Chapter IV. Abstract. adoption and substantiated the need for additional investigation. The recent

Transcription

1 Chpter IV. The Effect of Supplementl Row Cultivtion on Soil Erosion nd the Agronomic Performnce of Conservtion Tillge Flue-cured Tobcco Abstrct Producer cceptnce of conservtion tillge for flue-cured tobcco production hs been low since prctice introduction in the lte 1960 s. Yield reduction, tobcco qulity issues, uncceptble weed control, nd indequte trnsplnting equipment limited doption nd substntited the need for dditionl investigtion. The recent developments of revolutionry herbicide nd n improved trnsplnter hve renewed interest in conservtion tillge for tobcco production in the piedmont region of Virgini nd North Crolin. A three-yer study ws conducted to evlute soil erosion nd the gronomic chrcteristics of flue-cured tobcco produced using five conservtion tillge production systems. Row cultivtion ws investigted t ppliction frequencies of zero, one (lyby only), two (erly plus lyby, nd lte plus lyby), or three (erly plus lte plus lyby) nd comprison mde to conventionl tillge receiving four cultivtions. Conservtion tillge, without supplementl row cultivtion, reduced soil erosion 92 percent compred to conventionl tillge. Row cultivtion did not significntly increse conservtion tillge system soil erosion. The yield of conservtion tillge produced tobcco ws significntly incresed with supplementl row cultivtion. One, two, nd three cultivtions incresed yield 18, 28, nd 31 percent, respectively. The yield of conservtion tillge tobcco receiving t lest two cultivtions ws similr to 46

2 conventionl tillge. Qulity of the cultivted conservtion tillge tobcco ws similr to conventionl tillge. Introduction The production of flue-cured tobcco using conservtion tillge techniques hs been limited primrily to reserch studies nd smll plntings since introduction in the lte 1960 s by Moschler et l. (1971). Yield reduction, poor trnsplnt stnd nd limited weed control options served s obstcles tht limited widespred producer cceptnce of the production prctice. Conventionl tobcco production relies on multiple tillge opertions prior to crop trnsplnting for preprtion of the plnting surfce nd subsequent row cultivtion for both weed control nd modifiction of soil surfce chrcteristics. This frequent soil disturbnce leves the soil prone to erosion by destroying soil structure nd ccelerting the degrdtion of cover crop residues. Although soil erosion resulting from conventionl tillge culture is excessive (Wood nd Worshm 1986), the high income generted from tobcco sles reduces the impct of this long-term issue. A recent decrese in tobcco frm number, increse in tobcco frm size, nd n incresed environmentl wreness hs led to the questioning of long-term conventionl tobcco production sustinbility. Soil conservtion prctices ssocited with tobcco production rely primrily on crop rottion nd/or instlltion of conservtion structures for soil erosion reduction. Conservtion structures re expensive to instll, remove lnd from production, nd interfere with mneuverbility of multiple row equipment. Although effective for 47

3 reducing soil erosion, these structures cn be prohibitive to mny frm opertions. An ttrctive lterntive to the use of these prctices is conservtion tillge. Conservtion tillge offers the opportunity for these frm opertions to decrese crop rottion length nd utilize highly erodible croplnd for tobcco production while mintining reducing soil erosion. Conservtion tillge tobcco production ws first discussed by Moschler et l. (1971) following the widespred doption of no-tillge techniques for food crop production. Uncceptble tobcco yield reductions were ttributed to poor soil-root contct nd deleterious effect of reduced soil temperture. Subsequent reserchers observed similr yield reductions (Link 1984; Shilling et l. 1986; Wood nd Worshm 1986; Wiepke et l. 1988) ttributed to trnsplnter mlfunction, weed competition nd the presence of stle or old seedbed. Reserchers indicted the need for further investigtion before widespred producer doption of conservtion tillge. A recent development in improved trnsplnter technology, the Subsurfce Tiller Trnsplnter (SST-T) by Morse et l. (1993), combined with the vilbility of newer herbicides for weed control, offered the potentil of incresing the yield of conservtion tillge tobcco. In n effort to exmine the impct of these developments, three-yer reserch study ws implemented t the Virgini Tech Southern Piedmont Agriculturl Reserch nd Extension Center in Blckstone, Virgini. Row cultivtion ws dded to this study to improve seedbed ertion, weed control nd modifiction of soil surfce chrcteristics. In ddition, row cultivtion reduces plnt lodging nd ground sucker formtion by building row-ridge round the bse of tobcco plnts. 48

4 The objectives of this study were to: 1. evlute the effect of row cultivtion tretment on soil erosion, tobcco yield nd tobcco qulity of five conservtion tillge flue-cured tobcco production systems nd conventionl tillge. 2. determine the prticle size composition of collected soil erosion. Mterils nd Methods Field experiments were conducted t the Virgini Tech, Southern Piedmont Agriculturl Reserch nd Extension Center ner Blckstone, Virgini in 1995, 1996 nd 1997 on n eroded Myodn sndy lom soil (Typic Hpludult, fine lomy, siliceous, thermic) with slope of pproximtely 5 percent. The plow lyer of this soil consisted of pproximtely 60 percent snd, 30 percent silt nd 10 percent cly. The snd composition ws pproximtely 5, 15, 15, 15, nd 10 percent very corse, corse, medium, fine nd very fine prticles, respectively. Six tillge tretments were replicted four times nd evluted in rndomized complete block design. Tretments exmined the trnsplnting of flue-cured tobcco (Nicotini tbcum L.) into herbicide killed rye cover crop nd the subsequent effect of row cultivtion on soil erosion nd tobcco gronomic chrcteristics. Conventionl tillge (Tretment T1), cultivted four times (t fertilizer sidedress, erly, lte nd lyby), ws compred to five conservtion tillge production systems receiving cultivtion s described below: 49

