CROP MANAGEMENT SYSTEMS AND MAIZE GRAIN YIELD UNDER NARROW ROW SPACING

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1 346 Strieder et l. CROP MANAGEMENT SYSTEMS AND MAIZE GRAIN YIELD UNDER NARROW ROW SPACING Mércio Luiz Strieder ; Pulo Regis Ferreir d Silv *; Lisndro Rmbo 2 ; Luís Sngoi 3 ; Adrino Alves d Silv ; Pulo Césr Endrigo ; Dougls Btist Jndrey UFRGS Depto. de Plnts de Lvour, C.P Porto Alegre, RS Brsil. 2 Syngent Seeds Desenvolvimento de Produtos, Rod. BR 452, km Uberlândi MG, Brsil. 3 UDESC Depto. de Fitotecni, C.P Lges, SC Brsil. *Corresponding uthor <pulo.silv@ufrgs.br> ABSTRACT: Reduction in row spcing provides more uniform distribution mong plnts tht cn increse grin yield. The benefits of nrrow row spcing cn depend on the plnt rchitecture nd on the kind of crop mngement system. The objective of this study ws to ssess the effects of nrrow row spcing on the grin yield of mize hybrids growing under different mngement systems. Six experiments were crried out in Eldordo do Sul, Stte of Rio Grnde do Sul, Brzil, during the 2003/04 nd 2004/05 growing sesons. Ech experiment corresponded to crop mngement system. Tretments consisted of two row spcings (0.8 nd 0.4 m), two hybrids (Pent nd Flsh) nd two plnt densities, which vried with the crop mngement system nd growing seson. Besides plnt density, the crop mngement systems differed in the quntities of fertilizers pplied t sowing, sidedress nd use of irrigtion. A complete rndomized block design ws used in ech experiment, in tretment fctoril scheme with four replictions. The increses in grin yield with nrrow row spcing were smll, rnging from zero to 4%. They depended on the growing seson nd were mnifested only with yields higher thn 0 t h, regrdless of the hybrid. The number of grins per re ws the component tht best explined the response of grin to nrrow row spcing, regrdless of plnt density, hybrid nd crop mngement system. Nrrow row spcing is worth mngement strtegy to enhnce mize grin yield when high input cropping systems re used. Key words: Ze mys, plnt rrngement, hybrid, yield components, fertility nd irrigtion levels SISTEMAS DE MANEJO E PRODUTIVIDADE DE GRÃOS DE MILHO SOB ESPAÇAMENTO ENTRELINHAS REDUZIDO RESUMO: A redução do espçmento entrelinhs melhor distribuição entre plnts n áre e pode incrementr produtividde de grãos. Os benefícios d redução do espçmento entrelinhs podem depender d rquitetur de plnt e do sistem de mnejo empregdo. A pesquis objetivou vlir os efeitos d redução do espçmento entrelinhs n produtividde de grãos de híbridos de milho cultivdos em diferentes sistems de mnejo. Seis experimentos form conduzidos cmpo, em Eldordo do SulRS, nos nos grícols 2004/05 e 2005/06. Cd experimento correspondeu um sistem de mnejo. Os trtmentos constrm de dois espçmentos (0,8 e 0,4 m), dois híbridos (Pent e Flsh) e dus densiddes de plnts, vriáveis com o sistem de mnejo e nos grícols. Além d densidde, os sistems de mnejo diferirm ns quntiddes plicds de dubo n semedur, em cobertur e n suplementção hídric. Em cd experimento, o delinemento experimentl foi o de blocos csulizdos, em ftoril 2 2 2, com qutro repetições. Os incrementos n produtividde de grãos com redução do espçmento form de pequen mgnitude, vrindo de 0 4%. Eles dependerm d estção de crescimento e se mnifestrm pens com produtividdes superiores 0 t h, independente do híbrido. O número de grãos por áre foi o componente que melhor explicou respost d produtividde com redução do espçmento, independentemente de densidde, híbrido e sistem de mnejo. A redução do espçmento é um estrtégi de mnejo válid pr incrementr produtividde de grãos qundo são dotdos níveis de mnejo muito ltos. Plvrschve: Ze mys, rrnjo de plnts, híbrido, componentes d produção, níveis de fertilidde e irrigção INTRODUCTION The photosyntheticlly ctive solr rdition intercepted (PAR int ) by the cnopy is one of the min requirements to obtin high yields in the bsence of wter shortge (Melges et l., 989). A strtegy to in

