An Attempt to Reduce Nitrogen Fertilization Levels and Their Impact on the Growth and Productivity of Garlic (Allium sativum L.) Under Different Planting Dates

Abstract

Applying nitrogen fertilizers in agriculture can cause uncontrolled gas emissions, such as N₂O and CO_2, leading to global warming and serious climate changes. In this study, we evaluated the greenhouse gas emissions (GHGs) that are concomitant with applying different rates of N fertilization, i.e., 50, 75, 100, and 125% of the recommended dose (727 kg N ha⁻¹) for two cultivars (Balady and Sids-40) of Allium sativum L. grown under three planting dates (15 September, 1 October, and 15 October). For this purpose, two field experiments were carried out during the two growing seasons of 2020/2021 and 2021/2022. Treatments were arranged in a split–split plot design with three replicates: planting dates were set up in the main plots, nitrogen levels were conducted in the submain plots, and garlic varieties were in the sub-subplots. The obtained results can be summarized as follows: Planting on 15 September significantly increased vegetative growth parameters (i.e., plant height, leaves area, number of leaves plant⁻¹, and leaves dry weight) and total bulb yield, in both seasons. The application of the highest rate of N (125%) gave significantly higher records for vegetative growth parameters, while the 75% nitrogen treatment appeared to give the highest total bulb yield in both seasons. The means of plant growth characteristics and total bulb yield were significantly increased by the cultivation of the Balady cultivar. In addition, the results show that GHGs were positively correlated with increasing the rate of N fertilization. It could be recommended that planting on 15 September and fertilizing with 75% N fertilizer from the recommended dose for Balady cultivar achieve maximum yield and its components.

1. Introduction

The growth and development of garlic (Allium sativum L.) are mainly affected by environmental conditions, such as soil, photoperiod, and temperature, as well as agricultural practices, i.e., planting date, cultivar, fertilization, and irrigation, which, among others, influence the growth, yield, and bulb quality of garlic [1].

In Egypt, garlic is one of the most important vegetable crops, ranking second in popularity after onions; it is a flowering plant of the Alliaceae family [2]. The production of global garlic stood at about 28 million tons, and the garlic area reached 1.6 million hectares [3]. Egypt ranks as the fourth leading country in the world after China, India, and South Korea for garlic production [3]. It is cultivated for both local consumption and export, and it is used in the pharmaceutical industry. Garlic has many medical values, such as antibacterial, antifungal, anticancer, lowering of blood sugar, blood lipids, and blood platelet aggregation, as well as power supplies; it is also used as an insecticidal [4,5]. So, increasing the productivity of garlic and its quality are important goals that usually depend on many factors, including planting time and nitrogen fertilization. In this regard, planting time plays an important role in the growth, yield attributes, and bulb yield of garlic [6].

In Egypt, the growth period of garlic is centered in the autumn season because it prefers mild weather. As a result, only early-planted crops can utilize the full advantages of the cool period. However, farmers cannot always adopt early planting due to climatic limitations and cropping patterns. For this reason, plants are exposed to increasingly high temperatures before the initiation of clove and during the period of growth and development [7]. So, the yield becomes low, and sometimes, a percentage of plants fail to initiate bulbs at all. Garlic growth is mostly affected by the time of planting, since a short photoperiod and low temperature encourage vegetative growth, while a long photoperiod and high temperature encourage bulb production. The date of sowing influences the garlic bulb’s growth and development. According to Murmu et al. [8], the planting period is a critical aspect that influences garlic development and output. Early garlic planting resulted in huge bulbs, which resulted in higher weight. Therefore, a study was undertaken to find the effect of planting time on the growth, development, yield, and yield attributes of two newly released garlic varieties.

Nitrogen (N) is an important element for increasing the yield and quality of vegetables such as garlic. Nitrogen availability is very important for plant growth as it is a major part of the chemical chlorophyll, which plays a significant role in the process of photosynthesis [9,10]. As the level of N increased, the growth trend of the number of leaves, leaf length, and plant dry matter increased [11]. The higher N content promotes vegetative growth and enhances high protein content while reducing anthocyanin synthesis [12]. There is a significant relationship between the application dose of N and plant growth, crop quality, and productivity. The application of N in optimum quantity is a prerequisite for obtaining a higher yield of garlic [13]. Sebnie et al. [14] have shown that a dose of N of 92 kg ha⁻¹ is essential for economic garlic yield. Reddy et al. [15] recommended an N dose of 150 kg ha⁻¹ to obtain the desired plant height, bulb size, and yield, while [16] recommended an N rate of 125 kg ha⁻¹ to obtain more cloves of garlic. Zaman et al. [17] tested various N levels on garlic and recommended a rate of 150 kg ha⁻¹ for an economically acceptable garlic yield, while [18] recommended 100 kg N ha⁻¹ to obtain more cloves of garlic. However, Diriba-Shiferaw et al. [19] noted that under extreme nitrogen deficit conditions, the N dose can be increased to up to 400 kg ha⁻¹ to obtain a quality garlic product.

Recently, Usman et al. [20] reported variations in plant vigor among six garlic genotypes tested, and Sids-40 recorded the highest plant vigor compared with the other varieties. On the other hand, it became clear from the results of another study conducted by [1] that the Balady cultivar showed significant improvement in growth and yield parameters compared with Sids-40.

The academic and applied research emphasized that lots of fertilizers are lost through leaching with drainage water, leading to environmental pollution; this phenomenon is highly remarked under the conventional methods of fertilizing. So, increasing the efficiency of fertilizer use will be very effective, which is applied through sustainable agriculture, to mitigate climate change [21]. Agricultural soil is the largest anthropogenic N₂O source, and 80% of atmospheric N₂O increase is attributed to food production [22]. The usage of nitrogen fertilizer in agriculture is still increasing [23]. At present, agricultural production is ranked second to industrial production as a source of greenhouse gasses, and it accounts for about 35% of the total emissions [24]. Soil N₂O emissions dominated by N application account for over 70% of the global emissions from agricultural production [25]. In grain cropping systems, continuous planting increases the frequency of N fertilizer inputs, and excess N residues accumulate in the soil to increase the soil N₂O emission flux [26]. Therefore, this study aims to evaluate the effect of planting time and determine the influence of nitrogenous fertilizer levels on the performance of two garlic varieties and their relationship to nitrous oxide emissions from the soil. In addition, studying their effects on benefit-to-cost ratio as primary indicators of economic profitability.

