Influence of Irrigation and Integrated Nutrient Management on Garlic (Allium sativum L.) Production in Ethiopia: A Review

1. Introduction

Garlic, a member of the Alliaceae family, originated in Central Asia and has been used in China, India, and Egypt for centuries. It is the second most significant crop in the Allium family and is used as a spice for flavoring food and in medicine to treat and cure illnesses (Voigt, 2004; Labu & Rahman, 2019). Garlic thrives in subtropical to temperate regions and thrives in well-drained sandy, silty-clay soils with a pH of 7 (Alemu and associates, 2016). In 2020, 28.1 million metric tons of garlic were produced worldwide, a 3.9% increase from the previous year. China and India are the two countries in the Asia-Pacific region that use garlic extract the most, as it is a fundamental ingredient in various cuisines.

Garlic is cultivated globally, with Egypt, Thailand, China, India, Korea, and Spain being top producers. Asia produces 87% of garlic, with China and India contributing the most. Africa produces only 2.8%. China’s yield is four times higher than the world average, and garlic’s global area coverage increased from 1,142,220 ha in 2003 to 1,422,408 ha in 2011 (FAO 2003; FAOSTAT 2011).

Garlic is a major bulb crop for domestic and international markets, with cash crops exported to the USA, Europe, the Middle East, and African nations for foreign money as stated by Kilgore et al. (2007). The yield disparities between Ethiopia and industrialized nations may be attributed to differences in technical resources and agricultural management practices, rather than genetic variances. Organic agriculture, as described by Foissy et al. (2013) and Jarvan et al. (2017), is based on ecological processes and ecosystem management. One useful organic fertilizer for maintaining soil fertility is FYM. Ensuring a proper equilibrium between nutrient inputs and outputs is essential for both immediate productivity and long-term viability on organic farms. Farmyard manures are the primary source of nutrients, even on small farms (Fageria, 2012; Baksiene et al., 2014). Ibrawuchi et al. (2007) found that the application of FYM may effectively alter the soil pH from an acidic condition to a neutral one. This shift in pH promotes both short-term crop productivity and long-term environmental sustainability.

Organic fertilizers release nutrients more slowly than mineral fertilizers due to microbe breakdown (Hintsa et al., 2016). However, they improve soil moisture capacity, increase crop responsiveness, add nutrients, improve rooting habitat, and replenish soil organic matter (Fairhurst, 2012). Organic fertilizers enhance microbial activity, augment soil organic matter, and provide essential macro- and micronutrients required by plants (Angin et al., 2017). Diacono and Montemurro (2011) and Fageria (2012) found that Soil organic matter plays a vital role in maintaining the sustainability of agricultural systems by improving the physical, chemical, and biological properties of the soil.

Ethiopia’s agricultural sector, which provides 40% of the country’s GDP, has to be enhanced to improve rural living conditions and economic sustainability (IWMI, 2010). Despite the country’s substantial irrigable area and water resources, Ethiopia’s agricultural sector is not entirely profiting from irrigation land and water management technology. Poor agricultural productivity is attributed to farmers’ inadequate utilization of inputs like fertilizers due to uncertain moisture availability and soil degradation. To address this, secure irrigation access and effective farmed area utilization are recommended (GTP, 2010). The food security strategy in Ethiopia’s growth plan focuses on expanding irrigated agriculture and integrated fertilizer usage.

Garlic, a crucial crop, faces various biotic and abiotic stresses, including rainfall, irrigation schedules, and insufficient or excessive mineral nutrition (Jaleel et al., 2007; Cheruth et al., 2008). Its thin root system necessitates consistent fertilizer and water application. Soil moisture levels also impact garlic quality and yield (Shock et al., 1998). Low levels lead to low yields, while high levels waste water, cause nutrient leakage, and cause rots. Variations in crop yields between seasons and sites are likely due to nutrient availability, cropping season, soil, planting date, plant population, and cultural practices. Water is the primary factor limiting agricultural and economic development during the dry cropping season Cheruth et al., 2008). Nutrient depletion in crop-producing areas, particularly in East Africa, is a significant issue due to land cultivation and soil deterioration. According to Henao and Baanante (1999), The rate of depletion is estimated to be between 47-88 kg ha^-1 year^-1, with highlands experiencing up to 100 kg ha^-1 year^-1. Soil erosion, P fixation, and leaching are major causes, and population pressure exacerbates the problem.

Ethiopia’s diverse agroclimatic zones impact agricultural productivity, particularly for crops like garlic, which are susceptible to soil fertility and water availability fluctuations. The growing demand for garlic has led to a shift towards integrated, sustainable farming methods. Irrigation is a major factor affecting garlic production, especially in areas with variable rainfall patterns. Effective irrigation techniques reduce water-induced stress, ensure water supply, and improve water use efficiency, making the right method essential for Ethiopia’s agroclimatic conditions. This review aims to fill a knowledge gap in Ethiopia by examining the combined effects of irrigation and integrated nutrient management on garlic production. It compiles existing knowledge, identifies research trends, and suggests synergies between these techniques for maximum garlic output, aiming to close the existing knowledge gap.

2. Methodology

Gathering the existing literature or research outputs from peer-reviewed publications is the first step in this study. A comprehensive literature search was conducted utilizing the Web of Science and Google Scholar search engines. The papers were chosen by doing targeted searches for relevant literature on soil fertility studies of garlic crops in Ethiopia in peer-reviewed journals pertaining to agronomy and soil. The following are important terms: “garlic production,” “Ethiopia,” “integrated organic and inorganic nutrient management,” “inorganic fertilizer management,” “organic fertilizer management,” “soil fertility management,” “irrigation,” and “water use efficiency.” whenever the review paper was connected to peer-reviewed literature.

