Nitrogen response and agronomic use efficiency of N fertilizer in diverse commercial maize hybrids at Bako, Western Ethiopia

Agronomic Effi ciency indicated the grain yield production potential of variety in response to the applied nutrients. Field experiment was conducted at the research Farm of Bako National Maze Research Center Western Ethiopia during 2020/2021 in order to investigate the nitrogen response and agronomic effi ciency of various maize genotypes. Ten maize varieties were tested under two level of nitrogen (N1 = 0 kg/ha and N2 = 184 kg/ha) in factorial arrangement with three replications. Each variety was planted in uniform spacing of 75x30 cm. Then response of each variety for the applied nitrogen were evaluated. Agronomic effi ciency of Nitrogen Fertilizer associated with grain yield of various commercial maize varieties was calculated using average grain yield and applied nitrogen to indentify the agronomic effi ciency of each maize varieties. Based on calculation result maize hybrid BH661 showed the highest agronomic effi ciency (35.42), where as Gibe3 showed the lowest value (4.68) compared to others tested varieties. This result indicated that Gibe3 respond poorly for the applied nitrogen where as Hybrid BH 661 highly responded for the increasing applied N input. The result has indicated the need of specifi c recommendation for nutrient scarce area, that lack nitrogen or for farmers who lacks money to buy nitrogen fertilizer should be used Gibe3 to get better yield. On other hand in optimum or high nitrogen available condition the hybrids which have high agronomic effi ciency should be sown to boost maize grain yield but with taking into account the optimum rain fall and agro ecology of each variety. Research Article Nitrogen response and agronomic use effi ciency of N fertilizer in diverse commercial maize hybrids at Bako, Western Ethiopia Begizew Golla* Bako National Maize Research Center, Ethiopian Institute of Agricultural Research, P. O. Box 2003, Addis Ababa, Ethiopia Received: 29 July, 2021 Accepted: 21 August, 2021 Published: 24 August, 2021 *Corresponding author: Begizew Golla, Bako National Maize Research Center, Ethiopian Institute of Agricultural Research, P. O. Box 2003, Addis Ababa, Ethiopia, E-mail:


Introduction
The importance of nitrogen for plant growth and productivity is increasingly being recognized, and in many cases it is considered as the most growth and yield limiting factor [1]. The application of fertilizer to improved germ-plasm on responsive soils will boost crop yield and improve the agronomic effi ciency [2]. However, various maize genotypes respond differently for the applied nitrogen. High yielding maize genotypes performed well where N supply is suffi cient [3], whereas some hybrids have shown better performance under different N-levels due to their ability to capture N from both pools (Fertilizer and soil N) more effectively than the susceptible ones [4,5]. The selection of genotypes with adaptation to low N and high N input levels requires an interaction between genotypes and N levels [6].
Therefore, it is necessary to evaluate maize hybrids under the condition of distinct availability in order to be able to identify the more promising hybrids for each condition [7].
The general nitrogen fertilization for maize production in Ethiopia has not been verifi ed the response and agronomic effi ciency of each variety. This blanket N recommendation for all maize varieties leads to insuffi cient N application for highly responding high yielding varieties and excess application with economical and environmental impact for low effi cient and low yield varieties. Therefore to identify their yield response for the applied nitrogen it requires refi ning agronomic effi ciency of each variety under different level of nitrogen. The effi ciency and responsiveness of agronomic traits to the main macronutrients is becoming increasingly important due to the risk of supply, as it is a fi nite resource [7]. Since most portion of N lost through leaching, N application should be synchronized with crop need [8,9]. The yield potential of maize continuously shifted with 20 cm plant spacing and 75 cm row spacing. Replanting was done a week after planting if there were missing holes. Full dose of phosphate fertilizer in the form of TSP at the national recommended rate of 69 kg P 2 O 5 ha -1 was applied uniformly to all plots. Half dose of N fertilizer was applied 22 days after sowing and the remaining half dose of N fertilizer was applied 37 days after sowing in side-banding application method. Hand weeding and other crop management practices were applied uniformly to all plots as per the recommendation for maize.

Data recorded
Plant height (cm): It was measured from the soil surface to the base of the tassel of ten randomly taken plants from the net plot area at physiological maturity. Finally, agronomic Effi ciency (AE) was calculated from harvested grain yield and applied nitrogen by using the formula Na [13][14][15]: Where, Gf = grain yield of the fertilized plot (kg), Gu = grain yield in the unfertilized plot (kg) and Na = quantity of nitrogen applied (kg).

