The grain yield response of different varieties to K was quadratic in nature. The quadratic yield response curve of different varieties was explained by following equations:
Y= 2.6323 + .03020K -0.0002K2 for BRRI dhan31
Y = 3.342 + .0245K - .00001K2 for BRRI dhan32
Y = 3.1006 + .0377K -.0003K2 for BRRI dhan40
Y = 3.2277 + .0438K -.0004K2 for BRRI dhan42
The calculated rate of K that maximizes yield was 86, 91.5, 121.3, 55.7 in BRRI dhan31, BRRI dhan32, BRRI dhan40, BRRI dhan41. The estimated grain yield with 86, 91.5, 121.3, 55.7 kg K/ha would be 4.09, 4.47, 4.34 and 4.73 t/ha respectively. The calculated economic optimum rate was 79,77.5,86.3 & 53.1 kg K/ha in BRRI dhan31, BRRI dhan32, BRRI dhan40, BRRI dhan41,respectively. The estimated grain yield with 79, 77.5, 86.3 & 53.1 kg K/ha would be 4.08, 4.45, 4.29 & 4.73 respectively.
In the boro season05, two popular BRRI modern varieties(BRRI dhan28, BRRI dhan29) and two promising breeding lines (BR6144-36-5-2 and BR4828-54-4-1-4-9) were tested with same K fertilizer doses as T. Aman season. A flat dose of N P S @ 145-25-24 kg/ha respectively was applied on STB.
In Boro season, rice yield increased with increasing K dose. All varieties produced highest yield at K80 treatment. Similar trend also observed in straw yield.
The grain yield response of different varieties of K was quadratic in nature. The quadratic yield response curve of different varieties was experined by the following equations:
Y = 3.7567 + 0.0477x - .0003x2 for BRRI dhan28
Y = 4.1704 + .065x -.0009x2 for BRRI dhan29
Y = 2.6838 + .1187x - .0009x2 for BR6144-36-5-2
Y = 3.6897 + .0497x - .0004x2 for BR 4828-54-4-1-4-9