# Vermicompost and NPSZnB Fertilizer Levels on Maize (Zea mays L.) Growth, Yield Component, and Yield at Guto Gida, Western Ethiopia

Authors: Abdela Tufa
Journal: International Journal of Agronomy
 (2023)

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## Abstract

The application of organic and inorganic fertilizers together increases crop productivity and soil fertility. However, it is crucial to identify the combined application level. A field experiment was carried out in the Guto Gida district in 2021 to determine the effect of vermicompost levels and chemically mixed NPSZnB fertilizer rates on the growth and yield of maize. Four vermicompost levels (0, 2.5, 5, and 7.5 t·ha−1) combined with four artificial NPSZnB fertilizer rates (0, 50, 100, and 150 kg·ha−1) were used for the study in a randomized complete block design (RCBD) with 3 replicates. Crop phenology and biomass yield were both significantly influenced by the main effects of vermicompost level and NPSZnB rate. Vermicompost and NPSZnB fertilizer applied together had a large effect on plant height, leaf area index, ear weight, thousand kernel weight, and grain yield. The largest grain yield (8.03 t·ha−1) was produced by the interaction of vermicompost at 7.5 t·ha−1 with 150 kg·ha−1 NPSZnB, followed by all levels of vermicompost at and above 5 t·ha−1 with 100 and 150 kg·ha−1 NPSZnB. Additionally, plots treated with a combined application of vermicompost and NPSZnB fertilizer at rates of 5 t·ha−1 × 100 kg·ha−1 and 5 t·ha−1 × 150 kg·ha−1, respectively, recorded the greatest values of ear weight (276.1 g) and thousand kernel weight (49.79 g). However, the lower yield was obtained from plots that were untreated with both vermicompost and NPSZnB, and the plot treated only with 50–150 kg·ha−1 of NPSZnB. In conclusion, integrated applications of vermicompost at 5 t·ha−1 and NPSZnB fertilizer at 100 kg·ha−1 increased maize yield by about 10.36%, with a net benefit of 140486.00 ETB·ha−1 and a marginal rate of return of 797.98%. As a result, vermicompost application at 5 t·ha−1 rate with synthetic NPSZnB fertilizer at 100 kg·ha−1 is found suitable for the study area.


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## Body

## 1. Introduction

Maize (Zea mays L.) is a monocotyledonous annual plant and the most widely cultivated crop in tropical areas of the world, and it is farmed for both human and animal consumption [1]. The most important major food crop in Ethiopia ranks second in terms of area coverage with an average total grain production of 4.24 t·ha−1 [2], and it is grown on more than two million hectares [3]. According to data from the Central Statistical Agency [3], maize is planted in an area of around 2.5 million hectares, or roughly 23.97 percent of the total area used for cereal crops.Today, food security is one of the major challenges to the rapidly growing worldwide population. Millions of people now live below the poverty line and are hungry as a result of declining agricultural output brought on by the shrinking area of arable land and climate change [4]. Additionally, overuse of agrochemicals and deep tillage caused soil acidity, soil infertility, and soil quality contamination, which decreased soil organic matter content, biodiversity, and productivity. In underdeveloped nations, these unsustainable farming techniques threaten food security and produce significant economic limitations [4, 5].Fertilizing crops using organic fertilizer made from organic matter, which has enormous potential to improve soil biodiversity and health, is an alternate strategy for sustainable and commercially viable agricultural production with little environmental contamination. Vermicompost is one of many alternatives and technologies that are frequently employed in sustainable agriculture and one of the stabilized organic fertilizers with a low C : N ratio that contains a variety of nutrients that are available to plants right away [6, 7]. It is produced by feeding earthworms with chopped plant biomass materials mixed with cow dung and water under the shade of trees, especially horticultural trees.In conjunction with other resources that limit crop growth, organic matter releases several plant nutrients into the soil solution that have a major impact on crop growth rate and yield [8]. Vermicomposting is a method for decomposing organic waste that is both affordable and environmentally friendly [9]. Based on the source of the vermiworm feed, it is made from various organic material sources and contains various vital plant nutrients [10]. It is more advantageous to use organic matter in combination with other organic or inorganic fertilizers than to apply it alone [11], and their inclusion in crop production systems reduces the negative impacts of salt and drought [12]. It also increases soil organic matter [13], decreases exchangeable soil acidity [14], improves the availability of soil nutrients [15], increases micronutrient levels in the soil [16], and increases crop yield [17, 18]. Vermicompost-based fertilizer boosts soil fertility, the physicochemical properties of soil, and the cation exchange capacity (CEC) [19]. In addition, vermicompost significantly improves soil structure, porosity, soil temperature, aeration, and water retention [20, 21]. In the highlands of western Ethiopia, the utilization of organic matter to address the issue of soil infertility, enhance the physicochemical qualities of soil, and establish ideal soil conditions to increase crop yield in acidic soil has been growing [22]. The rate of vermicompost and NPSZnB in the research area, however, was not further investigated. Hence, the current study was carried out to determine the effects of vermicompost and mineral NPSZnB fertilizers on the growth, yield, and yield-related variables of maize.


## 2. Materials and Methods

### 2.1. Experimental Site

The study was carried out during the 2021 growing season (May–November) in the Guto Gida district in western Ethiopia’s East Welega Zone. The experimental site is situated between (09° 11′N and 37° 09′E), between 1450 and 1700 meters above sea level. The region has a monomodal (1200–1450 mm) rainfall distribution, a long rainy season that lasts from late April to mid-October, and an average annual temperature range of 14.6–31.5°C (Figure1). The mixed farming system used in the research area is notable for producing crops like maize, millet, sorghum, peanuts, soybean, and sesame as well as raising livestock.Figure 1
Mean monthly rainfall and temperature recorded for last five years (2016–2021).The soil in the research region is nitisol, an acidic soil with a red tint that predominates in the western parts of Ethiopia (Guto Gida Agricultural Office, 2021, unpublished data). The experimental site’s topsoil (0–30 cm) was classified as a clay loam with total nitrogen (0.16%), organic carbon (1.78%), and a pH of 5.02 (Table1).Table 1
Vermicompost nutrient composition and the physicochemical features of the study site soil in Guto Gida, Western Ethiopia.
ParametersPresowing soil propertiesNutrient composition of vermicompostParticle distribution (%)—Clay39—Silt29—Sand32—Textural classClay loam—Chemical properties——pH (H2O) 1: 2.5 (w/v)5.027.18Organic carbon (%)1.7813.4Organic matter (%)3.0623.10Total nitrogen (%)0.161.79Available phosphorus (mg kg−1)4.2643.7Exchangeable Ca (cmol/kg)3.1125.9Exchangeable Mg (cmol/kg)1.2917.1Exchangeable K (cmol/kg)0.2421.5CEC (cmol/kg)14.81142CEC stands for cation exchange capacity.


### 2.2. Experimental Material

For the experimental study, the low-land hybrid maize variety “BH-546,” released by the Bako Agricultural Research Center, was used. The maize hybrid BH-540 is a single cross created from two genetically separate parents; it thrives in environments with rainfall ranging from 1000 to 1200 mm and altitudes between 1000 and 2000 meters above sea level. Depending on the surrounding environment, it can reach a height of 200–240 cm. On research stations’ and farmers’ fields, harvestable grain yields range from 7 to 8 t·ha−1 and 4.5 to 6.0 t·ha−1, respectively.


### 2.3. Treatments and Experimental Design

The experiment was carried out in a randomized complete block design (RCBD) with 16 treatments (4 × 4) and three replications, with each factorial combination consisting of four vermicompost levels (0, 2.5, 5, and 7.5 t·ha−1) and four inorganic NPSZnB fertilizer rates (0, 50, 100, and 150 kg·ha−1). The compound fertilizer NPSZnB has a ratio of 17.8% N, 35.7% P2O5, 7% S, 2.2% Zn, and 0.1% B and contains highly homogeneous granules of essential plant nutrients. In the highlands of western Ethiopia, 100 kg·ha−1 of NPSZnB and 200 kg·ha−1 of urea (CO(NH2)2) are the recommended fertilizer rates for maize. Because of this, the amounts of nitrogen needed at 0, 50, 100, and 150 kg·ha−1 of NPSZnB fertilizer rate with urea were 0, 8.9, 17.8, and 26.7 kg·ha−1 + 92 kg·ha−1 of urea, yielding 92, 100.9, 109.8, and 118.7 kg·ha−1 of nitrogen, respectively. The full description of the treatment is provided in Table 2. Each plot was 5.1 m by 4.5 m in length and width (22.95 m2).Table 2
The treatment used for the experiment.
Treatments (T)Treatments combinationT10 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT20 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT30 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT40 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBT52.5 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT62.5 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT72.5 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT82.5 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBT95 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT105 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT115 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT125 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBT137.5 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT147.5 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT157.5 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT167.5 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBThe acronym NPSZnB represents the fertilizers containing 17.8% nitrogen, 35.7% P2O5, 7% sulfur, 2.2% zinc, and 0.1 boron.


### 2.4. Experimental Procedure

Before planting, the experimental field was physically leveled and plowed by oxen to create a fine soil tilth. Within each row and between each row, maize seed was sown at intervals of 0.30 m and 0.75 m, respectively. To maintain the recommended population (44,444 plants ha−1), two seeds hill−1 were planted, and one week following emergence, it was thinned down to one plant hill−1. In each plot, 102 plants were planted in 6 rows, with 17 plants in each row. Urea (CO(NH2)2) was applied in a split application, i.e., half of the recommended dose (100 kg·ha−1) was applied during the time of planting, and the remaining half (100 kg·ha−1) was applied 40 days later. According to the treatment levels, vermicompost was put in the soil two weeks before planting and mixed well with the soil to lessen loss from rain and wind uptake. The remaining required cultural and agronomic practices were applied uniformly for all treatments following the local recommendations, and the full dose of inorganic NPSZnB fertilizer was applied at the rates (0, 114.75, 229.5, and 344.25 g plot−1) as per the treatment at the time of planting.