5 Timing of Cultivtion Tretment erly lte lyby T2 X X X T3 X -- X T4 -- X X T X T6 -- no cultivtion -- The cultivtion designtions of erly, lte, nd lyby describe the reltive time of cultivtion fter tobcco trnsplnting (Appendix B). Both the erly nd lte cultivtion involve light stirring of the soil to improve ertion nd control weeds. Conversely, the lyby cultivtion involves intensive soil disturbnce to form row-ridge round plnts before they become too tll for dditionl cultivtion. Reserch plots in ll yers were 16 feet wide, 40 feet long nd composed of four bedded rows. Plot preprtion begn in lte October prior to ech yer s study with moldbord plowing, disking, subsoil ripping nd bedding. Prior to cover crop seeding, bed tops were leveled to height of pproximtely 8 inches. Rye (Secle cerele vr. Abruzzi) ws brodcst seeded t rte of 3 bushels per cre nd 500 lbs. per cre (N:P 2 O 5 :K 2 O) fertilizer brodcst to enhnce rye growth. Glyphoste (Roundup TM ) ws pplied t the rte of 3 lbs..i. per cre in mid-april of ech yer to kill the rye cover crop. Supplementl weed control ws chieved using npropmide (Devrinol TM ) pplied to ll plots t 1.5 lb..i. per cre immeditely following lyby cultivtion in 1995 nd 50

6 1996. The herbicide progrm ws modified for 1997 following the commercil relese of sulfentrzone (Sprtn TM ). Both clomozone (Commnd TM ) t 1.0 lb..i. per cre nd sulfentrzone (Sprtn TM ) t lb..i. per cre were brodcst pplied prior to tobcco trnsplnting in tnkmix with glyphoste (Roundup TM ). Flue-cured tobcco, vriety K-326, ws trnsplnted into the rye cover crop using two-row Subsurfce Tiller Trnsplnter TM (B nd B No-till, Lurel Fork, VA; Morse et l. 1993) equipped with Lnnen TM model RT-2 crousel trnsplnter units (Lnnen Plnt Systems, Iso-Vimm Finlnd). Trnsplnted plnt popultion ws pproximtely 6000 plnts per cre. Center rows of ech plot were bedded, plnted, fertilized nd cultivted together to insure uniform row spcing within the soil collection re. All rows within given repliction were plnted in the sme direction to produce similr pttern of residue nd soil surfce disturbnce. Imidcloprid (Admire TM ) ws pplied t 0.09 lbs..i. per cre for fle beetle nd phid control long with 10 pounds per cre (N:P 2 O 5 :K 2 O) Miller (Miller Chemicl nd Fertilizer Corp., Hnover, PA) Supreme strter fertilizer in the trnsplnt wter. A complete tobcco grde fertilizer, (N:P 2 O 5 :K 2 O), ws knifed in two bnds t rte of 700 pounds per cre pproximtely 6 inches from trnsplnts using Yetter fertilizer coulters (Yetter Mnufcturing Compny, Colchester, IL.). Additionl sidedress fertilizer consisting of 280 pounds per cre (N:P 2 O 5 :K 2 O) ws pplied in similr fshion pproximtely 3 weeks fter trnsplnting using Cole fertilizer pplictor equipped with nrrow cultivtor feet. Remedil insect nd sucker control prctices were consistent with Virgini Coopertive Extension recommendtions (Reed et l., 1996). 51

7 Tobcco requires pproximtely 1 inch of wter ech week during the period from lyby to topping for optiml growth (Reed et l., 1996). Due to rinfll deficits during this period, tobcco ws irrigted twice in 1996 using trveling guns nd once in 1997 using sttionry sprinklers to id tobcco growth. Norml irrigtion prctices t the Southern Piedmont Agriculturl Reserch nd Extension Center include n pproximte wter output of ¼ inch per hour. For this study, wter output of ½ inch per hour ws used to ccelerte soil erosion. Approximtely one inch of irrigtion wter ws pplied on June 30 in 1996 while two inches were pplied on July 10 in 1996 nd July 9 in A KMC TM (Kelley Mnufcturing Compny, Tifton, GA) two-row rolling spider cultivtor ws used for row cultivtion. The center rows of ech plot were cultivted simultneously nd ll cultivtion ws pplied going down slope. This direction ws chosen to minimize soil collection system disturbnce (Chpter III). The percent soil surfce residue cover ws mesured using the line-trnsect method described by Sloneker nd Moldenhuer (1977) nd recommended by Lflen et l. (1981). Mesurements were mde on the row-ridge side, between the third nd fourth row of ech plot, pproximtely 5 inches from plnts t 8 dys following lyby cultivtion during 1996 nd Row-ridge sides were chosen for mesurement due to plnt interference with digonl plcement of the tpe. The effect of tretment on tobcco growth ws quntified using clcultion of lef re. The length nd width of ll leves were mesured on two plnts per plot in 1996 nd 1997 throughout the growing seson. Repeted mesurements were mde 52

8 using the sme plnts on 10 to 14-dy intervl. Lef re (Suggs et l., 1964) ws clculted s: Lef Are = length X width X (1) A comprison of the upper-stlk lef development ws mde using the lef re of the third lef from the plnt pex determined on the lst observtion dte ech yer. In ddition, the tretment effect on crop development ws compred using the number of dys to flower. Field bloom counts were tken on two-dy intervl following the first observtion of erly button formtion nd continued until the completion of topping. The number of dys to flower ws determined s the observtion dte on which t lest 50 percent of plnts were in flower. Soil erosion ws quntified in 1996 nd 1997 from the re locted between the second nd third row of ech plot (4 feet wide nd 40 feet long) using the collection system described in Chpter III. Following significnt rinfll events (greter thn 0.5 inch), collected runoff wter ws pumped from collection boxes nd sediment removed. Collected soil mteril ws plced into 18 gllon plstic tubs lined with open 33 gllon blck plstic bgs nd llowed to dry inside greenhouse. After drying to moisture content of pproximtely 10 percent, sediment ws weighed nd moisture smples tken for correction to oven-dry bsis (2 percent moisture). Rinfll dt ws recorded onsite using Rinwise TM model RGEL electronic recording rin guge (Rinwise Inc., Br Hrbor, ME). Prticle size nlysis of the collected soil mteril followed the procedure of Dy et l. (1956) utilizing n ASTM No. 152H Bouyouces scle hydrometer for cly frction 53