2. Materials and Methods

2.1. Site Description and Soil Type

A field experiment was conducted at a private farm in El-Horriya Village, West El-Fashn Area, Bani Swaif governorate (28°48′58″ N 30°43′25″ E), Egypt (Figure 1), during the two autumn seasons of 2020/2021 and 2021/2022 to study the effect of planting dates and different cultivars on the growth, yield, and chemical composition of garlic fertilized by different rates of N fertilizer.

Table 1. Means of climatic parameters during Allium sativum growth and development at the experimental site (2020/2021 and 2021/2022 seasons).

	Air Temperature (°C)			Solar Radiation (W m−2)	Relative Humidity (%)			Wind Speed (m s−1)
Date	Avg	Max	Min	Avg	Avg	Max	Min	Avg	Max
2020/2021
September 2020	28.5	39.9	20.8	149	51.8	90.7	12.7	2.7	5.3
October 2020	24.4	36.2	13.5	124	53.4	89.2	18.3	2.0	5.5
November 2020	19.2	30.5	10.3	86	59.1	92.2	18.3	1.0	4.8
December 2020	14.5	22.7	9.84	128	63.4	93.8	30.6	0.9	4.1
January 2021	11.6	24.9	7.91	152	54.0	95.0	13.3	0.8	3.6
February 2021	13.7	29.5	8.48	178	55.6	92.8	14.1	0.9	4.3
2021/2022
September 2021	28.7	39.5	20.9	218	51.1	85.9	20.4	1.3	4.3
October 2021	23.2	35.5	14.5	147	59.5	95.2	19.7	1.1	3.9
November 2021	20.4	35.8	10.0	124	54.3	97.5	12.2	1.0	3.8
December 2021	14.6	24.4	8.39	111	63.7	96.0	25.9	1.1	3.7
January 2022	11.7	20.1	7.25	130	54.9	88.1	26.6	0.8	3.0
February 2022	14.2	29.0	9.39	158	64.2	99.5	13.9	0.9	4.3

shows the mean meteorological elements (i.e., air temperatures, relative humidity, wind speed, and solar radiation for the 2020/2021 and 2021/2022 seasons) that were obtained from the Central Laboratory of Meteorology, Ministry of Agriculture and Land Reclamation, Egypt, for this area of study. The average air temperature ranged from 11.6 to 28.5° in the first season and from 11.7 to 28.7° in the second season. The average relative humidity was 56.2 and 57.9% for the two studied seasons, respectively. The drip irrigation system was set up with a control head (media and screen filters, pressure gauges, and control valves). The main line was a 75.0 mm diameter PVC pipe with a pressure rating of 6.0 bar, and the sub-main line was a 50.0 mm diameter PVC pipe with a pressure rating of 6.0 bar. Lateral lines were 16.0 mm diameter polyethylene tubes with built-in emitters, 30.0 cm emitter spacing, and a manufacturing emitter discharge of 4.0 L h⁻¹, at an operating pressure of 1.0 bar. The irrigation water had a pH of 7.11 and an electrical conductivity of 0.84 dS m⁻¹. The studied soil’s main physical and chemical properties were determined in situ and at the laboratory at the beginning of the field trial, before cultivation, by the standard methods outlined by [27]. The experimental soil had a sandy texture (Typic Torripsamments) with conventional tillage, 0.83% organic matter, available N (11.6 mg kg⁻¹), available P (4.91 mg kg⁻¹), available K (60.3 mg kg⁻¹), a pH of 7.81, and an EC_e of 2.82 dS m⁻¹.

2.2. Experimental Design

The experiment included three planting dates (D): 15 September (D1), 1 October (D2), and 15 October (D3), which were combined with two cultivars (V), i.e., Balady (V1) and Sids-40 (V2), of Allium sativum under four nitrogen levels, 50, 75, 100, and 125%. The recommended dose was 727 kg N ha⁻¹ by the Egyptian Ministry of Agriculture for garlic cultivation. The experimental design (Figure 2) was a split–split plot design with three replications. Planting dates were distributed in the main plot, nitrogen treatment was applied in subplots, and cultivars were allocated in sub-subplots. Each experimental plot included four ridges, 5 m in length and 70 cm in width, with an area of about 11.2 m², where three ridges were planted, and the fourth one was left without planting as a guard ridge between plots.

2.3. Planting Technique

Garlic seeds (cloves) for each cultivar were planted on 15 September, 1 October, and 15 October in the first and second seasons, respectively. Individual cloves of garlic were planted in a spacing of 30 cm × 10 cm between rows and plants, respectively, and covered lightly by soil. Regarding the two studied cultivars, the Balady cv. seems to be a local variety grown in Egypt for its intense aroma, ripe cloves with white covering scale, and relatively long storability. Sids-40 cv. is primary sourced in China; it boasts huge cloves that are easy to peel and has mature cloves with white skin and purple vertical stripes. Both cultivars were obtained from the Sids Research Station of the Agricultural Research Center (ARC) in Giza, Egypt. Regarding the soil preparation before planting, adding 48 m³ of cattle manure fertilizer, 960 kg superphosphate, and 120 kg ammonium sulfate per hectare is recommended, according to the Egyptian Ministry of Agriculture for garlic cultivation. As for nitrogen fertilization, the following treatments were applied: 50, 75, 100, and 125% of the recommended dose. Horticultural practices that were commonly applied in garlic management were followed based on the recommendations of the Ministry of Agriculture in Egypt.

2.4. Measurements

2.4.1. Vegetative Growth and Leaves Chemical Composition

A sample of three plants from each plot was collected after 135 days of planting to assess the plant height, plant leave area, number of leaves plant⁻¹, and dry leaves weight. Moreover, the collected plant leaves were sampled and separated into two groups; one was kept fresh to determine proline content according to the method of [28] modified by [29]. Total chlorophyll was measured using a chlorophyll meter SPAD-502Plus (Infitek, China). The other group was oven-dried at 70 °C for 48 h and digested by the H₂SO₄/H₂O₂ mixture according to the method described by [30]. The total nitrogen in leaves was determined using the Kjeldahl method by the Kjeldahl system (Vapodest, Germany) according to the procedure described by [30]; total phosphorus was determined by the citric acid and ammonium molybdate method using the Spectrophotometer (UV-visible-160A, Shimadzu, Kyoto, Japan) according to [31]; and total potassium in plant leaves was determined using the Flame photometer (Jenway, UK) as described by [31].

2.4.2. Yield Parameters

At the full maturity stage (190 days from the clove sowing), the bulbs were harvested with three samples of each experimental plot to determine the yield and its component characters, i.e., total yield, bulb diameter, bulb neck diameter, average clove weight, and number of cloves bulb⁻¹, in addition to the bulbing ratio, average bulb weight, fresh and dry bulb weight, and cloves dry matter percentage.

