L. Bruce Reynolds 1 INTRODUCTION

Transcription

1 NUTRIENT SOLUTION BICARBONATE CONCENTRATION EFFECTS ON GROWTH MEDIA ph, ELECTRICAL CONDUCTIVITY, AND ON FLUECURED TOBACCO YIELD AND QUALITY FOR TRANSPLANTS PRODUCED IN A HEATED GREENHOUSE IN A DIRECTSEEDED FLOAT SYSTEM L. Bruce Reynolds 1 The effects of bicrbonte (HCO 3 ) concentrtions on the production of fluecured tobcco seedlings in directseeded flot greenhouse system were investigted nd compred to seedlings produced in muck seedbeds over threeyer period. The HCO 3 concentrtions used (0, 100, 200, 400, nd 800 mg/l) were creted nd mintined t the desired levels by cidifiction with H 2 SO 4 or by ddition of NHCO 3 to tnks contining 100 L of fertilized groundwter. Ech 100 L tnk (tretment) contined four 253cell fom trys nd ws locted in heted nd forcedir ventilted doublepoly greenhouse mintined t 15 to 30 C. Excellent qulity seedlings were produced in ll tretments except the 800 mg/l HCO 3. Initil nutrient solution ph vried with HCO 3 concentrtion nd declined linerly with time for ll tretments. Initil plug medi ph lso vried with HCO 3 concentrtion; ph incresed for bout 25 d then declined to level just bove tht of the nutrient solution ph. Chnges in solution nd plug medi ph were ttributed to HCO 3 dditions nd loss to the tmosphere, dditions of H 2 SO 4 nd cidic fertilizers, nd uptke of nutrients by the seedlings. Electricl conductivity (EC) of the nutrient solution incresed for the first 30 d due to the evportion of wter nd the ddition of H 2 SO 4, NHCO 3, nd fertilizer, but then declined s nutrients were consumed by the seedlings. EC vlues of plug medi vried with HCO 3 concentrtion, but remined well below levels considered toxic to plnt growth. Nitrogen loss from the 800 mg/l tretment, which filed to produce ny significnt plnt growth, ws ttributed to the formtion of queous mmoni tht ws eventully lost to the tmosphere. Nitrite nitrogen concentrtion vried from 0 to 3.3 mg/l, but ws not correlted with seedling dmge in preliminry trils. Flot system seedlings were 1.6 cm tller t time of trnsplnting, 3 cm shorter in erly July, nd required 2.7 d longer to flower thn seedlings produced in the muck seedbed; yield nd qulity were similr. Excellent qulity flot system seedlings cn be grown with untreted wter tht contins up to 400 mg HCO 3 /L (6.6 meq L 1 ) in heted greenhouses. Additionl key words: Nicotin tbcum, stunted growth, mmoni. INTRODUCTION In Ontrio, fluecured tobcco (Nicotin tbcum) seedlings hve trditionlly been grown in muck seedbeds in unheted greenhouses (2, 21) or in overhedwtered plug trys in heted greenhouses (19). Over the pst 7 yr number of Ontrio tobcco growers hve tried flot system (14) for seedling production with vrible, but predominntly successful results. Currently, bout 15% (D.L. Vn Hooren, Tobcco Specilist, Ontrio Ministry of Agriculture, Food nd Rurl Affirs, personl communiction) of Ontrio growers produce t lest prt of their trnsplnt requirements by this method in heted greenhouses. For the first 20 to 30 d in the flot system, seedlings re in subirrigted soilless (pet, perlite, vermiculite) medium with the wter level bout 4 cm below the surfce. This provides growing environment tht is very wet in comprison to muck seedbeds or overhed wtered plug trys. Under fvorble temperture conditions, the seedlings roots protrude through the bottom of the try by the end of this period nd for the next 25 to 35 d grow in combintion of sturted soilless medium nd hydroponic nutrient solution. High bicrbonte (HCO 3 ) levels my hve multiple dverse ffects on plnts, including low shoot dry mtter content on celery (13), chlorosis resulting from Fe 1 Agriculture nd AgriFood Cnd, Southern Crop Protection nd Food Reserch Center, P. O. Box 186, Delhi, Ontrio, N4B 2W9. deficiency in celery (20), severe chlorosis, slow growth rtes nd stunting on tomto nd petuni (4), nd chlorosis, stunting, nd low plnt vigor in tobcco seedlings produced by the flot system (14,15). Acidifiction to neutrlize 80% of the vilble HCO 3 (15) or to reduce HCO 3 levels to < 60 mg/l (6) re recommended. Groundwter in the Southwestern region of Ontrio typiclly contins 230 to 450 mg HCO 3 /L (3.8 to 7.4 milliequivlents (meq)/l). Acidifiction to reduce HCO 3 levels in groundwter is n dditionl lbor input nd expense for the grower, including the cost of the cid nd for the wter nlysis ($40 CAN per