COVER CROP MANAGEMENT IN NO-TILL TOBACCO

Transcription

1 COVER CROP MANAGEMENT IN NO-TILL TOBACCO R.L. Ellis 1, G.D. Morgn 2,3, G.N. Rhodes, Jr 1., nd T.C. Mueller 1 The use of no-till tocco production systems provides opportunities to minimize soil erosion nd reduce production costs. Bsed on the potentil enefits ssocited with no-till in tocco production nd dditionl weed mngement opportunities ville, reserch ws initited to evlute tocco crop growth, yield, nd qulity s well s new weed mngement opportunities in no-till tocco production. In this study, whet ws plnted s winter cover crop nd destroyed prior to trnsplnting in order to otin three whet residue levels. Medium nd high whet residue levels were otined y pplying pre-plnt urn-down hericide t either 30 or 15 d efore plnting, respectively, with no susequent tillge opertions during the growing seson. The low whet residue tretment consisted of conventionl tillge opertions used to incorporte whet residue nd prepre the seed ed for tocco trnsplnting. Two preemergence hericide progrms (sulfentrzone + clomzone nd sulfentrzone + pendimethlin) were superimposed over ech whet residue level tretment. Two tocco types, urley nd drk fire-cured, were trnsplnted into seprte field experiments with modified no-till tocco trnsplnter. Whet residue levels, tocco plnt growth, nd hericide efficcy were ssessed i-weekly for eight weeks fter plnting. Crop yields nd qulity were quntified t the end of the seson. Both no-till tretments mintined higher whet residue levels throughout the seson thn the conventionl tillge tretment. Both hericide progrms provided sufficient erly nd mid-seson control of rodlef signlgrss, smooth pigweed, common rgweed, entirelef morningglory, nd common cockleur. Tocco yields were comprle for ech weed mngement progrm; however, yields were lower in oth no-till tretments (medium or high whet residue) compred to conventionl tillge (low whet residue). Tocco lef qulity ws not influenced y tillge regime or weed mngement progrm. Despite tocco yield suppression in the no-till systems, dequte tocco stnd estlishment nd weed mngement in no-till tocco crop is otinle nd provides opportunities for complince with soil conservtion requirements. ADDITIONAL KEY WORDS: Nicotin tcum, residue, soil conservtion, weed mngement INTRODUCTION Tocco is mjor gronomic crop grown on more thn 290,000 hectres in the U.S. with vlue of over $2.9 illion (20). Tocco must e intensively mnged to otin high yield nd cceptle qulity. Weed mngement costs, including cultivtion, hericides, nd roguing, re significnt portion of totl pest mngement strtegy for tocco. Tocco fields re cultivted severl times within the growing seson due to the limited vilility of leled hericides for tocco weed control (6,18,24). These tillge nd cultivtion opertions gretly increse the potentil for soil erosion nd do not fulfill soil conservtion complince requirements (27). Smll-crege producers re forced to reduce tocco production, otin more lnd, or grow no-till tocco to comply with soil conservtion requirements (24). In ddition to soil conservtion, no-till tocco system my enefit producers y decresing lor nd fuel costs, improving the qulity of lower leves, nd llowing for more timely insecticide nd fungicide pplictions (13,15,21,26). The introduction of sulfentrzone (N-[2,4-dichloro-5- [4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4- trizol-1-yl]phenyl]methnesulfonmide), rod-spectrum preemergence hericide, provides new weed mngement opportunities for tocco producers (5,9,22). Comintions 1 Former grdute student, Professor, nd Professor, Deprtment of Plnt Sciences, University