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Field Crops Research 122 (2011) 140–150

Contents lists available at ScienceDirect

Field Crops Research

journa l homepage: www.e lsev ier .com/ locate / fc r

rop management affects dry-milling quality of flint maize kernels

.G. Ciriloa,∗, M. Actisb, F.H. Andradeb,c,d, O.R. Valentinuze

Instituto Nacional de Tecnología Agropecuaria (INTA), Estación Experimental Agropecuaria Pergamino, Pergamino, Ruta 32, Km 4.5 – CC 31,ergamino (B2700WAA), Buenos Aires, ArgentinaFacultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata, Balcarce, Buenos Aires, ArgentinaInstituto Nacional de Tecnología Agropecuaria (INTA), Estación Experimental Agropecuaria Balcarce, Balcarce, Buenos Aires, ArgentinaConsejo Nacional de Investigaciones Científicas y Técnicas (CONICET), ArgentinaInstituto Nacional de Tecnología Agropecuaria (INTA), Estación Experimental Agropecuaria Paraná, Paraná, Entre Ríos, Argentina

r t i c l e i n f o

rticle history:eceived 2 September 2010eceived in revised form 17 March 2011ccepted 17 March 2011

eywords:lint maizery-milling qualityrop managementost-silking growth

a b s t r a c t

Dry-milling performance of maize (Zea mays, L.) kernels primarily depends on their hardness. The flinttype is harder than the dent and semi-dent maize, yielding a higher proportion of big endosperm piecesin the mill. Nevertheless, crop growing conditions could modify milling properties. The objective of thiswork was to analyze the effect of different crop environments and management practices on dry-millingquality of flint maize kernels. Two orange-flint hybrids from different eras of breeding differing in flinttype expression and grain yield potential were evaluated. They were grown at three different locations ofthe Argentina’s main maize-production area under different sowing dates, plant densities, and fertiliza-tion rates during two growing seasons. Crop post-silking growth, grain yield and its components (kernelnumber and weight), kernel size and hardness-associated properties (test weight, percent floaters and

ardness-associated properties milling ratio), and flaking-grit yield were analyzed. Most of observed differences in physical propertiesof kernels, particularly for the high-yielding new hybrid with unstable flint expression, were associ-ated with the source–sink ratio established during the post-silking period (explored range from 154 to617 mg kernel−1). This variable mainly results from changes in crop growth during that period. Increasesin weight per kernel improved hardness-associated properties. High crop grain yields together with topdry-milling quality were achieved when the new high-yielding hybrid was cropped with an appropriated

crop management.

. Introduction

The dry-milling industry of maize requires a raw material pos-essing quality properties that allow a higher recovery of largerrits after milling (Lee et al., 2007). These properties are highlyssociated with kernel hardness which is expressed by means ofts mechanical resistance to the mill (Wu, 1992). This behavior

ainly depends on the type of endosperm that prevails in the ker-el (Watson, 1988). Two fractions are distinguished in the maizeernel endosperm: a horny type fraction, translucent and with vit-eous aspect and high density, located on the peripheral region;nd a floury type fraction, opaque and with low density, locatedt the core. The proportion between both fractions determines the

esulting kernel hardness. In orange-flint maize, the horny fractions predominant yielding greater kernel hardness, whereas in dent

aize the floury fraction prevails. According to trading require-ents (Serignese and Pescio, 1995), an orange-flint maize should

∗ Corresponding author. Tel.: +54 2477 439014; fax: +54 2477 439047.E-mail address: acirilo@pergamino.inta.gov.ar (A.G. Cirilo).

378-4290/$ – see front matter. © 2011 Published by Elsevier B.V.oi:10.1016/j.fcr.2011.03.007

© 2011 Published by Elsevier B.V.

have a test weight ≥79 kg h l−1 along with a percent floaters valueof ≤12 (in a liquid mixture, ı = 1.305 g cm−3) and a milling ratio(coarse-to-fine particle ratio after milling) ≥4 to achieve the maxi-mum milling quality. Moreover, kernel size should be large (≥50%of kernels should be retained in a sieve with a mesh with 8 mm-opening round holes, and ≤3% of kernels should pass through the6.5 mm-sieve), with a minimum commercial weight of 265 mg (i.e.,228 mg in dry basis).

Orange-flint maize in Argentina is grown under specific con-tracts between farmers and industry or exportation brokers. TheEuropean Union imports orange-flint maize from Argentina pay-ing better prices according to a trading agreement with specifiedquality requirements (MAGyP, 2010). Farmers may receive higherprice for their production of this type of maize from millers andbrokers to compensate for the lower yields compared to semi-denthybrids (Eyhérabide et al., 2004). Along the first two-thirds of the

last century, Argentina produced almost exclusively orange-flintmaize of high quality, which was world wide known as “Plata”-type(i.e., with hard endosperm, smooth crown, and orange pigmenta-tion). After that period, local efforts in maize breeding were mainlyfocused on productivity. Then, a progressive introduction of exotic

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ent germplasm into native flint maize took place in Argentina.s a consequence of this process, grain yield of orange-flint maizeaised but dry-milling quality was progressively reduced. Instabil-ty in the expression of hardness traits in the new flint hybrids canesult in grains that do not meet the contract-stipulated require-ents. Environmental and agronomic effects have been reported as

ffecting maize kernel hardness (Eyhérabide et al., 2004) and sizeBorrás and Otegui, 2001; Cirilo et al., 2003). Thus, we speculatehat many of those new orange-flint hybrids, with increased yieldotential but unstable hardness, might express higher quality whenrown under proper conditions. Our hypothesis is that adjustmentso maize production technology when cropping those new hybridsesult in kernels with the top quality demanded by the dry-millingndustry. The objective of this study was to determine the effect ofifferent environments of the Argentina’s main maize-productionrea and the influence of agricultural management practices onrain yield, hardness-associated properties, kernel size and flakingrits yield in an old and a new orange-flint hybrids.

