Determination of Nitrogen Rate for Optimum Yield, N Uptake and Use Efficiency of Upland Rice (Oryza sativa L.) Varieties at Gimbo District, Southwestern Ethiopia”

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.