RJOAS February 2025
by Sigaye Melkamu Hordofa (Ethiopian Institute of Agricultural Research, Wondo Genet Agricultural Research Center, Shashemane, Ethiopia)
The study presents the results of a three-year field trial aimed at assessing the responses of maize through the application of urea stable-under balanced fertilizer on different soil types and locations of Ethiopia. The experiments consisted of 9 treatment levels: Control, 92kg ha-1 N R-N (30N/62N) from Urea in Split, 92 kg ha-1 N R- N from Urea Stable,92 kg ha-1 N R- N (30N/62N) From Urea Stable in Split, 92 kg ha-N (1/2 of the R-N from Urea Stable at Once , 46 kg ha-N (1/2) of the R-N (15N/31N) from Urea Stable in Split,138 kg ha-N (1/2) more than R-N (46N/92N) from Urea Stable in Split, 138 kg ha-N (1/2) more than R-N (46N/92N) form normal Urea in Split, and 38 kg ha-N (1/2) more than R- N from Urea Stable at once; laid-out in RCBD in three replications. Statistical analysis revealed that higher nitrogen application, mainly through Urea stable fertilizers, significantly improved both maize yield and biomass production at both locations. At Dore Bafano, the 92N kg ha-1 (30/62) from Urea stable treatment resulted in the highest maize grain yield (9.4 t ha⁻¹) and above-ground biomass (27,1 t ha⁻¹). In contrast, at Meskan, the 138N kg ha-1 (46/92) Urea stable treatment produced the highest grain yield (9.2 t ha⁻¹) and biomass (27.9 t ha⁻¹). However, the analysis result of unfertilized plot show the lowest gain yields and biomass at both locations. These findings underscore the critical role of balanced nitrogen fertilization in optimizing maize productivity in nutrient-deficient Cambisols and Chernozem soils types, contributing to the enhancement of agricultural sustainability in Ethiopia.
Maize (Zea mays L.) is one of the world’s leading cereals, ranking second in production after wheat (FAO, 2022). Ethiopia is the seventh maize-producing country in Africa. It is the second in area coverage next to Tef (Eragrostis tef (Zucc.)), with a total land area of 10,478,217 ha being under cereals, of which maize covered about 17.68% (2,274,305.93 ha) (CSA. 2022). Despite the large area under maize production, its current national average yield is about 4.2 t ha-1 (CSA. 2022), which is far below the world’s average yield of 5.8 tha-1 (Chimdi et al., 2012). Although numerous factors contribute to wide yield gaps, low external inputs, particularly N, poor soil fertility, reduced water-holding capacity of the soil, and poor soil infiltration problems are among the major factors paid for low maize productivity (Teklewold et al., & Chimdi et al., 2022).
Among all the plant nutrients essential for crop growth, nitrogen is the nutrient which most often limits crop production (Mosier et al., 2001). Nitrogen has a unique place in crop production system just because of its large requirement as it has critical role in almost all metabolic activities of plants and its heavy losses associated with soil-plant systems (Ladha et al., 2003). To fulfil this large N requirement of crop plants, globally farmers use around 120 million metric tons of nitrogenous fertilizer each year (FAO, 2014). Farmer needs to apply huge amounts of nitrogen fertilizer in agricultural crops because of its lower recovery (30-50%) due to its various losses from soil-plant system (Fageria, 2002). Nitrogen is universally deficient in almost all agricultural soils and cropping systems of the world so, it is essential to use external nitrogen inputs (N fertilizers) to produce the crops for satisfying the ever-increasing demands of human populations (Mosier et al., 2004 and Lawlor.et al., 2001).
Conventionally, to fulfil this large requirement of nitrogen, farmers completely depend on chemical nitrogen. Excess use of nitrogen as crop input can cause disruptions in its transformation and natural movement among its various pools resulting in imbalance of several ecosystem functions and services (Hutchinson et al., 2003; Meena et al., 2014). Sustainable agriculture production requires balanced and judicious, efficient, eco-friendly, and environmentally sound management practices. To achieve the national goal of agricultural sustainability and food security, vertical diversification of agriculture in terms of more crops output from unit quantity of land through judicious use of fertilizer inputs especially nitrogen has special significance in modern agriculture (Fageria and Barbosa, 2001 and Kumar et al., 2016).
