Response of garlic ( Allium sativum L.) to vermicompost and mineral N fertilizer application at Haramaya, Eastern Ethiopia

Garlic ( Allium sativum L.) is an important vegetable crop in Ethiopia. The yield of the crop is often constrained by low and unbalanced nutrient supply in the soil. This study was undertaken to assess response of garlic variety Chelenko I to vermicompost and mineral N fertilizer application on growth and bulb yield of the crop during the 2016/2017 main rainy season. The treatment consists of a factorial combination of four levels of vermicompost (0, 2.5, 5 and 7.5 t ha -1 ) and five levels of mineral N fertilizer (0, 52.5, 80, 105 and 130 kg N ha -1 ), laid out in a randomized complete block design in a factorial arrangement and replicated three times. Data was collected on plant growth, yield component and bulb yield of garlic. Results revealed that significant (P < 0.05) maximum leaf length (41.08 cm), bulb weight (39.17 g/bulb), harvest index (63.94%) and total bulb yield (12.93 t ha -1 ) were recorded at the rate of 7.5 t ha -1 of vermicompost application while maximum average leaf width (1.25 cm), clove number (13.57 cm), and bulb dry matter (51.66%) were obtained at maximum rate of 130 kg ha -1 mineral N fertilizer. The results indicated that application of vermicompost at 7.5 t ha -1 and 130 kg Nha -1 mineral fertilizer gave the highest total garlic bulb yield of 12.9 and 12.69 t ha -1 , respectively.

Garlic (Allium sativum L.) is an important vegetable crop in Ethiopia.The yield of the crop is often constrained by low and unbalanced nutrient supply in the soil.This study was undertaken to assess response of garlic variety Chelenko I to vermicompost and mineral N fertilizer application on growth and bulb yield of the crop during the 2016/2017 main rainy season.The treatment consists of a factorial combination of four levels of vermicompost (0, 2.5, 5 and 7.5 t ha -1 ) and five levels of mineral N fertilizer (0, 52.5, 80, 105 and 130 kg N ha -1 ), laid out in a randomized complete block design in a factorial arrangement and replicated three times.Data was collected on plant growth, yield component and bulb yield of garlic.Results revealed that significant (P < 0.05) maximum leaf length (41.08 cm), bulb weight (39.17 g/bulb), harvest index (63.94%)and total bulb yield (12.93 t ha -1 ) were recorded at the rate of 7.5 t ha -1 of vermicompost application while maximum average leaf width (1.25 cm), clove number (13.57cm), and bulb dry matter (51.66%) were obtained at maximum rate of 130 kg ha -1 mineral N fertilizer.The results indicated that application of vermicompost at 7.5 t ha -1 and 130 kg Nha -1 mineral fertilizer gave the highest total garlic bulb yield of 12.9 and 12.69 t ha -1 , respectively.

