Review on Production and Importance of Basil (Ocimum basilicum L) and Roles of Fertilizer on Basil Yield

Basil (Ocimum basilicum L.) is one of the most popular medicinal and aromatic plants that belong to Lamiaceae family and the Ocimum genus is known with its highly aromatic leaves, utilized either fresh or dried for culinary. Basil is grown in many countries of the world as spice, medicinal, and aromatic plant. The medicinal and aromatic properties of basil are associated with the presence of an essential oil that accumulates in large amount in its leaves and inflorescences. It performs well in warm and humid climate. However, basil is sensitive to frost and heavy rain fall. The growth and yield of basil is affected by different factors. Moreover, nutritional requirements of the crop are considered to be the most important factor among many plant growth factors. Nitrogen contributes to greatest extent to increase the biosynthesis of essential oil and its composition in numerous aromatic plant species. Essential oil yield and its chemical composition of these plant species significantly depend on the rate of nitrogen, phosphorous and sulfur.


Importance of Basil
Ocimum are important groups of aromatic and medicinal plants which yield many essential oils and aromatic chemicals and find diverse uses in perfumery and cosmetic industries as well as indigenous system of medicine. It is used in food industries and dental product (Prasad, et al,. 1986;Vieira and Simon 2000). Many medicinal and aromatic plants, including basil, are typically consumed without further processing after harvest (Banchio et al., 2008).
Among various Ocimum species, O. basilicum is commercially and extensively cultivated for essential oil production. Basil is grown in many countries of the world as spice, medicinal, and aromatic plant. The medicinal and aromatic properties of basil are associated with the presence of an essential oil that accumulates in large amount in its leaves and inflorescences. Basil oil is mixture of numerous compounds and its composition is extremely rich and varied. The major essential oil components of basil are: methyl chavicol, linalool, 1, 8cineole and methyl (Niederwireser 2001). Scientific research has investigated the health benefits associated with basil's essential oils. Different studies reveal the anti-viral, anti-microbial, antioxidant, and anti-cancer properties of the oils (Chiang et al., 2005;Bozin, et al., 2006). Moreover, basil oil and its pure components have antimutagenic activity . Basil produces range of polyphenolic compounds including rosmarinic acid, a characteristic it shares with herbs in the genus Lamiaceae. Rosmarinic acid is a cinnamic acid derivative with potent antioxidant activity and known antiviral, antibacterial, and anti-inflammatory properties. In addition, several purple basil cultivars also contain anthocyanins which are powerful antioxidants, and the polyphenolic pigments responsible for the red and blue colors found in many plants (Nguyen and Niemeyer, 2008).
Traditionally, basil leaves are used in folk medicine as a remedy for a large number of diseases, including cancer, convulsion, diarrhea, epilepsy, gout, nausea, sore throat, toothaches, bronchitis coughs, constipation, warts, worms and kidney malfunction (Simon et al., 1990;Duke et al., 2008). Hot tea of basil plant leaves is good for treating nausea, dysentery, and flatulence. Externally, basil formulations can be used for different skin infections such as treatment of acne, snake bites and insect stings (Khatri et al., 1995). Basil also possesses various beneficial effects, e.g., antiseptic, carminative, antimicrobial and antioxidative properties (Baranauskiene et al., 2003). The essential oil of basil is used as antifungal and insect-repelling agent (Reuveni et al., 1984;Werner 1995). The curative properties of basil result from the presence of essential oils, phenolic compounds, flavonoids (Nurzyńska-Wierdak et al. 2012) and other substances revealing anti-bacterial (Nour et al. 2009), anti-mycotic and antioxidant activities (Sekar et al. 2009).

Factors Influencing Growth, Biomass and Oil Yield
The principal interest in the cultivation of the crop is for its essential oil (EO) and maximization of economic yield returns. Basil crops may be grown solely for its essential oil and/or other products. Therefore, in the cultivation, basil plants should be grown to maximize the yield of both essential oil and fresh leaves. The growth and essential oil accumulation and composition of basil could be markedly affected by different factors such as environmental factors, physical and chemical properties of soil, seed source, plant age, parts of plant that which used for oil isolation, oil isolation method, genetic and agronomic practices (irrigation, fertilization, time of harvesting) etc. (Marotti et al., 1996;Shahram 2011).