In Ethiopia, for the last five decades Urea as a source of nitrogen and DAP as a source of nitrogen and phosphorus fertilizers were applied to obtain optimum harvest. Though, blaming especially to Urea has come immediately as its side effects in high solubility and hence increasing the soil acidity given that other conditions are met. Besides, one of the major challenging issues especially in high rainfall area in connection with loss of nitrogen through ammonium volatilization or fixation by clay minerals. On the other hand, in low moisture areas, its low solubility and toxic effect burns the root to reduce its growth and the performance of the crops grown under this condition also challenges the use of these fertilizers (Cassman K. et al., 2002).
However, to solve these difficulties and to increase the efficiency of the most limiting plant nutrient, which is nitrogen, different products have been developed and tested somewhere else Ethiopia. One of those products is UREA stable; it is based on urea (46%) with an added urea inhibitor N-(n-butyl)-thiophosphoric triamid (NBPT). The UREA stable is a concentrated nitrogen fertilizer that can be applied as a granular for crops as well as liquid fertilizer through irrigation water for the orchard. Besides, it supposed to have basic advantage of having a combination of rapidly soluble, well absorbable nitrogen with urease inhibitor that helps to improve nitrogen penetration to plant roots by restraining the sorption and fixation of NH4+ in the surface soil layer, which slows the effect of this nitrogen form down. Plus, it helps to reduce its losses due to ammonia volatilization into the atmosphere during surface application. Despite all these advantages this product has been evaluated and tested very well in our context under balanced fertilization. Therefore, this experiment was designed to investigate optimum rate nitrogen from urea stable fertilizer under balanced fertilizer at Sidama and Central regions of Ethiopia.
Field experiments were conducted over three consecutive years (2021–2023) in the Dore Bafano and Meskan districts of Ethiopia's Central Rift Valley. These locations were chosen for their significance in maize production and distinct differences in soil fertility and climatic conditions, providing an ideal basis for assessing maize productivity. The experimental site in Dore Bafano is located at 07° 1’ 1.63″ N latitude and 38° 12’ 21″ E longitude, with an elevation of 1,718 meters above sea level (asl). This site experiences a semi-arid climate with a long-term average annual rainfall of 958 mm, 81% of which occurs during the growing season from April to October. The average annual temperature is 21°C.
The experimental site in Meskan is located at 08° 05’ 3″ N latitude and 38° 21’ 56″ E longitude, with an altitude of 1,846 meters above sea level (asl). Like Dore Bafano, Meskan has a semi-arid climate, though it receives a slightly higher average annual rainfall of 987 mm, with 84% of this rainfall falling during the growing season (April to October). The average annual temperature is 20.4°C.
The experimental site location soils were classified as Cambisols for Dore Bafano and whereas Meskan is classified as Chernozem according to Soil Taxonomy soil classification system (USDA. 2022.). Cambisols are well-drained soils commonly found in regions with moderate to high rainfall, offering a fertile base for agricultural activities. The Chernozem,
a soil type typically found in cooler climates with high organic matter content, making it highly fertile and suitable for crop production. These differences provide an opportunity to explore how soil types (Cambisols in Dore Bafano and Chernozem in Meskan) affect maize growth and productivity under similar climatic conditions.
The primary crops grown in these areas include maize (Zea mays L.), sorghum (Sorghum bicolor), haricot bean (Phaseolus vulgaris), and millet (Eleusine coracana). The faring practice in both study areas typically follow-conventional farming practices, including monocropping and the application of blanket fertilizer recommendations. In both locations, maize was the preceding crop, and conventional tillage methods were applied prior to planting. These common agricultural practices, combined with the variation in soil types and climate, provide valuable context for evaluating the effects of soil properties on maize productivity over the study period.
