Effect of nitrogen on growth and yield of short duration transplanted inbred and hybrid rice varieties

An experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during June to December 2015 with a view to finding out the effect of nitrogen levels on the yield performance of short duration inbred and hybrid transplant rainy season rice varieties. Four short duration rice varieties (three inbred viz. BINA dhan7, BRRI dhan39, BRRI dhan56 and one hybrid Dhanigold), and 5 levels of nitrogen viz. 0, 40, 80, 120 and 160 kg N ha-1 were included in the experiment under a split–plot design with three replications. The result revealed that variety, nitrogen rate and their interactions had significant on grain yield of short duration transplant rainy season rice. Hybrid variety Dhanigold gave the highest yield (5.13 t ha-1) followed by BRRI dhan56 (4.80 t ha-1) while the lowest was produced by Binadhan-7 (4.28 t ha-1). The highest yield (5.93 t ha-1) was obtained from Dhanigold with 120 kg N ha-1 which was followed by BRRI dhan56 at 120 kg N ha-1 (5.42 t ha-1). The highest yield was attributed to the increased production of effective tiller and grains panicle-1. The optimum dose of nitrogen estimated for Binadhan-7, BRRI dhan39, BRRI dhan56 and Dhanigold are 131.31, 122.97, 126.50 and 133.14 kg ha-1, respectively. Thus, this study concludes that the highest yield of short duration rice varieties Binadhan-7, BRRI dhan39, BRRI dhan56 and Dhanigold could be obtained by applying nitrogen at 131.31, 122.97, 126.50 and 133.14 kg ha-1, respectively.

research works have been done to know the response of long duration varieties to various nitrogen levels and the farmers of Bangladesh use increased amount of nitrogen fertilizer to get higher yield. Nitrogen use efficiency for rice crop largely ranges between 25% and 35% and seldom exceeds 50%. This lower recovery of applied fertilizer N by rice plant is largely caused by losses of N from the soil-plant system. Nonetheless, nitrogen management is a very important factor because excessive use of nitrogen results in lodging of plant, reduction of yield and also has negative implications for the environment (Jiang et al., 2005;Fageria et al., 2008). On the other hand, deficiency of nitrogen hampers the production of rice. Therefore, application of the optimum rate of nitrogen is necessary to attain higher yield of different short duration rice varieties. Many studies related to the nitrogen application rates for different rice varieties have been done elsewhere but the study on the optimization of N levels for short duration inbrid and hybrid rice varieties are scarce.
BJECTIVES: The present study was therefore, undertaken with a view (i) to compare the yield of different short duration rice varieties, (ii) to study the effect of rate of nitrogen on grain yield and related attributes of these short duration rice varieties and (iii) to determine the optimum nitrogen rates for different short duration rice varieties.  Flood irrigation was given in the experimental field to maintain a constant level of standing water up to 6 cm in early stage to enhance tillering and 10-12 cm in later stage to discourage late tillering. The field was finally drained out before 15 days of harvest. The plants were infested with yellow stem borer (Scirpophaga incertulas) which was successfully controlled by applying Diazinon 60EC @ 1 L ha -1 . At maturity when 90% of the seeds became golden yellow in color, the crop was cut from randomly selected three square meter area of the central portion of each plot manually at the ground level to record grain and straw yields. Data recording: Data on growth parameters like plant height, number of tillers hill -1 , dry matter production and crop growth rate were recorded at 40, 50 and 60 days after transplanting (DAT). Four hills were randomly selected and uprooted from each plot excluding border rows to record data on plant height and number of tillers hill -1 at 10 day intervals beginning at 40 DAT and continued up to harvesting. BRRI dhan56 and Binadhan-7 were harvested on 31 October and 02 November while BRRI dhan39 and Dhani gold hybrid were harvested on 03 November 2015. The harvested crops of each plot was separately bundled, properly tagged and then brought to the threshing floor. The harvested crops were threshed manually. The grains were cleaned and dried to a moisture content of 14%. After sun drying the final grain and straw yields plot -1 were recorded and converted to t ha -1 . Grain yield and straw yield were altogether regarded as biological yield. Prior to harvesting, five hills were randomly selected from each plot for recording necessary data on crop growth parameters and yield related attributes. Statistical analysis of data and determination of optimum