Soil sampling and analysis
Pre-planting soil analysis was done in order to understand modifi cation of plant density and nitrogen level because of high mobile nature of available nitrogen and continues releasing of new hybrid with high nitrogen requirements [10]. In addition most small house holders have cultivated maize without nitrogen application or with insuffi cient amount of nitrogen due to lack of money to buy fertilizer. Identifying maize varieties which produce better yield under low or no nitrogen application will provide alternative for these small house holders. Maize is mostly grown by resource-poor farmers who cannot afford to fertilize at optimum rates and till now very little effort was made in developing maize genotypes that suit the needs of small-scale farming systems [3].
Food security in Ethiopia, and elsewhere in Africa, is a major socio-political issue on which economic wellbeing is depends on the success of its agriculture [11]. In developing country, particularly in Ethiopia maize is grown majorly for the purpose of food security that emphases on grain production. Maize is one of the major and strategic cereal crops that play an important role in food security and farmers' livelihoods in Ethiopia [12]. Nitrogen Agronomic Effi ciency refers the amount of additional grain harvested per kilogram of nitrogen applied to a grain crop. Thus studding agronomic effi ciency that refl ects the direct production impact of an applied fertilizer is most effective to achieve the goal of grain production or food security.
The aim of this study was to observe the nitrogen response and agronomic effi ciency of various commercial maize varieties.

Description of experimental site
The experiment was conducted at Bako Research farm in 2020 to 2021. Bako located at 9º 06' N Latitude and 37º 09' E Longitude. It has mid altitude sub-humid agro-ecological with altitude of 1650 m.a.s.l. The soil type is dominantly nitosol.

Experimental materials
Fertilizer: Nitrogen fertilizer in the form of urea (46% N) was used for this experiment. Triple Supper phosphate (TSP) fertilizers were used as a source of Phosphorus.

Treatments and experimental design
Two levels of N fertilizer (N1 = 0 kg/ha and N2 = 184 kg/ha) were used for this experiment. The levels of the two factors (N levels and cultivars) were combined in factorial arrangement with three replications. The gross plot size was 5 m× 4.5 m (22.5 m 2 ) with row length of 5 m, but net plot size 5 m × 3 m (15 m 2 ) was used for harvesting to minimize the border effects on the crop yields. The treatments were randomly assigned to the experimental unit within a block (replication). The replication was separated by 2 m wide space.

Statistical analysis
Analyses of variances for the data recorded were conducted using the SAS version 9.3. Least signifi cant difference (LSD) test at 5% probability was used for mean separation if the analysis of variance indicated the presence of signifi cant treatment differences.

Results and discussion
The analysis of variance revealed a signifi cant (P<0.01) effect of nitrogen on plant height, fl owering date, number of ears, kernels per ear and grain yield of maize varieties.
As indicated in Tables 1,2 all maize genotype responded positively for all parameters when nitrogen level changed from 0kg/ha to 184 kg/ha. Plant height was increased with increased nitrogen where as tasseling and silking date were shortened with increased nitrogen (Table 1). This could be due to the positive effect of nitrogen for rapid growth that resulted reduction in day to tasseling and silking. Similar results were reported by [16,17]. In addition the response varied among each variety. The highest value of plant height, day to tasseling and silking where recorded at hybrid BH66 (Table 2). BHQPY545 produced highest number of ears when nitrogen increased from 0 to 184 kg N/ha where as the highest number of kernels per ear was recorded at hybrid BH549 (Table 3). However, number of kernels per ear was increased when nitrogen level increased (Table 3). These results are in agreement with those of many other workers [1,18,19].
The result also showed that some varieties has not bring any signifi cant change in their grain yield when N level increased from 0 to 180 kg N/ha, whereas most varieties showed highly signifi cantly difference in their grain yield when N level increased. Compared the grain yield of each variety under 0 kg N/ha and under 180 kg N/ha three varieties (Gibe3, BH549 and Limu) showed the lowest response for the applied N. These varieties showed non-signifi cant grain yield difference between 0 kg N/ha and 180 kg N/ha application that consequent the lowest agronomic effi ciency (Table 3).
On other hand the rest varieties showed highly signifi cant yield difference under 0kg N/ha and 180 kg N/ha that consequent the highest agronomic effi ciency (  [4,5].

Conclusion
This result indicated the response of hybrids for the applied nitrogen. So under optimum or high nitrogen available condition the hybrids which have the highest agronomic effi ciency such as BH661 should be sown to boost maize grain yield, whereas under the no N in put condition or for the farmer who have not enough money to buy fertilizer it is better to use varieties with low agronomic effi ciency such as Gibe3, which gives better yield without nitrogen application. But with considering other production factors and their adaptation range such as altitude and rain fall. Although these results were based on single growing season and single location it gives clue the varieties effi ciency for the applied N.