2.1. Crop Over View

2.1.1. Botanical and Morphological Characteristics of Garlic

Botanically speaking, garlic is a member of the Allium family Alliaceae, which also contains essential crops of vegetables like shallots (A. asacloncum), onions (Allium cepa), and leeks (A. ameloprisum). According to Filgiuolo et al.,2001; and Ipek et al., 2003, garlic constitutes a species of diploids (2n = 2x = 16) with mandatory apomixis which reproduces through vegetative means.

Despite being propagated asexually, cultivars of garlic exhibit significant phenotypic variation. These cultivars are highly adaptable to a variety of settings. Garlic plants have thin, tape-shaped leaves that are roughly 30 cm long, just like onions. Roots can be found up to 50 cm or somewhat deeper. White-skinned bulbs, or heads, are separated into pieces known as cloves. A white or reddish papery coating, or “skin,” covers the six to twelve cloves that may be present on each head (Hector et al., 2012).

It is anticipated that the sexual propagation of garlic will promote genotype-to-genotype genetic trait exchange and enhance garlic cultivars by classical breeding (Kamenetsky et al., 2004). Cloves are planted to spread garlic instead of actual seeds. Typically, each bulb is planted separately and has twelve or more cloves within. The best garlic bulbs should only be planted with their larger outer cloves since larger cloves produce larger, mature bulbs when harvested.

When the bulb is ready to be planted, do not split it; doing so too soon can reduce yields. Choose “seed bulbs” that are healthy, big, smooth, and disease-free. Dig a hole or trench, carefully set the unpeeled clove into it with the pointed side up (the ends of the scar stem down), and cover it with dirt to plant garlic properly. A straight neck is guaranteed when the cloves are arranged upright (McLaurin, 2012).

Common garlic cultivars have a somatic chromosome number of 2n=16, with some Campania-based plants being tetraploid (4n=32) and some possibly triploid. Garlic frequently has chromosomal abnormalities as a result of many translocations involving eight or even ten chromosomes. According to Jo et al. (2012), several sterile cultivars have a normal karyotype.

2.1.2. Origin, Domestication, and Distribution

Since ancient times, garlic (Allium sativum L.) has been grown throughout the world, but primarily in Asia (Anand et al., 2017). Owing to its curative and preventative qualities, it is used as a traditional medicine in addition to being a food ingredient. Garlic has a pungent flavor that comes from a variety of organosulfur compounds, including cycroalliin, diallyl disulfide, allicin, and alliin, which are good for you. According to Ryu and Kang (2017), these substances exhibit anti-inflammatory, antibacterial, and anticarcinogenic properties.

These properties have contributed to an increase in the consumption of garlic among health-conscious consumers (Suleria et al., 2015). Most nations in both the tropical and temperate zones cultivate garlic. The developing world dominates the world’s garlic trade, and over the last 10 years, their fraction of trade has expanded at the cost of the developed world (FAO, 2004). The top three nations’ production quantities in 2019 were 23.26 million metric tonnes for China, 2.91 million metric tonnes for India, and 466.39 thousand metric tonnes for Bangladesh, according to FAOSTAT 2019. There is a concentration of garlic production in the United States and abroad. China is the second-largest garlic exporter after Spain. Commercial agriculture takes occurs in Egypt, Ethiopia, Algeria, Sudan, Morocco, Tunisia, Niger, Tanzania, Nigeria, and Kenya in Africa. In Africa, Egypt is the biggest producer and exporter. Nigeria produces relatively little; the bulk is cultivated in the northern states, such as Kano, Kaduna, Kebbi, Sokoto, Jigawa, Bauchi, Katsina, and Zamfara States (Kudi et al., 2008).

In the past, garlic traveled to the Mediterranean. It is a crop that has been farmed since 1600 BC in Egypt and is also considered ancient in China and India. Nowadays, garlic is grown in both hemispheres, from the equator to latitudes around 50°, although it is most extensively eaten in Latin America, China, and the Mediterranean area. Garlic is cultivated throughout tropical Africa, notably in the Sahel and at high elevations in East and Southern Africa during the cold season. With a considerable level of genetic variation in the local cultivars, it is a commonly farmed crop in the savanna zone. Hot, steamy lowlands are seldom, if ever, home to it.

2.1.3. Production and Productivity of Garlic in Ethiopia

In fact, several options and possibilities in Ethiopian agricultural ecology when it comes to garlic production. Garlic production in Ethiopia decreased from 16,411.19 coverage hectares in 2013–14 to 15,980 coverage hectares in 2020–21, however current output is still below potential (CSA, 2021; Shege et al., 2021). With about 78% of the world’s garlic output (22.27 million tons), China is the biggest producer in the world (Desta et al., 2021). The United States, Russia, the Republic of Korea, Bangladesh, Egypt, Spain, India, Myanmar, and Uzbekistan were ranked after China (FAO 2023). Ethiopia produced a pitiful 113,928.43 tons total from 14,576 hectares of land, with an average yield of 7.8 tons/ha (FAO 2023). This indicates that Ethiopia produces less garlic than the world average of 18.4.

