EFFECTS OF DIFFERENT LEVELS OF FLOODING AND ADDITIONAL APPLICATION OF TWO NUTRIENTS ON BORO RICE (Binadhan-8) IN SALINE SOIL

Salinity Binadhan-8 Nutrient Irrigation A field experiment was conducted at Kalikapur village of Kaliganj upazila under Satkhira district in order to observe the effects of flooding duration and additional application of K and S on transplanted boro rice cv. Binadhan-8 during January May 2013. The experiment was laid out in a split-plot design where the main plots comprised of five flooding levels viz. continuous flooding (W1), flooding for 10 days (W2), flooding for 20 days (W3), flooding for 30 days (W4), flooding for 40 days (W5), and the sub-plots of four additional (over the recommended dose) nutrients rates viz. S43 + K25 (T1), K38 (T2), S32 + K38 (T3), and K50 (T4), with three replications. The duration of flooding showed significant positive effect on the yield and yield components of boro rice cv. Binadhan-8. The highest values for plant height (106.8 cm), panicle length (28.4 cm), number of plants hill-1 (15.3), grain yield (4.8 t ha-1) and straw yield (6.5 t ha-1) were recorded in continuous flooding (W1) while these values were decreased with the decrease in the duration of flooding from 40 days to 10 days. Additional application of K and S also significantly influenced all of the parameters. Results revealed that the highest values for plant height (102.8 cm), panicle length (26.6 cm), plants hill-1 (15.4), 1000-grain weight (23.9 g), grain yield (4.8 t ha-1) and straw yield (6.1t ha-1) were obtained from T3 where S and K were applied @ 32 and 38 Kg ha-1 in addition to the recommended fertilizer rate. The interaction of flooding and nutrients significantly manipulated the yield and yield attributes. Due to interaction of flooding and nutrients, the highest growth and yield was observed in continuous flooding with S32 + K38 (W1T3). The results indicated that the flooding with fresh water and use of additional nutrients (K and S) had a remarkable effect in growing boro rice cv. Binadhan-8 in saline soils of Bangladesh.


Salinity Binadhan-8 Nutrient Irrigation
3), grain yield (4.8 t ha -1 ) and straw yield (6.5 t ha -1 ) were recorded in continuous flooding (W1) while these values were decreased with the decrease in the duration of flooding from 40 days to 10 days. Additional application of K and S also significantly influenced all of the parameters. Results revealed that the highest values for plant height (102.8 cm), panicle length (26.6 cm), plants hill -1 (15.4), 1000-grain weight (23.9 g), grain yield (4.8 t ha -1 ) and straw yield (6.1t ha -1 ) were obtained from T3 where S and K were applied @ 32 and 38 Kg ha -1 in addition to the recommended fertilizer rate. The interaction of flooding and nutrients significantly manipulated the yield and yield attributes. Due to interaction of flooding and nutrients, the highest growth and yield was observed in continuous flooding with S32 + K38 (W1T3). The results indicated that the flooding with fresh water and use of additional nutrients (K and S) had a remarkable effect in growing boro rice cv. Binadhan-8 in saline soils of Bangladesh.

INTRODUCTION
Rice (Oryza sativa L.) is the principal source of food for more than one third of the world's population. It is rated as one of the major food crops in the world, but is also considered extremely salt-sensitive (Maas and Hoffman, 1977).The total area and production of rice in Bangladesh are about 11.7 million hectares and 31.98 million metric tons, respectively (BBS, 2011). Soil salinity is a worldwide problem. Bangladesh is no exception to it. Coastal area in Bangladesh constitutes 20% of the country of which about 53% are affected by different degrees of salinity (Islam, 2005). Various agricultural regions have significantly lost their productivity due to soil salinity in last several decades. The worst salinity conditions are reported from the Khulna, Bagerhat, Satkhira and Patuakhali districts (SRDI, 2010). Salinity from flood irrigation can occur over time wherever irrigation occurs; since almost all water (even natural rainfall) contains some dissolved salts. When the plants use the water, the salts are left behind in the soil and eventually begin to accumulate. Since soil salinity makes it more difficult for plants to absorb soil moisture, these salts must be leached out of the plant root zone by applying additional water. Salinization from irrigation water is also greatly increased by poor drainage and use of saline water for irrigating agricultural crops (ILRI, 1989). Nelson (1978) reported that potassium has a positive role in plant growth under saline conditions, because this element plays an essential role in photosynthesis, osmoregulatory adaptations of plant to water stress. On the other hand, Sharma (2001) stated that the application of gypsum could alleviate the adverse effects of salinity and increase tolerance to salinity in rice plants. The aim of the present study was to explore the impact of flooding (with fresh water irrigation) duration and additional application of K and S (as gypsum) on transplanted boro rice cv. Binadhan-8 in a saline area of Bangladesh.

