Better Soils. ! An Agricultural Bu reau Project

Transcription

1 < = = Bette Soils! An Agicultual Bu eau Poject

2 =, WHY IS IFE 'N THE SOI IMPORTANT? Biota sustain plant gowth \ojl is alive with billons of micobes, micoscopic animals and lage animals such as temites and cahvoms. \\'ithout this teeming population the soil is clead and unable to sustain plant gowth. Changing the balance Befoe the land vas cleaed soil biota lived in hamonv vith he stable vegetati.e cove. As soon as the tecs and scub vee cleaed, the land plouehed and pastues o cops planted a ne. biological balance had to devciop. 4 1 Tvo way elationship with faming If the iaming vas exploitative '".ith buning, ploughing, no iming and lov fetilize inputs, then the soii micobes and animals suffe and thei numbes decline (scc gaph 1). \\'hen his happens, the soil plocesses vhich ae essentiai fo aqjcultue such as oganic matte beakdovn, nitoecn fixaion, nitogen c.cling and soil stuctue mainenance all decline. This is w'hv ve have to do eelthing possible to maintain an acti\.e h.ing soil population, Remembe. An acive soil biota is essential to impove and sustain agicultual poducion.. \Ve can insue a heakhv soil bv inceasing the iood suppl.fo the micobes and soil animals.. A healthl' food supplv can be achieved dough inceesing esidue etun, inceasing pastue poducdon and maintaining soil ph abo.e 5.5. Tlee maio factos affec:t life in the soil: 1. Input of Plant Residues. Oganic matte is the tuel which dives he soil biota. The highe the inpu of plant esidues the highe the biological activitv and the geate the impovement in soil fedlin. 3 b 't *l ) 2. Soil ph. Soil acidio develops afte land is cleaed and pasues o cops go\.n. This aciditv comes fom pocesses such as:. nitogen fixation bv legumes i:iteq :C I. gowing of shaliou'ooed cop.nd pasuc plns. leaching of mineal nitogen such as nitate. Soil acidiq'is not diecd,caused bt'the use of supephosphate but fathe bv the inceased piant poduction fcillowing the use of fetilizes. J

3 As sols become moe acidic micobial acivin slov's dovn and eatthvons clisappea. T his esults in oganic matte beakdo$'n, nitogen fixation and poducilitl being educed. Rcscach I did some veas ago shovcd that micobial numbes and soil cspiadon moe than doubled when a pnstute soil u'as limed fom ph 4 5 o 6 5. Iiming of aeicult,ial soils is a common Pactice o\esees but hcc in Austalia lming h n, bcn uitle)i ad,'pcd. much to he dimcn oi 'n. p.,j:ctiit. 3. Cultivation. Even time a soil is culdvatcd thee is a ilush in micobiai activiy w'ih a loss of valuable oganic matte and this leads to a beakilovn in soil stuctue. So wheeve possiblc, u,'c nced to minimize cultiadon. Whee do soil biota live? Tl.e majoin'of soil oganisims ae found in the top 1Ocm of soi1. Agicltual pactice s vhich change the envionment in the top 1Ocm oi soil,.'1ll lmpnct on he npe and numbc of soil oganisims pesent. Ilanv soil oganisims ae smalle than soil paicles. If top soil is being lost bv eosion so ae soil oganslms. Figue 1: Soil biota cacy out 5 keyfunctions xuith poduction. which inteact Miofloo Bocel ond fngl hove divese me'obolicopobiiies ond oe the p nc ple oqens lo he cyc ng ot n!lienls e.g nilogen, phosphous ond sulphu. They moy be {ee ivinq o symbioiic ond oclive in the deconiposiion o bildup of ooon c mone. Thev o so he o in $etd6dio. ol sdle soil o9gego s. Micolouno Potozoo ond nemolode oe o cuciol link bei'een micofoo ond oge fono. they eguloie the populotions of bocieio ond {ungl ond ploy o.moio ole in ihe mineolisotion nutienis..o (, =! oo Plonl esidues Funclions Mites ond collembolo feed on lie ond he p Fogmen ogon,c ei,des They oe pfedoos of fungi ond micotouno, ploylng 6n impolonl ole in eouloting micobiol popu olions and nutien l!nove liocofounq Eoahwoms, lemiles ond d!ngbeetles, etc oe impoont bioloo col ooenh loomen,no ooon,.,",i", ond.ot'ni o lc"qe sufoce oeo to be exposed. Theiy olso he p he fom:tion of so oggegoes ono so poes O Conuentonol h oge l No Tilloge Difeenl podaction slslens a/te tbe.hodaeb fo plant uidues beakdoun. Soste: llls.k Gapta CRC Fo lul c,: atd llanag*nent,, \3 sa _ 3ilE; :a :

