Scientific registration n o : 285 Symposium n o : 13B Presentation: Poster. BHUIYAN Nurul I (1), SAHA Pranesh K (2) INTRODUCTION

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1 Scientific registration n o : 285 Symposium n o : 13B Presentation: Poster Effect of P-Fertilization on Ripening, Yield and P- Nutrition of Rice Under Different Levels of Soil P Effet de la fertilisation phosphatée sur la matûration, le rendement et la nutrition phosphatée du riz à différents niveaux de disponibilité en P du sol BHUIYAN Nurul I (1), SAHA Pranesh K (2) (1)Soils Division, Bangladesh Agricultural Research Council, Farmgate, New Airport Road,Dhaka-1215, Bangladesh (2) Soil Science Division, Bangladesh Rice Research Institute, Gazipur, 1701, Bangladesh INTRODUCTION The use of chemical fertilizers in Bangladesh Agriculture has been increasing at a faster rate over the last three decades. But there has been a great concern world-wide to minimize the use of agrochemicals for higher profit and safer environment. Among the chemical fertilizers used in Bangladesh Agriculture, phosphatic fertilizers rank the second position after nitrogen. This fertilizer is very costly because of the non-availability of the raw materials of this fertilizer at the local level. Moreover, the response of wetland rice, the country s main crop, to P fertilization is generally lacking in many soils of Bangladesh. This is perhaps due to the buildup of P fertility in soil because of the repeated P-fertilizer application. In general 25 kg P/ha is recommended for MV rices under wetland culture irrespective of P fertility of soils. But P requirement of rice is considerably lower than those of N and K. About 3.0 kg P is generally required by MV rices to produce a ton of rough rice. Kummer (1986) reported that the application rates close to or slightly above the amount of phosphate taken up by the crop appear to be sufficient even for high yields and continuous cultivation of rice. Many reports indicated higher availability of native and applied phosphorus to rice when a soil is submerged and wetland rice frequently does not show response to phosphorus addition (Patrick and Mahapatra, 1968; Mahapatra and Patrick, 1971; Islam and Islam, 1973; Chang, 1976; Ponnamperuma, 1977). On the other hand, the recovery of the added phosphorus from the inorganic fertilizers rarely exceeds percent. De Datta (1981) reported that the recovery of fertilizer phosphorus by rice is even less than 10 percent. A large fraction of the soluble phosphate applied to wetland soils is fixed or retained on the surface of the solid phase of the soil, although the mobility of phosphorus in wetland soils is greater than in dryland soils (Chang, 1976). Considerable residual effect of the fertilizer phosphorus on the succeeding crop has also been reported by many workers (Meelu and Rekhi, 1981; Prasad et al, 1985; Singh and Brar, 1986). The response of wetland rice to P-fertilization is greatly influenced by the P fertility status of 1

2 soils. Thus in order to make a realistic P-fertilizer recommendation, it is essential to know the response behaviour of wetland rice to rates of P-fertilizer application under different levels of available soil P. In view of the above considerations, the present study was undertaken to determine the effect of rates of P-fertilizer application on ripening, yield and P-nutrition of wetland rice under different levels of available soil P so as to make necessary modification on the present P-fertilizer recommendation. MATERIALS AND METHODS A 6-year long P-frequency trial was conducted using a Boro-fallow-T.Aman cropping pattern on a permanent layout at BRRI farm soil (Aeric haplaquept) during the period of Analyses of initial soil sample indicated that the soil of the experimental field was a clay loam in texture, neutral in reaction (ph 7.1) and had organic carbon content 1.0% and available P 8.5 ppm (Mod.Olsen). A total of 300, 150, 100, 75 and 0 kgs P/ha were applied from TSP in five treatments depending on variations in frequencies of P-fertilizer application during the 6-year period. These variable amounts of added P have resulted five different levels of soil available P (Modified Olsen Method) at the end of the study period, such as 5.2, 13.5, 9.2, 6.4 and 6.6 ppm. In 1993 Boro (Dry) season, a P-response trial was conducted on the same layout to evaluate P response of MV rices under each level of available soil P. The study was continued for T.Aman (Wet) season of Three different rates of fertilizer P (0, 15, 30 kg P/ha) from TSP were applied at random to each level of available soil P. All P-fertilizer as per treatment was applied as basal and thoroughly incorporated with soil before planting. Blanket doses of N, K and S fertilizers for both Boro and T.Aman rices were applied following the standard methods of their application. Appropriate cultural and management practices including plant protection measures were followed during each cropping season. A modern Boro variety (BR29) and a T.Aman variety (BR11) were used as test crops. Data on yields (grain & straw) and field duration of Boro and T.Aman rices were recorded and analysed statistically following the standard procedures. A portion of the grain and straw samples were oven dried at 70 C and then ground in a willey Mill. These samples were analysed for P content by digesting with triacid mixture (Yoshida et al, 1972). RESULTS AND DISCUSSION Grain and Straw Yield: Results clearly show an interaction effect of the levels of available soil P and rates of added P- fertilizer, particularly on the grain yield of rice in both Boro and T.Aman seasons (Table 1 a, d). In Boro season, grain yield increased significantly with increasing rates of P-fertilizer application only at the lowest level of available soil P (Table1a). But at higher levels of available soil P, application of P-fertilizer at any rates did not increase grain yield. It is surprising to note that at highest level of available soil P (13.5 ppm), P- fertilizer application gradually depressed the grain yield and the yield decreased was significant at the highest rate (Table 1a). Straw yield on the other hand increased significantly with 15 kg/ha P-application only at the lower level of available soil P (Table 1b). 2