### 2.5. Vermicompost Preparation and Application

Vermicompost was prepared from chopped and dried maize stock and cow dung. The maize stock was reduced in size to maximize the surface area available to vermiworms. It was then combined in a 3 : 1 ratio with cow dung solution and allowed to partially decompose for three weeks before being ready in 60 days. At the bottom of the 182.88 cm × 60.96 cm × 60.96 cm bed, a layer of 15 to 20 cm of chopped maize stock was kept as bedding material. Partially decomposed vermicompost was then moved from one bedding material (box) to another within a month interval for proper decomposition and to maintain aeration until the compost matured at 60 days (23). An adult red earthworm(Eisenia fetida), which is 3 to 5 months old, 8 to 10 cm long, 0.5 to 0.6 g heavy, and 500 to 1000 in number, was released on the top layer of the bed with 10 earthworms to break down mixed cow manure and corn stock. After the worms were placed on the bed, water was immediately sprayed on the surface of the chopped material to enhance material decomposition. Water was sprinkled daily and covered with polythene to keep the material moist (60 to 70% moisture content) and prevent evapotranspiration from the bedding material (23). Vermicompost, which was put into the soil two weeks before the planting of maize, was a mature and well-decomposed product with a pH of 7.18, organic carbon of 13.4%, and total nitrogen of 1.79% (Table 1).


### 2.6. Soil Sampling, Analysis, and Vermicompost Chemical Composition

Before planting, random soil samples were taken in a zigzag pattern at a depth of 0 to 30 cm. Composite samples were air-dried, prepared, and homogenized to make an analysis and identify the soil’s physicochemical characteristics, such as texture, pH, organic carbon, total nitrogen, exchangeable calcium, magnesium, potassium, cation exchange capacity (CEC), and available phosphorus. The soil samples were mashed up, passed through a 2 mm sieve, and then examined at the Holota Soil Laboratory to determine their physicochemical makeup. The distribution of soil particle size was determined by the hydrometer method, and the pH of the soil was determined by using a pH meter at 1 : 2.5 soils-to-water ratio [23, 24]. The amounts of soil organic carbon, total nitrogen, and available phosphorus were measured using the techniques created by Walkley Black Oxidation [25], Kjeldahl [26], and Bray-I [27], respectively. Similar to this, vermicompost’s physical and chemical characteristics were examined before being applied to the soil at the Holota Soil Laboratory Test, Holota, Ethiopia.


### 2.7. Data Collection and Analysis

#### 2.7.1. Phenology and Growth Parameter

Days to 50% tassel and silk, days to 90% maturity, and other phenological parameters of maize were calculated as the number of days from the day of planting to the time at which 50% of each plot produced tassels, began to produce pollen, and formed a black layer at the point where the kernel attached to the corn cob, respectively. Plant height was assessed as the distance from the ground level to the location where the tassel appeared and started to branch out at the physiological maturity stage from randomly selected 10 plants per net plot. The leaf area index (LAI) was calculated as the ratio of total leaf area obtained from 10 plants per net plot (L × W × K) to the land area occupied by the plant (0.75 m × 0.30 m = 0.225 m2), where L = leaf length, W = leaf width, and K = correction factor (0.75) [28].


#### 2.7.2. Yield Components and Yield of Maize

Data from 10 pretagged plants per net plot area were used to calculate the number of ears plant−1, ear weight (g), and the number of kernels ear−1. Using an electronic grain counter and a sensitive balance, thousand-grain weights (g) were counted from a bulk of shelled grain and measured at the standard moisture level (12.5%). Additionally, the total biomass harvested from each experimental plot at the time of harvest and the weight of the bulk of grain harvested from the net plot were used to determine the biological yield (t·ha−1) and grain yield (t·ha−1) correspondingly. The harvest index (%) was calculated by dividing grain yield (t·ha−1) by above-ground biomass yield (t·ha−1).


### 2.8. Economic Analysis

According to the CIMMYT procedure, a partial budget analysis of grain yields was conducted to choose a level of vermicompost application that would be economically viable and lucrative when combined with the rate of NPSZnB fertilizer [29]. After deducting 10% from the grain output to estimate the true yield under farmers’ conditions, the prices for NPSZnB fertilizer (17.50 ETB kg−1) and the cost of applying vermicompost and NPSZnB fertilizers (0.30 ETB kg−1) were utilized for a partial budget analysis. At the local market of the research area, the yield of maize was appraised at an average open market price of 20 ETB kg−1 in December 2021.


### 2.9. Data Analysis

The various collected data were examined using Genstat Software 18 [30], following the statistical techniques given by Gomez and Gomez [31]. An analysis of variance (ANOVA) for a randomized complete block design was used for the statistical test, and Fisher’s protected least significant difference was used to identify parameters with significant differences between treatments at a p = 0.05 level of probability.


## 2.1. Experimental Site

The study was carried out during the 2021 growing season (May–November) in the Guto Gida district in western Ethiopia’s East Welega Zone. The experimental site is situated between (09° 11′N and 37° 09′E), between 1450 and 1700 meters above sea level. The region has a monomodal (1200–1450 mm) rainfall distribution, a long rainy season that lasts from late April to mid-October, and an average annual temperature range of 14.6–31.5°C (Figure1). The mixed farming system used in the research area is notable for producing crops like maize, millet, sorghum, peanuts, soybean, and sesame as well as raising livestock.Figure 1
Mean monthly rainfall and temperature recorded for last five years (2016–2021).The soil in the research region is nitisol, an acidic soil with a red tint that predominates in the western parts of Ethiopia (Guto Gida Agricultural Office, 2021, unpublished data). The experimental site’s topsoil (0–30 cm) was classified as a clay loam with total nitrogen (0.16%), organic carbon (1.78%), and a pH of 5.02 (Table1).Table 1
Vermicompost nutrient composition and the physicochemical features of the study site soil in Guto Gida, Western Ethiopia.
ParametersPresowing soil propertiesNutrient composition of vermicompostParticle distribution (%)—Clay39—Silt29—Sand32—Textural classClay loam—Chemical properties——pH (H2O) 1: 2.5 (w/v)5.027.18Organic carbon (%)1.7813.4Organic matter (%)3.0623.10Total nitrogen (%)0.161.79Available phosphorus (mg kg−1)4.2643.7Exchangeable Ca (cmol/kg)3.1125.9Exchangeable Mg (cmol/kg)1.2917.1Exchangeable K (cmol/kg)0.2421.5CEC (cmol/kg)14.81142CEC stands for cation exchange capacity.


## 2.2. Experimental Material

For the experimental study, the low-land hybrid maize variety “BH-546,” released by the Bako Agricultural Research Center, was used. The maize hybrid BH-540 is a single cross created from two genetically separate parents; it thrives in environments with rainfall ranging from 1000 to 1200 mm and altitudes between 1000 and 2000 meters above sea level. Depending on the surrounding environment, it can reach a height of 200–240 cm. On research stations’ and farmers’ fields, harvestable grain yields range from 7 to 8 t·ha−1 and 4.5 to 6.0 t·ha−1, respectively.


## 2.3. Treatments and Experimental Design

The experiment was carried out in a randomized complete block design (RCBD) with 16 treatments (4 × 4) and three replications, with each factorial combination consisting of four vermicompost levels (0, 2.5, 5, and 7.5 t·ha−1) and four inorganic NPSZnB fertilizer rates (0, 50, 100, and 150 kg·ha−1). The compound fertilizer NPSZnB has a ratio of 17.8% N, 35.7% P2O5, 7% S, 2.2% Zn, and 0.1% B and contains highly homogeneous granules of essential plant nutrients. In the highlands of western Ethiopia, 100 kg·ha−1 of NPSZnB and 200 kg·ha−1 of urea (CO(NH2)2) are the recommended fertilizer rates for maize. Because of this, the amounts of nitrogen needed at 0, 50, 100, and 150 kg·ha−1 of NPSZnB fertilizer rate with urea were 0, 8.9, 17.8, and 26.7 kg·ha−1 + 92 kg·ha−1 of urea, yielding 92, 100.9, 109.8, and 118.7 kg·ha−1 of nitrogen, respectively. The full description of the treatment is provided in Table 2. Each plot was 5.1 m by 4.5 m in length and width (22.95 m2).Table 2
The treatment used for the experiment.
Treatments (T)Treatments combinationT10 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT20 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT30 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT40 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBT52.5 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT62.5 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT72.5 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT82.5 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBT95 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT105 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT115 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT125 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBT137.5 t·ha−1 vermicompost + 0 kg·ha−1 NPSZnBT147.5 t·ha−1 vermicompost + 50 kg·ha−1 NPSZnBT157.5 t·ha−1 vermicompost + 100 kg·ha−1 NPSZnBT167.5 t·ha−1 vermicompost + 150 kg·ha−1 NPSZnBThe acronym NPSZnB represents the fertilizers containing 17.8% nitrogen, 35.7% P2O5, 7% sulfur, 2.2% zinc, and 0.1 boron.


## 2.4. Experimental Procedure

Before planting, the experimental field was physically leveled and plowed by oxen to create a fine soil tilth. Within each row and between each row, maize seed was sown at intervals of 0.30 m and 0.75 m, respectively. To maintain the recommended population (44,444 plants ha−1), two seeds hill−1 were planted, and one week following emergence, it was thinned down to one plant hill−1. In each plot, 102 plants were planted in 6 rows, with 17 plants in each row. Urea (CO(NH2)2) was applied in a split application, i.e., half of the recommended dose (100 kg·ha−1) was applied during the time of planting, and the remaining half (100 kg·ha−1) was applied 40 days later. According to the treatment levels, vermicompost was put in the soil two weeks before planting and mixed well with the soil to lessen loss from rain and wind uptake. The remaining required cultural and agronomic practices were applied uniformly for all treatments following the local recommendations, and the full dose of inorganic NPSZnB fertilizer was applied at the rates (0, 114.75, 229.5, and 344.25 g plot−1) as per the treatment at the time of planting.


## 2.5. Vermicompost Preparation and Application

Vermicompost was prepared from chopped and dried maize stock and cow dung. The maize stock was reduced in size to maximize the surface area available to vermiworms. It was then combined in a 3 : 1 ratio with cow dung solution and allowed to partially decompose for three weeks before being ready in 60 days. At the bottom of the 182.88 cm × 60.96 cm × 60.96 cm bed, a layer of 15 to 20 cm of chopped maize stock was kept as bedding material. Partially decomposed vermicompost was then moved from one bedding material (box) to another within a month interval for proper decomposition and to maintain aeration until the compost matured at 60 days (23). An adult red earthworm(Eisenia fetida), which is 3 to 5 months old, 8 to 10 cm long, 0.5 to 0.6 g heavy, and 500 to 1000 in number, was released on the top layer of the bed with 10 earthworms to break down mixed cow manure and corn stock. After the worms were placed on the bed, water was immediately sprayed on the surface of the chopped material to enhance material decomposition. Water was sprinkled daily and covered with polythene to keep the material moist (60 to 70% moisture content) and prevent evapotranspiration from the bedding material (23). Vermicompost, which was put into the soil two weeks before the planting of maize, was a mature and well-decomposed product with a pH of 7.18, organic carbon of 13.4%, and total nitrogen of 1.79% (Table 1).


