Nitrogen Nutrition Affect the Growth and Bulb Yield of Garlic ( Allium Sativum L.)

Nitrogen (N) is one of the critical nutrients for productivity and quality of cultivated crop species. However, its overused in crop cultivation caused several environmental concerns. Hence its proper use in agriculture is not only pre-requisite for sustainable crop cultivation but also necessary to control environmental pollution. A field trial was designed at experimental area of Department of Horticulture, Sindh Agriculture university Tando Jam, Pakistanto test the response of garlic varietiesto N nutrition in terms of growth and bulb attributed traits during the winter season, 2020-21 . The N effect on growth and yield associated traits of two garlic varieties (local white and purple top) were investigated by applying four Nrates that included 0, 50 kg, 100 kg and 150 kg ha -1 . The findings of the trial exhibitedthat N application at various rates had substantial positiveimpact on the growth and bulb development of garlic at (P<0.05). The garlic plantation receivedNat maximum rate (150 kg ha -1 ) resulted tallest plants,better neck thicknesswith more leaves plant -1 . The N also positively affected the bulb yield and other yield parameters of garlic.The maximum bulb yield was obtained when plants were nourished with 150 Kg N ha -1 that was 381.98 % more than the control. It was noted that increase inN rates was statistically dominant over other doses. The varietal influence on garlic indicated that variety purple top performed better than local white in terms of yield associated traits..These findings provide new insight regarding the significance of N nutrition in improving the growth and bulb yield of garlic genotypes


Introduction
Garlic is economically important bulbous vegetable crop of family Amaryllidaceaeand probably got origin from Central Asian Countries (Amarakoon and Jayasekara, 2017).The cultivation of garlic introduced to other countries through trade (Santhoshaet al., 2013).Garlic is known as second most important bulbous crop followed by onion (Wen et al., 2020).Garlic is grown in a variety of places, the sunny, dry areas, humid and moderately dry environment (Sayadiet al., 2020).Because of its diversity, the importance of garlic planting is well known globally (Liu et al., 2020).Garlic has a high medicinal value and is used to treat chronic diseases of the stomach, eye and ears (Efionget al., 2020) It is used both as a form of fresh and dry powder (Gonzalez et al., 2009;Chen et al., 2018).It is useful in the treatment of heartrelated diseases (Aviello et al., 2009;Colín-González et al., 2012).China is the major Producer of Garlic and is estimated that its production is about 77 % of world production (FAO, 2017).Available reports show that garlic production exceeding 22.23 million tons; whereas share of Asian countries is more than 80 % (FAO, 2018).The garlic consumption is increasing day by day from the last decade.Its consumption increased from 1.6 kg to 3 kg per person per year (Gonzalez et al., 2009).Pakistan is one of the major importer of garlic since local production cannot meet domestic needs that's why a large amount of garlic comes from abroad to meet the needs of the country.(Baldwin et al., 2014).Thus, a large number of foreign exchanges were made on the import of garlic.Globally, considerable increase in economic importance of garlic has been noticed in the recent past.However, yields obtained in Pakistan are critically low.The main reason for low yields is the lack of high yielding varieties, adapted to local conditions and improper and non-judicious used of plant nutrients especially nitrogen (N) (Khan et al. 2016).The inadequate supply of organic manures and continuous cropping have caused deficiency of plant nutrients including N in our soil and such conditions led to decreased yield of cultivated crop species (Abbaszadeh et al., 2014).Despite N availability abundantly on earth, N deficiency is most common nutritional problem that affects plants (Don Eckert, 2010).Nitrogen availability is very important for plant growth as it is anmajor part of the chemical chlorophyll, which playsasignificant role in the process of photosynthesis (Getu, 2015).The higher N content promotes vegetative growth, enhance high protein content, while reduces anthocyanin synthesis (Luji et al. 2016).N stimulates plant growth strongly, expand crop canopy and intercept solar radiation (Milford et al., 2000).N is regarded as main nutrient that affects crop production significantly; it is a component of biological molecules including proteins and nucleic acids (Good et al., 2004).N deficiency leads to decline chlorophyll content plant leaves, reduction in leaf area, growth retardation, poor yields and even plant may die (Amtmann and Armengaud, 2009).The application of N in optimum quantity is pre-requisite for getting the higher yield of garlic (Mulatuet al., 2014). Sebnieet al. (2018) have shown that dose of N of 92 kg ha -1 is essential for economic garlic yield.Reddy et al. (2000) recommended N dose of 150 kg ha -1 to obtain the desired plant height, bulb size and yield; while Talukderet al. (2000) recommended N rate(125 kg ha -1 ) to obtain more cloves of garlic.Zaman et al. (2011) tested various N levels on garlic and recommended a rate of 150 kg ha -1 for economically acceptable garlic yield; while Ahmad et al. (2012) recommended 100 kg N to get more cloves in garlic.However, Shiferawet al.
(2013) noted that under extreme nitrogen deficit conditions N dose can be increased up to 400 kg ha -1 to obtain a quality garlic product.The above N application recommendations are based on studies in various parts of the world with diverse soils and climatic conditions.In order to optimize the nitrogen demand of garlic under local soil and climatic conditions, current research was conducted to test the response of garlic genotypes to N nutrition under Tandojam conditions.