of Tennessee, Knoxville, TN, 37996, nd 2 Assistnt Professor, Rm 349B, Heep Center, Texs A&M University, College Sttion, TX Corresponding uthor: G. D. Morgn; E-mil: gmorgn@g.tmu.edu of sulfentrzone nd preemergence grss hericides provide good control of mny of the prolemtic weeds present in cultivted tocco (4,6,27). Nonetheless, limited informtion is ville on the efficcy of preemergence hericides in no-till tocco systems where pre-plnt incorported hericides re not used. The possiility of comining sulfentrzone nd preemergence grss hericides expnds the possile viility of conservtion tillge in tocco systems. Cover crops re n importnt prt of conservtion tillge systems (28). Winter cover crops provide numerous eneficil functions, including reduced soil erosion, greter soil ggregte stility, enhnced wter infiltrtion, incresed soil orgnic mtter, nd incresed nitrogen recovery (8,10,14). These enefits should prove to e exceptionlly eneficil for soil tilth in long-term tocco production, especilly for fields plnted on rolling terrin. Cover crops lso provide dditionl opportunities for weed mngement ecuse they moderte soil temperture, crete physicl rrier to weeds, nd cn hve llelopthic effects (12,19,21,28). Before cover crops nd no-till systems re recommended to tocco frmers, proper mngement strtegies for the use of cover crops must e determined. Improper mngement of cover crops my prove detrimentl to crop yields due to competition for resources etween cover crop nd the primry crop (7). An importnt mngement strtegy for use of cover crops in tocco production is the timing of cover crop desicction. Delying cover crop desicction until immeditely prior to plnting my deplete soil moisture nd immoilize nitrogen, which would negtively impct the susequent crop. However, delyed desicction of cover crop will increse 44 Tocco Science (2000/2001) 45:44-48

2 mulch levels tht my provide dditionl weed suppression during the growing seson(21). Tocco trnsplnts must hve good root-to-soil contct for the vigorous erly-seson growth tht is importnt in estlishing uniform crop stnd. No-till tocco trnsplnters tht re cple of plcing trnsplnts into undistured soil such tht sufficient soil-to-root contct occurs hve een unville commercilly. Morrison et l. (13) developed modified trnsplnter tht provides greter thn 90% stnd estlishment for urley tocco under notill conditions. Hydroponiclly-grown tocco trnsplnts my lso contriute to the producers ility to otin uniform tocco stnds in no-till systems ecuse of incresed survivl rtes compred to re root trnsplnts produced in outdoor seededs. Incomplete weed control nd lck of suitle trnsplnting equipment hve previously limited the implementtion of sustinle no-till tocco systems. Since no-till tocco systems re importnt to soil conservtion, nd cover crops my improve long-term soil tilth, sustinle no-till tocco system using the current crop nd weed mngement opportunities ws exmined. The ojectives of this reserch were to: 1) evlute efficcy of different hericide comintions in no-till system; 2) investigte whet s cover crop nd determine the optimum time of crop desicction; nd 3) compre yield nd qulity of urley nd drk fired-cured (DFC) tocco grown in conventionl versus no-till system. MATERIALS AND METHODS Field experiments were estlished t the Highlnd Rim Experiment Sttion locted t Springfield, TN in 1999 nd Two seprte studies were conducted ech yer in the sme field for urley nd DFC tocco on Dickson silt Tle 1. Hericide ppliction, tocco trnsplnt, topping, nd hrvest dtes Burley Drk-fired Burley Drk-fired 30 dy urn-down dy urn-down PRE nd PPI ppliction Trnsplnt