## 2.6. Soil Sampling, Analysis, and Vermicompost Chemical Composition

Before planting, random soil samples were taken in a zigzag pattern at a depth of 0 to 30 cm. Composite samples were air-dried, prepared, and homogenized to make an analysis and identify the soil’s physicochemical characteristics, such as texture, pH, organic carbon, total nitrogen, exchangeable calcium, magnesium, potassium, cation exchange capacity (CEC), and available phosphorus. The soil samples were mashed up, passed through a 2 mm sieve, and then examined at the Holota Soil Laboratory to determine their physicochemical makeup. The distribution of soil particle size was determined by the hydrometer method, and the pH of the soil was determined by using a pH meter at 1 : 2.5 soils-to-water ratio [23, 24]. The amounts of soil organic carbon, total nitrogen, and available phosphorus were measured using the techniques created by Walkley Black Oxidation [25], Kjeldahl [26], and Bray-I [27], respectively. Similar to this, vermicompost’s physical and chemical characteristics were examined before being applied to the soil at the Holota Soil Laboratory Test, Holota, Ethiopia.


## 2.7. Data Collection and Analysis

### 2.7.1. Phenology and Growth Parameter

Days to 50% tassel and silk, days to 90% maturity, and other phenological parameters of maize were calculated as the number of days from the day of planting to the time at which 50% of each plot produced tassels, began to produce pollen, and formed a black layer at the point where the kernel attached to the corn cob, respectively. Plant height was assessed as the distance from the ground level to the location where the tassel appeared and started to branch out at the physiological maturity stage from randomly selected 10 plants per net plot. The leaf area index (LAI) was calculated as the ratio of total leaf area obtained from 10 plants per net plot (L × W × K) to the land area occupied by the plant (0.75 m × 0.30 m = 0.225 m2), where L = leaf length, W = leaf width, and K = correction factor (0.75) [28].


### 2.7.2. Yield Components and Yield of Maize

Data from 10 pretagged plants per net plot area were used to calculate the number of ears plant−1, ear weight (g), and the number of kernels ear−1. Using an electronic grain counter and a sensitive balance, thousand-grain weights (g) were counted from a bulk of shelled grain and measured at the standard moisture level (12.5%). Additionally, the total biomass harvested from each experimental plot at the time of harvest and the weight of the bulk of grain harvested from the net plot were used to determine the biological yield (t·ha−1) and grain yield (t·ha−1) correspondingly. The harvest index (%) was calculated by dividing grain yield (t·ha−1) by above-ground biomass yield (t·ha−1).


## 2.7.1. Phenology and Growth Parameter

Days to 50% tassel and silk, days to 90% maturity, and other phenological parameters of maize were calculated as the number of days from the day of planting to the time at which 50% of each plot produced tassels, began to produce pollen, and formed a black layer at the point where the kernel attached to the corn cob, respectively. Plant height was assessed as the distance from the ground level to the location where the tassel appeared and started to branch out at the physiological maturity stage from randomly selected 10 plants per net plot. The leaf area index (LAI) was calculated as the ratio of total leaf area obtained from 10 plants per net plot (L × W × K) to the land area occupied by the plant (0.75 m × 0.30 m = 0.225 m2), where L = leaf length, W = leaf width, and K = correction factor (0.75) [28].


## 2.7.2. Yield Components and Yield of Maize

Data from 10 pretagged plants per net plot area were used to calculate the number of ears plant−1, ear weight (g), and the number of kernels ear−1. Using an electronic grain counter and a sensitive balance, thousand-grain weights (g) were counted from a bulk of shelled grain and measured at the standard moisture level (12.5%). Additionally, the total biomass harvested from each experimental plot at the time of harvest and the weight of the bulk of grain harvested from the net plot were used to determine the biological yield (t·ha−1) and grain yield (t·ha−1) correspondingly. The harvest index (%) was calculated by dividing grain yield (t·ha−1) by above-ground biomass yield (t·ha−1).


## 2.8. Economic Analysis

According to the CIMMYT procedure, a partial budget analysis of grain yields was conducted to choose a level of vermicompost application that would be economically viable and lucrative when combined with the rate of NPSZnB fertilizer [29]. After deducting 10% from the grain output to estimate the true yield under farmers’ conditions, the prices for NPSZnB fertilizer (17.50 ETB kg−1) and the cost of applying vermicompost and NPSZnB fertilizers (0.30 ETB kg−1) were utilized for a partial budget analysis. At the local market of the research area, the yield of maize was appraised at an average open market price of 20 ETB kg−1 in December 2021.


## 2.9. Data Analysis

The various collected data were examined using Genstat Software 18 [30], following the statistical techniques given by Gomez and Gomez [31]. An analysis of variance (ANOVA) for a randomized complete block design was used for the statistical test, and Fisher’s protected least significant difference was used to identify parameters with significant differences between treatments at a p = 0.05 level of probability.


## 3. Result and Discussion

### 3.1. Experimental Site Physicochemical Characteristics of Soil and Vermicompost

The physicochemical makeup of the soil at the study location before planting and that of the vermicompost used are shown in Table1. The experimental soil pH of the study site was moderately acidic as rated by Tekalign [32], available phosphorus (4.26 mg·kg−1) was at a low level, total nitrogen (0.16%) was present in a low range, and a cation exchange capacity of 14.81 was found to be poor (Table 1). Vermicompost had values for pH, organic carbon, organic matter, total nitrogen, calcium, potassium, and cation exchange capacity that were relatively high when compared to presowing soil (Table 1). These findings suggest that adding more vermicompost to the soil has a tremendous potential to improve soil structure, soil pH, and soil porosity and decrease soil bulk density because organic fertilizers in nature have larger pore spaces and lower bulk densities than soil. According to [6], increasing vermicompost levels enhance soil organic matter, total nitrogen, and pH, which is consistent with the current finding.


### 3.2. Phenology and Growth Parameters of Maize

Vermicompost concentrations and inorganic NPSZnB fertilizer rates significantly influenced days to 50% tasseling, days to 50% silking, and days to 90% physiological maturity, although their interactions were not significant for all phenological parameters of maize. However, the interaction effect of NPSZnB fertilizer rate and vermicompost levels had a significant impact on growth metrics such as plant height and leaf area index. The rate of vermicompost applied at 7.5 t·ha−1, which was on par with rates applied at 5.0 t·ha−1 and 2.5 t·ha−1, resulted in the longest days to tasseling (71.55), whereas the shortest days (70.21) to grow tassels were reported in plots not treated with vermicompost (Table 3). In comparison to the control treatment, which tasseled r quickly (69.86 days), maize cultivated with NPSZnB fertilizer applied at a rate of 150 kg·ha−1 took a maximum of 72.06 days to develop tassel (Table 3). In agreement with the findings of the current study, [33] reported a considerable influence of inorganic fertilizer on the number of days to 50% tasseling. In terms of days to 50% silking and days to 90% maturity, maize in the control plot silks and reaches maturity quickly, whereas the highest number of days to 50% silking (76.44 days) was found in the vermicompost-treated plot at 7.5 t·ha−1, which was on par with the results from 5.0 t·ha−1 and 2.5 t·ha−1. Vermicompost applied at 7.5 t·ha−1 was on par with all vermicompost levels, except for the control treatment, in terms of days to 90% maturity (142.7 days). Similar to this, the NPSZnB fertilizer rate at 150 kg·ha−1, which was on par with the value obtained from 100 kg·ha−1, produced the longest days to silking (76.39 days) and maturity (142.80 days) (Table 3).Table 3
Main effect of vermicompost levels and inorganic NPSZnB fertilizer rates on the number of days to 50% of the days to tassel, number of days to 50% silking, and the number of days to 90% physiological maturity of maize in Guto Gida, Western Ethiopia.
Treatments50% days to tassel50% days to silk90% days to maturityVermicompost (t·ha−1)070.21b75.33b141.40b2.571.21a75.67ab142.20ab5.071.43a76.33a141.90ab7.571.55a76.44a142.70ap value0.0030.0030.042LSD (0.05)0.950.911.20NPSZnB (kg·ha−1)069.86cd74.79b141.10cd5070.21bc75.00b141.60bc10070.86b76.06a142.30ab15072.06a76.39a142.80ap value0.001<0.0010.015LSD (0.05)0.740.710.94CV (%)1.61.40.96LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Higher soil fertility and increased nutrient uptake for all basically needed plant nutrients may be the cause of the delayed phenological parameters of maize that responded to the longer vegetative development period of the plant. Increased maize vegetative growth, expanded leaves, and better nitrogen usage efficiency may be the causes of the prolonged days to tasseling, days to silking, and days to maturity in plots treated with increased amounts of NPSZnB fertilizer (0–150 kg·ha−1). In agreement with this finding, Lal [34] showed that elevated levels of organic and inorganic nitrogen sources result in a prolonged vegetative development period (crop phenology). As vermicompost levels rose from 5 to 20 t·ha−1, watermelon flowering was delayed [35].The study also showed that the interaction between vermicompost levels and the rate of chemical NPSZnB fertilizer had a considerable impact on the growth parameters of maize, including plant height and leaf area index (LAI). The greatest plant height (282.80 cm) was achieved by the maize plant growing in a plot treated with 150 kg·ha−1 of NPSZnB fertilizer at zero level of vermicompost, whereas the least plant height (252.5 cm) was obtained in the control plot or plot untreated with vermicompost and NPSZnB fertilizers (Table 4). This finding may be the result of the inorganic nitrogen in NPSZnB fertilizer having a beneficial influence on rapid maize vegetative growth. Additionally, the addition of vermicompost improves soil pH and increases nutrient uptake by plants, resulting in enhanced production of vegetative growth and parts, specifically increased plant height and leaf blade size. According to a study by [36], plants grow taller when chemical fertilizer levels hold nitrogen fertilizer. However, [11] observed that the height of the maize plant treated with vermicompost plus NPK was greater than that of the vermicompost or minerally fertilized plot. Additionally, increasing the vermicompost level was found to boost pak choi height [37].Table 4
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer rates on plant height (cm) and leaf area index (LAI) of maize in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Plant height (cm)Leaf area index00252.50f3.937h050260.80e4.398fg0100273.70b4.497efg0150282.80a4.714b-f2.50267.40cd4.327g2.550268.50c4.309g2.5100267.30cd4.771b-e2.5150266.30cd4.791b-e5.00266.80cd4.493efg5.050269.00c4.541d-g5.0100268.80c4.982b5.0150270.00bc4.790b-e7.50267.40cd4.574c-g7.550263.70de4.835bcd7.5100270.00bc4.889bc7.5150269.60c5.657ap value0.0010.048LSD (0.05)3.9260.335CV (%)0.94.4LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Similar to this, the greatest leaf area index (5.657) was calculated from a plot treated with vermicompost at 7.5 t·ha−1 associated with 150 kg·ha−1 NPSZnB fertilizer and was followed by a 4.982 leaf area index assessed from a combination of 5 t·ha−1 vermicompost and 100 kg·ha−1 of NSPZnB, while the lowest leaf area index (3.937) was registered from the control plot untreated with vermicompost and NPSZ (Table 4). The largest leaf area index (5.657) at greater vermicompost levels and NPSZnB may be connected to the direct role of vermicompost in enhancing the physical, biological, and chemical characteristics of the soil to produce favorable conditions for crop growth and development. When applied together, vermicompost and mineral fertilizer may release greater amounts of plant nutrients and more quickly make nitrogen from mineral fertilizer NPSZnB available, both of which may play a significant role in more vigorous plant development compared to other treatments. Khan et al. [38] found increased plant height with increasing application levels of nitrogen-containing fertilizer, which is consistent with the findings of the current investigation. Similar findings were made by [39], who noted higher plant height and leaf area with greater nitrogen fertilizer available over the course of a maize crop’s life cycle.