9 (< mm) determintion nd nest of ASTM # 18, 35, 60, 140 nd 270 sieves for snd frction determintion. For comprison purposes, the weighted verge percents of snd (very corse, corse, medium, fine, very fine), silt, nd cly were clculted s: where: Weighted verge % = % prticle size frction X proportion of totl erosion (2) individul event erosion Proportion of totl erosion = (3) seson totl erosion Wter smples were obtined immeditely prior to wter removl from collection boxes for determintion of turbidity, nitrte, nd solution phosphorus. A 125 ml Nlgene TM plstic bottle ws submerged in ech collection box nd immeditely trnsported to the lbortory for refrigertion nd subsequent processing. Orthophosphte (solution phosphorus) nd turbidity were determined using the method of the United Sttes Environmentl Protection Agency (U.S. EPA 1974) nd nitrte ws determined by the method of Keeney nd Nelson (1982) with n Orion NO 3 - electrode. Four sequentil hrvests ccording to tobcco mturity were performed ech yer on the second nd third row of ech plot. Plot weights nd officil USDA grdes were recorded nd tobcco yield, verge price, vlue per cre nd grde indices clculted. Grde index (Bowmn et l. 1988) provides quntittive evlution of cured lef qulity, verge price represents the seson s verge uction price for the observed grdes, nd vlue per cre reflects the verge gross revenue of cured lef produced on n 54

10 cre. Totl lkloids (Dvis 1976) nd reducing sugrs (Horwirtz 1980) were nlyzed from core smple of cured lef seprted by hrvest number. Air-dry root weight, plnt height, nd stlk dimeter were mesured in 1996 nd 1997 from six plnts per plot immeditely following hrvest completion. Rndomly smpled plnts were physiclly removed using shovel to minimize the brekge nd loss of roots. Soil ws wshed from root systems by gentle stirring ction in 18- gllon tub of wter. Following soil removl, root systems were llowed to ir dry before weighing. Stlks were cut t the soil surfce junction nd dimeter, height nd root weight determined. Anlysis of vrince ws performed using the PROC GLM procedure in SAS (SAS Institute, 1989) nd tretment mens seprted using the LSD test. Liner contrsts were performed to compre soil erosion, prticle size movement nd yield mong tretments. Soil prticle size dt ws trnsformed prior to nlysis using n rcsin trnsformtion (Little nd Hills 1978). Results Soil erosion Quntity. Quntittive differences in soil erosion mong tretments were observed in 1996 nd Figure 4.1 illustrtes the sesonl soil erosion collected in 1996 nd The eleven nd nine erosion collections (Appendix A) of the 1996 nd 1997 tobcco growing sesons, respectively, re depicted by the seprte br segments comprising ech respective tretment. 55

11 Sesonl soil erosion ws significntly reduced by conservtion tillge tobcco culture (1996, P = ; 1997, P = ). No significnt increse in conservtion tillge soil erosion ws ssocited with n incresed row cultivtion frequency. One lyby cultivtion (T5) incresed soil erosion 5 nd 6 percent nd two cultivtions incresed soil erosion 3 nd 8 percent (T4), nd 8 nd 10 (T3) percent in 1996 nd 1997, respectively. The most intensively cultivted conservtion tillge system (T2), receiving three cultivtions, incresed soil erosion 9 nd 11 percent compred to the lest erosive tretment (T6) in 1996 nd 1997, respectively. The lck of n interction between tretment nd yer (P = ) llowed for combined nlysis of soil erosion using both yers (Tble 4.1). Conservtion tillge significntly reduced soil erosion (P = ) 82 to 92 percent compred to conventionl tillge. Supplementl row cultivtion did not significntly increse conservtion tillge soil erosion. Soil erosion ws incresed 5, 7 nd 9 percent by one, two nd three cultivtions, respectively. Soil disturbnce resulting from trnsplnter opertion nd instlltion of the soil collection system, combined with the lck of plnt cnopy (Appendix C), contributed to soil erosion during the erly growing seson. The effect is most pprent in the first two collections of 1996 nd the first collection of 1997 for the five conservtion tillge production systems, but especilly for tretment T6. The first two collections of 1996 contributed 72 percent nd the first collection of 1997 contributed 58 percent of the totl growing seson soil erosion. Runoff wter ws chnneled in the nrrow subsurfce tilled 56

12 zone nd smll gully formed. This gully formtion occurred prior to row cultivtion nd ws similr for ll conservtion tillge tretments. Erosion due to irrigtion ws ccounted for in the July 11 collection of 1996 nd the July 15 collection of Irrigtion did not increse soil erosion compred to nturl storm events. Liner contrsts reveled sesonl soil erosion ws significntly reduced by conservtion tillge culture in 1996 (P = ) nd 1997 (P = ). Row cultivtion did not increse conservtion tillge soil erosion s evidenced by the lck of significnt difference mong the cultivted conservtion tillge systems (T2, T3, T4, nd T5) nd the non-cultivted system (T6) in 1996 (P = ) nd 1997 (P = ). Prticle Size Distribution The weighted verge cly, silt, nd snd composition of soil erosion (Figure 4.2) followed the sme generl trend in both 1996 nd Cly (1996, P = ; 1997, P = ) nd silt (1996, P = ; 1997, P = ) composition of erosion ws not significntly ffected in either yer, but both incresed s cultivtion frequency incresed. The snd composition of soil erosion ws significntly ffected in 1997 (very corse, P = ; corse, P = ; medium, P = ; fine, P = ; very fine, P = ) but not 1996 (very corse, P = ; corse, P = ; medium, P = ; fine, P = ; very fine, P = ) (Figure 4.3). Very corse snd composition ws significntly incresed by conventionl tillge culture, but no significnt differences existed mong the conservtion tillge system tretments. Simrily, corse snd composition of sediment ws significntly higher for conventionl tillge compred 57

