Control of Gas Emissions (N₂O and CO₂) Associated with Applied Different Rates of Nitrogen and Their Influences on Growth, Productivity, and Physio-Biochemical Attributes of Green Bean Plants Grown under Different Irrigation Methods

Abstract

The use of nitrogenous fertilizers in agriculture can cause uncontrolled gas emissions, such as N₂O and CO₂, leading to global warming and serious climate change. In this study, we evaluated the greenhouse gases emissions (GHGs) that are concomitant with applied different rates of N fertilization, such as 60%, 70%, 80%, 90%, 100%, 110%, and 120% of the recommended dose in green beans grown under three irrigation systems (surface, subsurface, and drip irrigation). The obtained results showed that GHGs were positively correlated with increasing the rate of N fertilization. Meanwhile, the subsurface irrigation system followed by drip irrigation achieved the highest significant (p ≤ 0.05) values regarding the growth and pod yield attributes. Furthermore, N supplements at 90% and/or 100% of the recommended dose under the subsurface irrigation system led to the highest concentration of chlorophyll, vitamin C, total protein, and activities of antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD), and peroxidase (POX). Proline and pod fibers were decreased in parallel with increasing the N rate, while water use efficiency (WUE) was improved with increasing the rate of N supplements up to 100% or 110% of the recommended dose.

1. Introduction

Climate change has the potential to both positively and negatively affect the location, timing, and productivity of crops, livestock, and fishery systems on local, national, and global scales. It will also alter the stability of food supplies and create new food security challenges by 2050 [1]. Several studies have shown that climate change threatens agricultural productivity [2,3]. Rising concentrations of carbon dioxide (CO₂) and other greenhouse gases (GHGs) in the atmosphere are the main causes of global climate change that are associated with risks in many sectors [3]. Climate change poses a major challenge to Egyptian agriculture because of the complex role agriculture plays in rural and national social and economic systems [1].

Green beans (Phaseolus vulgaris L.) are an important consumed legume widely used as a protein source and for other nutrients in Latin America and Africa, accounting for approximately 50% and 25% of the world’s consumption in volume, respectively [4,5,6]. As reported by FAO [7], the total worldwide cultivated area of green beans is 3.96 million acres, producing 26,981,784 tons in 2019. However, as a consequence of global climate change, extreme weather conditions, in particular drought, could expose green beans to severe losses in yield that could affect more than 60% of the dry bean production worldwide [6,8,9].

In Egypt, green beans are a major cash crop that are used for both export and local markets. The cultivated area reached about 41.5 thousand acres, with a production of about 170 thousand tons in 2020 [10]. Green beans are considered an important protein source with high nutritional value for Egyptian families [11]. Approximately 3.5% of the total world output of green beans comes from Egypt [12]. The mineral nutrition of plants is still one of the most important factors that determine the final production of plants [7].

Nitrogen is an essential nutrient that you need to grow plants in large quantities, it is essential for plant growth, and its deficiency in soil is usually common. Soil mineral fertilizers in agricultural systems are important because the need for food plants degrades in the shortest possible time. Nitrogen deficiency reduces the number of branches per plant, plant height, stem diameter, pod length, on green beans, and a significant source of greenhouse gas (GHG) emissions comes from the manufacture of synthetic nitrogen (N) fertilizers consumed in crop production processes. The application of synthetic N fertilizers is recognized as the most important factor contributing to direct N₂O emissions from agricultural soils based on statistical data and the relevant literature [13].

Agriculture is the largest water consumer worldwide, where it utilizes 70% of the total renewable freshwater resources [14], and the available surface water for irrigation is expected to decrease by 14% by 2050 due to competition with domestic uses, manufacturing, and thermal electricity generation [15]. However, water resources are facing scarcity and limitations for expanding cultivation and plant production in many arid and semi-arid areas, including Egypt [16]. As a result, 52% of the global population is expected to live in areas affected by water stress [17], as a result of the effects of climate change and population growth. Egypt is seeking to increase the cultivated cash crops, including green beans, to raise the income and self-sufficiency of the local markets. An initiated strategic program for reclaiming 1.5 million acres of desert is being executed during the coming years until 2030 [18].

The last expansion of land exploitation was followed by an increase in irrigated agriculture and, therefore, freshwater withdrawals [19]. The maximization of irrigation water use efficiency will be contingent upon developing efficient water delivery systems and increasing efficiency [20,21,22]. One of the suggested strategies for optimizing irrigation scheduling is adopting modern irrigation systems, such as drip and subsurface irrigation systems in the fields, instead of traditional surface irrigation [23,24]. Drip irrigation has been promoted as the most efficient irrigation system; it can achieve water use efficiency 70% higher than flood irrigation [25]. Efficient water delivery systems can contribute towards increased crop yield and improving crop water and fertilizer efficiency [23]. In addition, improving water use efficiency (WUE) without any reduction in productivity to satisfy present and future requirements of a high population growth rate is a very important issue. This may help to reduce water consumption, reduce irrigation water losses, and increase cultivated area [26]. Therefore, increasing agricultural output in a warmer and drier climate will in part require efficient irrigation systems that minimize evaporative losses and seepage through effective scheduling of irrigation to match plant demand [27]. Environmental stresses and climate change impact agricultural production and the food supply and are the primary causes of crop losses, reducing average yields for most major crops by more than 50% [28,29].

Some farmers are prone to overapplying fertilizers in order to maximize crop yield. The N fertilizer overuse increased the nitrous oxide (N₂O) emissions, where the unabsorbed N nutrient by the crop is lost from the soil by leaching or denitrification with NO/ N₂O emission [30]. N₂O is one of the major sources of GHGs in the agriculture, which is associated mainly with the soil [31]. N₂O emission from soil is due to nitrification, denitrification, and nitrifier-denitrification [32]. The fertilizer nitrogen (N) rate is the best single indicator of increasing N₂O emissions for the agriculture [31,33]. As a result, it can optimize fertilizer use efficiency to achieve the lowest N fertilizer amount while delivering the highest crop yield.

