be regulted by soil minerls, nutrient, orgni mtter ontent nd soil mirobil ommunity. Therefore, the biohr medited effets on nutrient yling in soil my be dynmi, possibly driven by both biohr properties tht hnge over time nd the soil properties tht regulte the geing proess. Nitrogen, vitl onstituent of ellulr orgns of plnts, is often limiting plnt growth due to its high losses in soils through lehing, voltilistion nd denitrifition proesses. Biohr pplition to soil n inrese N retention nd plnt uptke through redued N loss (Steiner et l. 2008).With others possible mehnisms, biohr derived CEC through geing my inrese N retention. Moreover, intertions mong soil- ged biohr-soil orgni mtter my lso ffet GNM (Nelissen et l. 2014). Mirobil tivity nd plnt growth re not only ffeted by N vilbility in soils, but lso by P biovilbility, nd mirobes re often more sensitive to P limittion thn plnts (Clevelnd nd Liptzin 2007). In grsslnds with legume speies, P my beome omprtively more limited thn N. Addition of P, therefore, my inrese mirobil growth nd ould stimulte GNM, prtiulrly in P limited grsslnds. Moreover, high level of P in soil n redue N loss through elevted plnt uptke (Brl et l. 2014), lthough n opposite effet on N loss hs lso been observed (He nd Dijkstr 2015). It is not ler whether biohr, fter being ged in soils, will inrese N retention or not, prtiulrly when stimulus is provided with P ddition. Here, in grsslnd field experiment, we exmined the effets of n ged biohr on GNM nd N retention in plnts nd soils for two different soil types. Mterils nd methods Study site nd biohr field tril The experiment ws onduted t two sites (500 m prt) t Lnsdowne Frm, Cobbitty (34 1'16"S, '56"E) of The University of Sydney. The two sites hve different soil types, i.e., nd (Isbell 2002). In Jnury, 2013, biohr (mde from eulyptus wood, pyrolysed t 550 C) ws pplied (20 Proeedings of the 2016 Interntionl Nitrogen Inititive Conferene, "Solutions to improve nitrogen use effiieny for the world", 4 8 Deember 2016, Melbourne, Austrli. 1

2 t/h) to plots of m. The bsi soil nd biohr properties re presented in Tble 1. A grsslnd ws estblished with 3 grss nd 8 legume speies t plnting rtio of 60% nd 40%, respetively. The grss speies were Phlris quti, Fesut rundine, Bromus wildenowii while the legumes were Medigo stiv, Medigo polymorph, Trifolium subterrneum ssp. brhylyinum, Trifolium subterrneum ssp. subterrneum, Trifolium vesiulosum, Trifolium repens, Trifolium frgiferum, Trifolium spumosum. The plots were irrigted regulrly nd mowed every 2 months, while the biomss ws lso removed. 15 N trer study The 15 N trer study ws strted in September 2014, 21 months fter the biohr pplition to soils. A totl of 96 polyvinyl hloride (PVC) ollrs (10 m in dimeter) were inserted into eh pot. P. quti of similr growth ws seleted s the speies of investigtion. To ll ollrs, 200 mg 15 N/m 2 ws pplied s ( 15 NH 4 ) 2 SO 4 (98% enrihed) by injeting 6 ml solution with three equl injetions t depth of 3 m. Hlf of the ollrs dditionlly reeived 100 mg P m -2 s C(H 2 PO 4 ) 2 long with the 15 N solutions. These six PVCs in eh plot were hrvested in pirs ( 15 N nd 15 N+P) t three different times, i.e., () diretly fter the injetion (T 1 ), (b) on dy 2, (T 2 ) nd () on dy 28 (T 3 ). Plnt biomss ws lipped t ground level while soil smples were olleted t two different depths, i.e., surfe soil (0-6 m) nd sub-surfe soil (6-15 m). Soil ph in wter (1:5, w/v), eletril ondutivity (EC, 1:5 w/v), vilble P (0.03 M NH 4 F M HCl, 1:10, w/v) nd NH 4 + -N nd NO 3 - -N (1 M KCl extrtion, 1:5, w/v) were determined for smples t ll three smpling dtes. The tion exhnge pity (CEC) ws mesured using 1 M NH 4 OA (ph=7) replement method with seprte soil smples (0-15 m). The plnt nd soil smples were dried, ground nd nlysed for 15 N isotopi omposition nd N onentrtions using n isotope rtio mss spetrometer (IRMS). Also, the isotopi omposition of soil NH 4 + ws nlysed fter olletion in filter pper disks enveloped inside PTFE diffusion trps. The GNM ws lulted using the following eqution- GNM = {(N o -N t )/t}*ln{ 15 N 0 (tm %)/ 15 N t (tm %)}/Ln(N o /N t ) Where N 0, N t re the N onentrtion in soil t time zero nd fter 48 h while t is the time the two mesurements (48 h). 