RESPONSE OF TRANSPLANTED AMAN RICE VARIETIES TO SPLIT APPLICATION OF POTASSIUM

Split application Potassium Fertilization Grain yield Rice The research was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh, to investigate the effect of time of split application of potassium on the yield of three transplanted (T) aman rice varieties. Rice varieties were BRRI dhan39, BRRI dhan40 and BRRI dhan41. Potassium was applied at the rate of 80 kg K ha. Experimental plot size was 5m (2.5m ×2.0 m). Four split application of potassium [K1= Control (No K application), K2= 40 g K plot at 15 DAT (days after transplanting), K3= 20 g K plot at15 DAT+20 g K plot at 30DAT, K4= 10 g K plot at 15 DAT+ 10 g K plot at 25DAT+ 10 g K plot at 30 DAT+ 10 g K plot at 45 DAT] were considered as treatments. From the experiment it was found that split application of potassium had no significant effect on plant height, length of panicle, thousand grains weight. It was evident that two splits application of potassium i.e., 20 g K plot at 15 DAT+20 g K plot at 30 DAT with BRRI dhan41 gave maximum no. of tiller hill, effective tiller hill, grains panicle, grain yield and straw yield, biological yield and harvest index. But varieties differed among themselves in terms of yield contributing characters and yield, and BRRI dhan41 performed the best. Therefore, based on the findings of the present study, it may be concluded that for obtaining higher yield BRRI dhan 41 can be grown following application of potassium at the rate of 80 kg ha in two equal split at 15 and 30 days after transplanting.


INTRODUCTION
Bangladesh is an important rice growing country of the world. The economy of Bangladesh is influenced markedly by rice. It covers 80 percent of the total cropped area (AIS, 2002). Rice is grown 9.94 million hectares of land with a total production of 2.35 ton ha -1 in Bangladesh (BBS, 2006). Among the three rice crops aus (summer rice), transplant aman (grown in monsoon) and boro (grown in winter), transplant aman rice covers about 56% of the total rice area. It covers the largest area of 5.6 million hectares with a production of 9.3 million tons of rice (BBS, 2004). The average yield of aman rice is 1.64t ha -1 and HYV transplant aman rice is 3.83 t ha -1 .The benefits of health of rice include its ability to provide instant energy, regulate and improve bowel movements, stabilize blood sugar levels and slow down the aging process. It's also plays a role in providing Vitamin B1 to the human body. On the other hand, potassium is a major inorganic constituent of plants and its deficiency affects several metabolic processes. A number of physiological disorders are directly related to insufficient uptake of potassium. Potassium helps control or reduces the severity of plant diseases and increase the plant resistance to drought and other stress. It also helps overcome "bronzing disease" caused by iron toxicity and prevents root damages caused by hydrogen sulphide or by organic substances. It performs many functions in plants such as promoting growth and increasing yield, aiding in the translocation of carbohydrates to maintain cell permeability, increases the efficiency of the leaf in manufacturing sugars, strengthening plants tissues and preventing lodging, increasing resistance to pests, promoting root growth in conjunction with adequate supply of phosphates, acts an activator of a number of amino acid-activating enzymes. Singh et al. (2006) conducted an experiment in a silt loam soil to evaluate the effect of potassium and potassium levels on growth yields and seed quality of hybrid rice. They reported that 80 kg K ha -1 .was found better to obtain higher production and good quality of hybrid rice.

MATERIALS AND MOTHODS
The experiment was carried out at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh. The experimental site belongs to the agro-ecological zone 'Old Brahmaputra Floodplain', having Non-calcareous dark grey floodplain soil (UNDP and FAO, 1988). The land was medium high land with silt loam texture. The pH value of the soil was 6.5, low in organic matter content. Its general fertility level was also low ( total N is 0.08%, available P is 7.0 mg kg -1 , exchangeable K is 0.07 me/100 gm soil, available S is 7.5 me kg -1 ). Potassium was applied in the field at the rate of 80 kg K ha -1 . Four levels of K [K1= Control (No K application), K2= 40 g K plot -1 at 15 DAT (days after transplanting), K3= 20 g K plot -1 at15 DAT+20 g K plot -1 at 30DAT, K4= 10 g K plot -1 at 15 DAT+ 10 g K plot -1 at 25DAT+ 10 g K plot -1 at 30 DAT+ 10 g K plot -1 at 45 DAT] were considered as treatments.
The experiment was laid out in a split plot design with 3 replications having unit plot size of 5m 2 (2.5m ×2.0 m). Varieties were: BRRI dhan39, BRRI dhan40, BRRI dhan41 accommodated in the main plot and split application of potassium fertilizer (muriate of potash) was placed in the sub plot. Total number of plot was 36. The layout was done on 20 July having 1 m and 75 cm spacing between replications and the unit plots, respectively. Land preparation involved ploughing, harrowing and leveling in the field to make it suitable for crop establishment by a four wheel tractor. Soil was flooded and irrigated once with sufficient water to bring the top soil saturation and create an overlying water layer. The water depth was 5 cm but 10 cm was maintained for about one week after transplanting. From 30 days before head formation and flowering to the start of maturity, soil was frequently covered with water to a depth of 8 or 10 cm. A continual flow of water was maintained. The field was drained completely 30 to 45 days before harvest to ensure that the field would be dry enough for harvest. The source of K was commercially produced Muriate of Potash. Urea, Triple super phosphate, gypsum and zinc sulphate was applied at 120,100, 60 and 10 kg ha -1 respectively during final land preparation. Thirty days old seedlings were transplanted from a nursery bed to the main field maintaining 3 seedlings hill -1 with a spacing of 20 cm×15 cm. Necessary intercultural operations such as weeding, irrigation, pest management etc were performed accordingly and whenever needed to ensure the growth of a successful crop. Ten hills plot -1 were randomly uprooted before harvesting in order to collect the following data : Total number of tillers hill -1, number of effective tillers hill -1 , panicle length, number of grain panicle -1, number of unfilled spikelets panicle -1, grain yield, straw yield, biological yield, harvest index ( HI). Data on grain and straw yield were recorded on a plot basis after drying in the sun maintaining 14% moisture, threshing, winnowing and finally converted to grain/straw weight per hectare.
All data were statistically analyzed with the help of MSTAT (Gomez and Gomez, 1984). Analysis of variance (ANOVA) was measured and significant differences between means were calculated by Ducan's multiple range test (DMRT).