### 3.3. Yield Components and Yield

#### 3.3.1. Ear Weight (g)

Vermicompost applied in combination with mixed NPSZnB fertilizer at various rates considerably altered the ear weight of maize. The maximum ear weight (277.80 g), which was at par in the application of vermicompost at all levels with 100 kg·ha−1, was obtained when vermicompost level at 5 t·ha−1 was combined with an inorganic NPSZnB fertilizer rate at 150 kg·ha−1, except plots not treated with vermicompost at the same rate of NPSZnB fertilizer. The lowest ear weight (237.10 g) was obtained from the plot not treated with both vermicompost and NPSZnB fertilizer, which was comparable to the outcome of the plot not treated with vermicompost and a 50 kg·ha−1 inorganic NPSZnB fertilizer rate (Table 5). Improved crop growth and greater dry matter output as a result of improved nutrient uptake, particularly nitrogen, from inorganic and vermicompost (organic) sources may be the cause of increased ear weight with increased NPSZnB fertilizer at levels of vermicompost. Additionally, greater ear weight with higher vermicompost levels may be caused by a change in the composition of the soil’s organic matter as a result of the vermicompost’s decomposition and mineralization, which would boost the early nutrient supply from commercial fertilizers (NPSZnB). Ear weight was increased with a higher level of both organic fertilizer (vermicompost) and inorganic fertilizer and was favorably affected when organic and inorganic sources of fertilizer were used together [40, 41]. In contrast, [42] reported the maximum bean pod weight when treated with 100% vermicompost.Table 5
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer rates on-ear weight (g) and thousand kernel weight (g) of maize in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Ear weight (g)Thousand kernel weight (g)00237.10f42.14e050239.60ef44.49d0100248.30de44.31de0150268.00bc44.82cd2.50247.60de43.38de2.550250.50d44.90cd2.5100274.60ab48.03ab2.5150268.00bc48.90ab5.00250.20d43.59de5.050260.30c45.27cd5.0100276.10ab49.79a5.0150277.80a48.75ab7.50249.00d44.28de7.550268.30bc46.98bc7.5100276.50ab48.75ab7.5150276.90ab48.87abp value0.0040.045LSD (0.05)8.9712.225CV (%)2.13.0LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.


#### 3.3.2. Thousand Kernel Weight (g)

The use of chemically blended NPSZnB fertilizer rates and vermicompost levels together had a significant effect on thousand kernels’ weights. The highest grain weight (49.79 g) came from an integrated application of vermicompost and blended NPSZnB fertilizer at a rate of 5.0 t·ha−1 with 100 kg·ha−1, which was at par to 7.5 t·ha−1 × 150 kg·ha−1 (48.87 g), 7.5 t·ha−1 × 100 kg·ha−1 (48.75 g), 5 t·ha−1 × 150 kg·ha−1 (48.75 g), and 2.5 t·ha−1 × 150 kg·ha−1 (48.03 g). In comparison, the plot not treated with any of the two fertilizers had the lowest thousand kernel weight (42.14 g) (Table 5). Greater soil fertility, enhanced nutrient uptake, and an effective photosynthetic process may all contribute to a heavier thousand kernel weight at higher vermicompost levels and higher rates of NPSZnB, which may be assimilated to economic yield (grain). The fact that the control treatment resulted in lower weight could be a result of the decreased nutrient content of the soil, which would make fewer nutrients available for healthy and optimal plant growth. Similar to previous research, [11] reported enhanced thousand-grain weight when vermicompost and NPK were applied together as opposed to separately. The linear increase in thousand seed weight coincided with the amounts of mineral and organic fertilizers.


#### 3.3.3. Number of Kernel Ear−1

The main effect of the inorganic NPSZnB fertilizer rate had a significant influence on the number of kernels in ear−1. The vermicompost ratios and their interactions with the rates of inorganic NPSZnB fertilizer, however, had not shown a significant effect. An increase in the number of kernels ear−1 was seen with increased incorporation of NPSZnB fertilizer rates from 0 to 150 kg·ha−1. In comparison to the control plot and the plot treated with 50 kg·ha−1 of NPSZnB fertilizer, which produced the least amount of kernel ear−1, the plot treated with 100 kg·ha−1 and 150 kg·ha−1 of chemically blended NPSZnB fertilizer produced a greater number of kernel ear−1 (Table 6). Increased numbers of kernel ear−1 with increased NPSZnB fertilizer rates may be associated with greater availability of nitrogen and phosphorus, as well as the micronutrients zinc and boron. Even though it was not statistically significant, the number of kernels ear−1 increased when vermicompost concentration rose from 0 to 7.5 t·ha−1. This may be because vermicompost application increased the soil’s biophysicochemical characteristics, such as its CEC and organic carbon, phosphorus, and nitrogen content. Vermicompost also increases soil moisture since it is an organic material with a large surface area, which improves nutrient uptake and utilization efficiency and may result in more kernels ear−1. According to [43], vermicompost-treated plots of rice had 8.65% more grains per panicle than plots that had only received mineral fertilizer. Following the current study [36, 41], it was found that plots treated with a combined mineral and organic fertilizer application had longer cobs and more kernels per cob−1 than plots received with separate applications of the two fertilizers.Table 6
Main effects of vermicompost levels and inorganic NPSZnB fertilizer rates on the number of kernel ear−1, biological yield (t·ha−1), and harvest index (%) of maize in Guto Gida, Western Ethiopia.
TreatmentsNumber of kernels ear−1Biological yield (t·ha−1)Harvest index (%)Vermicompost (t·ha−1)0540.1318.31c36.002.5546.0019.67ab35.795.0562.3020.33a34.827.5569.6620.52a35.14p value0.106<0.0010.103LSD (0.05)33.1360.9382.021NPSZnB (kg·ha−1)0522.40b18.76b35.2050522.54b18.95b35.24100555.20a19.81a35.04150566.80a20.34a35.95p value<0.001<0.0010.415LSD (0.05)25.6670.7271.565CV (%)6.305.605.60LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.


#### 3.3.4. Above Ground Biomass (t·ha−1)

The biological yield of maize was significantly influenced by the main effects of vermicompost and chemically blended mineral NPSZnB fertilizer. The increased biomass weight of 19.67–20.52 t·ha−1 was obtained by applying vermicompost at a level of 2.5–7.5 t·ha−1. In contrast, plots that were not given vermicompost had the least above-ground biomass of 18.31 t·ha−1 (Table 6). Concerning NPSZnB fertilizer rates, the highest and lowest values (18.76 t·ha−1 and 20.34 t·ha−1) were obtained from the application of NPSZnB at 150 kg·ha−1 and were statistically similar to the values obtained from 100 kg·ha−1 of NPSZnB and control, respectively (Table 6). The enhanced nutrient content in the soil improved nutrient uptake, and the timely availability of nitrogen released quickly from NPSZnB fertilizer could all result in an increased biological yield of maize with an increased amount of vermicompost and NPSZnB. This could be because vermicompost has better soil properties that encourage root growth, which could lead to higher growth of above-ground plant parts. Increases in the growth components of maize, such as leaves, sheaths, stems, cobs, and grain, as well as water retention as a consequence of the high specific area properties of vermicompost fed to the soil, lead to an increase in the crop’s above-ground biomass. Additionally, applying vermicompost to the crop during the growth phase may result in favorable conditions for yield-determining components and, consequently, biological yield. Vermicompost contains sufficient quantities of vital plant nutrients. Compared to maize that was not treated with vermicompost fertilizer, [33] reported an increased total dry weight of maize with a higher amount of vermicompost and NPS fertilizer. Similar results were reported by Nasab et al. [44], who found that the biomass weight of maize increased by 13.58% when vermicompost application increased from 4 to 12 t·ha−1. Application of vermicompost at 10 t·ha−1 and mineral fertilizer together increased rice biomass compared to cow dung applied at the same level plus mineral fertilizer or only mineral fertilizer [43]. The study found that applying 50% vermicompost and 50% of the locally recommended NPS together increased biomass by 8.72% when compared to applying 100% of the locally recommended NPS alone [45]. Furthermore, increased vermicompost application alone or with other organic and inorganic fertilizers increased above-ground biomass [46].


