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Effects of a new wide-sweep opener for no-till planter on seedzone properties and root establishment in maize (Zea mays, L.):A comparison with double-disk openerT. Vameralia, M. Bertoccob,*, L. SartoribaDipartimento di Agronomia Ambientale e Produzioni Vegetali, University of Padova, Agripolis,Viale dellUniversita 16, 35020 Legnaro, Padova, ItalybDipartimento Territorio e Sistemi Agro-forestali, University of Padova, Agripolis,Viale dellUniversita 16, 35020 Legnaro, Padova, ItalyReceived 17 February 2005; received in revised form 13 July 2005; accepted 29 July 2005AbstractAccording to the kind of opener applied, no-tillage seeders can variously modify soil physical properties in relation to soiland climate conditions, thus potentially affecting crop emergence and early growth.The technological evolution of seeders for direct drilling of arable crops, progressively achieved in recent years, has beenconsiderable, but new improvements now available need to be individually tested. In a field trial at Udine (NE Italy), the effectsofanewkindofwide-sweepopener(i.e.,sidecoulterscurvedupwardsintheirfinalpartandslightlyangledtowardsthedirectionof work) on soil physical properties in the seed zone and on crop emergence and early root growth of maize were evaluated infour different soils over a 2-year period (20022003), in comparison with the widely used double-disk opener.With respect to the double-disk opener, ingeneral thewide-sweep type led to higher soilresidue mixingwithout excessivereduction of the soil-covering index being observed, ?27 and ?6%, respectively. The wide-sweep opener also showed lowerbulk density and soil penetration resistance in the top 5-cm soil layer of the seed furrow, although no greater root length densitywas found in maize at the three-leaf stage, probably due to the smoothing effect caused by the side coulters at the seeding depth.Acertaindelayinplantemergenceinsomecaseswasalsorevealedforthewide-sweepopener,whichmayberelatedtothelowersoil/seed contact.Deviations from this general behaviour in the various soils (texture and initial conditions) are discussed.# 2005 Elsevier B.V. All rights reserved.Keywords: Maize; No-tillage; Opener type; Root growth; Seed zone physical properties/locate/stillSoil & Tillage Research 89 (2006) 196209Abbreviations: CI, covering index; DAS, days after sowing; DDO, double-disk opener; FRSD, furrow roughness standard deviation; PR,penetration resistance; RI, residue incorporation; RLD, volumetric root length density; SOC, soil organic carbon; WSO, wide-sweep opener* Corresponding author. Tel.: +39 049 8272723; fax: +39 049 8272774.E-mail address: matteo.bertocco.1unipd.it (M. Bertocco).0167-1987/$ see front matter # 2005 Elsevier B.V. All rights reserved.doi:10.1016/j.still.2005.07.0111. IntroductionIn the last few years, the economic and environ-mental implications of conventional tillage, such aserosion, compaction and inverting soil layers, have ledto re-examination of no-tillage even in Italy (Sartoriand Peruzzi, 1994). Especially, in the heavy soils ofthis country, deep ploughing aims at increasing soilporosity, at least temporarily, in order to createsuitable conditions for both seed germination and rootgrowth. Simplification of weed management andhigher grain yields of summer crops like maize aregenerally achieved with respect to no-tillage, asevidencedbythefewdataavailableintheliteratureforItaly (e.g., Bona et al., 1995).The performance of no-tillage seeders depends onseveral factors related to field conditions, includingtype and amount of residues at soil surface, openerdesign (Morrison, 2002) and the crop to be sown. Theimplementsoftheseseedersmusthavehighflexibility,so that various crops can be sown in differing fieldconditions with correct seed deposition (e.g., density,distance, depth). In no-tillage practices, the character-istics of the seed-furrow play an important role ingermination. Many authors have pointed out that themost significant factors regulating germination, suchas soil matric potential, temperature (Lindstrom et al.,1976; Schneider and Gupta, 1985) and sowing depth(Alessi and Power, 1971; Mahdi et al., 1998) areaffected by the soil/opener interaction (Tessier et al.,1991a,b). In particular, in order to maintain constantsowing depth, various types of linkages betweenopener and seeder toolbar have been proposed duringthe last few decades. For instance, connection with aspring system, the oldest but simplest solution, is notalways adequate to guarantee uniformity of sowingdepth, especially in heavy soils. Great improvementshave