2.4.3. Biochemical Components in Bulbs

According to [32], the ascorbic acid (vitamin C) of the bulb was determined in the fresh bulbs following the 2, 6, dichlorophenol indophenol visual titration method. Total soluble solids (TSSs) in the juice extracted from ground bulbs expressed as Brix value were determined by a digital refractometer as well. The total sugars and carbohydrates in bulbs were determined as glucose after acid hydrolysis and spectrophotometrically determined using a Spectrophotometer [33]. Catalase (CAT; EC 1.11.1.6) activity was assayed according to the method of [34]. The total soluble phenol in garlic bulbs was first determined using the method described by [35]. The determination of the free amino acid composition method was used by [36].

The Kjeldahl method determined the total nitrogen content in bulbs as outlined by [30]. Then, protein content was calculated by multiplying nitrogen content by 6.25. Also, total carbohydrates in bulbs were determined as glucose after acid hydrolysis and spectrophotometrically determined [33].

2.4.4. Nitrogen Use Efficiency (NUE)

It was determined by dividing the bulb yield ha⁻¹, by the nitrogen quantity ha⁻¹, and expressed as bulb kg N kg⁻¹ according to [37].

2.4.5. Calculating Greenhouse Gas Emissions from Soil

Both nitrification and denitrification reactions produce the intermediate gaseous nitrous oxide (N₂O) through microbial activities in the soil; eventually, this gas is released into the atmosphere. The emission of N₂O from the field was estimated at the end of the experiment according to [38] and ensuring the validity of the results using this equation under the Egyptian conditions by [39,40,41]; the following equation was adopted:

N₂O emission = [1.47 + (0.01 × F)] × N₂OMW × N₂OGWP

where F: Mass of N applied from synthetic fertilizer, kg N ha⁻¹; N₂OMW: Ratio of molecular weight of N₂O to 2N, kg N₂O (kg N)⁻¹

N₂OMW = (14 × 2 + 16)/(2 × 14) = 1.57

N₂OGWP: Global Warming Potential for N₂O, kg CO_2-e (kg N₂O)⁻¹

Global Warming Potential (GWP) was calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy. Gasses with a higher GWP absorb more energy than gasses with a lower GWP and thus contribute more to global warming. The GWP value of 298 for N₂O used in the protocol (N₂OGWP) is the 100-year value used in the most recent IPCC fourth assessment report, according to [42]. The CO_2-e equivalents emission for each gas (CO₂, N₂O, and CH₄) were summed together to give total CO_2-e.

2.5. Profitability

The economic analysis was performed by calculating the cultivation cost for different agro-inputs, i.e., soil preparation, hiring, electricity, irrigation, seedlings purchase, fertilizers, pesticides, labor, and other mandatory experimental requirements. The returns of applying treatments were calculated (LE ha⁻¹) based on the local market price according to [43].

2.6. Statistical Analysis

All data collected were subjected to analysis of variance (ANOVA) to test treatment effects for significance using the Statistix 10 software package (2013). The differences among means for all traits in the two studied seasons were compared using Duncan’s multiple range test, with a 5% probability level and a standard error (SE) according to [44].

3. Results

3.1. Vegetative Growth Parameters

The data in

Table 2. (a) Vegetative measurements mean (plant height, leaves area, number of leaves plant⁻¹, and leaves dry weight) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied season of 2020/2021. (b) Vegetative measurements mean (plant height, leaves area, number of leaves plant⁻¹, and leaves dry weight) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied season of 2021/2022.