2.1.4. Importance of Garlic

For thousands of years, people have employed natural products from plants, animals, and microorganisms, either in their pure forms or as unrefined extracts, to treat a wide range of illnesses (Parekh and Chanda, 2007). One plant that has been used for centuries to treat infectious disorders is garlic (Allium sativum L.), which has been the subject of extensive research for several years (Onyeagba et al., 2004). There has long been debate concerning the taxonomic classification of garlic and related taxa. At least 33 sulfur-containing compounds, multiple enzymes, the minerals calcium, iron, potassium, magnesium, selenium, and zinc, as well as fiber, water, and the vitamins A, B1, and C, are all present in garlic. Additionally, garlic contains the following 17 amino acids: proline, glycine, alanine, cysteine, valine, methionine, isoleucine, leucine, tryptophan, swine, glutamine, threonine, histidine, arginine, aspartic acid, and phenylalanine (Josling, 2005). Garlic’s strong smell and many of its therapeutic properties are attributed to its higher concentration of sulfur compounds than any other Allium species.

With good reason, garlic is recognized to be among the most natural and remarkable plants with healing capabilities. It contains tumor-fighting capabilities and the capacity to prevent and destroy germs, and fungus, decrease the levels of cholesterol in the blood and glucose levels, and also reduce clotting of the blood. To prevent sickness and protect health, it may help improve the immune system (Abdullah et al., 1988). It may speed up the body’s removal of waste products by activating the lymphatic system. It is also known to be a potent antioxidant that defends cells from harm caused by free radicals. Certain malignancies, heart disease, strokes, and viral infections may all be averted with its support. About two hundred distinct chemicals present in garlic alone can guard the human body against a broad variety of ailments. Garlic’s sulfur-containing components defend the human body by stimulating the development of certain beneficial enzymes (Mansell and Reckless, 1991).

2.2. Climatic Requirements and Adaptation

One of the most important Allium vegetable crops globally both in terms of production and financial value is garlic. There is a vast geographical range for the adaption and cultivation of garlic. Leading manufacturers internationally include Egypt, Thailand, China, India, Korea, and Spain. Some countries, such as China, produce more garlic than dried onions. Asia produces 87% of the world’s garlic, with China and India being the two biggest producers, jointly accounting for 78% of the crop. Africa yields just 2.8% of the world’s total output of garlic.

One of the major bulb crops grown in Ethiopia for domestic use is garlic, which provides a living for a large number of peasant farmers throughout the nation (Metasebia and Shimeles, 1998; Getachew and Asfaw, 2000). In Ethiopia and throughout the world, garlic is a significant vegetable crop. Garlic average output climbed in Ethiopia from 11,845.53 hectares in 2015/16 to 15,381 ha in 2016/17. Approximately 50,683 farmers grew garlic in the Eastern Hararghe Zone, even though data regarding average productivity, and production are not available (CSA, 2017).

While the total amount of garlic produced climbed from 79,421 to 222,548 tonnes of bulbs in 2012/13, with an increase in land from 6,042 ha in 2001–02 to 21,258 ha in 2012/13, its productivity fell from 13.20 to 10.47 t ha^-1, correspondingly (CACC, 2002; CSA, 2012). The majority of garlic grown for the domestic market is grown in homestead gardens owned by subsistence farmers in many other highland parts of Ethiopia; yields are generally poor, averaging about 11.7 t ha^-1 (CSA, 2010) and 11.31 t ha^-1 (CSA, 2012) in East Showa. More than 58% of the whole yield was used for domestic use, 24.5% for the market, and 16% for seed. Garlic is utilized in this nation to make indigenous medicines and as an ingredient in the stew known as “wot” (CSA, 2010). The country’s mid- and highlands are where garlic is primarily grown (Getachew and Asfaw, 2000; CACC, 2002). The majority of garlic grown for the domestic market is grown in homestead gardens owned by subsistence farmers, who primarily grow it as a cash crop to export for foreign exchange.

The most frequently planted Allium species in Ethiopia is garlic, which is very tolerant of a variety of temperatures and soil conditions. Climate-wise, the ideal sites to produce garlic are those with a reasonably mild winter with some rainfall and a bright, dry summer that is excellent for bulb growth and harvesting (Brewster, 1994; Lemma and Herath, 1994). Garlic plants, according to Rubatzky and Yamaguchi (1997), are exceptionally hardy and can sustain low temperatures seven below freezing but they might not survive the winter in some severely cold areas. Most nations from the equator to around 500 latitudes produce garlic, which grows best in temperatures between 12 and 24 ⁰C (Nonnecke, 1989).

Bulbs need high temperatures to thrive, but in the early stages, colder temperatures stimulate vegetative growth; altitudes between 500 and 2000 meters amsl offer optimal conditions for development (Rice et al., 1990). The development of bulbs and vegetative growth are inhibited by high humidity and precipitation. Plants are quickly affected by waterlogging and need water. Therefore, moisture in the upper 30 cm of the soil’s surface should be maintained around the field’s capacity for growth to produce maximum output (Brewster, 1994; Rubatzky and Yamaguchi, 1997). As a high-value crop, garlic requires rich soil, adequate drainage, and friable soil preferably with a large level of organic matter, and water that isn’t lacking until two weeks before harvest. The crop likes soil with a pH of 6.5-7.5 since it is prone to greater acidity, and an excess of water supply two weeks before harvesting time impacts the storage quality (Bachmann, 2001; Potgieter, 2006. The crop generates a coarse root system, but it also requires some hardness the soil has to be well-drained and free of compaction for excellent root-to-soil contact. Bulbs grow discolored in poorly drained soil; they are distorted and challenging to harvest in clay loam soil.

