Abstract:
Decline in soil fertility is a major constraint in Abol Woreda of Gambella region due to the
continuous cropping, removal of crop residues after harvest, poor application of organic
manures to soils, etc. The scientific information available concerning the response of upland
NERICA-4 rice variety to rates of N and P fertilizers in Gambella for its optimum productivity is
limited. Therefore, a field experiment was carried out during the 2014 cropping season at Abol
woreda, Gambella, southwestern Ethiopia to investigate optimum rates of N and P fertilizers for
highest yield of rice. The treatments consisted of factorial combinations of four rates of N (0, 46,
92, and 138 kg N ha-1) and P (0, 23, 46, and 69 kg P ha-1) was laid out in a randomized
complete block design (RCBD) with three replications. The effects of Nitrogen were significantly
(P ≤ 0.05 ) difference for harvest index and significantly (P ≤ 0.01 ) differences for 1000-grain
weight, plant height, panicle length, grain yield, straw yield, number of filled spiklets and
unfilled spiklets, productive tillers, number of tillers and Dry grain weight. On the other hand,
many growth, yield, and yield components did not differ significantly (P > 0.05) due to
application of P except number of unfilled spikelets, straw yield, and grain yield. Conversely, the
interaction of N and P was significant (P ≤ 0.01) for all yield and yield components except straw
yield, harvest index and panicle length. Application of N and P significantly (P ≤ 0.01) increased
grain yield of rice up to the level of 92 kg N and 69 kg P ha−1
. Highest grain yield (6.053 t ha-1
)
was obtained with the combined application of 92 kg N and 69 kg P ha −1
, and the yield
advantage over the control was 113.66% (3.22 t ha-1
). The economic analysis revealed that 92 kg
N ha-1 with all rates of P (0, 23 and 46 kg) gave highest net benefits. Grain yield was
significantly and positively correlated with straw yield (r = 0.66**), productive tillers (r =
0.423**), plant height (r = 0.632**), grain weight (r = 0.54**), panicle length (r = 0.453**),
number of spikelets per panicle(r = 0.441**) and Number of filled grain (r = 0.362**). This
indicates that N and P increase grain yield of rice by positively affecting the important yield
components. Therefore, as a recommendation, farmers in the study area can apply 92 kg N ha-1
with no phosphorus application to improve the grain yield of rain-fed NERICA-4 rice as well as
for highest economic benefit.
