Hindwi Pulishing Corportion Applied nd Environmentl Soil Science Volume 215, Article ID 673264, 8 pges http://dx.doi.org/1.1155/215/673264 Reserch Article Soil Microil Community Structure nd Trget Orgnisms under Different Fumigtion Tretments Sdikshy R. Dngi, 1,2 Jmes S. Gerik, 1 Reecc Tirdo-Corlá, 1,3 nd Husein Ajw 2 1 USDA-ARS, 9611 S. Riverend Avenue, Prlier, CA 93648, USA 2 University of Cliforni, Dvis, 1636 Est Alisl Street, Slins, CA 9395, USA 3 Crops nd Agro-Environmentl Science Deprtment, University of Puerto Rico-Mygüez, Box 9, Mygüez, PR 681, USA Correspondence should e ddressed to Sdikshy R. Dngi; sdikshy.dngi@gmil.com Received 12 Ferury 215; Accepted 13 Mrch 215 Acdemic Editor: Rfel Clemente Copyright 215 Sdikshy R. Dngi et l. This is n open ccess rticle distriuted under the Cretive Commons Attriution License, which permits unrestricted use, distriution, nd reproduction in ny medium, provided the originl work is properly cited. Producers of severl high-vlue crops in Cliforni rely hevily on soil fumignts to control key diseses, nemtodes, nd weeds. Fumignts with rod iocidl ctivity cn ffect oth trget nd nontrget soil microorgnisms. The ility of nontrget soil microorgnisms to recover fter fumigtion tretment is criticl ecuse they ply n importnt role in sustining the helth of griculturl nd nturl soil systems. Fumigtion tril ws conducted in Prlier, CA, nd the study focuses on the effects of different rtes of nd lso methyl romide fumigtion with polyethylene (PE) nd totlly impermele film (TIF) trps on trget nd nontrget soil microorgnisms using field smples. Results indicted tht the popultions of trget orgnisms, such s Fusrium oxysporum nd Pythium spp., werereducedtllrtesoffumignts. Phospholipidfttycid (PLFA) nlysisindictedthtllmjor nontrget soil microil groups such s Grm positive cteri, Grm negtive cteri, fungi, nd rusculr mycorrhizl fungi (AMF) were ffected y methyl romide (MeBr) fumigtion tretment. In generl, the effects of (299 L/h) under PE trp hd the lest impct on microil community structure nd etter effect on controlling trget microorgnisms nd, therefore, indicted the etter option mong fumigtion tretments. 1. Introduction Fumignts re used to control wide rry of soil-orne pests including nemtodes, pthogens, nd weeds. In Cliforni nd Florid, soil fumignts re extensively used to grow strwerries, tomtoes, nd other high vlue csh crops [1]. Therefore, to ensure etter crop yield nd provide greter enefits to growers, soil fumigtion hs ecome n importnt griculturl prctice worldwide [2]. Most of the fumignts re known to hve rod iocidl ctivity [3, 4], ut their effect on soil microil community structure ws not known until recently [5 7]. After the phse-out of MeBr in the United Sttes y Jnury 1, 25, severl other replcements re now in use such s chloropicrin (CP), Telone (1,3- dichloropropene or 1,3-D), methyl isothiocynte (MITC), nd dimethyl disulfide (DMDS). Studies y Iekwe et l. [3] indicte tht MeBr hs the gretest impct on soil microil communities nd 1,3-D hs the lest impct. Also, study y Dngi et l. [8] concluded tht DMDS fumigtion did not impct the ctivity of eneficil microorgnisms. The effects of other recently used fumignts with vrious surfce seling techniques on microil community structure nd iomss re still unknown. The effects of fumignt on eneficil nontrget orgnismstthefieldpplictionrelrgelyunknowndueto theprolemsssocitedwithsmplecollectionsoonfter the ppliction of fumignts nd prtly due to the lck of pproprite methods to descrie microil community composition [3, 9]. Genome-sed nd PLFA pproches cn eusedfornlysisofcommunitystructure.phospholipid ftty cid nlysis provides quntittive iomss mesurement, is very sensitive to environmentl perturtions, cn detect shifts in microil community composition following tretments [1], nd my even e more sensitive in detecting shifts in microil community composition when compred to nucleic cid sed methods [11, 12].
