Response of short duration aman rice varieties to date of transplanting

An experiment was carried out at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during June to December, 2013 to investigate the response of some short duration aman rice varieties to date of transplanting. The experiment consisted of three transplanting dates viz. 26 July, 5 August and 15 August and seven short duration T. aman rice varieties viz. BRRI dhan33, BRRI dhan39, BRRI dhan49, BRRI dhan56, BRRI dhan57, BRRI hybrid dhan4 and Binadhan-7. The experiment was laid out in split plot design with three replications. Transplanting dates were allocated into the main plot and varieties into the sub plot. Results indicate that Binadhan-7 produced the highest grain yield (4.90 t ha –1 ), straw yield (5.58 t ha –1 ), biological yield (10.44 t ha –1 ), and harvest index (47.10%). Lowest grain yield (3.27 t ha –1 ), straw yield (3.96 t ha –1 ) and biological yield (7.20 t ha –1 ) were produced by BRRI dhan57. BRRI dhan49 had taken the longest field duration (120 DAT) while BRRI dhan57 had taken the shortest field duration (88 DAT). Plant height (119.12 cm), number of total tillers m -2 (276.40), number of effective tillers m –2 (260.02), number of grains panicle –1 (109.19), grain yield (4.75 t ha –1 ), straw yield (5.22 t ha –1 ), biological yield (9.97 t ha –1 ) and harvest index (47.64%) were highest on 26 July transplanting; decreased on 5 August transplanting and drastically declined on 15 August transplanting. The present study concludes that the highest yield for short duration T. aman rice cultivation could be possible by Binadhan-7 transplanting on 26 July.


Introduction
Rice is the staple food of Bangladesh and the strategies and actions of Bangladeshi agriculture are guided by the goals of 'self-sufficiency' in food grain production with main focus on rice.Over 95% people depend on rice for their daily diets and it engages over 85% of the total agricultural labour force in Bangladesh.Transplant aman rice varieties are generally cultivated in rainfed ecosystem which covers about 48.97% of total rice area and contributes to 38.14% of total rice production in the country (BRRI, 2012).Modern varieties of T. aman cover about 68% of rice area in the aman season (BBS, 2012).
Cultivation of short duration T. aman rice in south-western part of Bangladesh where soil remain moist before harvest may create opportunity to reduce cost of production for mustard relay cropping (Khan et al., 2006).Short duration T. aman-rabi crops-late boro cropping system is a climate resilient eco-friendly technology that would help increase system productivity by 15-20% and could help towards maintaining food security in the country.(Rahman, 2013).Short duration T. aman rice can also create opportunity to facilitate legume pulses and green manuring crops before late boro sowing which can contribute significantly to achieve the twin objectives of increasing productivity and improving the sustainability of the cropping system (Quayum et al., 2012).Some short duration T. aman rice varieties (viz.BRRI dhan56, BRRI dhan57 & Binadhan-7) are not only photo insensitive, but also drought resistant (BRRI, 2010 andBINA, 2012).Choosing optimum date of transplanting for high yielding cultivars occupies an important part of high production package (Akhter et al., 2007).Different authors used different planting dates to check contrasting temperature regimes, precipitation and growth periods in various T. aman rice varieties (Laborte et al., 2012;Rahman et al., 2004 andRahman et al., 2007).They concluded that late transplanting date coincided reproductive phase with temperature stress.But early planting could not be possible all the time due to existing cropping pattern, climate change and socio-economic condition.The study was undertaken to identify the best short duration T. aman rice variety and find out the optimum transplanting date.

Materials and Methods
The experiment was carried out at the Agronomy Field Laboratory of Bangladesh Agricultural University, Mymensingh, during July to December 2013.Two sets of experimental treatments were included in the study.
A. Date of transplanting: The experiment was laid out in a split-plot design with three replications by assigning date of transplanting in the main plot and variety in sub plot at random.Seeds were collected from the Bangladesh Rice Research Institute, Joydebpur, Gazipur and Bangladesh Institute of Nuclear Agriculture, Mymensingh.
Seedlings were raised at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh.Main land was prepared according to layout in 24 July 2013.Seedlings were transplanted in the unit plots on 26 July, 5 August and 15 August 2013 respectively at the rate of three seedlings hill -1 maintaining spacing of 25 cm×15 cm.Fertilizer application, thinning and gap filling, weeding, irrigation and drainage and other intercultural operations were done as and when necessary according to the BRRI guideline.The crops were harvested at maturity and data on plant height (cm), number of total tillers m -2 , number of effective tillers m -2 , number of non-effective tillers m -2 , panicle length (cm), number of filled grains panicle -1 , number of sterile spikelets panicle -1 , 1000 grain weight (g), grain yield (t ha -1 ), straw yield (t ha -1 ), biological yield (t ha -1 ), harvest index (%) and field duration (days) were collected from the randomly selected ten hills from each plot.All relevant data were analyzed using the "Analysis of Variance" technique and the mean differences were determined by Duncan's Multiple Range Test.