13 to the cultivted conservtion tillge systems (T2-T5), but not the non-cultivted conservtion tillge system (T6). Medium snd composition of sediment resulting from conventionl tillge tobcco culture ws similr to the non-cultivted tretment system (T6) nd the lyby only tretment (T5), but significntly higher thn the conservtion tillge tretments receiving two cultivtions (T3 nd T4). Fine snd composition of conventionl tillge erosion ws significntly higher thn tretment T4. Liner contrst nlysis of rcsin trnsformed vlues reveled the conservtion tillge system receiving no supplementl row cultivtion significntly incresed corse (P = ), medium (P = ), fine (P = ), nd very fine snd (P = ) composition of sediment compred to the cultivted conservtion tillge systems (T2 - T5) in Conventionl tillge significntly incresed the very corse (P = ), corse (P = ), medium (P = ), fine (P = ), nd very fine snd (P = ) composition of sediment in 1997 nd corse snd (P = ) in 1996 compred to the cultivted conservtion tillge tretments (T2-T5). Chemistry of Runoff Wter Solution phosphorus (orthophosphte) (Tble 4.2) ws considerbly reduced by conventionl tillge tobcco culture in 1996 (P = ) nd 1997 (P = ) compred to the non-cultivted conservtion tillge system (T6). Row cultivtion did not increse solution phosphorus levels of runoff wter. Liner contrsts reveled solution phosphorus ws significntly reduced by the non-cultivted conservtion tillge production system (T6) in 1996 (P = ) but not 1997 (P = ) 58

14 Turbidity (Tble 4.2), mesure of wter cloudiness, ws incresed in 1996 (P = ) nd 1997 (P = ) by conventionl tillge compred to the conservtion tillge system receiving no row cultivtion (T6). Row cultivtion did not increse turbidity, but liner contrsts reveled cultivted conservtion tillge (T2, T3, T4, nd T5) incresed turbidity compred to no cultivtion (T6) in 1996 (P = ) nd 1997 (P = ). Miniml nitrogen loss ws observed for ll tretments (< 1ppm) nd supportive of observtions mde by Johnson et l. (1979) regrding 99 percent nitrogen loss ssocited with sediment. Sediment nutrient concentrtion ws not quntified s prt of this study. Agronomic Mesures Yield Flue-cured tobcco yield ws significntly ffected by conservtion tillge culture in ll three yers of gronomic dt collection (Figure 4.4). The 1995 (P = ) nd 1997 (P = ) tobcco yields were similr, but lower thn those of 1996 (P = ). The highest yield in 1996 resulted from conventionl tillge (T1), but the highest yield in 1995 nd 1997 resulted from the most intensively cultivted conservtion tillge tretment (T2). The lowest nd second lowest yield in ll yers ws observed for the conservtion tillge systems receiving no or only one row cultivtion, respectively. Conservtion tillge tobcco yield ws significntly reduced when row cultivtion ws withheld. The non-cultivted conservtion tillge system (T6) yield ws significntly reduced compred to conventionl tillge nd the conservtion tillge systems receiving 59

15 row cultivtion (T2-T5) in 1995, 1996, nd The verge yield reduction due to conservtion tillge with no supplementl row cultivtion (T6) for the 3-yer study ws 28 percent compred to the conventionl tillge production system (T1), nd 18 percent compred to the lowest yielding cultivted conservtion tillge production system (T5). Conventionl tillge tobcco yield ws similr to the cultivted conservtion tillge systems (T2-T5) in 1995 nd 1997, but significntly higher thn the conservtion tillge system receiving only lyby cultivtion (T5) in Conservtion tillge tobcco yield ws incresed 18 percent by one cultivtion (T5), 28 percent by two cultivtions (T3 nd T4), nd 31 percent by three cultivtions (T2). Liner contrsts reveled the non-cultivted conservtion tillge system (T6) significntly reduced tobcco yield compred to the cultivted conservtion tillge systems (T2-T5) in 1995 (P = ), 1996 (P = ), nd 1997 (P = ). Conversely conventionl tillge nd tretments T2, T3, T4 nd T5 were similr in the three yers of gronomic dt collection (1995, P = ; 1996, P = ; 1997, P = ). The lck of n interction between tretment nd yer (P = ) llowed for the combined nlysis of yield cross ll three yers (Tble 4.1). Conservtion tillge tobcco yield ws similr to conventionl tillge yield when minimum of two cultivtions (T2, T3, nd T4) ws used. Conservtion tillge receiving no row cultivtion (T6) nd lyby only (T5) cultivtion significntly reduced tobcco yield. One cultivtion (T5) incresed yield 18 percent, two cultivtions (T3 nd T4) incresed yield 28 percent nd three cultivtions incresed tobcco yield 31 percent. 60

16 Mesures of Cured Lef Qulity Tobcco vlue (Figure 4.5) (1995, P = ; 1996, P = ; 1997, P = ) ws lrgely consequence of tobcco yield since the grde index nd price of cured tobcco were not significntly ffected (Tble 4.3). Conservtion tillge receiving no supplementl row cultivtion (T6) exhibited the lowest vlue in ll three yers of study nd the conservtion tillge system receiving erly, lte nd lyby cultivtion (T2) ws highest in 1995 nd 1997 nd conventionl tillge (T1) highest in The noncultivted conservtion tillge system (T6) significntly reduced tobcco vlue in 1995 nd 1997, but ws similr to the lyby cultivted (T5) conservtion tillge system in Plnt Growth Vribles Tretment effect on plnt growth ws pprent from plnt lef re determined throughout the growing seson (Tble 4.4), ir-dry root weight, stlk dimeter nd stlk height (Tble 4.6). Lef re ws significntly reduced by the non-cultivted conservtion tillge system (T6) in 1996 compred to conventionl tillge (T1) nd the conservtion tillge systems T2, T3 nd T5. Similrly, non-cultivted conservtion tillge culture significntly reduced lef re compred to conventionl tillge (T1), tretment T2 nd tretment T3, but not tretments T4 nd T5 in Upper stlk lef development ws similr for ll tretments during 1996 nd Although no significnt tretment effects were observed in either yer, the noncultivted conservtion tillge system (T6) consistently exhibited the lowest lef re. 61

17 The number of dys to flower (Tble 4.5) ws significntly ffected in 1996, but not in 1995 nd Conventionl tillge ws the erliest to flower while conservtion tillge receiving no supplementl row cultivtion (T6) ws the ltest in most yers. Row cultivtion decresed the number of dys to flower s ppliction frequency incresed. Stlk dimeter Stlk dimeter (Tble 4.6) ws significntly ffected in 1996 nd 1997 by conservtion tillge culture. Conservtion tillge receiving no supplementl row cultivtion (T6) displyed the smllest stlk dimeter in both yers while conventionl tillge culture nd tretment T3 displyed the lrgest stlk dimeter in 1996 nd 1997, respectively. Vlues observed for lyby cultivted conservtion tillge (T5) were significntly reduced compred to conventionl tillge (T1), conservtion tillge receiving erly nd lyby cultivtion (T3) nd lte nd lyby cultivtion (T4), but were significntly higher thn the non-cultivted conservtion tillge system (T6) in Non-cultivted conservtion tillge culture (T6) significntly reduced stlk dimeter in Plnt height Although significnt differences in plnt height (Tble 4.6) were observed in 1997, plnt height is poor indictor of tobcco growth. Stlk height is subjective mesure dependent on the personl judgment involved in breking the flower during topping nd consequently setting plnt height. 62