nitrogen dose: Data recorded for growth, yield and yield contributing characters were compiled and tabulated in proper form for statistical analyses. Analysis of variance was done with the help of MSTAT-C computer package programme. The mean differences among the treatments were evaluated with DMRT test. The relationship between grain yield and fertilizer dose were fitted by the following quadratic model using 'R' statistical programme: = + + 2 … . (1) Where, Y = seed yield (t ha -1 ), X= the dose of the nitrogen applied (kg ha -1 ), a, b and c are the parameters of the model. The optimum dose of nitrogen for each of rice varieties were then determined using the parameters of the quadratic equation (equation 1): = − 2 ⁄ . ESULTS AND DISCUSSIONS: Plant height: Plant height varied significantly due to variety and nitrogen level at 40, 50 and 60 days after transplanting (DAT) and also at harvest but the interaction between variety and nitrogen level was not significant. At 40, 50 and 60 DAT, variety BRRI dhan56 exhibited the tallest plant while Binadhan-7 produced the shortest plants. At harvest, the plant height of BRRI dhan56 was 123.80 cm while that for Binadhan-7 was 106.50 cm (table 1). The present result showed that plant heights vary among the varieties and the variation might be caused due their genetic variability (Islam et al., 2013). In case of nitrogen dose, the tallest plant was obtained at 120 kg N ha -1 and the shortest with control (no nitrogen) plots. The plant heights obtained with 120 kg N ha -1 at 40, 50 and 60 DAT and at harvest were 80.67, 93.02, 117.30 and 125.0 cm, respectively. The plants in the control plots at 40, 50 and 60 DAT and at harvest were 69.57, 83.86, 105.50 and 112.8 cm, respectively. In the present study showed that the plant height increased with increase of nitrogen levels and attained the highest value at 120 kg N ha -1 and then declined with further addition of nitrogen fertilizer (table 2). Similar results have been reported by the previous researchers. For example, Das (2007) observed the tallest plant (91.86 cm) with 120 kg ha -1 of nitrogen while Ahmed et al. (2000) found that with 80 kg N ha -1 . On the other hand, Somasundaram et al. (2002) found the highest plant height of variety SSRC91216 at 150 kg N ha -1 . However, all the authors reported that further increase in N rate decreased the plant height gradually. The increase in plant height might be due to increased amount of nutrients uptake by plants from higher rates of nitrogen applied in the soil. The increased nitrogen uptake may have played a significant role in plant growth, internode elongation, photosynthesis and metabolism and assimilate production (Ghoneim et al., 2018). Tiller production: The number of total tillers hill -1 was significantly influenced by variety and nitrogen level at all the sampling dates but their interaction was not significant. The number of total tiller increased with time and the highest was attained at 60 DAT for all the inbred varieties and then declined at harvest. However, in the hybrid variety Dhanigold the highest value was attained at harvest (table 3). Dhanigold showed the highest number of total tillers hill -1 at 60 days and also at harvest which were 13.47 and 14.11 hill -1 , respectively. Among the inbred varieties, the highest number of tillers hill -1 at 60 days and also at harvest was found with variety BRRI dhan56 which were 12.32 and 11.89, respectively. Binadhan-7 produced the lowest number of tillers hill -1 . The variation in R number of total tillers hill -1 might be attributed to varietal characters (Nuruzzaman et al., 2000). The number of total tillers hill -1 was influenced by nitrogen level and highest values were attained at 120 kg N ha -1 . Then the number decreased with further increase in the nitrogen level. The highest number of total tillers hill -1 (13.95) was recorded at 120 kg N ha -1 (table 4). The lowest number of total tillers hill -1 (9.28) was recorded in control (0 kg N ha -1 ). Thus the result showed an increased trend of tiller production hill -1 with increase of nitrogen level. However the tiller production decreased with the increase of nitrogen dose above that maximum level. Sultana and Ali (2014) found the highest tiller production with 90 kg N ha -1 while Rahman et al. (2019) found the highest tiller production with 150 kg N ha -1 . Many authors reported that the production of total tillers hill -1 was positively correlated with amount of applied nitrogen. The progressive improvement in the formation of tillers might be due to the increased supply of nitrogen. The present study reveals that hybrid variety Dhanigold has the highest tiller production capacity and showed the similar response to nitrogen level like those of other inbred varieties.