INTRODUCTION
Garlic (Allium sativum L.) is primarily grown for its cloves, which are used mostly as food flavoring condiments due to groups of sulphur containing compounds: allin and allicin (Messiaen and Rouamba, 2004).Green tops are eaten fresh and cooked especially in tropical areas and consumption of immature bulbs for salad use is also popular (Block, 2010).Despite its importance, in Ethiopia, imbalanced fertilizer use, lower soil fertility status in many soil types and lack of proper marketing facilities are among key production constraints (Getachew and Asfaw, 2000;Mohamed et al., 2014) which considerably reduce yield.Among the *Corresponding author.E-mail: fikreged@yahoo.com.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License primary macronutrients, nitrogen (N), phosphorous (P) and potassium (K) are the most commonly reported deficient plant nutrients in most Ethiopian soils (Yohannes, 1994).
Crop nutrient requirements vary with species, variety, soil type and season, a blanket recommendation of 105 kg N ha -1 and 92 kg P 2 O 5 ha -1 each of N and P fertilizer are being used for garlic variety 'Tseday' production in many areas (EARO, 2004).This is also used for 'Chelenko I' (Tewdros et al., 2014) without research recommendation.This is one of the gaps addressed in the study area.
The traditional organic inputs such as crop residues, and animal manures cannot meet crop nutrient demand over large areas because of the limited quantities available, the low nutrient content of the materials, and the high labour demands for processing and application (Pratap et al., 2012).As interaction of organic and inorganic is valued, Verma et al. (2013) reported that the combined application of organic and inorganic fertilizers provided all the essential nutrients required by plants for its growth and development.
In addition, the application of bio-fertilizers like vermicompost (VC) has been recognized as an effective means for improving soil aggregation, structure and fertility, increasing microbial diversity and populations, improving the moisture-holding capacity of soils, increasing the soil cation exchange capacity (CEC) and increasing crop yields (Hargreaves et al., 2008).
An important feature of VC is that, during processing of the various organic wastes by earthworms, many of the nutrients that it contents are changed to forms that are more readily taken by plants such as nitrate or ammonium nitrate, exchangeable P and soluble K, Ca and Mg (Suthar and Singh, 2008).Therefore, complementary use of chemical fertilizers and organic manures has assumed great importance nowadays to maintain as well as sustain a higher level of soil fertility and crop productivity (Shalini et al., 2002).
In Ethiopia, garlic cultivation decreased from 16,411.19 ha, in 2013/14 to 15,381 ha in 2016/17 with a total production of 159,093.58 and 138,664.3tons of bulbs with the productivity of 9.7 and 9.02 t ha -1 , respectively (CSA, 2017).Though the area covered by garlic, its production and productivity were not indicated in Eastern Hararghe, about 50,683 farmers produced local varieties of garlic.The yield of recently released garlic variety, 'Chelenko I', gave 9.3 t ha -1 on research field appreciated and selected for Eastern and Western Hararghe areas (Tewdros et al., 2014).
Varieties may also differ in their response to source and rate of applied fertilizers (Zhou et al., 2005).Moreover, no work has been done on effect of mineral N and VC on the performance of garlic in the area.Therefore, the study was initiated to assess the effect of VC and mineral N fertilizer on growth and bulb yield of garlic.

Description of the study area
The experiment was conducted at Haramaya University main campus, Rare research field during the main crop growing season, August to December 2016.The area is geographically located eastern part of the country at altitude of about 2006 m above sea level.The site has a bimodal rainfall distribution pattern and is representative of a sub-humid, mid-altitude agro-climatic zone.The mean annual rainfall is 790 mm (Belay et al., 1998;Simret et al., 2014) and the minimum and maximum temperatures are 3.8 and 25°C, respectively (Tekalign and Hammes, 2005).The soil of the experimental site is a well-drained deep alluvial with sandy loam texture (Simret et al., 2014).

Experimental materials, treatments and experimental design
Garlic variety 'Chelenko I ' which was released in 2014 for mid to high altitude garlic growing areas of eastern and western Hararghe Zones by Haramaya University, was used.It is well adapted with productivity of 9.3 t ha -1 and moderately susceptible to garlic rust in Eastern Ethiopia.It takes about 132 days to mature (Tewodros et al., 2014).
The treatments consist of four rates of VC (0, 2.5, 5.0 and 7.5 t ha -1 ), and five mineral N fertilizer rates (0, 52.5, 80, 105 and 130 kg N ha -1 ); thus, the total treatments were 20.The experiment was laid out in randomized complete block design with three replications in a factorial combination.

Experimental procedures and crop management
Experimental field was ploughed by a tractor and plots were leveled and ridges of about 20 cm high were prepared.The gross plot size was 2.0 x 1.5 m (3.0 m 2 ).In between blocks and plots 0.75 m and 0.5 m space was left, respectively.VC was applied about two weeks before planting to randomly assigned treatments to each plot.One fourth, half and the remaining one fourth of the N fertilizer as per the treatment was also applied as urea at planting, and three weeks and six weeks after emergence of the garlic plants, respectively.In all the plots P (92 kg P2O5 ha -1 ) was applied at planting through triple superphosphate.Healthy and uniform medium-sized cloves of 1.5 to 2.50 g (Fikreyohannes et al., 2008), were selected and planting was done on 11 August 2016 at the depth of 3 to 4 cm.The cloves were planted on the ridge at a spacing of 30 cm between rows and 10 cm between plants.Thus, there were five rows in each plot and 20 plants in a row.The outer most one row on each side of a plot and 20 cm on both ends of each row were considered as border.Thus, the net plot size was 0.9 x 1.8 m = 1.62 m 2 .When 70% the plants showed neck fall (Getachew and Asfaw, 2000;EARO, 2004), harvesting of bulbs was done (on the 16 th of December 2016).

