The low yield of wheat in the country may be due to the use of low-yielding varieties, inadequate and erratic rainfall, diseases, low soil fertility and waterlogging in the Vertisol areas [ 6 ]. Vertisols occupy about These soils are characterized by very low water infiltration rate or low saturated hydraulic conductivity and, therefore, are susceptible to waterlogging under high-intensity rainfall conditions. In addition, the Ethiopian Vertisols tend to exhibit low total N content mainly due to leaching and denitrification [ 7 ] limiting wheat production; hence, application of N is one of the major inputs used by farmers to achieve desired crop yields on these soils [ 8 ].
The remainder of the applied N is lost to the soil through leaching and runoff, where the often excessive application can affect natural ecosystems through N pollution.
Loss of N also contributes to significant direct economic losses to the grower particularly when N fertilizer costs are high [ 9 ]. Thus, the application of the appropriate rate of N fertilizer is considered to be a primary means of increasing wheat grain yield, in improving N uptake and use efficiency and consequently nitrogen harvest index [ 10 ]. Many studies have shown genetic variation of wheat in nitrogen utilization efficiency NUtE and nitrogen uptake efficiency NUpE and nitrogen recovery efficiency NRE [ 11 ] and that the use of the best-adapted genotype can contribute to improved efficiency in how cereal crops acquire and use soil N or fertilizer N.
The studies showed that interactions of genotype and nitrogen supply affect NUE. However, improved varieties are often developed without considering their ability to grow and yield under low soil nutrient status and have been selected for high yield under high nutrient input conditions [ 12 ].
In contrast, the use of modern wheat cultivars can contribute to improve nitrogen use efficiency [ 13 ]. In addition, studies indicate that the development and use of wheat cultivars with higher NUE can contribute to reducing the amount of nitrogen to be applied without decreasing grain yield [ 14 ]. Therefore, selection of wheat varieties with high NUE on the basis of agricultural practices could increase economic return and reduce environmental pollution.
In Ethiopia, wheat is grown during high rainfall season and loss of applied N through leaching, denitrification and runoff especially in Vertisols is the major factors which resulted in inefficient use of N fertilizer [ 15 ].
Such overuse of nitrogenous fertilizers can be a major source of environmental pollution ground water pollution , due to nitrate leaching and runoff [ 17 ], and is costly. These drawbacks have motivated in making important changes in recent fertilization practices such as use of reduced amount of nitrogen fertilizer in combination with wheat varieties with elevated nitrogen use efficiency.
However, limited research has been done on the effects of N rate in relation to genetic variations for NUE in Ethiopia. Therefore, the present study was conducted to evaluate the effect of nitrogen application on grain yield, nitrogen uptake and nitrogen use efficiency of wheat varieties at Enewari, central highlands of Ethiopia. The study was conducted for two consecutive years from July to December during the and main cropping seasons in the district of Moretina-Jiru at the Enewari experimental field station in the central highlands of Ethiopia.
This area is typical of the rain-fed wheat-growing regions of Ethiopia with average annual rainfall of The dominant soil type of the area is Vertisol known for its high waterlogging and drainage problems. Rainfall in the study area varied considerably between the two growing years.
The total rainfall during the cropping season July—December was Differences in temperatures between the two growing seasons were relatively modest Fig.
Prior to planting, surface 0—20 cm soil samples, from ten spots across the experimental field, were collected, composited and analyzed for soil physicochemical properties at Debre Berhan Agricultural Research laboratory and results are presented in Table 1. Monthly total rainfall and mean maximum and minimum temperatures in and growing seasons at Enewari, central highlands of Ethiopia.
Three popular bread wheat varieties, namely, Menze, Tsehay and ET, were used as a test crop. ET is a tall variety, while Tsehay and Menzie are medium in height. All of them are recommended for the area as they are high yielding and resistant to yellow rust.
The plot size for planting was 1. Four central rows with a net plot size of 2. The distance between the plots and blocks were kept at 0. The experimental plots were prepared by tractor plowing and harrowing. In accordance with the specifications of the design, a field layout was prepared and each treatment was assigned randomly to experimental plots within each block independently.
Plots were kept free of weeds by hand weeding. No insecticide or fungicide was applied since there was no outbreak of insects or diseases. Harvesting was done manually using hand sickle. The dried samples were milled, and the grain and straw N content of the plant samples were determined using the micro-Kjeldahl method as stated by American Association of Cereal Chemists AACC [ 20 ]. Total nitrogen uptake TNU was calculated as the sum of the respective Ng and straw nitrogen uptake values.
Then, nitrogen recovery and nitrogen use efficiency by the crop were determined using the formulae described by Fageria et al. Finally, the nitrogen harvest index NHI was determined as the ratio of nitrogen uptake by grain and nitrogen uptake by grain plus straw as described by Fageria et al. After verifying the homogeneity of error variances, combined analysis of variance was done using the procedure of SAS [ 22 ]. The analysis of variance for grain yield showed significant difference between years, and among nitrogen rates and varieties.
