https://orcid.org/0000-0003-1133-0796
Figures
Abstract
The decline in soil nutrients in Ethiopia, particularly in Western Amhara, is causing low crop productivity. Some researchers have argued that the application of K, S, Zn, and B in blended, individual, and complex forms affects crop yield. Identification of the prime yield-limiting nutrient is the key to solvesoil nutrient problems. A field experiment was conducted at Burie-Wemeberema, Debere Elias, Gozamen and Gonji Qolela districts of Western Amhara in the 2022 cropping season. A composite soil sample was taken at a depth of 0–20 cm to determine soil chemical properties. Bread wheat and tef were used as a test crop. The gross plot sizes were 4m x 3m and the spacing between blocks and rows was 1.0 and 0.2 m, respectively. The experiment was laid out in a randomized complete block design with three replications and comprised of nine treatments: control, NPKSZnB-blended, NPKZnB, NPKSB, NPKSZnB, NPSZnB, NP, NPKSZnB-individually applied, and NPSZnB-compound+K. R programming software version 4.2.2 was used for data analysis, and treatment means were separated at P < 0.05 using the LSD test. The analysis of variance results showed that nitrogen and phosphorus are the most yield-limiting nutrients so far in the study area. Besides, omissions of potassium, sulfur, zinc, and boron did not show a significant (P < 0.05) effect on bread wheat and tef grain yield reduction as compared to the applied recommended nitrogen and phosphorus at all landscape positions of all study sites. Blended and compound nutrients also didn’t show a significant grain yield advantage as compared to the applied NP nutrients. Applied potassium, sulfur, zinc, and boron nutrients in blended, individual, and compound forms did not increase wheat and tef grain and biomass yields in all study areas. Currently, additions of K, S, Zn, and B nutrients in the fertilizer package do not have a significant grain yield advantage as compared to the recommended NP nutrients. We believe the present information on fertilizers in blended, compound, and individual forms is insufficient to draw any concrete conclusions. Therefore, we suggested further research to confirm which form of fertilizer and nutrient source is better for future crop production.
Citation: Alemayehu B, Bazie Z, Amare T, Alemu E, Yibabie T, Tenagne A, et al. (2025) Effect of nutrient omissions on bread wheat and tef crops grain yield in Western Amhara, Ethiopia. PLoS One 20(10): e0335174. https://doi.org/10.1371/journal.pone.0335174
Editor: Vasudev Meena, ICAR-Indian Institute of Rapeseed-Mustard Research, INDIA
Received: March 13, 2025; Accepted: October 7, 2025; Published: October 30, 2025
Copyright: © 2025 Alemayehu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the manuscript and uploaded as a Supporting Information files during the revised manuscript submission.
Funding: The author(s) received no specific funding for this work.
Competing interests: The authors have no cmpeting interest.
1. Introduction
More than 80% of Ethiopia’s population is dependent on agriculture, which contributes 50% to the country’s gross domestic product (GDP) and 80% to its export earnings [1]. Continuous crop production using high-yielding varieties, erosion and inadequate replacement of essential nutrients cause serious soil nutrient depletion [2]. Plant nutrition is the key critical factor controlling crop yield [3]. Consequently, this leads to a deficiency of essential plant nutrients. The deficiency of essential nutrient elements has been implicated in limiting the uptake of nutrients, growth, and yield of crops. The absence of macro and micro plant nutrients in the soil reduces crop yield. Deficiency of nitrogen and phosphorus significantly causes wheat and tef grain yield loss and their applications increase crop yield [4–8]. Research findings also indicated that the application of potassium, sulfur, and boron nutrients also increases crop yield [9,10].
Tef [Eragrostis tef (Zucc.) Trotter] is one of the most important gluten-free staple food crops in Ethiopia and has grown widely in the country for human consumption [11]. Tef has high nutritional content and is considered a protein source [12,13]. Despite its productivity is low as compared to the increased human population and demand in Ethiopia. Its national productivity is less than 1.8 t ha-1 [14]. (Wheat (Triticum aestivum L.) is also one of the most important cereal crop contributing to ensuring world food security [15]. Wheat is the third cereal crop produced after maize and rice in the world [15]. In Ethiopia, wheat is the third major cereal crop after tef and maize [14].