been obtained with parallel linkage, since thisallows the opener to follow soil surface profilesaccurately.Many of the characteristics of the seed zone in no-tillage depends on the type of opener attached to theseeder (Wilkins et al., 1983) and the two main typesused tine and disk may lead to great differences.The tine opener typically creates an appreciablebursting effect in the soil and generally moves aconsiderable quantity of fine damper aggregatestowardsthesoilsurfaceafactparticularlyappreciablein tools having an asymmetric shape (Darmora andPandey, 1995) but which may be negative if a rainlessperiodoccurs aftersowing,assoildryingisaccelerated(Chaudhuri, 2001). In similar conditions, the diskopener may cause more progressive water loss inthe soil layer above the seeds than the tine opener(Tessier et al., 1991a,b), although great drawbacks areobservable in wet clay soils because a permanentunclosed furrow is commonly created (Sartori andSandri, 1995).It is widely recognised that management of cropresidues (previous crop) is one of the most importantconstraints for adopting no-tillage (Carter, 1994). Tineopenersshiftorganicdebrisinthesoilsurfacefromthecrop row sideways, with possible plugging of theseeder in the case of heavy residues, whereas diskopeners may lead to hairpinning, with a consequentbad soil/seed contact and possible toxic effect onseedlings (Hultgreen, 2000). Unmanaged residues cancreate many problems in direct sowing, but theirpresence at the soil surface is generally beneficial inlimiting some negativeeffects on soil, like erosion andwater losses (Gill and Aulakh, 1990).As regards soil and climate conditions, openersshould achieveseveral aims, like uniformityof sowing i.e., spacing and depth production of a suitableamount of fine soil aggregate to ensure soil/seedcontact, reduction of water losses, avoidance of seedcontact with either fertilizers or crop residues andlimitation of furrow compaction, which may obstructroot growth (Willatt, 1986; Tsegaye and Mullins,1994; Bueno et al., 2002). The type of opener wasfound to affect emergence and plant establishmentmarkedly (McLeod et al., 1992), especially in crust-forming soils, for which better results are generallyobtained with the double-disk opener (Hemmat andKhashoei, 2003).The technological evolution of no-tillage seedersfor arable crops, progressively achieved in this sector,has been great, but the large number of improvementsnow available must be individually tested and care-fully evaluated. In addition, much of the literature onthis subject refers almost exclusively to opener/soilinteractions, without analysing effects on crop growth.The effects of furrow shape and its properties on thedraft force required by different opener types havebeen widely studied in relation to soil conditionsand operating parameters, such as depth or speedT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209197(Gebresenbet and Jo nsson, 1992; Collins and Fowler,1996; Sa nchez-Giro n et al., 2005). Instead, only a fewstudies have examined some crop parameters and theygenerally deal with drills for autumn sowing ofcereals. For instance, Chaudhry and Baker (1988)found that various types of opener led to differenttypes of growth of barley seedlings, i.e., greater shootand root weights when both winged (T-shaped groove)or hoe (U-shaped groove) types are used instead of thetriple-disk one.In this framework, the present study evaluates theperformance of an innovative wide-sweep opener,linked to the frame by a double linkage unit. Its effectson some soil physical properties in the seed zone, cropemergence and early root growth of maize wereevaluated in various soils over a 2-year period in NEItaly and compared with those of a double-diskopener, which is the most widespread in Italy.2. Materials and methods2.1. Description of equipmentThe performances of a new wide-sweep opener(WSO) with which the no-till air seeder Cerere(Tecnoagricola, Udine, Italy) has been equipped, wascompared with that of a double-disk opener (DDO)adopted by the no-till planter Max Emerge 2 (JohnDeere Italia, Milan, Italy).The WSO has a straight axis, ending with a frontchisel and two rear side 18-cm wide coulters, whichare slightly angled towards the direction of work andcurved upwards (908) in their final part (25 mm high)(Fig. 1). The front chisel cuts soil 2530 mm deeperthan the coulters. Seed delivery to each unit is througha single pneumatic tube from the centralised volu-metric metering system, which allows the seeder toassume a certain degree of polyvalence. Althoughvarious types of deposition (i.e., row spacing) can beset, in