2.3. Nutrient Requirements of Garlic Crop

According to Campbell et al. (2004), a sustainable agricultural system is profitable, produces wholesome, safe food, preserves resources, and improves the environment. The foundation for increasing agricultural yield from currently farmed land is fertilizers (Ryan, 2008). Due to the negative effects that excessive crop nutrient consumption has on the environment and economy, balanced fertilization is necessary, and crop nutrient requirements should be determined by physiological needs and anticipated yields (Ryan, 2008). The soil’s fertility level, the crop’s variety, the reason for planting, etc., all affect how much fertilizer is needed for garlic crops. The fertility level of the soils is one of several aspects that considerably impact the production of garlic crops primarily due to the exceptionally large amounts that are picked out of soils in contrast to the other essential nutrients, the most important nutrients, P, and K are becoming increasingly scarce in the mineral-rich soils of many African countries (Marschner, 1995; Rao et al., 1998), and this is also common for Ethiopian soils (Yohannes, 1994). Most Ethiopian soils are nutrient-deficient, mainly in nitrogen and phosphorus, according to soil fertility studies done at various locations for distinct crops. These tests have shown large production responsiveness from applied phosphate and nitrogen fertilizers (Asnakew and Tekalign, 1991; Berga et al., 1994; Yohannes, 1994).

Because of their short and without branch systems of roots, bulb crops are more sensitive to nutrient withdrawal than most other agricultural plants, particularly the stationary kinds. As a consequence, they need more fertilizers, which they typically react to effectively (Brewster, 1994). Bulb crops are high-value crops whose better production and quality are major economic factors. Depending on the soil’s nutritional quality, garlic needs a moderate to high quantity of fertilizer (Berga et al., 1994). Currently, numerous types of fertilizers are administered to boost garlic yields. Because the different fertilizers provide variable levels of plant nutrients, they have unique impacts on the soil environment. The quality of the crop must be protected in combination with human attempts to boost garlic yields by substantial fertilizer application (Cantwell et al., 2006). Because they are heavy feeders, bulk crops require sufficient N, P, and K in the form of inorganic, organic, or a mix of fertilizers. The production, quality, and storability of bulbs are all adversely influenced by inadequate concentrations of these nutrients in the soil (Gubb and Tavis, 2002).

To encourage soil aggregation and improve aggregate stability, organic matter (compound) is added to the soil along with compost and created by the ensuing biological activity (Bot, 2005). Composting causes instantaneous, calculable changes in the quantities of nutrients, trace metals, and other chemical components in soil, according to Buzie-Fru (2010). According to Fijalkowski et al. (2012), compost affects the pH of the soil because it contains both carbonate and organic matter, which raises the pH while acting as a buffer to keep the system at a neutral level. Research suggests that adding organic materials regularly, especially composted ones increases the physical fertility of the soil primarily by enhancing aggregate stability and reducing soil bulk density (Diacono and Montemurro, 2011). However, composts can directly combat disease, encourage the growth of microorganisms that compete with them, and help plants build disease resistance (Ebrahimi et al., 2018).

2.4. Integrated Use of Organic and Inorganic Fertilizers

One of the most crucial techniques in garlic production today is the usage of well-balanced sources of nutrients to generate high-yield, high-quality garlic bulbs. It’s typical to see proposals for organic inputs in place of mineral fertilizers. However, owing to their low nutrient content, restricted availability, and labor-intensive processing and application requirements, farmers’ employment of organic inputs, crop wastes, and animal manures is inadequate to meet crop nutrient needs across vast regions. As a consequence, most African farmers apply a mix of organic and inorganic inputs (Palm et al., 1997). To retain a greater enhancement of soil fertility and crop production, it is increasingly important to apply chemical fertilizers and organic manures in complementary methods (Shalini et al., 2002). Farmyard manure (FYM) is one of the most important soil amendments accessible to farmers in mixed agricultural systems. It boosts crop yield and improves the physical and chemical qualities of soils by adding organic matter and other nutrients (Harendra et al., 2009; Alam et al., 2010). One option for achieving a reasonable output level with a significant amount of fertilizer that leads to sustainable agriculture is the integrated nutrient supply technique (Bhagwan et al., 2012). The current combination application is appreciated because there isn’t enough organic material. According to Verma et al. (2013), plants could obtain all of the necessary nutrients for growth and development when organic and inorganic fertilizers were applied together. Thus, it is essential to combine VC with mineral N fertilizer to boost plant productivity while lowering environmental pollution. Increasing the yield of garlic in the Eastern Hararghe Zone is a major goal of crop research. According to Riba et al. (2013), garlic plants responded differently to various rates of compound fertilizers.

2.5. Effects of Fertilizer on Garlic Production

According to Foissy et al. (2013), organic farming is a production technique that relies less on the external flow of agricultural inputs and more on ecological processes and ecosystem management. According to Jarvan et al. (2017), one of the most helpful organic fertilizers for conserving soil fertility in alternative agricultural systems is FYM. The maintenance of soil organic matter and the balance of organic carbon are closely connected to the preservation and promotion of soil potential fertility (Baksiene et al., 2014). Even on modest farm holdings, farmyard manures are the principal source of nutrients (Fageria, 2012). According to Ibrawuchi et al. (2007), the injection of FYM altered the pH of the soil from an acidic condition to a neutral one.

When compared to mineral fertilizers, the release of nutrients from organic sources occurs more slowly since the nutrients need to break down with microbes to become available (Hintsa Meresa et al., 2016). Using organic sources improves soil moisture capacity, increases crop responsiveness to mineral fertilizers, adds nutrients that mineral fertilizers do not possess, improves rooting habitat, and replenishes soil organic matter (Fairhurst, 2012). Studies revealed that the addition of organic fertilizer enhances the organic matter of the soil, promotes the growth of microbes, and delivers micronutrients as well as macronutrients required by the plant in a more effective method (Angin et al., 2017). Diacono and Montemurro (2011); and Fageria (2012) showed that soil organic material (SOM) plays a critical role in sustaining the sustainability of agricultural systems by increasing soil’s physical, chemical, and biological qualities.