Vermicompost and soil sample analysis
Vermicompost sample, obtained made from Lantana camara, Partinium hystrophorous and farmyard manure, was analyzed before applying on the soil.Samples were taken randomly from the entire bag.It was broken into small crumbs and prepared for determination of chemical properties.The sample was air-dried and sieved through a 2 mm sieve.It's EC and pH was determined from the filtered suspension of 1:2.5 soils to water ratio using a glass electrode attached to a digital EC meter and pH meter.Sample was analyzed for electric conductivity (EC), total N, available P, exchangeable K, organic matter and organic carbon.Total N was determined using the Kjeldhal method (Jackson, 1958).Available P was determined by extraction with 0.5 M sodium bicarbonate (NaHCO3) according to the methods of Olsen et al. (1954).Exchangeable K was determined with a flame photometer after extraction with 0.5 ammonium acetate according to Hesse (1971).Organic carbon of soil was determined by the Walkley-Black (1934) method.
In similar a way, soil sampling was done before planting.The samples were taken randomly using an auger in a zigzag pattern from the entire experimental field.Before planting, ten soil samples were taken from the top soil layer to a depth of 20 cm and composited in a bucket to represent the site.The soil was broken into small crumbs and thoroughly mixed.From this mixture, a composite sample weighing 1 kg was filled into a plastic bag.The chemical content of the soil was determined using similar procedures used for the VC as it was developed for the soil.Soil texture was determined by Bouyocous hydrometer method (Moodie et al., 1954).

Growth parameters
Leaf width (cm): L eaf width of 10 individual leaves of the above selected plants was measured from the widest point of leaves and the average was taken as the leaf width.

Leaf length (cm):
The length of the leaf from leaf sheath to the tip of the leaf was measured from 10 randomly taken plants and their average was expressed as leaf length.

Yield components and yield
Mean bulb weight (g): Ten bulbs were randomly taken from the net plot area and their weight was recorded by using sensitive balance.The average weight was expressed as bulb weight.

Clove number per bulb:
The number of cloves was counted from the above 10 bulbs and their mean were taken as clove number per bulb.
Total bulb yield (t ha -1 ): This was determined by weighing plants in the three central rows (sum of marketable and unmarketable bulbs) leaving the plants in both end of the row and weighed after curing at ambient condition using a sensitive balance and converted t ha -1 .

Bulb dry matter (%):
The average dry matter weight (g) of bulbs after curing were measured by drying 10 randomly sampled bulbs in an oven with a forced hot air circulation at 70°C until a constant weight was obtained.The percent of bulb dry matter was calculated by taking the ratio of the dry weight to the fresh weight of the sampled bulbs and multiplying it by 100.

Harvest index (%):
This was calculated as the ratio of bulb yield to biological yield (total weight of garlic plant including above and below ground yield) recorded from 10 plants sampled from the net plot area.This was computed by dividing mean weight of mature bulb of plants taken (economic yield) by the biomass yield of plants (biological yield) taken using the equation (Pessarakli, 2001):

Data analysis
Data collected was subjected to analysis of variance (ANOVA) using SAS software version 9.0 and the means separated by using Turkey's Method at 0.05 level of significant if treatments are found significant.

