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Effects of a new wide-sweep opener for no-till planter on seed zone properties and root establishment in maize (Zea mays, L.): A comparison with double-disk opener T. Vamerali a, M. Bertoccob,*, L. Sartorib aDipartimento di Agronomia Ambientale e Produzioni Vegetali, University of Padova, Agripolis, Viale dellUniversita 16, 35020 Legnaro, Padova, Italy bDipartimento Territorio e Sistemi Agro-forestali, University of Padova, Agripolis, Viale dellUniversita 16, 35020 Legnaro, Padova, Italy Received 17 February 2005; received in revised form 13 July 2005; accepted 29 July 2005 Abstract According to the kind of opener applied, no-tillage seeders can variously modify soil physical properties in relation to soil and 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 been considerable, but new improvements now available need to be individually tested. In a fi eld trial at Udine (NE Italy), the effects ofanewkindofwide-sweepopener(i.e.,sidecoulterscurvedupwardsintheirfi nalpartandslightlyangledtowardsthedirection of work) on soil physical properties in the seed zone and on crop emergence and early root growth of maize were evaluated in four 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 excessive reduction of the soil-covering index being observed, ?27 and ?6%, respectively. The wide-sweep opener also showed lower bulk density and soil penetration resistance in the top 5-cm soil layer of the seed furrow, although no greater root length density was 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,whichmayberelatedtothelower soil/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 Soil 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.2005.07.011 1. Introduction In the last few years, the economic and environ- mental implications of conventional tillage, such as erosion, compaction and inverting soil layers, have led to re-examination of no-tillage even in Italy (Sartori and Peruzzi, 1994). Especially, in the heavy soils of this country, deep ploughing aims at increasing soil porosity, at least temporarily, in order to create suitable conditions for both seed germination and root growth. Simplifi cation of weed management and higher grain yields of summer crops like maize are generally achieved with respect to no-tillage, as evidencedbythefewdataavailableintheliteraturefor Italy (e.g., Bona et al., 1995). The performance of no-tillage seeders depends on several factors related to fi eld conditions, including type and amount of residues at soil surface, opener design (Morrison, 2002) and the crop to be sown. The implementsoftheseseedersmusthavehighfl exibility, so that various crops can be sown in differing fi eld conditions with correct seed deposition (e.g., density, distance, depth). In no-tillage practices, the character- istics of the seed-furrow play an important role in germination. Many authors have pointed out that the most signifi cant factors regulating germination, such as soil matric potential, temperature (Lindstrom et al., 1976; Schneider and Gupta, 1985) and sowing depth (Alessi and Power, 1971; Mahdi et al., 1998) are affected by the soil/opener interaction (Tessier et al., 1991a,b). In particular, in order to maintain constant sowing depth, various types of linkages between opener and seeder toolbar have been proposed during the last few decades. For instance, connection with a spring system, the oldest but simplest solution, is not always adequate to guarantee uniformity of sowing depth, especially in heavy soils. Great improvements have been obtained with parallel linkage, since this allows the opener to follow soil surface profi les accurately. Many of the characteristics of the seed zone in no- tillage depends on the type of opener attached to the seeder (Wilkins et al., 1983) and the two main types used tine and disk may lead to great differences. The tine opener typically creates an appreciable bursting effect in the soil and generally moves a considerable quantity of fi ne damper aggregates towardsthesoilsurfaceafactparticularlyappreciable in tools having an asymmetric shape (Darmora and Pandey, 1995) but which may be negative if a rainless periodoccurs aftersowing,assoildryingisaccelerated (Chaudhuri, 2001). In similar conditions, the disk opener may cause more progressive water loss in the soil layer above the seeds than the tine opener (Tessier et al., 1991a,b), although great drawbacks are observable in wet clay soils because a permanent unclosed furrow is commonly created (Sartori and Sandri, 1995). It is widely recognised that management of crop residues (previous crop) is one of the most important constraints for adopting no-tillage (Carter, 1994). Tine openersshiftorganicdebrisinthesoilsurfacefromthe crop row sideways, with possible plugging of the seeder in the case of heavy residues, whereas disk openers may lead to hairpinning, with a consequent bad soil/seed contact and possible toxic effect on seedlings (Hultgreen, 2000). Unmanaged residues can create many problems in direct sowing, but their presence at the soil surface is generally benefi cial in limiting some negativeeffects on soil, like erosion and water losses (Gill and Aulakh, 1990). As regards soil and climate conditions, openers should achieveseveral aims, like uniformityof sowing i.e., spacing and depth production of a suitable amount of fi ne soil aggregate to ensure soil/seed contact, reduction of water losses, avoidance of seed contact with either fertilizers or crop residues and limitation of furrow