Materials and Methods
Experimental site: Present study was done during 2020-2021 at Department of Horticulture Garden, Sindh Agriculture University.The experimental site lies at 28°35'N to 81°37'E.It is divided by four different seasons: rainy monsoon (June-October), cold winter (November-February), and warm spring (March-May).The soil was silty loam, non-saline (0.7 dSm -1 electrical conductivity) alkaline in nature having pH (8.5) with poor organic matter (0.64 %) and N content (0.032 %), respectively.The phosphorous and potassium contents in the soil were (3.4 and 285 ppm)analyzed using spectrophotometer and flame photometer, respectively.Experimental design and treatment details: The trial was based on randomized complete block design (RCBD) design factorial with a 4x3 (12m 2 ) plot/experimental unit size.The growth and yield performance of two garlic varieties local white and purple top were determinedby applying four nitrogen (N) treatments with three replications.The N treatments included 0 kg, 50 kg, 100 kg and 150 Kg N ha -1 .Preparation of the land: The soil was prepared by providing two dry ploughings and clod crushing followed by land levelling for a uniform distributionof irrigation water.

Sowing of Cloves:
The cloves of two most famous varieties of the garlic ( Local white and purple top) were sown on both sides of ridges at the distance of 5 cm between plants.The sowing was done in the 15 th of October, 2020.All the standard cultural practices were followed during the entire course of trial Fertilizer application: For N nutrition, Urea (46 % N) was used in three split applications.Therecommendedrates of P (60 Kg ha -1 ) and K (50 kg ha -1 ) were used as single super phosphate (SSP) contains 18% P2O5 and Sulphate of potash (SOP) contains 50 % K2O.The first split of urea was applied along with full doses of SSP and SOP at the time of sowing of crop.The other splits of urea were applied at the interval of 40 and 60 days respectively.Parameters Measured: When the crop reached maturity, ten plants plot -1 were marked and tested by the growth and bulb associated parameters Data Recorded Plant height (cm):Measuring tape was used to calculate the plant height from bottom to the top of the plant.

Neck thickness (mm):
The Neck thickness was measured by using vernier caliper.Three readings were noted top bottom and end of plant.After thatmean of three values were considered.Leaves plant -1 : Leaves number plant -1 was counted separately from sample plants Cloves bulb -1 :Cloves were recorded by counting cloves from individual bulb of the marked plants Single clove weight: The cloves from the bulbs were separated and weighed in grams (g) by using electronic balance.Single Bulb Weight: The single bulb weight was done using electronic weight balance Blub Yield plot -1 (kg): From each sub-plot, the total number of bulbs were collected and carefully counted in all treatments and replications.Bulb yield ha -1 : The average yield is determined by counting and measuring the bulbs found in each plot and then converted into yield ha -1 applying formulaala given below: Statistical analysis: ANOVA (Analysis of Variance) was done through computer software Statistix 8.1 (Statistix, 2006).The treatment means were separated by using least significant difference (LSD) test at 0.05 probability.