The objectives of this study were as follows: (1) to monitor greenhouse gas emissions with different doses of nitrogen fertilization and irrigation systems; (2) to assess the effectiveness of optimal fertilization and irrigation practices in reducing greenhouse gas emissions, while maintaining green bean productivity; and (3) to make recommendations and discuss the implications of reducing nitrogen fertilizer doses under various irrigation systems.

2. Materials and Methods

2.1. Experimental Site, Cultivar. and Cultivation

The experiment was carried out during two successive seasons of 2019 and 2020 at the experimental farm of the Faculty of Agriculture, Ain Shams University, at Imam Mllik village, Kom Hamada, El–Beheira governorate, Egypt (latitude 30°30′36.5″ N and longitude 30°18′34.3″ E), to investigate the effect of nitrogen fertilizer levels on vegetative growth, seed yield, and quality of green beans (Phaseolus vulgaris L.) under different irrigation systems. The irrigation water had a pH of 7.08 and an electrical conductivity of 0.75 dS/m⁻¹. The main physical and chemical properties of the studied soil were determined in situ and in the laboratory at the beginning of the field trial, before cultivation, by the standard methods outlined by [34,35]. The experimental soil had a sandy texture, 1.04% organic matter, a pH of 7.72, and an ECe of 2.54 dSm⁻¹.

Table 1. Means of climatic parameters and reference evapotranspiration (ET_o) during green bean growth and development at experimental site (during 2019 and 2020 season).

Weeks *	Temperatures (°C) RH **						SRAD ***		Wind Speed		ETo
	Max		Min		(%)		(MJ/m2/day)		(m/s)		(mm day−1)
	2019	2020	2019	2020	2019	2020	2019	2020	2019	2020	2019	2020
1	30.9	28.8	8.40	9.10	56.8	57.0	21.6	22.8	2.97	2.94	3.12	3.36
2	34.4	34.2	10.1	10.1	56.7	52.6	18.0	22.5	2.43	2.42	2.56	3.75
3	38.4	37.3	11.8	11.0	56.2	58.3	24.3	24.7	2.70	2.52	2.76	4.18
4	36.4	37.1	12.0	12.7	52.2	52.4	24.9	25.3	2.79	2.79	2.95	3.96
5	34.4	36.9	17.7	14.4	49.3	48.7	25.0	25.2	2.79	2.96	3.04	3.75
6	34.6	36.0	18.2	16.2	37.8	51.6	25.3	25.7	2.97	2.46	2.86	3.76
7	35.3	34.6	20.1	18.1	48.3	52.9	25.5	25.9	2.52	2.81	2.81	3.84
8	34.9	35.4	19.2	19.0	48.4	55.1	25.9	26.3	2.70	2.87	2.94	3.79
9	34.6	36.7	20.3	19.8	51.2	57.6	23.9	24.1	2.79	2.58	2.84	3.76
10	33.2	36.1	18.7	20.0	53.6	56.8	24.1	24.4	2.43	2.29	2.49	3.61
11	31.9	36.3	17.3	20.3	56.3	54.3	21.6	22.0	3.06	2.07	2.71	3.47
12	31.5	34.8	17.0	17.8	55.6	56.7	21.2	21.8	2.38	2.61	2.63	3.42
13	31.0	34.0	15.7	16.6	52.5	61.0	20.7	20.6	1.89	2.27	2.19	3.38
14	29.1	29.0	14.3	12.3	51.3	60.6	21.6	21.4	2.88	2.79	2.99	3.16
15	27.3	24.3	10.6	9.80	52.2	60.0	15.7	19.2	2.70	2.13	2.55	2.97
16	22.0	22.4	9.10	8.30	62.1	56.7	11.2	13.9	2.91	2.19	2.69	2.40

Note: * Cultivation date started on 15 and 21 February during the two growing season, respectively, and the experiment ended at the middle of June. ** RH means relative humidity, *** SRAD means solar radiation (MJ/m²/day), ET_o = evapotranspiration (mm/day).

shows the weekly mean weather factors (i.e., maximum and minimum air temperatures, relative humidity, wind speed, and solar radiation for the 2019 and 2020 seasons) that were obtained from the Central Laboratory of Meteorology, Ministry of Agriculture and Land Reclamation, Egypt, for this area of study.

Seeds of the “Bronco” green bean cultivar were sown on 15 February 2019 and 21 February 2020, for the first and second seasons, respectively. All other agricultural practices of cultivation were performed as recommended by the Ministry of Agriculture, Egypt [36]. Ordinary superphosphate (15.5% P₂O₅) at 300 kg/acre was banded on rows at two times; the first (200 kg) was added during the soil preparation and the second one (100 kg) was carried out during the flowering period. Ammonium nitrate (33% N) at 250 kg/acre (control treatment, recommended dose) and potassium sulphate (48% K₂O) at a rate of 100 kg/acre were applied after three weeks from sowing with the first irrigation and as well as after one month from the first addition. Chemical fertilizers were injected within the irrigation water system (fertigation).

2.2. Experimental Design

The treatments comprised three irrigation systems (subsurface irrigation, drip irrigation, and surface irrigation) and seven nitrogen levels (60%, 70%, 80%, 90%, 100%, 110%, and 120%), with the 100% nitrogen fertilizer dose as a recommended dose (85 N kg/acre). The experimental design was a split plot with three replications, with irrigation systems in the main plots and nitrogen fertilizer levels assigned to subplots. The area of the experimental plot was 14 m² (3.5 m × 4 m) and consisted of five rows, and each row was 4 m length and 0.7 m width. The plant distance was 0.3 m apart on one side, and an alley (3 m wide) was left as boarder between each two irrigation treatments (Figure 1). The total number of experimental plots was 63 (3 irrigation treatments × 7 nitrogen fertilizer treatments × 3 replications).

2.3. Irrigation Systems

2.3.1. Drip Irrigation

Manifold lines were 32 mm in diameter, and a polyethylene (P.E.) pipe was used to supply laterals (drip lines) with the irrigation water. Drip tubing (type GR, 16 mm diameter), with in-built emitters at 0.3 cm spacing, was used (delivering 4 L per hour); the long of the drip line was 30 m, one drip line was placed on each row, 2 bar pressure was maintained at drip tubing, the water source used was a river, and the water was transferred by the control station of the farm. The experimental plot had a flowmeter as shown in the Figure 1.