Physical and chemical properties of the soil
The result of laboratory analysis of selected physical and chemical properties of soils of the experimental area is presented in Table 1.The textural class of the soil was sandy clay loam based on the soil textural triangle of the International Society of Soil Science System (Moodie et al., 1954;Rowell, 1994).The pH of the experimental soil was 7.4 which is moderately alkaline on the basis of pH limit (7.4 to 7.8) according to Jones (2003).The pH is in the range of 6.5 to 7.5 favorable for garlic production (Bachmann, 2001).The OM of the experimental soil was 2.55%.According to Tekalign (1991), OM ranging from 0.86 to 2.59 is low, hence the soil might respond to the applied VC and mineral N fertilizers, as its organic matter content was low.
As per the rating (0.12 to 0.25%) described by Berhanu (1980), the total N content of the soil (0.18%) was medium.This value showed that the crop might respond to the applied VC and mineral N fertilizers (Table 1) due to increased soil fertility with application of both fertilizers.According to the rating (5 to 9 mg P kg -1 ) suggested by Cottenie (1980), the available P of the soil was low (Table 1).This may be because of low percent of OM content of the soil (Table 1) which is also in agreement with the suggestion of Clark et al. (1998) who indicated that soil OM influences P availability to crops directly by contributing to P pool.However, Toung et al. (2000) reported that P response is likely in soils that have less than 20 mg kg -1 extractable P. The CEC of the experimental soil was 18.61 (cmol (+) kg -1 ).This value was medium according to the rating (15 to 25) suggested by Landon (1991).This indicated that the soil of the experimental site might respond to the different VC and mineral N fertilizer.Hazelton and Murphy (2007) categorized exchangeable soil K contents of 0.3 to 0.7 Cmolc kg soil -1 as medium.In accordance with this category, the exchangeable soil K content of the experimental soil is in medium category.This indicates external application of mineral and/or organic fertilizers containing K is important for enhancing the fertility of the crop and yield of the crop.

Vermicompost analysis result
It is crucial to analysis nutrient contents of VC as it is soil activator, soil conditioner, and soil fertility booster with all required plant nutrient, vitamins, enzymes, growth , pH: 7.25, total N 0.56%, 25.82 ppm of available P, exchangeable K 23.69 Cmol(+)/kg VC, 15.39% of OM and OC 8.92% as indicated in Table 2.These VC increases soil fertility without polluting the soil, as well as the quantity and quality of crops.Moreover, beneficial effects of VC on plant growth under water deficit conditions may be due to better aeration to the plant roots, increasing amount of readily available water, induction of N, P and K exchange, thereby resulting in better growth of the plants.Application of bio-fertilizers such as VC have been recognized as an effective means for improving soil aggregation, structure and fertility, increasing microbial diversity and populations, improving the moisture-holding capacity of soils, increasing the soil cation exchange capacity and increasing crop yields.Municipal solid waste compost can also reduce the volume of the waste, kill pathogens that may be present, decrease germination of weeds in agricultural fields, and destroy malodorous compounds (Hargreaves et al., 2008).

Leaf width
Analysis of variance showed that main effect of VC and mineral N fertilizer significantly (P < 0.05) affected leaf width but there was no significant observation due to their interactions.Application of 5 t VC ha -1 gave significantly optimum leaf width over the application rate of 2.5 t VC ha -1 and control, but statistically same with the application rate of 7.5 t VC ha -1 (Table 3).Verma et al. (2013) reported that chlorophyll contents of garlic leaf that contribute to leaf width increased significantly with application of 5 t VC ha -1 . Similarly, Mehdi et al. (2012) reported significantly increased leaf area index in response to the applied municipal solid waste and VC under well-watered, moderate and severe stress conditions.Abou El-Magd et al. ( 2012) also reported that the highest vegetative growth parameters were recorded with application of organic materials like poultry manure, farm-yard manure, sheep manure and compost.
N fertilization at the rate of 105 kg ha -1 gave significantly optimum higher leaf width over the other low N rates and statistically at par with application of 130 kg ha -1 (Table 3).As N increased from 0 to 105, leaf widths was increased by 15%.Adequate application of N plays an important role in the production of vigorous vegetative and optimum leaf expansion of garlic and influences garlic bulb size produced (Stork et al., 2004).Kakar et al. (2002) reported that N fertilization is necessary for ensuring successful vegetative growth of garlic.Similarly, Tadesse (2015) also reported that application of N significantly increased leaf width in comparison with lower dose and nil application of N fertilizer.The result revealed that leaf width increase with increased levels of fertilizers is directly proportion to leaf area index.