2 Nrrow row spcing for mize 347 crese PAR int is the choice of plnt rrngement, one of the crop mngement prctices tht most influences grin yield nd tht cn be mnipulted by modifying row spcing, density nd plnt distribution in the row (Ottmn & Welch, 989; Loomis & Amthor, 999; Argent et l., 200b; Silv et l., 2006). The benefits nd limittions of nrrow row spcing for mize hve been widely discussed during the lst ten yers. Some dvntges of reducing row spcing include the more efficient use of environmentl resources, better weed control nd higher grin yield. However, mny studies with nrrow row spcing in mize hve shown smll increses (zero to 0%) in grin yield compred to conventionl spcing (Sngoi, 990; Sngoi et l., 998 nd 200; Tesdle, 998; Argent et l., 200; Flesch & Vieir, 2004). These smll size responses indicte tht other fctors my limit the dvntges of using nrrow row to increse grin yield, such s hybrid rchitecture nd mngement system. Modern mize hybrids tolerte higher plnt densities thn hybrids used in the pst (Duvick & Cssmnn, 999; Tollenr & Lee, 2002; Sngoi et l., 2002), nd the use of nrrow rows hs greter potentil to enhnce grin yield t crowded stnds (Silv et l., 2006; Sngoi & Silv, 2006). Considering the ltertions introduced by breeding progrms in recent hybrids, the hypothesis of this study ws tht there would be positive response to nrrow row spcing, especilly in situtions where high grin yield levels re ccomplished nd other limiting fctors, besides those relted to plnt distribution, re met. The objective of this study ws to ssess the effects of nrrow row spcing on grin yield, its components nd on other gronomic chrcteristics of two mize hybrids, cultivted under three crop mngement systems nd two plnt densities. MATERIAL AND METHODS Six field experiments were crried out in Eldordo do Sul Stte of Rio Grnde do Sul, Brzil (30º05 S, 5º W, men ltitude 46 m), three in 2003/04 nd three in 2004/05. The climte of the region is humid subtropicl, with,446 mm men nnul rinfll nd 426 mm concentrted from November to Februry (Bergmschi et l., 2003). This period includes flowering, grin formtion nd grin filling of mize when sown in the first 5 dys of October. The soil ws clssified s typicl dystrophic red cly soil (Embrp, 999) nd hs been cultivted for the lst 3 yers under the no till system, with soyben nd mize rottion in the summer. The physicl nd chemicl ttributes of the soil re: cly content: 338 g kg ; ph in wter: 5.2; vilble P: 6. mg L ; vilble K: 67 mg L ; orgnic mtter: 23 g kg nd ctionic exchnge cpcity: 87 mmol c L (Tedesco et l., 995). Phosphorus nd potssium soil contents were extrcted through the Mehlich I method. In the two growing sesons, ech of the three crop mngement systems (medium, high nd very high) corresponded to one experiment. The tretments consisted of two row spcings (0.4 nd 0.8 m), two hybrids (Flsh, with erect leves nd Pent with flttened leves) nd two plnt densities, which vried with the crop mngement system nd growing seson (Tble ). In the six experiments, complete rndomized block design ws used in tretment fctoril scheme (n = 4). The two genotypes were Flsh nd Pent, singlecross hybrids with very erly nd erly cycles, respectively. Besides the plnt density, the crop mngement systems differed regrding the quntity of fertilizer pplied t sowing nd sidedress, nd in the use of irrigtion (Tble ). The fertilizer levels nd plnt densities used in the medium nd high crop mngement systems were bsed on the Tble Chrcteristics of the three mize crop mngement systems in ech growing seson. Crop mngement system 2 plnt m kg h Medium / W ithout High With Very high With / In the medium crop mngement system, irrigtion ws performed only with high wter shortge during the most criticl period from 4 dys before (V 5 stge) to twenty dys fter flowering (R 3 stge). Minerl fertilizers Plnt density N P 2 O 5 K 2 O 2003/ /05 Sowing Side dress Sowing Supplementl irrigtion