Planting Dates	N Levels	Cultivars			Cultivars			Cultivars			Cultivars
		Balady	Sids-40	Mean	Balady	Sids-40	Mean	Balady	Sids-40	Mean	Balady	Sids-40	Mean
		Plant Height (cm)			Plant Leaves Area (cm2)			No. of Leaves Plant−1			Leaves Dry Weight (g)
(a)
15 September	50%	48.12 ± 0.35 K	71.24 ± 1.19 E	59.68 ± 5.2 CDE	486.44 ± 8.33 L	535.02 ± 17.76 JK	510.73 ± 13.96 F	9.53 ± 0.03 F	7.20 ± 0.1 N	8.37 ± 0.52 GH	7.23 ± 0.06 FG	5.18 ± 0.03 M	6.20 ± 0.46 F
	75%	50.96 ± 0.36 IJK	74.58 ± 1.21 D	62.77 ± 5.31 A	524.73 ± 5.95 JKL	582.69 ± 8.1 HI	553.71 ± 13.72 A	9.70 ± 0.06 EF	7.50 ± 0 LM	8.60 ± 0.49 A	7.29 ± 0.1 FG	6.01 ± 0.17 L	6.65 ± 0.3 A
	100%	52.34 ± 0.6 IJ	77.53 ± 2.1 BCD	64.94 ± 5.72 B	524.29 ± 4.52 JKL	607.43 ± 20.62 FGH	565.86 ± 20.85 B	9.80 ± 0.15 E	7.60 ± 0.06 L	8.70 ± 0.5 B	6.9 ± 0.49 GHI	6.32 ± 0.06 KL	6.61 ± 0.26 B
	125%	58.43 ± 0.67 G	75.99 ± 1.11 BCD	67.21 ± 3.97 C	584.9 ± 7.52 HI	630.69 ± 14.06 EFG	607.79 ± 12.48 D	10.0 ± 0.1 D	8.07 ± 0.09 JK	9.03 ± 0.44 DEF	8.27 ± 0.05 D	7.29 ± 0.05 FG	7.78 ± 0.22 D
	Mean	52.46 ± 1.16 F	74.83 ± 0.94 C	63.65 ± 2.44 C	530.09 ± 11.01 D	588.96 ± 12.65 C	559.52 ± 10.24 C	9.76 ± 0.07 C	7.59 ± 0.1 F	8.68 ± 0.23 C	7.42 ± 0.19 C	6.20 ± 0.23 E	6.81 ± 0.19 C
1 October	50%	49.51 ± 0.83 JK	75.78 ± 0.24 BCD	62.65 ± 5.89 DE	501.55 ± 6.26 KL	555.95 ± 21.45 IJ	528.75 ± 15.74 EF	9.70 ± 0.06 EF	7.37 ± 0.09 MN	8.53 ± 0.52 EF	7.84 ± 0.07 DE	5.95 ± 0.02 L	6.89 ± 0.42 E
	75%	53.25 ± 0.91 HI	74.8 ± 0.92 CD	64.03 ± 4.85 E	554.34 ± 1.49 IJ	600.51 ± 11.38 FGH	577.43 ± 11.53 FG	10.03 ± 0.03 D	7.90 ± 0.06 K	8.97 ± 0.48 H	8.11 ± 0.02 D	6.47 ± 0.05 IJK	7.29 ± 0.37 F
	100%	55.78 ± 1 GH	78.1 ± 1.02 BC	66.94 ± 5.03 B	587.41 ± 12.83 GHI	655.51 ± 16.67 DE	621.46 ± 17.9 C	10.27 ± 0.07 C	8.17 ± 0.03 IJ	9.22 ± 0.47 C	8.73 ± 0.03 C	7.11 ± 0.05 GH	7.92 ± 0.36 C
	125%	63.52 ± 1.33 F	82.16 ± 0.99 A	72.84 ± 4.23 C	681.14 ± 7.12 D	767.93 ± 10.58 BC	724.53 ± 20.23 D	10.53 ± 0.07 B	9.13 ± 0.12 G	9.83 ± 0.32 D	9.81 ± 0.14 B	8.11 ± 0.03 D	8.96 ± 0.39 D
	Mean	55.51 ± 1.61 E	77.71 ± 0.93 B	66.61 ± 2.49 B	581.11 ± 20 C	644.97 ± 24.81 B	613.04 ± 16.95 B	10.13 ± 0.1 B	8.14 ± 0.2 E	9.14 ± 0.23 B	8.62 ± 0.23 B	6.91 ± 0.24 D	7.77 ± 0.24 B
15 October	50%	53.24 ± 0.73 HI	78.71 ± 0.91 B	65.97 ± 5.72 CD	538.07 ± 9.43 JK	657.01 ± 4.84 DE	597.54 ± 27.01 DE	9.80 ± 0 E	7.97 ± 0.03 K	8.88 ± 0.41 FG	8.17 ± 0.02 D	6.36 ± 0.03 JKL	7.26 ± 0.41 E
	75%	56.15 ± 0.69 GH	77.06 ± 1.06 BCD	66.6 ± 4.71 E	589.46 ± 3.64 GHI	636.72 ± 27.24 EF	613.09 ± 16.21 GH	10.07 ± 0.09 D	8.27 ± 0.09 I	9.17 ± 0.41 HI	8.75 ± 0.07 C	6.78 ± 0.05 HIJ	7.77 ± 0.44 F
	100%	57.93 ± 0.79 G	84.33 ± 1.32 A	71.13 ± 5.94 F	630.91 ± 8.78 EFG	755.5 ± 7.31 C	693.21 ± 28.32 H	10.50 ± 0.06 B	8.63 ± 0.09 H	9.57 ± 0.42 I	9.69 ± 0.03 B	7.59 ± 0.36 EF	8.64 ± 0.5 G
	125%	69.42 ± 1.48 E	63.65 ± 2.44 C	76.85 ± 3.44 CD	797.37 ± 17.68 AB	559.52 ± 10.24 C	814.28 ± 13.05 D	11.37 ± 0.09 A	8.68 ± 0.23 C	10.5 ± 0.39 DE	10.45 ± 0.11 A	6.81 ± 0.19 C	9.67 ± 0.35 D
	Mean	59.18 ± 1.9 D	71.24 ± 1.19 E	70.14 ± 2.52 A	638.95 ± 29.68 B	535.02 ± 17.76 JK	679.53 ± 20.67 A	10.43 ± 0.18 A	7.20 ± 0.1 N	9.53 ± 0.23 A	9.27 ± 0.26 A	5.18 ± 0.03 M	8.34 ± 0.28 A
		N fertilization * Cultivars			N fertilization * Cultivars			N fertilization * Cultivars			N fertilization * Cultivars
	50%	75.24 ± 1.17 B	75.24 ± 1.17 B	62.77 ± 3.11 D	582.66 ± 20.52 D	582.66 ± 20.52 D	545.67 ± 14.04 D	7.51 ± 0.12 H	7.51 ± 0.12 H	8.59 ± 0.27 D	5.83 ± 0.17 G	5.83 ± 0.17 G	6.79 ± 0.26 D
	75%	53.45 ± 0.82 E	75.48 ± 0.67 B	64.47 ± 2.72 C	556.18 ± 9.58 E	606.64 ± 11.89 C	581.41 ± 9.61 C	9.93 ± 0.07 C	7.89 ± 0.11 G	8.91 ± 0.26 C	8.05 ± 0.21 C	6.42 ± 0.13 F	7.24 ± 0.23 C
	100%	55.35 ± 0.91 D	79.99 ± 1.34 A	67.67 ± 3.09 B	580.87 ± 16.17 D	672.81 ± 23.21 B	626.84 ± 17.68 B	10.19 ± 0.11 B	8.13 ± 0.15 F	9.16 ± 0.27 B	8.44 ± 0.43 B	7.01 ± 0.21 E	7.72 ± 0.29 B
	125%	63.79 ± 1.7 C	80.81 ± 1.37 A	72.3 ± 2.32 A	687.8 ± 31.28 B	743.27 ± 30.37 A	715.54 ± 22.19 A	10.63 ± 0.2 A	8.94 ± 0.24 E	9.79 ± 0.25 A	9.51 ± 0.33 A	8.1 ± 0.23 C	8.8 ± 0.26 A