Topping Hrvest Glyphoste used s urn-down hericide. Prqut used s urn-down hericide. Tle 2. Burley tocco whet residue cover in 1999 nd Cover % Cover % Cover HIGH 43 c MEDIUM LOW 0 c 0 c c 0 c 0 c 0 LSD (P=0.05) Whet residue levels. Dt ws collected t 2, 4, 6, nd 8 weeks fter trnsplnting. c Mens in the sme column followed y the sme letter re not significntly different t P = 0.05, LSD. lom (fine-silt, siliceous, semictive, thermic Glossic Frgiudults). Composite soil smples were tken ech seson nd indicted soil ph of 5.6 in 1999 nd 6.1 in Phosphorus nd potssium fertilizers were pplied ccording to University of Tennessee soil test nlysis nd recommendtions. Split pplictions of mmonium nitrte were pplied s 220 kg h -1 t trnsplnting nd 50 kg h -1 side-dress ech yer. Stndrd culturl prctices were pplied with respect to insect nd disese mngement. Overhed irrigtion ws pplied sed on crop needs to minimize wter s yield-limiting fctor. The field history included soyen-whet rottion for five yers prior to initition of this reserch. Tillge tretments For oth yers, whet ws estlished s winter cover crop in Novemer prior to spring trnsplnting of tocco. Whet ws drilled on 19 cm centers into prepred seeded t seeding rte of 136 kg h -1 nd n ppliction of 70 kg h -1 of nitrogen ws pplied in Ferury. Drk fired-cured cv. TND 950 nd urley cv. TN 90, which re representtive of the region, were plnted in oth yers. Tocco trnsplnts were grown from seed in Styrofom trys in greenhouse flot eds nd were trnsplnted into the field t the two- to three-lef stge of growth (10 to 15 cm shoot height). Inter-row spcing for trnsplnts ws 110 cm nd intr-row spcing ws 51 cm nd 91 cm for the urley nd DFC, respectively. The finl plnt popultion ws 1,700 nd 3,000 plnts per hectre for DFC nd urley types, respectively. Plots were rrnged in split-plot tretment rrngement with four replictes. Min plots (whet residue level) were 4.3 m wide y 36 m in length; nd su-plots (hericide tretments) were 4.3 m wide y 9 m in length. Whet residue levels were creted y using three different methods of mnging the whet cover crop, including conventionl tillge 30 d prior to trnsplnting (LOW whet residue), no-till with whet desicction 30 d prior to trnsplnting (MEDIUM whet residue), nd no-till with whet desicction 15 d prior to trnsplnting (HIGH whet residue). The conventionl tillge tretment consisted of cultivtion using disc hrrow to chop the stnding whet, followed y 25 cm depth moldord plow, nd severl psses with disc hrrow to prepre the trnsplnting seeded. The MEDIUM residue tretment received 1700 g i h -1 of glyphoste [N-(phosphonomethyl) glycine] 30 d prior to trnsplnting. Prqut [1,1 -dimethyl-4,4 - ipyridinium dichloride] ws pplied 15 d prior to trnsplnting t rte of 690 g i h -1 to otin the HIGH residue tretments, due to pre-plnt glyphoste lel restrictions in tocco (23). Both no-till tretments (MEDIUM nd HIGH whet residue) received 690 g i h -1 of prqut, one dy prior to tocco trnsplnting. The whet cover crop ws in the Feekes 10.3 nd Feekes 9.0 growth stge when hericides were pplied to the 15 d nd 30 d prior-totrnsplnt tretments, respectively. All urn-down hericide pplictions were pplied t 140 L h -1 t 6.2 km hr -1 with trctor-mounted spryer. Tocco Science (2001/2002) 45:

