It is a fact that rice plants require more nutrients especially nitrogen, to produce more yield. The efficiency of nitrogen fertilizer especially urea is very low in rice but urea is the principal source of nitrogen for rice in Bangladesh. This important element has been found to be deficit in most of the soils of Bangladesh. However, the nature and magnitude of N loss largely depend on the sources and methods of N fertilizer application. Prilled urea (PU) is a fast releasing nitrogen fertilizer which is usually broadcasted in splits, that causes considerable loss as ammonia volatilization, immobilization, denitrification and surface run off. Fertilizer N loss as ammonia volatilization from the flooded rice field could be as high as 40-60% (Sreenivasan and Subrahmanyan, 1995). On the other hand, deep placement of slow releasing nitrogenous fertilizer such as urea supergranule (USG) reduces the N loss as well as increases N use efficiency in wetland rice. According to Crasswell and De Datta (1980), broadcast application of urea on the surface soil causes losses up to 50% but point placement of USG in 10cm depth results in negligible loss and also provides a bonus of nitrogen to the soil. Modified urea fertilizers are designed to control one or more types of N loss to which ordinary urea is commonly susceptible. To minimize the losses of nitrogen, slow releasing of nitrogenous fertilizer has been advocated with deep placement. Slow release nitrogenous fertilizer dissolves slowly in the soil providing a steady supply of available nitrogen throughout the growing period of the crop. Placement of urea supergranules in the root zone is the most effective method for increasing the nitrogen use efficiency and rice yield (Sharma, 1985). It is known that the response of crops to nitrogen varies due to variety. So, it becomes essential to investigate the response of newly developed hybrid rice varieties to different forms of urea fertilizer and mode of its application under rainfed conditions. The superiority of USG, a slow releasing nitrogenous fertilizer, over PU is not yet well established especially under irrigated or rainfed conditions in Bangladesh. Therefore, a study was undertaken with a view to study the response of some hybrid and inbred rice varieties to the application methods of urea supergranules and prilled urea in transplant aman season.
Materials and Methods
The experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University (BAU), Mymensingh in the aman season during June to December 2000. Soil of the experimental field was more or less neutral in reaction (pH=6.45), low in organic matter content (1.37%) and its general fertility level was also low. The experimental area was under the sub-tropical climate. Two factors were included in the experiment: (a) variety BRRI Dhan 34 , Sonar Bangla-1 and Alok 6201; (b) method of application of urea supergranule (USG) and prilled urea(PU)-recommended method of USG, recommended method of PU, furrow placement of USG, side placement of USG, two third USG+ one third PU at 10 days after transplanting (DAT )and half USG + half PU at 10 and 30 DAT. The experiment was laid out in randomized complete block design with three replications. Each replication (block) was divided into 18 unit plots where treatment combinations were allocated at random. Unit plot size was 4.0x2.5m2 with 1.0m distance between two replications. A piece of high land was selected for raising seedlings. Sprouted seeds were sown in nurseries on 20th June 2000. The experimental land was first opened with a tractor drawn disc plough and then puddled thoroughly by ploughing and cross ploughing with a country plough and subsequently leveled by laddering. The field layout was made on 13th July 2000 according to experimental specification immediately after final land preparation. Individual plots were cleaned off weeds and stubbles and finally leveled by wooden plank.
BRRI Dhan 34 was fertilized with 130kg ha1 PU/USG, 100kg ha1 triple super phosphate (TSP), 70kg ha1 muriate of potash (MP), 60kg ha1 gypsum and 10kg ha1 ZnSO4. Sonar Banlga-1 was fertilized with 260kg ha1 PU/USG, 90kg ha1 TSP, 67kg ha1 MP, 112kg ha1 gypsum and 15kg ha1 ZnSO4. Alok 6201 was fertilized with 260kg ha1 PU/USG, 130kg ha1 TSP, 120kg ha1 MP, 70kg ha1 gypsum and 10kg ha1 ZnSO4.
TSP, MP, gypsum and ZnSO4 were applied as basal during final land preparation in all the plots. But PU or USG were applied as per experimental specifications. USG was applied at 10 DAT and recommended method of PU was applied at 10, 30 and 45 DAT. One seedling hill1 was transplanted on 15th July 2000 maintaining hill spacing of 15cm and row spacing of 25cm. All intercultural operations like gap filling, weeding and irrigation were performed as and when necessary. No remarkable pest infestation was noticed. Ten hills (excluding border hills) from each plot were randomly selected, uprooted and properly tagged before harvesting for recording the necessary data. The crop was harvested at full maturity when 90% of the grains turned golden yellow in colour. Sonar Bangla-1 was harvested on 19th October, Alok 6201 was harvested on 24th October and BRRI Dhan 34 was harvested on 23rd November 2000. Alok 6201 took 5 days more to mature in comparison with Sonar Bangla-1 and BRRI Dhan 34 took 30 days more to mature compared with Alok 6201. Pedal thresher was used to thresh the crop of individual plots. Grains were sun dried to a moisture content of some 14% and then weighed. Straw was sun dried and weighed. Yields of both grain and straw were converted to t ha1. The collected data was analyzed following the ANOVA technique and the mean differences were adjudged by the Duncans Multiple Range test (Gomez and Gomez, 1984) by using a statistical computer package MSTAT.