	Mean	55.72 ± 1 B	77.88 ± 0.71 A		583.38 ± 14.26 B	651.35 ± 15.07 A		10.11 ± 0.08 A	8.12 ± 0.12 B		8.44 ± 0.18 A	6.84 ± 0.17 B
(b)
15 September	50%	42.00 ± 1.25 M	65.31 ± 1.11 F	53.66 ± 5.26 DE	401.77 ± 1.12 M	487.13 ± 16.08 HIJ	444.45 ± 20.4 F	8.77 ± 0.09 IJ	7.07 ± 0.03 Q	7.92 ± 0.38 D	6.26 ± 0.03 J	4.91 ± 0.01 N	5.59 ± 0.3 E
	75%	44.38 ± 0.7 LM	67.2 ± 0.99 EF	55.79 ± 5.13 A	431.72 ± 10.24 KLM	494.66 ± 24.68 HI	463.19 ± 18.46 A	9 ± 0.06 GH	7.3 ± 0.12 OP	8.15 ± 0.38 A	6.75 ± 0.07 HI	5.38 ± 0.06 M	6.06 ± 0.31 A
	100%	45.33 ± 0.73 KL	73.19 ± 1.49 CD	59.26 ± 6.28 A	432.07 ± 6.28 KLM	543.93 ± 16.74 EFG	488 ± 26.26 B	9.53 ± 0.09 CD	7.4 ± 0.06 NOP	8.47 ± 0.48 B	7.03 ± 0.03 FGH	5.79 ± 0.03 KL	6.41 ± 0.28 B
	125%	50.65 ± 1.32 H	74.09 ± 0.97 CD	62.37 ± 5.29 B	465.39 ± 31.59 IJKL	570.6 ± 3.3 CDE	517.99 ± 27.48 E	9.4 ± 0.12 DE	7.5 ± 0.06 NO	8.45 ± 0.43 D	7.41 ± 0.44 E	6.26 ± 0.02 J	6.83 ± 0.32 D
	Mean	45.59 ± 1.05 E	69.95 ± 1.24 C	57.77 ± 2.66 B	432.74 ± 9.9 E	524.08 ± 12.71 C	478.41 ± 12.36 C	9.18 ± 0.1 C	7.32 ± 0.06 F	8.25 ± 0.2 C	6.86 ± 0.16 C	5.58 ± 0.15 F	6.22 ± 0.17 C
1 October	50%	46.18 ± 0.99 JKL	68.05 ± 0.8 EF	57.11 ± 4.92 CD	423.25 ± 3.62 LM	489.94 ± 25.9 HI	456.6 ± 18.95 E	9 ± 0 GH	7.27 ± 0.09 PQ	8.13 ± 0.39 D	6.81 ± 0.06 GH	5.05 ± 0.03 N	5.93 ± 0.39 E
	75%	47.16 ± 0.67 IJKL	72.55 ± 1.67 D	59.86 ± 5.73 F	472.4 ± 8.9 IJK	561.08 ± 18.67 DEF	516.74 ± 21.88 FG	9.17 ± 0.09 FG	7.6 ± 0.06 MN	8.38 ± 0.35 E	7.23 ± 0.1 EF	5.83 ± 0.05 K	6.53 ± 0.32 F
	100%	48.17 ± 1.26 H–K	75.43 ± 0.67 BCD	61.8 ± 6.13 B	486.39 ± 16.82 HIJ	610.09 ± 10.85 C	548.24 ± 29.07 BC	9.57 ± 0.03 CD	7.93 ± 0.03 L	8.75 ± 0.37 B	7.85 ± 0.1 D	6.49 ± 0.04 IJ	7.17 ± 0.31 B
	125%	54.64 ± 1.46 G	77.48 ± 0.53 AB	66.06 ± 5.15 BC	568.81 ± 14.05 CDE	650.27 ± 11.63 B	609.54 ± 19.96 D	9.87 ± 0.03 B	8.23 ± 0.07 K	9.05 ± 0.37 C	8.73 ± 0.03 B	7.06 ± 0.02 FG	7.89 ± 0.37 C
	Mean	49.04 ± 1.11 D	73.38 ± 1.15 B	61.21 ± 2.66 A	487.71 ± 16.59 D	577.84 ± 19.56 B	532.78 ± 15.67 B	9.4 ± 0.1 B	7.76 ± 0.11 E	8.58 ± 0.19 B	7.65 ± 0.22 B	6.11 ± 0.23 E	6.88 ± 0.22 B
15 October	50%	46.06 ± 1.21 JKL	69.39 ± 1.37 E	57.73 ± 5.28 DEF	444.52 ± 7.87 JKLM	528.84 ± 6.44 EFGH	486.68 ± 19.4 F	9.3 ± 0.06 EF	7.77 ± 0.03 LM	8.53 ± 0.34 D	7.43 ± 0.05 E	5.54 ± 0.04 LM	6.49 ± 0.42 E
	75%	49.3 ± 0.42 HIJ	76.08 ± 1.15 BC	62.69 ± 6.01 EF	501.36 ± 6.31 GHI	657.16 ± 9.97 B	579.26 ± 35.23 G	9.43 ± 0.03 DE	8.2 ± 0 K	8.82 ± 0.28 E	7.9 ± 0.05 D	6.37 ± 0.1 J	7.14 ± 0.35 F
	100%	49.98 ± 1.85 HI	76.44 ± 0.17 BC	63.21 ± 5.98 G	518.1 ± 12.87 FGH	678.72 ± 5.58 B	598.41 ± 36.46 G	9.7 ± 0 BC	8.57 ± 0.03 J	9.14 ± 0.25 F	8.33 ± 0.02 C	7.2 ± 0.03 EF	7.77 ± 0.25 G
	125%	55.73 ± 0.84 G	57.77 ± 2.66 B	67.64 ± 5.39 B	594.53 ± 6.62 CD	478.41 ± 12.36 C	658.11 ± 29.09 C	10.13 ± 0.12 A	8.25 ± 0.2 C	9.5 ± 0.29 C	9.75 ± 0.04 A	6.22 ± 0.17 C	8.62 ± 0.51 C
	Mean	50.27 ± 1.17 D	65.31 ± 1.11 F	62.81 ± 2.75 A	514.63 ± 16.59 C	487.13 ± 16.08 HIJ	580.62 ± 19.26 A	9.64 ± 0.1 A	7.07 ± 0.03 Q	9 ± 0.16 A	8.36 ± 0.26 A	4.91 ± 0.01 N	7.5 ± 0.25 A
		N fertilization * Cultivars			N fertilization * Cultivars			N fertilization * Cultivars			401.77 ± 1.12 M
	50%	67.58 ± 0.82 D	67.58 ± 0.82 D	56.17 ± 2.83 D	501.97 ± 11.23 E	501.97 ± 11.23 E	462.58 ± 11.46 D	7.37 ± 0.11 H	7.37 ± 0.11 H	8.19 ± 0.21 D	5.17 ± 0.1 G	5.17 ± 0.1 G	6.0 ± 0.22 D
	75%	46.95 ± 0.77 F	71.94 ± 1.45 C	59.44 ± 3.13 C	468.49 ± 10.98 F	570.96 ± 25.38 C	519.73 ± 18.29 C	9.2 ± 0.07 C	7.7 ± 0.14 G	8.45 ± 0.2 C	7.3 ± 0.17 C	5.86 ± 0.15 F	6.58 ± 0.21 C
	100%	47.83 ± 0.96 F	75.02 ± 0.67 B	61.42 ± 3.35 B	478.85 ± 14.09 EF	610.91 ± 20.35 B	544.88 ± 20.02 B	9.6 ± 0.04 B	7.97 ± 0.17 F	8.79 ± 0.22 B	7.74 ± 0.19 B	6.49 ± 0.2 E	7.11 ± 0.2 B
	125%	53.67 ± 0.99 E	77.04 ± 0.98 A	65.36 ± 2.91 A	542.91 ± 22.2 D	647.52 ± 22.37 A	595.21 ± 19.86 A	9.8 ± 0.12 A	8.2 ± 0.2 E	9 ± 0.22 A	8.63 ± 0.36 A	6.94 ± 0.18 D	7.78 ± 0.28 A
	Mean	48.3 ± 0.71 B	72.9 ± 0.78 A		478.36 ± 10.06 B	582.84 ± 13.4 A		9.41 ± 0.07 A	7.81 ± 0.09 B		7.62 ± 0.16 A	6.11 ± 0.14 B