Results and Discussion
Effect of variety and date of transplanting on different plant characters of short duration T. aman rice BRRI dhan56 produced the tallest plant of 128.53 cm.BRRI dhan57 produced the shortest plant of 110.04 cm which is statistically similar to Binadhan-7(110.51cm) (Table 1).Transplanting on 26 July has given the tallest plant (119.12cm).Plant height decreased with delay in transplanting (at 5 August 117.64 cm).The shortest plant (115.11cm) was observed for transplanting on 15 August (Table 2).
The highest number of total tillers m -2 was counted in Binadhan-7 (342.05) and the lowest number of tillers m -2 (216.38) was observed in BRRI dhan33 (Table 1).The highest number of total tillers m -2 (276.40) was produced from 26 July transplanting.Total tillers m -2 decreased with delay in transplanting at 5 August (269.63).Maximum number of total tillers m -2 (360.0) was produced from 26 July transplanting of Binadhan-7 (Table 2).The lowest number of total tillers m -2 (161.0) was in BRRI dhan57 for transplanting on 15 August.The variation was due to varietal characters and late transplanting.
The results showed that the highest number of effective tillers m -2 (333.33) was produced by Binadhan-7 and BRRI dhan33 produced the lowest (202.11).The highest number of effective tillers m -2 was observed in 26 July.Lowest number of effective tillers m -2 (244.19) was produced when the seedling was planted on 15 August (Table 2).Maximum number of effective tillers m -2 (350.0) was produced by Binadhan-7 planted on 26 July.The lowest number of effective tiller m -2 (156.0) was produced from 15 August transplanting of BRRI dhan57 (Table 5).The maximum number of grains panicle -1 (149.80) was observed in BRRI dhan33 for transplanting on 26 July.Minimum number of grains panicle -1 (77.77) was observed respectively in BRRI dhan57 for transplanting on 15 August (Table 5).
The lowest number of sterile spikelets panicle -1 (16.85) was recorded for 26 July transplanting and the highest number of sterile spikelets panicle -1 (19.46) was recorded on 15 August.The highest number of sterile spikelets panicle -1 (31.70) was counted in BRRI hybrid 4 for 15August transplanting and the lowest number of sterilespikeletspanicle -1 (14.30) was found inBinadhan-7 with 26 July transplanting (Table 5).
Highest biological yield (10.40 t ha -1 ) was obtained from Binadhan-7 and the lowest one (7.20 t ha -1 ) was produced from BRRI dhan57 (Table 4).The highest biological yield (9.97 t ha -1 ) was produced from 26 July transplanting .The lowest biological yield (9.12 t ha -1 ) was produced from 15 August which was statistically similar with 5 August transplanting (Table 3).The highest biological yield (10.83 t ha -1 ) was produced by Binadhan-7 for 26 July transplanting.The lowest biological yield (6.47 t ha -1 ) was produced by the transplanting on 15 August of the variety BRRI dhan57 (Table 6).
Highest harvest index (47.10%) was produced by Binadhan-7.Highest harvest index (44.45%)obtained from 26 July transplanting and the lowest harvest index (44.13%)from 15 August transplanting (Table 3).The highest harvest index (48.91%)was observed in Binadhan-7 with 26 July transplanting (Table 6).Binadhan-7 shown highest Harvest index among other varieties in different planting date respectively.Planting in 26 July has shown highest harvest index for all the varieties.Binadhan-7 has given highest grain yield and 26 July is the most suitable transplanting date in terms of producing grain yield.So the harvest index of Binadhan-7 on 26 July transplanting was highest and it was the most suitable combination among all other experimental treatments.
Date of transplanting significantly affect the duration of different phenological stages of aman rice.Days to panicle initiation (41.66DAT), days to flowering (56.77DAT) were shortest in BRRI dhan57 and it matured at 88 DAT (shortest field duration was observed) while days to panicle initiation (60.77DAT), days to flowering (79.88 DAT) were longest in BRRI dhan49 and matured at highest 120 DAT (Table 1).

Yield t ha -1
Binadhan-7 requires 102 DAT to mature and it was the most suitable variety showing highest yield.15 August transplanting gives the shortest field duration and lowest yield because during the month of September temperature was 23.15°C which might have been forced the plant to mature early.Again, 26 July transplanting date showed the long duration of maturity (100days).26 July is the most optimum date of transplanting as is produced highest yield.Binadhan-7 is the best short duration variety and 26 July is the optimum date of transplanting in aman season.

Conclusion
Based on the results of the present study the following conclusions may be drawn by Binadhan-7 transplanted on 26 July has given the best result for grain yield.Optimum transplanting date for grain yield of short duration aman rice was 26 July.Higher grain yield was obtained from early than late transplanting.Yield decreased on 5 August transplanting and for 15 August transplanting yield of all the varieties was lowest.

Fig. 3 .
Fig. 3. Field durations of phenological stages of some T. aman rice varieties

Table 2 . Effect of date of transplanting on plant characters of short duration T.aman rice
*Binadhan-7 produced the lowest (9.72) number of non-effective tillers m -2 (Table1).The number of noneffective tillers m -2 was minimum (9.50) for transplanting on 26 July (Table2).Number of non-effective tillers increase if transplanting is delayed; (in 5 August 14.26) and the maximum number of non-effective tillers m -2 (17.38) was produced for transplanting on 15August.