Nine treatments were evaluated under balanced fertilization and laid out in randomized complete block design with three replications for each experimental site (Table1).
The hybrid maize variety BH 546 was used as a test crop. Similarly, the hybrid maize variety BH 546 was used as the test crop. The pathways between blocks and plots were 1.5 m and 1 m, respectively. Each sub-subplot had a size of 4.8 m × 3 m (14.4 m2) and accommodated six maize rows with inter- and intra-row spacing of 80 and 25 cm, respectively. Each row and plot had 12 and 72 plants, respectively. Based on Ethio-SIS maps or recommendations on each site, optimum/sufficient amount of other nutrients were applied during seed sowing to all plots uniformly (Ethio-SIS, 2016). Nitrogen fertilizer (from normal or conventional urea and urea stable) were applied in the split form, one time at sowing and half at the vegetative growth stages; See (Table1) for details of treatments set up time of application. Other agronomic practices were carried out uniformly in all experimental units.
Composite soil samples were collected before sowing using an Edelman drill at a depth of 0-20 cm to assess the inherent nutrient status of the experimental site. After physical homogenization, representative three composite subsamples per site were prepared for physicochemical analysis. The samples were pulverized and sieved through a 2 mm sieve after being air-dried at room temperature. However, 0.5 mm mesh wire was used for the determination of organic carbon (OC) and total nitrogen (TN). These soil samples were then analyzed for various properties, such as texture, pH, organic matter, total nitrogen, total sulfur, available phosphorus, exchangeable potassium, cation exchange capacity, and boron were analyzed based on standard laboratory procedures.
The data of maize yield and yield components were gathered at physiological maturity from each location, which corresponded to 175 days after sowing, respectively. The samples were collected from a net plot area of 4 m2 (1.25 m × 3.2 m) by rejecting the border rows, from three replications. 'e harvested grain yield was adjusted to a 12.5% moisture level Nelson et al., (1985), and it was converted into hectare bases.
Before the analysis of variance (ANOVA), the normality of the data was checked using the Shapiro–Wilk normality test. The statistical analysis was performed independently for each location, using the SAS 9.4 software package (SAS, 2014), considering the experimental treatment as a fixed factor and replication as a random factor. At a probability level of P≤0.05, differences between treatment means were separated using the protected Fisher’s least significant difference (LSD) (Steel et al., 1980).
This section presents and discusses the initial physicochemical properties of the soils at the Dore Bafano and Meskan locations, which were analyzed before the application of treatments. These soil properties are essential in understanding the inherent fertility, nutrient availability, and overall suitability for maize production at both sites.
The textural class of the soil at Dore Bafano was silt loam (40% sand, 34% silt, 26% clay), while Meskan soil was loam (18% sand, 34% silt, 48% clay). According to Fageria et al. (2011), loam soils like those at Meskan are generally favored for agriculture due to their balanced moisture retention and drainage properties. Conversely, Dore Bafano’s silt loam texture may lead to higher water retention but also increased risk of soil compaction, especially in areas with higher rainfall, as highlighted by Liu et al. (2016). The higher clay content in Meskan suggests a better ability to retain nutrients compared to the relatively lighter, more free-draining soil at Dore Bafano. The soil pH at Dore Bafano was 6.45, slightly acidic, whereas Meskan’s pH was 7.30, closer to neutral. The pH of Dore Bafano is within the optimal range for most crops, though slightly acidic soils may enhance micronutrient availability (Ali et al., 2017). On the other hand, Meskan’s neutral pH may be less prone to micronutrient deficiencies, but it could also limit the availability of some trace elements, as found by Abdou et al. (2020). The pH difference between these locations suggests that Meskan may have fewer challenges related to nutrient uptake in terms of micronutrients, but its soil chemistry could be less favorable for certain crops that prefer slightly acidic conditions.