. Materials and methods

.1. Field experiments

Two hybrids of orange-flint maize were evaluated: (i) Cóndorfrom Syngenta Agro S.A.), a new hybrid with high grain yieldotential but unstable flint-type expression, and (ii) Morgan 306from Dow AgroSciences S.A.), an old hybrid with limited grainield potential but strong flint-type expression. Years of releaseor Cóndor and Morgan 306 were 1984 and 2000, respectivelyINASE, 2010). Field experiments were conducted at three repre-entative locations in the Argentina’s main maize-production area:i) Balcarce (latitude 37◦ 50′ S, longitude 58◦ 15′ W), with lowerhermal and radiation offer for crop growth; (ii) Pergamino (lati-ude 33◦53′S, longitude 60◦34′W), with intermediate temperaturend radiation levels; and (iii) Paraná (latitude 31◦43′S, longitude0◦32′W), with higher temperature and radiation regimes. Exper-

ments were conducted during two cropping seasons (2003–2004nd 2004–2005). Four different crop management treatmentsere imposed: (i) control: early sowing date (mid-October) withpopulation of 7.5 plants m−2; (ii) high density: early sowing

ate (mid-October) with a population of 9 plants m−2; (iii) refer-ilization: early sowing date (mid-October) with a population of.5 plants m−2 and nitrogen (N, 10 g m−2) and sulfur (S, 4 g m−2)ddition to the soil at pre-silking (VT crop stage; Ritchie et al.,008) [a mixed source of urea (45% N) plus ammonium sulfate (21%+ 24% S) was applied]; and (iv) late sowing: late sowing date (mid-ecember; except for Paraná in the second season when sowing

ook place on January 3rd) with 7.5 plants m−2. At each location,reatments were arranged in a split-plot design with three repli-ates. Crop management treatments were assigned to the mainlots and the hybrids to the sub-plots. In all experiments, each sub-lot had 35 m2 (5 rows, 0.7 m apart, and 10 m long). Every plot wasertilized at the crop stage V6 (Ritchie et al., 2008) with 4–8 g N m−2

source: urea) according to local expert estimates for maize produc-ion. Phosphorus requirements were also covered by pre-sowingpplication of 3 g P m−2 (source: calcium triple superphosphate).nsects, weeds and diseases were appropriately controlled. Plots

ere hand-planted at three seeds per hill, and thinned to theesired plant population at V3 (Ritchie et al., 2008). Water stressas prevented by means of sprinkler irrigation, keeping avail-

ble soil water content over 50% in the uppermost 1 m of soilhroughout the growing season. Mean air temperature and dailyncident solar radiation data were obtained from standard weathertations installed not farther than 500 m from each experimentalite.

arch 122 (2011) 140–150 141

2.2. Grain yield and its components

At harvest time all plant ears in 4 m of each of the three centralrows per plot (8.4 m2) were sampled to determine total grain yield.Resulting kernel samples were weighed and their moisture wasdetermined. Grain yield was corrected to 140 g kg−1 kernel mois-ture. Weight per kernel was determined by weighing samples (ovendried at 60–65 ◦C for 20 days) of 500 kernels each per plot takenfrom harvested grain bulks, and average dry weight per kernelwas determined. Kernel number per unit area was calculated fromweight per kernel and grain yield expressed on a dry weight basis.

2.3. Post-silking biomass accumulation and post-silkingsource–sink ratio

Post-silking biomass accumulation was determined by takingplant samples at silking (i.e., when 50% of the plants reachedsilking) and physiological maturity (i.e., when 50% of the plantsreached 75% milk line in kernels from the mid portion of ears)from the three central rows of each plot. The sample size was 10plants per plot, leaving appropriate border rows and border plantswithin the sampled rows. Plants were cut at ground level, grinded,oven dried in an air-forced oven at 60–65 ◦C for at least 10 daysand weighed. Mean plant weight of samples and plant densitywere used to calculate dry matter per square meter. Post-silkingbiomass accumulation was calculated as the difference betweenbiomass at physiological maturity and at silking. Post-silkingsource–sink ratio (in mg per kernel) was calculated as the ratiobetween post-silking biomass accumulation and kernel numberat harvest per unit area. This ratio was used as an estimator ofphotoassimilate availability per growing kernel during grain filling.The ratio overestimated the aboveground plant biomass increaseper kernel during the effective grain-filling period since it includedthe lag phase during which the kernels do not grow (Cirilo andAndrade, 1996; Borrás and Otegui, 2001).

2.4. Physical properties associated with kernel hardness

2.4.1. Test weightTest weight was determined in kernel samples of ≈400 g from

each harvested plot, using a Tripette & Renaud TR-77400 instru-ment. Values were expressed in kg h l−1. Higher test weight valuesare generally related to flintier kernels (Watson, 1988; Robutti et al.,2000b).

2.4.2. Percent floatersPercent floaters values were determined according to Lepes et al.

(1976). One hundred of whole kernels from each harvested plotwere placed in a 250 ml beaker with ≈170 ml of carbon tetrachlo-ride and kerosene mixture, with a 1.305 g cm−3 density at 25 ◦C.After being briefly stirred with a glass rod, the floating kernels werecounted. Values were expressed in percentages. Lower values ofthis test indicate flintier kernels (Robutti et al., 2000b).

2.4.3. Milling ratioMilling ratio was determined as described by Pomeranz et al.

(1986) for the coarse-to-fine particle ratio. Samples of 50 g of wholekernels from each harvested plot were ground for 15 s in a Stein Labmill. Ground kernels were sifted at full speed for 1 min in a ChopinRotachoc mechanical sifter, equipped with circular sieves of 1 and

0.5 mm mesh opening. Quantities of coarse material retained by the1 mm sieve and of fine material passing through the 0.5 mm sievewere weighed with a precision of 0.1 g. The weight ratio betweenboth fractions was the milling ratio, which is higher for flintierkernels (Robutti et al., 2000b).

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.5. Kernel-size proportion

The proportions of kernels sized over 8 mm and below 6.5 mmere determined in samples of 500 whole kernels from each har-

ested plot, using a mechanical vibrate sifter (Zony Test, Rey andonzoni, Buenos Aires, Argentina). The samples were run for 1 minhrough two metal sheet sieves with 8 and 6.5 mm mesh openingound holes, respectively. Kernels retained in the 8 mm sieve andhose passing through the 6.5 mm sieve were weighted. The weightf each fraction was expressed in percentages with respect to theample total weight.

.6. Flaking-grit yield

Flaking-grit yield was measured with a grain-cracking hammerachine (Metallurgical Factory “La Perforametal”, Buenos Aires,rgentina). Samples of 100 g from each harvested plot were soaked

n water during 2–3 min. The different swelling between the peri-arp and the germ generated a cutting force on the connective tissuerom the pericarp to the endosperm, from the pericarp to the germnd from the germ to the endosperm, enhancing component sep-ration (Eckhoff and Paulsen, 1996). Conditioned kernel samplesere introduced in the cracking machine hopper to be fractioned

t 2000 rpm during 10 s. Germs and pericarps were removed in theame grain-cracking machine. Resulting endosperm fractions wereifted in the mechanical sifter described above, equipped with a cir-ular sieve with a wired mesh of 2.8 × 2.8 mm opening at full speedor 1 min. Material retained by the sieve was weighed in an Ohausrecision Standard TS 4 KS electronic balance (Ohaus Corp., Florhamark, NJ). The weight of that fraction was expressed in percentageith respect to the sample total weight.