MATERIALS AND METHODS
The study was conducted in a farmer's field at Kalikapur village in Kaliganj upazila under Satkhira district during the boro season (January to May 2013). The experimental site belongs to the Agro-ecological Zone of the Ganges Tidal Floodplain. The general soil type was the Calcareous Dark Grey Floodplain Soils. The soil was clay in texture, having pH 7.4, total nitrogen 0.1%, available phosphorus 4.37mg kg -1 , and available potassium 0.082 cmolc kg -1 . The salinity of water in the experimental site was gradually increased from January to May 2013 (except February) having EC values of 3.70, 2.90, 4.50, 5.31, 8.8 dS m -1 , respectively. The variety used for the experiment was Binadhan-8. It was developed by the Bangladesh Institute of Nuclear Agriculture. It was released in 2010 as salt tolerant boro rice variety.
The experiment was laid out in a split-plot design with three replications. The size of the individual plot was: 3m x 4m. The block to block and plot to plot distances were maintained as 1m and 40cm, respectively. Total 1000 m 2 area was used for this study. The main plots were used for five flooding levels viz. continuous flooding (W1), flooding for 10 days (W2), flooding for 20 days (W3), flooding for 30 days (W4), flooding for 40 days (W5), and the sub-plots were used for four treatments of additional (over the recommended dose) nutrients rates viz. S43 + K25 (T1), K38 (T2), S32 + K38 (T3), and K50 (T4), with three replications. In cases of W2 to W5, the flooding was done with fresh water at 15 days after transplanting. The subscript in the nutrients treatments means the amount of particular nutrient @ kg ha -1 . A basal dose of 120 kg N, 14 Kg P, 36 Kg K, and 8 kg S from urea, TSP, MoP and gypsum, respectively, were applied in all plots as per the recommended dose of the soil of that AEZ (BARC, 2005). The full amount of TSP, MoP and gypsum were added as broadcast during final land preparation. Urea was applied in three equal splits viz. three days of transplanting, 28 days after transplanting (tillering stage) and 50 days of transplanting (panicle initiation stage).
The similar trend was also observed for the yield of Binadhan-8. The highest grain yield (4.84 t ha -1 ) and straw yield (6.47 t ha -1 ) were recorded in continuous flooding (W1) and the lowest (3.94 and 5.16 t ha -1 , respectively) in W2 ( Table 1).The grain yield was significantly decreased with the reduction in flooding duration, although straw yield for 30 and 40 days flooding were statistically similar.

Effect of additional application of nutrients on Binadhan-8
Application of additional nutrients (K and S) significantly influenced all parameters of rice ( Table 2). The highest values for plant height (102.80 cm), panicle length (26.60 cm), plants hill -1 (15.44), the 1000-grain weight (23.88 g) were obtained from T3, where S and K were applied at the rate of 32 and 38 kg ha -1 , respectively. Except 1000-grain weight, the next highest values were observed in T1, where 43 Kg S and 25 Kg K were applied. The application of K alone (T2 and T4) showed inferior result compared to both additional nutrients application (T1 and T3).

Interaction effect of flooding level and additional application of nutrients on Binadhan-8
It is evident from Table 3 that the interaction between different levels of flooding and additional application of nutrients had significant effect in respect of all parameters. The highest plant height (108.7 cm), panicle length (28.99 cm), number of plants hill -1 (21.53), number of 1000-grain weight (25.43 g) ,grain yield (5.14 t ha -1 ), straw yield (6.82 t ha -1) were obtained from continuous flooding, S32 + K38 (W1T3) while the lowest value obtained from flooding for 10 days, K38 (W2T2) except number of plants hill -1 . The highest grain yield obtained from W1T3 was also statistically comparable with those obtained from W4T3 and W5T3treatment combinations.

DISCUSSION
Rice is one of the most widely grown crops in coastal areas (Akbar and Yabuno, 1972). Binadhan-8, a salt tolerant boro rice variety was tested in saline area to see the impacts of prolonged flooding with fresh water (in the form of irrigation) and additional application of two nutrients K and S on its yield performance. It was observed that the different levels of flooding had significant effect on the yield and yield components. The most yield and yield components were increased with increasing flooding duration, on the other hand, it decreased due to short duration flooding. Rice yield usually decreases at salt stress, but in this study it was increased due to application of fresh water in different duration. Certain depth of irrigation water is kept in the field for growing successful rice crop. This practice simultaneously helps in leaching of soluble salt consequently reducing soil salinity (SRDI, 2010). If sufficient irrigation water of good quality is available, introduction of rice crop is possible in saline area resulting in the additional production of grain yield.
Binadhan-8 was responded significantly due to application of different nutrients (K and S) over the normal recommended rate. Combined application of these two nutrients gave the better results than using K alone. Potassium application alleviated the stress condition and significantly improved dry matter yield and yield components in rice (Ebrahimi et al., 2012).The number of tillers increased significantly (P<0.01) by the application of potassium over control (Mohiti et al.,2011). Similar result found by Fatema and Khan (2013) who conducted a field experiment to evaluate the potentiality and effectiveness of gypsum in saline soils collected from coastal areas of Bangladesh. Growth and yield parameters of rice, such as, plant height, number of tillers, etc. were found to be significantly (p ≤ 0.05) induced by the application of gypsum. Hanay et al. (2004) examined that use of gypsum, calcite, calcium chloride, and other chemical agents that provide Ca, which tends to replace exchangeable Na, is effective for saline soil amelioration.
Nutrients play essential roles in plant metabolism. In addition to osmotic adjustment, genotypic differences in inorganic ions uptake under salinity have implications for maintaining adequate nutrition and for optimizing nutrients/elements related salinity tolerance mechanisms. Binadhan-8 is a saline tolerant high yielding paddy variety. It can tolerate the salinity level of 8 to 10 dS m -1 which was released by the Seed Certification Agency in 2010. The range of existing water salinity levels in this experiment site was 3.7-8.8 dS m -1 . It was successfully cultivated in this saline level and gave a good yield with the application of fresh water irrigation for a prolonged duration and additional K and S application over the recommended fertilizer rates.

CONCLUSION
The result of the experiment provides clear understanding that Binadhan-8 can be grown successfully in a saline area under the continuous flooding and application of additional S32 + K38 nutrients per hectare.