our field trial as the first test of this prototypeopener maize was sown in rows 0.45 m apart, adistance commonly used in the experimental site.The structure of the seeder equipped with the WSOincludes one rigid and one folding frame. The first issupported by a front head-shaft to couple the seeder tothe tractor and two rear low-pressure wheels fortransport. The folding frame aims at guaranteeing thatthe soil profile can be followed by the openers asregularly as possible. For this reason, it has threeindependent jointed sections, each 1.5 m wide andlinked to the rigid frame with four elastic joints. Eachsection has five openers, for a total of 15 sowing rows,which are laid on three seeding lines and equippedwith a single parallel linkage for improved stability. Inaddition, each section is supported by a front wheeland a rear packer tandem (Fig. 2). The latter is anessential component for the working the seeding unitin this seeder; it is made of 10 wheels per section, with3.508 tyres and 0.9 bar pressure.The seeder equipped with the DDO is an eight-unitmounted no-till planter with pneumatic seed meteringand 0.75 m row spacing, resulting in a 6 m workingwidth. The DDO used here is composed of a single,fluted,round-bladedcoulterandadouble-disk,associated with two side rollers and two rear V-mounted wheels (Fig. 2).Performance valuation of opener types requiresdifferences among seeders to be kept to a minimum,although this is not always completely possible,T. Vamerali et al./Soil & Tillage Research 89 (2006) 196209198Fig. 1. Sketch of wide-sweep opener (WSO) attached to Cerere no-till air seeder: (a) front chisel; (b) side coulter; (c) end of coulter(curved upwards); (d) multiple seed dispenser; (e) part of parallellinkage.especially when opener design differs greatly, ashappened inthiscasestudy. Nevertheless, thefollowing results exclusively focus on those para-meters of the seed zone which were mainly affectedby the working system of openers and associatedpresswheelsratherthanbyothermechanicalcomponents.2.2. Field trialsTests were conducted over a period of 2 years(20022003) at a private farm in Teor (Udine, NEItaly: 458550N, 138100E, 8 m a.s.l.) in four fields withdiffering initial conditions (Table 1). The effects ofopeners were evaluated on some soil physicalT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209199Fig. 2. Cerere multi-function trailed no-till air seeder with awide-sweep opener (top) and Max Emerge 2 no-till planter with double-disk opener(bottom).properties in the seed zone, surface soil morphologyand crop emergence and early root growth of maize(Zea mays, L.).In 2002, soils were both clay, with differingamountsofsoilorganiccarbon(SOC),1.45and2.27%in fields A and B, respectively. In 2003, the two fieldshad a different soil texture, with silty loam (field C)and silty-clay loam (field D), but with values of SOCwhich were more similar than in 2002. According tothe FAO classification, the soils of all fields wereclassified as Eutric fluvisols.Following suppression of cover crop with herbicidein March of both years, maize was sown on April 26,2002 and April 15, 2003, according to a theoreticalpopulation density of 8.2 and 7.7 plants m?2andwithin-row distances of 27.1 and 17.3 cm for WSOand DDO, respectively. The small discrepancy of seeddensity between openers was the minimum possible,compatible with the adjustment variations of theseeders. In any case, at least within the aim of thisresearch, the different plant spacing between openerscould not have affected the study parameters.In the test location, annual rainfall, as average ofperiod 19611990, is 1200 mm, 680 mm (57%) ofwhich falls between April and August. The annualaverage temperature is 12.9 8C, with a monthly peakin August (24 8C) and a minimum in December(1.5 8C). During the 2003 crop cycle (AprilAugust),the average temperature was higher and rainfall lowerthan the reference 30-year period values, whereas in2002, the opposite occurred for temperature butrainfall was very similar. In fact, total rainfall in 2002was 1410 mm, 46% (650 mm) of which fell during thecrop cycle, whereas in 2003, it was 966 mm, 37%(362 mm)ofwhichfellduringthecropcycle.Climaticdata, like rainfall and temperature, were provided bytheLocalRegionalAgencyforEnvironmentalProtection (ARPA) (Palmanova, Udine, Italy).Experimental observations on soil physical proper-ties and root density of maize were completed within25 days of sowing and no water was applied duringthis period. Data were measured after the completepassage of the seeder, so that soil parameters wereaffected by both opener and press wheels, allowingcomparisons between seeding units.The experiment involved one 20 m long ? 