Environmental factors
Performances of crop plants depend on temperature, solar radiation, moisture and soil fertility for their growth and nutritional requirements. Temperature plays an important role in plant growth and yield. Plants respond to temperature change in most of their metabolic activities such as photosynthesis respiration and transpiration (Murtagh, 1996). Climatic conditions during basil cultivation substantially affect the growth, flowering and chemical composition of the crop (Purkayasta and Nath, 2006;Nurzyska -Wierdak, 2007;Shatar et al. 2007). The authors reported that the number of leaves, fresh plant weight and concentration of basil essential oil increase under the influence of growing high temperatures (30/25 o C). They give this range of temperature and the 12-hour day as the optimal conditions for producing fresh basil herb. Chang et al. (2008) reported d a distinct influence of solar radiation upon basil growth, as well as on quantity and quality of essential oil. The authors report that basil growth takes its best course under full sunlight; however, plants tolerate slight shading. The morphological and chemical variability of Ocimum basilicum L. creates great possibilities for growing different cultivars of this valuable herbal plant. The chemical composition of basil essential oil is dependent on genetic, ontogenetic, environmental factors and agro technical factors, such as cultivation method, harvest term, fertilization, or irrigation similarly as in other oil plants (Nurzyska -Wierdak 2002;İpek et al. 2012).

Effect of fertilizer on growth and yield of basil
Growth and yield of basil, like other plants, depend upon the availability of all nutrients in the environment. The yield and quality is depends on macro-and micronutrient taken up .

Effects of nitrogen fertilizer on growth, biomass and oil yield of basil
Nitrogen (N) is one of the basic nutrients used by plants to build many organic compounds, such as amino acids, peptides, proteins, enzymes, or nucleic acids Shi 2011, Ma et al. 2012). Amino acids and enzymes play a key role in the biosynthesis of numerous compounds which are essential oil constituents (Koeduka et al. 2006). It is an important macronutrient necessary for the proper functioning of the plant. It has significant effect on yield amount and quality of oil plants.   Rao et al., 2007 Nitrogen is required by plants in comparatively larger amounts than other elements. Nitrogen deficiency generally results in stunted growth and chlorite leaves caused by poor assimilate formation that leads to premature flowering and shortening of the growth cycle (Larimi et al 2014).
The presence of N in excess promotes development of the above ground organs with abundant dark green (high chlorophyll) tissues of soft consistency and relatively poor root growth (Lincoln and Edvardo, 2006). Nitrogen applied in the cultivation of herbal plants also stimulates the synthesis of other biologically active substances. Nitrogen contributes to the greatest extent to an increase in the biosynthesis of essential oil and its composition in numerous aromatic plant species (Renata, 2013). Essential oil yield and chemical composition of these plant species can be significantly depend on the rate of nitrogen. Arabaci and Bayram (2004) reported increase in fresh and dry basil herb yield, as well as in essential oil content and yield, under the conditions of N fertilizer application. The study of these authors showed the effect of applied N on essential oil composition of basil. Sifola and Barbieri (2006) reported that the basil cultivar had an impact on the effectiveness of N application in terms of increase in the amount of essential oil in the basil herb.
Study of Nguyen and Niemeyer (2008) showed that changes in the level of N fertilization during the growing period of basil had a significant impact on the production of phenolic compounds, in particular rosmarinic acid. Nitrogen application in growing basil contributes not only to an increase in essential oil content, but also increases the concentration of linalool and borneol in the oil, with a simultaneous decrease in the content of methyl chavicol and 1, 8-cineole (Taie et al., 2010). Studies of different researchers revealed that N application can increase essential oil yield of basil.  report that maximum basil oil yield is obtained when 50-60 kg of N per hectare is applied; in addition, N significantly modifies the percentage of linalool, eugenol, bornyl acetate, and eucalyptol in basil essential oil.
Ali Sabah Alhasan et al 2020 reported that nitrogen fertilizer rates significantly affected basil growth and essential oil yield. According to the Authors the highest essential oil was recorded duet to application of moderate nitrogen fertilizer rates. Figure 2. Effect of applying different nitrogen fertilizer rate on seed yield and essential oil yield Source: Ali Sabah Alhasan et al 2020 Rao et al. (2007) verified that elevated N availability (doses over 100 kg ha -1 ) resulted in higher plant yield and essential oil content of basil. Alizadeh et al. (2010) reported that high correlation between shoot dry mass in relation to total dry matter weight, essential oils content, extraction efficiency of essential oils and phenolic compounds content of basil plants. Other nutrients, such as phosphorus, sulfur, calcium, magnesium and microelements, are also capable of changing essential oil yield and composition (Renata, 2013).

Effects of phosphorous fertilizer on growth, biomass and oil yield of basil
Plants need phosphorus (P) for growth, utilization of sugar and starch, photosynthesis, nucleus formation and cell division. Phosphorus compounds are involved in the transfer and storage of energy within plants. Energy from photosynthesis and the metabolism of carbohydrates is stored in phosphate compounds for later use in growth and reproduction. Plants require adequate P from the very early stages of growth for optimum crop production (Grant et al. 2005).
Crop removal of P may range from 3 to 30 kg P ha -1 ; therefore crop production will gradually deplete available soil P in the absence of P application. Conversely, excess P supply in the soil is a major environmental concern. Accumulation of P in the soil from applications of animal manures, biosolids or chemical fertilizer in excess of that taken up by the crop can increase the risk of P movement to surface and ground waters (Grant et al., 2005). A good supply of P has been shown to increase root growth (Marschner, 1999;Tisdale et al, 1990). Ramezani and Rezaei 2009 conducted the study on effects of P fertilizer on basil. The result of study indicated the pattern of increasing of the essential oil by application of P treatments, essential oil content of basil in the study was significantly increased in different Potassium phosphate rates. The authors reported that, from the practical point of view, the increase in fresh and dry biomass and oil yield induced by P application has positive effects since the commercial value of basil and farmer incomes also depends on the amount of essential oil produced. According to Kapoor et al., (2004) addition of P fertilizer in the case of fennel, (Foeniculumvulgare Mill.) has also affected the yield and composition of essential oil.

Effects of sulfur fertilizer on growth, biomass and oil yield of basil
Sulfur (S) is essential plant macronutrient for crop production. It is increasingly recognized as the fourth major plant nutrient after nitrogen, phosphorus and potassium. The importance of S in agriculture is being increasingly emphasized and its role in crop production is well recognized (Jamal et al., 2005).
Sulfur has a broad spectrum of action that improves the general appearance of the plant, strengthens its natural defense, increases resistance to nutritional and climatic stresses and pest attack, and also influences positively other important aspects for essential oil production and development of shoots (Rezende, 2003). Sulfur is part of plant proteins as a component of the amino acids cysteine and methionine and coenzymes (Marschner, 1999). Jamal et al. (2010) reported that in intensive crop rotations including oil crops, sulfur uptake can be very high, especially when the crop residue is removed from the field along with the product. According to these authors, the removing crop residue from the field with the product leads to S depletion in soil if the corresponding amount of S is not applied. Use of sulfur in crop production has received little attention for many years, because it has been considered that the atmosphere supplied the soil with adequate amounts of S (Jamal et al., 2010). Insufficient concentrations of sulfur reduce plant production in many parts of the world, and S deficit has been observed in soils and agricultural systems for the last few years due to several factors: depressed emission of S to atmosphere, low concentration of S in most of mineral fertilizers, which does not balance the loss of S caused by its uptake by crops, low level of organic fertilization and migration of sulfate to deeper soil horizons and ground water (Zhao et al. 1999, Fismes et al. 2000, Scherer 2001, McGrath et al. 2003, Walker and Dawson 2003, Matula 2004.
Different studies conducted on the effects of sulfur on basil crop. The study revealed that, an increased amount of S causes a rise in production of essential oil and eucalyptol in basil oil   Figure. 3. Oil production as a function of sulfur fertilization at three locations Source: .
The authors concluded that since the result of study showed strong response of basil oil yield to S, further research with S application rates and intermediate N background may be needed to estimate the optimal basil yield and compositional response to nitrogen and sulfur.
Sulfur is best known for its role in the formation of amino acids methionine (21% S) and cysteine (27% S); synthesis of proteins and chlorophyll; oil content of the seeds and nutritive quality of forages (Tandon, 1986;Jamal et al., 2005). Sulfur is especially important for oil crops. Study indicated that, the amount of S required to produce one ton of seed is about 3 -4 kg S for cereals, 8 kg S for legume crops and 12 kg S for oil crops (Scherer, 2009). In general, this author concluded that oil crops require about the same amount of S as, or more than, phosphorus for high yield and product quality.
An insufficient S supply can affect yield and quality of the crops; caused by the S requirement for protein and enzyme synthesis as well it is a constituent of amino acids and methionine. According to Marschner (1999), sulfur deficiency could reduce N uptake, potential crop yield, and the quality of plants. To overcome the problems associated with S deficiency a number of S containing fertilizers as well as other S containing byproducts from industrial processes are available (Jamal et al., 2010).

Conclusion
Basil (Ocimum basilicum L) is a crop grown for its aromatic properties, while the green leaves are used fresh or dried used as an aromatic spice for flavoring of dishes, salads, stews, sausages and other food. The oil of basil also used for flavoring of food stuffs, confectionery, condiments, and in toiletry products. Performances of crop plants depend on temperature, solar radiation, moisture and soil fertility for their growth and nutritional requirements. Fertilizer is one of the important factor affect the growth and yield of basil. Generally, basil (Ocimum basilicum L) is a medicinal and aromatic crop, easy to grow and use as herb and essential oil.