3 348 Strieder et l. technicl recommendtions for mize of the sttes RS nd SC (CQFS RS/SC, 2004; Reunião, 2005). The two experiments with very high crop mngement system, were bsed on trils conducted previously t the sme plce by Argent et l. (2003) nd by Forsthofer et l. (2006). Mize ws sown on 2 October 2003 nd 3 October Plnt densities were djusted to the required vlues 4 dys fter seedling emergence, t the V 2 stge, following the development scle proposed by Ritchie et l. (993). In ll the crop mngement systems, the sowing nd sidedress fertilizers were performed by hnd on the row. At sowing, it consisted of mixture of ure (45% N), triple super phosphte (42% P 2 O 5 ) nd potssium chloride (60% K 2 O) nd for sidedressing just ure. The rtes of ech pplied fertilizer re described in Tble. The N levels pplied on sidedressings vried with the crop mngement system. Thus, in the medium crop mngement system 60 kg h were pplied t the five expnded lef stge (V 5 ). In the high crop mngement system, 50 nd 70 kg h of N were sidedressed t the V 4 nd V 0 stges, respectively. In the very high crop mngement system, 45, 65 nd 75 kg h of N were pplied t the V 3, V 9 nd preflowering stges, respectively. During the two yers the meteorologicl dt to clculte the wter blnce were obtined from meteorologicl unit locted t.3 km from the experimentl re. Although only the dt regrding the period between October nd Mrch re presented for ech growing seson, the wter blnce ws clculted between September nd April, considering 75 mm s vilble wter cpcity in soil. In the high nd very high crop mngement systems, mize irrigtion requirements were considered similr. They were estimted by the instlltion of three tensiometers t 0.2 m nd three t 0.4 m depth in three replictes. In the medium crop mngement system, irrigtion ws crried out only when there ws gret wter shortge during the most criticl period, between 5 dys before the booting (V 5 ) nd 20 dys fter flowering (R 3 ). Whenever the wter potentil in the soil ws less thn 0.04 MP, sprinkle irrigtion ws pplied t the rte of 8 mm h. Weeds nd pests were controlled eqully in ll experiments not to ffect crop performnce. yield, its components nd kernel crude protein content were determined. yield ws ssessed in the three centrl lines of ech experimentl unit of 0.8 m row spcing nd in the six centrl lines on the 0.4 m row spcing, excluding 0.5 m t ech row end, comprising n experimentl re of 9.6 m 2. Vlues of grin weight were corrected to the stndrd moisture of 3%, nd extrpolted to one hectre. The number of ers per re ws estimted by the rtio between the number of ers collected in the plot nd the respective useful re. The mss of one grin ws obtined by counting nd weighting smples of 0 grins. The number of grins per re ws estimted by the rtio between grin mss of the plot nd the mss of one grin. The kernel crude protein content ws determined by grinding 20 g grin smple from the plot to obtin the N content nd multiplying the vlue by 6.25 (% N corresponds to 6.25 g protein) (Tedesco et l., 995). The dt from ech experiment were submitted to the nlysis of vrince by the F test (p < 0.05). When sttisticl significnce ws reched, the mens of the tretments were compred by the DMS test (p < 0.05), ll proceeded using the Sttisticl Anlysis System (SAS Institute, 996) for blnced dt (PROC ANOVA). Dt from ech crop mngement system, for ech growing seson, were nlyzed individully s one experiment, ccording to the chrcteristics of the tretments nd the proposed objectives. Becuse the objectives of this study here we only shown the results of simple effects of nrrow spcing or its interction with plnt density or with the hybrid. RESULTS AND DISCUSSION The wter shortge observed during most mize cycles ws greter thn the historic men of the region t both growing sesons. In the first yer, there were wter shortges rnging from 0 to mm t stge V 6, between stges V 5 nd R 3 nd between R 4 nd R 6 (Figure ). In the second yer, the wter shortge ws even more intense thn in the first, especilly mm of wte Wter shortge (mm) 2003/2004 Wter shortge (mm) 2004/2005 Men wter shortge (mm) between 969/ mm irrigtions pplied in 2003/2004 t the high nd very high ( ) nd medium ( ) crop mngement levels 20 mm irrigtions pplied in 2004/2005 t the high nd very high ( ) nd medium ( ) crop mngement levels 0 V 4V6 V9 7 V5 R 0 R2 R3 3 R4 6 R5 R6 Out Nov Dez Jn Fev Mr Devepment stges / nd months of the yer Figure Wter shortges t 0dy intervls throughout mize cycle for three crop mngement systems, reltive to two growing sesons nd the historic men between 969/999, in Eldordo do SulRS. Dt obtined from the griculturl meteorologicl deprtment of FA/ UFRGS. / According to the development scle proposed by Ritchie et l. (993).