2 Applied nd Environmentl Soil Science The microil community composition chnges s result of fumignt pplictions my led to chnges in the functionl diversity of tht community nd the soil qulity [1]. Microorgnisms in soil re crucil in sustining the helth of nturl nd griculturl soil systems [1] nd significntly contriute to nutrient cycling, orgnic mtter decomposition, plnt nutrient uptke, nd mintennce of soil structure [13, 14]. Therefore, it is very importnt for them to recover fter tretment with fumignts for the development of helthy soils. Fumigtion tretments cuse ltertions in soil microil popultions nd cn contriute to physicl, chemicl, nd iologicl chnges in soil [4, 15, 16]. Severl perturtions during fumignt ppliction re either through trctormounted shnks or through irrigtion systems nd, lso, the use of plstic trps cn impct these soil vriles [17]. Furthermore,theimpctoffumigntpplictionmethodson soil properties needs to e given serious considertion. Soil fumigtion is needed to control soil-orne pthogens such s Pythiumnd Fusrium species [18]. These pthogens hve rod host rnge, cusing generl root or crown rots. Pythium spp. tend to ttck juvenile or herceous plnts, while Fusrium solni cuses generlized root rot nd Fusrium oxysporum cuses vsculr wilt. All of the pthogens re cple of cusing yield reductions of most ornmentl crops currently grown in fumigted soil. The effects of fumignt on the soil microil community structurendiomssswellstrgetsoilpthogensre importnt to gin rod understnding of the iocidl ctivity of these fumignts. Therefore, the ojectives of this study were to determine the efficcy of fumigtion tretments on oth trget (Pythium spp. nd Fusrium oxysporum) nd nontrget microorgnisms (Grm positive cteri, Grm negtive cteri, fungi, AMF, ctinomycetes, nd protozo) insoilndtocompretheseorgnismsinfumigtedversus nonfumigted control soils. We hypothesized tht (1) methyl romide nd high rte of would e effective to control Fusrium oxysporum nd Pythium spp., (2) fumigted plots would result in lower microil iomss thn control soils, nd (3) microil community structure in fumigted soil would e different thn in nonfumigted soils. 2. Mterils nd Methods 2.1. Field Tril, Tretment, nd Plot Description. Fumigtion tril ws conducted in Novemer 211 t the USDA-ARS Sn Joquin Vlley Agriculturl Sciences Center, Prlier, CA.Thefieldplottestsrepresentthectulfieldconditions nd, in the present study s stted in the previous study y Go et l. [17], tretments were replicted three times with rndomized complete lock design to reduce errors from field vriility. Fumignts were shnk pplied nd theplotswere3mlongnd584mmwide.thesoilws Hnford sndy lom (corse-lomy, mixed, superctive, noncid, nd thermic Typic Xerorthents), common soil type of the est side of Sn Joquin Vlley. This soil hd ph 8., 45 ppm dissolved orgnic cron (DOC), nd 22 3% of wter holding cpcity (WHC). Fumigtion nd Tle 1: Fumignt type, ppliction rte, nd method used in Prlier, CA, USA. Tretment Appliction rtes (L/h) Trp Appliction method Bre () 449 Bre Shnk with N 2 delivery () 449 PE Shnk with N 2 delivery () 229 Bre Shnk with N 2 delivery () 229 PE Shnk with N 2 