The crop production in Ethiopia is markedly constrained by soil nutrient depletion and limited fertilizer input. Nitrogen is among the most yield-limiting factors of cereal crops, especially in sub-Saharan Africa (SSA). A meta-analysis of 82 studies was carried out to evaluate the response of major cereal crops, viz. wheat, maize, barley, teff, and sorghum, to nitrogen fertilization in Ethiopia. The results showed that N-application significantly increased yields of all the five crops examined herein. The average yields of the treatment effects over controls for the five crops were 3775.8 kg ∙ha −1 and 2593.3 kg ∙ha −1, respectively. The overall yield response to nitrogen treatments for all the crops was 64.8% (wheat, 96.5%; maize, 40.65%; barley 84.36%; teff, 50.48%; and sorghum; 23%). Overall, nitrogen agronomic efficiency (AE N) and partial factor productivity (PFP N) were 18.2 and 71.81 kg ∙kg −1, respectively. A downtrend of nitrogen use efficiency with an increase in N rate was realized. The yield response was higher for the nitrogen treatment effects of >100 kg ∙N ∙ha −1 (123.9%), clay soils (75.46%), low initial soil organic carbon (SOC) and available phosphorous (AP) (92.4% and 101.6%), respectively, Therefore, we recommend the application of nitrogen fertilizer (>100 kg ∙N ∙ha −1), especially on infertile soils for improved grain yield and NUE in aforementioned cereal crops in Ethiopia and similar regions in sub-Saharan Africa (SSA).
Food insecurity is one of the major concerns, particularly in sub-Saharan Africa (SSA) given the escalating population, climate change and persistently stagnated crop yields [
Although the government of Ethiopia allocates about 10% of its total expenditure to the agricultural sector (which is the benchmark of New Partnership for Africa’s Development (NEPAD) for sub-Saharan Africa); the productivity of cereal crops is below the global average due to several biotic and abiotic factors [
The use of chemical fertilizer in arable land in SSA and specifically in Ethiopia is far below the global average. The average fertilizer use in Ethiopia remains 16 kg∙ha−1 and it is about 34 kg∙ha−1 in maize production [
Nitrogen fertilizer is the most limiting factor of the growth and development of crops and it is an essential macronutrient required in large amounts [
Understanding the crop response and NUE to nitrogen fertilizer application is an important aspect of developing a strategy of site-specific soil nutrient management and optimized fertilizer recommendation [
In the present study, the effect of N-application on yield and the NUE of the top five cereal crops (maize, teff, wheat, barley, and sorghum) was evaluated. The overall effect of nitrogen fertilizer on yield and NUE and the magnitude of yield response due to different explanatory factors was presented using a quantitative approach.
Peer-reviewed articles published from 1996 to 2020 were accessed from Google Scholar, ScienceDirect, ResearchGate, and Francis and Taylor databases. We used the search string (maize* OR corn* OR wheat* OR sorghum* OR teff* OR barley*) AND (nitrogen* OR nitrogen fertilizer* OR nitrogen use efficiency*) AND (yield*) AND (Ethiopia*). For a study to qualify in this meta-analysis, the following selection criteria had to be met:
· the study was conducted in the field, not pot or greenhouse experiments
· each treatment had a minimum of three replications
· the study reported grain yield and/or NUE
· the experiment was conducted in Ethiopia, and
· experimental and control treatments were applied to the same agricultural site and system.
Results presented in graphs were extracted using GetData Digitizer 2.26 software (http://getdata-graph-digitizer.com/). Overall, 82 studies that met the aforementioned criteria qualified for the final database (see Table1 and TableS1 in supplementary information). Finally, the experimental sites of the studies included in this meta-analysis were plotted using ArcMap 10.4 (ESRI, 2018) (
Relevant variables were dissected and included in our database to assess the magnitude of yield response (
Crops | Number of studies | n | Minimum | Maximum | Treatment yield (mean ± SD) |
---|---|---|---|---|---|
Barley | 14 | 151 | 805.6 | 9804 | 3111 ± 1539 |
Maize | 17 | 257 | 1494 | 10,900 | 5627.6 ± 2298 |
Sorghum | 12 | 136 | 386 | 5929.7 | 2997.5 ± 1025 |
Teff | 13 | 129 | 663.6 | 3680 | 1670.1 ± 640.6 |
Wheat | 26 | 341 | 1087.8 | 8161 | 3781.5 ± 1298.8 |
Overall | 82 | 1014 | 386 | 10,900 | 3775.8 ± 2006.4 |
n: number of observations; treatment yield: +N yields; minimum, maximum and the average treatment yield was expressed in kg∙ha−1.