3 Tocco ws trnsplnted using modified conventionl tillge two-row tocco trnsplnter (25). A fluted coulter ws dded preceding the shoe to cut through residue nd egin opening slot for the shoe to follow. Approximtely 90 kg of dditionl weight were dded to the rer of ech trnsplnting unit to id in soil penetrtion nd provide more pressure on press wheels. Press wheels were modified to provide etter slot closure nd etter root-to-soil contct. No-till plots were trnsplnted nd then the trnsplnter ws djusted for use in conventionl tillge plots. In 1999, the soil ws dry nd irrigtion ws required to moisten the soil to llow for sufficient trnsplnting depth. Adequte soil moisture ws ville in 2000 nd no trnsplnting prolems were encountered. Whet residue levels did not negtively influence tocco trnsplnting depth, root to soil contct, or tocco stnd. Weed Mngement Tretments Su-plots consisted of two different hericide tretments, hnd weeded (weed-free), nd n untreted weedy control. Both hericide tretments were comintions with sulfentrzone. A preplnt ppliction of sulfentrzone (350 g i h -1 ) tnk-mixed with clomzone [2- (2-chlorophenyl)methyl-4,4-dimethyl-3-isoxzolidinone] t 630 g i h -1 ws pplied immeditely prior to tocco trnsplnting. The second preemergence hericide comintion tretment ws sulfentrzone (350 g i h -1 ) nd pendimethlin [N-(1-ethylpropyl)-3,4-dimethyl-2,6- dintroenzenmine] (930 g i h -1 ). Sulfentrzone + pendimethlin ws pplied s preemergence tnk mix ppliction on the MEDIUM nd HIGH whet residue tretments (23). In conventionl tillge tretments, pendimethlin lone ws pplied nd incorported with trctor-mounted rotry tiller tht ws followed y preplnt ppliction of sulfentrzone to the soil surfce prior to trnsplnting. In 2000, preemergence nd preplnt incorported hericide pplictions were delyed due to rin nd susequently the trnsplnting in 2000 ws postponed n dditionl 2 wk from the initil urn-down pplictions when compred with 1999 (Tle 1). All su-plot hericides were pplied t 170 L h -1 with CO 2 -pressurized ckpck spryer using 8002 flt fn tips operted t 280 kp. Field Mesurements nd Dt Anlysis. A line trnsect method ws used to quntify whet residue levels i-weekly for 8 wk fter trnsplnting (WAT) for ech whet residue level (17). Tocco plnt height nd Tle 3. Drk-fired cured tocco whet residue cover in 1999 nd Cover % % HIGH 51 c MEDIUM LOW 0 c 0 c 0 c 0 c 0 c 0 c 0 c 0 c LSD c (P=0.05) Whet residue levels. Dt ws collected t 2, 4, 6, nd 8 weeks fter trnsplnting. c Mens in the sme column followed y the sme letter re not significntly different t P = 0.05 (LSD). percent hericide efficcy rtings were determined t 2, 4, 6, nd 8 WAT from the two center rows of ech four-row plot. Tocco plnt height ws mesured for 10 rndomly chosen plnts within ech plot. Brodlef signlgrss (Brchiri pltyphyll (Grise.) Nsh) nd smooth pigweed (Amrnthus hyridus) were present in 1999 nd Common cockleur (Xnthium strumrium) densities were sufficient for evlution only in 1999, nd entirelef morningglory (Ipomoe hederce vr. integriuscul Gry) nd common rgweed (Amrosi rtemisiifoli) were evluted only in the 2000 seson. Tocco yields were quntified on weight per hectre sis t the time of mrket preprtion. Tocco ws hrvested from the two middle rows of ech four-row plot. The untreted weedy control plots were not hrvested due to predicted low yields nd grde nd hrvesting complictions ssocited with high weed densities. Ech plot ws evluted nd federl grde ws ssigned (3,11). These federl grdes re ssigned numericl vlues nd grde index ws clculted sed on these vlues. An nlysis of vrince ws clculted using the Proc Mixed nd Proc GLM procedures of SAS (Cry, North Crolin) nd mens were seprted ccording to Fisher s Protected LSD (P < 0.05). Burley nd DFC tocco yield, weed control, nd grdes were comined over yers sed on non-significnt yer-y-tretment interctions. Annul tocco height nd whet residue dt re reported due to significnt yer-y-tocco height nd whet residue interctions. RESULTS AND DISCUSSION The urn-down