.7. Statistical analysis

Combined analyses of variance over locations and years wereade to evaluate the effects of hybrids, locations, crop manage-ents and their interactions on the response variables (except

or percent floaters and proportion of kernels sized below 6.5 mmecause data for those variables did not meet normality and vari-nce homogeneity requirements). Both locations and years weressumed as fixed effects in the analyses. The Tukey mean compari-on test was applied to determine significant differences (p < 0.05).

Two models were used in the regression analysis of the relation-hips among variables for each hybrid: a linear model (Eq. (1)), and,hen appropriated, a bilinear with plateau model (Eqs. (2) and (3);orrás and Otegui, 2001):

= a + bx, (1)

= a + bx, for x ≤ c, (2)

= a + bc, for x ≤ c, (3)

here y stands for the response variable, x for the independentariable, a for the intercept, b for the slope, and c for the thresh-ld in the bilinear with plateau model. The fitting of the modelsas performed by an optimization technique (Jandel, 1991). Theodel with the highest r2 was always chosen. Parameters were

ompared with their respective confidence interval (p < 0.05). Theegression slopes were compared by a t-test (p < 0.05; Steel and

orrie, 1960). No significant differences in model parameters wereetected between years within each hybrid; consequently, a sin-le equation for both years could be fitted in all cases. All statisticnalyses were done using the InfoStat statistical software (InfoStat,009).

arch 122 (2011) 140–150

3. Results

3.1. Environmental conditions during the grain-filling period

Daily mean air temperature during the grain-filling period (fromsilking to physiological maturity) for early sowings was from 3to 6 ◦C higher in Paraná than in Balcarce (Table 1). Sowing delaysexposed such period to a mean temperature 3–6 ◦C lower than forearly sowings, depending on latitude. Likewise, daily mean incidentradiation during the same period increased 6–7 MJ m−2 from southto north for early sowings. Similarly, reductions in incident radia-tion from 3 to 9 MJ m−2 were registered when sowing was delayed,depending on year and location (Table 1).

3.2. Grain yield and its components

Significant hybrid, location and management effects on grainyield were found (Table 2). The hybrid Morgan 306 yielded 15–18%less than the hybrid Cóndor (two-year average: 8.3 Mg ha−1 vs.10 Mg ha−1, respectively). A location by hybrid interaction wasobserved for grain yield since the difference in favor to Cóndorwas more noticeable in Pergamino than in the other locations.Pergamino always showed higher mean grain yields than the north-ern and southern locations. In turn, the highest yields at eachlocation were achieved when maize was sown early at low den-sity and was refertilized with N and S at pre-silking stage. Thesedifferences were more evident during the first year and for Cón-dor (Table 2). The delay in sowing date resulted in lower maizeyields, but this effect was relatively more pronounced at Pergamino(Table 2).

Hybrids differed in kernel number at harvest. The hybridCóndor produced more kernels than the hybrid Morgan 306(3506 kernels m−2 vs 2877 kernels m−2, averaged across years,locations and crop managements; Table 2). The crop environ-ment also promoted significant differences in kernel number.Averaged across hybrids and crop managements, kernel num-ber was lower at Paraná (2799 kernels m−2 as a mean for bothyears) than at the other locations (3267 and 3509 kernels m−2

for Balcarce and Pergamino, respectively). However, the differ-ence between hybrids in kernel number was smaller in Paraná(ca. 390 kernels m−2) than in Pergamino (ca. 901 kernels m−2). Inturn, fewer kernels were harvested when plots were sown latein the season (2526 kernels m−2, averaged across years, hybridsand locations) than with the others crop managements (averageof 3414 kernels m−2; Table 2). Nevertheless, this effect was lessnoticeable at Balcarce and more pronounced during the secondyear at Paraná when sowing delay was the greatest. When datafrom all tested locations, crop managements and years were pooledtogether for each hybrid, grain yield was strongly associated withkernel number (Fig. 1A).

Weight per kernel was also affected by the treatments (Table 2).Morgan 306 showed heavier kernels than Cóndor (251 mg vs.243 mg, respectively as general means). In turn, weight per kernel inPergamino was always higher than in the other locations. Heaviestkernels were harvested when maize was sown early in the seasonat low plant density and refertilized near silking, whereas late sow-ings produced kernels with low weight in most cases. Nevertheless,weight per kernel for late sowings at Paraná showed an oppositebehavior in both years. In fact, it was as high as that obtained in earlysowings in the first year but too low in the second year (Table 2).

Reductions in weight per kernel in response to late sowings weremore pronounced at Balcarce than at the other locations for bothyears (27% vs. 19% in 2003–2004, and 19% vs. 6% in 2004–2005;Table 2). Grain yield also significantly responded to increases inweight per kernel in both hybrids (Fig. 1B).

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Table 1Mean temperature and mean daily incident radiation averaged during grain-filling period (from silking to physiological maturity) of two orange-flint maize hybrids grownat three locations with four different crop managements without water restrictions during 2003–2004 and 2004–2005 growing seasons.

Mean temperature (◦C) Mean daily incident radiation (MJ m−2)

Location Sowing date 2003–2004 2004–2005 2003–2004 2004–2005

Balcarce Early sowing 20.0 ± 3.4a 18.3 ± 3.9 17.3 ± 5.4 15.7 ± 5.4Late sowing 17.2 ± 4.6 15.8 ± 3.6 12.7 ± 5.0 12.4 ± 3.6

Pergamino Early sowing 22.1 ± 3.0 22.1 ± 3.8 24.7 ± 5.0 21.9 ± 6.0Late sowing 21.0 ± 2.6 19.2 ± 3.3 19.8 ± 5.6 16.7 ± 5.3

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Paraná Early sowing 23.4 ± 3.3Late sowing 20.7 ± 4.4

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.3. Post-silking biomass and post-silking source–sink ratio

Hybrids did not differ in post-silking biomass productionTable 2). Contrarily, location and crop management significantlyffected this variable (Table 2). Mean values of post-silking biomassere higher at Pergamino than at the northern and southern loca-

ions (1437 g m−2 vs 1074 g m−2 for Pergamino and for the othersocations, respectively; Table 2). Late sowings markedly decreasedrop dry matter accumulation from silking to physiological matu-ity. Averaged across hybrids and locations, post-silking biomassccumulated in late sown plots only reached nearly 60% of that cor-esponding to early sowings (797 g m−2 vs 1328 g m−2 for late andarly sowings, respectively). This effect was more noticeable dur-ng the second season because of the unusual behavior of late sownlots at Paraná (Table 2). Pooling the post-silking biomass datacross hybrids and crop managements a significant positive asso-iation was found with mean daily incident radiation during theost-silking period (r2 = 0.58, n = 12, p < 0.01), which varied accord-

ng to sowing date and location. In turn, cumulative post-silkingiomass also correlated with the number of harvested kernels inoth hybrids (Fig. 1C).