5 mwide plot per type of opener. According to proceduresof data analysis discussed by Gomez and Gomez(1984) for experiments in farmers fields, this trialmay be viewed as a comparison of two openers indifferent locations or environments, our fields beinglocated far away from each other. Plot size wasidentified as the field area large enough to accom-modate the experiment and with the least soilheterogeneity. Withinplots,soilsamplings andmeasurements were made before or after sowing witha different number of randomised replicates, depend-ingon the parameterinquestion.Statistical analysisofdata (ANOVA) was performed with Statgraphics 5.0Plus Software (Manugistics Inc., Rockville, MD,USA) and differences among means data wereevaluated by the LSD test at P ? 0.05.Parameters measured in the trial are reportedbelow.T. Vamerali et al./Soil & Tillage Research 89 (2006) 196209200Table 1Initial conditions of four fields in 2-year trial and soil characteristics in Teor (NE Italy)Year20022003Field AField BField CField DPrevious cropGlycine max Merr.Glycine max Merr.Sorghum vulgare L.Sorghum vulgare L.Cover crop (species of mixture)Avena sativa L.Avena sativa L.Triticum aestivum L.Triticum aestivum L.Vicia sativa L.Vicia sativa L.Vicia sativa L.Vicia sativa L.Vicia faba minor L.Secale cereale L.FAO soil classificationEutric fluvisolEutric fluvisolEutric fluvisolEutric fluvisolTexture (010 cm depth)ClayClaySilty loamSilty-clay loamSand (%)2119229Silt (%)21205355Clay (%)58612536Soil organic carbon (%)1.452.270.991.452.3. Sowing depthIn 2002 and 2003, respectively, at completeemergence, along four and two transects laid acrossfive sowing rows, one seedling per row therefore, atotal of 20 and 10 plants was completely extractedfrom the soil, allowing the length of the chlorophyll-free coleoptile to be measured. This measure wasconsidered as the depth of seed deposition; uniformityof sowing depth was calculated as the coefficient ofvariation of that depth, i.e., the ratio between standarddeviation and theoretical depth (3 cm). The higher thevalues of this parameter, the lower the uniformity.2.4. Plant emergenceTheemergenceratewascalculatedasthepercentage of emerging seedlings counted in a 3-m2sampling area distributed over five sowing rows (eightand five replicates in 2002 and 2003, respectively), atdifferent times after sowing. Counts were made 8, 10,12, 14, 21 and 25 days after sowing (DAS) in 2002 and6, 8, 14, 19 and 25 DAS in 2003. The percentage ofemergence was determined as the ratio betweennumber of emerging seedlings counted at each timewith respect to their final number (last observationdate). The Gompertz model (Goudriaan and van Laar,1994) turned out to be the most suitable for best-fittingthe time-course (x = time) of emergence (Y) asfollows:Y ce?e?bx?mCoefficients of regression c, b and m and the coeffi-cient of determination (R2) of each curve (treatment)are listed in Table 2. Graphically, the coefficientsindicate the maximum Y value (c), the x value at halfc (m) and the slope at flex (b).2.5. Seedbed roughnessSoil disturbance at the surface caused by theopeners was measured across sowing rows (fivereplicates in both years) in terms of seedbed rough-ness.The contour of the soil profile was marked withblack spray on an A4 sheet of white paper (21 cm ?29.7 cm), the longer side of which was set in the soiland supported by a zinc plate of the same size,orthogonally to the sowing row.According to the definition of Sandri et al. (1998),the roughness index was calculated as furrow standarddeviation (FRSD), i.e., the standard deviation ofheights (42 data) from the bottom of the sheet to thelower contour of the black paint measured at 0.5-cmintervals within 20-cm wide profiles centred aroundthe sowing row.2.6. Covering indexThe soil-covering index (CI) due to crop residueswas determined on digital pictures, taken by OlympusCamedia C2000Z camera, of fixed-size square areas(0.4 m ? 0.4 m) of the soil surface (four replicates inboth years) centred around the sowing row andrandomly set within plots. The same number ofreplicates was also considered before sowing. Residueincorporation (RI) was calculated as the differencebetween CI values before and after sowing.After transferring the images to a computer, avirtual 25-point regular square grid was overlaid onT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209201Table 2Coefficients of regression (?S.D.) (Gompertz model) describing time-course of emergence in various treatmentsFieldOpenerCoefficientsR2cbmAWide-sweep96.2824 ? 2.93960.4236 ? 0.05968.7565 ? 