4 Nrrow row spcing for mize 349 during the reproductive period (R to R 6 ). Wter deficits vried from 0 nd 55 mm mong the V 2 nd R 3 stges nd in R 5. Becuse of the irregulr rinfll below the demnds of the crop, in the experiments with high nd very high crop mngement ten irrigtions of 20 mm were mde in the first yer, distributed throughout the cycle. In the second yer, irrigtions were performed, eight of which concentrted between the V 2 nd R 4 stges. In the two yers, irrigtion supplied most of the plnt wter demnd. However, dequte wter vilbility my not hve been sufficient for full plnt development, becuse temperture, reltive ir humidity nd the nutritionl stte lso ffect mize metbolism nd plnt growth. The low wter vilbility during the mize cycle reduces grin yield in severl cropping regions, the gret losses occurring between 5 dys before (V 5 ) nd 20 dys fter flowering (R 3 ), becuse during this period of the cycle the tmospheric evportion is of the order of 8 mm dy (Mtzenuer & Mchdo, 2002) in our study re. In other studies with mize (Silv et l., 999), it ws verified tht in time the reduction in grin yield occurs minly due to increses in the nthesissilking intervl, which reduces the number of grins per plnt. In Eldordo do Sul RS, wter shortge throughout the mize cycle my occur in more thn 60% of the yers (Mtzenuer & Mchdo, 2002). Under these conditions, the mize grin yield shows tht dequte wter distribution during the criticl period is more importnt thn the totl quntity of rinfll nd/or irrigtion throughout the cycle. These results re in greement with those reported by Mtzenuer & Mchdo (2002) when studying wter vilbility for mize in yers of different rinfll in Eldordo do SulRS. Thus, the doption of irrigtion my be considered n essentil prctice to obtin high mize grin yield in the min cropping regions of Brzil. Medium crop mngement system In the medium crop mngement system, corresponding to the decrese of row spcing from 0.8 to 0.4 m did not ffect grin yield, regrdless of plnt density, hybrid or growing seson (Tble 2). In the 2003/04 growing seson, the verge grin yield ws 8. t h in the two row spcings nd in the second yer, yield vlues were lower, 2. nd 2.3 t h, respectively, in the smller nd greter row spcing (Tble 2). In both yers, the response of grin yield components to nrrow row spcing did lso not depend on plnt density or hybrid (Tble 2). However, in 2003/04 the reduction of row spcing from 0.8 to 0.4 m incresed the number of ers per re (3%), decresed grin mss (5%), but did not lter the number of grins per re. In the second yer, row spcing did not influence ny of the grin yield components, regrdless of plnt density or hybrid. The kernel crude protein content ws 22% lower in the 0.4 m row spcing compred to the 0.8 m spcing during the first growing seson, but only in the low plnt density (4.5 pl m 2 ) (Tble 3). There ws n inverse response in the second yer, with increses of 0 nd 6% in kernel crude protein content for both hybrids, respectively, when row spcing ws reduced to 0.4 m (Tble 3). The increse in plnt density from 4.5 to 6.0 pl m 2 reduced by 9% the kernel crude protein content only in the greter row spcing, in 2003/04. High crop mngement system The verge grin yield in the experiments with high crop mngement system were.8 nd 9. t h, respectively, in the first nd second yers. In 2003/2004, row spcing reduction from 0.8 to 0.4 m incresed grin yield (0%), the number of ers (2%) nd grins per re (5%) nd reduced grin mss (2%), regrdless of plnt density or hybrid (Tble 2). In 2004/2005, row spcing did not ffect grin yield nd its components, regrdless of plnt density or