2.3.2. Subsurface Drip Irrigation

Before the green bean seed was sown, a subsurface trickle irrigation system was installed between the rows at 15 cm depth. The same type and specifications of drip tubing were used as in the drip irrigation system.

2.3.3. Surface Irrigation

The surface irrigation system is done by distributing water through small Mesqa and smaller order ditches called Marwa (control treatment); it is the most common irrigation system in Egyptian agriculture.

2.4. Estimation of Water Requirements

The crop evapotranspiration, ET_c, was calculated by multiplying the reference crop evapotranspiration (ET_o) by a crop coefficient (K_c) according to [37]:

ETc = Kc × ETo…… mm/day

where:

• ET_c is the crop evapotranspiration (mm d⁻¹);
• K_c is the crop coefficient (dimensionless);
• ET_o is the reference crop evapotranspiration (mm d⁻¹).

The irrigation requirements (IR) for each treatment were calculated as follows:

IR = ETc × (LR) × 4.2/Ea…… (m³/4200 m²/day)

where:

• LR% = leaching requirement percentage;
• Ea = the irrigation system’s efficiency.

(The value in the subsurface irrigation system was 95%, the drip irrigation system was 85%, and the surface irrigation system was 55%). The irrigation water quantities for green beans at the experiment site throughout the two growing seasons are mentioned in

Table 2. Calculated irrigation water amounts (m³/acre⁻¹) based on irrigation systems of green bean.

	Subsurface Irrigation		Drip Irrigation		Surface Irrigation
Year	2019	2020	2019	2020	2019	2020
Irrigation water amounts (m3/acre−1)	1996	2022	2231	2260	3447	3493

. Irrigation was carried out every 8 days in the drip irrigation and subsurface irrigation system, and 20 days in the case of surface irrigation, according to the weather conditions in the study area.

2.5. Vegetative Growth Parameters and Chlorophyll Content

Samples of 10 plants of each experimental plot were taken to determine growth parameters after 65 days from the planting date as follows: plant height (cm), number of leaves per plant, total leaves area (cm²), leaf fresh weight (g/plant), and leaf dry weight (g). Leaf chlorophyll reading (SPAD) was determined using chlorophyll meter (SPAD 502, Osaka, Japan), which estimates the SPAD value according to the method of [38].

2.6. Proline Content and Plant Enzymes

The collected plant leaves were sampled, separated into two groups, and one was kept fresh to determine proline content according to the method of [39], modified by [40]. The other plant leaves group was oven dried at 70 °C for 48 h, then digested by an H₂SO₄/H₂O₂ mixture according to the method described by [41]. Peroxidase (POX, EC 1.11.1.7) activity was assayed using the method of [42]. Super oxide dismutase (SOD; EC 1.12.1.1) activity was measured according to the method of [43]. Catalase (CAT; EC 1.11.1.6) activity was assayed according to the method of [44]. The enzyme activities were measured by using the Spekol spectrocolorimeter (Carl Zeiss AG; Jena, Germany).

2.7. Fruit Yield and Its Quality

The green pods were harvested at three weekly dates, starting 60 days after sowing. A sample of 10 plants from each plot was collected to assess the pod number per plant, total yield marketable yield, pod length, and pod thickness. These were determined using random representative samples. Representative green pod samples (three plants from each plot) from each plot were selected for chemical analysis to determine crude protein in the green pods: the pod total N was determined, and a factor of 6.25 was used for conversion of total N to protein percentage according to [45]. A random sample of pods was taken from the second harvest from each plot and used to determine total soluble solids by Carle Zeis Refract meter. Fiber in pods was determined according to [46]. Vitamin C was determined in fruit tissues blended in 10 mL of 3% oxalic acid solution; then, 10 mL of blended fruit juice was titrated against 2, 6 dichloro-phenol indophenol, [47] as well as fiber (total dietary fiber), according to [48].

2.8. Water Use Efficiency (WUE)

WUE was calculated according to [49] as follows; the ratio of crop yield (y) to the total amount of irrigation water used in the field during full season (IR):

WUE (kg/m³) = Y (kg)/IR (m³)

2.9. Measuring Greenhouse Gas Emissions from Soil

Both reactions of nitrification and denitrification produce the intermediate gaseous nitrous oxide (N₂O) through microbial activities in the soil and eventually this gas is released to the atmosphere. The emission of N₂O from field was estimated according to [31]; 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) has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more energy than gases with a lower GWP, and thus contribute more to global warming. The GWP value of 298 for N₂O used in the protocol (N₂O_GWP) is the 100-year value used in the most recent IPCC fourth assessment report according to [50]. The CO_2-e equivalent emissions for each gas (CO₂, N₂O, and CH₄) were summed together to give total CO_2-e.

2.10. Statistical Analysis

Data were subjected to an analysis of variance (ANOVA) for a factorial design, after testing for the homogeneity of error variances according to the procedure outlined by [51]. Statistically significant differences between means were compared at p < 0.05 using Duncan’s multiple range test.

3. Results

3.1. Vegetative Growth under Irrigation and Fertilization

The vegetative measurements showed significant higher values at the subsurface irrigation system (

Table 3. Vegetative measurements’ means at different irrigation systems and nitrogen treatments during the studied seasons of 2019 and 2020.