18 Air-dry root weight Although the pttern of root weight differences mong tretments were similr in ll yers of dt collection, significnt differences were only observed in Conventionl tillge (T1) displyed the highest root weight in 1996 while the conservtion tillge system receiving erly, lte nd lyby cultivtion (T2) ws highest in Root weight ws significntly reduced by conservtion tillge receiving only lyby cultivtion (T5) nd no cultivtion (T6). An increse in cultivtion frequency incresed conservtion tillge tobcco root weight. Root weight ws incresed 41 percent by the erly, lte, nd lyby cultivtion (T2), erly nd lyby (T3) nd lte nd lyby (T4) cultivtions compred to the non-cultivted conservtion tillge system (T6) in Chemicl Constituents of the Cured Lef Totl Alkloids The totl lkloid content of cured tobcco ws significntly ffected in 1995 nd 1997 by the conservtion tillge culture systems. Totl lkloid content (Tble 4.7) ws higher in 1995 nd 1997 compred to Conventionl tillge (T1) exhibited the highest totl lkloid content, while the non-cultivted conservtion tillge system (T6) displyed the lowest content in ll yers. Conventionl tillge significntly incresed totl lkloids compred to the conservtion tillge systems receiving erly nd lyby cultivtion (T3), lyby cultivtion (T5) nd no cultivtion (T6). The conservtion tillge production system receiving erly, lte nd lyby cultivtion (T2) displyed significntly higher totl lkloid concentrtion compred to the conservtion tillge systems receiving lyby cultivtion (T5) nd no cultivtion (T6). The vlues for 63

19 conservtion tillge receiving lte nd lyby cultivtion (T4) were significntly higher thn the conservtion tillge tretment receiving no cultivtion (T6). During 1997, conventionl culture vlues were similr to those observed for the conservtion tillge system receiving erly nd lyby cultivtion (T3), but significntly higher thn ll other production systems. The non-cultivted conservtion tillge system (T6) ws significntly lower thn conventionl tillge (T1), conservtion tillge receiving lte nd lyby cultivtions (T3), but similr to ll other tretments. Reducing Sugrs Percent reducing sugr concentrtion of cured tobcco ws higher in 1996 compred to 1995 nd Conventionl tillge culture (T1) significntly reduced reducing sugrs (Tble 4.7) in 1997 compred to the most frequently cultivted conservtion tillge system (T2) nd the conservtion tillge tretment receiving erly nd lyby cultivtion (T3). Although differences observed mong tretments in 1995 nd 1996 were not significnt (P>0.05), n incresed frequency of cultivtion incresed the level of reducing sugrs. Totl lkloids:reducing sugrs Significnt differences in the rtio of totl lkloids to reducing sugrs (Tble 4.6) were observed during The most frequently cultivted conservtion tillge system (T2) exhibited significntly higher rtio thn conventionl tillge (T1), conservtion tillge receiving only lyby cultivtion (T5) nd conservtion tillge receiving no cultivtion (T6). The rtio resulting from conventionl tillge culture ws the lowest in 64

20 ll yers. The observed reducing sugr to lkloid rtios of 1995 nd 1997 were less thn five nd indictive of potentil smoke qulity problems (Tso 1990). Residue Quntity Soil surfce residue following lyby cultivtion ws significntly ffected in 1996 (P=0.0001) nd 1997 (P=0.0001) (Figure 4.6). Conservtion tillge receiving no supplementl row cultivtion (T6) significntly incresed residue quntity ech yer while conventionl tillge (T1) significntly reduced residue quntity compred to the other tretments. Soil surfce residue resulting from tretment T5 ws significntly higher thn the quntity observed from the other cultivted conservtion tillge tretments (T2, T3, nd T4) in 1996 but similr to these tretments in Residue quntity decresed s the frequency of cultivtion incresed. Weed Pressure Weed popultions were not quntified s prt of this study, but visul observtions indicte weed quntity decresed s row cultivtion frequency incresed. Conservtion tillge, receiving no cultivtion (T6), exhibited the gretest mount of weed growth in ll yers while conventionl tillge (T1) displyed the lowest mount of weeds. Problemtic weeds ech yer included lrge crbgrss (Digitri snguinlis), common rgweed (Ambrosi rtemisiifoli), nd crpetweed (Mollugo verticillt). Crpetweed nd erly seson crbgrss were esily controlled with row cultivtion, but lte seson growth posed problems. The use of clomozone nd sulfentrzone significntly improved weed control in

21 Discussion Conservtion tillge offers gret promise for both lrge nd smll crege fluecured tobcco producers frming highly erodible croplnd in the Piedmont region of Virgini nd North Crolin. Soil erosion losses ssocited with tobcco production (Wood nd Worshm 1986) cn be minimized without scrificing tobcco yield nd frm income. The previously described limittions to conservtion tillge tobcco production cn be negted using row cultivtion s described in this study. The present study expnds upon nd complements the previous investigtions of conservtion tillge tobcco production. Reserchers (Moschler et l. 1971; Link 1984; Shilling et l. 1986; nd Wood nd Worshm, 1986) primrily compred conventionl tillge to the non-cultivted conservtion tillge production system, tretments T1 nd T6 in the present study, respectively. Yield reductions of 9 to 18 percent indicted the need for dditionl investigtion before widespred cceptnce of the production prctice by producers. Higher yield reductions ssocited with tretment T6 in the present study, rnging from 24 to 33 percent, confirmed the need for modifiction to the previously described conservtion tillge tobcco production systems. A key production system modifiction exmined in this study included the use of row cultivtion t vrying times during the erly portion of the growing seson. Row cultivtion incresed tobcco yield without significntly incresing soil erosion. Other key improvements included the use of improved herbicides, the Subsurfce Tiller Trnsplnter TM (SST-T) nd improved fertilizer incorportion. 66