#### 3.3.5. Grain Yield (t·ha−1)

Analysis of variance revealed that the combined application of organic fertilizer (vermicompost) and mineral fertilizer (NPSZnB) had a significant influence on the grain production of maize. The highest grain yield (8.03 t·ha−1) was recorded from the integrated application of vermicompost with blended NPSZnB fertilizer at a rate of 7.5 t·ha−1 and 150 kg·ha−1, which was statistically similar to the grain yield harvested from plots treated with 5 t·ha−1 × 100 kg·ha−1, 5 t·ha−1 × 150 kg·ha−1, and 7.5 t·ha−1 × 100 kg·ha−1 (Table 7). The lowest grain yield, 6.96 t·ha−1, was produced from a treatment not treated with either vermicompost or inorganic NPSZnB fertilizer (Table 7). The effectiveness of vermicompost at higher rates, as well as the increased number of kernel ear−1 and enhanced thousand-grain weights at this level, may be related to the increased grain output at the higher level of vermicompost. Additionally, the potential for vermicompost to reduce soil bulk density, exchangeable aluminum, and iron, and restrict root growth and nutrient uptake may account for the higher grain yield with increased vermicompost application. Vermicompost and mineral fertilizer used together may result in better soil properties such as pH, porosity, aeration, temperature, moisture, permeability, soil biodiversity, and fertility for plant growth, which may promote more photosynthate allocation. Vermicompost boosts soil-plant nutrients, including potassium, calcium, and micronutrients like copper, zinc, and iron when combined with other minerals. These nutrients support many physiological processes in plants, which resulted in higher grain yields as a consequence of improved fertilizer usage efficiency and increased cation exchange capacity of the soil with organic matter.Table 7
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer on grain yield (t·ha−1) and grain yield increased (%) in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Grain yield (t·ha−1)006.96h0507.03gh01007.24ef01507.47de2.507.22fg2.5507.32def2.51007.74cd2.51507.78bc5.007.29ef5.0507.54d5.01007.99ab5.01507.97ab7.507.30ef7.5507.71cd7.51007.97ab7.51508.03ap value0.005LSD (0.05)0.227CV (%)2.1LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Similar to the current study, several findings showed that maize grain production improved when organic and inorganic fertilizers were applied together [47]. According to Chimdessa and Sori [33], the addition of 3 t·ha−1 of vermicompost increased grain production by approximately 66.88% compared to the treatment using 100 kg·ha−1 of the locally advised NPS rate. Additionally, past research indicated that higher vermicompost quality and vermicompost levels boosted grain yield [11, 44, 48–50]. Similarly, [36, 45, 51–53] found that grain yield responded well when organic fertilizer and mineral fertilizer were applied together. Moreover, Hoque et al. [43] reported that rice yield increased by 5.68% when vermicompost at 10 t·ha−1 and mineral fertilizer were applied in combination, and compared with applying only the recommended rate of mineral fertilizer. In contrast to the present study, Abera et al. [54] in their three consecutive years study, reported a lower yield of maize in plots treated with only vermicompost from 4–12 t·ha−1or in plots treated with both vermicompost (25–75% of 4 t·ha−1) and 50–75% of recommended mineral NPS fertilizer compared with the plot treated with only NPS at the recommended rate (100%).


#### 3.3.6. Harvest Index (%)

Analysis of variance revealed that the main effects of blended NPSZnB fertilizer, vermicompost, and their interaction had no statistically significant effects on the harvest index of maize (Table6). However, [55] reported a significantly higher harvest index when organic and inorganic fertilizer were used together compared to separate utilization. Similarly, [56] also found an increased harvest index of maize treated with a higher level of vermicompost, lime, and chemical fertilizer.


### 3.4. Economic Analysis

Analysis of variance showed that integrated application of vermicompost and mineral NPSZnB fertilizer at 5 t·ha−1 × 100 kg·ha−1 yielded the highest net benefit (140486 ETB·ha−1) with a marginal rate of return of 797.98%, followed by a net benefit of 136970 ETB·ha−1, which was obtained at 2.5 t·ha−1 × 100 kg·ha−1, with a marginal rate of return of 769.66% (Table 8). The combined application of vermicompost at a rate of 0 t·ha−1 with NPSZnB fertilizer at a rate of 50 kg·ha−1 produced a minimum net benefit of 125650 ETB·ha−1 with a marginal rate of return of 47.64% (Table 8). In contrast, the plots treated with 150 kg·ha−1 with NPSZnB fertilizer and 2.5 t·ha−1 and 5.0 t·ha−1 of vermicompost were dominated (Table 8). Therefore, it was found that applying vermicompost at a level of 5 t·ha−1 along with 100 kg·ha−1 of mineral NPSZnB fertilizer rate was economically viable for maize production in Guto Gida district, Western Ethiopia, according to this partial budget study.Table 8
Partial budget analysis of maize yield for determination of the economically profitable level of vermicompost and NPSZnB fertilizer rate.
TreatmentV/compost (t·ha−1)NPS (kg·ha−1)Grain yield (t·ha−1)Adjusted grain yield (t·ha−1)Gross benefit (ETB·ha−1)TVC (ETB·ha−1)Net benefit (ETB·ha−1)MRR%T1006.966.261252260.00125226.00—T20507.036.33126540890.00125650.0047.64T301007.246.521303201780.00128540.00324.72T401507.476.731345142670.00131844.00371.24T52.507.226.50130014750.00129264.00—T62.5507.326.591317601640.00130120.0096.18T72.51007.756.981395002530.00136970.00769.66T82.51507.787.001400763420.00136656.00DT95.007.296.561311661500.00129666.00—T105.0507.546.791357742390.00133384.00417.75T115.01007.997.191437663280.00140486.00797.98T125.01507.977.181435324170.00139362.00DT137.507.306.571314002250.00129150.00—T147.5507.716.941387803140.00135640.00729.21T157.51007.977.181435144030.00139484.00431.91T167.51508.037.231445404920.00139620.0013.60Application costs of vermicompost and mineral NPSZnB fertilizer = 30 ETB quintal−1; unit cost of NPSZnB fertilizer = 17.5 ETB·kg−1; maize price 20 ETB·kg−1; ETB = Ethiopian birr; NPSZnB = fertilizer containing 17.8%N, 37.5%P2O5 7%S, 2.2%Zn, and 0.1%B; TVC = total variable cost; MRR = marginal rate of return; and D = dominated.


## 3.1. Experimental Site Physicochemical Characteristics of Soil and Vermicompost

The physicochemical makeup of the soil at the study location before planting and that of the vermicompost used are shown in Table1. The experimental soil pH of the study site was moderately acidic as rated by Tekalign [32], available phosphorus (4.26 mg·kg−1) was at a low level, total nitrogen (0.16%) was present in a low range, and a cation exchange capacity of 14.81 was found to be poor (Table 1). Vermicompost had values for pH, organic carbon, organic matter, total nitrogen, calcium, potassium, and cation exchange capacity that were relatively high when compared to presowing soil (Table 1). These findings suggest that adding more vermicompost to the soil has a tremendous potential to improve soil structure, soil pH, and soil porosity and decrease soil bulk density because organic fertilizers in nature have larger pore spaces and lower bulk densities than soil. According to [6], increasing vermicompost levels enhance soil organic matter, total nitrogen, and pH, which is consistent with the current finding.