	1st Season								2nd Season
Irrigation System	Nitrogen Level (%)
	60	70	80	90	100	110	120	Mean	60	70	80	90	100	110	120	Mean
	Plant Height (cm)
Surface (control)	54.2 k	44.4 m	61.01 hi	57.8 j	68.4 ab	61.7 ghi	61.9 f–i	58.5 C	46.6 jk	50.3 hi	52.2 gh	46.0 k	55.9 e	55.5 ef	52.2 gh	51.3 C
Drip	49.0 l	59.7 ij	62.4 efgh	68.5 abc	62.7 e–h	64.2 e–g	65.7 bcd	61.6 B	63.2 bc	45.4 k	52.8 fgh	45.2 k	53.1 e–h	64.9 bc	55.1 efg	54.2 B
Subsurface	64.6 def	65.2 cde	66.8 bcd	70.8 a	68.4 ab	61.5 ghi	51.0 l	64.1 A	62.1 c	62.4 c	63.9 bc	67.7 a	65.4 ab	58.9 d	48.9 ij	61.3 A
Mean	56.0 D	56.2 D	63.4 B	65.6 A	66.5 A	62.5 B	59.5 C		57.3 BC	52.7 D	56.3 C	53.0 D	58.1 B	59.8 B	52.1 D
	Leaf Number/Plant
Surface (control)	16.3 g	17.2 efg	18.6 b–e	18.1 c–f	18.5 b–f	17.1 fg	18.8 b–d	17.8 C	16.9 d	17.7 cd	17.9 a–d	17.6 cd	16.9 d	18.4 a–d	18.4 a–d	17.7 B
Drip	18.5 b–f	19.0 a–d	18.4 b–f	19.6 a–c	19.1 a–d	17.9 def	19.7 ab	18.9 B	18.8 abc	18.4 a–d	18.5 a–d	18.0 a–d	18.5 a–d	19.5 ab	16.9 d	18.4 A
Subsurface	19.2 a–d	19.8 ab	18.6 b–e	20.4 a	20.5 a	19.8 ab	19.2 a–d	19.6 A	18.3 a–d	19.0 abc	17.8 bcd	19.5 ab	19.6 a	18.9 abc	18.4 a–d	18.8 A
Mean	18.0 B	18.7 AB	18.6 AB	19.3 A	19.3 A	18.3 B	19.2 A		18.0 AB	18.3 AB	18.1 AB	18.4 AB	18.3 AB	19.0 A	17.9 B
	Total Leaves Area (cm2)
Surface (control)	119 l	125 k	141 i	120 l	133 j	141 i	153 g	133 C	116 i	119 i	137 g	117 i	129 h	140 fg	143 f	129 C
Drip	143 i	141 i	155 g	185 b	161 f	172 d	155 g	159 B	132 h	138 g	140 fg	154 d	147 e	170 b	156 d	148 B
Subsurface	161 f	168 e	179 c	192 a	161 f	146 h	149 h	165 A	154 d	160 c	171 b	184 a	154 d	140 fg	142 f	158 A
Mean	141 E	144 D	158 B	166 A	152 C	153 C	152 C		134 F	139 E	149 B	152 A	143 D	150 AB	147 C
	Leaf Fresh Weight (g/plant)
Surface (control)	41.5 lm	43.3 j-l	45.7 ij	38.9 m	39.0 m	41.8 k-m	44.3 i-l	42.0 C	24.3 j	33.8 hi	32.5 hi	30.3 ij	32.8 hi	36.7 ghi	46.7 cde	33.9 C
Drip	44.5 i-k	51.0 h	51.5 gh	60.6 ab	52.0 gh	56.4 cde	55.4 def	53.1 B	39.2 fgh	41.9 efg	38.6 fgh	43.5 efg	51.0 bc	37.0 ghi	52.5 bc	43.4 B
Subsurface	53.6 e-h	54.1 efg	58.7 bc	63.0 a	57.6 cd	53.0 fgh	46.3 i	55.2 A	51.3 bc	51.7 bc	56.2 ab	60.3 a	55.1 ab	50.7 bcd	44.3 def	52.8 A
Mean	46.5 E	49.4 CD	52.0 B	54.1 A	49.5 CD	50.4 C	48.7 D		38.3 C	42.5 B	42.4 B	44.7 AB	46.3 A	41.5 BC	47.8 A
	Leaf Dry Weight (g/plant)
Surface (control)	4.41 g	4.15 g	7.79 f	6.20 f	6.67 f	4.08 g	6.47 f	5.71 A	3.47 f	4.38 f	4.46 f	4.84 f	4.55 f	4.40 f	6.97 e	4.72 C
Drip	10.4 e	15.8 c	13.1 d	16.5 bc	13.0 d	13.0 d	17.8 ab	14.2 A	6.51 e	6.77 e	9.89 d	6.59 e	7.57 e	10.32 d	10.49 d	8.31 B
Subsurface	13.6 d	13.5 d	13.5 d	17.1 abc	18.5 a	16.4 bc	10.9 e	14.8 A	13.0 c	13.0 c	13.0 c	16.4 ab	17.7 a	15.7 b	10.4 d	14.2 A
Mean	9.48 C	11.5 B	11.5 B	13.3 A	12.7 A	11.2 B	11.7 B		7.67 C	8.03 C	9.10 B	9.27 AB	9.93 AB	10.15 A	9.28 AB

Note: Means followed by the same letter within column are not significantly different (p < 0.05)—capital letters indicate the significances for means; small letters indicate the significances for interactions.

) for all the applied nitrogen levels, where the plant height for the subsurface, drip, and surface irrigation reached 64.06, 61.59, and 58.48 cm, respectively, in the first season, and 61.30, 54.24, and 51.27 cm, respectively, in the second season. The leaf number/plant also revealed the highest value by the subsurface irrigation with 19.62 leaves, followed by the drip irrigation with 18.87 leaves, and the surface irrigation with 17.82 leaves in the first season, and in the second season, the leaf number/plant were 18.78, 18.37, and 17.69 leaves for the subsurface, drip, and surface irrigation, respectively.

The total number of leaves followed the same behavior as leaf number/plant, where in the first season the total number of leaves was 165.05, 158.70, and 133.02 for the subsurface, drip, and surface irrigation, respectively, and 157.95, 148.05, and 128.88, respectively, in the second season. As well, for the fresh and dry weight of leaves, the higher values were exhibited by the subsurface irrigation that gave 55.18 and 14.79 g/plant, respectively, in the first season, and 52.80 and 14.16 g/plant, respectively, in the second season. While the drip irrigation displayed 53.06 leaf fresh weight (g/plant) and 14.22 leaf dry weight (g/plant) in the first season, and 43.39 and 8.31 g/plant, respectively, in the second season. The lower values of the fresh and dry leaf weight were significantly affected by the surface irrigation, with 42.04 and 5.68 g/plant, respectively, in the first season, and 33.86 and 4.72 g/plant, respectively, in the second season. Regarding the applied nitrogen levels, the measured values demonstrated varied behavior at the applied nitrogen levels for each irrigation system and each measurement.