Variations in biomass accumulated during the post-silkingeriod and in the number of kernels harvested per unit areaenerated a wide range of source–sink ratios during that periodTable 2). Values of this ratio ranged from 272 to 582 mg kernel−1

n 2003–2004, and from 154 to 617 mg kernel−1 in 2004–2005.ource–sink ratio showed a strong association with post-silkingiomass accumulation (Fig. 1D). The hybrid Morgan 306 alwayshowed higher post-silking source–sink ratio than the hybrid Cón-or (average of 405 mg kernel−1 vs 342 mg kernel−1, respectively;able 2). This difference resulted from the low kernel number sety Morgan 306 and the similar post-silking biomass productionetween hybrids (Table 2). In turn, source–sink ratio values wereigher at the intermediate location of Pergamino (419 mg kernel−1)han at the northern and southern locations (355 mg kernel−1, as a

ean for both locations; Table 2). This variable also showed signif-cant crop management effects. Late sowings had very low valuesor the ratio because of reductions in post-silking biomass produc-ion were stronger than reductions in kernel set when sowing waselayed. Nevertheless, significant interactions between crop man-gement, year, and location were found (Table 2). In fact, the highiomass accumulation during the post-silking period in the firstrowing season at Paraná, and the low kernel set in the secondeason at Pergamino contributed to explain those interactions.

Similar bilinear models between weight per kernel and theource–sink ratio could be fitted for each hybrid (Fig. 2A). Weighter kernel increased when the source–sink ratio augmented in

esponse to crop managements and locations variations. The valuesf plant weight gained per kernel that rendered maximum weighter kernel were 336 and 358 for Morgan 306 and for Cóndor, respec-ively. In most cases, data corresponding to Condor were lower thanhis threshold. The source–sink ratio that maximized weight per

24.2 ± 3.5 23.4 ± 6.5 22.8 ± 6.517.7 ± 4.3 16.7 ± 6.8 13.1 ± 6.4

kernel was greater than the 1:1 relationship, showing both hybridsvery few cases at the remobilization range (i.e., at the left side ofthe 1:1 ratio; Fig. 2A). Nevertheless, caution must be taken becauseof the overestimation of source–sink ratio made in this work. Inmost cases kernels of both hybrids surpassed the minimum weightof 228 mg demanded for the dry-milling industry. The exceptionscorresponded to late sowing or high plant density (Table 2).

3.4. Kernel-size proportions

Late sowing reduced the proportion of kernels sized over 8 mm,but the magnitude of this effect depended on location (mean reduc-tion of 41% in Balcarce and 25% at the other two locations; Table 2).In turn, hybrid Morgan 306 showed higher values than Cóndorfor this variable in all locations but with larger differences atPergamino (83% higher in Pergamino vs 63% higher in the remaininglocations; Table 2). The proportion of kernels sized below 6.5 mmwas also affected by the treatments (Table 2). Hybrid Morgan 306showed lower values than Cóndor for this variable (1.2% vs. 2.6%, asaverage for both years), but refertilization reduced this difference.Late sowing produced higher proportion of small kernels, but thiseffect was more pronounced at the southern location (Table 2).

As expected from Fig. 2A, differences in kernel size propor-tions were also related to the post-silking source–sink ratio by abilinear response (Fig. 2B and C). However, no single fitted equa-tions were suitable for both hybrids. Hybrids did not differ in thesource–sink ratio threshold to achieve the maximum proportion ofbig kernels or in the slope of the response, but they showed dif-ferent values for the plateau (76.5% and 51.5% for Morgan 306 andCóndor, respectively; Fig. 2B). In most cases hybrid Cóndor did notfit the dry-milling industry requirement for big kernel proportion(i.e., ≥50%), except when it was sown early and was refertilizednear silking (Table 3). Both hybrids also showed similar responseof small kernel proportion to the source–sink ratio established aftersilking (Fig. 2C), differing only in the value of the plateau (0.7% and1.5% for Morgan 306 and Cóndor, respectively). In most cases, datawere lower than the maximum value demanded by the dry-millingindustry, except for late sowings at the southern location and forthe extremely delayed sowing date at Paraná in the second season(Table 3). Differences in kernel shape could explain the lower pro-portion of kernels retained over the sieve of 8 mm and the higherproportion of small kernels that passed through the sieve of 6.5 mmfor Cóndor than for Morgan 306. In fact, when sifted, the round andshort kernels of the hybrid Morgan 306 were retained by the sieveswhile the long and thin kernels of the hybrid Cóndor passed throughthe opening round holes of the meshes.

3.5. Hardness-associated properties

The hybrid Morgan 306 always recorded higher test weightthan Cóndor (average of 80.5 kg h l−1 vs. 78.2 kg h l−1, respectively;Table 3). In turn, maize kernels achieved the highest test weight

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Table 2Grain yield (140 g kg−1 kernel moisture), kernel number, weight per kernel (in dry basis), post-silking biomass and post-silking source–sink ratio of two orange-flint hybrids grown at three locations with four different cropmanagements without water restrictions during 2003–2004 and 2004–2005 growing seasons. Only significant interactions are shown.