smple in 1998). These nlyses re necessry to determine the HCO 3 levels nd thereby the mount of cid to be dded per liter of wter in the flot tnks. Wter volume in the flot tnk must lso be ccurtely estimted in order to clculte the correct mount of cid to dd. Another smple nd nlysis fter the ddition of cids, or t lest ph check, often is recommended to verify the ccurcy of the procedure. Acidifiction is further complicted by the number of cids tht re vilble to growers (nitric, phosphoric, hydrochloric, nd sulphuric) nd the necessity to compenste for the nitrogen nd/or phosphorus content of the cid when clculting future fertilizer dditions to the flot tnks. The cids lso vry widely in concentrtion, prticulrly sulphuric cid, nd the units tht re used to express concentrtion (normlity, molrity, specific grvity, percent, etc.). Finlly, vrious lbortories nd grower publictions use different units to express the concentrtion of HCO 3 (mg HCO 3 /L, ppm HCO 3 with meq weight = 61 Tobcco Science (2000) 44:

2 mg for most Ontrio lbortories nd grower publictions versus mg/l HCO 3 s the CCO 3 equivlent with meq weight = 50 mg for most USA lbortories nd grower publictions) (6, 14, 15, 17). Observtions mde in preliminry trils conducted in 1994 in unheted greenhouses nd in growers unheted greenhouses with untreted groundwter indicted tht chlorotic stunted growth due to HCO 3 toxicity usully occurs 25 to 30 d fter seeding. In some yers this growth problem severely reduces the number nd qulity of trnsplnts vilble to the grower. Affected trys were occsionlly mixture of stunted yellow plnts nd norml sized green plnts. In every cse the green seedlings hd roots protruding into the tnk nutrient solution, while the stunted yellow plnts were confined to the plug medi. Hmilton nd Lowe (12) observed tht tobcco root tips were killed when exposed to nitrite concentrtions exceeding 5 mg/l in greenhouse hydroponics system. They lso reported tht toxic levels of nitrite could ccumulte in field soils tht contin newly incorported orgnic mtter in combintion with soil moisture levels t or ner field cpcity. They suggested tht toxic levels of nitrite might prevent new root growth in trnsplnted burley tobcco, condition dignosed s orgnic mtter toxicity. The effects of lkline ph nd low oxygen levels on the ccumultion of nitrite nitrogen nd its toxic effects on plnts hve been reported (7,8,18), but their effects on plnt growth in the flot system re not known. In preliminry trils, nlysis of plug medi from flot trys nd from overhed wtered trys tken 14, 19, 22, 28, nd 34 d fter seeding produced mens of 3.3 (men of 28 smples) nd 2.0 (men of 14 smples) mg nitrite/l for the flot system nd overhed wtered plug system, respectively (Reynolds nd Ros, unpublished dt). Despite the fct tht nitrite concentrtions were reltively low in both systems, smll number (<5%) of stunted yellow seedlings per try were observed. Plug trys tht contined both yellow stunted nd norml green seedlings were obtined from locl grower bout 36 dys fter seeding. Anlysis of pired smples (2 stunted nd 2 norml plugs from eight different trys) indicted men nitrite concentrtions of 2.5±0.5 nd 2.1±0.4 mg/l for stunted yellow nd norml green seedlings, respectively (Reynolds nd Ros, unpublished dt). These results suggest tht something other thn nitrite ws ffecting plnts. In greenhouses with supplementry het to mintin minimum of 15 C, no stunted yellow seedlings were observed nd good qulity tobcco trnsplnts were produced with untreted groundwter in reserch trils nd in grower greenhouses. Given the difficulty of flot wter cidifiction nd the uncertin benefits of cidifiction in heted greenhouse, it ws importnt tht the efficcy of this procedure be determined under Ontrio greenhouse conditions. The gol of this reserch ws to determine the effects of nutrient solution HCO 3 in heted greenhouse on nutrient solution ph nd electricl conductivity (EC), plug medium ph nd EC, nd the greenhouse nd field growth of fluecured tobcco seedlings. MATERIALS AND METHODS Greenhouse nd field trils were conducted t the Agriculture nd AgriFood Cnd, Southern Crop Protection nd Food Reserch Center, Delhi frm in 1995, 1996, nd Wood forms (140 cm x 70 cm x 19 cm) were constructed, lined with 6 mil cler plstic, plced in doublewlled heted poly greenhouse, nd filled with 100 L of groundwter contining 0, 100, 200, nd 400 mg/l