where αis the plant growth value at panicle initiation and ß is
the N fertilization rate at panicle initiation stage. Plant growth
value was calculated by the product of plant height (cm) the
number of tillers per m2 x SPAD reading. These readings were
calculated as the average value of 20 plant samples replicated at
three locations within each field. All P2O5 fertilizer and 70% of
K2O fertilizer were applied with basal N fertilizer before paddy
field preparation, and 30% of K2O fertilizer was applied mixed
with N top-dressing fertilizer prescribed by plant growth analy-
sis at panicle initiation stage. Upper limit of N was 120 kg ha-1 to
avoid heavy fertilization and P2O5 and K2O was limited to a
minimum of 30 kg ha-1 when large quantities of available P2O5
and K2O existed in the paddy field soil.
Basal fertilizers were applied from 14 to 15 May and incor-
porated into soil by puddling. Twenty-six-day-old rice seedlings
were transplanted over 8 days with row spacing of 30 cm and