Effect of split application of K
Effect of split application of K on effective tillers hill -1 , non-effective tillers hill -1 , panicle length, grain panicle -1 , unfilled spikelets panicle -1 , 1000 grains weight of grain yield, straw yield, biological yield is shown in Table 2. Potassium has a pronounced effect on three T.aman rice varieties i.e., BRRI dhan39, BRRI dhan40, BRRI dhan41 in producing maximum number of tillers hill -1 , grain panicle -1 , grain yield, straw yield, biological yield. Two split of potassium gives maximum number of tillers hill -1 , effective tillers hill -1 , grain panicle -1, grain yield, straw yield, biological yield and minimum of number of non-effective tillers hill -1 , unfilled spikelets panicle -1 . On the other hand, at the basal dose, maximum number of unfilled spikelets panicle -1 was found. Four splits application of potassium i.e., 10 g K plot -1 at 15 DAT+ 10 g K plot -1 at 25DAT+ 10 g K plot -1 at 30 DAT+ 10 g K plot -1 at 45 DAT showed better performance than basal dose incase of total tillers hill -1 , effective tillers hill -1 , grain panicle -1, grain yield, straw yield and biological yield. More non-effective tillers hill -1 was found in four split application of potassium than basal. Maximum number of non-effective tillers hill -1 was found in one split application of potassium i.e. when 40 gm K was applied in the experimental plot. Fallah (1997) in his experiment with rice crop applied 250 kg K ha -1 at 5 different dates. He reported that grain yield was increased by K application and was highest when K applied in two equal splits (50% as basal application + 50% forty-five days after transplanting). Meena et al. (2003) conducted a field experiment at the Indian Agricultural Research Institute, Delhi to study the productivity and economics of Oryza sativa L. as influenced by K application. The experiment was laid out in split plot design with two levels of potassium, viz. 62.5 and 125 Kg K ha -1 . Significantly higher number of tiller, dry matter accumulation, grain and straw yields were recorded with the application of 62.5 Kg K ha -1 applied in two equal splits (half at transplanting and half at maximum tillering).

Interaction Effect of Variety and K split application
Total Tiller Hill - 1 The variety BRRI dhan41 with four splits application of K gives the highest number of total tillers hill -1 . The lowest number tillers hill -1 was found in variety BRRI dhan41 with basal application of K which is statistically similar to variety BRRI dhan39 with basal application of K. Table 3 shows that the highest number of effective tillers hill -1 was counted in the combination of variety BRRI dhan41 with two splits application of K which is statistically similar to the combination of variety BRRI dhan41 with four splits application of K. Lowest number of tillers hill -1 was found in BRRI dhan39 with basal application of K.

Number of non-effective tillers hill -1
The trend of interaction effect between variety and split application of potassium was found to have adverse effect in BRRI dhan40on the production of non-effective tillers hill -1 with one split application which is statistically similar to BRRI dhan39 with four split application of K. Less number non-effective tillers hill -1 was found BRRI dhan41 with two split application of K which might have caused greater production.

Grain Panicle -1
The combination of variety BRRI dhan41 with two splits application of K produced higher number of grains panicle -1 and variety BRRI dhan39 with basal application of K shows the lower number of grain panicle -1 .

Unfilled spikelets panicle -1
The maximum number of unfilled spikelets panicle -1 was observed in BRRI dhan39 with no K application which is statistically similar to BRRI dhan39 with one split application. The lowest number of unfilled spikelets panicle -1 was found in BRRI dhan40 with one split application of K which is statistically similar to BRRI dhan 40 with two split, BRRI dhan 41 with one split, two split and four split application of K.

Grain yield
The highest number of grain yield was found in the interaction between variety BRRI dhan41 with two splits application of K which is statistically similar to the interaction between variety BRRI dhan41 with four splits application of K and variety BRRI dhan40 with two splits application of K. Lowest number of grain yield found in BRRI dhan39 with basal dose.

Straw yield
The highest number of straw yield was found in the interaction between variety BRRI dhan41 with two splits application of K which is statistically similar to the interaction between variety BRRI dhan41 with four splits application of K and variety BRRI dhan40 with two splits application of K. In every variety, straw yield increased gradually in one split then two split application of potassium, In case of four split application of potassium, except BRRI dhan39 other two varieties showed less number of straw yield.

Biological yield
The maximum Biological yield was obtained from BRRI dhan40 with two split application of potassium which is identical with BRRI dhan41 with two split application of potassium and four split of Potassium. There is a great difference in biological yield of BRRI dhan40 and BRRI dhan41 in compared to BRRI dhan39 in case of two split application of potassium.

CONCLUSION
Based on the findings of the present study, it may be concluded that for obtaining higher yield BRRI dhan 41 can be grown following application of potassium at the rate of 80 kg ha -1 in two equal split at 15 and 30 days after transplanting.