4 t a t) ) :) UAM THE BENEFTCIA FUNGI THAT FEED PI.ANTS i' iesiy of Adeloide :) :) :l,\iost plants don't just ha'e oots, thev have \ANls vesicula aiuscula mvcohiza. \:AlIs ae fungi vhich live in a hamonious elationship vith plant oos. This is a svmbiosis in v'hich the fung pc,vije hc plan vith.,",u,i",, fom the soil, especiallv phosphous ;nd zinc, in exchanue fo sugas povided bv the plants. About 800,'of all plants, ncluding mos fielcl cops and man\,.teesj habou the iungi as an integal and nomal component oi thei oot s\.stems. {s with all funei \A\Is also help hold soil paticles toqethc. I{ow VAll{S live t D e e a t e a a a,.. f ) i J J 'i'\l 'i4i yat' itside planl oot.. Sutttte: plattt: absettt. Futgi,lite din I )l,ll gettinale font.::.:.:..i:ob. nliens beynd saniues h dead oolfagnes o dead ootja;4uens atul.poes : :..:. tl oal!. as /age s?acj. Ftngi ae dantanl nkntsi4qnet,ao/.. a,be sd/ is dy,. Thee ae about 150 species of the fungi, s'hich mav havc small peicences tb difteent soil t.pes and envionments, but in geneal thev ae all capable of colonising oots of all susceptible plants (see Table 1 fo suscepible/hos cops), vhich is an impotant facto in thei managemen. Some plants, especiallv tees ike Eucalpts, ochids and some heahland shubs, ha.e a diifeent npe of smbioic fungus,hich woks in a simila wa,to \\\I. If vou ae inteested in e\.egetadon lou also need to conside he nge of diffeent beneficial fungi that mav be impotant. Can I see \',\\Is cannot be seen uniess the oot is stained and vieu'ed unde a micoscope. 1. I it soil The \lll fungi do not cause anv disease, so thee is no discolouaion o oo o oots? distotion. This makes it difiicult to detemine vhethe thev ae pesent in the oots o he soil. Hoveve, the chances ae thev $'ill be thee and u,.oking to impove the nuien upake of ou cops and he sebjlin.of vou soil. ack of \AIIs will educe plant gowth but this again mav be hacl to detemne in a p.ddock.iueion.

5 Figue 2: Mycochizal phosphous soil (V'Ms) and. phosphctte esponses in lou' ),lt, 4 +Y \=/ Not inoculoted +** fy ^l l9 116 l* \_' Glomus mosseoe This pictue sbous hou, bath phtqltate Jitilise and I IIIs can ineast te gotl t aj nbc/0c. h lon' P soik the pllttt/s glu uey bad!', bat qovth can lte ittcensed eitl:te b,jililise appli.atiot yhich tlicctll intetses I) supp!1 o b1 AI'ls u:hnh hep tbe plant extacf P evet in the ueut d ictent toi/. 11' the balanu is ight the applitatia ai litili.w axd helpjon I.AlIs can aok ta,uelbe. \AIis extend the plant oot svstem and the whole mvcohiza (funeus plus plant) Hout does can exploit the soil nutients much moe effccicl,han he piant alone. the fungus Some plant nutients, such as phosphous (P) and ztnc (2i1, mo\:e vev slovlv in the Plant soil soiition. ^fheefoe, whcn pn,,.,.., these nutiens fom the soil nca elationship " the oot thee can be a delav befoe thet'ae eplaced at the oot suface.,\,on o; uoh? nutient depletion mav occu nea the oot slowing dou'n plant nutient uptake. The iungi gou,'out into the soil, someimes seveal cenimelcs fom hc oo and pick up nuien: at a distance vhee thev ae still eadilv available. The fungal sands ftvphae) then tanspot the nutients quicklv back o the plen a kind of apid ansi s\'sem o\ ecominq the slov movement in the soil. Toleance to dought can be inceased as he apid tansit svstem ovecomes slov moyement of nutients in dv soil. Thee is no good evidence that the tungi actually tanspot wate. Additionalli, the hlphae ae ve\.', vey naow (onh' about 10 mlhonhs o[ a mee acoss, u le'sl. Tfis means tha thev have a huge suface aea fo nutient absopion and thev can squeeze into soil poes that ae not accessible to ooi which u ill be l0 Ume, o moe, the vijh o[ a VA\{ fungal hpha. YAII hvphae gowing ou of the oots bind soil paticles togethe, hke a 'sacky sting bag'. This impoves soil :.bilit and can help o pc en e.sion. ltlll goa hside lhe oots. Tl:e1, extend be16na/ lhe Tane af natie depletiat. The1, pouide a apid tdnsit gsten fo paa/;' sokble nutients eg P d:zn. i i :a?ete! 5t I