0.22540.998ADouble-disk99.2545 ? 0.75700.5999 ? 0.03047.9177 ? 0.05620.999BWide-sweep97.1697 ? 3.23630.4957 ? 0.08718.3468 ? 0.24150.997BDouble-disk99.02 ? 0.67670.8779 ? 0.06487.5918 ? 0.05390.999CWide-sweep98.8516 ? 0.55341.2774 ? 0.60057.4987 ? 0.23630.999CDouble-disk97.8762 ? 1.73581.4639 ? 2.06257.3201 ? 0.95820.999DWide-sweep98.5250 ? 0.88901.3280 ? 0.88937.4308 ? 0.38200.999DDouble-disk98.7097 ? 0.52682.3322 ? 16.65157.0413 ? 6.76300.999the images, so that the presence or absence of residuesat each node could be counted manually. The CIwas calculated as the number of nodes intersectingresidues, according to the literature (Laflen et al.,1981; Cavalli and Sartori, 1988).2.7. Soil moisture and bulk densityImmediately after sowing (about 4 h later) 5-cmdeep undisturbed soil cores 8 cm in diameter werecollected, using a hand auger above the centre ofthe sowing row (five replicates). Gravimetric watercontent and bulk density were determined after oven-drying at 105 8C to constant weight. In 2003 weresamples also taken at six and eight DAS to determinesoil moisture only.2.8. Soil penetration resistanceIn both years, soil penetration resistance in furrowswas measured using a surface pocket penetrometer(Eijkelkamp, Glesbeek, NL) equipped with a flat-tipped measuring pin (6.4 mm diameter). Measureswere made every 1 cm over 5 cm deep profiles(vertical direction) at one side of the furrows for bothwide-sweep and disk openers, with three replicates(see Fig. 3). Profiles were taken at positions very closeto the sowing row, around 1 cm away. In both years,three replicates were also considered for data takenbefore sowing.2.9. Root growthSoilsampleswerecollectedbymeansofahandauger(8-cmdiameter,5-cmheight)atthethree-leafstageat25and 30 DAS, on May 21, 2002 and May 15, 2003,respectively. At thisearlygrowthstage,the diameterofthe auger was suitable to collect almost the whole rootsystem of seedlings (preliminary tests) and root deve-lopmentwasnotyetaffectedbytheadoptedplantinter-distances. Samples were taken at two interval depths,05and510 cm,centringtheaugerabovesingleplants,with six and three replicates in 2002 and 2003,respectively, for a total number of 48 samples in 2002and24in2003.Soilsampleswerestoredat?18 8Cuntilwashingfor2 hinan2%(w/v)oxalicacidsolution.Soilparticles were then separated in a hydraulic sieving-centrifugation device with 500 mm mesh size (Cahoonand Morton, 1961). Root samples were further cleanedby water sedimentation of heavy particles for 2 minand then stored in a 10% (v/v) ethanol solution at 4 8C.From each root sample, one (or more, when rootlengthseemedtobevisuallytoohightobearrangedinasingle tray) 300-DPI resolution (11.8 pixel mm?1)black-and-white pictures of roots and extraneousobjects (e.g., small pebbles, crop residues, weed seeds)mixed in with them were acquired by digital scanning.Forthispurpose,rootswerefloatedonatransparenttrayof 3-mm thick plexiglass, surrounded by a waterproofgasket, leaving a usable surface of 26.5 cm ? 17.4 cm,filled with a 3-mm water layer to improve separationT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209202Fig.3. Shapeofopenfurrowinwide-sweep(topleft)anddouble-disk(topright)openersandasketchedrepresentation(bottom).Verticalarrowsindicate profiles of soil penetration resistance measurements.andspacingofrootsagainstunwantedresidues.ImageswereprocessedbyKS300Rel.3.0software(CarlZeissVision GmbH, Mu nchen, Germany), interfaced with aspreadsheet for recording data. Root length wasdeterminedbythealgorithmfibrelength(FbL)availablein the software and opportunely modified (Vameraliet al., 2003), as follows:FbL PERIM ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiPERIM2? 16AREAq4where PERIM and AREA are, respectively, the peri-meter and area ofobjects considered,withthe possibleoccurrence of empty regions.In order to identify roots against extraneousobjects, values of the elongation index, i.e., ratiobetween square perimeter and area, of 75 were usedduring image processing. A minimum object area (16pixels) was also adopted to reduce background noise.Volumetric root length density (RLD) in soil wascalculatedbyreferringthelengthofeachsampletothestandard volume of soil (251.3 cm3).The mean root diameter was calculated as the ratiobetween the projection area and the length of rootobjects in a sample.The biomass of dried root samples (105 8C toconstant weight) was also measured after imageacquisition. This operation required prior manualseparation of organic debris by means of tweezers.3. Results and discussion3.1. Sowing depth and plant emergenceBoth openers allowed seeds to be placed at thesame