HCO 3 on 31 Mrch 1995 nd 0, 100, 200, 400, nd 800 mg/l HCO 3 on 27 Mrch 1996 nd Bicrbonte concentrtions were determined by titrtion with 0.05 N HCl (16). The 0, 100, nd 200 mg/l concentrtions were creted by cidifiction with sulphuric cid to neutrlize excess HCO 3. The 400 nd 800 mg/l concentrtions were creted by the ddition of sodium bicrbonte. Chemicl nlyses of the source nd djusted wter tretments were completed (Tble 1). A 1.5 m x 1.5 m muck seedbed ws precision seeded t density of 990 seeds/m 2 nd mintined following culturl prctices recommended for tobcco seedlings grown in greenhouse muck seedbeds. Seedlings from this seedbed were used s check tretment for seedling nd field growth comprisons (2). Four 253cell white polystyrene fom trys per tretment were sown with pelleted seed (cv Delfield) on 5 April, 29 Mrch, nd 1 April in 1995, 1996, nd 1997, respectively, nd plced in the pproprite flot tnks. Ech tnk ws fertilized with 10 g/tnk of N (PlntProd High Nitrte All Seson Feed, 75% NO 3 N + 25% NH 4 N) on 18, 21, nd 19 April nd second 10 g/tnk of N on 12, 14, nd 13 My in 1995, 1996, nd 1997, respectively. This fertilizer hs residul cidity requiring 175 g of CCO 3 /kg of fertilizer to neutrlize. Wter level mesurements nd nutrient solution smples were tken t regulr intervls for the determintion of ph, EC, totl N, nd HCO 3 concentrtions. Nutrient solution volumes nd tretment Tble 1. Men chemicl chrcteristics of groundwter before nd fter mendment to 0, 100, 200, nd 400 mg/l HCO 3 in 1995 nd 0, 100, 200, 400, nd 800 mg/l HCO 3 in 1996 to Tretment ph EC N SO 4 C Mg Cl K P μs/cm mg/l Groundwter Tnk 1 0 mg/l Tnk mg/l Tnk mg/l Tnk mg/l Tnk mg/l b Men of 12 mesurements tken 1995 to b Men of 8 mesurements tken 1996 to Tobcco Science (2000) 44:2734

3 specified concentrtions of HCO 3 were mintined by the ddition of wter, sulphuric cid, nd/or sodium bicrbonte. The greenhouse ws heted to mintin minimum of 15 C nd ventilted with two fns locted t one end to mintin mximum of bout 30 C. Bseline EC (defined s conductivity not relted to fertilizer) incresed prior to fertiliztion due to dditions of wter to mintin tnk liquid volume nd dditions of H 2 SO 4 nd/or NHCO 3 s required to mintin tretment specified bicrbonte levels (Figure 1). Nitrogen concentrtions were estimted by clculting the difference between totl EC nd estimted bseline EC for the dy of smpling nd compring the results to the EC vs. N concentrtion chrts for provided by the fertilizer mnufcturer (mg/l N = ( EC)). Totl N/tnk ws then clculted s the concentrtion x tnk volume on the dy of smpling. Plug try medium smples lso were tken nd diluted 1 volume medium plus 2 volumes distilled wter for the determintion of ph nd EC. Singlerow field plots rrnged in rndomized complete block design with four replictions were estblished on 30, 26, nd 27 My in 1995, 1996, nd 1997, respectively. Seedlings from the four plug trys per flot tnk or the muck seedbed check were trnsplnted into 23 m rows with row spcing of 1.07 m nd plnt spcing of 0.6 m. Seedling height t time of trnsplnting ws Figure 1. Bseline EC for tnk solutions s ffected by dditions of wter to mintin tnk volumes, dditions of sulphuric cid or sodium bicrbonte to mintin tretment bicrbonte levels, nd length of time in greenhouse for combined yr 1996 nd The combined 0 ( ), 100 ( ), nd 200 ( ) mg/l bseline EC estimtes for 1996 nd 1997 = (dy) R 2 =0.99***. The combined 400 ( ) mg/l bseline EC estimtes for 1996 nd 1997 = (dy) R 2 =0.93**. The combined 800 ( ) mg/l bseline estimtes for 1996 nd 1997 were not ffected by length of time in greenhouse nd re estimted s 1250 (μs/cm). determined on subsmple of 10 representtive plnts selected from ech of the four plug trys per flot tretment or on four subsmples of 10 plnts selected t rndom from the muck seedbed. Seedling dry weight t time of trnsplnting ws determined on subsmple of 10 representtive plnts selected from ech of the four plug trys per tretment in 1997 only. Trnsplnt field survivl rte ws determined bout 2 wk fter trnsplnting. Plnt height just prior to bud elongtion ws mesured on 5, 2, nd 7 July in 1995, 1996, nd 1997, respectively. Dys to flower, defined s the time required for 50% of the plnts to hve one or more open florets, ws determined for ech field plot. Tobcco ws hrvested in five primings nd cured in downdrft stick kiln. The tobcco ws sorted into grdes ccording