Plant height (cm) Days after transplanting (DAT)
Harvest 40  Total dry matter (TDM) accumulation: Total dry matter (TDM) of rice plant (g m -2 ) was significantly influenced by variety and nitrogen level for all the sampling dates including at harvest. The interaction effect of variety and nitrogen level was significant for TDM at 60 DAT and at harvest but not at 40 and 50 DAT (table 5). The TDM production of all the four varieties increased with the age of rice plant. Among the varieties, Dhanigold hybrid showed the highest TDM (31.75, 41.74, 68.85 and 111.30 g m -2 ) respectively. TDM production is influenced by nitrogen rates and the highest TDM at 40, 50 and 60 DAT and at harvest were 27.91, 40.34, 69.74 and 116.80 g m -2 with 120 kg N ha -1 (table 6). The second highest values were found with 160 kg N ha -1 which were 27.47, 38.21, 66.87 and 110.70 gm -2 , respectively. The lowest TDM hill -1 was 24.98, 34.13, 56.27 and 86.00 gm -2 , respectively in the control plots at different dates, respectively. Azarpour et al. (2014) and Mo et al. (2013) reported that above ground TDM at maturity was highest in 225 kg ha -1 . The interaction effect showed that the highest dry matter (g m -2 ) at 60 DAT in Dhani gold (hybrid) was with 120 kg N ha -1 while that at harvest was the highest with BRRI dhan56 with 120 kg N ha -1 which was similar to that of Dhani gold (hybrid) at 120 kg N ha -1 (table 7).     Thus, the present study reveals that the highest TDM could be accumulated at 120 kg N ha -1 in both Dhanigold and BRRI dhan56. The TDM accumulation differed in different varieties due to their difference in the genetic makeup. The highest TDM production in the hybrid variety Dhanigold probably attributed to its taller height and higher number of tillers hill -1 . It has been reported that modern inbred and hybrid transplant Aman rice varieties produces highest TDM as the plants are tallest and are having maximum number of leaves and tillers (Islam, 2011;Mia and Shamsuddin, 2011;Panwar et al., 2012).

Variety
Yield contributing characters: Number of effective tiller hill -1 , number of non-effective tiller hill -1 , number of total grain, filled grain and unfilled grain panicle -1 were affected significantly by variety, nitrogen rate and their interaction. The interaction between variety and nitrogen level showed that the highest number of effective tillers hill -1 (13.87) was recorded in Dhanigold hybrid with 120 kg N ha -1 and the lowest (6.20) was found in Binadhan-7 with no nitrogen control plots (  Table 8. Interaction effect of variety and level of nitrogen on yield and yield contributing characters of rice (In a column, figures with same letter (s) or without letter do not differ significantly whereas figures with dissimilar letter differ significantly (as per DMRT). ** =Significant at 1% level of probability, * =Significant at 5% level of probability, NS = Not significant; V1 = Binadhan7, V2 = BRRI dhan39, V3 = BRRI dhan56, V4 = Dhanigold (Hybrid); N0 = Zero (Control), N1 = 40 N, N2 = 80 N, N3 = 120 N, N4 = 160 N). It was found that cultivation of Dhani gold hybrid at 120 kg N ha -1 produced the highest number of total grains panicle -1 (169.00) and filled grains panicle -1 (149.80). The lowest number of total (106.80) and filled grain panicle -1 (87.97) was obtained from Binadhan-7 with no nitrogen control (0 kg N ha -1 ) treatment. The highest weight of 1000-grain (24.39 g) was found with 120 kg N ha -1 which was followed by that (24.17g) at 160 kg N ha -1 . The lowest one (23.34 g) was recorded from the control. The variation in effective tiller production in varieties and nitrogen rates could be associated with the variation in genetic makeup of the variety (Panwar et al., 2012). The adequate nitrogen probably favored the cellular activities during panicle initiation and development which led to