The plant height measurement manifested a higher value by the subsurface irrigation at the nitrogen level of 90% for the first and second seasons, with values of 70.77 and 67.73 cm, respectively. The highest value was also by 90% nitrogen level at the first season with a value of 68.05 cm and by 110% nitrogen level at the second season with a value of 64.87 cm at drip irrigation. Whereas the highest values for the surface irrigation were presented by the nitrogen level at 100% in the first and second seasons, with values of 68.38 and 55.85 cm, respectively. Eventually, the highest value of the plant height for the three applied irrigation systems was manifested by the nitrogen level at 100% with a value of 66.46 cm in the first season and by the nitrogen level at 110% with a value of 59.76 cm in the second season. As well, the mean higher value of the leaf number per plant for all the applied irrigation systems exhibited 19.34 and 19.33 for the 90% and 100% nitrogen levels, respectively, in the first season, and 18.95 for the 110% nitrogen level in the second season. The drip and surface irrigation showed the highest number of leaves per plant at the highest nitrogen level (120%) with values of 19.68 and 18.82, respectively, and at the subsurface irrigation system, the standard nitrogen level (100%) presented the highest value with 20.46 in the first season. While in the second season, the subsurface, drip, and surface irrigation systems exhibited their highest values at the nitrogen levels of 90%, 100%, and 110%, with values of 19.58, 19.53, and 18.44, respectively. In the first season, the highest total areas of leaves were dominantly revealed at the nitrogen level of 90% for the drip, subsurface, and the mean of the applied irrigation systems, with values of 184.91, 192.30, and 165.95 cm², respectively, while only the surface irrigation showed its highest value at 120% nitrogen level with 152.67 cm². In the second season, the highest areas were exhibited by 110%, 120%, and 90% nitrogen levels for the drip, surface, and subsurface irrigation systems, with values of 169.69, 143.44, and 184.04 cm², respectively, and 151.65 cm² at the nitrogen level of 90% for the mean irrigation systems.

The highest values for the mean irrigation systems for the leaves’ fresh and dry weight were demonstrated at the 90% nitrogen level with 54.14 and 13.26 g/plant, respectively, whereas for the drip irrigation the highest values were displayed at 60.58 and 17.76 g/plant at the 90% and 120% nitrogen levels, respectively. For the surface irrigation the highest values were displayed at 45.70 and 7.79 g/plant at the 80% nitrogen level for both, respectively, and for the subsurface irrigation the highest values were revealed at 63 and 18.47 g/plant at the 90% and 100% nitrogen levels, respectively. In the second season, the results showed the highest values of the leaf fresh weight with the highest applied nitrogen level, with values of 52.53, 46.66, and 47.84 g/plant for drip, surface, and mean irrigation systems, respectively, but the subsurface irrigation system exhibited its highest leaf fresh weight at the 90% nitrogen level with a value of 60.29 g/plant.

The leaf dry weight also manifested its highest value for the drip and surface irrigation systems as the leaves’ fresh weight at the highest applied nitrogen level, with values of 10.49 and 6.97 g/plant, respectively, and at the standard nitrogen level for the subsurface irrigation system, with a value of 17.68 g/plant. The mean value of the applied irrigation system was the highest at 110% nitrogen level with 10.15 g/plant. Eventually, the dominant irrigation system with the highest values for the vegetative measurements was the subsurface irrigation system in the first and second seasons, whereas the 90% nitrogen level showed up the highest at most of the measurements in the first season and the 110% nitrogen level in the second season.

3.2. Crop Yield under Irrigation and Fertilization

The crop measurements as presented in

Table 4. Crop measurements’ means at different irrigation systems and nitrogen treatments in seasons 2019 and 2020.