to the Ontrio Frm Products nd Sles Act nd yield, verge vlue, nd gross returns clculted for ech plot (1). Multiple regression nlysis for dt combined over yers 1996 nd 1997, excluding the muck seedbed tretment, were conducted on the nutrient solution nd plug medi ph nd EC vlues, fertilizer dditions, HCO 3 concentrtion, nd number of dys in greenhouse using the regression procedure of CoHort Softwre (Version 5.922, Box 19272, Minnepolis, MN.). Anlysis of vrince ws conducted on ech of the remining mesured or clculted vribles, excluding the muck seedbed tretment, using the Generl Liner Model (GLM) procedure of CoHort Softwre nd the comprison of tretment mens tested t the 0.05% probbility level by Lest Significnt Differences. The muck seedbed check ws compred to the HCO 3 tretments by single degree of freedom contrsts. While significnt yer effects were observed for some vribles, no significnt yer by tretment interctions were observed for the seedling nd field growth dt. Therefore, dt combined over yers re presented. RESULTS AND DISCUSSION Men HCO 3 concentrtions mintined in the flot tnks were close to desired levels for ll three yrs of the study (Tble 2). Significnt mounts of nutrient solution volume were lost to evportion, nd rnged from 2.0 L/m/d for the first 14 d to 2.8 L/m/d for the lst 14 d in the greenhouse. The volume of nutrient solution lost by the 800 mg/l HCO 3 tretment ws not significntly different thn the other tretments. Due to the need to replenish wter lost Tble 2. Men bicrbonte concentrtions mintined in flot tnk nutrient solutions for 46, 55, nd 63 dys in yers 1995 to Tretments Men mg/l Tnk 1 0 mg/l 37±4 b 27±5 43±9 35±4 Tnk mg/l 109±10 88±5 108±10 103±5 Tnk mg/l 195±12 172±6 196±15 189±7 Tnk mg/l 376±10 401±9 402±29 395±13 Tnk mg/l N/A 769±24 719±55 741±26 Mens of 11, 12, nd 17 determintions in 1995, 1996, nd 1997, respectively. b ± Stndrd error of the men. Tobcco Science (2000) 44:

4 to evportion with untreted groundwter nd loss of HCO 3 to the tmosphere s CO 2, the mintennce of tretment HCO 3 concentrtions required regulr mendments with H 2 SO 4 or NHCO 3. A men of 13, 7, nd 0.9 meq of H 2 SO 4 /d/tnk were dded to the 0, 100, nd 200 mg HCO 3 /L tnks nd men of 17 nd 34 meq of NHCO 3 /d/tnk were dded to the 400 nd 800 mg HCO 3 /L tnks. The initil djustment of wter HCO 3 concentrtion significntly ffected solution ph, resulting in mens rnging from 5.7 t 0 mg HCO 3 /L to 8.2 t 800 mg HCO 3 /L. The fertilizer lso dded smll mount of cidity to the nutrient solution, but hd only minor ffect on solution ph. There ws liner decline in nutrient solution ph with time for ll tretments (Figure 2). A fertilizer term (mg/l N dded on given dy), which ws pplicble to the Plnt Products fertilizer used, ws included in the multiple regression formul for surfce response plots s the fertilizer formultion, timing of dditions, nd concentrtion hs direct effect on ph nd EC. Plug medi ph lso ws ltered by the initil HCO 3 concentrtion, but to lesser degree thn the ph effect observed in wter. The ph rnged from 6.0 t 0 mg HCO 3 /L to 6.8 t 800 mg HCO 3 /L fter 2 to 4 d of exposure. Dt indicted tht medi ph incresed for bout the first 25 d for ll tretments, then declined to just bove the nutrient solution ph by 55 d. The mgnitude of ph increse during the first 25 d vried with HCO 3 concentrtion (Figure 2). Nutrient solution EC ws ffected by initil djustments to HCO 3 concentrtion nd incresed with time nd the ddition of fertilizer (Tble 1). Nutrient solution EC nd plug medi EC vried with tretment (Figure 3). Medi EC ws minimlly ffected initilly by HCO 3 tretment, nd, to smll degree, lso tended to increse with time nd the ddition of fertilizer. Agin fertilizer term, specific to the Plnt Products fertilizer used in these trils, ws dded to the multiple regression formule to more ccurtely describe the response surfce. Men plug medi EC level for ll tretments for the first 30 d ws 479 μs/cm nd men plug medi EC level for the 800 mg HCO 3 /L tretment for the first 30 d ws 509 μs/cm. Only the 800 mg HCO 3 /L tretment filed to produce usble trnsplnts (Tble 3). Seedlings in the 800 mg HCO 3 /L tretment filed to develop pst the 4lef stge nd no new growth ws observed fter 25 d. Trnsplnts in the other tretments grew normlly nd could not be seprted by simple visul observtion in the greenhouse. In 1997 only, seedling dry weight t