Results and Discussion
Effect of variety: Variety exhibited significant influence on all the plant characters including grain and straw yields of rice (Table 1). BRRI Dhan 34 produced the tallest plant (163.74cm), highest number of grains panicle1 (177.43), and lowest number of sterile spikelets panicle1. As a result, BRRI Dhan 34 became the highest grain yielding variety (4.87t ha1). Sonar Bangla-1 ranked second regarding grain yield but produced highest number of total tillers hill1 (12.45) and highest 1000-grain weight (24.11g). Although in respect of productive tillers hill1 Alok 6201 produced the highest value (8.48) but this variety failed to give the highest grain yield due to lowest number of grains panicle1 (91.87) and highest number of sterile spikelets panicle1 (51.87). As a result, Alok 6201 produced lowest grain yield (3.86t ha1). Grain yield differences due to variety were also reported by Anwar et al. (1999). The highest straw yield (7.72t ha1) was observed in BRRI Dhan 34. While the lowest one (5.58t ha1) was observed in Sonar Bangla-1. Variation in straw yield was also reported by Anwar et al. (1999). The highest harvest index (43.46%) was observed in Sonar Bangla-1 while BRRI Dhan 34 (38.69%) and Alok 6201 (37.98%) were statistically similar in terms of straw yield.
Effect of application method of USG and PU: The effect of application method of USG and PU was not significant in respect of number of total tillers hill1, panicle length, number of sterile spikelets panicle1 and 1000-grains weight (Table 2). The tallest plant (134.42cm) at harvest was recorded with half USG and half PU at 10 and 30 DAT. The highest number of productive tillers hill1 (8.53) was recorded with two third USG and one third PU at 10 DAT which was statistically similar to side placement of USG (8.24), recommended method of USG (8.2), and half USG + half PU at 10 and 30 DAT (7.93).
These results are not in agreement with those obtained by Jee and Mahapatra (1989). Number of grains panicle1 was found highest (124.96) with recommended method of USG which was at par with side placement of USG. Sarder et al. (1988) also agreed to this view. Grain yield (4.21t ha1) and straw yield (6.38t ha1) were recorded lowest with recommended method of PU. Number of total tillers hill1 (11.01) and number of productive tillers hill1 (7.31) were found to be lowest but straw yield (6.78t ha1) was recorded the highest with furrow placement of USG. Side placement of USG produced the shortest plant (126.20cm). Plant height (134.42cm), grain yield (4.5t ha1) and harvest index (41.45%) were found to be highest with half USG + half PU at 10 and 30 DAT. Bhale and Salunke (1993) also recorded highest grain yield with half USG + half PU. But Mishra et al. (1994) reported highest grain yield with prilled urea applied in three splits.
Effect of interaction: Variety coupled with USG and PU application method significantly influenced the plant height, number of productive tillers hill1, number of grains panicle1, grain yield, straw yield and harvest index (Table 3). The tallest plant was produced in BRRI Dhan 34 grown with half PU + half USG at 10 and 30 DAT. The highest number of grains panicle1 (188.4) was given by BRRI Dhan 34 grown with recommended method of USG. The results clearly indicate that BRRI Dhan 34 produced the lowest number of sterile spikelets panicle1 regardless the method of USG and PU application. BRRI Dhan 34 produced the highest grain yield when grown with furrow placement of USG with half USG and half PU at 10 and 30 DAT BRRI Dhan 34 produced the highest straw yield (8.33t ha1) when grown with recommended method of USG or side placement of USG. Sonar Bangla-1 grown with recommended method of PU produced highest harvest index (47.26%).
|Table 1:||Effect of variety on different plant characters of hybrid and inbred rice varieties
||Effect of application method of USG and PU on different plant characters of hybrid and inbred rice varieties
|NS =Not significant; In a column, figures with the same letter or without letter do not differ significantly whereas figures with dissimilar letter differ significantly (as per DMRT).|
F1= Recommended method of USGF2= Recommended method of PUF3= Furrow placement of USG
F4= Side placement of USGF5= Two third USG +one third PU at 10 DAT F6= Half USG+half PU at 10 and 30 DAT
||Effect of interaction of variety and method of application of USG and PU on different crop characters of hybrid and inbred rice varieties
|NS= Not significant; In a column, figures with the same letter or without letter do not differ significantly whereas figures with dissimilar letter differ significantly (as per DMRT). See Table 2 for F1-F6|
From the above discussion it is clearly found that different varieties responded differently to different methods of application of USG and PU. BRRI Dhan 34 gave highest grain yield in furrow placement of USG which was identical with half USG and half PU at 10 and 30 DAT. Sonar Bangla-1 produced highest grain yield in recommended method of USG which was similar to recommended method of PU i.e. USG had no advantage over PU in this variety. In case of Alok 6201, two third USG and one third PU at 10 DAT produced highest grain yield which was statistically similar to recommended method of PU. Half USG + half PU at 10 and 30 DAT also gave similar results.Considering the price of USG and its laborious method of application half USG and half PU may be recommended for BRRI Dhan 34 and Alok 6201. Sonar Bangla-1 responded similarly to recommended method of USG and recommended method of PU. On the same ground the use of prilled urea in Sonar Bangla-1 may be suggested.