6 ,N l. i..1 tl [] t_ ; sg I F = =! 5 s s Do ttl I plants host I A,I fungi? T'nc 'ees ln't ccime absolutclv fec because thc fungus needs sugas po.ided i. :ht li.nt. I'nde most co.ditions the plan pocluces sugas to spee, so the,cost,,,: slp,ing the fungi is weil in.".ested. This esults in enhanced nutient upakc.i:!i lo eilecive use of fetiuses.,\:.o: S(til' of plan species, including manv impotant cops, do fom \\\I. T.ble 1 liss common cops and vhethe thet ac hos o nonhosts. S,mc imp'tant non hosts vhich neve fom \AlI ae canola and othe membes oi thc cabbage famil; lupins and beets ftee Table 1). Othe famiies of cop plants do host thc fungi, bu the degee to vhich thev cspond o the svmbiosis is vaiable and oiten elates to he speed oi o.t g.,v.h and deelopment of oot hais by the plant and to soil conditions, paticulalv nutient levels. Table 1. Some examples of cops with diffeent e sp o tt s i tt enes s to VAM va.t MODERATE TO OW VERY OW Hout ae l::v alfected b1' soil conditions? fobo becns linseed ond ino o peos ch ckpecs leniis medic velcil subciove lucene cilus lelluce co psicum wheci ools ye A knovieclge of of v'hich cops ae n.n ho:. and u hicl ae highh csponsive could l.elp impo."e cop poductivitl especiallv in soils vith lo.v nutien a,ziiabilit, Ideallv htehlv esponsive cops should not iollov' non hosts. Iack of esponse docs not mean that the beneiicial fungi ae absent. \At{s u'ill continue to multiplv in al1 host cops eg:dless of the cop's esponqi\en(5c. This c.n h.e po.it.e benetl. fo.t e<n(,n\\ e cop l.en the otaion Tab/e 1 pauidu a atgh gtide ta cap espaft elles, bt/l it ij i//,palanl la ale thal lhee uill be taialions u,ith cahiua and sai/ conditia.. To gov and epoduce, \AN{ fungi need living plants w.hich ae hosts. Ilovee, thel'ae adaped to su,ie as'esting stages,in most soil npes and conclitions aound the v'odd, includng hot and dn,, w.et and fozen soils. Thev ae pesent in soils of all textues, fom sand. so s to those w.ith a hiqh ca' content and ae also pesent a a vide ange of soil ph. A mixue of species is usuallv pesent, adapted to the local conditions. The spoes and intecdve oot fagments can suvi.e vel'wel in hot conditions as long as the soil is dy, vhich is impoan fo copping in tiediteanean climates Iike South Austalia, Spoes will become active in moist conditions, but ii host plants ae absent, thev will die. Faise beaks mav educe but cetainlv not eiminate coloni,adon vhen he cop finelh ges going.

7 VA '\,1 clo not usc soil oganic matte as a food souce. Diffeent species can associate with al1 host plant species (bu not thc nonhoss, of coutse). Host plants vill ptoide sugas fo the fungi and so help to maintain populations. Rotations Rotations that inclucle eithe long bae fallow (espcciallv whcn thc soil is.vet) o nonhosts vill educe \i\i populations. The effect of bae fallov has been shovn bv cseach in Queensland, vhee 'ong Fallow Disode' has been iound to bc caused bv low populations of \A\I. Hottt does ntanasemeflt influence VAM? This is because in u,'am moist soils wihout plants, the \ANI sfoe5 geminlc. bu. hei c:nno fintl pl;n. he\' die. I t' fallow pesists fo 12 months o lonqe, he \,'AI1 spoes cen,f;'1'. ] 'l^,l ^,, In South Austaia long fallovs ae not used and often the soil is dv in the summe) so gcmination does not occu and poblems ae much less likeh.. Nonhos cops, like canola, also educe \:\I populations and the amount of VANI in the oots of the folloving cops. At pesent is seems that onc vca of canola vi11 not ceate a majo poblcm, but ii seveal veas of canola o mustads ae go\\.n fo soil fumigation, then the \AlI will be ecluced, ttgethe lith tl.e disease oganisms. oyfalku ll)l spoes,oettinate in uaist sai/. If hosl p/anl aols ae tal aaihhle /be All ai// die. Tillage Conentionai tllage and ohe soil distubance has a negati,e impact on \At{ function. It beaks up tungal theads in soii and destoys thei connections vih the plant so that tiev canno! vok to incease uptake of nutients. Soil compaction This no onh'educes oo gowh. but educes the benehts of \ANI. Reseach is in pogess to iind out how he fungal theads gow though compacted soil and v'hethe some fung ae able to do this bette than othes.

8 E^ {.) l : l ' E,1 1,.., t_ E, _ J t J.) E, ), l Fetilise Pesticides and soil fnigants I{igh fctihse applicaions, especiallv phosphous educe the plant's need fo \i.'\\i and can educe tl.e tungal popllaions too, The effect vaies u'ih the esponsiveness oi tbe cop. \\;l.eat essentiallt'loses its \'\\I patne vlen fctilises ae high, but peas, beans and man.pastue legumes mev still have the \{\I and benefit fom them, but to a }esse degee. Son.e fungicides, ii thev get into the sojl, will educe \ANI populations. NIost hebicidcs do not seem to havc a diect chemical etfect on \i\11, but d"ev do kill the pl:n. and heefoe cduc. hc li ing tl,'d souce of the \l,\{ fungi. Soil fumigants eliminate ll soil biota, including VAII. This can be a poblem in hoiculue. s.pccial it h( cop is padcul:l ecpons\ e u \'.\[. Stubble management Retaining stubbic ','ill etun nutients to he soil and the \ANI vill help to take hese diecdv o tl.e plants. Stubble buning kills VAII, especiallv hot buns. Some eseach has shovn that buning stubble tiom a peanut cop educed the pecentage of the oot length of the next cop fom 72o,io to 16t,./a. Taking into account diffeences in the cop gowth, this tanslated to a educion of \,t\icolomsed oots fom 12 mctes pe plant, to 1.5 metes pe pant. Oganic management has been shown to incease VA,\I populadons in the oots of cfops. D t I u f= f3 f," lo lu I Do VAIII inteact with othe soil oganisms? VAX,Is compete with othe membes of the soil biota fo soil nuients and hence incease the competitive abihw of hei host plants. Thev incease nodulation and nitogen fxation in legumes by supplving the phosohate that is essential io effecti.e nodulation.