time of trnsplnting ws determined. The 0, 100, 200, nd 400 mg HCO 3 /L tretments produced seedlings of equl dry weights with men of 0.46±0.04 g/plnt. Stem elongtion for the 0 nd 400 mg HCO 3 /L tretments ppered to be slightly less thn for 100 mg HCO 3 /L tretment; however, this minor difference hd no effect on trnsplnt survivl, dys to flower, plnt height in July, yield, verge lef vlue, or gross returns (dt not presented). Single degree of freedom contrsts of the muckbed check plnts ginst plnts from the grouped 0, 100, 200, nd 400 mg HCO 3 /L tretments indicted tht muckbed seedlings were shorter, flowered erlier, nd produced tller plnt by erly July. Bicrbonte in wter exists in equilibrium with tmospheric CO 2 dependent upon wter ph. High concentrtions of HCO 3 cn occur only t high ph; low Figure 2. Surfce response grphs of nutrient solution nd plug medi ph s ffected by bicrbonte concentrtion, ddition of fertilizer, nd length of time in greenhouse for combined yr 1996 nd Nutrient solution ph = (mg/L bicrbonte) 0.001(mg/L fertilizer dded for dy) 0.022(dy) R 2 =0.52***. Plug medi ph = (mg/L bicrbonte) (mg/L fertilizer dded for dy) (dy) (dy) 2 R 2 =0.42***. Figure 3. Surfce response grphs of nutrient solution nd plug medi EC s ffected by bicrbonte concentrtion, ddition of fertilizer, nd length of time in greenhouse for combined yr 1996 nd Nutrient solution EC = (mg/L bicrbonte) + 4.3(mg/L fertilizer dded for dy) (dy) 0.61(dy) 2 R 2 =0.75***. Plug medi EC = (mg/L bicrbonte) 0.23(mg/L fertilizer dded for dy) (dy) 2 R 2 =0.34***. 30 Tobcco Science (2000) 44:2734

5 concentrtions occur t low ph. Gseous CO 2 (8) is either bsorbed or relesed in response to chnging ph s illustrted by the following generlized formul (6): CO 2 + H 2 O H + + HCO 3 Therefore, the mendment of groundwter to produce different nutrient solution HCO 3 concentrtions lso ffected ph nd incresed solution EC due to the SO 2 4 or HCO 3 ions dded. For the 0 mg HCO 3 /L tretment, the SO 2 4 concentrtion ws just bove the 200 mg/l mximum recommended level nd for the 800 mg HCO 3 /L tretment the N level ws well bove the 60 mg/l mximum recommended level (6). Tobcco is very tolernt of N +, however, nd in pst trils flot tnks contining 190 mg N + /L produced tobcco seedlings of equl qulity to those grown in flot tnks with <10 mg N + /L nd <100 mg HCO 3 /L (Reynolds, unpublished dt). Evportion resulted in concentrtion of slts t the medi surfce, but the men plugmedium EC ws <500 μs/cm for the first 30 d, which is well below the 1750 μs/cm soluble slts toxicity threshold for soilless medi EC bsed on 1:2 dilution (5). It is possible tht some of the evportive loss observed ws directly from the wter surfce rther thn through the plug try vi the soilless medium; less thn 5% of the nutrient solution surfce ws exposed. It does not pper tht slt concentrtions becme problem in ny tretment, t lest for the first 25 d, nd overll conditions for seedling germintion nd growth were well within cceptble limits. Erly plnt growth proceeded normlly for ll tretments. Nutrient solution ph declined linerly for ll tretments, indicting net increse in H + ions over time. This response ws expected in the 0 mg HCO 3 /L tretment given the regulr mendments with H 2 SO 4 to mintin low HCO 3 concentrtions, but not in the 800 mg HCO 3 /L tretment, which ws lkline initilly nd received regulr mendments of NHCO 3 to mintin high HCO 3 concentrtions. In the 0, 100, nd 200 mg/l tretments, HCO 3 present in the initil 100 L of wter dded to ech tnk, CO 2 bsorbed from the tmosphere, fertilizer crbontes, nd HCO 3 in the wter dded to replce tht lost to evportion would be the primry mens by which H + ions would be lost in the cidifiction of HCO 3 into H 2 O nd CO 2 ( ). The primry source of H + ions would be the H 2 SO 4 dded to the flot tnk, the residul cidity of the fertilizer nd the uptke of nutrients by the seedling roots protruding into the nutrient solution. Estimtes of the ction/nion contribution from ll sources indicted net ccumultion of H + ions, which my lso explin the decline in ph observed (Tble 4). Bsed on these estimtes nd estimtes of totl N per tnk (Tble 5), one cn suggest tht bout 12.8 g of N/tnk ws tken up by the seedlings (bout 400 g totl seedling dry wt/tnk with N content of 3.2%), bout 2.7 g of N/tnk remined in the tnks t the end of the experiment, nd bout 4.5 g of N/tnk ws lost