increased number of productive tillers hill -1 . The results indicate that the number of effective tillers hill -1 increased with the increase of nitrogen dose up to certain limit. The improvement in the formation of effective tillers with increasing nitrogen level might be due to availability of higher amount of nitrogen that enhanced tillering up to specific dose (Ahmed et al., 2000). The difference in number of total and filled grains panicle -1 among the varieties might be due to their differences in genetic constitution. It might be noted that the supply of nitrogen contributed to spikelet formation which probably contributed to increased number of grains panicle -1 and the maximum was achieved at the optimum level of nitrogen of 120 kg N ha -1 . Significant increase in the number of filled grains panicle -1 with increase in level of nitrogen was reported by Mendhe et al. (2002). Thousand grains weight varied significantly by nitrogen level only but not by the variety and the interaction between variety and nitrogen level. The previous study reveals that the weight of 1000-grain increased with the increased of N level and showed a quardratic relationship with the nitrogen levels. Grain and straw yields: Grain and straw yields were significantly influenced by variety, nitrogen rate and their interaction. The highest grain yield (5.93 t ha -1 ) was recorded in Dhanigold hybrid at 120 kg N ha -1 (table 8). The lowest one (3.50 t ha -1 ) was found in Binadhan-7 at control (0 kg N ha -1 ). The highest grain yield (5.34 t ha -1 ) was obtained with 120 kg ha -1 and the lowest grain yield (3.66 t ha -1 ) from control plots (without N levels). The highest yield in Dhani gold hybrid might be attributed to the production of maximum effective tillers m -2 and filled grains panicle -1 . The previous workers reported that the varieties which produced higher number of effective tillers hill -1 and higher number of grains panicle -1 exhibited higher grain yield ha -1 (Ali et al., 2014). The grain yield increased with the increase of nitrogen application. Mo et al. (2013) reported that increment of application of nitrogen up to 187.5 kg N ha -1 increased the grain yield and then declined. The highest straw yield (6.89 t ha -1 ) was recorded in Dhanigold yield at 120 kg N ha -1 and the lowest one (4.50 t ha -1 ) was found in Binadhan-7 at control (0 kg N ha -1 ) . In the present study, the short duration hybrid rice variety Dhanigold responded best at 120 kg N ha -1 .
BRRI dhan56 and many other varieties gave the highest yield at 75 kg N ha -1 in another study by Jisan et al. (2014).

Determination of optimum nitrogen dose:
The yield response of the short duration four aman rice varieties in relation to nitrogen rates can be best explained by the quadratic equations (figure 1). The test analysis indicated that more than 96, 88, 94 and 92% of the variation in crop performance occurred in variety Binadhan-7, BRRI dhan39, BRRI dhan56 and Dhani gold hybrid, respectively. The estimated coefficients of the polynomial regression models showed significant variation (table 9). The estimated optimum dose of nitrogen for Binadhan-7, BRRI dhan39, BRRI dhan56 and Dhani gold hybrid are 131.31, 122.97, 126.50 and 133.14 kg ha -1 , respectively.   Table 9: Estimation of the model determining the relationship between the nitrogen dose applied and yield of four short duration rice varieties. ONCLUSION: The present study concludes that the highest grain yield of short duration aman rice could be obtained by growing a hybrid rice variety Dhani gold at 133 kg N ha -1 applied in three equal splits at 15, 30 and 45 days after transplanting. The estimated optimum dose of nitrogen for Binadhan-7, BRRI dhan39, BRRI dhan56 and Dhani gold hybrid are 131.31, 122.97, 126.50 and 133.14 kg ha -1 , respectively.

BRRI dhan56
Dhani gold Hybrid C C R