22 Concerns expressed by previous investigtors regrding phytotoxic effect of glyphoste treted residue on tobcco stnd estblishment (Chppell nd Link 1977) were not confirmed in this study. Explntions include improved trnsplnter movement of residue out of direct contct with trnsplnts. Although the rye cover crop biomss ws pproximtely 2.5 tons per cre nd cover crop height ws pproximtely 5 feet in both yers, it lodged hevily following glyphoste ppliction. This lodging reduced the movement of residue onto djcent rows during plnting. Although subsurfce tiller performnce ws exceptionl in creting trnsplnt trench, the subsoil ws indequtely loosened. Root weight reductions indicte the inbility of tobcco roots to expnd outside of the trnsplnter tilled zone. Row cultivtion incresed root weight by shking nd loosening the stle soil to improve root penetrtion nd rinfll infiltrtion. In ddition, cultivtion ided in plnt resistnce to lodging (Chpter V.) by forming rised row-ridge round the bse of tobcco plnts. A noticeble tobcco growth phenomenon ws observed in ll yers of study resulting from conservtion tillge. Tobcco stlks exhibited growth to the side nd then upwrds. Possible explntions for this growth include soil settling in the subsurfce tiller trench, n uneven soil-plnting surfce creted by subsurfce tiller enhnced soil buckling nd residue enhnced microclimte. Nturl residue degrdtion enhnced row cultivtion between the erly nd lyby ppliction. Rolling cultivtor function ws dequte, but residue wrpped round cultivtor components nd hindered proper opertion. Residue ws physiclly removed from the cultivtor spiders fter ech plot to llevite this concern, but this would be 67

23 prohibitive on lrge frm opertion. Specilly designed cultivtors for high residue situtions such s the Sukup TM Model 9400 (Sukup Mnufcturing Compny, Sheffield IA) would reduce this residue clogging concern. Yield differences between yers were relted to rinfll quntity (Tble 4.8). Higher rinfll in 1996 incresed tobcco yield cross ll tretments. The lowest yield (T6) in 1996 ws higher thn the highest yield (T2) in both 1995 nd An dequte vilbility of wter llows tobcco to utilize growth inputs for lef development rther thn root explortion of the soil. Shilling et l. (1986) reported the incresed suppression of conservtion tillge tobcco yield during yers with dequte rinfll. Yield reductions of pproximtely 25 percent were observed during the dry growing sesons of both 1995 nd 1997, while yield reduction of 33 percent ws observed during the wet 1996 seson. The moisture holding nd soil surfce protection dvntges ssocited with soil surfce mulch cover re most pronounced during dry yers. Mulch intercepts sunlight nd slows the formtion of hrd soil surfce lyer, but would slow soil drying nd contribute to plnt losses due to drowning during extremely wet growing conditions. Although row cultivtion exposes soil nd breks surfce residue into finer frctions, tobcco yield ws incresed by n incresed row cultivtion frequency. The non-cultivted conservtion tillge system (T6) exhibited the highest mount of residue throughout the growing seson, yet exhibited the lowest yield. This indictes surfce residue is effective in conserving moisture only if dequte moisture is vilble in the underlying soil profile. 68

24 Tobcco yield ws reduced by the non-cultivted conservtion tillge system (T6) by seling nd compction of the soil surfce resulting from excessive rinfll (Tble 4.8) following fll bed preprtion. Rinfll ccelerted the movement of smller soil prticles downwrd through the soil profile nd enhnced the formtion of hrd soil surfce crust. The plnting opertion destroyed this surfce crust nd loosened the soil in the zone of the subsurfce tiller, but reformtion quickly resulted. Row cultivtion gin destroyed this crusted lyer to llow incresed wter infiltrtion nd esier root penetrtion during the erly portion of the growing seson. Consequently, the crusted lyer reformed shortly fter lyby cultivtion due to high intensity rin events (Appendix A) combined with high summer tempertures. This observtion is typicl of the tobcco producing soils in the Piedmont region of Virgini. Root system development cn be relted to growing seson wether conditions (Tble 4.6). Root weight resulting from the wet 1996 growing seson ws considerbly reduced compred to tht of the dry 1997 seson. During wet yers, less plnt energy is expended for root development. Short periods of dry wether, combined with reduced root systems, plce undue stress on plnts nd cn reduce plnt performnce nd consequently reduce yield. The incresed totl lkloid concentrtion observed in the dry production sesons of 1995 nd 1997 confirm the wether relted nture of compound synthesis. An incresed totl lkloid concentrtion is usully ssocited with dry growing conditions nd coupled with low reducing sugr levels (Weybrew et l., 1983). The effect of tretment on totl lkloid content exhibited similr pttern to root weight. Totl 69

25 lkloid content ws highest in yers with high root weights. This observtion supports the report by Tso (1990) indicting tobcco lkloids re synthesized in the plnt root system nd then trnslocted to leves. Soil erosion observtions similr to those of Wood nd Worshm (1986) indicte n enormous reduction in soil erosion ssocited with conservtion tillge, nd more importntly cultivted conservtion tillge. Soil erosion is dependent on soil surfce roughness, rinfll durtion, rinfll intensity, site slope nd slope length. The noncultivted conservtion tillge system (T6) reduced soil erosion the gretest due to n incresed soil surfce roughness relted to incresed cover crop residue mulch. Cover crop residues crete protective brrier for the soil surfce tht reduces rinfll energy nd the dislodgment of soil prticles from direct impct. Although row cultivtion destroyed this protective residue brrier, soil surfce with enhnced roughness ws creted. Soil prticle dislodgment during rinfll incresed, but the roughened soil surfce impeded wter flow nd enhnced wter infiltrtion. The incresed solution phosphorus nd reduced turbidity of the non-cultivted conservtion tillge tretment (T6) during 1996 supports the literture. Miniml soil disturbnce fter trnsplnting limited the vilbility of loose soil prticles for dsorbing phosphorus from solution. An dditionl source of phosphorus to the pplied fertilizer is decomposing cover crop residue. Cultivtion incresed residue decomposition, but lso incresed residue exposure to soil prticles which cn subsequently bind phosphorus. Cultivtion tretment hd miniml impct on tobcco yield nd soil erosion, but both incresed s the frequency of cultivtion incresed. The use of row cultivtion t 70