15 N 0 nd 15 N t represent the N enrihment (tom%) t zero nd fter 48 h, respetively. The tretments (soil type, biohr, P ddition) nd their intertive effets were nlysed using full ftoril nlysis of vrine with prtil nested design, where plots were nested within soil types. Tble 1. Biohr nd soil properties before strting the field experiment Soil/biohr ph (H 2O) C/N Snd Silt Cly EC (ds/m) CEC (mol /kg) Orgni Biohr Results nd disussion Soil properties After 21 months of biohr pplition, totl C ontent in soil ws signifintly greter (p=0.04) in plots with biohr (2.71%) ompred to the ontrol plots (1.94%) (Tble 2). The totl N ontent ws signifintly greter (p<0.01) in the (1.91%) ompred to the (0.65%). Soil ph ws higher by 0.23 units in the thn the while biohr inresed soil ph on verge by 0.28 units. Similrly, there ws higher EC in the ompred to the, while biohr pplition used n inrese in EC by ds/m. There ws no signifint min or intertive effet of soil type nd biohr pplition on NH 4 + -N nd NO 3 - -N. However, we found signifint intertive effet of soil type nd biohr pplition on vilble P (p<0.01), with n inresed vilble P in the when biohr ws lso pplied. P tretment did not ffet soil vilble NH 4 + or NO 3 - or vilble P. Tble 2. Soil properties 21 months fter biohr pplition Soil types (ST) Biohr pplition (B) Totl C # Totl N ph (H2O) EC (ds/m) CEC # (mol /kg) NH4+ -N NO3 - -N Avilble P - 2.0± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±8-1.9± ± ± ± ± ± ± ± ± ±0. 6.9± ± ± ± ± ±4 b ST NS <0.01 <0.01 <0.01 <0.01 NS NS <0.01 B 0.04 NS <0.01 < NS NS <0.01 ST * B NS NS NS NS NS NS NS <0.01 C Proeedings of the 2016 Interntionl Nitrogen Inititive Conferene, "Solutions to improve nitrogen use effiieny for the world", 4 8 Deember 2016, Melbourne, Austrli. 2

3 * Represents the ombined dt of T 2 (2 dys fter 15 N pplition) nd T 3 (28 dys fter 15 N pplition) while ** represents ombined dt of T 1 (1 dy of 15 N pplition), T 2 nd T 3. # indite tht mesurement ws onduted with whole soil lyer (0-15 m) while rest of the mesurements ws bsed on surfe soil nlysis (0-6 m). Gross N minerlistion Averged ross ll other tretments, biohr pplition signifintly redued GNM by 21.2% (P < 0.05), while P ddition inresed it by 47.5% (P < 0.01, Figure 1). However, biohr deresed GNM in the, while it ws not ffeted in (ST B intertion, P < 0.05). In both soil types, P ddition inresed GNM but with lrger inrese in the (ST P intertion, P < 0.05). In ft, there ws three wy intertion mong soil type, biohr pplition nd P ddition. The highest GNM ws observed in the with both biohr nd P pplition (4.67 mg N/kg/dy), while the lowest GNM ws observed in the sme soil when only biohr ws pplied (1.85 mg N/kg/dy). The redued GNM in the, my be explined by SOM stbilistion into biohr through sorption (Lehmnn et l. 2011) nd further by formtion of orgno-minerl omplexes (Hernndez-Sorino et l. 2015) using redued mirobil tivity. The elerted GNM in the with biohr nd P ddition (Figure 1), indites tht the mirobil tivity in the ws promoted due to greter ess to lbile orgni C (overll, 21% greter lbile C ontent in the biohr reeived plots) nd higher vilble P (Tble 2). Gross minerlistion rte (mg N/ kgsoil/dy) b b Soil type: p>0.05 Biohr pplition: p=0.04 P ddition: p<0.01 ST*B: p=0.02 ST*P: p=0.02 B*P: p>0.05 ST*B*P: p=0.02 b b b 0 Figure 1. Men gross N minerlistion rte in the two experimentl soils with biohr nd phosphorus tretments. Error brs represent one stndrd error. Different letters bove brs indite differenes mong tretment ombintions (post ho Tukey s HSD, P<0.05). Explntion of bbrevitions: B: no biohr, +B: with biohr, - P: without phosphorus ddition, +P: with phosphorus ddition, ST: soil type. 15 N reovery The totl 15 N reovery ws signifintly greter in the ompred to the, t T 2 nd T 3 (P < 0.01, Figure 2), suggesting greter loss of 15 N in the. There ws no overll biohr effet but we found n intertive effet of soil type nd biohr pplition for both hrvests (P = 0.02 for T 2 nd P = 0.01 for T 3 ). The intertion ws more pronouned t T 3, where biohr inresed totl 15 N reovery by 21% in the while there ws no biohr effet in the. At T 2, the ombined effet of biohr nd P tretment redued 15 N reovery by ~9% ompred to biohr without P (biohr P intertion, P = 0.04). At