Leaf length
Analysis of variance indicated that the main effect of VC and N fertilization rate showed significant differences (p < 0.05) on leaf length but their interaction did not.
As shown in Table 3, the average maximum leaf length was found at the maximum rate of application of VC (7.5 t ha -1 ) which was significantly superior to rest of the treatments.Nil application of VC gave significant minimum leaf length and leaf length increased by 18.90% with the application of 7.5 t VC ha -1 as compared to nil VC application (Table 3).This increase in the vegetative growth might also be due to the effect of nutrients which are exerted by bio-enriched (Gomaa, 1995).This result is also in line with that of Mehdi et al. (2012) who reported significantly increased leaf area index in response to the applied municipal solid waste and VC under wellwatered, moderate and severe stress conditions.
The analysis of variance indicated that N significantly affected leaf length.Optimum leaf length was recorded with application of 105 kg N ha -1 .Application of N at rate of 105 kg ha -1 increased leaf length by about 14.67% as compared to untreated plot (Table 3).The increase in leaf length in response to the increased rate of N application may be attributed to the positive effect of N on vegetative growth and leaf expansion as suggested by Marschner (1995) and Halvin et al. (2003).
Similarly, Betewulign and Solomon (2014) reported that leaf length of garlic increased with increased rate of mineral N fertilizer.Kakar et al. (2002) also reported that N accounts for a higher percentage of the variation in leaf area when it was increased from 50 to 200 kg ha -1 .The leaf area is due to increased leaf length and width.Dirba et al. (2013) found that leaf area index of garlic treated with different levels of fertilizers was significantly increased over the untreated (control) plot at all sampling growth stages.

Bulb weight and clove number per bulb
Significant variations (p < 0.05) were obtained among bulb weights and clove number per bulb due to the main effect of VC and N application rate.However, their interaction had no significant influence on them (Table 4).Significant maximum mean bulb weight was obtained from plots treated with VC at the rate 7.5 t ha -1 as compared to the rest treatments.The maximum VC application rate gave 29.23% increase in bulb weight over the nil VC received plots (Table 4).The increase in mean bulb weight in response to increase in the rate of VC may be ascribed to several growth promoters, enzymes, beneficial bacteria and mycorrhyzae contained in it that led to high mean bulb weight by facilitating improved leaf growth and photosynthetic activities; thereby, increasing portioning of assimilate to the storage organ (Gupta, 2005).Alemu et al. (2016) reported that application of VC at the rate of 5 t ha -1 increased mean bulb weight by 8% as compared to the control plots.Weight of the bulb increased significantly up to the highest dose of 7.5 t VC ha -1 (Verma et al., 2013).Application of highest level of mineral N fertilizer rate produced significantly increased bulb weight by 25.47% over the control.The increase in mean fresh bulb weight in response to N application could be attributed to the increase in number of leaves produced, leaf length, and extended physiological maturity in response to the fertilization, all of which may have led to increased assimilate production and allocation to the bulbs (Kokobe et al., 2013).According to Bhagwan et al. (2012), successive levels of N fertilizers significantly increased the weight of garlic bulb.Besides, Tadesse (2015) also observed that the application of N significantly increased weight of bulb in comparison with lower dose and nil application of N fertilizer.Results indicated in Table 4 for clove number per bulb, VC application at the rate of 2.5, 5 and 7.5 t ha -1 showed significantly increased garlic cloves number per bulb over the control.Statistically, these three levels were not different.Agarwal (1999) reported that VC is a nutritive organic fertilizer rich in macronutrients, micronutrients, beneficial soil microbes like N-fixing bacteria and mycorrhizal fungi.Additionally, VC contain enzymes like amylase, lipase, cellulase and chitinase, which continue to break down organic matter in the soil (to release the nutrients and make it available to the plant roots) even after they have been excreted (Gupta, 2005).Clove number of garlic increased significantly up to 5 t ha -1 of VC (Verma et al., 2013).Surindra (2009) found that integrated nutrient supply in the form of traditional inorganic NPK and in the form of organic manures brings an excellent biochemical changes in soil structure, which ultimately promotes plant growth and production.Alemu et al. (2016) also reported that application of VC showed significant difference in mean clove number.
Analysis of variance showed that application of 105 kg ha -1 mineral N fertilizer gave optimum clove number per bulb.This might be due to the fact N is a constituent of many fundamental cell components and plays a vital role in all living tissues of the plant.This result is in line with the result of Bhagwan et al. (2012) who reported that successive levels of fertilizers significantly increased the number of cloves per bulb.According to Zaman et al. (2011) and Hossein et al. (2014), the highest number of cloves per bulb was obtained from 150 and 125 kg N ha -1 , respectively and the lowest was found in the control treatments.

