Conclusion

Seedlings of 25-d-old with 0 day storage performed the best followed by 1 day stored seedlings. Yield gradually decreased with increased seedling age from 25 to 40 days with storage durations ranging from 0 to 3 days. Considering the possible delay in transporting of seedlings from the nearby districts to the flood affected area, it could be concluded that 25-d-old seedlings may be kept stored up to 1 day after uprooting to get better performance.

Introduction

Seeding age at transplanting is one the most important factors that substantially influences yield and other agronomic parameters (Karmakar and Sarkar, 2015). Seedling age of wet season (aman) rice is very important especially for stress prone area like flood and flash flood prone environment. Storage duration of uprooted seedlings is another burning issue for getting higher yield of wet season rice in flash flood and flood affected area. Farmers of these environments could not grow seedlings due to lack of nursery bed. Sometimes, nursery beds become damaged by excess water of flood or flash flood. Wet season rice covers the largest area of 5.60 mha (49.08% of the total rice area) and contributes to 38.10% (12.89 mt) of the total rice production in Bangladesh (BBS, 2013). Bangladesh is one of the most important rice growing countries of the world. Bangladesh ranks the fourth among the rice producing countries of the world following China, India and Indonesia (FAO, 2009; BRRI, 2015). However, the cultivable area is decreasing day by day due to the increasing population so that food security has been and will remain a major concern for Bangladesh. Natural calamities like flood, flash flood, and drought are always threat to rice production and it depends on the magnitude and frequency of hazards. Seedlings damage due to early or flash flood is very common feature in Bangladesh. Consequently, farmers suffer from the shortage of seedlings or compelled to transplant aged or too young seedlings when the floodwater recedes. As a result, seedlings limitation is a severe problem in this situation. At that time, rice seedlings of optimum age may be required to transport to the flood affected area from the nearby districts which may take 2 to 3 days. So, the optimum age and storage duration of uprooted seedling may contribute significantly yield and yield components of transplant aman rice. Therefore, the present study was undertaken to determine the optimum age of seedlings for wet season rice and investigate the storage effects of different aged seedlings on yield and yield components of wet season rice.

Materials and Methods

The experiment was conducted at the Agronomy field laboratory of Bangladesh Agricultural University, Mymensingh (24°75’ N latitude and 90°50’ E longitude at an elevation of 18 m above the sea level) during wet season (Aman) from July to December 2013. The soil of the experimental plot belongs non-calcareous dark grey flood plain type under the old Brahmaputra Alluvial Floodplain. The land was medium high with sandy loam texture having a soil pH 7.2 (BARC, 2012). The experimental field is situated under sub-tropical climate where usually the rainfall is heavy during April to September. A high yielding submergence tolerant rice variety, BRRI dhan52 was used in the experiment. The experiment consisted of two factors like seedling age (25, 30, 35 and 40-d-old seedlings) and storage duration of seedling after uprooting (0, 1, 2, and 3 days). The experiment was laid out in a split-plot design with 3 replications assigning seedling age in the main plots and storage duration in the sub-plots. The sprouted seeds were sown in the wet nursery bed on four dates viz., 26 June, 1^st July, 6^th July and 11^th July in 2013. Proper care was taken to raise the seedlings in the seedbed. Weeds were removed and irrigation was given in the nursery bed as and when necessary. The experimental land was prepared in puddle condition through plowing and cross plowing four times with a country plough followed by laddering to level the soil. The fertilizers urea, triple super phosphate (TSP), muriate of potash (MOP) and gypsum were applied experimental plots @ 195, 52, 82 and 60 kg ha^-1, respectively (BRRI, 2011). The entire amounts of TSP, MOP and gypsum were applied as basal dose at the time of final land preparation. Urea was top dressed in three equal splits at 15, 35 and 50 days after transplanting (DAT). The nursery bed was made wet by applying water on the previous days before uprooting the seedlings. The seedlings were uprooted carefully from nursery bed on 2, 3, 4 and 5 August 2013 without causing much mechanical injury to the roots to get 40, 35, 30 and 25 -d-old seedlings for transplanting. The uprooted seedlings were stored separately on the shade before transplanting for 3, 2, 1 and 0 day, respectively, as per treatments. Seedlings of 40, 35, 30 and 25 days with the combination of storage duration of 3, 2, 1 and 0 days were transplanted in the main field in same day on 5 August, 2013 with 3 seedlings hill^-1 at 25x15 cm² spacing. The crop was infested by rice stem borer which was controlled by applying Diazinon 60 EC as per recommendation of BRRI (2011). Uniform management practices were followed for all the treatments. Twelve hills were harvested diagonally in each plot to record the data on yield components. From center of each plot, six square meter area was harvested to record yield on 24 November 2013 at maturity. Grain and straw yield was adjusted to 14 and 3% moisture content, respectively and converted to t ha^-1 (Karmakar and Sarkar, 2015). The collected data were statistically analyzed using MSTAT. The significance of mean differences among the treatments was adjudged by Duncan’s Multiple Range Test (DMRT) and Least Significant Difference (LSD) Test (Gomez and Gomez, 1984).