Available phosphorus in Dore Bafano (4.52 mg kg-1) and Meskan (4.46 mg kg-1) were relatively low but comparable. Studies indicate that phosphorus is often a limiting factor in tropical soils (Fageria & Baligar, 2008), and the levels found here are below the optimum range for many crops. Both locations would likely benefit from phosphorus fertilization to improve crop productivity, as phosphorus plays a critical role in energy transfer and root development (Liu et al., 2016).
The total nitrogen content was 0.26% in Dore Bafano and 0.30% in Meskan. Both values are considered low, consistent with findings from Zhang et al. (2015), who reported that tropical soils often have low nitrogen availability, limiting plant growth. Nitrogen is a key nutrient for plant protein synthesis and growth (Ouyang et al., 2018), and both soils will likely require nitrogen fertilizers to meet crop demands, particularly for maize and other nitrogen-hungry crops. Organic carbon content was higher in Meskan (4.49%) than in Dore Bafano (3.51%), which is consistent with the findings of Fageria et al. (2011), who emphasized that higher organic carbon generally improves soil fertility by enhancing microbial activity and nutrient cycling. The higher organic carbon in Meskan suggests that it may have better soil health, promoting more efficient nutrient cycling and supporting better crop productivity. In contrast, Dore Bafano may benefit from organic amendments to increase carbon content and improve overall soil structure.
The CEC values were significantly higher in Meskan (60 cmol + kg-1) than Dore Bafano (20 cmol + kg-1). As noted by Fageria et al. (2008), CEC is a crucial indicator of a soil’s ability to retain and exchange essential nutrients like calcium, magnesium, and potassium. Meskan’s higher CEC suggests that it can hold more nutrients in the soil solution, potentially making it more fertile in the long term. This could allow for better nutrient availability to plants and reduced leaching losses, a benefit also noted by Liu et al. (2016) in soils with higher CEC.
Meskan exhibited much higher calcium concentrations (38.3 cmol + kg-1) than Dore Bafano (6.01 cmol + kg-1). This difference aligns with findings by Fageria et al. (2011), who found that soils rich in calcium improve soil structure, reduce acidity, and enhance root development. The higher calcium content in Meskan is likely to support better plant health and stability, particularly for crops sensitive to calcium deficiencies. Magnesium concentrations were significantly higher in Meskan (7.28 cmol + kg-1) compared to Dore Bafano (0.38 cmol + kg-1).
Magnesium is essential for photosynthesis and enzyme activation (Fageria & Baligar, 2008), and the higher levels in Meskan suggest that this soil may support better crop growth, especially in terms of chlorophyll production and photosynthetic efficiency. Potassium was more abundant in Dore Bafano (2.13 cmol + kg-1) than in Meskan (1.13 cmol + kg-1). Potassium is crucial for regulating water balance, enzyme activation, and disease resistance (Ali et al., 2017). Dore Bafano’s higher potassium concentration may enhance these processes, giving it a slight advantage in supporting stress-tolerant crop varieties. Sodium concentrations were higher in Dore Bafano (5.15 cmol + kg-1) compared to Meskan (2.03 cmol + kg-1). High sodium levels can lead to soil salinity issues, potentially impairing plant growth and nutrient uptake (Zhang et al., 2015). Meskan’s lower sodium content suggests it may be more favorable for crops, especially in terms of root health and nutrient uptake efficiency.
Dore Bafano had significantly higher iron levels (2.52 mg kg-1) than Meskan (0.62 mg kg-1). Iron is critical for chlorophyll synthesis and plant metabolism (Ali et al., 2017), and its higher concentration in Dore Bafano suggests that crops grown here may be less prone to iron deficiency, which is common in soils with high pH or low organic matter. Both locations had similar manganese concentrations (Dore Bafano: 3.03 mg kg-1, Meskan: 3.75 mg kg-1), indicating that both soils are adequate in this micronutrient. Manganese is essential for enzyme activation and photosynthesis, and its presence in sufficient amounts will support efficient nutrient metabolism (Fageria & Baligar, 2008). Copper concentrations were notably higher in Meskan (1.44 mg kg-1) compared to Dore Bafano (0.02 mg kg-1). Copper is essential for photosynthesis and various enzymatic processes (Zhang et al., 2015), and the higher copper levels in Meskan may provide an advantage for enzyme activity and plant growth.
Zinc concentrations were relatively similar in both soils, with Dore Bafano at 0.65 mg kg-1and Meskan at 0.75 mg kg-1. Zinc plays a critical role in enzyme function and protein synthesis (Fageria et al., 2011), and the levels in both soils appear sufficient for most crops, although zinc deficiencies may still occur under certain conditions, particularly if pH levels increase.
The study evaluated the impact of various fertilizer treatments on maize (Zea mays L.) grain yield and above-ground biomass at two distinct locations in Ethiopia Dore Bafano and Meskan over three consecutive years (2021–2023). The treatments consisted of different combinations of Urea stable and Urea at varying nitrogen (N) levels, and the outcomes were analyzed to assess their effects on maize productivity.
The statistical analysis results show that the grain yield was highly significant (P<0.01) through applying Urea Stable-Under Balanced Fertilizer. The maximum maize grain yield was recorded at the Dore Bafano site with the 92N kg ha-1 (30/62) from Urea stable treatment, which yielded an average of 9.1 ha⁻¹. This treatment also resulted in the highest above-ground biomass of 27.1t ha⁻¹, significantly outperforming all other treatments (p < 0.05). The 138N kg ha-1 (46/92) from Urea stable treatment also produced a high grain yield (8.1 t ha⁻¹) and above-ground biomass (23.3 t ha⁻¹), though slightly lower than the 92N kg ha-1 (30/62) from Urea stable treatment. These results are similar with other studies that have demonstrated the positive impact of Urea stable fertilizers on maize growth due to their enhanced nitrogen-use efficiency (NUE), leading to increased yields and biomass production (Ali et al., 2017 & Ouyang et al., 2018).
Conversely, the adverse control treatment (no fertilizer) resulted in the lowest grain yield (3.5 t ha⁻¹) and above-ground biomass (9.1 t ha⁻¹), confirming the critical role of fertilization in optimizing maize growth, particularly in nutrient-deficient Andosol soils. The treatments with lower nitrogen inputs, such as 46N kg ha-1from from Urea stable and 46N kg ha-1 (15/31) from Urea stable, exhibited moderate yields, with mean grain yields of 5.3 t ha⁻¹ to 6.2 t ha⁻¹. These results suggest that lower nitrogen levels can improve yields compared to no fertilization; they may not meet the crop’s complete nitrogen requirements, limiting yield potential.
At the Meskan site, the 138N kg ha-1 (46/92) from Urea stable treatment achieved the highest grain yield, averaging 9.3 t ha⁻¹, with an above-ground biomass of 27.7 t ha⁻¹. The 92 kg ha-1 (30/62) from Urea stable treatment also showed high performance, yielding 8.2 t ha⁻¹ and above-ground biomass of 26.6 t ha⁻¹, which were significantly higher than other treatments (p < 0.05). These results are consistent with similar findings by Liu et al. (2016), who reported that higher nitrogen application rates significantly increase maize yield and biomass in tropical and subtropical regions.
The negative control treatment at Meskan produced the lowest grain yield (3.3 t ha⁻¹) and above-ground biomass (10.1t ha⁻¹), reinforcing the importance of fertilization for maize productivity. Treatments with moderate nitrogen levels, such as the 92N kg ha-1 Urea stable and 46N kg ha-1 (15/31) from Urea stable, displayed intermediate results, with grain yields ranging from 5.1t ha⁻¹ to 5.9 ha⁻¹, showing a positive but less pronounced response compared to the higher nitrogen treatments.