depth in almost all field conditions, the averageseeding depth over 2 years 26.5 and 26.4 mm forwide-sweepWSO anddouble-diskDDO,respectively,not being significantly different; the exception was thedrier soil of field C (see data below), for which asignificantly shallower deposition was observed withthe WSO (17.4 mm versus 26.7 mm). The standarddeviation of seeding depths was also not very differentbetween openers, it being 0.73 and 0.63 mm in WSOand DDO, respectively,thus resulting in similar valuesof depth uniformity, although a relatively loweruniformity for tine or hoe openers could be expected,as commonly reported in the literature (Wilkins et al.,1983; Chaudhuri, 2001). Nevertheless, in our case, theintegrated seed deposition adjustment system asso-ciated with WSO allowed improved accuracy inseeding depth.As regards plant emergence, a general delay wasobserved for WSO with respect to DDO, especially in2002, in which almost 1 days delay field A: 0.84days; field B: 0.75 days was revealed in order todetect 50% of emergence, as evidenced by the mcoefficient of the Gompertz regressions (Table 2,Fig. 4). Delayed emergence was almost negligible inT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209203Fig. 4. Time-course of emergence in maize (Gompertz regressions) in four fields. Markers represent data.2003, probably because of the very short germinationtime (see high values of coefficientbin Table 2) due tothe high temperature at sowing and the very similarbulk density for the two openers in the first top 5 cmlayer. The dynamics of plant emergence were similarin WSO and DDO, particularly in field C, charac-terised by lower soil moisture at sowing a fact thatdid not allow variations of bulk density to be detected,regardless of opener type.When delay was observed, it may partly have beendue to the lower bulk density and associated lowerpenetration resistance (see below), observed aboveseeds for the wide-sweep opener with respect to thedisk model, which presumably led to lower soil/seedcontact. This hypothesis is supported by previousfindings for various crops (e.g., Morrison, 1989; Chenet al., 2004), with not only delayed emergence butalsoreduced plant population and yield in normal and drysoils when press wheels were not used.Modelling is a good tool to generalise the effects ofsoil conditions on emergence and it is known thattemperature and water potential more than oxygenconcentration are the main affecting factors, asexpressed by the concept of hydro-thermal time(Gummerson, 1986). Although a sigmoid model isgenerally used to represent the rate of emergence (seereview by Gue rif et al., 2001), we found a generallygoodfitwiththeGompertzcurve,amodelwidelyusedto represent growth dynamics in plants. Because theGompertz curve does not incorporate symmetryrestriction as in the sigmoid model (e.g., logistic)and has a shorter period of fast growth, verificationshould be made as regards whether or not this functionwould be more suitable when part of the emergencetime is variously affected by some limiting factors,such as water restriction or surface crusting.3.2. Effects on soil morphologySoil disturbance at the surface was significantlydifferentbetweenopenersandfieldswithdifferingsoilphysical properties (Table 3). On an average (fourfields), soil roughness was greater for WSO than forDDO, as evidenced by the higher FRSD, 0.91 and0.41, respectively. This result, clearly observable in allfields, was due to the different working system of thetwo openers, the front chisel and side coulters of theWSO exerting both greater and more extended (acrossrow) disturbance and soil mixing than the DDO. Theexamples of furrow surface traces of the two openers(field A: clay, 31.3% soil moisture) (Fig. 5) showconstantly greater profile heights in WSO and thegreater FRSD through the 20-cm long observeddistance (across row) is appreciable even graphically.The soil profile for DDO was typically V-shapedand the resulting soil roughness was similar amongfields, except for field C, which had low FRSD values,probably because of the limited impact of the disks inconditions of low soil moisture (21.2%) (Table 3).Although the surface trace of WSO was not exactlysymmetric, a generally lower furrow height with sidehumps was observed (Fig. 5). This shape should beconsidered as a result of the particular kind of workdone by the side coulters of WSO, which cut andreplace soil almost in its original position (see Fig. 3).Nevertheless, we did measure a certain variation insoil roughness in different conditions, with lowerFRSD in cases of reduced soil moisture (field