Results and Discussion

3.1.  Effect of seedling age and storage duration on yield and yield contributing characteristics

3.1.1.  Grain yield

Grain yield was significantly influenced by seedling age (Table 1). These findings are in conformity with Karmakar and Sarkar, 2015; Hussain et al., 2012; Krishna and Patil, 2009. The highest grain yield (5.52 t ha^-1) was observed when 25-d-old seedlings were transplanted and the lowest grain yield (4.02 t ha^-1) was obtained from 40-d-old seedlings (Table 1). Similar result was also reported by Sarkar et al. (2011) with the transplanting of 25-d-old seedlings. Grain yield exhibited a regular trend of decrease with the increase in seedling age. This finding was supported by Upadhyay et al. (2003) and Singh and Singh (1998). Older seedlings remained more days in the nursery bed. As a result basal node appeared in the seedlings. Again it took more time to establish in the main field. On the contrary, the younger seedlings got less time in the nursery bed for node formation and quickly they recovered the transplanting shock in the main field. Thus they start re-growth quickly

Table 1: Effect of seedling age on yield and yield attributes of wet season rice

which ultimately helped to work in favor of better growth of plant, yield components and yield. These findings are in good harmony with Karmakar and Sarkar (2015) who reported that younger seedlings could able to mitigate the transplanting shock within a shorter period of time compared to older seedlings. Moreover, panicle initiation started earlier and more spikelets formed in the plants of younger seedlings. Thus the yield components were improved and sterility percentage was decreased which were mainly responsible for the improvement of grain yield of the younger seedlings (Karmakar and Sarkar, 2015; Hussain et al., 2012; Krishna et al., 2008). Grain yieldwas significantly affected by the storage duration of uprooted seedlings (Table 2). The highest grain yield(5.31 t ha^-1) was observed with 0 day storage duration which was statistically identical (5.04 t ha^-1)  with 1 day storage duration but significantly different from other treatments and the lowest grain yield(4.04 t ha^-1) was obtained with 3 days storage duration (Table 2). Similar findings were also reported by Kaykobad (2001) and Islam (1995). Grain yieldexhibited a regular trend of decrease with the increase in storage durations of uprooted rice seedlings from 0 to 3 days. It is to be noted that the fresh seedlings (0 and 1 day storage duration) transplanted without a mentionable delay gave the highest grain yield. The delay in transplanting of uprooted

Table 2: Effect of storage duration of seedling on yield and yield attributes of wet season rice

seedlings decrease the grain yield significantly. Similar results found by Karim (2007) who reported that uprooted seedlings were found to be storable up to 2 days without any significant loss of grain yield. The production of the maximum grain yield with 0 day storage duration might have been the cumulative results of the favorable effects of number of effective tillers hill^-1 and no. of grains panicle^-1. The seedlings stored for 0 and 1 day i.e. freshly uprooted seedlings virtually did little suffer from any kind of stresses like reestablishment, nutrient uptake or other unfavorable situations due to uprooting as experienced by those stored for longer period from uprooting to transplanting. Grain yieldwas significantly influenced by the interaction between the age and storage duration of uprooted seedlings (Table 3). The highest grain yield (6.35 t ha^-1) was obtained from 25-d-old seedlings with 0 day storage duration and the lowest grain yield(3.38 t ha^-1) was observed in 40-d-old seedlings with 3 days storage duration (Table 3). The highest grain yield might be the contribution of more numbers of effective tillers hill^-1 and grains panicle^-1.