from the system. For the 400 mg HCO 3 /L tretment the mount of H + ions required to cidify the HCO 3 into H 2 O nd CO 2 ( ) is greter thn the mount of H + dded to the system. The ph, t n initil level of 8.1, is sufficiently lkline tht some clcite (CCO 3 ) nd mgnesite (MgCO 3 ) might be expected to precipitte, which effectively removes lklinity from the system nd thus could reduce the mount of H + required. The following generlized formule by Grdner nd Roth (1984) illustrtes the precipittion of CCO 3 ( ) nd MgCO 3 ( ) in unfertilized groundwter (9): C HCO 3 CCO 3 ( ) + H 2 O + CO 2 ( ) Mg HCO 3 MgCO 3 ( ) + H 2 O + CO 2 ( ) After the ddition of fertilizer in midapril nd erly My, the presence of NH 4 + in the nutrient solution would llow for precipittion of CCO 3 ( ) nd MgCO 3 ( ) s illustrted by the following rection formule (9): C 2+ + HCO 3 + NH 4 OH CCO 3 ( ) + H 2 O + NH 4 + Mg 2+ + HCO 3 + NH 4 OH MgCO 3 ( ) + H 2 O + NH 4 + If one llows for some of the free C 2+ remining in solution to precipitte out s clcite, fter llowing for the C content of the seedlings, then estimting the net ction/nion blnce indictes n ccumultion of H + ions which might explin the decline in ph observed. Tble 3. Effect of bicrbonte concentrtion on seedling growth in greenhouse nd field nd comprison of muck bed seedlings to flot tnk seedlings for combined yers 1995 to Tretment Seedling Height Dys to Plnt Height Plot Yield Averge Lef Gross Returns to Hert Flower in July Vlue cm dys cm kg/h $/kg $/h Tnk 1 0 mg/l 9.9 bc Tnk mg/l Tnk mg/l 10.4 b Tnk mg/l 8.7 c Tnk mg/l b Muck seedbed check Contrsts c * *** * NS NS NS Mens within columns followed by common letter re not significntly different ccording to LSD t P=0.05. b Tnk 5 did not produce ny usble seedlings; therefore, dt not presented. c Single degree freedom contrsts of muck bed seedlings vs 0, 100, 200, nd 400 mg/l HCO 3 flot tnk seedlings. *, *** Denote significnce levels of P=0.05 nd P=0.001, NS denotes nonsignificnce. Tobcco Science (2000) 44:

6 In the 800 mg HCO 3 /L tretment, the declining ph problem is further complicted by the lck of seedling or lge growth fter 25 d. Thus, consumption of solution fertilizer cnnot explin the unexpected loss of bout 4.8 g of N/tnk. At n initil ph of 8.2 some loss of lklinity from the system my occur due to the precipittion of CCO 3 ( ) nd MgCO 3 ( ), but this lone would not be sufficient to produce net increse in H + ion concentrtion nd the observed decrese in ph. One possible mechnism + my be the conversion of NH 4 to queous NH 3 (q) nd H + under lkline conditions (3). The H + relesed by this mount of mmoni voltiliztion might then ccount for the decline in ph observed. Plug medi ph incresed for bout the first 25 d nd then declined for the next 30 d to level just bove the nutrient solution ph. While evportion of nutrient solution through the plug medi would concentrte HCO 3 nd other minerl slts t the medi surfce, nd the loss of HCO 3 to the tmosphere, s previously described would consume H + nd increse the ph, this mechnism cnnot be responsible for the pttern of ph chnge observed in ll tretments. For the 0, 100, 200 nd 400 mg HCO 3 /L tretments, the reduction in ph fter 25 d my be the effect of plnts bsorbing ctions from the medi nd concurrent relese of H + ions to preserve chrge neutrlity in the roots. The eventul depletion of the buffering cpcity of the medium would result in ph decline. However, we lso observed the sme pttern of ph chnge in the 800 mg HCO 3 /L tretment, which did not produce ny significnt plnt or lge growth pst 25 d. It is possible tht in the 800 mg/l tretment, low oxygen conditions were creted in the nerly sturted medium tht ws covered with decomposing lge nd moss. When combined with men ph of 8.5 nd the relese of some orgnic cids from the decomposing medium nd lge, Tble 4. Estimted effects of nutrient uptke on the nion/ction blnce of flot tnk solutions for the purpose of predicting chnges in solution ph. Element Milliequivlent Weight Typicl Elementl Concentrtion Milliequivlents per kg seedling dry weight mg % meq/kg Anions NO 3 N b P (H 2 PO 4 ) S (SO 4 ) Ctions NH4 + N c K C Mg Mn Zn Fe Net chrge blnce (meq ctions/kg seedling dry weight) 1136 Men nutrient concentrtion in tobcco seedlings produced by the flot system in 1991 by Jones et l. (11). Solution contined 150 mg/l N from mg/l N from NH 4 NO 3. b NO 3 N = 75% of vilble N. c NH 4 + N = 25% of vilble N. there my hve been conversion of NH 4 + to NH 3 (q) nd H + (21). Although these compounds were not mesured in this study, relese of orgnic cids nd/or H + ions my explin the decline in medi ph observed. The NH 3 (q) form of nitrogen in soil solution hs lso been reported to be toxic t concentrtions of M to cucumber nd 0.15 M to brley roots nd might well be the cuse of both the stoppge of tobcco seedling growth observed some 20 to 30 d fter seeding s well s the decline in ph (8,10). Nutrient solution EC levels initilly incresed, but the mgnitude ws dependent upon the mount of H 2 SO 4, NHCO 3, nd fertilizer dded to the tnk nutrient solutions. For the 0, 100, 200, nd 400 mg HCO 3 /L tretments, the decline strted bout 30 d fter seeding nd suggests the uptke of nutrients by the plnt roots both from the nutrient solution nd from the plug medi. For the 800 mg HCO 3 /L tretment the decline in EC is much less thn observed for the other tretments nd cnnot be ttributed to the uptke of nutrients by growing plnts. For this tretment the decline in EC my be the result of NH 4 + being removed from the solution s NH 3 ( ) nd/or the precipittion of clcite s previously suggested. Plug medi EC chnged very little during the 55 d in the greenhouse, indicting miniml concentrtion of slts due to evportion. This result suggests the uptke of ions from the plug medium by the plnt roots, for those tretments tht produced seedlings pst 25 d, nd, erly in the seson, possible loss of HCO 3 ions to the tmosphere s CO 2 ( ). Lter in the seson for the 800 mg/l tretment, loss of ions to the tmosphere s NH 3 ( ), nd the formtion of precipittes such s CCO 3 ( ) nd MgCO 3 ( ) might explin the lck of slt ccumultion nd high EC vlues in the plug medi. Also, s previously discussed, it is possible tht not ll of the wter lost evported from the soilless medi surfce. Comprison of the muck seedbed seedlings to those produced in the 0, 100, 200, nd 400 mg HCO 3 /L tretments indicte tht the muck seedbed produced shorter seedling nd tht the erly growth rte, s indicted by plnt height in July, ws greter thn the flot plnts. This result my be due to the type of root system produced by the flot system. Flot plnts develop lrge hydroponic root systems protruding down through the bottom of the try tht my not be effective when trnsplnted into minerl soil, prticulrly dry soil. Observtions of root development in midjune suggest tht the originl root system is of little vlue to the trnsplnt nd tht the bulk of the root system in the field develops s secondry fibrous roots from 2.5 cm portion of the stem just bove the originl root node. In reserch trils, removl of the hydroponic roots from below the try 7 d prior to, or on the dy of trnsplnting did not significntly ffect trnsplnt performnce in the field (dt not presented) nd mny Ontrio growers 32 Tobcco Science (2000) 44:2734

7 Tble 5. Estimtes of totl N, bsed on EC vlue for Plnt Products fertilizer b, in flot tnk nutrient solutions for combined yr 1996 nd Dy Number Tnk 1 0 mg/l routinely remove the roots hnging below the try before trnsplnting s mens of improving the ese nd speed of pulling seedlings. Plot yield, verge lef vlue, nd gross returns of crops produced by muck seedbed trnsplnts were equl to crops produced by flot trnsplnts from the 0, 100, 200, nd 400 mg HCO 3 /L tretments. In conclusion, goodqulity tobcco trnsplnts were produced in flot trys in heted greenhouse with untreted groundwter contining up to 400 mg HCO 3 /L (6.6 meq). These flot system trnsplnts produced equl yield nd qulity compred to trnsplnts from the trditionl muck seedbed system in unheted greenhouses. The mjority of fluecured tobcco growers in Southwestern Ontrio do not need to cidify their flot wter prior to seeding, provided they mintin minimum greenhouse temperture of bout 15 C. The fster germintion nd more rpid seedling growth rtes resulting from supplementl het pper to permit the roots to grow into the nutrient solution before conditions in the plug medi become toxic. Our observtions nd results suggest tht the stunting nd chlorosis observed in unheted greenhouses nd in flot systems contining HCO 3 levels of 800 mg/l my be due to conditions in the plug medi nd not in the nutrient solution. We suggest tht the observed toxicity to smll tobcco seedlings my be the result of NH 3 (q) in