Abstract:
– Insufficient nitrogen supply in inappropriate
timing is an important constraint to productivity of upland
rice (Oryza sativa L.), and there is limited information
available on optimal timing of N application for upland rice
in Ethiopia including Jimma area. Field experiment was
conducted on three upland rice varieties (Gumara, Ediget
and Nerica-4) in a completely randomized block design with
3 replications to determine the effects of timing and ratio of
nitrogen application on growth and yield during the 2014
cropping season on acidic nitisol (soils possessing nitic
property) at the Jimma University, College of Agriculture
and Veterinary Medicine research site. The N-timing
treatments were: N1
(50% at sowing and 50% at active
tillering stage), N2
(25% at sowing + 50% at active tillering
stage and 25% at panicle initiation), N3
(25% at sowing +
25% at active tillering stage and 50% at panicle initiation),
and N4
(33% at sowing + 33% at active tillering stage and
33% at panicle initiation). The highest grain yields (1070
kg/ha), biomass yields (3333 kg/ha), total number of grains
per panicle, and harvest index were recorded from ‘Ediget’
variety at the N2 combination (25% at sowing + 50% at
active tillering stage and the remaining 25% at panicle
initiation), followed by N3 and N4 combinations. The lowest
grain yields (117 kg/ha) and biomass yields (767 kg/ha) were
recorded from Nerica-4 variety at the N2 combination.
Nerica-4 variety produced minimum grain and biomass
yields across all the N combinations. Most of the parameters
exhibited maximum performance under N2 and N3
combinations across all the varieties. The varietal treatments
had highly significant (P<0.001) effects on the total number
of panicles, grain yield, biomass yield and harvest index.
Grain yield was positively correlated (P<0.01) with plant
heights (r=0.68**), number of filled grains per panicle
(r=0.52**) and thousand grains weight (r=0.61**) and
negatively correlated with most of the traits. Number of
panicles was the most important component of yield,
accounting for about 87% of the variation in rice yield. Thus,
rice cultivation and its nitrogen fertilizer management in the
area is concerned, the variety ‘Ediget’ was recommended for
higher grain and biomass yields regardless of the N-timing
treatments. Concerning the N-timing treatments, the fa