Harvest index
The main effect of VC and N significantly (p < 0.05) influenced harvest index of garlic.The interaction effect of VC and mineral N fertilizer did not show significant effect on harvest index.
Significant maximum harvest index (63.94%)was recorded at the rate of 7.5 t VC ha -1 application over the other rate of application and followed by 5 t VC ha -1 application rate (Table 5).There was consistent increase in percent of harvest index.This could be attributed to the strong movement of assimilates from the leaves to the bulbs during the growing period.An important feature of VC is that, during the processing of the various organic wastes by earthworms, many of the nutrients that it contains are changed to forms that are more readily taken by plants such as nitrate or ammonium nitrate, exchangeable P and soluble K, calcium and magnesium (Suthar and Singh, 2008).Alemu et al. (2016) reported that VC had no significant effect on harvest index.
Application of 130 kg N ha -1 N gave significantly highest harvest index (60.52%)over other rates of mineral N fertilizer except 105 kg N ha -1 . Significantly lowest percent harvest index (51.82)was obtained from plots that did not receive N fertilization followed by 55.87 percent harvest index obtained from 52.5 kg N ha -1 application.N application at the rate of 52.5 kg ha -1 had significantly higher percent harvest index from nil application of N but was not significantly different as compared to the application rate of 80 kg N ha -1 (Table 5).The observed improvement in harvest index could be attributed to enhanced production of photosynthate due to increased leaf area, hence, greater partitioning of the photosynthate to the bulbs.The finding of Dargie (2015) showed that increased rate of N fertilizer from 0 to 64 kg ha -1 increased harvest index of onion by about 5.0%.This shows that mineral N fertilizer contributed to increase in harvest index.

Bulb dry matter
Significant increase in percent dry matter content of garlic bulbs were recorded due to main effect of VC and N fertilizers applied (p < 0.05).However, bulb dry matter percent was not significantly affected by their interaction effects.
Bulb dry matter percent was increased by 5.86% due to increased level of VC rate from 0 to 7.5 t ha -1 . Optimum bulb dry mater percent was obtained from the application rate of 5 t VC ha -1 which was significantly not different from the application of 5 t VC ha -1 (Table 5).Juan et al. (2006) showed that application VC increased the bulb dry weight due to the accumulation of non-structural carbohydrates whose distribution patterns change, thus favouring the metabolism of fructan precursors and accumulating as scorodose.The authors further explained that reserve substance (scorodose) accumulation in the VC treatment represented by scorodose polysaccharide, occurs for a longer period due to the earlier start of bulbing.This response translates into a 2-fold increase of the bulbs dry weight, increased size and therefore, higher quality and yield at harvest.Similarly, Fenwik and Hanley (1985) reported that, in garlic, the fructan polysaccharide is the scorode which accounts for 53% of garlic dry matter.
Application of 105 kg N ha -1 which was 50.72% dry matter, did not differ significantly from the application of 7.5 t VC ha -1 but significantly differ from the others low application rates.N application at the rate of 130 kg N ha -1 gave significantly highest dry matter percent (51.66%) over the nil application, 52.5 and 80 kg N ha -1 . Hence, the application 130 kg N ha -1 gave 12.06% increase in bulb dry matter when compared with the control.Hassan (2015) elaborated that increase of plant growth that contribute to bulb dry weight by increasing N level might be due to its role in photosynthesis, protein synthesis, cell division and enlargement which are the basal steps of plant growth.In addition, N plays an important role in the enzyme activity which reflects more products needed in plant growth.The author indicated that as N level increased, dry weight per plant increased up to the highest N level.Kakar et al. (2002) reported that N accounts for a higher percentage of the variation in dry plant mass when it was increased from 50 to 200 kg ha -1 .Alemu et al. (2016) also figured out that bulb dry matter percent was increased by 14.21% due to increased level of N rate from 0 to 46 kg ha -1 . Increasing rate of N application from nil to 130 kg N ha -1 bulb dry matter was increased by 12.06%.