## 3.2. Phenology and Growth Parameters of Maize

Vermicompost concentrations and inorganic NPSZnB fertilizer rates significantly influenced days to 50% tasseling, days to 50% silking, and days to 90% physiological maturity, although their interactions were not significant for all phenological parameters of maize. However, the interaction effect of NPSZnB fertilizer rate and vermicompost levels had a significant impact on growth metrics such as plant height and leaf area index. The rate of vermicompost applied at 7.5 t·ha−1, which was on par with rates applied at 5.0 t·ha−1 and 2.5 t·ha−1, resulted in the longest days to tasseling (71.55), whereas the shortest days (70.21) to grow tassels were reported in plots not treated with vermicompost (Table 3). In comparison to the control treatment, which tasseled r quickly (69.86 days), maize cultivated with NPSZnB fertilizer applied at a rate of 150 kg·ha−1 took a maximum of 72.06 days to develop tassel (Table 3). In agreement with the findings of the current study, [33] reported a considerable influence of inorganic fertilizer on the number of days to 50% tasseling. In terms of days to 50% silking and days to 90% maturity, maize in the control plot silks and reaches maturity quickly, whereas the highest number of days to 50% silking (76.44 days) was found in the vermicompost-treated plot at 7.5 t·ha−1, which was on par with the results from 5.0 t·ha−1 and 2.5 t·ha−1. Vermicompost applied at 7.5 t·ha−1 was on par with all vermicompost levels, except for the control treatment, in terms of days to 90% maturity (142.7 days). Similar to this, the NPSZnB fertilizer rate at 150 kg·ha−1, which was on par with the value obtained from 100 kg·ha−1, produced the longest days to silking (76.39 days) and maturity (142.80 days) (Table 3).Table 3
Main effect of vermicompost levels and inorganic NPSZnB fertilizer rates on the number of days to 50% of the days to tassel, number of days to 50% silking, and the number of days to 90% physiological maturity of maize in Guto Gida, Western Ethiopia.
Treatments50% days to tassel50% days to silk90% days to maturityVermicompost (t·ha−1)070.21b75.33b141.40b2.571.21a75.67ab142.20ab5.071.43a76.33a141.90ab7.571.55a76.44a142.70ap value0.0030.0030.042LSD (0.05)0.950.911.20NPSZnB (kg·ha−1)069.86cd74.79b141.10cd5070.21bc75.00b141.60bc10070.86b76.06a142.30ab15072.06a76.39a142.80ap value0.001<0.0010.015LSD (0.05)0.740.710.94CV (%)1.61.40.96LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Higher soil fertility and increased nutrient uptake for all basically needed plant nutrients may be the cause of the delayed phenological parameters of maize that responded to the longer vegetative development period of the plant. Increased maize vegetative growth, expanded leaves, and better nitrogen usage efficiency may be the causes of the prolonged days to tasseling, days to silking, and days to maturity in plots treated with increased amounts of NPSZnB fertilizer (0–150 kg·ha−1). In agreement with this finding, Lal [34] showed that elevated levels of organic and inorganic nitrogen sources result in a prolonged vegetative development period (crop phenology). As vermicompost levels rose from 5 to 20 t·ha−1, watermelon flowering was delayed [35].The study also showed that the interaction between vermicompost levels and the rate of chemical NPSZnB fertilizer had a considerable impact on the growth parameters of maize, including plant height and leaf area index (LAI). The greatest plant height (282.80 cm) was achieved by the maize plant growing in a plot treated with 150 kg·ha−1 of NPSZnB fertilizer at zero level of vermicompost, whereas the least plant height (252.5 cm) was obtained in the control plot or plot untreated with vermicompost and NPSZnB fertilizers (Table 4). This finding may be the result of the inorganic nitrogen in NPSZnB fertilizer having a beneficial influence on rapid maize vegetative growth. Additionally, the addition of vermicompost improves soil pH and increases nutrient uptake by plants, resulting in enhanced production of vegetative growth and parts, specifically increased plant height and leaf blade size. According to a study by [36], plants grow taller when chemical fertilizer levels hold nitrogen fertilizer. However, [11] observed that the height of the maize plant treated with vermicompost plus NPK was greater than that of the vermicompost or minerally fertilized plot. Additionally, increasing the vermicompost level was found to boost pak choi height [37].Table 4
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer rates on plant height (cm) and leaf area index (LAI) of maize in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Plant height (cm)Leaf area index00252.50f3.937h050260.80e4.398fg0100273.70b4.497efg0150282.80a4.714b-f2.50267.40cd4.327g2.550268.50c4.309g2.5100267.30cd4.771b-e2.5150266.30cd4.791b-e5.00266.80cd4.493efg5.050269.00c4.541d-g5.0100268.80c4.982b5.0150270.00bc4.790b-e7.50267.40cd4.574c-g7.550263.70de4.835bcd7.5100270.00bc4.889bc7.5150269.60c5.657ap value0.0010.048LSD (0.05)3.9260.335CV (%)0.94.4LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Similar to this, the greatest leaf area index (5.657) was calculated from a plot treated with vermicompost at 7.5 t·ha−1 associated with 150 kg·ha−1 NPSZnB fertilizer and was followed by a 4.982 leaf area index assessed from a combination of 5 t·ha−1 vermicompost and 100 kg·ha−1 of NSPZnB, while the lowest leaf area index (3.937) was registered from the control plot untreated with vermicompost and NPSZ (Table 4). The largest leaf area index (5.657) at greater vermicompost levels and NPSZnB may be connected to the direct role of vermicompost in enhancing the physical, biological, and chemical characteristics of the soil to produce favorable conditions for crop growth and development. When applied together, vermicompost and mineral fertilizer may release greater amounts of plant nutrients and more quickly make nitrogen from mineral fertilizer NPSZnB available, both of which may play a significant role in more vigorous plant development compared to other treatments. Khan et al. [38] found increased plant height with increasing application levels of nitrogen-containing fertilizer, which is consistent with the findings of the current investigation. Similar findings were made by [39], who noted higher plant height and leaf area with greater nitrogen fertilizer available over the course of a maize crop’s life cycle.


## 3.3. Yield Components and Yield

### 3.3.1. Ear Weight (g)

Vermicompost applied in combination with mixed NPSZnB fertilizer at various rates considerably altered the ear weight of maize. The maximum ear weight (277.80 g), which was at par in the application of vermicompost at all levels with 100 kg·ha−1, was obtained when vermicompost level at 5 t·ha−1 was combined with an inorganic NPSZnB fertilizer rate at 150 kg·ha−1, except plots not treated with vermicompost at the same rate of NPSZnB fertilizer. The lowest ear weight (237.10 g) was obtained from the plot not treated with both vermicompost and NPSZnB fertilizer, which was comparable to the outcome of the plot not treated with vermicompost and a 50 kg·ha−1 inorganic NPSZnB fertilizer rate (Table 5). Improved crop growth and greater dry matter output as a result of improved nutrient uptake, particularly nitrogen, from inorganic and vermicompost (organic) sources may be the cause of increased ear weight with increased NPSZnB fertilizer at levels of vermicompost. Additionally, greater ear weight with higher vermicompost levels may be caused by a change in the composition of the soil’s organic matter as a result of the vermicompost’s decomposition and mineralization, which would boost the early nutrient supply from commercial fertilizers (NPSZnB). Ear weight was increased with a higher level of both organic fertilizer (vermicompost) and inorganic fertilizer and was favorably affected when organic and inorganic sources of fertilizer were used together [40, 41]. In contrast, [42] reported the maximum bean pod weight when treated with 100% vermicompost.Table 5
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer rates on-ear weight (g) and thousand kernel weight (g) of maize in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Ear weight (g)Thousand kernel weight (g)00237.10f42.14e050239.60ef44.49d0100248.30de44.31de0150268.00bc44.82cd2.50247.60de43.38de2.550250.50d44.90cd2.5100274.60ab48.03ab2.5150268.00bc48.90ab5.00250.20d43.59de5.050260.30c45.27cd5.0100276.10ab49.79a5.0150277.80a48.75ab7.50249.00d44.28de7.550268.30bc46.98bc7.5100276.50ab48.75ab7.5150276.90ab48.87abp value0.0040.045LSD (0.05)8.9712.225CV (%)2.13.0LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.


### 3.3.2. Thousand Kernel Weight (g)

The use of chemically blended NPSZnB fertilizer rates and vermicompost levels together had a significant effect on thousand kernels’ weights. The highest grain weight (49.79 g) came from an integrated application of vermicompost and blended NPSZnB fertilizer at a rate of 5.0 t·ha−1 with 100 kg·ha−1, which was at par to 7.5 t·ha−1 × 150 kg·ha−1 (48.87 g), 7.5 t·ha−1 × 100 kg·ha−1 (48.75 g), 5 t·ha−1 × 150 kg·ha−1 (48.75 g), and 2.5 t·ha−1 × 150 kg·ha−1 (48.03 g). In comparison, the plot not treated with any of the two fertilizers had the lowest thousand kernel weight (42.14 g) (Table 5). Greater soil fertility, enhanced nutrient uptake, and an effective photosynthetic process may all contribute to a heavier thousand kernel weight at higher vermicompost levels and higher rates of NPSZnB, which may be assimilated to economic yield (grain). The fact that the control treatment resulted in lower weight could be a result of the decreased nutrient content of the soil, which would make fewer nutrients available for healthy and optimal plant growth. Similar to previous research, [11] reported enhanced thousand-grain weight when vermicompost and NPK were applied together as opposed to separately. The linear increase in thousand seed weight coincided with the amounts of mineral and organic fertilizers.


### 3.3.3. Number of Kernel Ear−1

The main effect of the inorganic NPSZnB fertilizer rate had a significant influence on the number of kernels in ear−1. The vermicompost ratios and their interactions with the rates of inorganic NPSZnB fertilizer, however, had not shown a significant effect. An increase in the number of kernels ear−1 was seen with increased incorporation of NPSZnB fertilizer rates from 0 to 150 kg·ha−1. In comparison to the control plot and the plot treated with 50 kg·ha−1 of NPSZnB fertilizer, which produced the least amount of kernel ear−1, the plot treated with 100 kg·ha−1 and 150 kg·ha−1 of chemically blended NPSZnB fertilizer produced a greater number of kernel ear−1 (Table 6). Increased numbers of kernel ear−1 with increased NPSZnB fertilizer rates may be associated with greater availability of nitrogen and phosphorus, as well as the micronutrients zinc and boron. Even though it was not statistically significant, the number of kernels ear−1 increased when vermicompost concentration rose from 0 to 7.5 t·ha−1. This may be because vermicompost application increased the soil’s biophysicochemical characteristics, such as its CEC and organic carbon, phosphorus, and nitrogen content. Vermicompost also increases soil moisture since it is an organic material with a large surface area, which improves nutrient uptake and utilization efficiency and may result in more kernels ear−1. According to [43], vermicompost-treated plots of rice had 8.65% more grains per panicle than plots that had only received mineral fertilizer. Following the current study [36, 41], it was found that plots treated with a combined mineral and organic fertilizer application had longer cobs and more kernels per cob−1 than plots received with separate applications of the two fertilizers.Table 6
Main effects of vermicompost levels and inorganic NPSZnB fertilizer rates on the number of kernel ear−1, biological yield (t·ha−1), and harvest index (%) of maize in Guto Gida, Western Ethiopia.
TreatmentsNumber of kernels ear−1Biological yield (t·ha−1)Harvest index (%)Vermicompost (t·ha−1)0540.1318.31c36.002.5546.0019.67ab35.795.0562.3020.33a34.827.5569.6620.52a35.14p value0.106<0.0010.103LSD (0.05)33.1360.9382.021NPSZnB (kg·ha−1)0522.40b18.76b35.2050522.54b18.95b35.24100555.20a19.81a35.04150566.80a20.34a35.95p value<0.001<0.0010.415LSD (0.05)25.6670.7271.565CV (%)6.305.605.60LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.


### 3.3.4. Above Ground Biomass (t·ha−1)

The biological yield of maize was significantly influenced by the main effects of vermicompost and chemically blended mineral NPSZnB fertilizer. The increased biomass weight of 19.67–20.52 t·ha−1 was obtained by applying vermicompost at a level of 2.5–7.5 t·ha−1. In contrast, plots that were not given vermicompost had the least above-ground biomass of 18.31 t·ha−1 (Table 6). Concerning NPSZnB fertilizer rates, the highest and lowest values (18.76 t·ha−1 and 20.34 t·ha−1) were obtained from the application of NPSZnB at 150 kg·ha−1 and were statistically similar to the values obtained from 100 kg·ha−1 of NPSZnB and control, respectively (Table 6). The enhanced nutrient content in the soil improved nutrient uptake, and the timely availability of nitrogen released quickly from NPSZnB fertilizer could all result in an increased biological yield of maize with an increased amount of vermicompost and NPSZnB. This could be because vermicompost has better soil properties that encourage root growth, which could lead to higher growth of above-ground plant parts. Increases in the growth components of maize, such as leaves, sheaths, stems, cobs, and grain, as well as water retention as a consequence of the high specific area properties of vermicompost fed to the soil, lead to an increase in the crop’s above-ground biomass. Additionally, applying vermicompost to the crop during the growth phase may result in favorable conditions for yield-determining components and, consequently, biological yield. Vermicompost contains sufficient quantities of vital plant nutrients. Compared to maize that was not treated with vermicompost fertilizer, [33] reported an increased total dry weight of maize with a higher amount of vermicompost and NPS fertilizer. Similar results were reported by Nasab et al. [44], who found that the biomass weight of maize increased by 13.58% when vermicompost application increased from 4 to 12 t·ha−1. Application of vermicompost at 10 t·ha−1 and mineral fertilizer together increased rice biomass compared to cow dung applied at the same level plus mineral fertilizer or only mineral fertilizer [43]. The study found that applying 50% vermicompost and 50% of the locally recommended NPS together increased biomass by 8.72% when compared to applying 100% of the locally recommended NPS alone [45]. Furthermore, increased vermicompost application alone or with other organic and inorganic fertilizers increased above-ground biomass [46].