hericides glyphoste nd prqut provided dequte crop desicction oth yers; however, weed seedlings emerged pproximtely two weeks following the glyphoste urn-down ppliction. Due to undnt emergence of weed seedlings following the whet residue urn-down tretments, prqut ppliction lso ws required prior to tocco trnsplnting to otin weed free trnsplnt ed. Whet residue levels rnged from 43 to 67% for the HIGH whet residue tretments nd 32 to 50% for the MEDIUM whet residue tretments t 2 WAT for oth urley nd DFC tocco (Tles 2 nd 3). The HIGH nd MEDIUM residue plots hd higher initil residue levels 2 WAT in 2000 compred to However, mid-seson whet residue levels (6 nd 8 WAT) remined reltively constnt in 1999, while the residue level decresed throughout the seson in 2000 (Tles 2 nd 3). The higher rte of residue degrdtion in 2000 my e explined y greter rinfll following the glyphoste nd prqut urn-down pplictions in 2000, which incresed the rte of residue decomposition. Whet residue in the HIGH whet residue tretments ws significntly greter thn in the MEDIUM residue tretments 2 nd 4 WAT; 4 WAT levels of whet residue were similr. Some differences in whet residue were oserved etween weed mngement schemes; however, differences were not consistent over mesurement dtes. Tocco plnt height did not differ with whet 46 Tocco Science (2001/2002) 45:44-48

4 residue levels for urley or DFC tocco for 1999 or DFC tocco in Burley tocco height in 2000 ws greter 4 to 8 WAT in LOW whet residue compred to MEDIUM whet residue, ut ws not greter thn the HIGH whet residue (dt not shown). Tocco plnt heights were similr for ll weed control tretments up to 4 WAT, indicting no detrimentl effects from the hericide tretments (6,9). Weed competition in untreted plots resulted in decrese in tocco plnt heights eyond 4 WAT compred to sulfentrzone + clomzone, sulfentrzone + pendimethlin, nd the weed-free tretments (dt not shown). Brodlef signlgrss control ws similr in oth sesons. Brodlef signlgrss control t 2 WAT ws 95% or greter for oth tocco types. At 8 WAT, control hd decresed to 81% nd 92% for urley nd DFC, respectively, cross ll whet residue levels. Though weed control ws sufficient, rodlef signlgrss control ws less in MEDIUM whet residue levels compred to the low whet residue level (dt not shown). No differences were oserved for rodlef signlgrss control etween hericide tretments (dt not shown). Smooth pigweed control remined greter thn 95% for oth tocco types, whet residue levels, nd weed mngement strtegies for ll mesurement dtes. The seson-long control of smooth pigweed with sulfentrzone grees with previous results (4,9,22). Other weeds, including common cockleur, entirelef morningglory, nd common rgweed, were only present in one of the two sesons. In 1999, common cockleur control ws similr for ll whet residue levels. Hericide efficcy ws slightly decresed eyond 2 WAT t HIGH nd MEDIUM whet residue levels. Weed control in urley tocco ws 75% in the MEDIUM residue level t 8 WAT, compred to 95% in the LOW residue level (dt not shown). Differences in common cockleur control in DFC tocco were minor, 90% in the HIGH level compred to 98% in the LOW level, t 8 WAT. Both hericides were eqully effective t mnging common cockleur in urley nd DFC tocco (22). In 2000, entirelef morningglory control remined greter thn 95% up to 4 WAT (9). However, entirelef morningglory control ws lower in the LOW whet residue tretments for DFC tocco thn MEDIUM nd HIGH residue levels t 8 WAT. In urley tocco, whet residue levels did not influence the entirelef morningglory control s drmticlly nd hericide efficcy remined high (dt not