9 \A\{ can incease the toleance of plants to some diseases and pests by compensating fo c.ot damge and mt\. c.en have diect ncgxive effects on he clisease causing ogenisms themseh.es. Some soil animais gazc on \'\I hi'phae and spocs, but unless the populations ae cn high ;d ou of balance he gzing m,. acuel.l help lo keq[' he unui.,ung and liqoous and elease nuticnts fom the dead hvphae. Table 2: IIow can I make the most ojf VAM in my soils? DO o Conslde the ole of VAM' in diffeent cops in the ololions. ls the cop o hosi o nonhosl, esponsive o nonesponsive? Will they buid up soi populctions?. lnclude host plcnts in the otolions to buic lp populotions, especio ly ofie o non hosf, essentiol tilloge o stubble buning. imil nonhosls in oiotions, especio ly befoe o vey fesponsive cop o Adopl minimum li loge to o,oid domoge lo :he fungus DON'T. Gow biofumigolion coos like, conoio o muslofds, lo moe ihon one yeo o Gow c high y esponsive cop immediole y che o nonhosf. Use convenliofol tl lcge, except whee eo 1y necessoy lo educe i iseose o Bun slubble evefy yeo. Occosiono buns mcy ce necessoiy

10 Et l' " l t. t. G,1, : G.) E, D_ = fs f" ls I HERBICIDES AND IFE IN THE SOI Appopiate use of hebicides cottld be less destuctie to soil biota CSIRO lond & Woe Pesticidcs ae an essential in moden agicultue. In Austaia ove $E00 million is spent each vea on pesticides, vith 65?'o of this expenditue on hebicides. Ifany hebicides ae apphed diecdv to the soil vhich has lead to questions about thei impact on the soil biota the ife in Soil. 1 tlitese Soil biota consist of a diese anse of oganisms; both floa (micooganisms) and ange of fauna (animals). These oganisms cav out kev soil funcdons and ae gouped bv ogaism both bodv size and function (See figue 1) Fo example the function of nutnen tl,pes and cychng is caied olt bl micoiloa, e.g. bacteia, micofauna e,g, potozoa and species mesofauna e g. collembola (spin.gtails). ca)'oltt All the oganisms invoh'ed in a speciiic function ae gouped and temed a ote ttnctiofl functional goup, eg. nitification is caied out bl nitiiving micooganisms. Agonomic pactices vhich intefee u'ith specific otanisms mal educe he output of a functional goup but mav not cause it to cease. Flou.e.e, this ma. esult in a new population balance which could lead to plant pathogenic oganisms be coming domnant. An undestanding of the impact of diftcent hebicides on vaious soil functions vi11 help fames vok in hamonv vih the soil biota and minimise the impct of hebicides on these functions. Please note: e The following inlomoiion dows on Auslolion ond intenoliona eseoch.. A moioily of hebicide esecch is cbootcy bcsed. This is beccuse fie d fluctuolions in tape ol.e od mo:s'u'e ond te uo cbi y ' py) co od cle;co p opeies of s. o, influence the soil ogonisns lo o geote extent thon the opplicciion of o peslicide. Diecl tcnsfe of esulis fom lob eseoch io fie d siluotions mov not be oooooiote. I im Physical vesus chenical weed contol The appopiate use of hebicides nat'be less destuctive to the soil en,ionment and soil oganisms than taditional veed contol techniques of cultizion and stubble buning, (see gaph 1 ) Fo this to hold tue the follov'ng managemen pactices need o be in plce:. the etention of stubble/oganic esidues, a majo cabon souce fo soil oganisms. lov mte: oi chemical apphclon. a 'ecovev peiod' fo soil biota is aiowed benveen hebicidc applictions. epeated application of the same hebicide within a shot peiod is avoided. 5 tl,