delivery () 229 TIF Shnk with N 2 delivery () 299 TIF Shnk with CO 2 delivery MeBr : CP () 499 PE Shnk MeBr, methyl romide; CP, chloropicrin; PE, polyethylene film; TIF, totlly impermele film. trp instlltion were done with commercil ppliction equipment nd mterils (TriCl, Inc., Hollister, CA). Telone C35 (Dow AgroSciences, Indinpolis, IN; 63.4% 1,3-D nd 34.7% CP) ws pplied t depth of 45 cm with shnks spced 5 cm prt t rtes of 449 (full or mximum lel rte) nd 299 (2/3 rte) L/h. The 2/3 rtes included cronted fumignts y dding CO 2 to fumignt tnk with the purpose to enhnce fumignt dispersion in soil. After fumigtion, the plots were covered with 1-mil PE trp (TriCl, Inc., Hollister, CA) or TIF trp (VporSfe; Rven Industries, Sioux Flls, SD) or left re. Methyl romide : CP (67% : 33%) ws pplied t 449 L/h with Noel plow nd covered with PE trp. The tretments nd other fumigtion descriptions re given in Tle 1.After out4weeksoffieldmonitoringonemissionndsoil fumignt movement, the trps were cut on 22 Novemer 211 nd removed one week lter. 2.2. Smpling. Soil smples were collected fter the trps were removed from upper 15 cm depth. The experiment ws rrnged s rndomized complete lock design with three replictions in ech tretment with totl of 24 plots. Three trnsects were rndomly plced on ech plot nd soil smples were collected from three eqully spced points long ech trnsect nd were composited. Smples for PLFA nlysis were plced in seled plstic gs, stored on dry ice immeditely fter collection, nd then returned to the lortory where they were plced t 2 C freezer until nlyzed. 2.3. Trget Orgnisms nd Soil Physicochemicl Anlysis. Determintion of Fusrium oxysporum nd Pythium spp. popultions ws performed using dilution plting on Komd s medium [19] ndp 5 ARP medium [2]. Soil ph ws determined y using 1 : 1 soil to deionized wter (DI)
Applied nd Environmentl Soil Science 3 Tle 2: Generl properties of Hnford sndy lom t Prlier, Cliforni. Tretment ph EC TC TN DOC C K Mg N S μs % ppm mg/kg 8.11 367.42.6 35.3 29. 152 6.6 6.46 1.84 7.89 615.1 57.6 46.9 198 1.34 8.1 3.21 T 2/3 COTIF 8.8 378.42 52. 28.1 168 6.26 6.71 2.2 T 2/3 NB 8.7 531.18.6 4.7 38.8 181 8.35 9.57 3.28 T 2/3 NPE 8.12 389 2.59.3 44.7 29.2 168 6.26 6.68 1.86 T 2/3 NTIF 8.11 529.13.5 38.8 38.9 225 8.12 7.35 2.44 8.1 469.44.7 37.2 34.6 167 7.28 7.52 2.33 8.3 462.3.8 55.3 32.5 185 7.13 7.47 2.43 Pr > F.29.12.2.7.57.42.18.49.69.3 SE.7 44.4.42.5 9.52 3.89 17.4.9 1.21.49 Mens followed y different letters in column re significntly different y Tukey s test t P <.5. EC, electricl conductivity; TC, totl cron;tn, totl nitrogen; DOC,dissolved orgnic cron,c,clcium; K, potssium; Mg, mgnesium; N, sodium; S, sulfur. (methyl romide, PE trp), (, 2/3 rte, CO2 delivery, TIF trp), T2/3 NB (, 2/3 rte, N2 delivery, re), (, 2/3 rte, N2 delivery, PE trp), (, 2/3 rte, N2 delivery, TIF trp), (, full rte, N2 delivery, re), nd (, full rte, N2 delivery, PE trp). wter rtio. Dissolved orgnic cron ws determined fter sturting the soil with DI wter (1 : 1 soil : wter) for 24 hours, shken for one hour on reciprocl shker, nd filtered through Whtmn numer 42 filter. Cron recovered in the wter extrct ws determined y using Fusion Totl Orgnic Cron Anlyzer from Teledyne Tekmr. Totl nitrogen (TN) nd totl cron (TC) contents were determined y dry comustion with Flsh 2 N & C Soil Anlyzer (Thermo Scientific, Pittsurgh, PA). Mcronutrients such s C, Mg, S, K, nd N were determined using ICP-OES (Vrin, Plo Alto, CA). 