	1st Season								2nd Season
Irrigation System	Nitrogen Level (%)
	60	70	80	90	100	110	120	Mean	60	70	80	90	100	110	120	Mean
	Pod Length (cm)
Surface (control)	11.5 ef	12.4 a–f	12.1 b–f	11.5 def	12.4 a–f	12.7 a–e	12.6 a–f	12.1 B	13.0 a	11.3 d	11.9 a–d	11.6 bcd	11.9 a–d	11.5 bcd	13.0 a	12.0 A
Drip	11.6 def	11.4 f	11.9 b–f	12.6 a–f	12.5 a–f	12.7 a–d	12.7 a–d	12.2 B	11.3 cd	12.9 a	12.6 a–d	12.5 abc	12.2 a–d	12.3 abc	13.0 a	12.4 A
Subsurface	12.4 a-f	13.0 abc	13.3 a	13.1 ab	13.2 a	11.8 c-f	12.1 a–f	12.7 A	11.9 a–d	12.4 a–d	12.7 ab	12.5 abc	12.7 ab	11.3 cd	11.6 bcd	12.2 A
Mean	11.8 B	12.2 AB	12.4 AB	12.4 AB	12.7 A	12.4 AB	12.5 AB		12.1 AB	12.2 AB	12.3 AB	12.2 AB	12.3 AB	11.8 B	12.5 A
	Pods Fresh Weight (g)
Surface (control)	3.53 cd	3.61 cd	3.61 cd	3.32 d	3.81 bc	3.43 cd	3.32 d	3.52 C	4.13 b–e	3.75 e–f	3.63 fgh	3.74 e–f	3.55 fgh	3.34 h	3.47 gh	3.66 C
Drip	4.41 a	4.19 ab	4.37 a	3.55 cd	3.44 cd	3.57 cd	3.66 cd	3.88 B	4.14 b–e	4.94 a	4.83 a	4.43 b	4.28 bcd	3.92 d–g	3.95 d–g	4.35 A
Subsurface	4.54 a	3.58 cd	3.71 cd	3.69 cd	3.81 bc	4.36 a	4.58 a	4.04 A	4.35 bcd	3.42 h	3.55 fgh	3.53 fgh	3.64 fgh	4.17 b–e	4.39 bc	3.86 B
Mean	4.16 A	3.79 B	3.90 B	3.52 C	3.69 BC	3.78 B	3.85 B		4.20 A	4.04 AB	4.00 AB	3.90 B	3.83 B	3.81 B	3.93 B
	Pods Thickness (mm)
Surface (control)	2.11 d	2.14 bcd	2.12 d	2.15 bcd	2.15 bcd	2.12 cd	2.15 bcd	2.13 B	2.12 b	2.13 b	2.12 b	2.13 b	2.16 b	2.11 b	2.16 b	2.14 B
Drip	2.10 d	2.21 bcd	2.15 bcd	2.18 bcd	2.32 ab	2.17 bcd	2.15 bcd	2.18 B	2.11 b	2.17 b	2.10 b	2.16 b	2.15 b	2.19 b	2.11 b	2.14 AB
Subsurface	2.24 bcd	2.42 a	2.26 a–d	2.27 a–d	2.24 bcd	2.30 abc	2.18 bcd	2.27 A	2.14 b	2.31 a	2.17 b	2.17 b	2.14 b	2.20 ab	2.11 b	2.18 A
Mean	2.15 B	2.25 A	2.17 AB	2.20 AB	2.24 AB	2.20 AB	2.16 AB		2.12 B	2.20 A	2.12 B	2.15 AB	2.15 AB	2.17 AB	2.09 B
	Pod Number/Plant
Surface (control)	10.9 g	13.0 f	13.7 ef	13.4 ef	14.7 de	15.6 cd	18.6 b	14.3 C	9.73 k	12.0 hij	12.7 ghi	10.7 jk	12.3 hi	13.0 fgh	14.4 ef	12.1 C
Drip	13.0 f	14.4 def	15.0 de	20.2 ab	16.0 cd	19.2 b	18.7 b	16.6 B	10.5 jk	11.7 hij	11.4 ij	13.0 fgh	14.2 efg	16.4 c	15.5 cde	13.2 B
Subsurface	15.5 cd	16.6 c	19.9 ab	21.0 a	19.5 ab	15.0 de	13.5 ef	17.3 A	14.9 de	15.9 cd	19.1 ab	20.1 a	18.6 b	14.3 ef	12.9 fgh	16.5 A
Mean	13.1 D	14.7 C	16.2 B	18.2 A	16.7 B	16.6 B	16.9 B		11.7 C	13.2 B	14.4 A	14.6 A	15.0 A	14.6 A	14.2 A
	Yield/Plant (g)
Surface (control)	44.5 l	45.1 l	45.0 l	49.4 k	50.2 k	55.5 ij	58.7 hi	49.9 C	38.9 i	41.2 i	44.2 h	40.3 i	45.2 h	45.5 h	49.5 g	43.5 C
Drip	53.8 j	61.1 gh	60.9 gh	71.3 abc	64.3 fg	70.4 bcd	66.4 ef	64.0 B	49.5 g	56.3 e	57.3 de	59.0 cde	59.0 cde	65.6 b	60.0 cd	58.1 B
Subsurface	63.47 fg	66.8 def	73.2 ab	74.2 a	69.1cde	63.5 fg	56.0 ij	66.6 A	60.7 c	64.0 b	70.0 a	71.0 a	66.1 b	60.8 c	53.6 f	63.7 A
Mean	53.9 E	57.7 D	59.7 C	65.0 A	61.2 BC	63.1 AB	60.4 C		49.7 C	53.9 B	57.2 A	56.8 A	56.8 A	57.3 A	54.4 B
	Total Yield (ton/acre *)
Surface (control)	3.20 f	3.29 ef	3.74 def	3.71 def	3.77 def	3.92 cde	3.94 cde	3.65 B	2.46 e	2.73 e	2.96 de	2.95 de	3.46 cd	3.51 cd	3.53 cd	3.08 C
Drip	3.89 cde	4.56 abc	4.51 abc	4.58 abc	4.63 ab	4.85 a	4.74 ab	4.54 A	3.45 cd	3.91 bc	3.86 bc	4.16 abc	4.39 ab	4.31 ab	4.20 abc	4.04 B
Subsurface	4.69 ab	4.82 a	5.04 a	4.76 ab	4.93 a	4.74 ab	4.05 bcd	4.72 A	4.49 ab	4.61 ab	4.83 a	4.56 ab	4.72 a	4.54 ab	3.87 bc	4.52 A
Mean	3.93 B	4.22 AB	4.43 A	4.35 A	4.45 A	4.50 A	4.24 AB		3.47 C	3.75 BC	3.88 AB	3.89 AB	4.19 A	4.12 AB	3.87 AB
	Early Yield (ton/acre *)
Surface (control)	2.84 hi	2.36 i	2.93 gh	2.96 gh	2.97 gh	3.47 fg	3.69 ef	3.03 B	1.95 h	2.22 gh	2.58 fg	2.51 fg	2.75 ef	2.54 fg	3.06 de	2.51 C
Drip	3.52 efg	3.79 def	3.49 efd	4.65 ab	3.94 c–f	4.46 abc	4.36 a–d	4.03 A	2.69 efg	3.50 cd	3.56 c	3.71 c	3.78 c	3.96 bc	3.89 bc	3.58 B
Subsurface	3.63 ef	4.09 b–e	4.64 ab	4.83 a	4.54 ab	3.95 c–f	3.66 ef	4.19 A	3.47 cd	3.92 bc	4.44 a	4.63 a	4.34 ab	3.77 c	3.50 cd	4.01 A
Mean	3.33 D	3.42 CD	3.68 BC	4.15 A	3.81 B	3.96 AB	3.90 AB		2.70 C	3.21 B	3.53 A	3.61 A	3.62 A	3.42 AB	3.48 A

Note: Means followed by the same letter within column are not significantly different (p < 0.05)—capital letters indicate the significances for means; small letters indicate the significances for interactions. * acre = 4200 m² and hectare = 2.4 acre.

include the pod and yield measurements. The highest values for the mean applied nitrogen levels were also demonstrated significantly by the subsurface irrigation system, where the highest means revealed 66.58 g, 4.19 ton/acre and 4.72 ton/acre, 17.28, 12.69 cm, 4.04 g, and 2.27 mm for the yield/plant, early and total yield, pod number/plant, pod length, pod fresh weight, and pod thickness, respectively at the first season, and 63.72 g, 4.01 ton/acre and 4.52 ton/acre, 16.54, and 2.18 mm for the yield/plant, early and total yield, pod number/plant, and pod thickness, respectively at the second season, except for the pod length and pod fresh weight, where the drip irrigation system had the mean highest values with 12.4 cm and 4.35 g, respectively. On the other hand, the mean irrigation systems values varied through the applied nitrogen levels for each season and measurement, where at the first season the 90% nitrogen level showed the highest values the yield/plant, early yield, and pod number/plant with values 64.96 g, 4.15 ton/acre, and 18.17, respectively, whereas pod length exhibited its highest value at the standard nitrogen level with values 12.7 cm.