C) (bothT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209204Table 3Effects of opener type on soil disturbance in various fieldsFieldWide-sweepDouble-diskCI (%)RI (%)FRSDCI (%)RI (%)FRSDBeforeAfterBeforeAfterA69 a37 b32 a1.04 a75 a68 a7 a0.43 aB79 a54 b25 b0.81 b83 a78 a5 a0.48 aC67 a44 b23 b0.70 b81 a77 a4 a0.29 bD67 a41 b26 b1.07 a88 a79 a9 a0.43 aMean71 a44 b27 A0.91 A82 a76 a6 B0.41 BLower-case letters indicate significant differences among observation times (beforevs. after sowing) for covering index (CI) or among fields fortwo other parameters (residue incorporation (RI) and furrow roughness standard deviation (FRSD). For same parameter, differences betweenopeners are expressed by capital letters (LSD test, P ? 0.05).openers) and high contents of organic carbon (field B)(only WSO) (Table 3), mainly because of the smallersize of top-soil aggregates.The different working systems of the two openershad also some effects on the covering index (Table 3).DDO did not modify at all the amount of residues atthe soil surface,northereforethose incorporated inthesoil, the CI before and after sowing being 82% and76% respectively. Instead, in WSO, the front chiselcaused appreciable incorporation of residues in allfields (RI = 27%, on average), the CI falling from 71to 44%, with a tendency towards higher values ofresidue incorporation with higher FRSD.The resulting different covering index in the twoopeners may variously affect soil protection (e.g.,erosion, water losses) and the fate of residues,which we did not evaluate in the flat plain of ourexperimental site. If we aim at limiting soil erosion,higher CI values are preferable, although a value(37%) almost double that reported by Dickey et al.(1985) (20%) for reducing erosion by 50% wasfound in the worst condition for WSO (field A). In anycase, incorporation of residues was restricted to thefirst top layer and the higher incidence observed forthe wide-sweep opener may positively facilitatetheir decomposition, with release of nutrients to thecrop.3.3. Physical properties of soil and root growthinteractionsBecause of the different soil disturbance due to thetypeofopener,differingdegreesofsoilmoistureinthetop 5 cm soil layer are to be expected. Nevertheless,measurements made before sowing and those takenwithin a few hours after sowing were almost similarfor both openers. In 2003, within 8 days of sowing andinthe absence ofrain,non-significantvariations insoilmoisture in fields C and D were also detected,although possible differences along the 05 cm profilecannot be excluded. This suggests that soil protectionagainst water losses due to residues (mulching effect)may be guaranteed even at the lower soil-coveringindex found for thewide-sweep opener with respect tothe double-disk one (44% versus 76%).In the 2-year experiment, the only differencesamong soils regarded their initial conditions ofmoisture. In 2002, both soils had the same moisturecontent (31.5%), whereas in 2003, a dry year, a lowervalue was measured in the silty loam (field C) than inthe silty-clay loam (field D) (20.9% versus 30.6%),mainly because of the greater amount of sand andlower content of clay.The type of opener did affect soil bulk density invariousways.WSOconsiderablyreducedbulkdensityin almost all soil types: 17% in field A, 20% in field Band14%infieldD(Fig.6).InfieldC,bulkdensitywasnot modified at all, fitting the lowest FRSD, againprobably related to the lowest both soil moisture andclay content. Instead, DDO had, in general very littleinfluence on this soil property, due to lower soildisturbance.In general, both openers reduced penetrationresistance (PR) in the seed zone, but with somedistinctions among soil types. In 2002, the differentamounts of organic carbon in the two experimentalfields although they both had the same clay texture greatly affected not only this soil parameter beforesowing,butalsotheeffectsoftheopeners.Manyofthedifferences between openers were observed with littleT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209205Fig. 5. Typical furrow surface trace for two openers in field A (clay soil, 31.3% soil moisture). LSD value for opener type ? distance fromfurrow interaction at P ? 