2.4. Soil PLFA Anlysis. Phospholipid ftty cids were extrcted from 1 g soil smples using modified Bligh- Dyer methodology [21]. Ftty cids were directly extrcted from soil smples using mixture of chloroform : methnol : phosphte uffer (1 : 2 :.8). Phospholipid ftty cids were seprtedfromneutrlndglycolipidfttycidsinsolid phse extrction column. After mild lkline methnolysis, PLFA smples were qulittively nd quntittively nlyzed using n Agilent 689 gs chromtogrph (Agilent Technologies, Plo Alto, CA) nd ftty cids were identified y retention time ccording to the MIDI eukryotic method (MIDI Inc., Newrk, NJ). Individul PLFA signtures were used to quntify the undnces of specific microil groups in soil smples. Grm positive cteri were identified nd quntified y thepresenceofiso-ndnteiso-rnchedfttycids,grm negtive cteri with monounsturted ftty cids. Fungi were identified nd quntified with 18:2 ω6c, rusculr mycorrhizl fungi (AMF) with 16:1 ω5c, nd ctinomycetes with 1-methyl ftty cids [22 25]. 3. Dt Anlysis Sttisticl nlysis ws undertken using SAS 9.1 [26]. PLFA pek res were comined into iomrker groups. Anlysis of vrince (ANOVA) ws conducted on totl PLFA nd on ech iomrker group in order to see how the totl microil iomss nd the iomss of ech group of orgnisms were ffected y different fumigtion tretments. A multivrite method (cnonicl discriminnt nlysis) ws used to compre soil microil communities from the different concentrtions/fumignts nd to determine similrity mong microil communities in the control nd fumigted soils. In this nlysis, MANOVA on the solute re of ech iomrker ws used to identify the liner comintion of vriles (referred to s cnonicl vrites) tht est seprted the soil microil community structure t the different plots. The cnonicl vrites re grphed to summrize group differences [27 29]. All sttisticl nlyses were evluted t the P <.5 significnce level. 4. Results 4.1. Generl Soil Chrcteristics. In order to understnd the impct of soil fumignts, soil chrcteristics, mcronutrients, nd losses of TC, TN, nd DOC were determined (Tle 2). Totl cron nd TN were significntly lower in methyl romide : chloropicrin fumigtion with PE trp () nd ll rtes of except in 2/3 ppliction rte of with PE trp (T2/3 NPE). Soil ph nd DOC did not significntly differ mong tretments. Among the mcronutrients studied, soil C nd Mg incresed significntly in tretment (46. mg C/kg nd 1.34 mg Mg/kg) compred to cronted with 2/3 ppliction rte with TIF trp () tretment (28 mg C/kg nd 6.26 mg Mg/kg). No significnt differences were oserved in K, N, nd S mong tretments. 4.2. Effects of Fumignts on Trget Microorgnisms. Popultions of Fusrium oxysporum nd Pythium spp. were significntly (P <.5) reduced in methyl romide : chloropicrin fumigtion with PE trp, with 2/3 ppliction rte,
