DETERMINATION OF ECONOMIC NITROGEN RATE, GROWTH, YIELD AND NITROGEN UPTAKE OF TRANSPLANTED AUS VARIETIES

Abstract

A field experiment was conducted at the Agronomy field, Bangladesh Rice Research Institute, Gazipur, Dhaka during the period from April to September 2019 to determine growth, yield, and nitrogen uptake and to determine the economic nitrogen application rates for popular transplanted aus varieties. The experiment was carried out in a randomized complete block design (RCBD) factorial with two factors. Factor A: three varieties as- BR26, BRRI dhan48, and BRRI dhan82; and Factor B: five levels of nitrogen rates as- 0, 40, 60, 80, 100 kg ha ii

-1 . The experimental data shows significance in the individual effect of variety and N rates on the grain yield and yield components but the combined effect of variety and N fertilizer rates was not significant. The grain yields of different varieties in different nitrogen levels would be explained by its panicle density, grains panicle -1 , and 1000-grain weight. The highest panicle m (269.67), grains panicle -1 (106.00) was produced in BRRI dhan48 with N 80 treated plots which the 1000-grain weight (22.85) was produced in BRRI dhan82 with N 80 . The highest grain yield of 5.52 t ha -1 was produced in BRRI dhan48 followed by BRRI dhan82 (4.52 t ha -1 ) and BR26 (4.51 t ha -1 ) with N 80 treated plots. The individual effect of variety and N rate was significant in the case of N concentration, N uptake in grain and straw, and nitrogen harvest index (NHI). Overall, the increased N rate increasing the N concentration of grain and straw irrespective of varieties. The higher N concentration and uptake were observed when N was applied at the rate of N 60 -N 100 kg ha in all the varieties. Among the varieties, BRRI dhan82 should the higher N uptake (61.23 kg ha 1 ) in grain. Higher total N uptake was also observed in BRRI dhan48 at the rate of 80 kg N ha -1 . NHI ranged from 55 to 72 % in different N levels, indicated 55 to 72% of the absorbed N translocated to the grains, and 45% to 32% remained in the dry matter of the varieties. The estimated economic nitrogen dose for maximum yield was determined by regression analysis and found that N rates of BR26, BRRI dhan48, and BRRI dhan82 were 97, 95, and 55 kg ha -1 , respectively. The findings of this study indicated that response of different N rate on three aus varieties was linear upto 80 kg N ha -1 which might be owing to better N uptake leading to a higher number of panicles and grains panicle -1 and that made yield increase, thereafter the response decreased. The study findings of the suggest that variety-specific N fertilization based on soil N status of aus rice is the best N management practice to maximize rice yield avoiding the excess use of N fertilizer.