Plant height (cm):
The maximum supply of N (150 kg ha -1 ) significantly produced taller plants with plant height 45.72 cm(Table -1).The decreasing trend in plant height was observed with the decrease of N supply.Plants nourished with N @100 and 50 kg ha -1 showed height of plants (39.23 and 29.25 cm), respectively.Whereas the minimum plant height (23.25 cm) was noted where plants were not nourished with N.On the basis of mean of varieties, the maximum plant height (35.19 cm) was observed in Local white variety (Table -1).The Purple top produced smaller plants with plant height (33.53 cm).----------------------X 10000 Plot size

Number of cloves bulb -1 :
The Data showed that N rates and varieties both showed significant variation for number of cloves bulb -1 .However, interaction between N rates x garlic varieties did not affect this trait significantly.The crop supplied N at adequate rate (150 kg ha -1 ) showed maximum cloves (40); followed by N application rates of 100 kg ha -1 and 50 kg ha -1 producing cloves number 35.83 and 30.66, respectively (Table -4).

Single clove weight (g):
The results demonstrated that nitrogen application rates had significant affect on bulb weight plant -1 ; and varietal effect on this trait was also significant (P<0.05).However, interactive effect of garlic varieties × N levels on this trait was not significant (P>0.05).It is obvious from the data that highest N application rate of 150 kg ha -1 caused maximum single clove weight (1.48 g); followed by N rates of 100 kg and50 kg ha -1 producing bulbs with single clove weight (1.04 and 0.83 g), respectively (Table -5).Whereas the minimum single clove weight (0.68 g) was recorded in control.In varieties, "Purple top" resulted in maximum single clove weight(1.41g) as compared to variety "Local white" (0.61 g) .

Single bulb weight (g):
The adequate N nutrition(150 kg ha -1 ) produced plants with relatively more weightbulb -1 (48.95); followed by 100 kg and 150 kg ha -1 N with the production of 34.46 and 25.68 g single bulb weight, respectively; while lowest bulb weight (11.23 g) was obtained in control plots where plants were not nourished with N (Table -6).On the basis of mean results of varieties, the maximum bulb weight (34.66 g) was observed in Purple top variety (Table -6).The Local white variety showed less single bulb weight (25.49g).
Bulb yield plot -1 :The garlic crop given N at the highest rate (150 kg ha -1 ) produced maximum garlic bulb yield plot -1 (10.56 kg); followed by N application rates of 100 kg and 50 kg ha -1 with average bulb yield of 9.96kg and 5.92kg plot -1 , respectively.However, the lowest bulb yield plot -1 (2.76 kg) was noted in control plots, kept without N fertilization (Table -7).In varieties, "Purple top" produced higher bulb yield (4.34 kg plot -1 ) than the yield plot -1 (3.71 kg) obtained in variety "Local white" (Table -7).
Bulb yield kg ha -1 : The garlic yield data (Table -8) revealed a significant impact of N levels and varieties on bulb yield ha -1 (P<0.05).The crop supplied adequate N nutrition (150 kg ha -1 ) showed maximum garlic bulb yield (8805.6 kg ha -1 ); followed by N rates of 100 kg and 50 kg producing average bulb yield of 8305.6 and 4939.9 kg ha -1 , respectively (Table -8).However, the minimum bulb yield ha -1 (2305.2kg) was noticed in control where plants were not nourished with N. In varieties, "Purple top" produced higher bulb yield (6442.2 kg ha -1 ) than the yield (5735.9 kg ha -1 ) noted in "Local white" variety (Table -8).