3 In T.Aman season, grain yield increased significantly with 15 kg/ha P application only when available soil P was the lowest (Table 1 d). At higher levels of available soil P, application of P-fertilizer particularly at the highest rate slightly depressed the grain yield similar to Boro season (Table 1 d). Straw yield on the other hand was not affected significantly by P-fertilizer application at any level of available soil P (Table 1 e). It is worth while to mention here that the magnitude of P-fertilizer effect at the lowest level of available soil P on the grain yield was higher in Boro season than in T.Aman season. This seasonal variation might be due to lower temperature and higher solar radiation of Boro season than that of T.Aman season. Annual grain yield data from 2 crops, presented in Fig. 1 show that P-fertilizer application progressively increased the grain yield at lowest level of available soil P (5.2 ppm), whereas at the highest level (13.5 ppm), increasing rates of P-fertilizer application gradually depressed the grain yield (Fig. 1). This depressing effect might be due to an antagonistic effect of higher levels of both soil and fertilizer P on some other plant nutrients in soil. This negative effect of P-fertilizer application at higher level of available soil P need to be investigated. Field Duration: Field duration of both Boro and T.Aman varieties were greatly influenced by the level of available soil P and P-fertilization. Field duration for Boro rice ranged from 122 to 150 days and for T.Aman rice ranged from 113 to 128 days depending on the level of available soil P and rate of P-fertilizer application. At lowest level of available soil P, maturity of Boro and T.Aman rice varieties were delayed by 25 and 12 days respectively when P-fertilizer was not applied. Application of P-fertilizer even at 15 kg P/ha enhanced crop maturity in both seasons and reduced the field duration considerably, particularly at lower levels of available soil P (Table 1 c, f). Recently, Seneweera et al (1993) after conducting experiment in phytotron has reported that the higher level of P enhanced rice flowering. Phosphorus Nutrition: Phosphorus content in and uptake by BR29 and BR11 at maturity stage as affected by different treatments are presented in Table 2 a-f. Results show that P content in grain and straw and total P uptake by both Boro and T.Aman rice varieties increased with increasing rates of P-fertilizer application, particularly when available soil P was around 6 ppm and less. When available soil P was around 9 ppm and more, P content in and uptake by those varieties were not affected by P-fertilizer application. Annual P uptake by 2 crops of the cropping pattern increased progressively with increasing rates of P-fertilizer application, particularly at lower levels of available soil P. At the highest level (13.5 ppm), P uptake decreased slightly with increasing rates of P- fertilizer application (Fig. 2). This reduced P uptake was associated with decreased grain yield under the same treatment. 3