Variables | Groups | |||
---|---|---|---|---|
1 | 2 | 3 | 4 | |
N-rate (kg∙ha−1) | <30 | 30 - 60 | 60 - 100 | >100 |
MAP (mm) | <700 | 700 - 1100 | >1100 | |
MAT (˚C) | <16 | 16 - 22 | >22 | |
Soil texture | Clay | Loam | Sand | |
Soil pH | <6 | 6 - 7 | >7 | |
AP (mg∙kg−1) | Extremely low | Low | Moderate | High |
SOC (g∙kg−1) | Extremely low | Low | Moderate | High |
yield under N-fertilizer application. The annual temperature ranged from 11.6˚C to 33.5˚C, whereas MAP ranged from 249.2 to 1800 mm. The percentage clay content was used to categorize the soil textural classes if it was not directly indicated in the study according to [
The percentage yield response, the yield obtained from the application of nitrogen fertilizer over control, was estimated as indicated in Equation (1). In order to determine the robustness of the study, sensitivity analysis of the response ratio (RR) i.e., the ratio between the yield on the nitrogen applied plot and control plot, was performed, using the standard procedure to evaluate the overall effect sizes as given in Equation (2). The RR distribution of cereal yield response under N-application is not a typical normal distribution (p < 0.05) (
% Y R = ( Y t − Y c Y c ) * 100 (1)
ln ( R Y ) = ln ( Y t Y c ) (2)
where YR, Yt, and Yc are yield responses, the grain yield of N-applied and N-omitted (control) yield, respectively.
The meta-analysis was performed in SPSS statistic version 22 and all plots
were designed in Sigma-Plot version 12.5 software. The mean effect size and bias-corrected and accelerated/BCA i.e., the 95% confidence interval (CI) for each categorical variable, were generated by bootstrapping at 4999 iterations in SPSS software. Differences between treatments (N-applied) and controls (N-omitted) were considered as significant (p < 0.05) if the 95% CI did not cross the line of zero effect (either a significant increase or decrease) and non-significant if it crosses the line of zero effect.
Overall, the application of nitrogen fertilizer significantly (p<0.05) lifted the average yield of all the crops to 3775.8 kg∙ha−1 (64.8%) when compared to the control treatments which had 2593.3 kg∙ha−1 (
The AEN and PFPN to nitrogen fertilization were presented in
The average AEN and PFPN values across all studies were 18.2 and 71.81 kg∙kg−1, respectively. Also, AEN and PFPN were declined with the increase of the N fertilizer. At N rates of <30, 30 - 60, 60 - 100, and >100 kg∙ha−1, the AEN values were 23.42 kg∙kg−1, 19.21 kg∙kg−1, 16.43 kg∙kg−1, and 14.35 kg∙kg−1, while PFPN were 139.5 kg∙kg−1, 74.14 kg∙kg−1, 51.93 kg∙kg−1, and 32.24 kg∙kg−1, respectively. Moreover, AEN and PFPN varied with crop type. The highest AEN and PFPN were realized in maize (23.8 and 104.13 kg∙kg−1) followed by barley (22.65 and 76.9 kg∙kg−1), and wheat (19.96 and 65.51 kg∙kg−1), respectively, while the lowest AEN and PFPN were recorded in sorghum (9.46 and 63.44 kg∙kg−1) followed by teff (6.36 and 26.92 kg∙kg−1), respectively.