The excess nitrogen level of 110% resulted in a high total yield of 4.5 ton/acre, while the low nitrogen levels of 60% and 70% resulted in high pod fresh weight and thickness values of 4.16 g and 2.25 mm, respectively. For the second season, the standard nitrogen level showed high values of pod number/plant and early and total yield, with values of 15.03 and 3.62 ton/acre and 4.19 ton/acre, respectively. While excess nitrogen levels of 110% and 120% revealed high yield/plant and pod length values of 57.29 g and 12.5 cm, respectively, low nitrogen levels of 60% and 70% revealed high pod fresh weight and thickness values of 4.2 g and 2.2 mm, respectively.

Individual element behavior displayed insignificantly high records at times, such as during the first season for pod length by drip irrigation at 110% and 120% nitrogen levels, with 12.74 and 12.73 cm, respectively, and pod thickness by surface irrigation at 90%, 100%, and 120% nitrogen levels, with 2.15 and 2.14 mm, respectively. Moreover, the early yield by surface irrigation showed high values at 90% and 100% nitrogen levels, with 2.96 and 2.97 ton/acre, respectively.

The insignificance was also evident in the second season, for example, in pod length, where the highest values were presented at the lowest and highest nitrogen levels, with 13 and 12.99 cm, respectively, for surface irrigation, and at 80% and 100% nitrogen levels, with 12.68 and 12.67 cm, respectively, for subsurface irrigation. The pod thickness was also demonstrated by surface irrigation at 2.16 mm at 100% and 120% nitrogen levels. Moreover, the mean of the applied irrigation systems of the early yield displayed higher values at the nitrogen levels of 90% and 100%, with 3.62 and 3.62 ton/acre, respectively. The surface irrigation system revealed the lowest value with the mean nitrogen level as determined by vegetative measurements, as well as the highest value with the highest nitrogen level.

3.3. Fruit Quality under Irrigation and Fertilization

The value and share of the different chemical measurements (

Table 5. Chemical measurements’ means at different irrigation systems and nitrogen treatments in seasons 2019 and 2020.