26 frequency of erly nd lyby ppers to offer trde-off between soil erosion, tobcco yield nd opertor lbor. The lyby cultivtion ppers deficient to consistently increse tobcco yield to n cceptble level wheres three cultivtions require dditionl opertor lbor nd ssocited equipment operting expenses. Cultivtion t n erly timing would provide the most efficient method of controlling smll weeds nd dislodging the hrd soil surfce crust to llow for incresed wter infiltrtion. A dely in first cultivtion to the lte timing would reduce weed control due to lrger nd more developed weeds. The effect of lef cnopy development on soil erosion is evident throughout the growing seson. During the first month of field production, lef development is slow nd the soil surfce remins unprotected from rinfll impct. Lef formtion is rpid following lyby cultivtion nd protective brrier for bedsides is quickly formed. Lef expnsion fter topping either concentrtes rinfll down the plnt stlk or into row middles. Often, bedsides remin dry following rin events due to this phenomenon. Sequentil hrvest subsequently reduces the mount of lef protection offered the soil surfce nd bedsides. Irrigtion enhnced soil erosion ws miniml in both yers, lthough n excessive output of wter ws pplied. The lck of n irrigtion effect is relted to the time of irrigtion ppliction. Irrigtion ws pplied immeditely fter cultivtion in both yers while the soil surfce ws loose, rough, nd extremely dry. Row cultivtion destroyed the hrd soil surfce crust nd llowed incresed infiltrtion of pplied wter. The incresed snd composition of soil erosion for conventionl tillge (T1) nd the non-cultivted conservtion tillge system (T6) is relted to soil surfce seling nd 71

27 crust formtion. Conventionl tillge displyed smll mount of incorported cover crop residue in the soil surfce lyer, but the non-cultivted conservtion tillge system (T6) exhibited hrd, stle seedbed prepred during the previous fll. The incorportion of surfce residue nd light disturbnce of the soil during row cultivtion hindered formtion of hrd surfce soil lyer in the cultivted conservtion tillge systems. Cly movement decresed from plots exhibiting this crust formtion due to binding of cly nd silt during the formtion process. Crust formtion creted hrd surfce conducive for the flow of wter nd the movement of lrger snd prticles. The incresed loss of cly nd silt observed from the cultivted conservtion tillge systems resulted from decresed binding of these prticles. A decresed loss of snd observed with row cultivtion resulted from the physicl brrier creted from the cut residue nd from the formtion of smll ridges nd vlleys which slowed runoff wter flow nd llowed for the settling of these lrger prticles. The impct of rinfll intensity nd durtion on soil erosion is clerly evident in both yers (Appendix A), but most pprent in the collections of September 9 nd September 16 during Erosion collected on September 9 resulted from Hurricne Frn, long durtion storm with high rinfll but reltively low intensity while the bulk of erosion on September 16 resulted from high intensity thunderstorm of short durtion. The quntity of rinfll mesured during the first 5 hours of the ltter storm ws higher thn the quntity mesured from 50 hours of the Hurricne. Erosion mesured on September 16 ws much higher compred to vlues observed for Hurricne Frn. During Hurricne Frn, there ws smll quntity of rinfll observed during the first 15 hours 72

28 of collection which dequtely wet nd softened the soil surfce before the deluge of rinfll observed from 35 to 50 hours. The mjority of rinfll fell during the first 5 hours for the September 16 collection nd erosion ws much higher compred to tht observed for the Hurricne. Conservtion tillge tobcco production, combined with multiple row cultivtion, offers vible method for reducing soil erosion nd mintining cceptble tobcco yield. Although dvnces in production technology were insufficient to overcome the yield reduction previously identified with conservtion tillge tobcco culture, multiple row cultivtion ws sufficient to increse tobcco yield to n cceptble level. Before widespred doption of conservtion tillge culture, tobcco producers need to evlute their individul opertions nd formulte long-term frm opertion pln. The mjority of tobcco producers in the Southern Piedmont region of Virgini rely on either one or two-yer crop rottion to stisfy the conservtion complince provisions of the 1985 Frm Bill. The use of conservtion tillge would llow these producers n opportunity to incorporte n dditionl yer of tobcco into their rottion pln. Conservtion tillge production would best work in the yer following conventionl tobcco production. Producers normlly till their lnd following tobcco hrvest to destroy tobcco stlks nd root systems before seeding of the smll grin cover crop. The formtion of bedded rows could esily be incorported into this tillge pln prior to the smll grin seeding opertion. The following rottion pln incorportes conservtion tillge into one yer tobcco rottion: 73

29 Yer 1 = Conventionl tobcco, fll bedding nd cover seeding Yer 2 = Conservtion tillge tobcco Yer 3 = Grin or hy crop Yer 4 = Conventionl tobcco The rottion cn be modified s follows for producer using two-yer crop rottion: Yer 1 - Conventionl Tobcco Yer 2 - Conventionl tobcco, fll bedding nd cover seeding Yer 3 Conservtion tillge tobcco Yer 4 Grin or hy crop Yer 5 Grin or hy crop Yer 6 Conventionl Tobcco The use of conservtion tillge for tobcco production following grin or hy crop is discourged due to vritions in soil surfce hrdness nd residue tht would be llevited with moldbord plowing, subsoil ripping nd multiple discings. Potentil production problems wrrnting further investigtion include nemtode, blck shnk nd grnville wilt control. These production concerns re widespred in the Piedmont region of Virgini nd control mesures need to be evluted for conservtion tillge tobcco production. The use of strip-tillge, more intensive nd deeper tillge opertion compred to the subsurfce tiller opertion, offers n opportunity for incorportion of effective chemicls nd improved control of these diseses. Producers need to consider herbicide use during the yers of conventionl tobcco production. Herbicide crryover from npropmide (Devrinol TM ) nd especilly 74

30 clomozone (Commnd TM ) cn stunt smll grin nd decrese stnd. One of the most importnt components of successful conservtion tillge production system is n dequte quntity of cover crop residue. Producers should minimize the crege devoted to conservtion tobcco production until experience with the production system is gined reltive to their individul soil conditions. Producers need to consider the incresed level of mngement required with conservtion tillge tobcco production nd relize tht conservtion tillge is not n nswer, but simply component to llow U.S. producers to become more competitive in the future. 75

