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Sarhad J. Agric. Vol.27, No.4, 2011

CORRELATIONS AMONG GRAIN YIELD AND YIELD ATTRIBUTES IN MAIZE HYBRIDS AT VARIOUS NITROGEN LEVELS INAMULLAH*, NAVEEDUR REHMAN*, NAZEER HUSSAIN SHAH**, MUHAMMAD ARIF* MUHAMMAD SIDDIQ*** and ISHAQ AHMAD MIAN**** * ** *** ****

Department of Agronomy, Agricultural University, Peshawar – Pakistan. Agricultural Research System, Peshawar – Pakistan. National Agricultural Research Center, Islamabad – Pakistan. Department of Soil & Environmental Sciences, Agricultural University, Peshawar – Pakistan. E-mail: [email protected]

ABSTRACT Three maize hybrids (Baber, Pioneer 30P45 and Syngenta 6621) were compared for yield and yield components and correlations were worked out among the yield parameters at various nitrogen levels in an experiment conducted at Agricultural University, Peshawar, Pakistan during summer 2009. The experiment was laid out in randomized complete blocks with split plot arrangement having three replications. Nitrogen levels (0, 180, 240 and 300 kg ha-1) were allotted to main-plots and hybrids to subplots. The higher levels of 240 and 300 kg N ha-1 recorded maximum and at par number of 1.3 and 1.2 ears plant-1, ear lengths of 14 and 13.5 cm, grains ear-1 of 422.1 and 481.2, 1000 grain weight of 280.56 and 303.68 g, grain yield of 3281.3 and 3696 kg ha-1, biological yield of 10889 and 11830 kg ha-1 and harvest indices of 30.1 and 31.42%, respectively. Syngenta 6621 recorded larger ear length of 14.6 cm, larger number of 451.5 grains ear-1, higher 1000 grain weight of 275.24 g, higher grain yield of 3033.8 kg ha-1 and higher biological yield of 11555.9 kg ha-1. All these values were statistically equal to those recorded by Pioneer 30P45. Pioneer 30P45 recorded the highest harvest index of 27.8%. The interaction of nitrogen and hybrids affected grains ear-1, grain yield, biological yield and harvest index substantially. When the nitrogen level was increased from 0 to 300 kg ha-1, ears plant-1 of Syngenta 6621, Pioneer 30P45 and Baber increased by 20%, 20% and 10%; grains ear-1 by 89%, 55% and 30.7%; thousand grain weight by 37.2%, 29.8% and 45.7%; grain yield by 143%, 151% and 102%; biological yield by 68%, 50.4% and 49.5% while harvest index increased by 45.5%, 66.5% and 36.3%, respectively. It was concluded that among the three yield attributes, ear plant-1 contributed 14.8%, grains ear-1 51.8% and 1000 grain weight contributed 33.4% to the average increase of 132% in the grain yield of hybrids. Based upon the correlations, ear length was also found a suitable marker for selecting a maize hybrid for higher grain yield along with other yield attributes i.e. ears plant-1, grains ear-1 and 1000 grain weight. Key Words: Maize (Zea mays L.), hybrids, nitrogen, yield, yield components Citation: Inamullah, N. Rehman, N.H. Shah, M. Arif, M. Siddiq and I. Mian. 2011. Correlations among grain yield and yield attributes in maize hybrids in various nitrogen levels. Sarhad J. Agric. 27(4): 531-538 INTRODUCTION Maize (Zea mays L.) is the second most important food crop after wheat in Khyber Pakhtunkhwa (KP) (Asif et al., 2007) and ranks third after wheat and rice in Pakistan (Chaudhry, 1994). Average maize yield in KP is low as compared with the average yield of Pakistan (MINFAL, 2009) although maize yield in Pakistan is itself lower than its potential yield. For example, in USA average grain yield of maize is 9658 kg ha-1, while in Pakistan and in KP, an average maize yield of 3415 and 1880 kg ha-1 is obtained, respectively (MINFAL, 2009). Grain yield is a function of genotype x environment interaction (Annicchiarico, 2002). A more acceptable crop genotype is the one which exhibits wide adaptability to varying environments. In a given environment, the grain yield of a particular maize genotype (variety or hybrid) depends on its potential grain yield components (Grafius, 1960). Grain yield of maize is product of three yield components i.e. the number of ears per unit area, the number of grains per ear and the unit grain weight (Gardner et al., 1985). Increase or decrease in any one of these components, keeping the size of other components constant, contributes to increase or decrease in grain yield, respectively, and thus any exercise whether agronomic (management) or breeding type (genotype), which increase any of these components, keeping the other components constant, will increase the final grain yield. Devi et al., (2001) reported that ears plant-1, ear length, number of seeds ear-1 and 100-seed weight directly influence the grain yield and indirectly affect several other parameters. Any kind of stress, for example a drought stress, during or around the stage(s) at which these components are formed may severely affect grain yield. As an agronomist and/or a plant breeder, two things should be kept in mind regarding the yield components: (i) the contribution or level of correlation of a yield component to total grain yield and (ii) measures needed to be carried out to reduce damages to

Inamullah et al. Correlations among grain yield and yield attributes in maize hybrids…

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grain yield incurred by decrease in the particular yield component. It has been reported that agronomic measurements like proper tillage (Duiker et al., 2006), proper seed rate (Sarlangu et al., 2007), row spacing and planting geometry (Maddonni et al., 2001), proper fertilizer application (Rasheed et al., 2004), timely sowing (Norwood, 2001) and weeds control (Chaudhry, 1994) increased yield attributes and ultimately the grain yield. Several reports are available regarding the phenotypic and genotypic correlations among physiology, phenology, grain yield and yield components (Yousuf and Saleem, 2001; Rafique et al. 2004; Iqbal et al. 2009), however, almost all of them have been written from the crop breeding point of view. Most of such experiments have either been conducted in pots or in controlled environments. Very few reports are available which explain the correlations among grain yield and yield components in experiments conducted on large agronomic scale. The present study was thus conducted to find out correlations among grain yield and yield components of local and exotic maize hybrids under field conditions. MATERIALS AND METHODS To study the correlation among grain yield and yield components of maize hybrids at various nitrogen levels, an experiment was conducted at Agricultural University, Peshawar, Pakistan (34o 00’ N, 71o 30’ E, 510 meters above sea level) during summer 2009. The experiment was laid out in randomized complete block (RCB) design with split plot arrangement having three replications. Previous crop in the field was spring wheat. Nitrogen was applied to the main-plots while hybrids to the subplots. Area of each subplot was 4.5 m x 5 m having six rows, 75 cm apart and 5 m long. All the recommended agronomic practices like hoeing, weedicides application and irrigation were followed uniformly. Four levels of nitrogen including control (0, 180, 240 and 300 kg ha-1) and three hybrids i.e. Baber (a double-cross produced by Cereal Crops Research Institute, Pirsabak, Nowshera), Pioneer 30P45 (Pioneer Hi-Bred International) and Syngenta 6621 (Syngenta International) were used. Data were recorded on ears plant-1, ear length, grains ear-1, 1000 grains weight, grain yield, biological yield and harvest index. Ten plants in each subplot were randomly selected, their ears were counted and averaged to record number of ears plant-1. Ten plants in each subplot after harvesting were randomly selected; their ear lengths were measured with the help of measuring tap. The data generated were averaged to record ear length. Ears harvested for grain yield were used for the determination of number of grains ear-1 by selecting ten ears randomly from each subplot, dried and shelled for grains ear-1. Data regarding thousand grains weight were recoded by counting randomly selected 1000 grains from each sub plot and weighed with sensitive electronic balance. Grain yield was recorded by weighing the grains shelled from the ears obtained from the central four rows of each subplot and converted it into kg ha-1 using the formula: Grain yield (kg ha-1) = {Grain yield (kg)/Area harvested (3 m x 5 m)} x 10000 Biological yield was also recorded by weighing the sun dried plants along with ears obtained from central four rows of each subplot. The biological yield thus obtained in each subplot was converted it into kg ha-1 using the formula: Biological yield (kg ha-1) = {Biological yield (kg)/Area harvested (3 m x 5 m)} x 10000 Harvest index was calculated using the formula: Harvest Index (%) = (Grain yield/Biological yield) x 100 (Reddy, 2004) For calculating the coefficients of correlation, data of the mentioned parameters were averaged across the hybrids at various nitrogen levels and then coefficients of correlation were worked out among the mentioned parameters using excel worksheet (Gomez and Gomez, 1984; Iqbal et al. 2009). Data were analyzed using the statistical package MSTAT-C (Russel and Eisensmith, 1983) and the significant differences between treatments were determined using least significant difference (LSD) test at probability level of 0.01 or 0.05 where the effects of the treatments were significant at 1% or 5% level of probability, respectively. RESULTS AND DISCUSSION Ears Plant-1 Number of ears plant-1 of maize hybrids was significantly affected by nitrogen at 1% level of probability (Table I). Higher and at par number of 1.3 and 1.2 ears plant-1 were recorded when 240 or 300 kg ha-1 N was applied, respectively, while the lowest number of 1 ear plant-1 was recorded in plots where 0 or 180 kg ha-1 N was applied. Khan et al. (1999) reported no profound effect of nitrogen on number of ears plant-1 when its level was increased from 0 to 150 kg ha-1, however, when N level was further increased to 210 kg ha-1, significant differences


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were observed as compared with 0 kg ha-1 N. Khan et al. (1999) are of the view that the maize hybrid 3335 which they used in their experiment, produced higher ears plant-1 only when higher level of N (210 kg ha-1) is used. In our experiment, there was no difference in ears plant-1, when 0 or 180 kg ha-1 N was used. Ears plant-1 increased substantially when N level was increased to 240 or 300 kg ha-1. Hybrids were not statistically different from each other in number of ears plant-1. However, Wajid et al. (2007) reported significant differences in ears plant-1 of various hybrids (B-202, M-919 and P-31-R-88). They are of the view that production of number ears plant-1 is a genetically controlled characteristic. Similarly, the interaction of nitrogen and hybrids also showed non significant effect on ears plant-1. Wajid et al. (2007) also reported no significant effect of the interaction of nitrogen and hybrids on maize ears plant-1. Ears plant-1 of maize hybrids as affected by various nitrogen levels Hybrids Nitrogen (kg ha-1) Mean Baber Pioneer 30P45 Syngenta 6621 0 1.0 1.0 1.0 1.0 b 180 1.0 1.0 1.0 1.0 b 240 1.2 1.2 1.4 1.3 a 300 1.1 1.2 1.2 1.2 a Mean 1.1 1.1 1.2 Means in the same category followed by at least one common letter are not significantly different at P 0.01 level. LSD value (P 0.01) for Nitrogen = 0.1105 Table I

Ear Length (cm) Ear length of maize hybrids was significantly affected by N at 1% probability level Table II. Longer and at par ear length of 14 and 13.5 cm was recorded when 240 and 300 kg ha-1 N was used respectively while the smallest ear length of 11.4 cm was recorded in control plots where N was not applied. Hybrids were also significantly different from each other at 1% level of probability in ear length. Longer ear length of 14.6 cm was recorded by Syngenta 6621 followed by Pioneer 30P45 with statistically equal ear length of 14.1 cm while Baber recorded the smallest ear length of 11.8 cm. Turi et al. (2007) reported that difference of ear length among maize genotypes is a genetic characteristic which is affected by the environment and inputs. The interaction effect of nitrogen and hybrids on ear length was statistically non significant which shows that change in the ear length of all the three hybrids took place in the same manner with change in nitrogen level. Table II Ear length (cm) of maize hybrids as affected by various nitrogen levels Nitrogen (kg ha-1) Hybrids Mean Baber Pioneer 30P45 Syngenta 6621 0 9.7 12.8 11.6 11.4 b 180 11.5 13.3 14.7 13.2 b 240 12.4 14.4 15.3 14.0 a 300 11.8 14.0 14.6 13.5 a Mean 11.8 b 14.1 ab 14.6 a Means in the same category followed by at least one common letter are not significantly different at P 0.01 level. LSD value (P 0.01) for Nitrogen = 1.607 LSD value (P 0.01) for Hybrids = 2.659

Grains Ear-1 Nitrogen affected number of grains ear-1 of maize hybrids at 1% probability level (Table III). Significantly higher number of 481.2 grains ear-1 was recorded when 300 kg ha-1 N was used, which was at par with number of grains ear-1 recorded at 240 or 180 kg ha-1 N. The lowest number of 295.6 grains ear-1 was recorded in control plots where N was not applied. Ali et al. (1999) reported increase number of grains ear-1 with increase in N level. Hybrids were also different from each other at 1% level of probability in number of grains ear-1. Higher number of 451.5 grains ear-1 was recorded by Syngenta 6621 followed by Pioneer 30P45 with 414.5 grains ear-1. However, the grains ear-1 produced by these two hybrids were not significantly different from each other. The lowest number 322.5 grains ear-1 was produced by Baber. Similar results have been reported by Wajid et al. (2007). The interaction effect of nitrogen and hybrids on number of grains ear-1 was also significant at 1% probability level. Higher number 533 grains ear-1 was recorded by Syngenta 6621 in plots which received 300 kg ha-1 nitrogen, which was at par with the number of grains ear-1 recorded by Syngenta 6621 at 240 or 180 kg ha-1 nitrogen. The lowest number of 290 grains ear-1 was produced by Baber in plots where no nitrogen was applied. This number was also at par with the grains ear-1 produced by Pioneer 30P45 and Syngenta 6621 in plots where no nitrogen was applied. Ali et al. (1999), however, reported no effect of the interaction of nitrogen and hybrids on grains ear-1.


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Grains ear-1 of maize hybrids as affected by various nitrogen levels Hybrids Nitrogen (kg ha-1) Mean Baber Pioneer 30P45 Syngenta 6621 0 290 f 320 ef 282 f 295.6 b 180 305 f 412 cde 452 abcd 389.9 ab 240 315 ef 428 bcd 522 ab 422.1a 300 379 def 496 abc 533 a 481.2 a Mean 322.5 b 414.5 a 451.5 a Means in the same category followed by at least one common letter are not significantly different at P 0.01 level. LSD value (P 0.01) for Nitrogen = 98.27 LSD value (P 0.01) for Hybrids = 85.23 LSD value (P 0.01) for N x H = 98.43 Table III

Thousand Grain Weight (g) Nitrogen affected 1000-grain weight of maize hybrids at 1% level of probability (Table IV). Significantly higher 1000-grain weight of 303.68 g was recorded when 300 kg ha-1 nitrogen was used, which was at par with the 1000-grain weight recorded at 240 kg ha-1 nitrogen. The lowest 1000-grain weight of 221.10 g was recorded in control plots where nitrogen was not applied. Hybrids were also different from each other at 1% probability level in 1000-grain weight. Higher 1000-grain weight (275.24 g) was recorded by Syngenta 6621 followed by Pioneer 30P45 (262.25 g). Thousand grain weights produced by these two hybrids were at par with each other. Significantly lower 1000-grain weight (251.85 g) was produced by Baber. The interaction of nitrogen and hybrids did not show any effect on 1000-grain weight at 5% probability level. Khan et al. (1999) and Sharar et al. (2003) also reported similar results. Table IV

Thousand grains weight (g) of maize hybrids as affected by various nitrogen levels Hybrids Nitrogen (kg ha-1) Mean Baber Pioneer 30P45 Syngenta 6621 0 206.67 224.67 231.96 221.10 c 180 228.67 245.33 267.33 247.11 bc 240 271.03 287.33 283.33 280.56 ab 300 301.03 291.67 318.33 303.68 a Mean 251.85 b 262.25 ab 275.24 a Means in the same category followed by at least one common letter are not significantly different at P 0.01 level. LSD value (P 0.01) for Nitrogen = 34.86 LSD value (P 0.01) for Hybrids = 20.34

Grain Yield (kg ha-1) Nitrogen affected grain yield of maize hybrids at 1% probability level (Table V), producing higher grain yield of 3697 kg ha-1 with 300 kg N ha-1 and the lower grain yield of 1585 kg ha-1 when N was not applied. Many authors including Abayomi et al. (2006), Mahdi and David (2005), Dobby et al. (2000), Muchow (1988) and Uhart and Andrade (1995) have reported increase in grain yield of maize with increase in N level. Among the hybrids Syngenta 6621 produced the highest yield of 3034 kg ha-1 which was statistically at par with the grain yield produced by Pioneer 30P45 (i.e. 2728 kg ha-1) while Baber produced the lowest grain yield of 2305 kg ha-1. Ragheb and Rassy (1989) reported that hybrids generally differ from each other in grain yield due to genetic factors and the different physiological performance. The physiological factors include extended root system with more root hairs to absorb more nutrients and the canopy architecture to intercept more photosynthetic light. The interaction of nitrogen and hybrids also affected grain yield 5% level of probability (Table V). Syngenta 6621 produced 1700 kg ha-1 grain yield when nitrogen was not applied, which increased to 4135 kg ha-1 with 300 kg ha-1 nitrogen. This increase from 1700 to 4135 kg ha-1 was 59%. Baber produced grain yield of 1489 kg ha-1 without nitrogen which increased to 3022 kg ha-1 with 300 kg ha-1 nitrogen, recording a 51% increase. Pioneer 30P45, on the other hand, produced grain yield of 3933 kg ha-1 with 300 kg ha-1 nitrogen, and 1566 kg ha-1 with no nitrogen. The increase in grain yield with 300 kg ha-1 nitrogen as compared with zero nitrogen was 60%. It shows that Pioneer 30P45 and Syngenta 6621 responded more actively to higher N levels. Similar findings have been reported by Chaudhry and Jamil (1998) and Akmal et al. (2010), who documented that various maize genotypes responded differently to different N doses. At 300 kg ha-1 nitrogen, the yield response of Baber and Syngenta 6621was not significantly higher than at 240 kg ha-1, however, Pioneer 30P45 showed significantly higher yield at 300 kg ha-1 than at 240 kg ha-1, which shows that Pioneer 30P45 has the potential to respond more actively in terms


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of grain yield to higher nitrogen levels and it may give higher grain yield with nitrogen doses higher than 300 kg ha1 , however, more experiments should be conducted in this regard. Grain yield (kg ha-1) of maize hybrids as affected by various nitrogen levels Hybrids Nitrogen (kg ha-1) Mean Baber Pioneer 30P45 Syngenta 6621 0 1489 f 1566 ef 1700 ef 1585 b 180 1977 def 2133 de 2466 cd 2192 b 240 2733 bc 3277 b 3833 bc 3281 a 300 3022 bc 3933 a 4135 a 3697 a Mean 2305 b 2728 ab 3034 a Means in the same category followed by at least one common letter are not significantly different at P 0.01 or P 0.05 level as shown in the LSD values below. LSD value (P 0.01) for Nitrogen = 618 LSD value (P 0.01) for Hybrids = 508 LSD value (P 0.05) for N x H = 556 Table V

Biological Yield (kg ha-1) Nitrogen affected biological yield of maize hybrids at 1% probability level (Table VI). Higher biological yield (11830 kg ha-1) was recorded when 300 kg ha-1 nitrogen was used which was at par with the biological yield produced at 240 kg ha-1 nitrogen. The lowest biological yield of 7545 kg ha-1 was recorded in control plots where nitrogen was not applied. This yield was at par with the biological yield produced in plots where 180 kg ha-1 nitrogen was applied. The hybrids were also different from each other at P 0.01 in biological yield. Higher biological yield (11556 kg ha-1) was recorded by the hybrid Syngenta-6621 while the lowest biological yield (8236 kg ha-1) was produced by Baber. D’Angrea et al. (2009) reported differences in biological yields of various hybrids and an increase in total biomass with increase in nitrogen levels. Biological yield (kg ha-1) of maize hybrids as affected by various nitrogen levels Hybrids Nitrogen (kg ha-1) Mean Baber Pioneer 30P45 Syngenta 6621 0 6555 h 7522 fgh 8555 fg 7545 b 180 7364 gh 8818 ef 10294 cd 8826 b 240 9222 de 10444 cd 13000 b 10889 a 300 9800 de 11316 c 14373 a 11830 a Mean 8236 c 9525 b 11556 a Means in the same category followed by at least one common letter are not significantly different at P 0.01 or P 0.05 level as shown in the LSD values below. LSD value (P 0.01) for Nitrogen = 1345 LSD value (P 0.01) for Hybrids = 1149 LSD value (P 0.05) for N x H = 1327 Table VI

The interaction of nitrogen and maize hybrids affected the biological yield at 5% probability level (Table VI). The highest biological yield of 14373 kg ha-1 was recorded by Syngenta 6621 in plots which received 300 kg ha-1 N, while the lowest biological yield of 6555 kg ha-1 was produced by Baber in control nitrogen plots. This yield was at par with the biological yield produced by Pioneer 30P45 in plots where nitrogen was not applied. Harvest Index (%) Nitrogen affected harvest index (HI) of maize hybrids significantly at P 0.01. Higher HI of 31.4% was recorded in plots applied with 300 kg ha-1 nitrogen, which was not statistically different from the HI of 30.1% recorded at 240 kg ha-1 N. The lowest HI of 21.1% was recorded in plots where nitrogen was not applied. Sabir et al. (2000) and Muhammad et al. (2002) reported an increase in HI in maize while Ali et al. (2002) reported that HI was not affected with change in nitrogen level. Among the hybrids, higher HI of 27.8% at P 0.01 was recorded by Pioneer 30P45 which was at par with the HI recorded by Baber. Syngenta 6621 recorded the lowest HI of 25.5%. Sabir et al. (2000) reported significant differences among hybrids in HI. The interaction of nitrogen and hybrids showed significant effect on HI at 5% probability level (Table VII). Syngenta 6621 exhibited an HI of 19.8% with no nitrogen while its HI increased to 29.5% with 240 kg ha-1 N not significantly different from HI produced at 300 kg ha-1 N. Baber produced an HI of 22.6% in plots not applied with nitrogen which increased to 30.8% with 300 kg ha-1 nitrogen. Pioneer 30P45, on the other hand, produced HI of 34.8% with 300 kg ha-1 nitrogen, and 20.9% with no nitrogen. Wajid et al. (2007), however, reported no significant effect of the interaction of nitrogen and hybrids on grains ear-1.