shown). Both sulfentrzone + pendimethlin nd sulfentrzone + clomzone provided good control of entirelef morningglory through 8 WAT for Tle 4. Tocco yield nd qulity s influenced y whet residue levels in urley nd drk-fired cured tocco Burley DFC Cover Yield Qulity Yield Qulity kg/h Index kg/h Index HIGH MEDIUM 1457 c LOW Whet residue levels creted. Mens in the sme column followed y the sme letter re not significntly different t P = 0.05, LSD. urley nd DFC tocco. Beginning t 2 WAT in urley nd 4 WAT in DFC tocco, common rgweed control ws lower t low whet residue levels compred to MEDIUM nd HIGH whet residue levels. Plots tht did not receive weed mngement tretment were not hrvestle due to low yields nd physicl impirment cused y extremely high weed densities. Similr to results reported y Wlker et l. (22) nd Breeden et l. (4), no yield differences were oserved in urley or DFC tocco yields mong the investigted hericides (dt not shown). However, urley tocco yields were lower for hericide tretments thn the weed-free check. Tocco yield losses my hve resulted from lte-seson weed competition, primrily rodlef signlgrss, within these tretments, ecuse tocco injury or growth reduction ws not oserved from either hericide. To minimize yield losses in these weed mngement progrms, postemergence ppliction of leled grminicide my e required. Burley nd DFC tocco yields were significntly lower in oth MEDIUM nd HIGH whet residue tretments compred to the LOW residue tretment (Tle 4). In urley, the MEDIUM whet residue tretments yielded less thn the HIGH residue tretments; however, DFC tocco yields were similr t oth whet residue levels. Similr yield reductions in reduced tillge systems with cover crops hve een reported in vrious crops (1,7) nd my e explined y fctors tht influence crop growth, such s nitrogen immoiliztion, soil temperture, soil moisture, nd soil ulk density (2,16). Tocco mngement strtegies my hve to e modified for no-till tocco with cover crop residue present to compenste for these potentilly yield inhiiting fctors. Potentil mngement lterntives include using cover crops with higher C:N rtio thn whet, such s legumes, or dding dditionl nitrogen through fertilizer. Mny of the enefits resulting from no-till crop mngement, such s improved soil properties nd comprle crops yields, my not e evident for severl yers (10). Tocco grde index ws comprle for oth urley nd DFC tocco regrdless of the weed mngement tretment, coinciding with findings y Breeden et l. (4). Whet residue levels did hve positive impct on urley tocco grdes t the MEDIUM residue level compred to the LOW residue levels. No differences in grde index were oserved for DFC tocco t ny whet residue levels (Tle 4). Adequte tocco crop stnd nd development re otinle in no-till system sed on results from this reserch. Once mjor concern, opportunities for erly weed mngement now exist in no-till tocco without the use of field cultivtion. However, mnging no-till progrms with winter cover crop my require devitions from conventionl tillge tocco in order to mximize tocco yield nd qulity. Despite potentil yield reductions, no-till tocco systems provide producers with the opportunity to comply with soil conservtion requirements without the need for dditionl lnd nd without scrificing tocco qulity. Tocco Science (2001/2002) 45:

5 ACKNOWLEDGEMENTS The uthors thnk the frm crew t Highlnd Rim Experiment Sttion, Springfield, TN, for their contriution nd dediction to this reserch. LITERATURE CITED 1. Bellinder, R., R.W. Wllce, nd E.D. Ellis Reduced rtes of hericides following hilling controlled weeds in conventionl nd reduced tillge potto (Solnum tuerosum) production. Weed Technol. 10: Bottenerg, H., J. Msiuns, C. Estmn, nd D. Eturn Yield nd qulity constrints of cge plnted in rye mulch. Biol. Agric. Hort. 14: Bowmn, D.T., R.D. Miller, A.G. Trt, C.M. Ssser, Jr., nd R.C. Rufty A grde index for urley tocco. To. Sci. 33: Breeden, G.K., G.N. Rhodes, Jr., nd T.C. Mueller Influence of ppliction vriles on performnce of Sprtn in tocco. Proc. Southern Weed Sci. Soc. 52: Bruff, S.A., nd H.G. Hncock Sulfentrzone: A promising new hericide for tocco. Proc. South. Weed Sci. Soc. 48: Bruff, S.A., H.G. Hncock, W.D. Mrtin, nd B.D. Sims Tocco weed control with sulfentrzone nd clomzone hericides. Proc. South. Weed Sci. Soc. 50: Burgos, N.R., nd R.E. Tlert Weed control nd sweet corn (Ze mys vr. rugos) response in no-till system with cover crops. Weed Sci. 44: Ditsch, D.C., nd M.M. Alley Nonleguminous cover crop mngement for residul N recovery nd susequent crop yields. J. Fert. Iss. 8: Hncock, H.G Sprtn DF performnce in tocco. Proc. South. Weed Sci. Soc. 51: Hussin, I., K.R. Olson, nd S.A. Eelhr Long-term tillge effects on soil chemicl properties nd orgnic mtter frctions. Soil Sci. Soc. Am. J. 63: Miller, R.D., nd P.D. Legg A grde index for Type 22 nd 23 fire-cured tocco. To. Sci. 34: Moore, M.J., T.J. Gillespie, nd C.J. Swnton Effect of cover crop mulch on weed emergence, weed iomss, nd soyen (Glycine mx) development. Weed Technol. 8: Morrison, J.E., J. Smiley, W. Atkinson, nd D. Milocker A no-tillge trnsplnter. To. Sci. 27: Needlemn, B.A., M.M. Wnder, G.A. Bellero, C.W. Bost, G.K. Sims, nd D.G. Bullock Interction of tillge nd soil texture: Biologiclly ctive soil orgnic mtter in Illinois. Soil Sci. Soc. Am. J. 63: Perce, R.C., nd J. Zeleznik Evlution of weed control options for no-till Burley tocco production. KY Agric. Exp. St. Prog. Rep. 385: Schoneck, M., S. Herert, R. DeGregorio, F. Mngn, K. Guillrd, E. Sidemn, J. Herest, nd R. Jye Cover cropping systems in the northestern United Sttes: 1. Cover crop nd vegetle yields, nutrients nd soil conditions. J. Sustin. Agric. 3: Shelton, D.P., E.C. Dickey, R. Knle, S.W. Melvin, nd C.A. Burr Estimting percent residue cover using the line-trnsect method. Conserv. Till. Pu. CTNC Shilling, D.G., A.D. Worshm, nd D.A. Dnehower Influence of mulch, tillge, nd diphenmid on weed control, yield, nd qulity in no-till flue-cured tocco (Nicotin tcum). Weed Sci. 34: Tesdle, J.R Interction of light, soil moisture, nd temperture with weed suppression y hiry vetch residue. Weed Sci. 41: United Sttes Deprtment of Agriculture. Ntionl Agriculturl Sttistics Service (verified ). 21. Wgner-Riddle, C., T.J. Gillespie, nd C.J. Swnton Rye cover crop mngement impct on soil wter content, soil temperture, nd soyen growth. Cn J. Plnt Sci. 74: Wlker, E.R., T.C. Mueller, G.N. Rhodes, Jr., nd R.M. Hyes Sprtn for weed control in tocco. Proc. South. Weed Sci. Soc. 51: Weed Science Society of Americ Hericide Hndook. K.K. Htzios, ed. Lwerence, KS. 24. Wickliffe, W.B., F.H. Yelverton, A.D. Worshm, nd G.G. Nghushn Rye cover crop mulch reduces hericide use in no-till tocco. Proc. South. Weed Soc. Sci. 49: Wills, J Trnsplnter modifictions for no-till production. Univ. TN Agric. Ext. Serv. Pu. PM Wood, S.D., nd A.D. Worshm Reducing soil erosion in tocco fields with no-tillge trnsplnting. J. Soil Wter Conserv. 41: Yelverton, F.H., A.D. Worshm, R.W. Lemons, nd W.B. Wickliffe Weed mngement in no-till tocco. Proc. South. Weed Sci. Soc. 47: York, A.C Cover crop nd weed mngement in conservtion tillge cotton-southest. Proc. Beltwide Cotton Conf. 1: Tocco Science (2001/2002) 45:44-48

6 49 Tocco Science (2001/2002) 45: