EFFECT OF SEASONAL AND ENVIRONMENTAL VARIATION ON YIELD AND YIELD COMPONENTS OF HYBRID MAIZE

The experiment was conducted during kharif II in 2006 & 07, rabi in 2006-07 & 07-08 and kharif I in 2007 and 2008 at ARS, Burirhat, Rangpur in RCB design to understand the influence of season and location specific environment effect on growth and yield of hybrid maize and selected suitable variety(s). Four hybrid maize varieties V1=BARI hybrid Maize (BHM)-2, V2=BHM-3, V3= BHM-5 and V4= Pacific-984 (as check) were tested during kharif II in 2006 while seven varieties V1= BHM-2, V2= BHM-3, V3= BHM-5 and V4= Pacific-984, V5= Pacific-60, V6= Pacific-11 and V7= Prolin were during the other seasons except rabi, 0708, where variety Pacific-555 was used in V7 instead of Prolin. Seeds were sown on August 30 and August 11 for kharif II of 2006 and 2007, respectively, November 28 and 17 for rabi 2006-2007 and 2007-08 and March 08 and 12 for for kharif I 2007 and 2008. The crops were harvested on January 25, 2007 and January 12, 2008 in the two consecutive kharif II seasons; May 10 and April 29 in rabi 2006-07 and 2007-08, and July 01 and 05 in kharif I 2007 and 2008, respectively. Yield parameters were mostly varied significantly. The highest yield was obtained from BHM-5 (9.03 t ha-1), which was followed by Pacific-984 (8.89 t ha1), BHM-3 (8.81 t ha-1) and BHM-2 (8.58 t ha-1) in kharif II, 2006 while in kharif II, 2007 the highest significant yield was noted in Pacific-984 (9.22 t ha-1). In rabi, 2006-07, significant highest grain yield was obtained from Pacific-60 (11.03 t ha-1), which was statistically identical with Prolin (10.20 t ha-1). The yield of Prolin was also statistically identical with Pacific-11 (10.01 t ha-1), BHM-5 (10.00 t ha-1), BHM-3 (9.92 t ha-1) and BHM-2 (9.51 t ha-1). Comparatively lower temperature during ear initiation (mean 29.6oC in rabi and 31oC in kharif II) and silking (mean 18.2oC in rabi and 20.2oC in kharif II) contributed much for higher trend of yield in rabi over kharif. In kharif I, 2007, the highest yield (9.55 t ha-1) was recorded from Pacific-60, which was identical to Pacific-984 (9.25 t ha-1), BHM-5 (9.11 t ha1) and BHM-3 (8.89 t ha-1). All the BARI hybrid maize varieties were suitable to grown in kharif I, kharif II and rabi season although BHM-3, BHM-5, Pacific-60 and Pacific-984 were better in Kharif I and Pacific-60, BHM-5, Prolin and Pacific-555 were found better in Rabi season.


Introduction
Among the cereals maize ranks 3 rd position after rice and wheat.Maize can be grown throughout the year.High yield per hectare, high food value and multipurpose use as well as its high demand expanding maize cultivation day by day.There is a demand of 1.2 million tons of maize only to feed the poultry industries of Bangladesh (BARI, 2001).Again, for starch industries, other industries and for human consumption maize has a great demand.The yield of hybrid maize is about 20-30% higher than that of open pollination composite ones, which encouraged the farmers to prefer hybrid maize.Now, 87% of the total maize area is under hybrid maize.Recently BARI has developed 5 hybrid maize varieties.High quality protein maize (QPM) rich in tryptophen and lycin associated with recently evolved BARI hybrid maize-5 and other predominant BARI hybrid maize varieties along with other commercial hybrid maize varieties, the performance of the same across the seasons as well as across the locations is yet to be studied.
The environmental scientist working with maize have concluded from long term weather data that higher mean seasonal temperature was negatively correlated with grain yield and final grain yield was dependent on the rate and duration of grain growth and dry matter accumulation (BARI, 2001;Law and Brander, 1999).Increase in temperature decreased net photosynthesis and optimum temperature ranged from 28 0 C to 37.5 0 C for higher photosynthesis (Brandner and Salvucci, 2002).Physiological parameter like NAR depends on temperature due to enzyme activity rubisco and at 28 0 C rubisco oxygenase activity was 100% (Edwards et al., 2001).However, the relationship among physiological parameters with the yield and yield components in three contrasting season has not been worked out in detail.The present investigation was carried out to understand the influence of season and location specific environment effect on growth and yield of hybrid maize and selected suitable variety (s) adaptive for specific areas.

Materials and Methods
The Vitavex 200 @ 5 g kg -1 seed for 10 minutes in airtight bag then kept open.Blanket application of cow dung @ 10 t ha -1 was made 7 days before sowing.The field was fertilized with 200-60-110-45-5-2 kg NPKSZn and B/ha, respectively.Onethird amount of N as Urea and rest full amount of all other fertilizer were applied in experimental unit plot one day before sowing.Seeds of different hybrids maize varieties were accommodated in 4.5 m × 6.0 m sized plot.Two seeds/hill were sown on August 30 and August 11 for kharif II, 2006and 2007, respectively, November 28 and 17 for rabi 2006-07 and 07-08, and March 08 and 12 for kharif I, 2007and 2008, at spacing 75 cm × 20 cm.Necessary gap filling were made by re-sowing within 8 days of sowing (DAS).Rest 2/3 rd Urea in equal splits was top dressed (TD) at 30 and 60 DAS.Weeding and mulching were done properly; final earthling up was made after 2 nd TD, which was followed by irrigation.Futher irrigation was made at 75 and 90 DAS.Despite that plant received about 405 mm and 554 mm of precipitation in kharif II 2006 and 2007 respectively.In rabi, the crop was irrigated 4 times at 60, 90, 110 and 120 DAS.The crop also received rainfall at 2 nd decades of December and February, slight in the month of March and 3 rd decade of April in rabi, 2006-07.The crop in kharif I was irrigated 4 times at 10 days interval starting form 25 DAE.The crop also received a total of around 880 mm rainfall in Kharif I, 2007.Diazinon 60 EC @ 2 ml L -1 of water was sprayed at 72 DAS.Guard was placed to avert bird (crow, parrot etc) damage.Minor variation about the maturity among the hybrid maize varieties was observed.Data on yield and yield components were taken properly, analyzed statistically and presented in tables 1 and 2.