4 Applied nd Environmentl Soil Science Fusrium oxysporum (CFU/g) 3 25 2 15 1 5 Fumigtion tretment Figure 1: Popultions of Fusrium oxysporum in soil smples collected from plots fumigted with (methyl romide, PE trp), (cronted, 2/3 rte, TIF trp), T2/3 NB(TeloneC35,2/3rte,re),(TeloneC35,2/3rte,PE trp), (, 2/3 rte, TIF trp), (, full rte, re), nd (, full rte, PE trp) liter per hectre. Different letters indicte significnt differences (P <.5). Error r indictes stndrd error. 8 7 6 5 4 3 2 1 Fumigtion tretment Figure 3: Totl mount of PLFAs from plots fumigted with (methyl romide, PE trp), (cronted Telone C35, 2/3 rte, TIF trp), T2/3 NB (, 2/3 rte, re), (, 2/3 rte, PE trp), (, 2/3 rte, TIF trp), (, full rte, re), nd (, full rte, PE trp) liter per hectre. Different letters indicte significnt differences (P <.5). Error r indictes stndrd error. Pythium spp. (CFU/g) 12 1 8 6 4 2 2 Fumigtion tretment Figure 2: Popultions of Pythium spp. in soil smples collected from plots fumigted with (methyl romide, PE trp), (cronted, 2/3 rte, TIF trp), T2/3 NB (TeloneC35,2/3rte,re),(TeloneC35,2/3rte,PEtrp), (, 2/3 rte, TIF trp), (, full rte,re),nd(telonec35,fullrte,petrp)literper hectre. Different letters indicte significnt differences (P <.5). Error r indictes stndrd error. nd full ppliction rte with PE nd TIF trps s compred to 2/3 nd full ppliction rte without ny trp nd control plots (Figures 1 nd 2). Furthermore, different trps plyed n importnt role long with the fumignts s re (without trp) plots hve more trget microorgnisms compred to PE or TIF trp. 4.3. Phospholipid Ftty Acid Biomrker Vlues. Totl PLFA concentrtion rnged from 3.497 to 6.4 μgg 1 soil (Figure 3). Methyl romide (),, 2/3 ppliction rte of with TIF trp (), nd full ppliction rte of with PE trp () contined the lowest PLFA nd the nonfumigted control plot hd the highest PLFAcontent.BiomrkerPLFAsforothGrmpositivend Grm negtive cteri were t their lowest concentrtion in soil from the,,, nd (Figures 4() nd 4()). Soils from 2/3 ppliction rte of without ny trp (),, nd full ppliction rte of without ny trp () hd significntly greter concentrtions of oth Grm positive (P <.5) nd Grm negtive (P <.5) cteril iomrker PLFA compred to other fumigtion tretments. Men vlues for mounts of oth the fungl iomrker nd the rusculr mycorrhizl fungl iomrker (Figures 4(c) nd 4(d)) were similr to the ptterns oserved in Grm positive nd Grm negtive iomrker. The vritions to this were the ctinomycetes PLFA iomrker (Figure 4(e)), where the concentrtions in the control plot were significntly lower thn nd high rtes of. Unlike the other PLFAs, men concentrtion of ctinomycetes iomrker ws significntly greter in soils fumigted with compred to control plot. 4.4. Microil Community Structure. Cnonicl multivrite nlysis indictes differences in soil microil community structureetweenthecontrolndfumigtedplots(figure 5). Cnonicl multivrite nlysis suggests tht soil microil communities in fumigted plot re significntly different compred to control nd fumigted plots (P <.5). Plot fumigted with is more similr to,, nd s shown y the closer proximity of iomrker clusters to one nother (Figure 5). Lower reltive undnce of cteri nd fungi ws found in plots fumigted with MeBr.
Applied nd Environmentl Soil Science 5 Grm + cteril PLFA 1.9.8.7.6.5.4.3.2.1 Grm cteril PLFA 1.6 1.4 1.2 1.8.6.4.2 Fumigtion tretment Fumigtion tretment () () Fungl PLFA.35.3.25.2.15.1.5 Mycorrhizl PLFA.25.2.15.1.5 Fumigtion tretment Fumigtion tretment (c) (d) Actinomycetes PLFA.35.3.25.2.15.1.5 Fumigtion tretment (e) Figure 4: Grm positive (), Grm negtive (), fungl (c), mycorrhizl (d), nd ctinomycetes (e) PLFA from plots fumigted with (methyl romide, PE trp), (cronted, 2/3 rte, TIF trp), T2/3 NB (, 2/3 rte, re), (Telone C35, 2/3 rte, PE trp), (, 2/3 rte, TIF trp), (, full rte, re), nd (, full rte, PE trp)liter per hectre. Different letters indicte significnt differences (P <.5). Error r indictes stndrd error. 5. Discussion Appliction of fumignts results in decline of trget nd nontrget soil microorgnisms nd iomss. Previous studies on the effect of fumignts on soil microorgnisms were limited to the lortory microcosm experiment [3, 3, 31], ut the effect of fumignts on the shift in microil community structure under field conditions hs not een documented for mny commercil fumignts nd ppliction methods. Iekwe et l. [3] found negtive effects of 1,3-D nd
6 Applied nd Environmentl Soil Science 2.5 2 Fungi 1.5 Actinomycetes 1.5 2 1.5 1.5.5 1 1.5 2.5 Mycorrhizl 1 Grm+ Grm 1.5 Figure 5: Cnonicl multivrite nlysis of vrince of PLFA iomrkers for Prlier tril. Vectors represent stndrdized cnonicl coefficients nd indicte the reltive contriution of ech iomrker group to ech cnonicl vrite. CP on ctinomycetes nd of methyl isothiocynte (MITC) nd MeBr on Grm negtive cteri using lortory microcosm experiment. There re few studies on either trget [3, 5] or nontrget[18, 32] soil microorgnisms; however, effects on oth trget nd nontrget soil microorgnisms using field smples re not well understood. Our study evluted oth trget soil microorgnisms such s species of Pythium spp. nd Fusrium oxysporum nd nontrget soil microorgnisms such s Grm positive, Grm negtive, AMF, fungi, nd ctinomycetes using field smples. Soil microil iomss (totl concentrtion of PLFAs), lthough not significnt, declined fter ppliction of soil fumignts s compred to nonfumigted control soil. All microil groups, except ctinomycetes, hd lower concentrtion of microil iomss fter fumigtion compred to nonfumigted control soils. Erly lortory studies y Iekwe et l. [3] evluted the effect of different fumignts, such s MeBr, MITC, 1,3-D, nd CP, on soil microil communities nd found tht MeBr hd thegretestimpctnd1,3-dhsthelestimpct.similrly, other studies hve oserved the decline in microil iomss fter fumigtion with different fumignts [5]. As smples re not llowed to e collected immeditely fter MeBr or other fumigtion, studies hve relied on lortory microcosm experiment for sic results fter fumigtion tretments to reflect field conditions [3, 5]. The present study evluted microil community structure nd iomss fter fumigtion tretments using field smples. Susequently, smples were collected only fter out 4 weeks of fumigtion; therefore, the immedite impct on microil community iomss nd structure could not e monitored. The present study showed tht the method of ppliction of fumignts nd the use of trp seem to hve plyed role in microil community structure. Becuse of their high voltility, soil fumignts re sujected to high emission losses nd the plstic trps ply n importnt role s surfce rrier in minimizing emissions [17]. In the Prlier tril, two different trps were used, PE nd TIF. Study lso found tht 2/3 ppliction rte of with PE trp nd re plots hd greter concentrtions of Grm positive cteri, Grm negtivecteri,fungi,ndmycorrhizlplfascompred to TIF trp. Moreover, the use of PE nd TIF trp significntly decresed the trget orgnisms in ll the fumignts used. The popultions of Pythium nd Fusrium were reduced with ll fumignts. However, fumignts were much effective in controlling Pythium spp. compred to F. oxysporum s oserved in the pst experiments [18]. Bre plot contined higher F. oxysporum nd Pythium spp. compred to TIF nd PE trp. The ility of soil microorgnisms such s cteri nd fungi to improve fter tretment with pesticide is criticl for the development of helthy soils [1]. Our study showed tht fungl nd AMF iomss tends to