3.1.2.  Plant height

Plant height at harvest was significantly affected by seedling age (Table 1). The tallest plant (114 cm) was found when 25-d-old seedlings were transplanted. The tallest plant was found in the crop of 25 -d-old seedlings due to early recovery of transplanting shock and better growth of the plants. Similar result was also reported by Sarkar et al. (2011). The shortest plant (106 cm) was obtained when 40-d-old seedlings were transplanted. Plant height exhibited a trend of decrease with the increase in seedling age. Plant height was significantly affected by the storage duration of uprooted seedling. The tallest plant (111 cm) was found with 0 day storage duration and the shortest plant (107 cm) was obtained with 3 days of storage duration (Table 2). This finding was justified by Kaykobad (2001). Plant height exhibited a trend of decrease with the increase in storage durations of uprooted rice seedlings from 0 to 3 days. This is due to the decrease in plant vigor with the increase in storage durations. Plant height varied slightly due to the interaction between the age and storage duration of uprooted seedlings and the differences among themselves were not enough to be significant. But numerically, the highest plant height (116 cm) was obtained in 25-d-old seedlings with 0 day storage duration and the lowest plant height (104 cm) was obtained in 35-d-old seedlings with 3 days storage duration (Table 3).

3.1.3.  Panicle production

No. of panicles hill^-1 was significantly affected by seedling age (Table 1). Younger seedlings produced more panicles per unit area compared to older seedlings (Pasuquin et al., 2008; Karmakar and Sarkar, 2015). The maximum no. of panicles hill^-1 (8.8) was obtained when 25-d-old seedlings were transplanted and the minimum no. of panicles hill^-1 (5.9) was observed when 40-d-old seedlings were transplanted. No. of panicles

Table 3: Interaction effects of age and storage duration of seedling on yield and yield attributes of wet season rice

hill^-1 was gradually decreased as the age of seedling increased. The results are in conformity with the findings of Hussain et al., 2012; Haque (2002). No. of panicles hill^-1 was significantly affected by storage duration of uprooted seedling. The maximum no. of panicles hill^-1 (9.6) was obtained with 0 day of storage duration and the minimum no. of panicles hill^-1 (4.4) was with 3 days of storage duration. Similar finding was also found by Islam (1995). The no. of panicles hill^-1 exhibited a trend of decrease with the increase in storage durations of uprooted seedlings from 0 to 3 days (Table 2). Panicles hill^-1was significantly influenced by the interaction between the age and storage duration of uprooted seedlings. The maximum no. of panicles hill^-1 (10.3) was obtained in 25-d-old seedlings with 0 day storage duration and the minimum no. of panicles hill^-1(3.3) was found in 35-d-old seedlings with 3 days storage duration (Table 3).

3.1.4.  Panicle length

Panicle length was significantly affected by seedling age (Table 1). The longest panicle (25.8 cm) was found when 25-d-old seedlings were transplanted. The longest panicle was found in the crop of 25-d-old seedlings due to longer period from initiation to emergence as well more vigor of plants. Similar result was reported by Sarkar et al. (2011). The shortest panicle (23.3 cm) was found when 40-d-old seedlings were transplanted. Panicle length exhibited a trend of decrease with the increase in seedling age. Panicle length varied slightly due to the storage duration of uprooted seedlings and the differences among themselves were not enough to be significant. But numerically, the longest panicle (25.2 cm) was obtained with 0 day storage duration and the shortest panicle (24.4 cm) was found with 3 days storage duration (Table 2). This result was justified by Das and Mukherjee (1992). Panicle length was significantly influenced by the interaction between the age and storage duration of uprooted seedlings. The longest panicle (27.2 cm) was obtained in 25-d-old seedlings with 0 day storage duration and the shortest panicle (21.8 cm) was found in 40-d-old seedlings with 1 day storage duration (Table 3).

3.1.5.  Grains panicle^-1

Seedling age had significant effect on grains production panicle^-1 (Table 1). The highest no. of grains panicle^-1(119) was found when 25-d-old seedlings were transplanted while the lowest grains panicle^-1(105) was obtained in 40-d-old seedlings. No. of grains panicle^-1exhibited a trend of decrease with the increase in seedling age. This finding was also supported by Yoshii and Sandier (1998). Younger seedlings produce more grains panicle^-1than the older ones due to longer vegetative period of younger seedlings. The results are corroborating with the findings of Sarwa et al., 2011. No. of grains panicle^-1was significantly affected by the storage duration of uprooted seedling. The highest no. of grains panicle^-1(125) was found with 0 day storage duration followed by 1 day storage (117) and the lowest grains panicle^-1(101) was obtained with 3 days storage duration (Table 2). Similar result was also obtained by Kaykobad (2001). No. of grains panicle^-1exhibited a trend of decrease with the increase in storage durations of uprooted rice seedlings from 0 to 3 days. This is due to the decrease in plant vigor with the increase in storage durations. Interaction age and storage duration of uprooted seedlings had also significant effect on grains panicle^-1(Table 3). The highest no. of grains panicle^-1(139) was obtained in 25-d-old seedlings with 0 day storage duration while the lowest grains panicle^-1(97) was found in 35-d-old seedlings with 3 days storage duration (Table 3).