11 Gaph 1: Impact of difjeentfaming biota populations nethods on soil Eothwoms $l Sustoinoble minimm ti loge, siubb e eienlion, oppopiote Fungol Hyphoe fl Toditiono cu voi on/ oun ng Decompose Bocleia Nilogen Fixing Bocieio Ae all chemicals OI(? Appopiatc chemical use wih subble etcnion mav be bette fo soil biota than cultivation and buning but it does not mean that it is 'good' fo soii biota. In geneal soil biota mav be effectcd bv hebicide applications eithe diecth'o indiectl'. A cliect eftect is vhcn the chemical kilis the oganism o inhibits is acti.in. lndiec effects include changes in soil tempetue and moistue due o emoval of veeds, the addiion of weed esidues u'ith iov C:N atios and changes in thc populations of pedatos and pet. Details of the impact of some v:idelv used agicultual hebicides ae contained in table 3. In manv cases thee ae no definidve ansvcs and oniv iimited wok has been caied out in Austa[a. Each hebicide needs to be consideed sepaatel,. Table 3: A summay offtndingsfo a ange of chemicals tested in Austalia o oaeseas. Applicctio of hebicides (such as SUs) sl.ould be quoidecl in situatiots uhee the cop is not obust and clisease leaels in soil ae medium, especiall! it qlkaline soils. T czines Goup C nhntn<',ntho<i< at phoiosysiem ll of Redced ob; i., of icoogo ss o g'o,\,/ o o s. to eigl ^ee.s o:e opp co ion l c'oo ol s ess;. Moy es,, ed.ceo ogen mineolisotion. Moy ccuse inceosed tncicence of p onl diseoses such os Rhizoctonio ond Tokeoii. Some hebicides o so educe colo s: o by myconizol fungi. No infomotion on ong tem effects. Unde long lem field opplicotions genec ly no effect on soil bioto poviding ogonic motte wos continuolly eiuned to the sotl. Sho em efeci on 50 ooc'e.:o esoec ollz. logen fiyes ond.os: involved with nitogen cyc ing. Moy inceose the chonces of sce I.ngo' ''o oo.eoooe.ndceo oiseose.. 70!,'\G S:

12 lal l.ot E) Fi ' ' ' ' : f" 'l H ) ) t ) J "t./ G:'c Disuptes of p onl : cowlh taaucl G'op [ Inhibitos of ciolosynthesis oi p,f ctosystem G yphosole Goup M In h ib ito s of EPSP Soils uith a Iealth)) biota,aal ecoue o compensate bette;fom the shottem,,egatiae ejtfects due to hebicide applicotion. No indicotion of long tem effects. t hos beeniound tc inlefee wifh lecume/hzobio symbiosis. Moy incecse ihe cho nces of some fungo, viol oi nemctcde iniuced iisecses. Negclive e::ecfs hove be: ecoded fci niiogen fixotion by hlzoblo ond educ:ion in co onisclion by mycohizc. long tem effects oe voiob e ond dependont on soil ype cnd envionmenl. Reduced ote ol subble deco:oosiiion when spcyed on 1o slubbie olhe thon on to lhe soi contoining stubb e. Nonsynnbiclic niogen ixing bccle:l oe inhlbilei even oi vety ow concenitoiions. No indicoiion of ony long tem effecis. Nitogen fixotion by egunes i hcs been shown to be educec in some cops. Any negotiv elfects oe dependenl on soil ype. In ecent laboaton'and field sudies caied out in Austalia a ange oi hebicidcs whee appied as single applications a a anqe of aes. The fblloving infomation details the kev esults. Shot tem vesus long ten impact The impact of a hebicide on soil biota mav be e.esible o ievesibie. A evesible impact is one vhee levels of micobial gos,'th ae etuned to'nomal' ove a peiod of time afte a singe application. The duation oi evesible impacts has been lbund to vv vith:. ate of appication. tlpe of hebicide. place of application soil, stubble o plant. fequenc of appication. Results fom both feld and laboatov eseach have shov'n smptoms of micobial stess (educed neu'micobial gowth) even at ecommended ates up o six to eigh weeks following the application some hebicides eg. Gean", ogan" (See tabie.l). These effects vhee found o be soil n'pe dependent. Fo example, in sandv soils with low oganic matte and lov micobial aca.iy the negative effecs oi these hebicides wee tbund to be geate. Table 4: The impact of diffeent chemicals on micobi&l biomass (MB) ancl cctbon dioxide poduction (MA) t f= fs fs J$ Fusllode@ p^,,..1 ^q ^ ll..g Gleon@ Pnnn at@ Bodol@ lnnn n i 1/