hybrid (Tble 2). In the first yer, row spcing reduction from 0.8 to 0.4 m promoted 27% increse in Pent kernel crude protein content (Tble 3). Pent hd lso 20% higher kernel crude protein content thn Flsh in the smller row spcing. An inverse response ws observed in the lrger row spcing, in which Flsh presented 3% edge over Pent. In the second yer, kernel crude protein content did not vry with row spcing. Very high crop mngement system When very high crop mngement system ws dopted, row spcing reduction from 0.8 to 0.4 m incresed grin yield (5%) nd the number of grins per re (4%) in 2003/2004 (Tble 2). In the second yer, the nrrow row spcing incresed grin yield from 9.8 to.2 t h (4%) for the plnt density of 9.9 pl m 2, nd no effect ws observed for the density of 7.5 pl m 2. Increse in plnt density from 7.5 to 9.9 pl m 2 enhnced grin yield from 9.6 to.2 t h (7%) only in the smller row spcing (0.4 m). As well s verified in the second yer of the medium nd high crop mngement systems, in the very high mngement systems the grin yield components did lso not vry with row spcing (Tble 2). In both yers, kernel crude protein content ws not ffected by row spcing, regrdless of plnt density or hybrid. Differences in grin yield between growing sesons for the three crop mngement systems cn be ttributed to greter wter shortge (Figure ) nd

5 350 Strieder et l. Tble 2 Mize grin yield nd its components in three crop mngement systems nd two growing sesons s function of row spcing, considering the men of two plnt densities nd two hybrids. Growing seson yield nd its components Medium mngement system 2003/04 yield (t h ). Row spcing m 8 8. Ers b s mss (mg) 2004/05 yield (t h ). Ers. 6 s 05 mss (mg) 3 High mngement system 282 b /04 yield (t h ) b Ers b s b mss (mg) 2004/05 yield (t h ). 6 Ers. 7 s 36 mss (mg) 74 Very high mngement system 303 b /04 yield (t h ) b 2004/05 rs m Ers s b mss (mg) 2 E nº ) (. 4 s mss (mg) In ech crop mngement system mens followed by different letters on the line differ by DMS s test (p < 0.05); ns No significtive by DMS s test (p < 0.05). the incresed plnt density (Tble ) observed in the second yer. For the three crop mngement systems, in the 2004/05 growing seson the intervl between the smllest nd highest plnt density ws 33% (.6 to 2.4 pl m 2 ), while in the first yer the vrition between the two densities ws between 23% to 33% (.5 pl m 2 ) (Tble ). Thus, in the second yer the plnt density intervls were more uniform between the three crop mngement systems. Specilly for the medium crop mngement system nd in the second yer, the greter wter shortge tht occurred throughout the mize cycle (Figure ) nd the higher plnt density cused higher reduction in grin yield. According to Mdonni & Otegui (2004), s density increses, the number of dominted plnts lso increses, chrcterized by slow development, smll stem dimeter nd reduced grin yield. As there ws less rinfll in the second thn in the first yer, in the medium crop mngement system the correct strtegy would hve been to use lower plnt popultion nd not higher density s occurred in the present study, specilly becuse the bsence of wter supplementtion. However, plnt density ws defined before mize ws sown nd the wter deficit intensity could not be foreseen. The grin yield differences mong crop mngement systems showed the mrked response of mize to chnges in field cropping prctices. The increses in fertilizer quntity nd plnt density nd the use of irrigtion enhnced yield vlues from the medium to the high nd very high mngement system t both growing sesons, which is corroborted by results reported by Argent et l. (2003) in the sme region.