### 3.3.5. Grain Yield (t·ha−1)

Analysis of variance revealed that the combined application of organic fertilizer (vermicompost) and mineral fertilizer (NPSZnB) had a significant influence on the grain production of maize. The highest grain yield (8.03 t·ha−1) was recorded from the integrated application of vermicompost with blended NPSZnB fertilizer at a rate of 7.5 t·ha−1 and 150 kg·ha−1, which was statistically similar to the grain yield harvested from plots treated with 5 t·ha−1 × 100 kg·ha−1, 5 t·ha−1 × 150 kg·ha−1, and 7.5 t·ha−1 × 100 kg·ha−1 (Table 7). The lowest grain yield, 6.96 t·ha−1, was produced from a treatment not treated with either vermicompost or inorganic NPSZnB fertilizer (Table 7). The effectiveness of vermicompost at higher rates, as well as the increased number of kernel ear−1 and enhanced thousand-grain weights at this level, may be related to the increased grain output at the higher level of vermicompost. Additionally, the potential for vermicompost to reduce soil bulk density, exchangeable aluminum, and iron, and restrict root growth and nutrient uptake may account for the higher grain yield with increased vermicompost application. Vermicompost and mineral fertilizer used together may result in better soil properties such as pH, porosity, aeration, temperature, moisture, permeability, soil biodiversity, and fertility for plant growth, which may promote more photosynthate allocation. Vermicompost boosts soil-plant nutrients, including potassium, calcium, and micronutrients like copper, zinc, and iron when combined with other minerals. These nutrients support many physiological processes in plants, which resulted in higher grain yields as a consequence of improved fertilizer usage efficiency and increased cation exchange capacity of the soil with organic matter.Table 7
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer on grain yield (t·ha−1) and grain yield increased (%) in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Grain yield (t·ha−1)006.96h0507.03gh01007.24ef01507.47de2.507.22fg2.5507.32def2.51007.74cd2.51507.78bc5.007.29ef5.0507.54d5.01007.99ab5.01507.97ab7.507.30ef7.5507.71cd7.51007.97ab7.51508.03ap value0.005LSD (0.05)0.227CV (%)2.1LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Similar to the current study, several findings showed that maize grain production improved when organic and inorganic fertilizers were applied together [47]. According to Chimdessa and Sori [33], the addition of 3 t·ha−1 of vermicompost increased grain production by approximately 66.88% compared to the treatment using 100 kg·ha−1 of the locally advised NPS rate. Additionally, past research indicated that higher vermicompost quality and vermicompost levels boosted grain yield [11, 44, 48–50]. Similarly, [36, 45, 51–53] found that grain yield responded well when organic fertilizer and mineral fertilizer were applied together. Moreover, Hoque et al. [43] reported that rice yield increased by 5.68% when vermicompost at 10 t·ha−1 and mineral fertilizer were applied in combination, and compared with applying only the recommended rate of mineral fertilizer. In contrast to the present study, Abera et al. [54] in their three consecutive years study, reported a lower yield of maize in plots treated with only vermicompost from 4–12 t·ha−1or in plots treated with both vermicompost (25–75% of 4 t·ha−1) and 50–75% of recommended mineral NPS fertilizer compared with the plot treated with only NPS at the recommended rate (100%).


### 3.3.6. Harvest Index (%)

Analysis of variance revealed that the main effects of blended NPSZnB fertilizer, vermicompost, and their interaction had no statistically significant effects on the harvest index of maize (Table6). However, [55] reported a significantly higher harvest index when organic and inorganic fertilizer were used together compared to separate utilization. Similarly, [56] also found an increased harvest index of maize treated with a higher level of vermicompost, lime, and chemical fertilizer.


## 3.3.1. Ear Weight (g)

Vermicompost applied in combination with mixed NPSZnB fertilizer at various rates considerably altered the ear weight of maize. The maximum ear weight (277.80 g), which was at par in the application of vermicompost at all levels with 100 kg·ha−1, was obtained when vermicompost level at 5 t·ha−1 was combined with an inorganic NPSZnB fertilizer rate at 150 kg·ha−1, except plots not treated with vermicompost at the same rate of NPSZnB fertilizer. The lowest ear weight (237.10 g) was obtained from the plot not treated with both vermicompost and NPSZnB fertilizer, which was comparable to the outcome of the plot not treated with vermicompost and a 50 kg·ha−1 inorganic NPSZnB fertilizer rate (Table 5). Improved crop growth and greater dry matter output as a result of improved nutrient uptake, particularly nitrogen, from inorganic and vermicompost (organic) sources may be the cause of increased ear weight with increased NPSZnB fertilizer at levels of vermicompost. Additionally, greater ear weight with higher vermicompost levels may be caused by a change in the composition of the soil’s organic matter as a result of the vermicompost’s decomposition and mineralization, which would boost the early nutrient supply from commercial fertilizers (NPSZnB). Ear weight was increased with a higher level of both organic fertilizer (vermicompost) and inorganic fertilizer and was favorably affected when organic and inorganic sources of fertilizer were used together [40, 41]. In contrast, [42] reported the maximum bean pod weight when treated with 100% vermicompost.Table 5
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer rates on-ear weight (g) and thousand kernel weight (g) of maize in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Ear weight (g)Thousand kernel weight (g)00237.10f42.14e050239.60ef44.49d0100248.30de44.31de0150268.00bc44.82cd2.50247.60de43.38de2.550250.50d44.90cd2.5100274.60ab48.03ab2.5150268.00bc48.90ab5.00250.20d43.59de5.050260.30c45.27cd5.0100276.10ab49.79a5.0150277.80a48.75ab7.50249.00d44.28de7.550268.30bc46.98bc7.5100276.50ab48.75ab7.5150276.90ab48.87abp value0.0040.045LSD (0.05)8.9712.225CV (%)2.13.0LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.


## 3.3.2. Thousand Kernel Weight (g)

The use of chemically blended NPSZnB fertilizer rates and vermicompost levels together had a significant effect on thousand kernels’ weights. The highest grain weight (49.79 g) came from an integrated application of vermicompost and blended NPSZnB fertilizer at a rate of 5.0 t·ha−1 with 100 kg·ha−1, which was at par to 7.5 t·ha−1 × 150 kg·ha−1 (48.87 g), 7.5 t·ha−1 × 100 kg·ha−1 (48.75 g), 5 t·ha−1 × 150 kg·ha−1 (48.75 g), and 2.5 t·ha−1 × 150 kg·ha−1 (48.03 g). In comparison, the plot not treated with any of the two fertilizers had the lowest thousand kernel weight (42.14 g) (Table 5). Greater soil fertility, enhanced nutrient uptake, and an effective photosynthetic process may all contribute to a heavier thousand kernel weight at higher vermicompost levels and higher rates of NPSZnB, which may be assimilated to economic yield (grain). The fact that the control treatment resulted in lower weight could be a result of the decreased nutrient content of the soil, which would make fewer nutrients available for healthy and optimal plant growth. Similar to previous research, [11] reported enhanced thousand-grain weight when vermicompost and NPK were applied together as opposed to separately. The linear increase in thousand seed weight coincided with the amounts of mineral and organic fertilizers.


## 3.3.3. Number of Kernel Ear−1

The main effect of the inorganic NPSZnB fertilizer rate had a significant influence on the number of kernels in ear−1. The vermicompost ratios and their interactions with the rates of inorganic NPSZnB fertilizer, however, had not shown a significant effect. An increase in the number of kernels ear−1 was seen with increased incorporation of NPSZnB fertilizer rates from 0 to 150 kg·ha−1. In comparison to the control plot and the plot treated with 50 kg·ha−1 of NPSZnB fertilizer, which produced the least amount of kernel ear−1, the plot treated with 100 kg·ha−1 and 150 kg·ha−1 of chemically blended NPSZnB fertilizer produced a greater number of kernel ear−1 (Table 6). Increased numbers of kernel ear−1 with increased NPSZnB fertilizer rates may be associated with greater availability of nitrogen and phosphorus, as well as the micronutrients zinc and boron. Even though it was not statistically significant, the number of kernels ear−1 increased when vermicompost concentration rose from 0 to 7.5 t·ha−1. This may be because vermicompost application increased the soil’s biophysicochemical characteristics, such as its CEC and organic carbon, phosphorus, and nitrogen content. Vermicompost also increases soil moisture since it is an organic material with a large surface area, which improves nutrient uptake and utilization efficiency and may result in more kernels ear−1. According to [43], vermicompost-treated plots of rice had 8.65% more grains per panicle than plots that had only received mineral fertilizer. Following the current study [36, 41], it was found that plots treated with a combined mineral and organic fertilizer application had longer cobs and more kernels per cob−1 than plots received with separate applications of the two fertilizers.Table 6
Main effects of vermicompost levels and inorganic NPSZnB fertilizer rates on the number of kernel ear−1, biological yield (t·ha−1), and harvest index (%) of maize in Guto Gida, Western Ethiopia.
TreatmentsNumber of kernels ear−1Biological yield (t·ha−1)Harvest index (%)Vermicompost (t·ha−1)0540.1318.31c36.002.5546.0019.67ab35.795.0562.3020.33a34.827.5569.6620.52a35.14p value0.106<0.0010.103LSD (0.05)33.1360.9382.021NPSZnB (kg·ha−1)0522.40b18.76b35.2050522.54b18.95b35.24100555.20a19.81a35.04150566.80a20.34a35.95p value<0.001<0.0010.415LSD (0.05)25.6670.7271.565CV (%)6.305.605.60LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.