Hybrid Location Crop management Grain yield (Mg ha−1) Kernel number (kernel m−2) Weight per kernel (mgkernel−1)

Post-silking biomass (g m−2) Source–sink ratio (mg kernel−1)

2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005

Cóndor Balcarce Control 10.5 11.1 3520 3634 255 263 1414 1125 403 310High density 11.1 11.2 3803 3683 250 261 1304 893 343 245Refertilization 12.0 12.0 3766 3713 273 279 1436 1299 381 351Late sowing 7.3 6.9 3211 3193 196 184 897 665 283 209

Pergamino Control 13.9 12.6 4638 3997 258 272 1986 1347 427 336High density 12.5 13.2 4221 4198 255 270 1757 1433 419 337Refertilization 14.2 13.7 4258 4124 287 285 1973 1607 466 391Late sowing 9.8 6.2 3872 2371 217 226 1041 856 272 361

Paraná Control 8.4 8.2 3401 3115 247 225 1256 654 377 209High density 6.3 8.5 2801 3350 219 218 927 1163 308 349Refertilization 8.9 10.3 3296 3519 271 248 1345 1208 410 346Late sowing 6.6 3.5 2558 1908 259 159 1295 306 507 169

Morgan306

Balcarce Control 8.7 9.8 2843 3160 264 266 1233 1220 434 397High density 9.8 9.4 3157 3239 267 249 1345 1206 429 372Refertilization 10.5 8.9 3193 2880 283 265 1407 1065 439 379Late sowing 7.0 6.0 2698 2580 224 200 785 671 293 261

Pergamino Control 10.6 10.5 3335 3379 273 268 1806 1228 541 366High density 10.8 11.2 3641 3467 255 277 1480 1403 403 404Refertilization 11.3 10.5 3377 3330 288 270 1963 1216 582 366Late sowing 7.5 4.0 2669 1270 242 269 1119 782 419 617

Paraná Control 7.4 7.8 3066 2611 242 254 1301 924 428 349High density 5.4 7.8 2437 2979 219 223 944 1184 383 395Refertilization 7.5 8.2 2900 2859 258 246 1681 1081 580 366Late sowing 6.8 2.5 2746 1233 246 169 951 190 359 154

Year (Y) ns (180)* (7)* (131)*** (33)***Location (L) (0.8)a,*** (221)*** (8)*** (160)*** (40)**Crop management (C) (0.6)*** (177)*** (6)*** (106)*** (26)***Hybrid (H) (0.3)*** (94)*** (3)*** ns (23)***Y*L ns ns (12)** ns nsY*C (0.8)*** (250)*** (9)*** (149)** (37)*L*C (1.0)** (306)** (11)*** ns (46)**L*H (0.5)*** (163)*** ns ns nsC*H (0.6)* ns (6)*** ns nsY*L*C (1.4)* (433)** (16)*** (259)*** (65)***Y*L*H ns ns (7)*** ns nsY*C*H ns ns ns (183)* (65)*L*C*H ns ns (11)** ns (80)**

a Tukey value for p ≤ 0.05. Statistical significances for main effects and interactions at *5%, **1%, and ***0.1%. ns: not significant.

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Table 3Proportion (in a weight basis) of kernels sized over 8 mm and under 6.5 mm, kernel hardness (estimated by test weight, percent floaters, and milling ratio) and flaking-grit yield of two orange-flint hybrids grown at three locationswith four different crop managements without water restrictions during 2003–2004 and 2004–2005 growing seasons. Only significant interactions are shown.

Hybrid Location Crop management Kernel size proportion (%) Test weight (kg h l−1) Percent floaters Milling ratio Flaking-grit yield (%)

P > 8 mm P < 6.5 mm

2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005 2003–2004 2004–2005

Cóndor Balcarce Control 52.7 55.9 1.3 ± 0.6b 1.4 ± 1.9 77.7 77.7 17 ± 10.4 7 ± 6.8 3.9 5.2 21.6 23.1High density 50.2 48.5 1.4 ± 0.5 1.8 ± 0.8 77.2 78.6 36 ± 11.4 7 ± 1.7 3.7 5.9 22.4 22.5Refertilization 55.5 62.8 1.1 ± 0.2 0.4 ± 0.4 78.0 79.1 5 ± 2.6 2 ± 1.2 4.9 5.7 23.3 23.4Late sowing 33.9 19.4 6.6 ± 0.7 9.3 ± 3.0 74.7 74.7 41 ± 3.1 67 ± 12.1 2.0 2.9 19.8 23.9

Pergamino Control 40.8 50.7 1.5 ± 0.7 1.2 ± 0.7 79.5 79.5 4 ± 1.2 9 ± 6.4 4.2 4.2 23.0 21.4High density 42.7 48.1 2.1 ± 0.3 1.9 ± 0.7 79.5 79.6 8 ± 9.1 4 ± 3.6 4.2 4.3 23.0 21.0Refertilization 56.5 50.2 1.0 ± 0.2 1.3 ± 0.5 80.1 79.6 1 ± 1.2 1 ± 1.0 5.2 5.2 22.6 21.6Late sowing 23.3 37.9 2.9 ± 0.5 2.7 ± 1.3 78.5 78.4 1 ± 1.2 3 ± 0.6 4.6 4.4 22.4 23.0

Paraná Control 54.4 29.5 1.6 ± 0.7 3.3 ± 1.5 78.4 77.9 16 ± 3.5 51 ± 4.9 3.7 2.8 22.0 20.5High density 41.5 33.6 3.2 ± 2.8 3.5 ± 2.1 78.0 78.3 34 ± 25.0 48 ± 26.9 3.7 2.9 22.1 22.2Refertilization 59.1 46.4 1.0 ± 0.7 1.5 ± 0.8 77.2 79.9 7 ± 4.0 2 ± 1.5 4.3 4.6 22.9 25.4Late sowing 51.1 19.1 1.7 ± 0.7 9.5 ± 1.4 79.4 76.9 1 ± 0.6 37 ± 3.1 4.3 5.2 22.3 23.6

Morgan306

Balcarce Control 77.7 73.9 0.5 ± 0.4 0.1 ± 0.1 80.2 79.9 2 ± 2.6 0 ± 0.6 4.4 6.3 22.6 23.6High density 78.8 79.1 0.1 ± 0.2 0.6 ± 0.5 80.3 80.2 1 ± 1.5 0 ± 0.0 4.9 6.7 22.4 22.8Refertilization 82.9 82.3 0.2 ± 0.3 0.2 ± 0.3 80.0 80.1 0 ± 0.0 0 ± 0.0 5.9 6.2 23.0 23.0Late sowing 54.4 54.2 7.1 ± 0.8 3.2 ± 1.3 76.5 76.9 3 ± 1.5 3 ± 2.3 2.1 3.4 20.5 20.3