Mean annual temperature, MAP, nitrogen application rate, soil texture, soil pH, SOC, and AP had a significant impact on cereal yield. The yield of five cereal crops could linearly and significantly increase with N-application rate and was maximum at >100 kg∙ha−1 (123.9%) and lowest (28.9%) where <30 kg∙ha−1 of N was applied (
The result revealed that the cereal yield response due to N-application was considerably higher at the pH range of 6 - 7 (77.2%) than at pH of <6 (58%) and >7 (58.3%) (
In the present meta-analysis study, N-application significantly increased grain yield in maize, teff, wheat, barley and sorghum by 64.8% overall (
We found the overall AEN and PFPN of 18.2 and 71.81 kg∙kg−1, respectively, which also largely varied with N rate and crop type. However, our results show an overall inverse relation between NUE and N-application rate (
The variability in crop response, soil fertility differences, and climatic conditions and other factors makes the management and improvement of NUE more difficult. More importantly, understanding such variabilities is highly essential to design area-specific nutrient management practices. Several approaches have been developed to improve NUE in agriculture such as integrated soil fertility management [
The present study revealed that the cereal yield response to N fertilizer was largely positive and significant, but the magnitude of yield response varied based on N-supply rate, MAP, MAT, soil texture, pH, initial SOC, and AP (
Temperature is an important yield determining factor and its deviation from the optimum due to climate change or other factors negatively impacts crop productivity. A study conducted in China revealed that a unit increase of climate warming resulted in a reduction of maize yield by 2.6% [
The soil pH is a major indicator that plays a significant role in the availability of soil nutrients and also affects plant nutrient uptake and use efficiency. The higher yield response in soils with pH values ranging from 6-7 (
The result showed that the application of N significantly increased yield in all the crops studied by 64.8% at an average N-application rate of 72.9 kg∙ha−1. The downtrend of AEN and PFPN was observed with the increase of N-rates. Overall yield response was varied under different explanatory factors such as MAP, MAT, N-application rate, soil texture, soil pH, AP, and SOC. The yield response was higher at a high N-application rate, low SOC and AP contents. We, however, recommend the application of optimum N-fertilizer (>100 kg∙N∙ha−1), especially in infertile soils, to enhance cereal crop productivity in Ethiopia. In this study, several important factors that influence the yield response were not evaluated due to insufficient reporting across the studies. Therefore, future studies are needed to focus on a comprehensive selection of variables that influence crop yield and nitrogen use efficiency.
The authors greatly acknowledge China Agricultural University (CAU) and Sino-Africa STB project for the vital support and conductive environment to conduct the study. We also acknowledge the anonymous reviewers for their constructive and directive suggestions.
The authors declare no conflicts of interest regarding the publication of this paper.
Yokamo, S., Jiao, X.Q., Jasper, K., Gurmu, F., Jahan, M.S. and Jiang, R.F. (2022) Grain Yield and Nitrogen Use Efficiency Vary with Cereal Crop Type and Nitrogen Fertilizer Rate in Ethiopia: A Meta-Analysis. Agricultural Sciences, 13, 612-631. https://doi.org/10.4236/as.2022.134041
Author and year of publication | Journal site | Types of crops | Parameters collected | |
---|---|---|---|---|
Abdenna D., et al., 2014 | J. of Environment and Human | Wheat | ST, pH, SOC, TN, AP, Yield | |
Assefa M., et al., 2015 | Int. Journal of Plant & Soil Science | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Woyema A., Bultosa G. and A. Taa, 2012 | African J. of Food, Agriculture, Nutrition and Development | Wheat | Temp, Yield | |