Total bulb yield
Yield is a complex parameter that results from the interaction of various yield contributing characters.The maximum total bulb yield (12.93 t ha -1 ) was recorded with application of 7.5 t VC ha -1 which was statistically different from the rest of the treatments (Table 5).
As indicated in Table 5, there was an increase of 38.73% in total bulb yield by application of VC at rate of 7.5 t ha -1 over control.This might be due to the fact that organic manure supplied to balanced nutrition to the crop, improved soil condition; thereby, resulting in better growth and development leading to higher yield attributes and yield.Pramanik et al. (2007) found that humic acids released from VC enhanced nutrient uptake by the plants by increasing the permeability of root cell membrane, and stimulating root growth.
Plots that received mineral N fertilizer at the rate of 130 kg ha -1 increased by 25.40% in yield as compared to the control or nil application of N. Mineral N fertilizer application at the rate of 130 kg N ha -1 resulted in significantly maximum total bulb yield (12.69 t ha -1 ) followed by 105 kg N ha -1 application rate which gave 11.82 t ha -1 . The least bulb yield was recorded from nil application of fertilizers (Table 5).This result suggests that N application to the soil is important to improve bulb yield of garlic significantly.This might be due to the fact that N is a major part of all amino acids that increases the vegetative growth and produces good quality foliage and promotes carbohydrate synthesis through photosynthesis and ultimately increased yield of plants.
Bulb crops are a heavy feeder, requiring optimum supplies of N, P, K and S and other nutrients which can adversely affect growth, yield and quality of bulbs under suboptimal levels in the soil (Gubb and Tavis, 2002).According to Bhagwan et al. (2012) successive levels of fertilizers significantly increased the weight of bulb, number of cloves per bulb and bulb yield.The authors reported that maximum bulb yield (13.86 t ha -1 ) was obtained with application of 100% recommended dose of fertilizer, which is 41.7% higher than the control.Singh and Singh (2006) and Kokebe et al. (2013) also reported that increase in the rate of N from 0 to 100 kg N ha -1 resulted in progressive increments in total bulb yield of onion.

Conclusions
Research was conducted to study the response of garlic to VC and mineral N fertilizer application rates with the objectives of assessing the effect of VC and mineral N fertilizer on growth and bulb yield of garlic.Growth parameters such as leaf width and leaf length were significantly influenced by the applied VC and N fertilizers.The highest leaf width (1.25.cm) and leaf length (41.08 cm) were recorded for 7.5 t VC ha -1 and 130 kg N ha -1 , respectively.Yield components and yield traits showed significant differences (p < 0.05) in response to the application of VC and mineral N fertilizer.Maximum bulb weight (39.17 g/plant), harvest index (63.94%)and total bulb yield (12.93 t ha -1 ) were recorded from the application rate of 7.5 t VC ha -1 . The highest clove number (13.57) and bulb dry matter (51.66%) were recorded from highest rate of 130 kg N ha -1 .Significantly highest total bulb yield, 12.93 and 12.69 t ha -1 , was obtained from maximum application rate of 7.5 t VC ha -1 and 130 kg N ha -1 mineral fertilizer, respectively.
Thus, it can be reasonably generalized that on short term basis, application of high amounts of VC fertilizers can result in highest total bulb yield than other low doses of either VC and mineral N fertilizer or their combination.Therefore, from the results of this study, it can be concluded that, the maximum total bulb yield of garlic was obtained with the application of 7.5 t VC ha -1 fertilizer as it also has positive impacts on soil biological, aggregation and chemical condition.

Table 1 .
Physical and chemical properties of the soil of the experimental site at Haramaya, Eastern Ethiopia.

Table 3 .
Main effects of vermicompost and N on leaf width and leaf length of garlic.

Table 4 .
Main effects of application vermicompost and N on bulb weight and clove number per bulb of garlic./p, gram per plant.Means followed by the same letter within a column are not significantly different at 5% level of significance. g

Table 5 .
Main effects of vermicompost and N on percent harvest index, bulb dry matter and total bulb yield of garlic.