Discussion
Nitrogen (N) significantly contributes in obtaining the acceptable crop yield and its deficiency in Pakistani soils is well documented (Khan et al. 2016).N consumption has a significant impact on the growth and development of garlic (Kakar et al. 2002).The results show that the N rates and varieties have significant effects on growth and total bulb yield.The growth characteristics and productivity of the control plants were very low.For plant height, data showed that the response of 150 kg N ha -1 was significantly high where taller plants were produced as against the deficient nitrogen conditions.Under different N conditions plant lengths of varieties were different, which may be due to different genetic responses of varieties to the availability, uptake and utilization of nitrogen (Hossein, et al., 2014).Other researchers Zaki et al., 2014 andZaman et al. 2011 also described good performance of garlic under ideal N conditions and reported that the height of the garlic plant increased from 42.4 to 64.7cm as nitrogen levels increased from 0 to 200 kg N ha -1 .In the current study, purple top performance was better as compared to local white.This result is consistent with the study of Abraham et al. (2014) who also found different response of varieties to different N conditions.Etoh and Simon (2002) also report significant differences in crop yields between varieties of garlic.Similarly, Yudhvir and Ramesh, 2003;Youssef, and Tony, 2014; explained that in different clones, data for different features showed significant differences (Hazem, 2013).Abou El-Magd, et al., (2012) also found significant differences under different nitrogen regimes.There was a significant difference in neck thickness between varieties and levels of nitrogen.Panse, et al., 2013 reported different varietal response for neck diameter under different N environments.This might be due to different genetic response of the varieties rather than application of N This is also consistent with previous studies performed by Hazem, (2013); Farooqui et al. (2009), which have shown significant response of garlic genotypes for most of the traits.There were significant differences in the number of leaves plant -1 between varieties.Moreover, different nitrogen rates also showed significant differences for leaves number.This reflects the essential role of N in the leaf growth and development.Moreover, it is well documented that N plays a major role in the formation of chlorophyll for photosynthesis, thereby promoting cell division and growth (Hazem, 2013).Adequate nitrogen is an important component of chlorophyll, which is essential for the growth and development of plants ( (Nori et al., 2012).The soil deficient in nitrogen, chlorophyll cannot be properly synthesized, leading to small size and shape of the leaves, and necrosis also occurs (Tibebu et al., 2014).In the present study, the increased N rate (150 kg ha -1 ) showed more value in all aspects of garlic (growth and yield characteristics).The decrease in nitrogen rate up to 100, 50 and 0 kg ha -1 showed reduction in growth and bulb development and lower values for most of the traits were recorded.It was further noted that with each increase in nitrogen supplementation, the performance of garlic crop increased significantly.This revealed that experimental soil showed signs of severe N deficiency.This was further advocated by analysis of soil.Due to continuous cropping, the soil has become severely deficient in N, such a situation has resulted in a significant decline in crop yields (Abbas et al., 2014).Moreover, this also reflected that by getting the acceptable garlic yield, the application of N at appropriate amount is required.The strong and positive effect of N nutrition has also been documented on other bulbous crop including onion (Bezabihand Girmay,2020;Piriand Naserin,2020).Other researchers including Bekeleetal., 2018 andTekesteetal., 2018 described that bulb size increased notably at optimal N supply to onion crop.

Conclusions and Suggestions
Adequate N supply enhanced the yield of garlic because performance gap between adequate N nutrition and control was markedly high.Both the varieties were sensitive to Low N supply and showed positive response to higher N nutrition.This indicates that experimental soil was severely deficient in N. The response of Purple top was better under all N conditions.Hence, for achieving higher garlic yield, variety "Purple top" may preferably be cultivated and fertilized with N at the rate of 150 kg ha -1 under Tando Jam conditions.However, the growth and yield performance of other cultivars of garlic may also be investigated by applying other nitrogen doses and sources under different agro-climatic conditions to validate the nitrogen requirements of the garlic.

Table 3 : Influence of Nitrogen rates and varieties on the Number of leaves plant -1 of garlic Nitrogen levels
-1 (8.98) than "Local white" variety with 8.05 leaves number in individual plant (Table-3).