## 3.3.4. Above Ground Biomass (t·ha−1)

The biological yield of maize was significantly influenced by the main effects of vermicompost and chemically blended mineral NPSZnB fertilizer. The increased biomass weight of 19.67–20.52 t·ha−1 was obtained by applying vermicompost at a level of 2.5–7.5 t·ha−1. In contrast, plots that were not given vermicompost had the least above-ground biomass of 18.31 t·ha−1 (Table 6). Concerning NPSZnB fertilizer rates, the highest and lowest values (18.76 t·ha−1 and 20.34 t·ha−1) were obtained from the application of NPSZnB at 150 kg·ha−1 and were statistically similar to the values obtained from 100 kg·ha−1 of NPSZnB and control, respectively (Table 6). The enhanced nutrient content in the soil improved nutrient uptake, and the timely availability of nitrogen released quickly from NPSZnB fertilizer could all result in an increased biological yield of maize with an increased amount of vermicompost and NPSZnB. This could be because vermicompost has better soil properties that encourage root growth, which could lead to higher growth of above-ground plant parts. Increases in the growth components of maize, such as leaves, sheaths, stems, cobs, and grain, as well as water retention as a consequence of the high specific area properties of vermicompost fed to the soil, lead to an increase in the crop’s above-ground biomass. Additionally, applying vermicompost to the crop during the growth phase may result in favorable conditions for yield-determining components and, consequently, biological yield. Vermicompost contains sufficient quantities of vital plant nutrients. Compared to maize that was not treated with vermicompost fertilizer, [33] reported an increased total dry weight of maize with a higher amount of vermicompost and NPS fertilizer. Similar results were reported by Nasab et al. [44], who found that the biomass weight of maize increased by 13.58% when vermicompost application increased from 4 to 12 t·ha−1. Application of vermicompost at 10 t·ha−1 and mineral fertilizer together increased rice biomass compared to cow dung applied at the same level plus mineral fertilizer or only mineral fertilizer [43]. The study found that applying 50% vermicompost and 50% of the locally recommended NPS together increased biomass by 8.72% when compared to applying 100% of the locally recommended NPS alone [45]. Furthermore, increased vermicompost application alone or with other organic and inorganic fertilizers increased above-ground biomass [46].


## 3.3.5. Grain Yield (t·ha−1)

Analysis of variance revealed that the combined application of organic fertilizer (vermicompost) and mineral fertilizer (NPSZnB) had a significant influence on the grain production of maize. The highest grain yield (8.03 t·ha−1) was recorded from the integrated application of vermicompost with blended NPSZnB fertilizer at a rate of 7.5 t·ha−1 and 150 kg·ha−1, which was statistically similar to the grain yield harvested from plots treated with 5 t·ha−1 × 100 kg·ha−1, 5 t·ha−1 × 150 kg·ha−1, and 7.5 t·ha−1 × 100 kg·ha−1 (Table 7). The lowest grain yield, 6.96 t·ha−1, was produced from a treatment not treated with either vermicompost or inorganic NPSZnB fertilizer (Table 7). The effectiveness of vermicompost at higher rates, as well as the increased number of kernel ear−1 and enhanced thousand-grain weights at this level, may be related to the increased grain output at the higher level of vermicompost. Additionally, the potential for vermicompost to reduce soil bulk density, exchangeable aluminum, and iron, and restrict root growth and nutrient uptake may account for the higher grain yield with increased vermicompost application. Vermicompost and mineral fertilizer used together may result in better soil properties such as pH, porosity, aeration, temperature, moisture, permeability, soil biodiversity, and fertility for plant growth, which may promote more photosynthate allocation. Vermicompost boosts soil-plant nutrients, including potassium, calcium, and micronutrients like copper, zinc, and iron when combined with other minerals. These nutrients support many physiological processes in plants, which resulted in higher grain yields as a consequence of improved fertilizer usage efficiency and increased cation exchange capacity of the soil with organic matter.Table 7
Interaction effect of vermicompost levels and inorganic NPSZnB fertilizer on grain yield (t·ha−1) and grain yield increased (%) in Guto Gida, Western Ethiopia.
Vermicompost (t·ha−1)NPSZnB (kg·ha−1)Grain yield (t·ha−1)006.96h0507.03gh01007.24ef01507.47de2.507.22fg2.5507.32def2.51007.74cd2.51507.78bc5.007.29ef5.0507.54d5.01007.99ab5.01507.97ab7.507.30ef7.5507.71cd7.51007.97ab7.51508.03ap value0.005LSD (0.05)0.227CV (%)2.1LSD = least significant difference; CV = coefficient of variation (%). Means in the same column followed by the same letter(s) are not statistically significantly different at a 5% probability level.Similar to the current study, several findings showed that maize grain production improved when organic and inorganic fertilizers were applied together [47]. According to Chimdessa and Sori [33], the addition of 3 t·ha−1 of vermicompost increased grain production by approximately 66.88% compared to the treatment using 100 kg·ha−1 of the locally advised NPS rate. Additionally, past research indicated that higher vermicompost quality and vermicompost levels boosted grain yield [11, 44, 48–50]. Similarly, [36, 45, 51–53] found that grain yield responded well when organic fertilizer and mineral fertilizer were applied together. Moreover, Hoque et al. [43] reported that rice yield increased by 5.68% when vermicompost at 10 t·ha−1 and mineral fertilizer were applied in combination, and compared with applying only the recommended rate of mineral fertilizer. In contrast to the present study, Abera et al. [54] in their three consecutive years study, reported a lower yield of maize in plots treated with only vermicompost from 4–12 t·ha−1or in plots treated with both vermicompost (25–75% of 4 t·ha−1) and 50–75% of recommended mineral NPS fertilizer compared with the plot treated with only NPS at the recommended rate (100%).


## 3.3.6. Harvest Index (%)

Analysis of variance revealed that the main effects of blended NPSZnB fertilizer, vermicompost, and their interaction had no statistically significant effects on the harvest index of maize (Table6). However, [55] reported a significantly higher harvest index when organic and inorganic fertilizer were used together compared to separate utilization. Similarly, [56] also found an increased harvest index of maize treated with a higher level of vermicompost, lime, and chemical fertilizer.


## 3.4. Economic Analysis

Analysis of variance showed that integrated application of vermicompost and mineral NPSZnB fertilizer at 5 t·ha−1 × 100 kg·ha−1 yielded the highest net benefit (140486 ETB·ha−1) with a marginal rate of return of 797.98%, followed by a net benefit of 136970 ETB·ha−1, which was obtained at 2.5 t·ha−1 × 100 kg·ha−1, with a marginal rate of return of 769.66% (Table 8). The combined application of vermicompost at a rate of 0 t·ha−1 with NPSZnB fertilizer at a rate of 50 kg·ha−1 produced a minimum net benefit of 125650 ETB·ha−1 with a marginal rate of return of 47.64% (Table 8). In contrast, the plots treated with 150 kg·ha−1 with NPSZnB fertilizer and 2.5 t·ha−1 and 5.0 t·ha−1 of vermicompost were dominated (Table 8). Therefore, it was found that applying vermicompost at a level of 5 t·ha−1 along with 100 kg·ha−1 of mineral NPSZnB fertilizer rate was economically viable for maize production in Guto Gida district, Western Ethiopia, according to this partial budget study.Table 8
Partial budget analysis of maize yield for determination of the economically profitable level of vermicompost and NPSZnB fertilizer rate.
TreatmentV/compost (t·ha−1)NPS (kg·ha−1)Grain yield (t·ha−1)Adjusted grain yield (t·ha−1)Gross benefit (ETB·ha−1)TVC (ETB·ha−1)Net benefit (ETB·ha−1)MRR%T1006.966.261252260.00125226.00—T20507.036.33126540890.00125650.0047.64T301007.246.521303201780.00128540.00324.72T401507.476.731345142670.00131844.00371.24T52.507.226.50130014750.00129264.00—T62.5507.326.591317601640.00130120.0096.18T72.51007.756.981395002530.00136970.00769.66T82.51507.787.001400763420.00136656.00DT95.007.296.561311661500.00129666.00—T105.0507.546.791357742390.00133384.00417.75T115.01007.997.191437663280.00140486.00797.98T125.01507.977.181435324170.00139362.00DT137.507.306.571314002250.00129150.00—T147.5507.716.941387803140.00135640.00729.21T157.51007.977.181435144030.00139484.00431.91T167.51508.037.231445404920.00139620.0013.60Application costs of vermicompost and mineral NPSZnB fertilizer = 30 ETB quintal−1; unit cost of NPSZnB fertilizer = 17.5 ETB·kg−1; maize price 20 ETB·kg−1; ETB = Ethiopian birr; NPSZnB = fertilizer containing 17.8%N, 37.5%P2O5 7%S, 2.2%Zn, and 0.1%B; TVC = total variable cost; MRR = marginal rate of return; and D = dominated.


## 4. Conclusion

Farmers are using vermicompost to amend the soil in highland parts of western Ethiopia. However, there is limited information regarding the ideal ratio of vermicompost with other types of mineral fertilizer. Therefore, the study was conducted to determine the effects of different vermicompost ratios and mineral NPSZnB fertilizer rates on the growth and productivity of maize in the Guto Gida district of western Ethiopia. The results of this study showed that the phenology, growth, and yield parameters of the maize crop were considerably influenced by the mixed use of vermicompost and inorganic NPSZnB fertilizer. The ear weight and thousand kernels weight improved by 11.19% and 12.37%, respectively, in the application of vermicompost and mineral NPSZnB fertilizer at 5 t·ha−1 + 100 kg·ha−1. Additionally, applying vermicompost at and above 5 t·ha−1 in conjunction with inorganic NPSZnB fertilizer at 100 kg·ha−1, and 150 kg·ha−1 resulted in higher grain yield. Moreover, combined applications at 5 t·ha−1 + 100 kg·ha−1 of vermicompost and NPSZnB fertilizer produced the maximum net benefit (140486 ETB·ha−1) and marginal rate of return (797.98%). In conclusion, integrated application of vermicompost and mineral NPSZnB fertilizer at 5 t·ha−1 × 100 kg·ha−1 is advised for the study area, as a mixed-use of the two fertilizers improves the soil environment and increases production and productivity.



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*Source: 7123826-2023-03-09.xml*