compaction, which may obstruct root growth (Willatt, 1986; Tsegaye and Mullins, 1994; Bueno et al., 2002). The type of opener was found to affect emergence and plant establishment markedly (McLeod et al., 1992), especially in crust- forming soils, for which better results are generally obtained with the double-disk opener (Hemmat and Khashoei, 2003). The technological evolution of no-tillage seeders for arable crops, progressively achieved in this sector, has been great, but the large number of improvements now available must be individually tested and care- fully evaluated. In addition, much of the literature on this subject refers almost exclusively to opener/soil interactions, without analysing effects on crop growth. The effects of furrow shape and its properties on the draft force required by different opener types have been widely studied in relation to soil conditions and operating parameters, such as depth or speed T. Vamerali et al./Soil Collins and Fowler, 1996; Sa nchez-Giro n et al., 2005). Instead, only a few studies have examined some crop parameters and they generally deal with drills for autumn sowing of cereals. For instance, Chaudhry and Baker (1988) found that various types of opener led to different types of growth of barley seedlings, i.e., greater shoot and root weights when both winged (T-shaped groove) or hoe (U-shaped groove) types are used instead of the triple-disk one. In this framework, the present study evaluates the performance of an innovative wide-sweep opener, linked to the frame by a double linkage unit. Its effects on some soil physical properties in the seed zone, crop emergence and early root growth of maize were evaluated in various soils over a 2-year period in NE Italy and compared with those of a double-disk opener, which is the most widespread in Italy. 2. Materials and methods 2.1. Description of equipment The performances of a new wide-sweep opener (WSO) with which the no-till air seeder Cerere (Tecnoagricola, Udine, Italy) has been equipped, was compared with that of a double-disk opener (DDO) adopted by the no-till planter Max Emerge 2 (John Deere Italia, Milan, Italy). The WSO has a straight axis, ending with a front chisel and two rear side 18-cm wide coulters, which are slightly angled towards the direction of work and curved upwards (908) in their fi nal part (25 mm high) (Fig. 1). The front chisel cuts soil 2530 mm deeper than the coulters. Seed delivery to each unit is through a single pneumatic tube from the centralised volu- metric metering system, which allows the seeder to assume a certain degree of polyvalence. Although various types of deposition (i.e., row spacing) can be set, in our fi eld trial as the fi rst test of this prototype opener maize was sown in rows 0.45 m apart, a distance commonly used in the experimental site. The structure of the seeder equipped with the WSO includes one rigid and one folding frame. The fi rst is supported by a front head-shaft to couple the seeder to the tractor and two rear low-pressure wheels for transport. The folding frame aims at guaranteeing that the soil profi le can be followed by the openers as regularly as possible. For this reason, it has three independent jointed sections, each 1.5 m wide and linked to the rigid frame with four elastic joints. Each section has fi ve openers, for a total of 15 sowing rows, which are laid on three seeding lines and equipped with a single parallel linkage for improved stability. In addition, each section is supported by a front wheel and a rear packer tandem (Fig. 2). The latter is an essential component for the working the seeding unit in this seeder; it is made of 10 wheels per section, with 3.508 tyres and 0.9 bar pressure. The seeder equipped with the DDO is an eight-unit mounted no-till planter with pneumatic seed metering and 0.75 m row spacing, resulting in a 6 m working width. The DDO used here is composed of a single, fl uted,round-bladedcoulterandadouble-disk, associated with two side rollers and two rear V- mounted wheels (Fig. 2). Performance valuation of opener types requires differences among seeders to be kept to a minimum, although this is not always completely possible, T. Vamerali et al./Soil (b) side coulter; (c) end of coulter (curved upwards); (d) multiple seed dispenser; (e) part of parallel linkage. especially when opener design differs greatly, as happened inthiscasestudy. Nevertheless, the following results exclusively focus on those para- meters of the seed zone which were mainly affected by the working system of openers and associated presswheelsratherthanbyothermechanical components. 2.2. Field trials Tests were conducted over a period of 2 years (20022003) at a private farm in Teor (Udine, NE Italy: 458550N, 138100 E, 8 m a.s.l.) in four fi elds with differing initial conditions (Table 1). The effects of openers were evaluated on some soil physical T. Vamerali et al./Soil uniformity of sowing depth was calculated as the coeffi cient of variation of that depth, i.e., the ratio between standard deviation and theoretical depth (3 cm). The higher the values of this parameter, the lower the uniformity. 