0.05: 16.32.organic carbon (field A). For instance, before sowing,PR was almost constant with depth (232 kPa, average05 cm), but it changed markedly after sowing, withgreat differences between openers, especially in thetop 3-cm layer (Fig. 7). On average (05 cm), PR wasreduced by 64% with WSO but only 23% with DDO,followingthelowerbulkdensity.InfieldB,penetration resistance before sowing was much lowerthan in field A (2.6 times), so that the effects of bothopeners were attenuated, especially that of DDO.In 2003, in both fields C and D, WSO significantlyreduced PR in a similar way as 2002 (Fig. 7), whereasT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209206Fig. 6. Effects of openers on soil bulk density (top 5-cm layer) in four fields. Vertical bars represent standard error. Percentage variations fromvalues measured before sowing are reported for both openers.Fig. 7. Variations in soil penetrationresistancewith depth(top 5-cm layer) in four fields for two openers. Horizontal barsrepresent standarderror.for DDO, only a slight reduction was measured alongsoil profiles with respect to the specific before-sowingpattern.When PR was standardised by the values observedbefore sowing, more homogeneous patterns werefound for the wide-sweep opener. A great reduction inPR was achieved in the upper 3 cm in all experimentalfields, followed by a marked increase in the remaining2-cm profile, their standardised values becoming 1(Fig. 8). This behaviour indicates that a differentsmoothing effect at the seeding depth may be causedby the side coulters, depending on soil type andmoisture. The effect of the double-disk opener on PRwas less evident even after standardisation, with atendency towards lower values at increasing depths.Despitethe generalreductioninpenetrationresistance in the first 3 cm for WSO, in almost allfields no significant increases in root growth (at thethree-leaf stage) in terms of either biomass or lengthwere revealed, these two root traits being significantlycorrelated (P ? 0.05) with a high coefficient ofdetermination (year 2002: R2= 0.78; year 2003:R2= 0.71). Conversely, unexpectedly lower RLDvalues were found in the top 5-cm layer with respectto DDO in field A (Fig. 9), probably because of theT. Vamerali et al./Soil & Tillage Research 89 (2006) 196209207Fig. 8. Profiles of soil penetration resistance standardised by thevalues before sowing, in four fields for two openers.Fig. 9. Distribution of soilroot length density (RLD, data from core sample image analysis) in four fields for two openers. Vertical barsrepresent standard error.above-notedsmoothingeffect,whichledsomerootstogrow plagiotropically (visual evaluation) at least inthis early stage, partially out of the auger soil volume.No differences between openers were observed interms of root growth at depths below 5 cm, nor at anyof the two depths in the other fields, a decrease withdepth being normal. The very high values of RLD infield B were due to the extremely low PR and the greatamount of organic carbon.As regards root diameter too, no differences couldbe foundbetweentheopeners inanyofthe testedfieldsor depths, although it is known that this root trait ismainly affected by the physical properties of the soil,e.g., penetration resistance, which was variouslymodified by both openers (Materechera et al., 1992;Tsegaye and Mullins, 1994). Nevertheless, it should berecalledthatthePRvaluesinthisstudywereneververyhigh, not exceeding 400 kPa (field C, 5 cm depth).4. ConclusionsThe increasing focus on soil tillage systems withlow environmental impact and costs has led to thedesign of new mechanical solutions, even in Italy. Inthis study, a new wide-sweep opener (WSO) for no-tillage was found to affect soil properties in the seedzone to different extents than the double-disk type(DDO).The WSO, connected to a parallel linkage system,achieved appreciable tillage of soil with higherincorporation of crop residues and uniform sowingdepth. Only penetration resistance and bulk densitywere affected by opener type. Although WSO reducedthese parameters more than DDO, the smoothingeffect observed at the sowing depth slightly reducedroot growth or orientation but not diameter at thethree-leaf stage of maize, as happened in the top 5 cmlayer of a clay soil with little organic carbon (field A).Independent of furrow zone properties, the twoopeners behaved stably in the various soils, but insome cases, because of particular initial conditions(e.g., lower moisture: field C), variations wereobserved, especially for WSO, as regards bulkdensity,soil roughness and sowing depth.These findings, which are a rare example of anintegrated approach applying mechanics, soil physicsand root morphology, indicate that closer integrationof several research topics should be taken intoconsideration, for more insights into the functioningof agricultural machinery.AcknowledgementsWe are grateful to Claudio Nerva for help intechnical drawing and to Gabriel Walton for revisionof the English text.ReferencesAlessi, J., Power, J.F., 1971. 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