T 3, P ddition slightly inresed totl 15 N reovery in the, but deresed it in the, using signifint intertive effet of soil type P ddition (P = 0.01), but P ddition did not hnge the totl 15 N reovery in either of the soils. Additionlly, we found n intertive effet mong soil type, biohr pplition nd P ddition t T 3 (P = 0.02), where biohr ddition inresed 15 N reovery in the without P, while the 15 N reovery for this tretment ws the highest in the remining unffeted by biohr or P. Proeedings of the 2016 Interntionl Nitrogen Inititive Conferene, "Solutions to improve nitrogen use effiieny for the world", 4 8 Deember 2016, Melbourne, Austrli. 3

4 On verge 40 nd 53% of the 15 N ws reovered in plnts t T 2 nd T 3, respetively (Figure 2). Plnt 15 N reovery ws signifintly greter in the thn in the (P < 0.01). At T 2, biohr pplition hd negtive effet on 15 N reovery in plnts (P < 0.01) with n overll redution of 21%. At T 3, P ddition redued 15 N reovery in plnts by 10% in the, while it did not ffet the 15 N reovery in (soil type P intertion, P = 0.02). In ddition, plnt 15 N reovery in the ws inresed with biohr but without P, while in the neither biohr nor P ddition ffeted the 15 N reovery in plnts (soil type biohr P intertion, P <0.01, Figure 2). The soil 15 N reovery (0-15 m) ws higher in the thn in the t T 3 while it ws opposite t T 2 (P < 0.01). In the, biohr did not hnge the 15 N reovery while it inresed 15 N reovery in the by 36% t T 2 nd 57% t T 3 (Figure 2). The 15 N reovery in the sub-surfe soil (6-15 m) ws generlly muh lower (~0.05%, dt not shown) thn in the surfe soil (0-6 m). At T 3, biohr redued 15 N reovery in the sub-surfe soil of the by 41%, but hd no effet in the (soil type biohr intertion, P = 0.04) but overll, the sub-surfe soil reovery ws lower in the thn in the (P < 0.01). On verge, the totl 15 N reovery ws signifintly greter in the (83%) thn the (63%). The elevted reovery in the resulted from n inresed N reovery in plnts (58% ompred to 37% in the ) s the ws more produtive (on verge 79% greter biomss prodution) thn the. Biohr pplition inresed totl 15 N reovery in the on verge by 12%, while the effet of biohr ws not evident in the. The elevted reovery of 15 N fter biohr pplition ws used by n inresed retention of N in the soil (Figure 2). We propose tht the inresed retention of N my be mnifested through dsorption of NH 4 + -N to the lrger CEC, whih my hve redued gseous N losses nd lehing. 250 A Reovery fter 2 dys (T 2 ) B Reovery fter 28 dys (T 3 ) 15 N reovery (g/m 2 ) b b b b b b b d b d b b b d b 0 Figure 2. Men totl (upper brs) nd soil 15 N reovery (lower brs) t T 2 () nd T 3 (b) in the two experimentl soils with biohr nd phosphorus tretments. Differene between totl nd soil 15 N reovery represents plnt 15 N reovery. Different letters bove brs indite differenes mong tretment ombintions (post-ho Tukey s HSD, P<0.05). For explntion of tretment bbrevitions, see Figure 1. Conlusion Twenty one months fter biohr pplition in grsslnd ontining grss nd lover speies, we found overll deresed GNM in the lyey with nd without P ddition, while n opposite effet ws found in the nutrient poor sndy, when P ws pplied. Biohr pplition my inrese mmoniumbsed fertiliser use effiieny in nutrient poor sndy soils due to n inresed retention of NH 4 + on the exhnge sites ssoited with biohr geing. However, biohr effets on NH 4 + retention my be less effetive in soils tht lredy hve dequte exhnge sites for N retention. Referenes Brl BR, Kuyper TW, Vn Groenigen JW (2014). Liebig s lw of the minimum pplied to greenhouse gs: llevition of P-limittion redues soil N 2 O emission. Plnt nd Soil 374, Cheng C-H, Lehmnn J, Engelhrd MH (2008). Nturl oxidtion of blk rbon in soils: Chnges in moleulr form nd surfe hrge long limosequene. Geohimi et Cosmohimi At 72, Clevelnd CC, Liptzin D (2007). C:N:P stoihiometry in soil: is there Redfield rtio for the mirobil biomss? Biogeohemistry 85, He M, Dijkstr FA (2015). Phosphorus ddition enhnes loss of nitrogen in phosphorus-poor soil. Soil Proeedings of the 2016 Interntionl Nitrogen Inititive Conferene, "Solutions to improve nitrogen use effiieny for the world", 4 8 Deember 2016, Melbourne, Austrli. 4

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