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Table VII

Harvest index (%) of maize hybrids as affected by various nitrogen levels Hybrids Nitrogen (kg ha-1) Mean Baber Pioneer 30P45 Syngenta 6621 0 22.6 ef 20.9 f 19.8 f 21.1 c 180 26.9 cd 24.2 de 23.9 e 25.0 b 240 29.6 bc 31.3 b 29.5 bc 30.1 a 300 30.8 b 34.8 a 28.8 bc 31.4 a Mean 27.5 a 27.8 a 25.5 b Means in the same category followed by at least one common letter are not significantly different at P 0.01 or P 0.05 level as shown in the LSD values below. LSD value (P 0.01) for Nitrogen = 3.64 LSD value (P 0.01) for Hybrids = 1.9 LSD value (P 0.05) for N x H = 2.828

Correlations among Yields, Yield components and Harvest Index of Maize Hybrids It was observed that ears plant-1 showed positive and significant (P 0.05) correlation with grains ear-1 (r = 0.617*), 1000-grains weight (r = 0.69*) and harvest index (r = 0.664*) and positive and highly significant (P 0.01) correlation with grain yield (r = 0.802**) and biological yield (r = 0.811**) (Table VIII). Vasic et al. (2001) reported positive and highly significant correlation (r = 0.871**) between ears plant-1 and grain yield. Yousaf et al. (2001), however, did not find any correlation of grains ear-1 with 100 grain weight and grain yield plant-1. Ear length showed positive and significant (P 0.05) correlation with 1000-grains weight (r = 0.681*) while positive and highly significant (P 0.01) correlation with grains ear-1 (r = 0.872**), grain yield (r = 0.724**) and biological yield (r = 0.748**). Rafique et al. (2004) reported positive correlations (P 0.05) of ear length with 1000 grain weight and grain yield. Table VIII Coefficients of Correlation (r) among ears plant-1 (EPP), ear length (EL), grains ear-1 (GPE), thousand grains weight (TGW), grain yield (GY), biological yield (BY) and harvest index (HI) of three maize hybrids grown at four nitrogen levels during summer 2009 EL GPE TGW GY BY HI EPP 0.576 0.617* 0.690* 0.802** 0.748** 0.664* EL --0.872** 0.681* 0.724** 0.811** 0.429 GPE ----0.785** 0.873** 0.911** 0.582* TGW ------0.930** 0.882** 0.778** GY --------0.926** 0.839** BY ----------0.578* * = Significant (P 0.05) ** = Highly significant (P 0.01)

Grains ear-1 showed positive correlation (P 0.05) with harvest index (r = 0.582*) and positive and highly significant (P 0.01) correlation with 1000-grain weight (r = 0.785**), grain yield (r = 0.873**) and biological yield (r = 0.911**). Asrar-ur-Rahman et al. (2007), however, reported negative correlations of grains cob-1 with 1000 grain weight (r = -0.084), grain yield (r = -0.359) and biological yield plant-1 (r = -0.166). They reported that grains cob-1 is correlated with cob height on the plant only, while grain yield is correlated with the number of cobs m-2 instead of 1000 grain weight and grains cob-1. Thousand grain weight showed positive and highly significant (P 0.01) correlation with grain yield (r = 0.93**), biological yield (r = 0.882**) and harvest index (r = 0.778**) as reported by Rafique et al. (2004). Grain yield showed positive and highly significant correlation with biological yield (r = 0.926**) and harvest index (r = 0.839**) while biological yield was found positively correlated (P 0.05) with harvest index (r = 0.578*).Wajid et al. (2007) also reported correlation (P 0.05) between total dry matter production and grain yield. CONCLUSION AND RECOMMENDATIONS It was concluded that increasing nitrogen levels upto 240 kg ha-1, increased ears plant-1, ear length, grains ear , 1000 grain weight, biological yield, grain yield and harvest index. Syngenta 6621 was found the highest yielding hybrid followed by Pioneer 30P45. Based upon the significance of correlations, ear length besides yield attributes i.e. ears plant-1, grains ear-1 and 1000 grain weight were found suitable markers and may be used for selecting maize hybrids for higher grain yield. -1


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