Nano Alemu, 2017 | Journal of Agricultural Science | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Fresew B., et al., 2018 | Agriculture and Food Security | Wheat | ST, pH, SOC, TN, AP, Yield | |
Melesse Harfe, 2015 | African J. of Agricultural Research | Wheat | ||
Beyenesh Z., and Nigussie D., 2017 | Int. J. of Life Sciences, | Wheat | Temp, ST, Yield | |
Tamado T., Dawit D., and J.J. Sharma, 2015 | East African Journal of Sciences | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Wubishet A. and Tilahun B., 2016 | Plant | Wheat | Yield | |
Wogene Solomon and Agena Anjulo, 2017 | Int. Journal of Scientific and Research Publications, | Wheat | ST, pH, SOC, AP | |
Sakatu Hunduma, 2017 | J. of Natural Sciences Research | Wheat | Temp, yield | |
Tilahun Chibsa et al., 2016 | American Journal of Research Communication | Wheat | Temp, RF | |
Adamu Molla, 2018 | Journal of Agricultural Science | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Tilahun Abera and Tamado Tana, 2019 | African Journal of Plant Science | Wheat | Temp, pH, Yield | |
Nano A., J.J. Sharma and Firdissa Iticha, 2016 | World Journal of Agricultural Sciences | Wheat | ST, pH, SOC, TN, AP, Yield | |
Taye Belachew and Yifru Abera2, 2011 | Journal of Biodiversity and Environmental Sciences (JBES) | Wheat | Temp, Yield | |
Alemu D., Ketema B., Tesfaye S., 2019 | International Journal of Plant Breeding and Crop Science | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Mulugeta Eshetu, et al., 2017 | Int. Journal of Science and Qualitative Analysis | Wheat | Yield | |
Sofonyas D., Lemma W. and Selamyihun K., 2018 | Ethiop. J. Agric. Sci | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Bereket H., et al., 2014 | Agr., Forestry and Fisheries | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Fresew B., et al., 2018 | Agriculture and Food Security | Wheat | ST, pH, SOC, TN, AP, Yield | |
Tolcha T., et al., 2020 | Plant | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Yohannes E. and Nigussie D., 2019 | J. of Natural Sciences Research | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Arega G., et al., 2013 | Int. J. of Agronomy and Plant Production | Wheat | Yield | |
FIKIRTE G., 2018 | MSc thesis to Gondar University, Ethiopia | Wheat | Temp, ST, pH, SOC, TN, AP, Yield | |
Fenta A., 2018 | ARPN J. of Agr. and Biological Science | Teff | Temp, pH, Yield | |
Ayalew B. et al., 2016 | ICARDA Project | Teff | ST, Yield | |
Yared T., Girma T., and Kabna A., 2019 | American Journal of Agricultural Research | Teff | ST, pH, SOC, TN, yield | |
Temesgen K., 2019 | Advances in Crop Science and Technology | Teff | Temp, ST, pH, SOC, TN, AP, Yield | |
Kefyalew A., Tilahun F., Tadesse H., 2017 | Journal of Biology, Agriculture and Healthcare | Teff | Yield | |
Tamirat W., 2019 | Int. Journal of Plant & Soil Science | Teff | Temp, ST, pH, SOC, TN, AP, Yield | |
Haftamu G., Mitiku H. and Charles F., 2009 | Mekelle University | Teff | Yield | |
Teshome M., Wassie H., Sofiya K., 2019 | Int. J. of Advances in Agr. Science and Technology | Teff | Temp, ST, pH, SOC, TN, AP, Yield | |
Fissehaye M., et al., 2009 | JOURNAL OF THE DRYLANDS | Teff | Temp, ST, pH, SOC, TN, AP, Yield | |
Abraha A., 2013 | MSc thesis to Haramaya Univesity, Ethiopia | Teff | ST, pH, SOC, TN, AP, Yield | |
Tsadik T., 2019 | Journal of Soil Science and Environmental Management | Teff | Temp, ST, pH, SOC, TN, AP, Yield | |
Berihanu S., 2019 | Int. Journal of Agriculture and Environmental Research | Teff | ST, pH, SOC, TN, AP, Yield | |
Abebe G., et al., 2020 | African Journal of Agricultural Research | Teff | Temp, ST, pH, SOC, TN, AP, Yield | |
Bayu, W., Getachew A., and Mamo T., 2002 | Acta Agronomica Hungarica | Sorghum | ST, pH, SOC, TN, AP, Yield | |
Sheleme K., et al., 2016 | Advances in Crop Science and Technology | Sorghum | Temp, pH, Yield | |
Nigus D., et al., 2017 | Archives of Agronomy and Soil Science | Sorghum | Temp, ST, pH, SOM, AP, Yield | |
Letemariam D., et al., 2020 | Int. Journal of Research Agriculture and Biosciences | Sorghum | Temp, pH, SOC, TN, AP, Yield | |
Zerihun S., 2016 | Journal of Biology, Agriculture and Healthcare | Sorghum | Temp, ST, pH, SOC, TN, P, Yield | |