Appropriate management of nitrogen supplies and preservation of soil fertility are essential for sustained crop cultivation. However, a key concern for many countries striving to sustain agricultural production and output is the loss of soil fertility. On the other hand, utilizing inorganic fertilizers exclusively could result in rapid increases in crop production. According to Doran and Parkin (1994), soil organic matter, which also functions as a substrate for soil microbes and a storehouse of plant nutrients, is a crucial factor in determining the quality of the soil (Dutta et al. 2003). To maintain garlic output and improve soil quality, organic manures must be added. Compared to artificial fertilizers, organic manure has a variety of drawbacks, such as poor nutrient content, sluggish breakdown, and varying nutritional compositions depending on its organic ingredients (Han et al. 2016). According to several writers, using chemical fertilizers in combination with organic manures reduces the harm that chemical fertilizers due to agroecology while simultaneously increasing yield, nutrient uptake, and quality (Chand et al., 2006; Thangasamy and Lawande, 2015; Han et al., 2016). Therefore, to improve garlic yield and maintain soil health, an integrated application of mineral fertilizers, organic manures, and biofertilizers is necessary.

Table 1. Effects of Integrated Organic and Inorganic Fertilizers on Garlic Production in Ethiopia. 

Citation	Fertilizer Combination	Bulb Yield (t/ha)	Key Findings
Alemayehu & Abate (2021)	112–37–16 kg/ha NPS + 15 t/ha cattle manure	22.05	Highest bulb yield and net benefits observed; marginal rate of return exceeded 1.492%.
Shumbulo et al. (2024)	150 kg/ha NPS + 15 t/ha chicken manure	20.27 (total),19.52(marketable)	Combined application resulted in maximum marketable bulb yield and total yield.
Tesfaye et al. (2024)	120 kg/ha NPS + 10 t/ha cattle manure	Not specified	Significant improvements in garlic yield and quality parameters.
Assefa et al. (2015)	130 kg/ha NPS + compost	4.76	Higher yield compared to control; compost application improved soil fertility.
Alemu-Degwale (2016)	10 t/ha vermicompost	Not specified	Vermicompost application enhanced garlic growth and yield.

Table 1. Effects of Integrated Organic and Inorganic Fertilizers on Garlic Production in Ethiopia. 

Citation	Fertilizer Combination	Bulb Yield (t/ha)	Key Findings
Alemayehu & Abate (2021)	112–37–16 kg/ha NPS + 15 t/ha cattle manure	22.05	Highest bulb yield and net benefits observed; marginal rate of return exceeded 1.492%.
Shumbulo et al. (2024)	150 kg/ha NPS + 15 t/ha chicken manure	20.27 (total),19.52(marketable)	Combined application resulted in maximum marketable bulb yield and total yield.
Tesfaye et al. (2024)	120 kg/ha NPS + 10 t/ha cattle manure	Not specified	Significant improvements in garlic yield and quality parameters.
Assefa et al. (2015)	130 kg/ha NPS + compost	4.76	Higher yield compared to control; compost application improved soil fertility.
Alemu-Degwale (2016)	10 t/ha vermicompost	Not specified	Vermicompost application enhanced garlic growth and yield.

2.6. Irrigation and Field Management

Ethiopia is the second most populated nation in Sub-Saharan Africa. Its subsistence rainfed-based farming system wouldn’t be able to provide the nation’s food needs owing to regional and seasonal rainfall unpredictability, degradation of the soil, fertility depletion, and the consequences of climate change (Zerssa et al., 2021). Furthermore, irrigation users’ yearly income might be enhanced eight times more than non-irrigation users’ (Berhe et al., 2022).

Watering garlic takes two to five centimeters of water every week. Water will affect yield most before bulbing, much like nitrogen does. Even though bulbing requires enough moisture, irrigation should be discontinued at least two weeks before the anticipated harvest date. Late-season watering usually results in skin discoloration and lower quality (Goldy, 2000). According to studies done in Australia by Hickey (2012), water stress in garlic crops should be avoided before they show the first signs of maturity for maximum yields. Since the fibrous root system is limited to the top layer of soil, enough water needs to be added to the soil to moisten it to this depth. When the first indications of maturity appear (yellowing of the tips or softening of the necks), stop watering. Keep cultivation shallow to prevent root trimming if it’s required for weed control or water infiltration. You could use a knife. Hand hoeing is required to get rid of any weeds that have sprouted up in the row (Hickey, 2012).

2.6.1. Nutrient Use Efficiency and Management of Garlic in Ethiopia

Ethiopia has a long history of using traditional irrigation techniques. Simple river diversion remains Ethiopia’s main irrigation technique (Awulachew et al., 2010). It is estimated that Ethiopia has 5.3 million hectares of potential for irrigation. Of the potential 3.7 million hectares, 1.6 million are accounted for by groundwater and rainfall collection systems, while the remaining 3.7 million hectares are accounted for by surface water collecting methods (small, medium, and large scale). As of 2015, only around 12% of the 857,933 hectares of irrigated land have been done thus (Molden et al., 2010). Water resources must thus be carefully managed in order to increase the area under irrigation while utilizing the water that is available (Oki and Kanae, 2006; FAO, 2011).

