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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 dell Universita 16 35020 Legnaro Padova Italy bDipartimento Territorio e Sistemi Agro forestali University of Padova Agripolis Viale dell Universita 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 2002 2003 in comparison with the widely used double disk opener With respect to the double disk opener ingeneral thewide sweep type led to higher soil residue mixing without 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 1 unipd 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 towardsthesoilsurface afactparticularlyappreciable 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 25 30 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 50 8 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 2002 2003 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 b x 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 0 5and5 10 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 day s 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 Gummerson 1986 Although a sigmoid model is generally used to represent the rate of emergence see review by Gue rif et al 2001 we found a generally goodfi twiththeGompertzcurve amodelwidelyused to represent growth dynamics in plants Because the Gompertz curve does not incorporate symmetry restriction as in the sigmoid model e g logistic and has a shorter period of fast growth verifi cation should be made as regards whether or not this function would be more suitable when part of the emergence time is variously affected by some limiting factors such as water restriction or surface crusting 3 2 Effects on soil morphology Soil disturbanc