significntly decrese in fumigted soils. Comprle results were reported y Klose et l. [5] on the effect of fumigtion on fungl nd AMF popultions which my e significnt for mngement decisions s there re numerous enefits of fungi nd AMF on crop production nd soil helth [33]. Similr trend ws oserved for Grm negtive nd Grm positive cteril iomss. Previous studies on cteril popultions shifts re vrile [34], s some reports hve suggested tht the soil cteril community fter fumigtion is dominted y Grm negtive cteri [35] while other studies hve reported tht Grm positive cteri recover preferentilly fter fumigtion [3, 31, 36]. Different trend ws oserved in the ctinomycetes PLFA iomrker, where the concentrtions in the control plot were significntly lower thn MeBr nd high rtes of. Severl other studies hve found n increse in ctinomycetes numers following fumigtion [1, 31]. Cnonicl vrite nlysis of PLFA dt indictes differences in soil microil community structure etween the control nd fumigted plots (Figure 5). Cnonicl nlysis suggests tht soil microil communities in the control nd T2/3 NB plots were completely different thn plots fumigted with MeBr nd with trps. Dt points for the control plots were more seprted thn treted plots. This supports the hypothesis tht soil fumignts cn e hrmful tosoilmicroilcommunities,tlestforshorttermfter fumigtion. Microorgnisms possess the ility to give n integrted mesure of soil helth [37] nd iotic fctors cn frequently
Applied nd Environmentl Soil Science 7 lter the nture of popultions nd their iochemicl potentil [14]. Some of the environmentl vriles influencing soil microorgnisms include ph, TC, TN, DOC, nd nutrient supply. Soil ph did not significntly differ mong tretments. Soil TC incresed in higher rte of T2/3 NPE tretments ndsoiltnincresedinlowerrteoftretments. Soil nitrogen input is minly derived from the following sources: N deposition [38]; litter decomposition [39]; nd cteril fixtion of tmospheric N 2 [4]. In our study, the min reson for the increse in soil N nd C ws proly due to smples contining leves, roots, or other tissues in soil. Also, we oserved little chnge in DOC concentrtion mong different tretments. tretment contined significntly greter C nd Mg s ws oserved in the previousstudyyrgndoksh[41], where they found considerle increse in the content of mcronutrients, especilly C nd Mg, in the fumigted soils compred to the nonfumigted control soil. 6. Conclusion Reserch on the impct of rod iocidl ctivity of fumignts on soil microil communities using field smples is unknown. The findings from the present study provide iocidl ctivity of fumignts in field conditions. Our dt hve shown tht the popultions of trget orgnisms were reduced t ll rtes of fumignts. Moreover, mong different rtes of, ws considered etter option due to hving the lest impct on microil community structure nd etter efficiency in controlling typicl soilorne plnt pthogens such s Pythium spp. nd Fusrium oxysporum. Arevitions EC: Electricl conductivity TC: Totl cron TN: Totl nitrogen DOC: Dissolved orgnic cron MeBr: Methyl romide CP: Chloropicrin PE: Polyethylene film TIF: Totlly impermele film. Conflict of Interests The uthors declre tht there is no conflict of interests regrding the puliction of this pper. Acknowledgments The uthors would like to cknowledge Dr. Sudun Go, USDA-ARS-SJVASC, Prlier, CA, for providing reserch site nd reserch guidnce nd Mrs. Ptrici Mungur nd Mrs. Mry Terrzs for ssistnce with field nd l work. Also, the coopertion of Dr. Peter D. Sthl nd Soil Ecology Lortory t the University of Wyoming for gs chromtogrphy nlysis ws gretly pprecited. They lso cknowledge the funding ssistnce provided y the Pcific Are-Wide Pest Mngement progrm for Integrted Methyl Bromide Alterntives to conduct this reserch. References [1] A. M. Iekwe, Effects of fumignts on non-trget orgnisms in soil, in Advnces in Agronomy,vol.83,pp.1 35,Elsevier,24. [2] H. Ajw, W. J. Ntow, R. Qin, nd S. Go, Properties of soil fumignts nd their fte in the environment, in Hyes Hndook of Pesticide Toxicology, pp.315 33,Elsevier,Sn Diego, Clif, USA, 21. [3] A. M. Iekwe, S. K. Ppiernik, J. Gn, S. R. Ytes, C.-H. Yng, nd D. E. 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