13 In simila expciments thc hebicides Allv*, Hoegasso and Pamqlat' u ec epplid dicctl, on to soil vithout anv stubble cove at tlvo and five times the ecommended ate. IIico oganisms wee found to be unde stcss and not functioning popelv si t..k eftc hc eppliction. ln most situations this low level of tunctioning continued up to nine weeks. I Ioweve vu'hen the chemical vas applied dectlv to the soil o to gou'ing plants de stess lime io soil oganisms v.as educed. Nluitiple application of the same o diffeent hebicides within he :i t.., <igh scck vinclov is a common pecdce in b.adece agticultue. The eseach has shown that it takes six veeks fo the micobial activitv o etun to nomal. Consequenth' multiple applications bcfoe the end of thc six to eight week ecoev peiod would be e\pected to educe soil biota function, especiallv if ogamc cabon food souces wee also limited. The duation of this educed biota function mav be less significant than the timing. The majoin of hebicides in boadace copping ae appied aound seeding. A gemination the piant is at its most mlneable as the oot svstem is stiil deeloping. Reduction in biota functions such as nutient elease and disease suooession ml'..,t,,^.t",t,. ;^..,,,.Jp,. o t^,. leave it i, ^^ moe susceptible..,"^^,it, to oot diseases, Application of anothe hebicide pio to thc biota ecoveins fom thc fist hebicide may accentuae the undesiable eiiccts. N{oe eseach vok is needed in this aea. Sttbble is honc to 60?; of the biota pop.tl..tion theejoe. applications to stubble u'ill impact o. q Iage popotion ojf the soil pop..latio A ecoae! peiod of six to eight teeks shoukl be allowed betu,ee.tpplications oj hebicides. Impact on finctions Disease Tansmission Some hebicides v'ee found to akc the balance bctu,'een bacteia and fungi populations nea the plant litte. Fo eample. some S'hcbicides and HoeEassi inceased the popotion of fungi nea litte. This could esult in he govth o[ opponnistic pathogenjc oganisms nea the stubble inceasing he chance of oot diseases development. Oganic Mattc Btcakdown Application of AJh,/'216 Hoegtassu at nvice the ecommended ate educed the abiliw of bacteial populations to usc some oi cabon substaes available fom decomposing esidues and nea the gowing oot. This could esult in a slowe ate of stubble beakdovn and associated nutient mineaisadon. Table 5 illustates tle significan eduction in celluh'tic bacteia and fungi afte hebicides ha.e been aoolied. Table 5: The numbe and pecentege of,nicooganisms oahich can beakdoun cellulose (a majo pat of stcut)found nea wheat stala afte the application of hebicides. popuoon/g suoote Contol taa% % emoining of coniol A ly' % 65 l0 2% c 09, This aak sugges* A@6 is bade on baxeia and Haegasf is noe detinntal /o fin,qi. 72 i N,_

14 E, : l ' t'' F ) l J t ll t i: fs fs Is I' Auoid applicatio of hebicides to legu tes llt.tt ntay ltctte fleg4tite ej[fects on symbi<ttic nitogen fixation Nutient Cycling Clthe u'ok hes shown that the nitifving bacteia, esponsible io the lnsiomadon of ammonia nitogen to plant availablc nitate, ae the mos susceptible to hebicide applicaons. Itoditied applications of fetilize N mx\ be ;ppc,ptiae ) c,,mpensatc fo cduced N minealisation duing the fist six to eight veeks follou'ing hebicide application. Ilebcide effect on mvcohizal colonisation is nvo folded. Fistlv hebicide effect the mvcohizal fungi i self and seconclll hebicides educe oot gowh affecung the available oot length fo mlcohizal colonisation. Gaph 2: Changes in leuels of mineal nitogen afte application a chemical to the soil. Endosulfonl Hoegoss Ally Conkol Rests ae sbop'n.$ a Petentag! oj tlte ntineal nitagen auilable unde the conto/. Ty'te lage pecetta?e s.+qest hlqh le:vk af nineali.atian Q' :oi/ aganisus. Pesticides as food Nlicooganisms feed on simple cabon compounds and agochemicals, theefoe all pesticides, to a lesse o geate exent, can be used as a food souce by the soil biota. Diffeen chemicals vill be used by ditfeent micobes, theefoe populaions of appopiate micobes must be pesent if the pesacide is to be degaded by micobes It mav take cime fo the populadons oi appopiate micobes to buildup. Duing *us peiod these pesticides may ham othe soil oganisms and tempoailv o pemanendv alte the balance of biota populauons pesent in the soil, Sulfonl'lueas ha.e been found to pesistent longe in alkalne soils. I Iou'ec, it is coming to light that in some alkaline soils sulfonluea esidues ae becoming Iess of a poblem. This is thought to be due to an incease in the numbe of ogenisms which beakdovn these chemicals in an alkaline en.ionment. Ilanagement pacdces that couid lead to he buildup of these micobes ae ns lec unknown. Nlicobial degadation of hebicides is an impotan method of beakdown. As the majoiy of micobes in southen Austalian soils ae located in the top 10 cm soil, movement of hebicides bey'ond this zone may esult in longtem ::I'N:J,, ne,ti(cn.c nf hehiilec of N Afie 6 doys I Ahe 24 doys

15 ,N SEARCH OF A RECIPE FOR DISEASE SUPPRESSIVE SOI By Stephen Neote, CS/RO ond and Wote Take hone nessages:. Discase suppessie soils ae found thoughou he wold. \Ve have shown that suppession develops due to changes in soil biologv. Suppession ideniiled in South Austalia is against seveal disease oganisms (pathogens) and exists in ota[ons ' Intensi.e copping and inceased cabon inputs ae associated with the de elopmen of s.ippession. Fo manv veas fames and sciendsts have lbcusecl on the soil oganisms hat cause disease, the pathogens. Hoveve, moe ecentl soil oganisms.vhich pevent disease have been put unde the micoscope and the seach is on fo faming pactices which encouage the multiplication of disease suppessive oganisms. Soil oganisms cav out a angc of funcdons (see Figue 1). One of dese tunctions is disease tansmission and suppession. Suppession s esc,ing the balance beween the soil oganisms in the soil so he pathogens do not dominate. A suppessive soil is one that, despite having conditions tha iaou the esablishment of a disease foming oganism, esults in he pahogen:. eithe not establishing,. establishing but not poducing disease,. esablishing and then dechung Suppession is not the elimination but the contoi of disease ioming oganisms. In agicultue we ae tving to achieve a lelel of suppessiveness which pevents disease le''els that cause economic loss. But suooession is telative a soil mav be suppessie. bu disease a e lou c le el s sill expeienced. Table 6: Adaantages and disadaantages of contolling suppesiae soils disease with. tokes moe inlensve monogemenl. moy esticl flexibility in eo y yeos. eq u ies new skills disecse conkol is noi ochieved ;mnec::a 11. l