the plug medi cting either lone or in conjunction with high ph nd/or high HCO 3 concentrtions to dmge young seedlings. ACKNOWLEDGMENTS Flot Tnk Bicrbonte Tretments Tnk mg/l Tnk mg/l Tnk mg/l The uthor grtefully cknowledges the finncil support of the Cndin Tobcco Reserch Foundtion for this project, ssistnce of Dr. N. Ros nd Mr. C. Cughill Tnk mg/l g/tnk of N ±0.4 c 10±0.5 9±0.5 10±0.8 11± ±0.2 6±0.5 6±0.4 7±0.2 7± ±0.5 4±0.4 4±0.2 5±0.2 7± ±0.3 12±0.4 13±0.4 13±0.1 15± ±0.3 10±0.3 10±0.4 12±0.2 14± ±1.3 7±0.4 7±0.6 10±0.7 14± ±0.2 6±0.2 7±0.3 6±0.2 11± ±0 4±0.4 5±1.7 5±0.3 13± ±0.4 2±0.3 2±0.4 2±0.3 15±0.1 EC clculted s tnk solution EC minus the corresponding tnk bseline EC (see Figure 3). Nitrogen concentrtion estimte in (mg/l) = ( EC). b 10 g N/tnk of Plnt Products dded to ech tretment on 21 April nd 14 My in 1996 nd on 19 April nd 13 My in c Men of 4 determintions for combined yr 1996 nd 1997 followed by the stndrd error of the men. for chemicl nlysis, nd the excellent technicl ssistnce of Ms. Lydi M. Peterson. LITERATURE CITED 1. Anonymous Ontrio Frm Products Grdes nd Sles Act Regultions respecting fluecured tobcco. Ontrio Ministry of Agriculture, Food nd Rurl Affirs. Toronto, Ontrio. Pges Anonymous Tobcco Production Recommendtions, Pub Ontrio Ministry of Agriculture, Food nd Rurl Affirs, Toronto, Ontrio. 3. Adms, F., nd J.B. Mrtin Liming effects on nitrogen use efficiency. Pges , in: Nitrogen in crop production. R.D. Huck, ed. Americn Society of Agronomy. 4. Biley, D.A., nd P.A. Hmmer Growth nd nutritionl sttus of petuni nd tomto seedlings with cidified irrigtion wter. Hort. Sci. 21: Biley, D.A., nd P. Nelson Proceedings: Floriculture crop nutrition workshop. N.C. Stte Univ., Rleigh, N.C. 6. Blom, T., B. Strver, W. Brown, nd J. Hughes Wter qulity for greenhouse crops. Ontrio Ministry of Agriculture, Food nd Rurl Affirs, Toronto, Ontrio. Fctsheet Cecen, F Investigtion of prtil nd full nitrifiction chrcteristics of fertilizer wste wters in submerged biofilm rector. Wter Sci. Tech. 34: Goyl, S.S., nd R.C. Huffker Nitrogen toxicity in plnts. Pges 97120, in: Nitrogen in crop production. R.D. Huck, ed. Americn Society of Agronomy. 9. Grdner, B.R., nd R.L. Roth Applying nitrogen in irrigtion wters. Pges , in: Nitrogen in crop production. R.D. Huck, ed. Americn Society of Agronomy. 10. Hgemn, R.H Ammonium versus nitrte nutrition of higher plnts. Pges 6786, in: Nitrogen in crop production. R.D. Huck, ed. Americn Society of Agronomy. 11. Jones, M.A., G.S. Miner, nd W.D. Smith Production of fluecured tobcco seedlings in greenhouses: I. Effects of medi nd fertiliztion on the directseeded flot system. Tob. Sci. 37: Hmilton, J.L., nd H.L. Richie Orgnic mtter nd N effects on soil nitrite ccumultion nd resultnt nitrite toxicity to tobcco trnsplnts. Agron. J. 75: Msson, J., N. Trembly, nd A. Gosselin Influence of ph nd bicrbonte content of nutrient solutions on growth of celery seedlings cultivted in petbsed medi. Act Hortic. 238: Tobcco Science (2000) 44:

8 14. Rideout, J.W., D.T. Gooden, G.D. Christenbury, B.A. Fortnum, D.G. Mnley, nd R.W. Sutton Tobcco trnsplnt production in greenhouses. Clemson Univ. Coop. Ext. Ser. Cir Rideout, J.W., D.T. Gooden, nd S.B. Mrtin Corrective mesures for growing tobcco seedlings using the flot system with wter high in bicrbontes. Tob. Sci. 39: Suter, A., nd K. Stoub Wters nd slt. Pge 322, in: AOAC Officil Methods of Anlysis: 15 th edition K. Helrich, ed. Assocition of Officil Anlyticl Chemists, Inc., Arlington, VA. 17. Smith, W.D., G.F. Peedin, F.H. Yelverton, nd C.R. Cmpbell Producing tobcco trnsplnts in greenhouses: Wter qulity. N.C. Coop. Ext. Ser. Cir. AG Villverde, S., P.A. Grciencin, nd F. Fdzpolnco Influence of ph over nitrifying biofilm ctivity in submerged biofilters. Wter Res. 31: Wlker, E.K., L.B. Reynolds, nd D.A. Stier Culture of tobcco seedlings in Todd cells. Ontrio Ministry of Agriculture, Food nd Rurl Affirs, Toronto, Ontrio. Fctsheet Wllce, A., nd A.M. AbouZmzm Nitrogen nd bicrbonte reltionships with iron nutrition in plnts. J. Plnt Nutr. 7: Wtson, M., nd Sheidow, N Producing tobcco trnsplnts in Ontrio. Ontrio Ministry of Agriculture, Food nd Rurl Affirs, Toronto, Ontrio. Fctsheet Wells, B.R., nd F.T. Turner Nitrogen use in flooded rice soils. Pges , in: Nitrogen in crop production. R.D. Huck, ed. Americn Society of Agronomy. 34 Tobcco Science (2000) 44:2734