The results from both locations indicate a clear positive response of maize yield and biomass to applying urea-stabilized fertilizers, particularly at higher nitrogen levels. The 92N kg ha-1 (30/62) from urea-stabilized treatment consistently yielded the highest maize yields at both Dore Bafano and Meskan, confirming the beneficial effect of balanced nitrogen application on maize growth in Andosol soils. These findings align with research by Abdou et al. (2020), which demonstrated that balanced fertilization with stabilized nitrogen fertilizers can improve yield and nutrient use efficiency in maize production systems.
The significant difference in maize performance between the treatments can be attributed to the varying nitrogen levels provided by the fertilizers. Higher nitrogen application, especially through Urea stable, enhanced nitrogen availability throughout the growing season, supporting better crop nutrition, accelerated growth, and higher biomass production (Fageria et al., 2011). Conversely, the lower nitrogen treatments, such as the 46N Kg ha-1 from Urea stable and 46 (15/31) Urea stable, did not provide adequate nitrogen for maize to reach its full potential, as evidenced by the moderate yields of these treatments. This suggests that while lower nitrogen levels can provide some yield benefits, they are insufficient for achieving optimal productivity in maize.
The negative control treatments, which lacked fertilizer application, consistently produced the lowest yields and biomass, underscoring the critical need for fertilization in Andosol soils, which are often characterized by low nutrient availability. Fageria and Baligar (2008) reported similar findings, noting that the absence of fertilizer results in significantly reduced maize yields, particularly in soils with low fertility.
Notably, the observed differences in maize performance between the two locations (Dore Bafano and Meskan) could be influenced by soil texture, organic matter content, and local climatic conditions. While both locations demonstrated a positive response to fertilization, Dore Bafano showed a more pronounced yield increase, particularly with the 92 (30/62) Urea stable treatment. This may reflect differences in soil nutrient status or climatic factors, such as rainfall distribution, that affect fertilizer uptake and crop growth (Zhang et al., 2015).
The results of this study clearly show that Urea stable fertilizers, especially when applied at higher nitrogen levels, significantly enhance maize productivity in Ethiopia’s Andosol soils. The treatment using 92N kg ha-1 (30/62) from Urea stable fertilizer at Dore Bafano and the 138N kg ha-1 (46/92) from Urea stable treatment at Meskan consistently produced the highest maize grain yields and biomass. This validates the importance of balanced nitrogen application. In contrast, the negative control treatments, which did not use fertilizer, resulted in considerably lower yields and biomass, highlighting the necessity of fertilization in regions with nutrient-poor soils. These findings are consistent with global research demonstrating that stable nitrogen fertilizers improve both yield and nitrogen-use efficiency. Therefore, optimizing fertilization strategies is crucial for enhancing food security and supporting sustainable maize production systems in Ethiopia.
It is recommended that farmers, particularly in regions with nutrient-deficient soils like Cambisols & Chernozem adopt Urea stable fertilizers at balanced nitrogen levels 92 kg ha-1 (30/62) or 138 kg ha-1 (46/92) to maximize maize yields and increase biomass production. Farmers should utilize precision fertilization techniques to apply the optimal amount of nitrogen, avoiding over-fertilization to reduce environmental impact and costs, while also preventing under-fertilization to ensure adequate nutrient supply for maximum maize growth. Additional research is necessary to explore the long-term effects of Urea stable fertilizers on soil health and sustainability, providing valuable insights into their broader environmental and economic impacts.
Moreover, complementary practices, such as increasing organic matter content and improving soil texture, should be integrated into fertilization strategies to enhance the long-term fertility of Andosol soils. This will contribute to the overall sustainability of maize farming in these regions. It is also crucial to provide farmers with adequate training on the benefits and application techniques of Urea stable fertilizers.
The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.
This research was conducted with funds from of Ethiopian Institute of Agricultural Research and National Soil and Water Research Directorate division.
We would like to acknowledge the Ethiopian Institute of Agricultural Research, and Wondo Genet Agricultural Research Center for providing the necessary facilities to carry out this work.
Original paper, i.e. Figures, Tables, References, and Authors' Contacts available at http://rjoas.com/issue-2025-02/article_10.pdf