6 Nrrow row spcing for mize 35 Tble 3 Kernel crude protein content in the medium nd in the high crop mngement system s function of two row spcing nd two plnt densities nd two hybrids in the two yers. Plnt density/hybrid Row spcing (m) % Medium crop mngement system 003/ Ab 2.6 A A 0.2 B Flsh Pent Flsh Pent Medium crop mngement system 004/ A 9.8 Ab 0.3 A 8.9 Bb High crop mngement system 003/ B 0.3 A.6 A 9. Bb For ech interction nd growing seson, mens followed by the sme lower cse letter in the line nd mens followed by the sme uppercse letter on the column, did not differ by DMS s test (p < 0.05). Positive effects of row spcing reduction on grin yield occurred in three of the six experiments nd did not depend on the hybrid (Tble 2). The more uniform sptil distribution mong plnts with nrrow row spcing, when the plnt density ws mintined, incresed grin yield in the high crop mngement system in the first yer (0%) nd in the very high in both yers (5 nd 4% in the first nd second yers, respectively). Thus, when there were increses in grin yield, they were smll, did not depend on the hybrid nd were only mnifested in crop mngement systems with grin yield greter thn 0.0 t h. The bsence of hybrid nd row spcing interction in five of the six experiments contrdicted results obtined by Argent et l. (200), who reported greter potentil in grin yield response to nrrow row spcing for hybrids with erect leves, such s Flsh. On the other hnd, the mgnitude of yield increses obtined with row spcing reduction confirmed results obtined by Mundstock (977), Sngoi (990), Sngoi et l. (998), Tesdle (998), Argent et l. (200 nd b), Flesh & Vieir (2004) nd BlbinotJúnior & Fleck (2005). The lck of grin yield response to the reduction of row spcing from 0.8 to 0.4 m in most trils (Tble 2) showed tht the potentil benefits of nrrow row spcing my not result in higher productivities, specilly when yield levels were low or medium (<8.0 t h ). The bsence of positive response to nrrow row spcing under less fvorble crop mngement systems showed tht there were other fctors, such s wter nd nutritionl shortges, lower grin yield potentil, unsuitble sowing time nd limittions in weed, pest nd disese control, which cn limiting crop yield more thn the plnt rrngement. The behvior of grin yield observed especilly in the medium crop mngement system did not support the rgument presented by Fundção Rio Verde (2002) tht more uniform distribution mong plnts, due to nrrow row spcing, incresed grin yield under conditions of wter nd nutritionl limittions, due to the more homogeneous plcing of the root system, better soil use nd greter efficiency in wter nd nutrient bsorption. A more uniform sptil distribution mong plnts ws n efficient strtegy to lift mize productivity only under stisfctory moisture nd soil fertility conditions, when grin yield ws high. In these cses, the more equidistnt plnt rrngement in the row provided by nrrow row spcing resulted in better use of the environmentl resources like wter, light nd nutrients. This conclusion is in greement with Strieder et l. (2007), who crried out study in the sme re of the present reserch, ssessing the effect of nrrow row spcing on mize hybrids with different lef rchitecture nd in high grin yield potentil. The number of grins per re lso incresed only in the experiments where row spcing reduction incresed grin yield (in the first yer with the high crop mngement system nd the two yers with very high crop mngement systems) (Tble 2). The number of grins per re ws the component tht best explined the vrition in grin yield with nrrow row spcing. The sme trend ws reported by Sngoi et l (2002) nd Mdonni & Otegui (2004). Kernel crude protein content ws not ffected by nrrow row spcing in five of the six experiments (Tble 3). Mintining the plnt density, the more uniform sptil distribution between plnts incresed kernel crude protein content only in the second yer in the medium crop mngement system which ws the tril with the lowest grin yield. Thus, the effects of row spcing on grin yield nd on the kernel crude protein contents shows tht grin qulity incresed only in the sitution with the lowest grin yield (2.2 t h ), while with productivities higher thn 8.0 t h, row spcing did not ffect this chrcteristic. Nrrow row spcing cn increse mize grin yield under high input crop mngement systems. In the present study the economic nlysis ws not to proceed to evlute if these grin yield increments reflect in higher economic return of the investments nd so, justify the greter mount of expenses in the highest mngement levels. However other studies conducted in the sme loclity (Sngoi et l., 2006;