Means followed by the same letter within the column are not significantly different (p < 0.05).

a for the first season and Table 2b for the second season showed the vegetative measurements mean (plant height, leaves area, number of leaves plant⁻¹, and leaves dry weight) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied seasons of 2020/2021 and 2021/2022, respectively. The results obtained showed that the planting dates significantly differentiated vegetative growth parameters. The tallest plants were obtained from planting garlic sets on 15 September, while the shortest plants were obtained from planting on 15 October in the studied first season. The results reveal that the studied vegetative growth parameters, i.e., plant height, number of leaves plant⁻¹, and leaves dry weight, increased significantly with increasing nitrogen levels of up to 125% of the nitrogen level. The Balady cultivar significantly improved in all the studied parameters compared with Sids-40.

Concerning the effect of planting date (15 September, 1 October, and 15 October), the results in (Table 2a,b) show that plant height and the number of leaves on plant(s)⁻¹ were significantly affected by planting date. Still, the effect on plant dry weight was insignificant. Generally, the highest values of plant growth parameters were recorded on the late planting date (October 15). On the other hand, the lowest values for plant growth parameters were recorded on the early planting date (September 15).

Vegetative growth parameters were increased significantly with the increase in nitrogen rates in both seasons (Table 2a,b). Expanding the application dose of nitrogen fertilizer up to 125% significantly increased plant growth, i.e., plant height and number of leaves plant⁻¹, but had an insignificant effect on dry weight plant⁻¹.

The results show that the effect of garlic cultivars on vegetative traits was significant, as it was found that the Balady cultivar showed a significant improvement in all studied variables compared with the Sids-40 cultivar, except for plant height.

Regarding the interaction between the different treatments, the results show that the best vegetative growth was achieved at the late sowing date by applying 125% N to the Balady cultivar. The interaction between the planting dates, nitrogen level, and two study cultivars had a significant effect on the vegetative growth parameters in both seasons (Table 2a,b). The interaction between planting dates on 15 September and fertilizing garlic plants with a 75% nitrogen level for the Balady cultivar gave the highest values for vegetative growth parameters in both seasons, followed by the interaction between cultivation in the first season and fertilized garlic plants with 50% of the nitrogen level of the Sids-40 cultivar.

3.2. Crop Measurements

Data in Table S1a,b for crop measurement means (neck diameter, bulb diameter, bulbing ratio, and bulb fresh and dry weights) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied seasons of 2020/2021 and 2021/2022 were found in the Supplementary Materials. Also, the data in Table S2a,b for crop measurement means (No. of cloves bulb⁻¹, total yield, chlorophyll readings, cloves dry matter, and ascorbic acid content of bulb) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied seasons of 2020/2021 and 2021/2022 were found in the Supplementary Materials. In general, the maximum total bulb yield was recorded from planting on 15 September, while the minimum values were recorded from planting on 15 October.

The total yield significantly decreased as nitrogen fertilizer rates decreased in both seasons (Table S2a,b). The lowest total bulb yield was produced from the lowest rates of nitrogen level (50%). In contrast, the highest total bulb yield was obtained from the 75% nitrogen treatments, in both seasons, and the nitrogen level of 125% did not achieve the highest productivity values.

The results show that the Balady cultivar showed a significant improvement in yield characteristics compared with the Sids-40 cultivar, where the Balady cultivar excelled in all traits except for the number of bulbs, as the Balady cultivar is characterized by a large clove size and a small number of bulbs in both seasons (Tables S1a,b and S2a,b).

The interaction between planting dates and nitrogen sources significantly affected yield and its components, as well as average bulb weight in both seasons (Tables S1a,b and S2a,b). The interaction between planting dates on 15 September and fertilizing garlic plants with a 75% N level gave the highest values of total yield, exportable, and marketable yields, as well as average bulb weight in both seasons, followed by the interaction between planting on 1 October and fertilizing garlic plants with a 100% N level. That was found in the Balady cultivar more than in the Sids-40 cultivar.

3.3. Chemical Components of Garlic Leaves and Bulb

The data in Table S3a,b for chemical measurement means (catalase activity, proline content, total soluble phenol, total sugars, and total carbohydrates) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied seasons of 2020/2021 and 2021/2022 were found in the Supplementary Materials. Also, the data in Table S4a,b for chemical measurement means (total soluble solids of bulbs, amino acids, protein, and N, P, and K contents) at different planting dates and nitrogen treatments of two Allium sativum varieties during the studied seasons of 2020/2021 and 2021/2022 were found in the Supplementary Materials. Obtained data show that planting dates on 15 September gave the highest values for the chemical components of the garlic bulb, as well as N, P, and K uptake by garlic plants. On the other hand, planting on 15 October had the lowest value in this respect.

Fertilizing garlic plants with 125% of N gave the highest values of the chemical components of the garlic bulb, in addition to N, P, and K concentrations in the leaves. The data in Tables S3a,b and S4a,b show that values of chemical components under investigation increased with increasing nitrogen levels. It may be due to the concentration effect, which increases osmotic potential inside plant cells to increase nitrogen uptake. Balady cultivar showed higher values of the studied components in plant leaves than the Sids-40 cultivar due to the genetic differences between them. Moreover, the results show that planting dates on 15 September gave the highest values for the concentrations of nitrogen, phosphorus, and potassium in the leaves, with two cultivation varieties in both seasons. On the other hand, planting on October 15 had the lowest value in this regard.

3.4. Greenhouse Gas Emission from Nitrogen Fertilization and Nitrogen Use Efficiency

The balanced greenhouse gas (GHG) emissions differed according to the different amounts of nitrogen fertilization applied (

Table 3. Greenhouse gas emissions (CO₂ equivalent) from nitrogen fertilization as affected by Allium sativum total yield ha⁻¹.