Fikadu T., et al., 2018 | OALib | Sorghum | Temp, ST, pH, SOM, AP, Yield | |
Ertiban W., 2016 | ICARDA | Sorghum | Temp, MAP, ST, pH, SOM, TN, AP, Yield | |
Fantaye B.M., 2019 | Journal of Advancements in Plant Science | Sorghum | Temp, ST, pH, SOC, TN, P, Yield | |
Wondimu B., N.F.G. Rethman and P.S. Hammes, 2005 | S. AfT. Tydskr. Plant Grond | Sorghum | ST, pH, SOC, TN, P, Yield | |
Esilaba A.O., et al., 2000 | African Crop Science Journal | Sorghum | Yield | |
Gebrelibanos G. and Dereje A., 2020 | Int. Journal of Agricultural Research | Sorghum | Temp, ST, pH, SOC, TN, AP, Yield | |
Feyera M., et al., 2020 | Nutrient Cycling in Agroecosystems | Sorghum | Yield | |
Geremew T., Kindie, T. and Tolessa, D., 2015 | Journal of Natural Sciences Research | Maize | Temp, ST, pH, SOC, TN, AP, Yield | |
Tolera A., Tolessa D., and Dagne W., 2017 | Int. Journal of Agronomy | Maize | Temp, ST, pH, SOC, TN, Yield | |
Abebe and Feyisa, 2017 | Int. Journal of Agronomy | Maize | Temp, ST, pH, Yield | |
Yihenew G., 2015 | Environmental Systems Research | Maize | ST, pH, SOC, Yield | |
Begizew G., Adugnaw M. and M. Getachew, 2018 | Open Journal of Plant Science | Maize | ST, pH, SOC, TN, AP, Yield | |
Wubalem Z., and Parshotam D., 2020 | IOSR Journal of Agriculture and Veterinary Science | Maize | Temp, ST, pH, SOC, Yield | |
Bejigo, Gizaw, 2018 | American Journal of Agriculture and Forestry | Maize | Temp, ST, pH, SOC, TN, AP, Yield | |
Shiferaw T., Anteneh A., and Tesfaye B., 2018 | Ethiop. J. Agric. Sci. | Maize | Temp, pH, SOC, TN, AP, Yield | |
Keyro A., and Zenebe M., 2019 | African Journal of Agricultural Research | Maize | Temp, ST, Yield | |
Besufikad E. and Tesfaye D., 2019 | ACTA Scientific agriculture | Maize | Temp, ST, pH, Yield | |
Yihenew G., 2007 | Ethiopian Journal of Natural Resources | Maize | ST, pH, SOC, AP, Yield | |
Zelalem B., 2013 | African Journal of Agricultural Research | Maize | Temp, ST, pH, SOC, TN, AP, Yield | |
Ewnetie T., et al., 2017 | American Journal of Plant Sciences | Maize | ||
KEYRO A., 2017 | Thesis submitted to AMU, Ethiopia | Maize | Temp, ST, pH, SOC, AP, Yield | |
Yihenew G., 2016 | Environmental Systems Research | Maize | ST, pH, AP, yield | |
Yacob A. and Meshu S., 2015 | Journal of Natural Sciences Research | Maize | Temp, ST, pH, TN, AP, Yield | |
Feyera M., et al., 2020 | Nutrient Cycling in Agroecosystems | Maize | Yield | |
Derebe T., Temesgen D., Habtamu A., 2018 | Int. J. of Research Studies in Agricultural Sciences | Barley | Temp, ST, pH, SOC, TN, AP, Yield | |
Mesfin K. and Zemach S., 2015 | American J. of Agriculture and Forestry | Barley | ST, pH, TN, Yield | |
Admas A., & Fikre H., 2014 | Barley | Temp, Yield | ||
Demisie E., Tamado T., Firdissa E., 2015 | Research & Reviews: J. of Crop Science and Technology | Barley | Temp, ST, pH, SOC, TN, AP, Yield | |
Sofonyas D., et al., 2018 | African J. of Agricultural Research | Barley | ST, pH, SOC, TN, AP, Yield | |
Getachew A., Berhane L., and Paul N., 2013 | Archives of Agronomy and Soil Science | Barley | Temp, pH, SOC, TN, AP, Yield | |
Feyera M., et al., 2020 | Agronomy J. | Barley | Yield | |
Ketema N., and Mulatu K., 2018 | J. of Natural Sciences Research | Barley | Temp, ST, pH, SOC, TN, AP, Yield | |
Dejene K., and Fetien A., 2014 | Momona Ethiopian J. of Science | Barley | Temp, ST, Yield | |
Girma Chala, 2017 | Int. J. of Research in Agr. Sciences | Barley | Temp, ST, pH, SOC, TN, AP, Yield | |
Amare A., and Adane L., 2015 | World J. of Agricultural Sciences | Barley | Temp, ST, pH, SOC, TN, AP, Yield | |
Meharie K., Kindie T., 2019 | J. of Crop Science and Biotechnology | Barley | Temp, ST, pH, SOC, TN, AP, Yield | |
Lake Mekonnen, 2018 | J. of Natural Sciences Research | Barley | Temp, pH, SOC, TN, AP, Yield | |
Woldekiros B., 2018 | J. of Biology, Agri. and Healthcare | Barley | Temp, ST, pH, SOC, TN, Yield | |
Note: Temp, ST, MAP, SOC, TN and AP represent temperature, soil texture, mean annual precipitation, soil organic carbon, total nitrogen and available phosphorous, respectively.