Therefore, increasing cropping intensity in irrigated regions and yields in both rain-fed and irrigated agriculture using a variety of techniques and technologies are the most realistic strategies to attain food security (Diriba, 2016; Awulachew et al., 2010; Fraiture and Perry, 2007; Seleshi and Zanke, 2004). Crop water consumption efficiency may be greatly increased by properly scheduling irrigation, which is based on crop evapotranspiration (Incrocci et al., 2014; Hanson et al., 2003). Ethiopia has traditionally employed irrigation at different agricultural levels, but no efficient or well-managed irrigation water system exists. Very little or no information is available about crop management practices and the appropriate use of irrigation water for the country’s rapidly expanding irrigation fields.

Garlic is vulnerable to water stress at every stage of growth, but especially during the bulb-formation stage, because of its shallow roots (Singh et al., 2010; Silabut et al., 2014). The amount of irrigation required depends on the kind of soil and the climate. However, most soils require 2.5 cm of water every week during the growing season. Water twice a week after planting until over 80% of the seeded cloves emerge for reliable and rapid sprouting. After that, the frequency can be reduced to once a week. In accordance with Singh and Chand (2003) and Yayeh et al. (2017), fluctuations in soil moisture between dry and wet circumstances may cause irregular growth and the creation of deformed bulbs.

Despite its importance, vast production potential, and strong consumer demand, garlic’s present productivity and output are limited and still seasonal. Low soil fertility, which is mostly caused by crop yield losses brought on by crop waste expulsion from farmland, crop nutrient absorption from the soil by crops, and erosion of surface soil, is one of the issues impeding the productivity of various crops in Ethiopia (Abay, 2016; Belay, 2015).

Crop rotation, intercropping, farmyard waste, and fallowing are all practices Ethiopian farmers have long used to maintain or increase soil fertility and lessen these problems (Befekadu et al., 2017). Manure application enhances the soil’s properties and nutritional state, increasing soil fertility and garlic output. Similar results were reported by Shivananda (2002), who discovered that adding organic elements to the soil, including compost, green manure, or farm yard manure, in addition to inorganic fertilizer improved the soil’s physical characteristics. Additionally, the author discovered that when 50% of the fertilizer was organic and 50% was inorganic, crops absorbed much more nitrogen, phosphorus, potassium, zinc, manganese, copper, and iron.

Nutrient utilization efficiency(NUE), depends on the plant’s ability to efficiently take nutrients from the soil as well as moisture availability and internal transit, storage, and remobilization of nutrients. Since plants absorb considerable amounts of nitrogen and phosphorus from the soil, these nutrients are regarded as the main macronutrients. Proper application of these nutrients can enhance garlic development and yield (Mulatu et al., 2014). Accordingly, studies carried out in several parts of Ethiopia by Diriba et al. (2015) showed that applying NPS in combination at varying rates of N, K, P, and S kg/ham increased the growth and yield potential of garlic. It is common practice to overspray N fertilizers in an attempt to generate large garlic crops. Because of the high amount of N applied, a significant portion of the applied N has already accumulated in the soil, resulting in low N usage efficiency. In addition, additional N may be lost to the atmosphere and groundwater (Jiang et al., 2013).

2.6.2. Concept of Deficit Irrigation

Massive global change in the climate combined with a steadily increasing world population have a catastrophic impact on agriculture, leading to drought issues that further exacerbate the world’s scarce water supplies (Chai et al., 2016; Hussain et al., 2009). Water is the main factor limiting agricultural yield (Steduto et al., 2012). FAO (2006) projected that by 2030, developing countries will require 15% more water for agriculture. Over 95% of Ethiopia’s agricultural output, according to IFAD (2005) and Zerssa et al. (2021), relies on the country’s varied patterns of precipitation, both in time as well as space. Furthermore, when competent water management techniques are implemented, irrigation users’ yearly revenue might increase eight times faster than non-irrigation users (Gebremeskel et al., 2022). However, small-scale irrigation systems function poorly (Abera et al., 2019; Habtu et al., 2020). Enhanced evapotranspiration reference (ETo) prediction techniques are necessary for accurate irrigation water demand estimation (Qiong et al., 2022).

The lack of consideration for crop demands or scarce water resources by farmers applying excessive volumes of water under uncontrolled flooded irrigation has resulted in low crop productivity and economic return (Beyene et al., 2018). According to Doro (2012), mismanaged irrigation might reduce crop output by as much as 60% when it comes to full evapotranspiration (ETc). The distinctive features of flooding irrigation, according to Wang et al. (2020), include low water homogeneity, difficulties managing the water, and a high rate of evaporation, which leads to little water usage efficiency as a consequence, it’s important to boost water usage efficiency by using the best water management strategies, such as deficit irrigation, postponing watering until necessary, and using effective irrigation techniques. For improved crop development and productivity, a comprehensive root zone system that optimizes the relationship between soil, water, plants, and atmosphere is necessary (Fanish, 2013).

Deficit irrigation (DI) is a technique of improvement whereby irrigation is applied during a crop drought-sensitive growing period. Outside these periods, provided rainfall supplies a minimum water supply, irrigation is modest or even unneeded. Water limitation, sometimes throughout the vegetative phases and the late-ripening season, is confined to drought-tolerant phonological stages. Cumulative irrigation input is consequently not proportionate to irrigation demand through the crop’s period. Although this ultimately adds to plant stress due to drought and consequently lack of production, DI optimizes the efficiency of irrigation water, which is the primary limiting factor (Abdalhi, and Jia, 2018). One strategy to increase water yield while lowering irrigation application is deficit irrigation (DI). Crop irrigation requirements in the past did not take the availability of water supply into account. These days, full irrigation is viewed as an unnecessary luxury that can be curtailed with little to no impact on a profitable crop (Sezen et al., 2019).