7 352 Strieder et l. Forsthofer et l., 2006) demonstrtes tht higher investments in technology my increse the potentil of mize grin yields. In these studies different mngement levels (low to high) were used nd lso nrrow row spcing on to the highest levels, s in the present study. According the uthors, these economic benefits re specilly importnt in the October sowings, like in the present study, when in South of Brzil its possible to hve synergy between the incidence of the mximum solr rdition level with full mize flowering, i.e., when the lef re index is the highest. Thus, there is highest light interception by the cnopy nd, ccording to these uthors, the doption of mize genotypes of higher grin yield potentil, the use of greter plnt densities nd the ppliction of more fertilizers, llow incresing the economic return on mize. Moreover, this cropping prctice cn lso be used by frmers lower cpcity to invest in technology due to other potentil benefits tht include: decrese in weed development nd infesttion (Tollenr et l., 997; Johnson et l., 998; Argent et l., 2000), reduced herbicide use nd dosge (Forcell et l., 992; Tesdle, 998; Blbinot Júnior & Fleck, 2005b) nd decresed the risk of toxic effects cused by fertilizer slinity on the seeds (Fundção Rio Verde, 2002). A further potentil dvntge is the incresed efficiency in soil nd wter conservtion, due to erly closure of row spces in the cnopy, decrese in superficil runoff nd soil nd wter losses from erosion (Sngoi et l., 200; Cogo et l., 2003). Furthermore, nrrow rows my increse the efficiency of using equipment on the frm, especilly for sowerfertilizers, becuse they llow uniform row spcing regultion for sowing the two min summer crops (mize nd soyben) without djustment (Mundstock & Silv, 2005). The potentil dvntges of using closer rows should be counterblnced by the producer with some limittions becuse, in ddition to frequently not incresing grin yield, doption of this cropping prctice hinders crop tretment ppliction in post emergence nd increses production costs, becuse hrvesting pltforms nd trctor tire dimeter need to be dpted to this row spcing. Progress hs been mde recently in the offer of equipment dpted for mize cropping with nrrow row spcing (Argent et l., 200b), lthough the cost of hrvesting pltforms is still high. CONCLUSIO Mize grin yield increses were smll with nrrow row spcing, depended on the growing seson, occurred only when grin yields were higher thn 0.0 t h nd did not provide more efficient use of the environmentl resources when mize yields were low or medium (<8 t h ). The hybrid plnt rchitecture did not interfere in mize grin yield response to nrrow row spcing. The number of grins per re ws the component mostly ssocited to grin yield response on nrrow row spcing, regrdless of plnt density, hybrid or crop mngement system. ACKNOWLEDGMENTS To CNPq for the grdute nd undergrdute scholrships, FAPERGS for the undergrdute scholrship nd the Syngent Seeds Compny for the reserch finncil support. REFERENCES ARGENTA, G.; SILVA, P.R.F.; BORTOLINI, C.G.; MEROTTO JÚNIOR, A.; FORSTHOFER, E.L.; STRIEDER, M.L. Redução d dose de herbicid utilizd n cultur do milho trvés d doção de menor espçmento entre linhs. Revist Plntio Direto, v.58, p.6669, ARGENTA, G.; SILVA, P.R.F; BORTOLINI, C.G.; FORSTHOFER, E.L.; MANJABOSCO, E.A.; BEHEREGARAYNETO, V. Respost de híbridos simples de milho à redução do espçmento entre linhs. Pesquis Agropecuári Brsileir, v.36, p.7 78, 200. ARGENTA, G.; SILVA, P.R.F.; SANGOI, L. Arrnjo de plnts em milho: nálise do estdodrte. Ciênci Rurl, v.3, p , 200b. 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