3.1.6.  Spikelet sterility 

Sterility percentagewas significantly affected by seedling age (Karmakar and Sarkar, 2015; Hussain et al., 2012; Mishra and Salokhe, 2008). The highest sterility percentage(22.9 %) was found when 40-d-old seedlings were transplanted and the lowest sterility percentage(15.8%) was obtained when 25-d-old seedlings were transplanted (Table 1). Sterility percentageincreased with the increase in seedling age. This finding was justified by Yoshii and Sandier (1998). Sterility percentagewas significantly affected by the storage duration of uprooted seedling. The highest sterility percentage(23.8 %) was found with 3 days storage duration and the lowest sterility percentage(15.0%) was obtained with 0 day storage duration (Table 2). This finding was supported by Kaykobad (2001). Sterility percentageexhibited a trend of decrease with the increase in storage durations of uprooted rice seedlings from 0 to 3 days. Sterility percentagewas significantly influenced by the interaction between the age and storage duration of uprooted seedlings (Table 3). The highest sterility percentage(27.9%) was obtained in 40-d-old seedlings with 3 days storage duration and the lowest sterility percentage(10.9%) was found in 25-d-old seedlings with 0 day storage duration (Table 3).

3.1.7.  Thousand grain weight

Weight of 1000 grains was not significantly affected by seedling age (Table 1). These findings are in conformity with the findings of Faghani et al.(2011) and Faruk et al. (2009) who found that seedling age had no significant effect on grain weight. But numerically, the maximum 1000-grain weight (21.6 g) was obtained in 25-d-old seedlings and the minimum 1000-grain weight (19.2 g) was found in 40-d-old seedlings (Table 1). Similar findings were also observed by Roy et al. (1992). ­Weight of 1000 grains varied slightly due to the storage duration of uprooted seedlings and the differences among themselves were not enough to be significant. But numerically, the maximum 1000-grain weight (20.8 g) was obtained with 0 day storage duration and the minimum of 1000-grain weight (20.2 g) was found with 3 days storage duration (Table 2). Similar finding was also found by Das and Mukherjee (1992). Weight of 1000 grains was significantly influenced by the interaction between the age and storage duration of uprooted seedlings. The maximum 1000-grain weight (22.97 g) was obtained in 25-d-old seedlings with 0 day storage duration and the minimum weight of 1000 grains (18.22 g) was found in 40-d-old seedlings with 3 days storage duration (Table 3).

3.1.8.  Harvest index

Harvest indexwas significantly affected by seedling age (Table 1). The highest harvest index(47.1 %) was found when 25-d-old seedlings were transplanted and the lowest harvest index(46.5%) was obtained when 40-d-old seedlings were transplanted (Table 1). Similar findings were also observed by Singh and Singh (1998). Harvest indexwas significantly affected by storage duration of uprooted seedling (Table 2). The highest harvest index(47.3%) was found with 0 day storage duration and the lowest harvest index(46.3%) was obtained with 2 days storage duration (Table 2). This finding was supported by Kaykobad (2001). Harvest indexwas significantly influenced by the interaction between the age and storage duration of uprooted seedlings (Table 3). The highest harvest index(48.6%) was obtained in 25-d-old seedlings with 3 days storage duration and the lowest harvest index(44.6%) was observed in 30-d-old seedlings with 2 days storage duration (Table 3). The results indicate that growth attributes as well as yield contributing characters especially grain and straw yield were gradually decreased with the increase in seedling age ranging from 25 to 40-d-old. From the results of the present study, it also appears that the storage duration of uprooted seedlings has profound influence on grain and straw yield of the transplanted aman rice. The yield gradually decreased with the increase in storage duration. The highest grain and straw yield was obtained from 25-d-old seedlings with 0 day storage duration.

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