Pergamino Control 83.5 83.1 0.1 ± 0.1 0.5 ± 0.2 81.5 81.6 0 ± 0.6 0 ± 0.6 5.1 5.0 23.8 20.0High density 77.1 85.2 0.4 ± 0.3 0.4 ± 0.2 81.8 81.7 0 ± 0.6 0 ± 0.0 5.1 5.4 22.3 21.0Refertilization 80.1 83.2 2.2 ± 3.2 0.5 ± 0.4 81.8 82.2 0 ± 0.0 1 ± 1.0 5.9 5.9 23.5 21.1Late sowing 65.6 81.8 0.5 ± 0.5 0.4 ± 0.3 80.9 81.1 0 ± 0.0 4 ± 5.3 6.3 5.3 22.0 25.3

Paraná Control 81.8 74.3 0.7 ± 0.4 0.8 ± 0.2 80.7 80.4 1 ± 1.5 3 ± 2.5 4.3 4.0 20.4 21.5High density 63.6 68.1 1.6 ± 0.9 0.4 ± 0.1 78.9 81.5 5 ± 4.4 3 ± 2.1 3.6 4.0 19.3 20.2Refertilization 81.8 75.8 0.2 ± 0.2 0.5 ± 0.3 80.1 81.9 1 ± 0.6 1 ± 1.5 5.0 5.0 22.2 22.6Late sowing 71.1 38.0 0.8 ± 0.3 6.8 ± 2.0 81.1 80.2 0 ± 0.6 1 ± 1.2 5.4 6.8 21.9 22.6

Year (Y) ns ns (0.3)** nsLocation (L) (4.4)a,* (0.5)*** (0.3)** nsCrop management (C) (4.0)*** (0.3)*** (0.2)*** (0.7)**Hybrid (H) (2.6)*** (0.2)*** (0.2)*** nsY*L (6.2)*** ns (0.4)*** (0.8)**Y*C (5.6)* (0.4)*** ns (0.9)**L*C (6.9)* (0.5)*** (0.4)*** (1.1)***L*H (4.6)* ns ns (0.7)*Y*L*C (9.8)** (0.7)*** (0.6)*** nsY*L*H ns (0.4)** ns nsL*C*H (9.1)* ns ns ns

a Tukey value for p ≤ 0.05b Means ± standard deviation. Statistical significances for main effects and interactions at *5%, **1%, and ***0.1%. ns: not significant.

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146 A.G. Cirilo et al. / Field Crops Research 122 (2011) 140–150

Fig. 1. Grain yield (140 g kg−1 kernel moisture) as a function of kernel number (A)and weight per kernel (in dry basis, B); post-silking biomass as a function of ker-nel number (C), and source–sink ratio established during the post-silking period asa function of post-silking biomass (D) for two orange-flint maize hybrids: Morgan306 (open symbols) and Cóndor (closed symbols), grown at three locations withfour different crop managements during two growing seasons. Each symbol corre-sponded to the mean of three replications. Bars in cross represent three times thevalue of the standard error of the mean for each variable. The inserts show fittedregressions for each hybrid.

Fig. 2. Weight per kernel (in dry basis, A), proportion of kernels sized over 8 mm (B),and proportion of kernels sized under 6.5 mm (C) as a function of the source–sinkratio established during the post-silking period for two orange-flint maize hybrids:Morgan 306 (open symbols) and Cóndor (closed symbols), grown at three locationswith four different crop managements during two growing seasons. Each symbolcorresponded to the mean of three replications. Bars in cross represent three timesthe value of the standard error of the mean for each variable (except for kernelssized under 6.5 mm because inadequacy of data for the analysis of variance). The

inserts show fitted regressions for each hybrid. The horizontal lines show minimum(in A and B) and maximum (in C) values required by the dry-milling industry forgrain premium quality. The dashed line shows the 1:1 ratio in A.

value at Pergamino (i.e., 80.5 kg h l−1, mean for both hybrids),whereas the lowest one was obtained at the southern location ofBalcarce (i.e., 78.1 kg h l−1). Crop management practices also sig-nificantly affected test weight (Table 3). In fact, the highest testweight value was measured when early-sown maize was refer-tilized (average of 80.0 kg h l−1), whereas the lowest one wereobtained at late sowings (i.e., 78.1 kg h l−1). The difference betweenboth crop managements was more evident at Balcarce (79.3 kg h l−1

vs. 75.2 kg h l−1, average of both hybrids and years; Table 3).Test weight of both hybrids had a bilinear response to increased

source–sink ratio after silking (Fig. 3A), with a breakpoint at 403 and350 mg kernel−1 for Morgan 306 and Cóndor, respectively. Belowthese thresholds, Cóndor showed a steeper slope of test weightincrease in response to an increase in source–sink ratio than Mor-

gan 306. Above those thresholds, hybrids also differed in the valueof the plateau (80.8 kg h l−1 vs 78.6 kg h l−1 for Morgan 306 andCóndor, respectively). These responses revealed that while the oldhybrid Morgan 306 matched the dry-milling industry requirement

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Fig. 3. Test weight (A), percent floaters (B), and milling ratio (C) as a function of thesource–sink ratio established during the post-silking period for two orange-flintmaize hybrids: Morgan 306 (open symbols) and Cóndor (closed symbols), grown atthree locations with four different crop managements during two growing seasons.Each symbol corresponded to the mean of three replications. Bars in cross representthree times the value of the standard error of the mean for each variable (except forpsap

ffht(

uhBdeBiC(etti

ercent floaters because inadequacy of data for the analysis of variance). The insertshow fitted regressions for each hybrid. The horizontal lines show minimum (in And C) and maximum (in B) values required by the dry-milling industry for grainremium quality.

or premium quality (i.e., 79 kg h l−1) in almost all situations (exceptor late sowing at Balcarce; Table 3), the new high-yielding hybridardly achieved it. In fact, only in those cases when plots were refer-ilized, test weight values for Cóndor approached that requirementTable 3).

The hybrid Morgan 306 presented lower percent floaters val-es than Cóndor (average of 1.2% vs. 17.0%, respectively for eachybrid; Table 3), but these differences were more noticeable atalcarce and Paraná. In turn, refertilization of early-sown maizeecreased percent floaters for hybrid Cóndor, reducing the differ-nces between hybrids (Table 3). This effect was more evident inalcarce and Paraná than in Pergamino. Moreover, delayed sow-

ng and high plant density resulted in increases in this variable foróndor, with larger effects in Balcarce (for both years) and Paraná

only for the second year) than in Pergamino (Table 3). A bilin-ar model could be established for the response of percent floaterso post-silking source–sink ratio only for Cóndor (Fig. 3B). Reduc-ions in source–sink ratio below 391 mg kernel−1 led to dramaticncreases in percent floaters over the tolerance of 12% admitted by

arch 122 (2011) 140–150 147

the dry-milling industry for premium quality. Almost 40% of datapoints corresponding to Cóndor in Fig. 3B (mainly from late sowingand high density at the southern and northern locations; Table 3)exceeded that limit, whereas all data from Morgan 306 were belowit.