Results and Discussion
Traditionally hybrid maize is sown either rabi or kharif I season.Here the hybrid maize varieties were grown during kharif II season.In lieu of sowing in August 30 if the crop could be sown on mid July.The crop could be received about 600 mm rainfall and also assumed to be harvested within November 2006.Dowswell et al. (1996) also opined that, in most tropical environments, maize requires 600-700 mm of moisture well distributed over the growing season.Forty five per cent of total maize area in the developing tropical countries of the world covers 36.7 million hectares.The environment is characterized by a high mean temperature (around 28 0 C) during the growing season (FAO, 1988).They have a high mean maximum temperature (around 32 0 C) and a high mean minimum temperature (around 22 0 C).At Rangpur region of Bangladesh there prevailed mean high temperature (around 33 0 C) and high mean minimum temperature (around 26 0 c) during growing season of maize.Sultan (2006) opined that the temperature 24 0 to 30 0 C is suitable for maize production.He also opined that fluctuation of the temperature results in fluctuation in field duration of maize.1.a & 2.a).Yields by BHM-3 (8.30 t ha -1 ), Pacific-11 (8.04 t ha -1 ), Prolin (7.57t ha -1 ) and BHM-2 (7.47 t ha -1 ) were also identical.Higher number of cob/plant, seeds/cob and 1000-grain wt.contributed to the higher yields.Significant highest cob length (17.9 cm) along with significant highest number of grains/primary cob (491), higher number of grains/secondary cob (266), significant higher 1000 grain wt. of primary cob (375 g) and highest weight (372 g) of secondary cob contributed much to pacific-60 for giving significantly highest yield (11.03 t ha -1 ) which was statically identical to Prolin (10.20 t ha -1 ).The yield of Prolin was also statistically identical with other hybrid maize.In rabi, 2007-08, cob length, number of seeds/cob, 1000 seed weight and yield were varied significantly (Table 2.b).Pacific-60 was also highest yielder (11.10 t ha -1 ), which was identically followed by BHM-5 (11.08 t ha -1 ) and Pacific-555 (10.00 t ha -1 ) but significantly higher than the other varieties.Cumulative favourable effects of higher number of seeds/cob 386, 414.33 & 391.67 and higher 1000 seed weight 380, 371.67 & 360, respectively contributed much for higher yields in Pacific-60, BHM-5 and Pacific-555.The yield trend with hybrid maize during rabi season was comparatively higher than that of kharif II maize.This might be due to (about 40 cm) taller plant stand associated with rabi maize.Again, average 2 more number of leaves/plant was observed in rabi maize than kharif II.Longer period taken for days to 50% tasseling (around 108 days) and days to 50 % silking (around 111 days) in rabi, 2006-07 over kharif II maize (around 58 and 62 days, respectively).Comparatively lower temperature during ear initiation and silking of rabi maize (mean maximum around 29.6 o C and mean minimum around 18.2 o C) over kharif II maize (mean maximum 31 o C and mean minimum 20.2 o C) contributed much for higher trend of yield in rabi, 2006-07 over kharif II, 2007.Similar trend was also observed in the kharif II, 2008. BARI (2001) opined that increase in temperature decreased spikelet fertility and grain number was found to be dependent to temperature and radiation regimes during the period from ear initiation to silking.
In kharif I, all the parameters varied significantly except cob length in 2008.The highest yield in 2007 (9.55 t ha -1 ) was recorded from Pacific-60, which was identical to Pacific-984 (9.25 t ha -1 ), BHM-5 (9.11 t ha -1 ) and BHM-3 (8.89 t ha -1 ) but significantly higher than the rest varieties (Table-1.c).Except Pacific-60, all other varieties produced identical yield.Significantly, higher number of cobs/plant (1.08) and 1000 grain weight (322.20g)attributed to highest yield in Pacific-60.Similar trend was also observed in Pacific-984, BHM-5 and BHM-3 where either number of cobs per plant or number of seeds per plant alone or along with 1000-grain weight favoured the higher yield.Similar trend was observed in kharif I, 2008 where the highest yield (9.4 t ha -1 ) was recorded from Pacific 60 identically followed by Pacific 555 (9.1 t ha -1 ), BHM 5 (9 t ha -1 ) BHM 3 (8.6 t ha -1 ) and Pacific 11 (8.3 t ha -1 ).BHM 2 produced significantly the lowest yield (7.8 t ha -1 ).

Conclusion
All the BARI hybrid maize varieties including check (Pacific-984) can be grown in kharif I and kharif II season although BHM-3, BHM-5, Pacific-60 and Pacific-984 are better in Kharif I. Again, considering the performance during rabi season, all the varieties can be grown as their yields were either higher or identical to the check variety Pacific-984 although Pacific-60, BHM-5, Prolin and Pacific-555 were found better.

Table 1 .
a .Performance of hybrid maize varieties during kharif II season of 2006 season at ARS, Burirhat, Rangpur Table 1.b.Performance of different hybrid maize during rabi season of 20006-07 at ARS, Burirhat, Rangpur Means in a column having similar or no letter did not differ significant at 5% level of significance Table 1.c.Performance of different hybrid maize during kharif I season of 2007 at ARS, Burirhat, Rangpur Means in a column having similar or no letter did not differ significant at 5% level of significance

Table 2
Means in a column having similar or no letter did not differ significant at 5% level of significance Table 2.c.Performance of different hybrid maize during kharif I season of 2008 at ARS, Burirhat, Rangpur