Abstract
Four experiments were conducted at the Agronomy Field Laboratory of the Bangladesh Agricultural University, Mymensingh during transplant aman seasons (June to December) of 1989 through 1992. All the experiments were laid out in the split-plot design to evaluate the effect of variety, planting date (seedling age), hill density, spacing, planting method and fertilizer levels in late planting aman rice.
The first experiment was conducted in 1989 and was repeated in 1990 to determine the effects of four transplant aman rice varieties (BR23, BR22, BR11 and Nizersail) and seven planting dates with corresponding age of seedlings (10 August/40-d, 10 September/70-d, 10 September/40-d, 15 September/75-d, 15 September/45-d, 20 September/80-d, 20 September/50-d). Significantly highest grain yield for the studied years was 4.72 t ha1, that obtained from 10 August planting with 40-d seedlings which gradually decreased with the advancement of planting dates. Considering the varietal performance for two years, it was observed that BR22 gave significantly the highest (4.60 t ha1) and BR11 gave the lowest (1.79 t ha1) grain yield. Interactions of 10 August planting with 40-d seedlings X BR23 gave significantly the highest grain yield (5.85 t ha1) that was followed by BR22 in the same interaction. This yield was gradually decreased with the advancement of planting dates for each variety and the yield of BR22 was slightly higher in the later plantings. BR11 did not flower at all in 20 September planting 50-d seedlings. Therefore, BR22 and BR23 were selected for further study for delayed plantation in the transplant aman season.
The second experiment was conducted in 1990 and was repeated in 1991 to
determine the effects of selected varieties (BR22 and BR23), three planting dates with corresponding seedling age (15 August/40-d, 30 August/60-d, 20 September/80-d), three planting densities (15 cm x 15 cm, 20 cm x 12 cm, 15 cm x 9 cm) with three fertilizer levels (N90P70K50S25Zn6, N80P60K40S20Zn4, N70P50K30S15Zn2). The highest pooled grain yield for two years (5.14 t ha1) were obtained due to 10 August planting (40-d seedlings) by BR23 which gradually decreased with the advancement of planting dates, and BR22 performed better than BR23 in the late plantings. The spacing of 15 cm x 9 cm with 8 seedling hill and No0P70K50S25Zn6 kg ha1 fertilizer level gave the highest average grain yield (4.82 t ha1) for the years under study and the year average lowest (3.83 t ha1) was due to 15 cm x 15 cm spacing planted with 2 seedlings hill1 x N70P50K30S15Zn2. The interactions of BR22 x 10 August planting with 40-d seedlings x (15 cm x 9 cm) x 4 seedlings hill x NgoP60K40S20Zn4 gave the highest average (1990/91) grain yield (5.32 t ha1) which gradually decreased with the advancement of planting dates wider spacings and older seedlings. BR23 gave higher yield than BR22 in the earlier plantings which was reverse in the late ones. Therefore, BR22 was finally selected for further evaluation with planting method and fertilization.
The third experiment was conducted in 1992 to determine the effects of two planting method (conventional and distributory method) with different planting densities (6 seedlings, 8 seedlings and 10 seedlings planted with different spacings) and 6 date of planting with respective seedling age (10 August/40-d, 20 August/50-d, 30 August/60-d, 20 September/80-d, 30 September/90-d). Planting date significantly affected the yield where the highest grain yield (5.34 t ha1) was produced due to 10 August planting (40-d seedlings) that gradually decreased with the advancement of planting dates and became the lowest (3.46 t ha1) in the 30 September planting (90-d seedlings). Planting method was remarkably influenced the performance of experimental crop where the highest grain yield (4.70 t ha1) was obtained due to the distributory method planted with 10 seedlings @2 seedlings hill-1 which gradually decreased with the decreasing planting densities for both the methods and the lowest grain yield (4.08 t ha1) was due to 6 seedlings hill-1 in the conventional method. Interactions of 10 August planting (40-d seedlings) × distributory method with 10 seedlings @ 2 seedlings hill1 gave significantly the highest grain yield (5.04 t ha1) that gradually decreased with the advancement of planting dates irrespective of the planting method and the lowest (3.07 t ha1) was in the 30 September planting (90-d seedlings) x 6 seedlings hill1× Conventional method.
Fourth experiment was conducted in 1992 to determine the effects of three planting dates with respective seedling ages (10 September/70-d, 20 September/80-d, 30 September/90-d) four fertilizer levels with varying nitrogen doses (N90P70K50S25Zn, N100P70K50S25Zn6, N100P60K40S20Zn6, N90P60K40S20Zn, kg ha1) and three planting densities (6 seedlings, 8 seedlings and 10 seedlings hill1). BR22 (selected from the earlier experiments) and 15 cm x 9 cm spacing (selected from the earlier experiments) were used. The first planting date i.e. 10 September planting with 70-d seedlings gave the highest grain yield (3.26 t ha1) which gradually decreased with the advancement of time of planting. On the other hand, N100P70K50S25Zn, (highest nitrogen with highest other fertilizer level) with 10 seedlings hill' gave the highest grain (3.37 t ha'') yield i.e. the higher nitrogen dose in a specific fertilizer level could increase the yield. Interactions of planting of 10 September (70-d seedlings) x N90P70K50S25Zn6 x 10 seedlings hill1 gave the highest grain yield (3.56 t ha1) which gradually decreased with the interaction of advancement of planting dates x lower level of fertilizers x lower planting density.
All of the experimental results were evaluated and targeted yield was predicted by developing four models. These models show that yield of rice was higher in the earlier plantings and gradually decreased with the advancement of planting dates. The yield loss could be compensated in later plantings by adopting technologies like distributory method of seedling transplanting, higher fertilizers level and using increased number of seedling by increasing seedlings number (1223) to get the targeted bearing tillers (1500) to achieve standard yield (5.42 t ha1). The models also showed that the yield compensation could be done in 10 August through 30 September from 5.83% to 27.35% by manipulation of seedlings hill', seedling distributory method and nitrogen level.