Significant effects of location, hybrid and crop management inthe coarse-to-fine particle ratio after milling were also measured(Table 3). Hybrid Morgan 306 always recorded higher milling ratiovalues than Cóndor (5.1 vs. 4.3, respectively). Refertilization of earlysown maize produced high milling ratio values at every locationfor both hybrids and years (Table 3). The milling ratio showed thehighest value at Pergamino (5.0) and the lowest one at Paraná (4.4).Nevertheless, the milling ratio decreased in Balcarce, but increasedin Paraná in response to delayed sowing, revealing a significantlocation by crop management interaction. In turn, no associationwas found when data from all treatment combinations and yearswere plotted against the source–sink ratio established during thepost-silking period (Fig. 3C).

Hardness-associated properties were linked to variations inweight per kernel. Linear models adequately described theseresponses. A different linear model was fitted for each hybridbetween test weight and weight per kernel, showing hybrid Cón-dor a steeper response than Morgan 306 (Fig. 4A). In turn, only forCóndor, variations in percent floaters could be explained by varia-tions in weight per kernel (Fig. 4B). In this hybrid, percent floatersincreased at a rate of 0.45% per mg of decrease in weight per kernel.Similar linear models were fitted for both hybrids for the responseof milling ratio to changes in weight per kernel only after excludingdata of late sown plots in Paraná during the second year (Fig. 4Cand Table 3). Interestingly, kernel quality would be enhanced asweight per kernel increases over the minimum weight per ker-nel demanded by the dry-milling industry (i.e., 228 mg). Moreover,weight per kernel below the limit of 228 mg was associated in mostcases with hardness properties out of market requirements (Fig. 4).

3.6. Flaking-grit yield

No significant effects of year, hybrid, or location were observedon flaking-grit yield (Table 3). In turn, this variable was affectedwhen crop management was modified. In fact, the highest flaking-grit yield was achieved when plots were refertilized (22.9%) and thelowest corresponded to plots sown at high density (21.8%). Never-theless, a significant location by crop management interaction wasfound. In fact, the highest flaking-grit yield value corresponded torefertilized plots at the northern and southern locations, whereaslate sowing showed the highest flaking-grit yield at Pergamino(Table 3). No association could be established between flaking-grityield and post-silking source-ratio or weight per kernel. Never-theless, a slight association was found between falking-grit yieldand milling ratio for the complete data set (y = 19.5 + 0.6x, r2 = 0.25;n = 48; p < 0.001).

4. Discussion

As expected, the new hybrid Cóndor had higher grain yield thanthe old hybrid Morgan 306, and variations in grain yield due tolocations and crop managements were strongly associated withvariation in the number of harvested kernel (Fig. 1A), in agreementwith previous reports (Muchow et al., 1990; Cirilo and Andrade,1994a; Otegui et al., 1995). Nevertheless, grain yield appeared to

be also associated with weight per kernel (Fig. 1B). In turn, weightper kernel was explained by the source–sink ratio established inthe period from silking to physiological maturity (Fig. 2A), as wasreported previously (Cirilo and Andrade, 1996; Borrás and Otegui,2001). The post-silking period considered in our work involved

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Fig. 4. Test weight (A), percent floaters (B), and milling ratio (C) as a function ofweight per kernel (in dry basis) for two orange-flint maize hybrids: Morgan 306(open symbols) and Cóndor (closed symbols), grown at three locations with four dif-ferent crop managements during two growing seasons. Each symbol correspondedto the mean of three replications. Bars in cross represent three times the value ofthe standard error of the mean for each variable (except for percent floaters becauseinadequacy of data for the analysis of variance). The inserts show fitted regressionsfor each hybrid. The horizontal lines show minimum (in A and C) and maximum (inBcif

mtggAGaspk

tipesg

heavier kernels (Table 2) also produced flintier kernels (Table 3).

) values required by the dry-milling industry for grain premium quality. The verti-al line shows minimum value required for weight per kernel. Data for late sowingn Paraná during the second growing season (enclosed in the circle) were excludedrom the fitted data set for each hybrid in C.

ost of the critical period for kernel set in maize (c.a., 1–2 wk beforeo 2–3 wk after silking; Andrade et al., 1999), as well as the wholerain-filling period (Cirilo and Andrade, 1996). Increases in plantrowth along these stages led to more (Cirilo and Andrade, 1994b;ndrade et al., 1999, 2002) and heavier (Cirilo and Andrade, 1996;ambín et al., 2006) kernels in maize. Moreover, source activityfter silking was reported to change in maize in response to theize of the sink (Borrás and Otegui, 2001). All these evidences sup-ort the strong association found between number of harvestedernels and biomass accumulated after silking (Fig. 1C).

Post-silking growth responded to variations in incident radia-ion according to location and sowing date (Table 1). Then, increasesn incident radiation during that period led to increases in biomass

roduction in agreement with previous reports for maize (Muchowt al., 1990; Cirilo and Andrade, 1994a). Consequently, whenowing date was delayed, the environmental conditions for croprowth during the post-silking period became worse, particularly

arch 122 (2011) 140–150

at the southern location (Table 1). Temperature during that periodwas closely correlated with incident radiation (r2 = 0.88, n = 12,p < 0.001). Then, variations in mean temperature during the post-silking period accompanied the observed variations in biomassproduction. Nevertheless, low mean thermal values for late sow-ings at the southern location would had contributed to their lowpost-silking biomass production by affecting radiation use effi-ciency as was reported for maize grown at Balcarce (Andrade et al.,1993).