Earlier studies on soil and plant tissue analysis indicated that nitrogen (N), phosphorus (P), potassium (K), sulfur (S) and micronutrients like zinc (Zn) and boron (B) become deficient in Ethiopian soils [16–18]. In addition, K and S were also reported as a yield-limiting nutrient in wheat and rice crop production, respectively [19,20]. Recent studies on micro and macronutrients conversely indicated that nitrogen and phosphorus are the most yield-limiting nutrients of crop production [4–7,20–22]. Potassium, Sulfur, Zinc, and Boron were reported as not a yield-limiting nutrient of crop production in soils of Northwestern Ethiopia [4,5,7,21]. Application of N and P nutrients increased the yield, while K, S, Zn, and B nutrients applications did not significantly increase the yield [4–7]. Asfaw et al. [21] also reported that macro and micronutrients like K, S, Zn and B are not yield-limiting nutrients and nutrient management priority should be towards N and P nutrients. However, some researchers argued that in addition to N and P, applications of K, S, Zn and B affect the yield of crops [9,10,23–26]. In Ethiopia, the current research information on crop yield responses to different nutrient forms and rates is not sufficient. Accordingly, a nutrient omission research was conducted to test the hypothesis that applying different nutrient rates and sources would improve wheat and tef yield in different landscape positions. Therefore, this study was conducted to identify yield-limiting nutrients under different landscape positions for wheat and tef production.
2. Materials and methods
2.1. Description of the study area
The study was conducted on Foot, Mid, and hill slope landscape positions of most wheat and tef producing areas. The landscapes were selected based on the slope and elevation of the area. The experiment was conducted on three major wheat-growing potential districts of western Amhara: Burie-Wemeberema, Debere Elias, and Gozamen within the geographical coordinates 10° 16’ 56“- 10° 40’ 52” N latitudes and 36° 00’ 1” – 37° 36’ 15” E longitudes. The elevation of Bure Wemberema district study sites found between 2036–2107 m, DebreElias 2194–2231 m and Gozamen 2209–2286 m above sea level. The tef experiment was conducted in Gonji Qolela district with geographical coordinates 11° 12’ 43” N – 11° 13’ 57” N latitudes and 37° 34’ 36” E – 37° 37’ 16” E longitudes. The elevation of Gonji Qolela study sites was found between 2282–2340 m above sea level. The research work was conducted with the permission and coordination of Amhara Regional Agricultural Research Institute (ARARI, Bahir Dar, Ethiopia) and International Crops Research Institute for the Semi-Arid Tropics (ICRISAT, Addis Ababa, Ethiopia). Before planting, soil analysis results indicated that the cation exchange capacity (CEC in cmol+ kg-1 soil) was medium to high (19.98 to 45.80), pH (H2O) of the soil was strong to slightly acidic (5.28 to 6.40), available phosphorus (Ava. P in mg kg-1) in the soil was low to medium (4.80 to 10.00), total nitrogen (TN in %) was low (0.10 to 0.29), and soil organic carbon (SOC in %) was very low to low (0.70 to 2.54) in all landscape positions of the study areas.
2.2. Experimental design
The experiment comprised nine treatments, namely NPKSZnB-blended (All 1), NPKZnB (All-S), NPKSB (All-Zn), NPKSZn (All-B), NPSZnB (All-K), NP, NPKSZnB-individually applied (All 2), NPSZnB-copound+K (All 3) and the control (without nutrients). All 1, All 2, and All 3 have the same nutrient contents but were applied in blended, individual, and compound forms. Urea, DAP, KCl, NPS, ZnSO4, and solubor (Borax decahydrate) (Na2B4O7.10H2O) were used as sources of nutrients for nitrogen, phosphorus, potassium, sulfur, zinc and boron, respectively. Fertilizer blending was done based on International Fertilizer Development Center (IFDC) guidelines using a small cement mixer at Debre Zeit Agricultural Research Center, Ethiopia. Nitrogen was applied in three splits for wheat (at planting, tillering, and booting stages) and in two splits for tef (at planting and tillering), while all other nutrients were applied at planting. The experiment was laid out in a randomized complete block design with three replications. Bread wheat (TAY variety) and Tef (Quncho variety) were used as a test crop. The gross and net plot sizes were 4m x 3m (12 m2) and 3.2m x 3m (9.6 m2), respectively, for both crops. Wheat crop was grown on 16 study sites, while tef crop was grown on 3 study sites. The spacing between blocks and rows were 1.0 and 0.2 m, respectively, for both test crops. The treatment setup is shown in Table 1.
2.3. Soil and agronomic data collections
2.3.1. Soil sampling and analysis.
Before planting, one composite sample at 0–20 cm soil depth was collected to determine selected soil chemical properties. All collected soil samples were air-dried and crushed to pass through a 2-mm sieve. The selected soil parameters: soil pH-H2O, Ava. P, TN, SOC, and CEC were analyzed at the Adet Agricultural Research Center’s soil laboratory. Soil reaction (pH) was measured in 1:2.5 soil-to-water suspensions following the procedure used by [27]. Soil organic carbon (SOC) content was measured by the wet digestion method using the Walkley and Black method [28]. The total nitrogen was estimated using the Kjeldahl method [29], while the available phosphorus was analyzed by following the Olsen method [30]. The ammonium acetate extraction procedures were used to determine the soil cation exchange capacity [31].
The soil pH (H2O) was slightly acidic at the foot slope and strongly acidic at the mid and hill slope positions of Burie-Womeberema. Similarly, the pH of the soil was under a strongly acidic range at all landscape positions of Debre Elias, while at Gozamen, it was in a slightly acidic range at all landscape positions. The soil OC (%) was very low at all landscape positions of Gozamen and the foot slope landscape position of Debre Elias. The soil TN (%) was in the low range at all landscape positions, which was below the international critical standards, the Ava. P (mg kg-1) was low to medium at all landscape positions, while the CEC was medium to high at all landscape positions of the study areas. The soil OC, TN, and Ava. P was numerically high at the Foot and mid slopes as compared to the hill slope landscape positions of Burie-Womeberema and Gozamen and the mid-slope of Debre Elias study sites (Table 2). This result agreed with the findings of Amede et al. [32], who reported soil at the foot and mid-slope had higher amounts of organic carbon, TN, and Ava. P as compared to hill slopes.
2.3.2. Agronomic data.
For both test crops, total aboveground biomass and grain yield were measured. Harvesting was done from a 9.6 m2 net plot area (3.2 m by 3 m), with the outside rows left as buffers to prevent border effects. Plants harvested from the net plot area were sun-dried to a constant weight and converted to kg per hectare for statistical analysis. The grain yield was also calculated after threshing the biomass harvested from the net plot area and converted into kilograms per hectare. We adjusted the grain yield to 12.5% moisture.
2.4. Statistical data analysis
After homogeneity and normality tests were done, the essential agronomic data collected from field experiments for each parameter were subjected to analysis of variance (ANOVA) using R programming software. Treatment means were separated based on the least significant difference (LSD) test at P ≤ 0.05.
2.5. Partial budget analysis
A partial budget analysis was performed to investigate the economic feasibility of nutrient applications for bread wheat production. The output data (grain yield) were collected during threshing time and the input data (market price for applied fertilizers) were collected during the experimental year (2022) and used for analysis. The average grain yield of bread wheat was adjusted downwards by 10% to perfect the difference between the experimental plots’ yield and the yield farmers would expect from the same treatment under their own management.
3. Results
3.1. Response of wheat and tef grain and biomass yields to nutrients
The analysis of variance (ANOVA) results showed that applying nutrients at all study sites resulted in a highly significant increase in wheat and tef grain and biomass yield as compared to the treatment in which no fertilizer was applied (Tables 3–6). The ANOVA results showed that potassium (K), sulfur (S), Zinc (Zn) and boron (B) nutrient omissions and or applications did not significantly affect the grain and biomass yield of wheat and tef in all landscape positions of all study areas. The ANOVA results revealed that there was no statistically significant bread wheat and tef grain and biomass yield observed among the treatments except the control in the landscape positions of the study areas. Omissions of K, S, Zn, and B nutrients did not show statistically significant bread wheat and tef grain and biomass yield reductions as compared to the applied recommended NP nutrients (Tables 3–6 and Fig 1).
All1 = NPKSZnB-blended, All2 = NPKSZnB-individually applied, All3 = NPSZnB-compound+K, NP = All-KSZnB.
Application of K, S, Zn, and B nutrients in blending, compound, and individual forms with N and P nutrients didn’t affect wheat and tef grain and biomass yields in all landscape positions of all study areas as compared to the applied recommended NP nutrients (Tables 3–6). The lower wheat biomass yield (878 kg ha-1) was recorded from the control treatment at the mid-slope landscape position of the Debre Elias district. Maximum wheat biomass yield (10677 kg ha-1) was recorded from the foot slope at Burie Wemeberma district. Lower wheat grain yield (259 kg ha-1) was recorded from the control treatment at mid-slope landscape positions of the Debre Elias district. Whereas the maximum wheat grain yields (3984 kg ha-1) were recorded from the foot slope at the Burie-Wemberema district. The lower tef grain yield (409 kg ha-1) was recorded from the foot slope landscape positions of Gonji Qolela district. Maximum tef grain and biomass yield (2239 and 7399 kg ha-1) were recorded from the mid-slope at Gonji Qolela district, respectively (Tables 3–6 and Fig 1).
The lower grain yields of wheat and tef crops were recorded from the control in all landscape positions and study areas (Tables 3–6). The lower yield of the control (unfertilized) indicates that the soil nitrogen and phosphorus nutrient supply status is insufficient to provide nutrients in optimum amounts (Table 2). This indicates that the current status of N and P applications is critically important. Our results showed that nitrogen and phosphorus nutrients caused significant wheat and tef yield reduction from the control treatment, since these nutrients increased yields with the addition of these nutrients.
We also compared treatments to determine how much yield was lost due to nutrient omissions across landscape positions. Due to nutrient omission, yield reductions ranged from 5 to 71% compared to the control treatment in the landscape positions of all study areas (Fig 2). The omission of K reduced wheat grain yield by 4.5% and 8.7% compared to the applied NP at the hill and mid-slope landscape positions, respectively. The omission of B reduced the yield by 5.8% at the mid-slope landscape position. A yield penalty of 65%, 71% and 67% was observed for the control treatment at the foot, mid and hill slope landscape positions, respectively (Fig 2).
All1 = NPKSZnB-blended, All2 = NPKSZnB-individually applied, All3 = NPSZnB-compound+K, NP = All-KSZnB.
3.2. Response of wheat plant height and spike length to nutrients
The omission of K, S, Zn, and B nutrients didn’t affect the vegetative growth of bread wheat during experimentation; almost all of the experimental pots showed similar vegetative performance. The ANOVA results showed that a highly significant increase in wheat plant height and spike length was observed, due to the applied nutrients compared to the control treatment (Table 7). These results revealed that omissions of K, S, Zn, and B nutrients did not show statistically significant wheat plant height and spike length reductions compared to the applied recommended NP. The lower wheat plant height (65.8 cm) and spike length (6.0 cm) were recorded from the control treatment at the mid-slope landscape position. Whereas the maximum plant height (102.8 cm) and spike length (8.9 cm) were recorded at the foot slope landscape position of the study area (Table 7).
4. Discussion
Omissions of K, S, Zn, and B nutrients did not show significant reductions in wheat and tef grain and biomass yields in all landscape positions of the study areas (Tables 3–6). This indicates that K, S, Zn, and B are not yield-limiting nutrients in the study areas. These results agreed with the previous studies applying K, S, Zn, and B nutrients in blended, compound, and individual forms, which did not show a significant increase in wheat crop yield [4]. This indicates that K, S, Zn, and B nutrients are not yield-limiting nutrients so far in most crop-producing areas of Western Amhara. In addition, Agegnehu et al. [4]. concluded that various wheat-growing areas in Ethiopia do not require K, S, Zn and B t o achieve high yields. These results were also in line with the findings of Amare et al. [7] and Alemayehu et al. [5], who reported that applying K, S, Zn, and B nutrients did not show a significant yield advantage over the applied recommended NP nutrients. Our results also confirm the earlier studies, K, S, Zn, and B nutrient applications did not bring a significant increase in wheat and tef grain yield [6].
These results also align with the findings of Asfaw et al. [21], who reported that for wheat production, currently, there is no need for supplemental application of fertilizers containing K, S, Zn and B nutrients. However, these results disagreed with the findings of Kumar et al. [22], who indicated that applying K, S, Zn, and B nutrients had a significant effect on rice and wheat grain yield, and the highest grain yield was recorded from the treatment that received all nutrients. These results also contradicted the findings of (Chala et al. [9] and Seifu et al. [10], who reported that applying K, S, and B nutrients containing fertilizers increased wheat and tef crop yield. These results also disagreed with the findings of Dargie et al. [24], who concluded that applying balanced K, S, Zn and B nutrients significantly increased wheat crop yield.
The lower plant height and spike length in the control treatment indicated that N and P are the most growth-limiting nutrients, as plant height and spike length increased when N and P nutrients were applied. These results agreed with the findings of Alemayehu et al. [5], who concluded that N and P are the most plant height and growth-limiting nutrients. Previous studies by Agegnehu et al. [4] and Bazie et al. [6] indicated wheat and tef yield and yield attributes were significantly limited by N and P nutrients.
4.1. Partial budget analysis
The partial budget analysis was done based on CIMMYT [33]. The financial (partial budget) analysis results showed that blended, compound or individual application of K, S, Zn and B nutrients is not economical compared to the recommended NP. In comparison to the control and other treatments, nitrogen and phosphorus nutrients gave a higher marginal rate of return (866%) and a net benefit of 95, 643 ETB ha-1. (Table 8). According to the partial budget analysis, applying N and P nutrients only is the most economical for our smallholder farmers. These results agree with Agegnehu et al. [4], Asfaw et al. [21] and Bazie et al. [6], who reported no need to supplement K, S, Zn, and B but they recommended only N and P nutrients for wheat and tef production. The trend in financial analysis for tef is similar to that for wheat.
5. Conclusions and recommendations
Applications of potassium, sulfur, zinc, and boron nutrients in blended, individual, and compound forms did not show a significant effect on wheat and tef grain and biomass yield advantage compared to the recommended NP in the study areas. On the basis of crop response, omissions of potassium, sulfur, zinc, and boron nutrients did not show a significant wheat and tef yield reduction in all landscape positions of the study areas. This indicates nitrogen and phosphorus are the most wheat and tef yield-limiting nutrients in the study areas. Based on our results, applying K, S, Zn and B nutrients for wheat and tef production is not economical for our smallholder farmers. We believe the present information on fertilizers in blended, compound, and individual forms is insufficient to draw concrete conclusions. Therefore, we suggested further research to confirm which form of fertilizer and nutrient source is better for future crop production.
Acknowledgments
We would like to thank the International Crop Research Institute in the Semi-Arid Tropics (ICRISAT), Adet Agricultural Research Center and Amhara Agricultural Research Institute (ARARI) for providing essential facilities to conduct this research work. We would also like to thank you, participating farmers, for allowing us their farm lands to conduct this study.
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