Response of Hybrid and Inbred Rice Varieties to the Application Methods of Urea Supergranules and Prilled Urea

INTRODUCTION

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 ha^–1 PU/USG, 100kg ha^–1 triple super phosphate (TSP), 70kg ha^–1 muriate of potash (MP), 60kg ha^–1 gypsum and 10kg ha^–1 ZnSO₄. Sonar Banlga-1 was fertilized with 260kg ha^–1 PU/USG, 90kg ha^–1 TSP, 67kg ha^–1 MP, 112kg ha^–1 gypsum and 15kg ha^–1 ZnSO₄. Alok 6201 was fertilized with 260kg ha^–1 PU/USG, 130kg ha^–1 TSP, 120kg ha^–1 MP, 70kg ha^–1 gypsum and 10kg ha^–1 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 hill^–1 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 ha^–1. The collected data was analyzed following the ANOVA technique and the mean differences were adjudged by the Duncan’s Multiple Range test (Gomez and Gomez, 1984) by using a statistical computer package MSTAT.