16 " l : f: f" i' FE., " t: [ io t [.' h+" il it: ) ).) J t; ll t t fs fs Is Vint. ntoist so//s 'll/l h igh letels of catb(tt t() n it<tgen u'ill hot e liglc leels oj ntic'<tbitl act it it)' 4.l,'elatielJ'haae t h ighe leuel ojf suppession What nakes a soil suppessive? \e,lv all soils ha.e the capacin to suppess cliscase. \Iicobial acdit', which depends on soii moistue, tcmpeetue and the atio of c:bon to nitogen, is the pecuso to suppession. Table J illusates the incease in soil oganisms in suppessile soils compaed to oganism levels in nonsuppessive soil a tiai sitcs in Avon, South Austa[a. Condiions that change biological activiw o elationships benveen ogensm: can effect snppession. \\Iatm, moist soils '"ith high levels of cabon to niogen ','ill have highe levels of mjcobial acti.iw and a elativelv highe leel of suppession. Figue 7: Diffeent leuels of soil biota in suppessiae and nonsuppessiue soil at Aaon SA.,'',icobiol Biomoss neci' siubcle Suvivol ove summe lnoculum to seed/oot Suvivol in Rhizosphee CA45a ' pedot oa ol nccui!m pedoicn in bulk sol ccmpel I on inhoil cn _ cclos Sfn 5AOc75 The degee of suppession vii also clatc to the balance bem'een diseasecausing oganisms and thosc oganisms which feed on these pathogens. Figue 3 iliustates that the le..el of disease inoculum vili vav fom season to season. Consequentl', a soil that is abie to supess modeate levels oi disease incolum mal no be able to suppess diseese in a vea vhen lage amounts of efieci.e disease oganisms haye suvived. Figue 3: Suuiual and effe ctia e n e s s ojf di s e ase inoculumlfom one season to the next ('Captal 1;

17 Table 8: Disease capacit! and stubble decomposition atesfotthe couns / stubble ecoaeedlfomfield incubation uthich contmenced in May. Nonsuppessive Rh izoclon io solon i Toke oli {Ggt) Stubb e b:eckdown?l boken down.lu y 40 cc "" >80% August <2f% >6C7 ju y 5C 60?a >80% /\UgUST lly 25% l2 molhs >7A% Ythee soils ee s/.tppesjbe tl) disea:e leelje// danaliml!' beht:een J 1' atd Atgttsl. At the sante tite ate o snbble beakdov, u.,hich ls caied att bl soil og'uisnts. l,aslhud lo be gedt? /lnde.vtppessic soi/s. Which diseases can be suppessed? In Euope, suppessive soils have been tound o suppess a single disease, fo example Takeall decline. Howeve, this suppession equies a monocultue o be maintained. Reseaches in South Austaia have found soils v'hich ae able to suppess a ange oi diseases unde a ange of cop fipes and which emain sppessi.e o.e diffeent seasons. Table 9: Disease in boad ace copping which may o mcty not be suppessed. PJ.i^f^^ ^!^.^ ^^ To keo Fusoium cown ol Nol suppessed Pythium ool ot CCN Unknown Po! encus What management pac.tices impove suppession? \Iaximising the etun of cop esidues to the soil has been found to incease micobial acti.in and tun a soil into a disease suppessive soil. Subbie etendon and minimising gazing have both been found to help maximise esidue etun. 16

18 *, i: $ F; Table 1O: Case llistoies Management systems uncle uhich disease supession has beenlfound to deaelope. Case Histoy 1: B o o b ctou'ie, South Austalia Soil Wpe: Red Btos'n Eath Anu:l ainfall: 425mm Poduction System: liu o thc dc elopmen of suppcs5i6n. lev famins otation system of wheat and baley cops witi gasst'pasues. sheep hea.ilv gazed pastues In thc ealy 80's mo.ed into. moe intensive copping nd stubble etention. neow sowng points to minimise soil disubance. 70kg DAP 't Zn and 60kg Uea. pastues spaved vea befoe fo weed contol, culiv.ecl atic le bek s ih naow,i()wins points and use of knockdown hebicidcs NIid 90's suppession ecoded Case Histoy 2: ock, South Austslia Soil type: Gey Calcaeous Sandy oan Anual ainfall: 400mm Ptoduction Svsten; Non suppessive soil. pasue/wieatt6alev otation. Unc c,ti ion vjh n,$ s,, ing a,,1n" afe the beak. Roundup thee weeks befoe seeding. Tiflualin betbe seecling 95kg 26:11 + Zn applied vith the seed Suppessive soil. contnuous cop, vhea/bale'/peas totation. onc culivlion u ih n,o,.v sovinu;,.,ins atlc the beak. Roundup thee veeks befoe seeding. Titlualin befoe seeing 95kg 26:11 + Zn applied vith tl.e seed E] Gaph J: Ifow long does it take fo a soil to becone suppes$ive? Suppession develops o.e a peiod oi uming. The duation vill depend on the conditions and the eun of oganic esidues. At Al.on diseasc suppession developed ove ten veas iespective of otadon o tillage. Decline in Rhizoctonio Root Domoge in Diec Dilled Wheof dt Avon ove the Peiod 19829O lnodilied non RaJet 1e95i F : 3 Rool Donoge Roling z (os) /! I i,/./i' ''!.. '... '\ '... '... '\ i... {\, Cu vo'ed PosbGlwheo..." D 4l D,ill Poe//wheo D <O lwh.oilwheo I T t t Yeo FS t. :.: 5C I getter SO t t7