2.6.3. Water Use Efficiency

According to Descheemaeker et al. (2013), boosting water productivity is crucial to better water management for food security, sustainable agriculture, and the health of ecosystems. Ethiopia now withdraws less water for agriculture and other uses each year than it does from renewable resources; this poor water use efficiency will surely represent a challenge to the region’s sustainable water management and usage (Gebrehiwot and Gebrewahid 2016). Using lakes and rivers, conventional surface irrigation has been widely used in Ethiopia. Crop water productivity implementation follows basic guidelines (Teshome et al. 2018).

A significant term in the evaluation of DI approaches is crop water efficacy (WP) or water use efficiency (WUE), which was discussed by Molden (2003). In terms of kilos per m³, water efficiency is defined as the amount of marketable yield (Ya) divided by the volume of water utilized by the crop (ETa): WP = Ya /Eta ETa refers to the quantity of water lost throughout the growing period as a consequence of crop transpiration or soil evaporation. In experiments, it is often impossible to discern between these two processes, so they are included together under the umbrella designation of evapotranspiration (ET) (Allen et al., 1998).

WP is applied as a benchmark to determine the highest water efficiency level in the CWP function. The following Figure depicts the logistic form of the CWP function (Hanks et al., 1969; Hanks, 1974). Plotting relative yield (Yrel: ratio of actual yield, Ya, to maximum yield under defined agronomic circumstances, Ym) versus relative evapotranspiration (ETrel: ratio of actual evapotranspiration, ETa, to crop ET under non-stressed, standard conditions, ETc) makes its axes dimensionless.

Figure 1. An agricultural production of water (CWP) function’s basic shape. There is a variance in the proportional widths of sections (a), (b), (c), (d), and (e). Relative evapotranspiration is the ratio of the seasonal quantity of water evapotranspired, (ETa) to the season crop water demand (ETc). Relative yield is the ratio of actual (Ya) to potential yield (Ym) under specified agronomic situations.

Table 2. Water Use Efficiency in Garlic Production under Different Irrigation Practices in Ethiopia. 

Study	Irrigation System	Deficit Irrigation Level	Water Use Efficiency (WUE)	Key Findings
Ayele (2023)	Conventional Furrow Irrigation (CFI)	85% ETc	Not specified	Moderate deficit irrigation (85% ETc) maintained yield with improved water use efficiency.
Ayele (2025)	Alternate Furrow Irrigation (AFI)	70% ETc	31.52 kg/mm	AFI at 70% ETc achieved highest irrigation water use efficiency (IWUE).
Ilmi (2025)	Alternate Furrow Irrigation (AFI)	100% ETc	28.64 kg/mm	AFI at 100% ETc provided comparable yield with significantly reduced water use.
Tefera (2021)	Not specified	20%above recommended ASMDL	Not specified	Reducing soil moisture depletion level by 20% increased WUE.

Note: ETc refers to crop evapotranspiration; ASMDL refers to allowable soil moisture depletion level.

Table 2. Water Use Efficiency in Garlic Production under Different Irrigation Practices in Ethiopia. 

Study	Irrigation System	Deficit Irrigation Level	Water Use Efficiency (WUE)	Key Findings
Ayele (2023)	Conventional Furrow Irrigation (CFI)	85% ETc	Not specified	Moderate deficit irrigation (85% ETc) maintained yield with improved water use efficiency.
Ayele (2025)	Alternate Furrow Irrigation (AFI)	70% ETc	31.52 kg/mm	AFI at 70% ETc achieved highest irrigation water use efficiency (IWUE).
Ilmi (2025)	Alternate Furrow Irrigation (AFI)	100% ETc	28.64 kg/mm	AFI at 100% ETc provided comparable yield with significantly reduced water use.
Tefera (2021)	Not specified	20%above recommended ASMDL	Not specified	Reducing soil moisture depletion level by 20% increased WUE.

Note: ETc refers to crop evapotranspiration; ASMDL refers to allowable soil moisture depletion level.

The relationship between water usage and growth, especially the formation of dry matter, is referred to as water use efficiency. The crop dry matter or yield produced per unit of water utilized by the plant is the expression used to represent water usage efficiency (Mokenen, 2011). Water use efficiency can be altered by raising the plant’s water consumption or by promoting the plant’s growth and production. Water consumption efficiency is positively impacted by soil management techniques like tillage and residue management as well as plant nutrition techniques like adding nitrogen and phosphorus. Adopting deficit irrigation and proper irrigation schedules could help increase the effectiveness of water use (Jones, 2004). The notion of nutrient utilization efficiency (NUE) illustrates how crops can take in and utilize nutrients for optimal yields. Nutrient uptake, assimilation, and utilization are the three primary plant activities that make up the NUE concept (Gonzalez, 2017).

Table 3. Summary of Key Findings on Garlic Production in Ethiopia. 

Citation	Focus Area	Key Findings
Ayele (2023)	Deficit Irrigation	85% ETc under Conventional Furrow Irrigation (CFI) achieved 8.2 t/ha yield with 7.8% loss from full irrigation. - 85% ETc under Alternate Furrow Irrigation (AFI) saved 50% water but incurred 19% yield loss. - Severe deficit (55% ETc) drastically reduced yield by 37.5%.
Ayele (2025)	Irrigation Techniques	85% ETc under CFI optimized water use without compromising yield, establishing an efficient irrigation strategy for sustainable garlic production in water-limited regions.
Alemayehu &Abate (2021)	Integrated Nutrient Management	Combined application of 112-37-16 kg/ha NPS inorganic fertilizers with 10-15 t/ha cattle manure resulted in the highest bulb yields (18.03-22.05 t/ha), net benefits (Ethiopian Birr 509,456-626,814 per hectare), and marginal rate of returns (1,492.35-2,005.15%).
Shumbulo et al. (2024)	Integrated Fertilizer Levels	Integrated application of NPS fertilizer and chicken manure improved garlic yield and quality. Specific fertilizer combinations and application rates were found to be effective for optimal garlic production in southern Ethiopia.