2.4. Plant emergence Theemergenceratewascalculatedasthe percentage of emerging seedlings counted in a 3-m2 sampling area distributed over fi ve sowing rows (eight and fi ve replicates in 2002 and 2003, respectively), at different times after sowing. Counts were made 8, 10, 12, 14, 21 and 25 days after sowing (DAS) in 2002 and 6, 8, 14, 19 and 25 DAS in 2003. The percentage of emergence was determined as the ratio between number of emerging seedlings counted at each time with respect to their fi nal number (last observation date). The Gompertz model (Goudriaan and van Laar, 1994) turned out to be the most suitable for best-fi tting the time-course (x = time) of emergence (Y) as follows: Y ce?e ?bx?m Coeffi cients of regression c, b and m and the coeffi - cient of determination (R2) of each curve (treatment) are listed in Table 2. Graphically, the coeffi cients indicate the maximum Y value (c), the x value at half c (m) and the slope at fl ex (b). 2.5. Seedbed roughness Soil disturbance at the surface caused by the openers was measured across sowing rows (fi ve replicates in both years) in terms of seedbed rough- ness. The contour of the soil profi le was marked with black spray on an A4 sheet of white paper (21 cm ? 29.7 cm), the longer side of which was set in the soil and supported by a zinc plate of the same size, orthogonally to the sowing row. According to the defi nition of Sandri et al. (1998), the roughness index was calculated as furrow standard deviation (FRSD), i.e., the standard deviation of heights (42 data) from the bottom of the sheet to the lower contour of the black paint measured at 0.5-cm intervals within 20-cm wide profi les centred around the sowing row. 2.6. Covering index The soil-covering index (CI) due to crop residues was determined on digital pictures, taken by Olympus Camedia C2000Z camera, of fi xed-size square areas (0.4 m ? 0.4 m) of the soil surface (four replicates in both years) centred around the sowing row and randomly set within plots. The same number of replicates was also considered before sowing. Residue incorporation (RI) was calculated as the difference between CI values before and after sowing. After transferring the images to a computer, a virtual 25-point regular square grid was overlaid on T. Vamerali et al./Soil Cavalli and Sartori, 1988). 2.7. Soil moisture and bulk density Immediately after sowing (about 4 h later) 5-cm deep undisturbed soil cores 8 cm in diameter were collected, using a hand auger above the centre of the sowing row (fi ve replicates). Gravimetric water content and bulk density were determined after oven- drying at 105 8C to constant weight. In 2003 were samples also taken at six and eight DAS to determine soil moisture only. 2.8. Soil penetration resistance In both years, soil penetration resistance in furrows was measured using a surface pocket penetrometer (Eijkelkamp, Glesbeek, NL) equipped with a fl at- tipped measuring pin (6.4 mm diameter). Measures were made every 1 cm over 5 cm deep profi les (vertical direction) at one side of the furrows for both wide-sweep and disk openers, with three replicates (see Fig. 3). Profi les were taken at positions very close to the sowing row, around 1 cm away. In both years, three replicates were also considered for data taken before sowing. 2.9. Root growth Soilsampleswerecollectedbymeansofahandauger (8-cmdiameter,5-cmheight)atthethree-leafstageat25 and 30 DAS, on May 21, 2002 and May 15, 2003, respectively. At thisearlygrowthstage,the diameterof the auger was suitable to collect almost the whole root system 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 2002 and24in2003.Soilsampleswerestoredat?18 8Cuntil washingfor2 hinan2%(w/v)oxalicacidsolution.Soil particles were then separated in a hydraulic sieving- centrifugation device with 500 mm mesh size (Cahoon and Morton, 1961). Root samples were further cleaned by water sedimentation of heavy particles for 2 min and then stored in a 10% (v/v) ethanol solution at 4 8C. From each root sample, one (or more, when root lengthseemedtobevisuallytoohightobearrangedina single tray) 300-DPI resolution (11.8 pixel mm?1) black-and-white pictures of roots and extraneous objects (e.g., small pebbles, crop residues, weed seeds) mixed in with them were acquired by digital scanning. Forthispurpose,rootswerefl oatedonatransparenttray of 3-mm thick plexiglass, surrounded by a waterproof gasket, leaving a usable surface of 26.5 cm ? 17.4 cm, fi lled with a 3-mm water layer to improve separation T. Vamerali et al./Soil the exception was the drier soil of fi eld C (see data below), for which a signifi cantly shallower deposition was observed with the WSO (17.4 mm versus 26.7 mm). The standard deviation of seeding depths was also not very different between openers, it being 0.73 and 0.63 mm in WSO and DDO, respectively,thus resulting in similar values of depth uniformity, although a relatively lower uniformity for tine or hoe openers could be expected, as commonly reported in the literature (Wilkins et al., 1983; Chaudhuri, 2001). Nevertheless, in our case, the integrated seed deposition adjustment system asso- ciated with WSO allowed improved accuracy in seeding depth. As regards plant emergence, a general delay was observed for WSO with respect to DDO, especially in 2002, in which almost 1 days delay fi eld A: 0.84 days; fi eld B: 0.75 days was revealed in order to detect 50% of emergence, as evidenced by the m coeffi cient of the Gompertz regressions (Table 2, Fig. 4). Delayed emergence was almost negligible in T. Vamerali et al./Soil Chen et al., 2004), with not only delayed emergence butalso reduced plant population and yield in normal and dry soils when press wheels were not used. Modelling is a good tool to generalise the effects of soil conditions on emergence and it is known that temperature and water potential more than oxygen concentration are the main affecting factors, as expressed by the concept of hydro-thermal time (Gummerso