Nitrogen Level (%)	Mass of N Rate Applied	Total Yield		Total N2O Emissions	Total CO2 Equivalent Emissions	CO2 Equivalent		Nitrogen Use Efficiency
		kg ha−1				g kg−1 Yield		g kg−1 Yield
	kg ha−1	First Season	Second Season	kg ha−1	kg ha−1	First Season	Second Season	First Season	Second Season
50%	364	18.9	17.9	5.8	1720	91	96	6.35	6.69
75%	545	21.5	20.6	8.7	2580	120	125	8.39	8.74
100%	727	21.0	19.8	11.5	3440	164	174	11.44	12.14
125%	909	20.2	19.0	14.4	4300	213	227	14.88	15.82

and Figure 3). After neglecting another factor and working only with the applied nitrogen levels and the mean yield of the sowing dates and cultivars at each nitrogen level, the highest amount of total N₂O and total CO₂-eq was obvious at the highest applied nitrogen level (125%) with 14.4 and 4300 kg ha⁻¹, respectively, in addition to the carbon dioxide equivalent kg⁻¹ of crop in the first and second seasons by 213 and 227 g kg⁻¹, respectively. The highest average productivity appeared at a nitrogen level of 75% at 21.5 kg ha⁻¹ in the first season and at a nitrogen level of 75% at 20.6 kg ha⁻¹ in the second season. However, the lowest GHG emissions, total N₂O and CO₂ equivalent (kg ha⁻¹), and the CO₂ equivalent kg⁻¹ yield at the first and second seasons (g kg⁻¹ yield) were manifested at the lowest applied nitrogen level (50%) with 5.80, 1720, 91, and 96, respectively, as well as the lowest mean yield, which was also presented at the 50% nitrogen level with 18.9 and 17.9 kg ha⁻¹ at the first and second seasons, respectively [45,46]. As for nitrogen use efficiency, the treatment of 125% gave the highest nitrogen use (14.88 and 15.8) kg⁻¹ of crop for the first and second seasons, respectively, and the use of lower fertilization levels gave the lowest nitrogen use (6.35 and 6.69) kg⁻¹ of garlic crop for the first and second seasons, respectively [47]. This is also illustrated in Figure 2, where the higher the levels of nitrogen fertilization, the higher the N₂O emissions.

3.5. Profitability

Table 4. An economic analysis of Allium sativum cultivars under the effect of the studied treatments during the two studied seasons of 2020/2021 and 2021/2022.

Planting Dates	Nitrogen Levels	Cultivars	Yield	Grass Income	Total Cost	Net Income	Incremental Income	Yield	Grass Income	Total Cost	Net Income	Incremental Income
			ton ha−1	Hectare	Cost EGP	EGP ha−1	EGP ha−1	ton ha−1	Hectare	Cost EGP	EGP ha−1	EGP ha−1
			First Season					Second Season
15 September	50% N	Balady	21.60	118,800	26,400	92,400	−9996	20.21	111,144	26,400	84,744	−6696
		Sids-40	14.88	148,800	29,760	119,040	16,644	14.33	143,280	29,760	113,520	22,080
	75% N	Balady	26.21	144,144	28,200	115,944	13,548	22.90	125,928	28,200	97,728	6288
		Sids-40	17.28	172,800	31,560	141,240	38,844	16.10	161,040	31,560	129,480	38,040
	100% N	Balady	24.07	132,396	30,000	102,396	0	22.08	121,440	30,000	91,440	0
		Sids-40	16.49	164,880	33,360	131,520	29,124	14.93	149,280	33,360	115,920	24,480
	125% N	Balady	22.90	125,928	31,800	94,128	−8268	20.66	113,652	31,800	81,852	−9588
		Sids-40	15.79	157,920	35,160	122,760	20,364	14.40	144,000	35,160	108,840	17,400
1 October	50% N	Balady	22.44	123,420	26,400	97,020	−5376	20.83	114,576	26,400	88,176	−3264
		Sids-40	16.18	161,760	29,760	132,000	29,604	15.14	151,440	29,760	121,680	30,240
	75% N	Balady	21.70	119,328	28,200	91,128	−11,268	24.10	132,528	28,200	104,328	12,888
		Sids-40	18.96	189,600	31,560	158,040	55,644	17.09	170,880	31,560	139,320	47,880
	100% N	Balady	24.65	135,564	30,000	105,564	3168	23.21	127,644	30,000	97,644	6204
		Sids-40	18.10	180,960	33,360	147,600	45,204	16.44	164,400	33,360	131,040	39,600
	125% N	Balady	23.66	130,152	31,800	98,352	−4044	22.92	126,060	31,800	94,260	2820
		Sids-40	17.33	173,280	35,160	138,120	35,724	15.72	157,200	35,160	122,040	30,600
15 October	50% N	Balady	22.85	125,664	26,400	99,264	−3132	21.82	119,988	26,400	93,588	2148
		Sids-40	15.50	155,040	29,760	125,280	22,884	15.22	152,160	29,760	122,400	30,960
	75% N	Balady	26.93	148,104	28,200	119,904	17,508	25.25	138,864	28,200	110,664	19,224
		Sids-40	17.71	177,120	31,560	145,560	43,164	18.10	180,960	31,560	149,400	57,960
	100% N	Balady	24.77	136,224	30,000	106,224	3828	24.43	134,376	30,000	104,376	12,936
		Sids-40	17.76	177,600	33,360	144,240	41,844	17.62	176,160	33,360	142,800	51,360
	125% N	Balady	24.62	135,432	31,800	103,632	1236	23.04	126,720	31,800	94,920	3480
		Sids-40	19.90	198,960	35,160	163,800	61,404	18.19	181,920	35,160	146,760	55,320

Average price EGP 5500 ton⁻¹ Balady, EGP 10,000 ton⁻¹ Sids-40. The average cost for Farmyard manure is EGP 3840 ha⁻¹. The average cost for mineral fertilizer is EGP 7200 ha^−1. The average cost for seeds is EGP 5760 ha⁻¹ Balady, EGP 9120 ha⁻¹ Sids-40. The average cost for pest control is EGP 7200 ha⁻¹. The average cost for agricultural labor is EGP 3600 ha⁻¹.

shows the effect of experimental treatments on the economic return of the Allium sativum crop, where the cost of producing a hectare of the Balady variety of garlic amounted to EGP 26400 and a hectare of the Sids-40 variety amounted to EGP 29760 (1 US Dollar = EGP 15.7 in the studied two seasons at the harvesting date). The increase in nitrogen fertilization led to an increase in the cost, as it reached 125% with the level of nitrogen fertilization, costing EGP 31800 for the Balady variety and EGP 35160 for the Sids-40 variety. Compared with the other treatments, the benefits (net income) from using the different treatments were higher than from cultivating the Balady variety. Reducing nitrogen fertilization positively impacted the economic return compared with increasing fertilization levels (125% N), and delaying the planting date positively affected the economic return, as the planting date of the half of October achieved the best net income. The smallest relative increase in income was obtained by early planting and the use of high levels of nitrogen fertilization. From the above, we conclude that planting the Sids-40 variety and rationalizing the use of nitrogen fertilization led to improved garlic net income and incremental income during the late planting date compared with the other treatments.