Table 3. Summary of Key Findings on Garlic Production in Ethiopia. 

Citation	Focus Area	Key Findings
Ayele (2023)	Deficit Irrigation	85% ETc under Conventional Furrow Irrigation (CFI) achieved 8.2 t/ha yield with 7.8% loss from full irrigation. - 85% ETc under Alternate Furrow Irrigation (AFI) saved 50% water but incurred 19% yield loss. - Severe deficit (55% ETc) drastically reduced yield by 37.5%.
Ayele (2025)	Irrigation Techniques	85% ETc under CFI optimized water use without compromising yield, establishing an efficient irrigation strategy for sustainable garlic production in water-limited regions.
Alemayehu &Abate (2021)	Integrated Nutrient Management	Combined application of 112-37-16 kg/ha NPS inorganic fertilizers with 10-15 t/ha cattle manure resulted in the highest bulb yields (18.03-22.05 t/ha), net benefits (Ethiopian Birr 509,456-626,814 per hectare), and marginal rate of returns (1,492.35-2,005.15%).
Shumbulo et al. (2024)	Integrated Fertilizer Levels	Integrated application of NPS fertilizer and chicken manure improved garlic yield and quality. Specific fertilizer combinations and application rates were found to be effective for optimal garlic production in southern Ethiopia.

Challenges and Knowledge Gaps

Despite the advantages of INM and optimal irrigation, a number of problems still exist:

• ✓ Due to resource limitations, suggested procedures have not been widely adopted.
• ✓ absence of norms particular to Ethiopia’s many agro-ecological zones.
• ✓ Long-term research is required to evaluate how sustainable these techniques are.
• ✓ To increase garlic productivity, these deficiencies must be filled with focused research and extension activities.

3. Conclusions

Garlic is the most important crop grown with alliums; onions are the most important crop worldwide. Its main uses in modern medicine are as a spice in cuisine and to treat and cure a variety of illnesses. Garlic thrives in highlands (1500–3456 m), but it grows best in areas with temperatures between 12 and 24 degrees Celsius, well-drained sandy, silty soils, and a pH of 7. It also stores incredibly well. Alemu and associates (2016). The FAO estimates that 28.1 million metric tons of garlic were produced worldwide in 2020, an increase of almost 3.9% from the year before. Due to the wide range of uses for garlic in the food and medical sectors, which are propelling the market globally, there has been a significant increase in both the area harvested and production.

Important variables affecting garlic production are identified in the review, including nutrient delivery techniques, soil fertility, and water availability. It talks about how different integrated nutrient management techniques, such as cover crops, crop residue integration, and organic and inorganic fertilizers, affect the quantity and quality of garlic produced. The review also looks at how various irrigation techniques, like drip irrigation and furrow irrigation, might maximize garlic yield and water use efficiency.

Considering that over 80% of Ethiopia’s population makes their living from agriculture, which also accounts for 40% of the country’s GDP, raising crop yields in Ethiopia is an important way of improving both the standard of living for those living in rural areas and the nation’s economic sustainability. Despite Ethiopia possessing potentially abundant irrigable land and water supplies, the country’s agricultural industry does not yet fully benefit from irrigated agriculture and the technologies for managing water and farmland utilization. Ethiopia has unusually low agricultural production as a result. Utilizing nutritionally balanced sources is crucial in today’s garlic growing to ensure big harvests of healthy garlic bulbs. It is normal practice to suggest mineral fertilizers instead of organic inputs. However, farmers’ organic inputs, crop wastes, and animal manures cannot provide crop nutrient demands across vast areas because of the constrained quantities available. The labor-intensive production and use of the resources, together with their low nutritional value. Because of this, most African farmers apply a combination of organic and inorganic inputs, putting them in the middle of the organic-to-inorganic fertilizer continuum.

To sum up, the review of the literature indicates that improved irrigation and integrated fertilizer management are essential for increasing garlic output in Ethiopia. The research emphasizes how crucial it is to have a comprehensive strategy that incorporates effective irrigation techniques with suitable fertilizer management techniques. The assessment emphasizes the necessity of recommendations that are site-specific and take into account the various agroecological zones and soil types found in Ethiopia. The report also highlights the potential advantages of sustainable farming methods and organic inputs in enhancing soil health and reducing environmental effects. It urges more studies to close the knowledge gaps that now exist, especially about the long-term consequences of integrated techniques on garlic output and the financial ramifications for farmers.

In general, this review offers significant perspectives to farmers, academics, and policymakers who are looking for effective and sustainable ways to increase garlic production in Ethiopia. The agriculture industry may boost yields while also advancing resource efficiency and environmental sustainability by combining nutrient management with irrigation techniques.

4. Future Directions

Future research should explore the impact of different irrigation schedules, deficit irrigation, optimal timing of irrigation, organic and inorganic fertilizers, biofertilizers, micronutrient supplementation, long-term effects of inorganic nitrogen management practices, interactions between soil microorganisms and garlic plants, and the potential of soil amendments to enhance garlic productivity. It is also important to study the adaptability of different garlic varieties to varying climatic conditions and the resilience of garlic crops to water stress and nutrient deficiencies under changing climate scenarios. Collaborative research involving agronomists, soil scientists, and plant physiologists is crucial for advancing our understanding of garlic production and sustainable management. This will help to improve the quality and yield of garlic, while also promoting sustainability and environmental sustainability.