19 FREE N'TROGEN FROM THE AIR Some focts, figues ond ules of thumb By Ross BolloC, SARD/. Bacteia fix nitogen egumes (cloves and lucene) 'fis' nitogen fom the i nt,, a fom u'hich can t,e cscd b hc pl.t. Th' f ocec\ i< cicd ou b he b.cci. Rhiz.,bi sp.. s hch live in the nodules on the legume oot. Symbiosis This is a smbiotic elationship, the plant ecei.es nitogen and d'e bacteia eceive sugas. Slov elease fetilise Niogen fixed b' legumc is oanic ningen.nd acts ike a slov elease fetilise. It becones aailabie o he plan as thc pj.tnesijuc. xe decompo'ed b othe soil oganisms. The pocess of con.eting oganic nitogen to the inoganic fom vhich is available to plants is called mineaisadon. Gasses, ceeals, o the legume mav take up this ino{anic nitogcn. "Rules of thumb" Nitogen fixotion Fo ecch tonne of legume Cy motle, 25kg of niiogen is fixed. A ecsoobe eg::e pcs, ncy t l25kg cf nikogen pe hectce. Thol is eculvo ent to 27akg of ueo. D.:'e Il.gesf,co ::e.' Gaph 4: Pefeed pii angeifo common pastue legumes Medlc.)!octove Boonso ucene Seode lo Sail textue and ainfa/l ai/l also izpact on gavth 18

20 ," t'' t i:!. l!.'. Iloses fo couses Dittccnt legumes need diffeent hizobia. Clo.e hizobia will not nodulee Ilcene. Equalli lucene hizobia u.ill no noduate vetch. Hence, ii lou sov e nes. legume in a pacldock, inocuation should be pacticcd. Ensue you use the coect inoculant stain. Rhizobial inoculants ae alive Remcmbe that hizobial inoculants contain iving bacte ia. Thev ae fagile. Don't expose them to excessive te mpcatue s o fecze them. Avoid miing tlem,ih pesticides and feilises. Sov,'seed as soon as possible afte inoculadon, ino a moist seedbed. Rhizobia equie wam moist soil condidons. Themust be the coect spccics fo he lcqume so ha niogn fidon occus. "Rules of thumb" Assessing nitogen fixotion When P onls oe besi ossessed B'lO weeks ofle geminolion. Whee Thee shcu d be ol eost 5 ed nodu es close to lhe top of the oot system. Red nodules Somelimes ihe nodules needs io be cut 1o see "e ed colo olio White nodules Numeous white nodulescotleed.. c.h.n.. l c^ h. bios.s s noi f ixing nihogen. OId nodule d..t e od. es ('ed)oy u" g een os lnei n fixotion octivi! declines with oge o' p cni stess. in subclove pionls ot f c',,eing, it is common lo obseve thoi a s tle sec,o^ o ode le c ose 'o he p cnl :ool is geen, the nodule lip emolns ei. This ed oec of the nodule is sti tixing nitogen. ',_: sc t Factos that s'ill linit nitogen fixation:. Hot dn soil ' Incompiblin oi hiznbum nd plan. ow pfi. High levels of niogen ienilizc. Impact of ph Soil ph can be the majo imitation to a good s mbiosis ftee gaph 4), Nitogen ixation b, subclove mav decline v'hee soil ph talls below 5. \\'hilst thee ae often sdll hizobia n the sol, thei abin'to nodulae thc clo.e mal be educed. iming to inceese soil ph is the best solution. ucene hizobia ae less toleant of low ph. They ae aelv found in soils u'hee the pij is less than 6. Hence, it is absolutelv essential that lucene seed is inoculatedand lime pelleted at soving. iming to incease soil ph is also a good stategi. 3:TTER SOi 19

21 Gaph 5: Appoximate elationship between atotttts o1f nitogenfixed and legume dy matte poductiott. 254 o z 2CO.9 o.! 100 z 50 o Ba:ed an Peoplet et a/, CSIRO ^ l1 v Edied b: Emma eonatd Jon amb Communications Desigt atd dloul b;,: ightning Designs I//ulatious b1: Angus FegussonSteu'at Jue 2aa0 Bette Soils is suppoted ly Gl'il;l Gains Reseach & Develoomenl Copo'ation e) AND RISOURC[S SA lbfytly"ttdu.!t$$ NatualHeitaqe lus teffi,il,ettfit'aqiiga'', :t) ::