4 CONCLUSION About 25 kg P/ha during Boro season and 15 kg P/ha during T.Aman season would be enough to produce 8-9 t/ha grain yield when available soil P is less than 6 ppm by modified olsen method. Amount of P-fertilizer application can be reduced to variable extent for the same level of grain yield when the available soil P is more than 6 ppm with similar soil characteristics. REFERENCES Chang, S.C Phosphorus in submerged soils and phosphorus nutrition and fertilization of rice. Pages in The fertility of paddy soils and fertilizer application for rice. Food and Fertilizer Technology Centre, ASPAC, Taipei, Taiwan. De Datta, S.K Principles and Practices of Rice Production. Jhon Wiley & Sons. N.Y. Islam, A., and W. Islam Chemistry of submerged soils and growth and yield of rice. 1. Benefit from submergence. Plant soil. 39: Kummer, K.F The efficiency of different phosphate fertilizers under upland conditions in the Tropics and Subtropics. Pages in Proceedings of the International Conference on the Management and Fertilization of Upland Soils in the Tropics and Subtropics, Nanjing; PRC. Mahapatra, I.C., and W.H. Patrick, Jr Evaluation phosphate fertility in water-logged soils. Int. Symp. Soil Fert. Evaluation Proc. Indian Soc. Soil Sci. New Delhi. 1: Meelu, O.P., and R.S. Rekhi Fertilizer use in rice-based cropping systems in northern India. FN, 26(9), Patrick, W.H., and I.C. Mahapatra Transformation and availability to rice of nitrogen and phosphorus in water-logged soils. Adv. Agron. 20: Ponnamperuma, F.N Physicochemical properties of submerged soils in relation to fertility. IRRI Res. Pap. Ser pp. Seneweera, S., P. Milhan and J. Conroy Influence of elevated CO 2 and phosphorus nutrition on the growth and yield of short-duration rice (Oryza Sativa L. CV. Jarrah). Australian J. Plant Physiology. 21, Singh, B., and S.P.S. Brar Long term effects of NPK and Zn fertilization in maize wheat rotation on crop yields and soil characteristics ( ). PAU, (memeographed). Yoshida, S., D.A. Forno, J.H. Cock and K.A. Gomez Laboratory Manual for physiological studies of rice. 2nd ed. International Rice Research Institute, Los-Banos, Philippines. Keywords: phosphorus, rice, fertilization, yield, ripening, mineral nutrition Mots clés : phosphore, riz, fertilisation, rendement, mûrissement, nutrition minérale 4

5 Table 1. Effect of rates of P-fertilizer application on yields and field duration of MV rices in a Boro-Fallow-T.Aman cropping pattern under different levels of available soil P. Added P Levels of available soil P (ppm) (Kg/ha) BORO SEASON (VARIETY-BR-29) (a) Grain yield (t/ha) c 4.08 a 3.93 a 3.99 a 3.88 a b 3.85 ab 3.70 a 3.96 a 3.68 a a 3.68 b 3.93 a 3.78 a 3.78 a (b) Straw Yield (t/ha) b 3.87 a 3.51 b 3.73 b 3.04 b a 3.74 a 4.19 a 3.71 b 4.08 a a 3.72 a 3.55 b 4.21 a 4.41 a (c) Field duration (days) T. AMAN SEASON (VARIETY-BR-11) (d) Grain yield (t/ha) b 4.03 a 3.95 a 4.14 a 4.00 a a 3.61 a 4.03 a 4.12 a 4.11 a a 3.57 a 3.59 a 3.89 a 4.11 a (e) Straw Yield (t/ha) a 4.97 a 4.69 a 4.71 a 5.08 a a 5.07 a 5.03 a 4.99 a 5.03 a a 5.04 a 5.02 a 5.05 a 5.06 a (f) Field duration (days) Means of parameters followed by common letter(s) within a column do not differ significantly by LSD at 5% level. 5

6 Table 2. Effect of rates of P-fertilizer application on P content in and uptake by MV rices in a Boro - Fallow - T.Aman cropping pattern under different levels of available soil P. Added P Levels of available soil P (ppm) (Kg/ha) BORO SEASON (VARIETY-BR-29) (a) Grain P-content (%) (b) Straw P-content (%) (c) Total P-uptake (kg/ha) T. AMAN SEASON (VARIETY-BR-11) (d) Grain P-content (%) (e) Straw P-content (%) (f) Total P-uptake (kg/ha)

7 Grain Yield (t/ha/yr) kg P/ha/yr 30 kg P/ha/yr 60 kg P/ha/yr Soil Available P (ppm) Figure 1. Annual grain yield of Boro (BR29) - Fallow - T. Aman (BR11) cropping pattern as affected by rates of P-Fertilization in soils with variable levels of soil available P. P uptake (kg/ha/yr) 0 kg P/ha/yr 30 kg P/ha/yr 60 kg P/ha/yr Soil Available P (ppm) Figure 2. Annual total P uptake by Boro (BR29) - Fallow - T. Aman (BR11) cropping pattern as affected by rates of P-Fertilization in soils with variable levels of soil available P. 7