YIELD AND PHOSPHORUS EFFICIENCY OF SOME LOWLAND RICE VARIETIES AT DIFFERENT LEVELS OF SOIL-AVAILABLE PHOSPHORUS

A field experiment was conducted on an Aeric Haplaquept soil to study the effect of phosphorus (P) deficiency in soil on the P nutrition and yield of five modern varieties of rice, viz., Purbachi, BR1, BR3, BR1 4, and BR29, popular with the rice farmers of Bangladesh. Soil-availab le P in the different plots of the experimental field varied widely, f rom 2.8 to 16.4 ppm. This plot to plot variation in soil-available P c ontent resulted from differences in the total amounts (0 to 480 kg ha( -1)) of P the plots had received over a period of 8 years in a long-te rm P fertilizer trial conducted previously in the same field. Phosphor us deficiency in soil drastically reduced the grain yield of all the r ice varieties. In severely P deficient plots, where soil-available P w as around 3 ppm, the yield was less than 1 ton ha(-1) while in plots c ontaining an adequate P level, i.e., >6 ppm, the yield was more than 4 t ha(-1). Rice yield increased linearly with an increase in soil P co ntent up to 6 ppm, and the highest grain yield for any variety, obtain ed at 6-7 ppm of soil-available P leveled off at this point. Soil P de ficiency not only decreased rice yield severely but also decreased P c ontent in straw and grain drastically. However, differences among rice varieties were noted in P nutrition, particularly at low soil P level s. The rice varieties differed markedly also in respect of internal P efficiency. The BR29 showed the highest internal P efficiency both at low and high soil P levels. In all the rice varieties, internal P effi ciency decreased with an increase in soil P levels.