31 Literture cited Bowmn, D.T., A.G. Trt, E.A. Wernsmn, nd C.T. Corbin Revised North Crolin grde index for flue-cured tobcco. Tob.Sci. 32: Chppell, W.E., nd L.A. Link Evlution of herbicides in no-tillge production of burley tobcco. Weed Sci. 25: Dvis, R.E A combined utomted procedure for the determintion of reducing sugrs nd nicotine lkloids using new reducing sugr method. Tob. Sci. 20: Dy, P.R Prticle frctiontion nd prticle size nlysis, In: Methods of Soil Anlysis, ed. by Blck et l. Am. Soc. Agron., Mdison, WI. Horwitz, W. (ed.) Officil methods of nlysis, 13 th edition. AOAC, Wshington, D.C. Johnson, H.P., J.L. Bker, W.D. Scrder, nd J.M. Lflen Tillge system effects on sediment nd nutrients in runoff from smll wtersheds. Trns. of ASAE 22(5): Keeney, D.R. nd D.W. Nelson Nitrogen Inorgnic forms. In A.L. Pge (ed.) Methods of soil nlysis, prt 2 Chemicl nd microbiologicl properties. Agronomy 9: Lflen, J.M., M. Amemiy, nd E.A. Hintz. Mesuring crop residue cover. J. Soil nd Wter Cons. 36(6): Link, L.A An evlution of no-tillge culture for burley tobcco. VA Agric. Exp. St. Virgini Tech. Bull Little, T.M. nd F. Jckson Hills Agriculturl Experimenttion. John Wiley & Sons, Inc. Cnd. Moschler, W.W., G.M. Sher, M.J. Rogers, nd T.R. Terrill No-tillge tobcco studies in Virgini. Tob. Sci. 15: Reed, T.D., J.L. Jones, C.S. Johnson, P.J. Semtner, B.B. Ross, nd C.A. Wilkinson Flue-cured tobcco production guide. VA Coop Ext pub , Blcksburg, VA. SAS Institute Inc SAS/STAT User s Guide, Version 6, Fourth Edition, Volume 1, Cry, NC:SAS Institute Inc., 943 pp. 76

32 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 Tobcco. Weed Science 34: Sloneker, L.L., nd W.C. Moldenhuer Mesuring the mounts of crop residue remining fter tillge. J. Soil nd Wter Cons. 32(5): Suggs, C.W., H.B. Peel, nd T.R. Seboch Mechnicl hrvesting of bright lef tobcco. Prt 16. Effects of hrvest size, number, schedule nd method on yield, vlue, price nd chemistry. Tob. Sci. 33: Tso, T.C Production, physiology, nd biochemistry of Tobcco plnts. Idels, Inc., Beltsville, MD. United Sttes Environmentl Protection Agency Phosphorus, All Forms. Methods for Chemicl Anlysis of Wter nd Wstes Weybrew, J.A., W.A.W. Ismil, nd R.C. Long The culturl mngement of fluecured tobcco qulity. Tob. Sci. 27: Wood, S.L., nd A.D. Worshm Reducing soil erosion in tobcco fields with notillge trnsplnting. J. Soil nd Wter Cons. 41:

33 Tble 4.1. Averge yield nd soil erosion of five conservtion tillge flue-cured tobcco production systems nd conventionl tillge. Tretment Yield Totl soil erosion no. tillge system 1 pounds per cre tons per cre T1 Conventionl tillge T2 CT - erly, lte, nd lyby b T3 CT erly nd lyby b T4 CT - lte nd lyby 2710 b 2.31 b T5 CT - lyby only 2498 b 2.38 b T6 CT - no cultivtion 2124 c 1.45 b P-vlue CV LSD (0.05) CT Conservtion tillge; erly cultivtion occurred t 14 dys fter trnsplnting (DAT) in 1995, 26 DAT in 1996 nd 30 DAT in 1997; lte cultivtion ws t 23 DAT in 1995, 33 DAT in 1996 nd 38 DAT in 1997; nd lyby cultivtion ws t 35 DAT in 1995, 39 DAT in 1996 nd 45 DAT in Mens within column followed by the sme letter re not significntly different. 78

34 Tble 4.2. Solution phosphorus nd turbidity of five conservtion tillge flue-cured tobcco production systems nd conventionl tillge in 1996 nd Tretment Solution phosphorus Turbidity no. tillge system 1 ppm percent bsorbency T1 Conventionl tillge 0.16 b 0.04 c T2 CT - erly, lte, nd lyby 0.15 b b 0.12 b T3 CT erly nd lyby 0.15 b c 0.11 b T4 CT - lte nd lyby 0.20 b 0.07 b 0.07 bc 0.13 b T5 CT - lyby only 0.19 b c 0.13 b T6 CT - no cultivtion c 0.03 c P-vlue CV LSD (0.05) CT Conservtion tillge; erly cultivtion occurred t 14 dys fter trnsplnting (DAT) in 1995, 26 DAT in 1996 nd 30 DAT in 1997; lte cultivtion ws t 23 DAT in 1995, 33 DAT in 1996 nd 38 DAT in 1997; nd lyby cultivtion ws t 35 DAT in 1995, 39 DAT in 1996 nd 45 DAT in Mens within column followed by the sme letter re not significntly different. 79

35 Tble 4.3. Grde index nd mrket price of five conservtion tillge flue-cured tobcco production systems nd conventionl tillge in 1995, 1996 nd Tretment Grde index Mrket price no. tillge system U.S. $ per pound T1 Conventionl tillge T2 CT - erly, lte, nd lyby T3 CT erly nd lyby T4 CT - lte nd lyby T5 CT - lyby only T6 CT - no cultivtion P-vlue CV LSD (0.05) ns ns ns ns ns ns 1 CT Conservtion tillge; erly cultivtion occurred t 14 dys fter trnsplnting (DAT) in 1995, 26 DAT in 1996 nd 30 DAT in 1997; lte cultivtion ws t 23 DAT in 1995, 33 DAT in 1996 nd 38 DAT in 1997; nd lyby cultivtion ws t 35 DAT in 1995, 39 DAT in 1996 nd 45 DAT in