4. Discussion

The early planting date gave the best vegetative growth, and these results are in line with those reported by [48] for onion, and by [49,50,51,52,53,54], for garlic. These results are mainly due to the low average temperature at the late transplanting date during the growth season, reflecting increases in plant growth and resulting in a good canopy able to enhance photosynthesis, hence increasing dry matter accumulation and, in turn, increasing total bulb yield ha⁻¹. These results are supported by those of [6,55].

The earliest planting gave the highest plant height, probably because the plants received a long cool period and shorter day length, which enhanced the vegetative growth of the plant before the formation of bulbs. This result is in harmony with the findings of [56]. They reported that in early planting, plants attained higher vegetative growth, which possibly led to the development of the largest bulbs. The tallest plants were obtained at the highest nitrogen rates (125%), while the shortest plants were obtained from the lowest nitrogen treatment. Similar results were obtained by [6,57].

The early planting date in September encouraged vegetation growth, and suitable temperatures during September and October gave the best growth, which is reflected in the yield. The largest bulb size from early planting contributed the highest yield. Smaller bulbs and lower yields were obtained from the late planting date, which did not revive the long cool growing period that was essential for the proper development of negative growth for garlic [2,56].

The total bulb yield, bulb diameter, and average clove weight significantly increased with 75% N fertilizer rates. These results are in accordance with those obtained by [18], who found that garlic yield was enhanced by increasing the level of nitrogen fertilization up to 480 kg N ha⁻¹ in clay loam soil, and this means that garlic yield correlated positively with N fertilization. These results may be attributed to the increase in the application of mineral fertilizers increasing plant height, and number of leaves plant⁻¹, which increased total bulb yield. These results are in agreement with those obtained by [58,59,60,61].

Nitrogen is one of the crucial nutrients for the growth and development of crops that, if not consumed in sufficient quantities, will limit plant growth [62]. On the other hand, it has been reported that excessive consumption of N in the soil has a negative effect on crop growth and production. Also, the abundance of soil N stimulates the production of new leaves from the terminal meristem of the stem and lateral buds of older leaves. It ultimately increases the yield of aerial parts [63]. Also, N is one of the main components of organic compounds, such as amino acids, proteins, and nucleic acids. Its deficiency delays phenological development in vegetative and reproductive stages. Applying the right amount of N fertilizer can significantly increase biomass, and N appears to maintain leaf surface survival; as leaf surface durability increases, the duration and rate of leaf photosynthesis also increase, allowing the plant to produce more dry matter [64].

The effect on N, P, and K uptake by bulbs and leaves may be due to these treatments increasing total dry weight plant⁻¹. These results agree with those reported by [11,56] for garlic. Nitrogen levels had a significant effect on N, P, and K uptake by bulbs and leaves and N, P, and K total uptake by plants [57,58].

The cumulative effect on N, P, and K concentration by bulb and leaf may be due to these treatments increasing total dry weight plant⁻¹. These results are consistent with those reported by [65,66] for garlic. The shortage of N decreases leaf size, which is the cause of the lower amount of light absorption and light use efficiency for plant photosynthesis that leads to decreased biological yield and vice versa [67]. Nitrogen intake should be commensurate with plant needs. Excessive use of N, due to many factors that affect its total amount in the soil, such as leaching, low N efficiency, and lack of plant use of excess N, increases N loss in the soil [68]. Therefore, proper management means providing the optimal N required by the plant to use it.

Given the effect of varieties on growth and yield, we find the Balady cultivar superior. The Balady cultivar gave higher values than Sids-40, possibly due to genetic variations [1]. On the other hand, the highest amounts of vegetative measure were revealed mostly at the fertilization levels of 100–125%, and for yield, the highest values were shown at 75% nitrogen levels. At the applied nitrogen levels of 75%, not only was the yield higher, but the GHG emissions decreased. The rate of the GHG emissions increase was higher than the rate of the nitrogen fertilization increase. This result agrees with that of [39,40,41], who reported that the increase in fertilizer application rate revealed a double increase in GHG emissions than the increase in yield. In general, as in Table 3, the increase in the nitrogen level always faced an increase in the N₂O emissions, as the emissions of N₂O positively correlated with the fertilizer N rate [69,70,71]. However, the increase in N₂O emissions caused by the applied nitrogen levels was not matched with an increase in total yield in both seasons. Still, it was compensated by an increase in nitrogen use per production unit.

Physiological mechanisms controlling N utilization in plants under different N management practices are crucial to improving N utilization efficiency, as well as reducing excess fertilizer application while maintaining acceptable yields and environmental quality [72]. Efficiency in uptake and utilization are the two components of NUE. In low N conditions, uptake efficiency is more important than utilization efficiency [73]. Nitrous oxide emissions create an adverse environmental impact in the form of nitrate, which is more mobile than any other nutrient [62,64]. Therefore, it is essential that nitrogen be used efficiently to reduce the risk of unproductive and polluting N loss in cropping systems and increase their productivity and profitability [74,75]. In a study on NUE, the authors of [76,77,78] found that the lowest NUE is obtained when the highest amount of N fertilizer is used. The highest value for NUE was observed in treatments that did not receive fertilizer or the amount of fertilizer received was low.

This study examines how planting date, nitrogen fertilizer application rate, and garlic variety affect factors such as plant growth, bulb size, chemical components, quality, and yield. Finding the earliest planting date and a moderate nitrogen application rate (75% of the recommended) led to the highest yield with lower cost and a higher return, as well as lower greenhouse gas emissions compared with higher nitrogen rate applications. This research offers valuable insights for farmers. These practices can potentially improve garlic production while reducing environmental impact [79,80,81,82].

5. Conclusions

The highlights of this study show that sowing date and cultivars are among the critical factors determining the yield and quality of garlic. The earlier sown garlic (15 September) will grow longer before bulb initiation, resulting in larger plants producing large bulbs and yield. Nitrogen fertilizer plays a vital role in plant growth and development. Nitrogen deficiency reduces plant growth and ultimately reduces yield. The GHG emissions increased with the increase in the applied N fertilizer; nevertheless, the total yield started to decrease at the 125% nitrogen level in both seasons. This demonstrates that the application of the N fertilizer will certainly increase the GHG emissions but not necessarily increase the yield. Therefore, optimal fertilization management alongside optimal planting dates and the appropriate variety will contribute to obtaining the highest yield while preserving the environment. In our study, it is recommended to plant on 15 September and fertilize with 75% N level for Balady cultivar to achieve maximum yield and its components.