The biomass produced by the crop per harvested kernel duringthe post-silking period explained most of the variations observed indry-milling quality of kernels when environments or crop manage-ments were modified (Figs. 2 and 3). The strong association foundbetween source–sink ratio and crop biomass production during thepost-silking period (Fig. 1D) highlight the relevance of crop grow-ing conditions at the reproductive stage, not only in the definitionof grain yield, but also in the determination of dry-milling quality.The early post-silking period (c.a., 2 wk after silking) was proposedto be critical for kernel size determination in maize (Gambín et al.,2006). At this stage, maize plants would set an individual kernelsink potential (e.g., number of endosperm cells or amyloplasts) thatinfluenced kernel growth. An enhanced availability of assimilatesto the kernel at this young stage yielded an increase in final weightper kernel through changes in kernel growth rate during the effec-tive grain-filling period (Gambín et al., 2006). Maize kernels usuallygrow in the field under conditions of adequate resource availabil-ity during the effective grain filling, which enables them to achievetheir sink potential established early in development (Borrás etal., 2004). Nevertheless, final weight per kernel can be affected byshortages in assimilate supply during filling that impaired reachingtheir potential size (Cirilo and Andrade, 1996; Andrade and Ferreiro,1996; Maddonni et al., 1998). Although the source–sink ratio calcu-lated in our work overestimated the actual ratio established duringthe effective grain-filling period, the framework for weight perkernel determination presented above supports the strong rela-tionship found between final weight per kernel and source–sinkratio calculated for the whole post-silking period (Fig. 2A). Infact, late sowing, with reduced biomass production after silking,resulted in final weight per kernel below the minimum marketrequirement (i.e., 228 mg in a dry basis; Table 2). Enhanced nitrogenavailability at silking by crop refertilization increased post-silkingbiomass production (Table 2) in agreement with nitrogen effectsreported for maize (Uhart and Andrade, 1995). Then, refertilizationof early sown plots led to improved source–sink ratio and, con-sequently, resulted in kernels largely heavier than the minimummarket requirement (Table 2). The response of final weight perkernel to variations in post-silking source–sink ratio explained thebehavior observed for kernel size proportions (Fig. 2 and Table 3).Differences in kernel shape (i.e., round and short kernels for Mor-gan 306, and long and thin kernels for Cóndor) and their resultingdifferent behavior over the sieves could explain the observed dif-ferences in kernel size proportion for both hybrids (Fig. 2B and C)at similar weight per kernel (Table 2).

Kernel hardness-associated properties (i.e., test weight, per-cent floaters and milling ratio) were strongly determined by thegenotype (Table 3), in agreement with the literature (Dombrink-Kurtzman and Bietz, 1993; Eyhérabide et al., 1996). Nevertheless,kernel hardness also responded to changes imposed by locationsand crop management practices, particularly for hybrid Cóndorwith unstable flint-type expression (Fig. 3). Those cropping condi-tions that allowed plots to achieve higher grain yields together with

Kernel hardness results from the endosperm biochemical compo-sition (Dombrink-Kurtzman and Bietz, 1993; Dombrink-Kurtzmanand Knutson, 1997; Robutti et al., 1997), and the interactions estab-lished between stored protein and starch were proposed to account

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or the differences in endosperm texture in maize (Chandrashekarnd Mazhar, 1999; Robutti et al., 2000b). Hardness-associatedroperties responded linearly to variations in weight per kernelhroughout the range explored in our work (Fig. 4). The plateaubserved for the association between hardness properties andource–sink ratio (Fig. 3A and B) was absent or less evident in theseelationships because of the linear-plateau response of weight perernel to source–sink ratio (Fig. 2A). Borrás et al. (2002) reported ailinear response of kernel protein content to increases in weighter kernel with a breakpoint at ca. 200–250 mg of individual kerneleight above which increases in protein content were matched by

ncreases in protein concentration. The range of weight per kernelxplored in our study included the breakpoint reported by Borrást al. (2002), suggesting that increases in weight per kernel beyondhat point would correspond to a stronger protein matrix in thendosperm.

The zeins are the storage proteins of maize endosperm. Thisrotein fraction is known to have significant effects on maize ker-el hardness (Dombrink-Kurtzman and Bietz, 1993; Robutti et al.,997). While structural proteins (e.g., albumins and globulins) areostly deposited during the early stages of grain filling in maize,

he zeins exhibit the largest increase during the last phases of kernelevelopment (Ingle et al., 1965). In fact, increases in total proteinontent of maize kernels in response to cropping conditions haveeen matched by a rise in zein content, and this protein fraction pre-ominated at high weight per kernel (Singletary et al., 1990). Thesevidences would underlie the responses of hardness-associatedroperties to the post-silking source–sink ratio (Fig. 3) and to theeight per kernel (Fig. 4) found in our work. Moreover, genotypic

ariability in zein content and composition was reported for maizeRobutti et al., 2000a) which would explain the different patternesponses observed for both hybrids (i.e., a steeper and strongeresponse for the high-yielding new hybrid Cóndor with unstableint expression, and a smoother and weaker response for the oldernd flintier low-yielding hybrid Morgan 306). Further researchesre needed to elucidate these speculations. Exploring a wider rangef source–sink ratio during the grain filling period would allowbetter description of the response of hardness-associated prop-

rties to this ratio and would provide insights about the patternf deposition of those endosperm components linked to kernelilling performance. These issues, together with the identifica-

ion of specific stages during the grain filling period when risesr decreases in source–sink ratio become more critical for deter-ining the endosperm composition would help to select the most

dequate crop management and the most suitable area to produceint maize with the highest dry-milling quality.

. Concluding remarks

Most of observed differences in dry-milling quality of flintaize due to environment or crop management modifications were

inked to the source–sink ratio established during the post-silkingeriod, which was strongly associated with changes in post-silkingiomass production. These changes in post-silking growth wereainly the result of variations in radiative conditions of the crop-

ing environment according to location and sowing date. Changesn reproductive growth affected photoassimilate availability notnly for kernel set and potential kernel size determination, but alsoor kernel filling. Hybrid differences in the response of hardness-ssociated properties to the post-silking source–sink ratio and to

he weight per kernel highlight the relevance of starch and proteinomposition in determining the strength of the endosperm and itsehavior at the mill.

Finally, our research brings experimental evidence on thechievement of high crop grain yields together with top grain qual-

arch 122 (2011) 140–150 149

ity for the dry-milling industry in orange-flint maize productionwhen a new high-yielding hybrid with reportedly unstable flinttype expression was cropped with an appropriated crop manage-ment. The maize crop responses reported in this work are useful toforesee the consequences of selecting different cropping practicesor production areas on flint maize quality.

Acknowledgements

The authors are thankful to the National Institute of AgriculturalTechnology (INTA) of Argentina for providing financial support forthis study included in the Project PNCER-2345 (52-022450).

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