This implies genotypes differ in absorption, and utilization of N depends on the environment. Grain yield is the function of genotype, environment and genotype—environment interaction [ 24 ]. In addition, the application of nitrogen increased drastically grain yield of the varieties tested as compared to the control in both growing years.
The increase in yield of the varieties with increasing N rates up to adequate level might be due to the role of N in increasing the leaf area and promote photosynthesis efficiency which promote dry matter production and increase yield. In line with this, improvements in wheat yield and its components under the acceptable increasing N rates were reported by Sticksel et al.
This might be attributed to the tall growth nature of the variety and the favorable amount rainfall during which increased N uptake efficiency and induced excessive vegetative growth at the highest N rate, and therefore, early lodging of ET was observed. This result is in line with [ 26 ], who reported that excess application of N resulted in lodging of wheat and caused a dramatic yield decrease. Furthermore, Ercoli et al. However, variety ET had increased yield with the highest N rate in as compared to Table 4.
In general, varieties Menze and Tsehay were high yielders as compared to the variety ET in both growing years. This implies that the two recent varieties were less resistant to waterlogging which occurred in as compared to High rainfall in might have aggravated the waterlogging effect which causes either incomplete remobilization of nitrogen or a reduction in the amount of nitrogen available for remobilization [ 28 ].
Waterlogging due to higher rainfall resulted in the leaching of nitrate below the rooting depth of crops and denitrification, a major loss of N fertilizer that can reduce grain yield. Similarly, there is a strong interaction between waterlogging and crop fertilizer response, with an inefficient use of available N in years characterized by high rainfall [ 29 ]. A lower N uptake in wheat crop resulted in a decrease in grain yield [ 28 ].
Nitrogen concentration in straw was significantly affected by the main effects of year, N rate and variety as well as by the interaction of N rate and variety. The highest amount of straw nitrogen concentration 0. However, the lowest nitrogen concentration in straw 0. The higher N concentration of straw with the increase in N rate might be due to the availability of sufficient nitrogen for the crop which might increase N concentration in the biological yield especially straw because of healthier roots and greater density.
The increase in straw N concentration observed with increasing N input is in agreement with the results of Worku et al. The result also showed that Tsehay and Menze varieties proved to contain the highest N concentration in their straw at the highest N rate compared with variety ET This could be due to a better genetic response of Menze and Tsehay varieties to applied N. But, the three-way interaction effect of year, N rate and variety for grain N concentration was not significant Table 3.
However, the lowest amount of nitrogen concentration in the grain 1. The highest grain nitrogen concentration in variety Tsehay at the highest N rate might be due to its better genetic response to the applied N and translocation of the absorbed N to the grain.
Similarly, Lopez-Bellido et al. The increase in grain nitrogen concentration of the varieties at highest N rate might be due to the sufficient availability of nitrogen that increased N mobilization to the grain at grain filling stage. In agreement with this result, Sinebo et al. In general, as compared to the year grain nitrogen concentration of variety Menze and variety Tsehay increased in in contrast to variety ET The increment was 8. Agricultural Research.
Strong, W. Effect of late application of Lindquist, J. Dielman, D. Mortensen, nitrogen on the yield and protein contact of G. Johnson and D. Wyse-Pester, Australian journal of experimental Economic importance of managing spatially agriculture and animal husbandry. Weed Wagner, N. Maxwell, M. Taper and Technology. Developing an Empirical Martin, M. Field and R. Field, McMullan, P. Daun and D. Declercq, Wilson, B.
Cousens and K. Ann Applied tolerant and Triazinesusceptible Canola Biology. Brassica napus and Brassica rapa. Canadian Mohamed, R.
Enan, Genotoxicity Journal Plant science. Mohajeri, F. Competition 2,4-D : Higher plants as monitoring systems, of different densities of wild mustard Brassica American-Eurasian Journal of Sustainable kaber with winter wheat Triticum Agriculture.
E-Kivi, M. E-Somarin, The Olaniyi, J. Ajibola, Phosphorus Fertilizers Application, American- Khan, G. Amanullah, Levels of Nitrogen Alone and in Combinaiton Eurasian Journal of Sustainable Agriculture. Ademiluyi, B. Omotoso, Comparative Evaluation of Tithonia diversifolia Liasu, M.
Ogundare, M. Ologunde, and NPK Fertilizer for soil improvement in Lei, L. Jiao and Y. Yan, Evaluating Journal of Sustainable Agriculture.
Zarea, M. Ghalavand, E. Mohamadi Eurasian Journal of Sustainable Agriculture. Rejali, Zahra Tabibzadeh 2 2 : Ghamsari, Green Manure, Mycorrhizas These studies have also shown that regardless of the year, yields did not increase above a spring rate of lb N per acre. Wheat generally does not benefit from a nitrification inhibitor since temperatures are relatively cool at application time and the application is made to a growing crop, this is especially true as the crop approaches Feekes GS 6.
However urea may benefit from a urease inhibitor products containing NBPT if conditions for volatilization exist for several days after application. Urea applications need at least a half inch rain within 48 hours to minimize volatilization losses unless temperatures remain relatively cool. The urease inhibitor will prevent volatilization for 10 to 14 days with the anticipation of a significant rainfall event during this time.
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