Abstract:
A field experiment was conducted at “Choba” on-farm, Gimbo district in Kaffa zone,
Southwestern Ethiopia during the 2015 main cropping season to determine optimum rate of N
application and the best variety based on N uptake, N use efficiency, and yield and yield
components of upland rice. A 4x4 factorial experiment was carried out using split plot design
with three replications. The treatments consisted of four rice varieties as main plot factor and
four N rates considered as the sub-plot factor. The analysis of variance revealed that variety
and N rate were significantly (P < 0.05) different for all parameters studied in the location.
Moreover, the interaction between variety and N rate was significantly (P < 0.05) different
for tiller and panicle numbers, total and filled spikelets per panicle, grain yield, biological
yield, grain harvest index as well as N use efficiency parameters except N concentration in
grain and straw at maturity. The interaction effect showed that highest number of tillers 266.0
and 260.7 per square meter recorded for NERICA-4 and Suparica-1, respectively at 69 kg N
ha-1
. NERICA-4 produced the highest number of panicles (227.3) followed by Suparica-1
(220.0) at 69 kg N ha-1
. Likewise, these two varieties were also produced the highest number
of filled spikelets per panicle at 69 kg N ha-1
, and gave 114.3 and 111.7 for Suparica-1 and
NERICA-4, respectively. However, all tested varieties produced highest number of total
spikelets per panicle when the N rate exceeds 46 kg N ha-1
indicating the higher production of
unfilled spikelets at increased N rate in low yielded varieties. Besides, the highest grain yield
of 4589.00 and 4575.00 kg ha-1
was also recorded for both NERICA-4 and Suparica-1,
respectively at 69 kg N ha-1
. The application of N fertilizer increased total N concentration
and uptake in grain and straw at maturity, while decreased agronomic (ANUE), physiological
N use efficiency (PNUE) and Apparent N recovery (ANRE %) except Suparica-1. The highest
ANUE, PNUE and ANRE (%) was obtained at the rate of 46 kg N ha-1 for Suparica-1and at
23 kg N ha-1 for NERICA-4. The correlation analysis was also indicated that positive and
highly significant associations between grain yield with yield components and N uptake at
maturity. Overall, varieties Suparica-1 and NERICA-4 were more efficient in producing grain
yield with the highest ANUE, PNUE, as well as, ANRE as compared to other varieties in the
location. However, based on partial budget analysis the highest Marginal Rate of Return
(MRR) was recorded for Suparica-1 and NERICA-4 at 46 kg N ha-1
. Therefore, it is possible
to conclude that varieties Suparica-1 and NERICA-4 at 46 kg N ha-1 recommended for
cultivation in the study area. However, repeating the experiment over years by increasing the
N levels would help to draw sound recommendations. Hence, future studies should look into
these issues to validate the current results in the location.
