The field experiment was conducted in Boro season of 2003. The seeds of BRRI dhan28 and BRRI dhan29 were sown in the seed bed on 10 November 2002 and 43-day-old seedlings were transplanted. Except the N which was considered with the treatments, all other cultural and management issues were taken care of for growing an ideal crop.The Treatments were N-fertilization at 3 different levels of SPAD meter readings, a control (no N) and BRRI recommended N dose. Three SPAD-based N management practices (SPAD35, SPAD37 and SPAD40), an N control and BRRI recommended N dose were compared for BRRI dhan28 and BRRI dhan29. In this study, both SPAD and LCC readings were taken at the same date and time with same leaf but the N was applied on the basis of SPAD reading only. The experiment was laid in RCB design with four replications. A detailed description of the treatments is given below:
T1 = N-control (Zero N)
T2 = BRRI recommended N
(Optimum N-dose recommended by BRRI)
T3 = SPAD35 based N management
(N was applied @ 30 kg ha-1 when SPAD meter reading became ≤ 35).
T4 = SPAD37 based N management
(N was applied @ 30 kg ha-1 when SPAD meter reading became ≤ 37).
T5 = SPAD40 based N management
(N was applied @ 30 kg ha-1 when SPAD meter reading became ≤ 40).
The SPAD meter readings were collected at seven days interval starting from 24 days after transplanting and continued up to 87 DAT. SPAD readings were taken at 24, 31, 38, 45, 52, 59, 66, 73, 80 and 87 DAT for both the test varieties. Nitrogen (as prilled urea) was applied @ 30 kg N ha-1 when the mean SPAD readings were found equal or below the predefined threshold levels. Treatments T3, T4 and T5 received a basal N application of 10 kg ha-1. In addition to SPAD, LCC readings were taken from the same leaves on the same dates and almost the same time.