	1st Season								2nd Season
Irrigation System	Nitrogen Level (%)
	60	70	80	90	100	110	120	Mean	60	70	80	90	100	110	120	Mean
	Vitamin C (mg/100 g FW)
Surface (control)	15.2 i	15.7 hi	16.6 g	14.3 j	16.3 gh	15.4 hi	15.3 i	15.5 C	16.9 ef	17.5 e	17.8 de	17.3 e	16.0 f	16.6 ef	17.3 e	17.1 B
Drip	18.9 f	19.8 c–f	19.9 c–e	21.3 ab	19.9 c–e	19.7 c–f	19.0 ef	19.8 B	19.5 bc	18.7 cd	19.0 c	19.6 bc	20.3 ab	20.9 a	20.3 ab	19.7 A
Subsurface	20.7 bc	20.7 bc	20.5 bcd	22.2 a	19.8 c–f	20.6 bcd	19.6 c–f	20.6 A	19.8 bc	19.8 bc	19.6 bc	21.2 a	18.9 c	19.7 bc	18.8 cd	19.7 A
Mean	18.3 CD	18.7 BC	19.0 AB	19.3 A	18.6 BC	18.6 BC	18.0 D		18.7 ABC	18.7 BC	18.8ABC	19.4 A	18.4 C	19.1 AB	18.8 ABC
	Fiber (%)
Surface (control)	1.22 l	1.27 kl	1.35 jk	1.29 kl	1.56 g	1.55 g	1.64 ef	1.41 C	1.21 hi	1.22 ghi	1.10 j	1.13 ij	1.40 e	1.31 fg	1.46 de	1.26 C
Drip	1.07 m	1.40 ij	1.71 de	1.83 abc	1.44 hi	1.81 bc	1.70 de	1.56 B	1.14 ij	1.25 gh	1.19 hi	1.30 g	1.52 cd	1.57 c	1.43 e	1.34 B
Subsurface	1.78 cd	1.50 gh	1.88 ab	1.90 a	1.77 cd	1.45 hi	1.11 m	1.63 A	1.70 b	1.43 e	1.80 a	1.82 a	1.69 b	1.39 ef	1.06 j	1.55 A
Mean	1.35 E	1.39 E	1.65 AB	1.67 A	1.59 C	1.59 BC	1.48 D		1.35 C	1.30 D	1.36 C	1.42 B	1.54 A	1.42 B	1.32 CD
	Catalase Activity (Unit/mg Protein)
Surface (control)	0.22 ef	0.22 ef	0.23 ef	0.24 ef	0.20 f	0.24 ef	0.36 cd	0.24 B	0.34 a–d	0.30 cde	0.28 cde	0.46 a	0.38 abc	0.23 de	0.33 bcd	0.33 A
Drip	0.19 f	0.37 cd	0.29 de	0.45 ab	0.33 cd	0.22 ef	0.22 ef	0.29 A	0.28 cde	0.22 de	0.38 abc	0.30 cde	0.30 cde	0.23 de	0.23 de	0.28 B
Subsurface	0.30 cde	0.34 cd	0.23 ef	0.47 a	0.23 ef	0.38 bc	0.20 f	0.31 A	0.29 cde	0.33 bcd	0.22 de	0.45 ab	0.22 de	0.37 abc	0.19 e	0.29 AB
Mean	0.24 C	0.31 B	0.25 C	0.39 A	0.25 C	0.28 BC	0.26 C		0.30 B	0.28 B	0.29 B	0.40 A	0.30 B	0.27 B	0.25 B
	Superoxide Dismutase Activity (Unit/mg Protein)
Surface (control)	7.60 l	7.41 l	10.2 g	10.2 g	10.3 efg	10.3 efg	12.6 d	9.82 C	13.7 bc	11.0 d–g	11.4 def	16.4 a	9.81 fg	10.3 efg	12.9 cd	12.2 A
Drip	10.3 fg	8.73 k	9.87 h	15.3 b	12.6 d	10.2 g	8.77 jk	10.8 B	11.4 def	10.3 efg	9.81 fg	11.0 d–g	12.5 cde	9.49 fg	9.43 fg	10.6 B
Subsurface	10.3 fg	13.1 c	10.6 ef	15.9 a	9.12 i	9.08 ij	10.7 e	11.3 A	9.81 fg	12.6 cde	10.2 fg	15.2 ab	8.73 g	8.69 g	10.2 fg	10.8 B
Mean	9.37 E	9.75 D	10.2 C	13.8 A	10.68 B	9.87 D	10.69 B		11.7 B	11.3 BC	10.5 BCD	14.2 A	10.4 CD	9.49 D	10.9 BC
	Total Protein (%)
Surface (control)	20.08 i	20.19 i	23.57 abc	20.34 i	22.05 d–g	22.01 d–g	22.99 b–e	21.60 B	20.19 g	20.92 efg	22.50 b–c	20.46 g	22.60 bc	22.03 cde	22.87 bc	21.65 A
Drip	20.50 hi	21.08 ghi	20.89 ghi	23.12 a–d	23.40 abc	22.01 d–g	22.54 c–f	21.93 B	20.46 g	21.27 d–g	20.22 g	22.32 bcd	22.97 bc	24.21 a	22.32 bcd	21.97 A
Subsurface	21.72 f–i	24.34 a	22.89 b–e	24.04 ab	23.44 abc	21.93 d–g	21.32 f–i	22.81 A	20.79 fg	23.29 ab	21.91 c–g	23.01 bc	22.43bcd	20.98 efg	20.40 g	21.83 A
Mean	20.77 C	21.87 B	22.45 AB	22.5 AB	22.97 A	21.98 B	22.28 AB		20.48 D	21.82 BC	21.54 C	21.93 BC	22.67 A	22.41 AB	21.86 BC
	Total Chlorophyll (SPAD)
Surface (control)	37.76 fg	42.40 b–e	34.87 gh	36.78 fg	33.61 h	37.54 fg	40.64 de	37.66 C	36.25 g	39.17 def	38.42 efg	38.94 def	37.40 fg	39.07 def	39.22 def	38.35 C
Drip	41.98 b–e	44.11 abc	39.25 ef	43.42 a–d	41.30 cde	41.35 cde	41.02 cde	41.78 B	39.01 def	40.53 cde	41.12 bcd	39.37 c–f	39.27 def	39.01 def	38.35 efg	39.52 A
Subsurface	40.82 de	42.96 a–d	43.01 a–d	45.16 ab	42.66 bcd	45.87 a	43.66 a–d	43.45 A	39.07 def	41.11 bcd	41.16 bcd	43.22 ab	40.82 b–e	43.90 a	41.79 abc	41.58 A
Mean	40.19 BC	43.16 A	39.04 C	41.79 AB	39.19 C	41.59 AB	41.77 AB		38.11 C	40.27 AB	40.23 AB	40.51 AB	39.16 BC	40.66 A	39.79 AB
	Proline (μmol/100g FW)
Surface (control)	25.63 n	56.70 l	58.35 kl	59.68 jk	60.50 j	54.26 m	63.31 i	54.06 C	48.43 l	62.22 gh	54.32 k	56.99 j	59.99 i	54.52 k	60.44 hi	56.70 C
Drip	64.22 i	70.32 fg	69.27 g	75.15 c	79.59 b	70.11 fg	71.42 ef	71.44 B	73.02 bc	71.56 cde	72.19 cd	73.35 bc	71.45 cde	80.51 a	71.60 cde	73.38 A
Subsurface	72.04 ef	82.78 a	72.92 de	78.16 b	74.28 cd	73.14 de	66.79 h	74.30 A	68.94 f	79.22 a	69.78 ef	74.80 b	71.09 c-f	69.99 def	63.92 g	71.10 B
Mean	53.96 E	69.93 B	66.84 CD	71.00 A	71.45A	65.83 D	67.17C		63.46 D	71.00 A	65.43 C	68.38 B	67.51 B	68.34 B	65.32 C
	Peroxide Activity (Unit/mg Protein)
Surface (control)	1209 l	780 q	1056 n	1020 o	838 p	1412 i	1666 e	1140 C	1009 k	1166 i	1086 j	861 l	875 l	1465 fg	1588 d	1150 C
Drip	1172 m	1292 k	1742 c	1629 f	1694 d	1489 h	1489 h	1501 B	1167 i	1159 i	1677 b	1637 c	1526 e	1625 c	1455 g	1464 B
Subsurface	1812 a	1761 b	1549 g	1694 d	549 g	1344 j	1218 l	1561 A	1734 a	1686 b	1482 f	1621 c	1483 f	1286 h	1166 i	1494 A
Mean	1397 D	1278 F	1449 AB	1447 B	1360 E	1415 C	1458 A		1303 F	1337 E	1415 B	1373 D	1295 F	1459 A	1403 C

Note: Means followed by the same letter within column are not significantly different (p < 0.05)—capital letters indicate the significances for means; small letters indicate the significances for interactions.

) showed different behavior from the first season than the second one. In the first season, the subsurface irrigation system revealed the highest values for the mean applied nitrogen levels, where the highest values for vitamin C, fiber, catalase activity, superoxide dismutase activity, chlorophyll, proline, peroxidase activity, and total protein were 20.57 mg/100 g FW, 1.63%, 0.31 unit/mg protein, 11.25 unit/mg protein, 43.45 SPAD, 74.3 mol/100g FW, 1561.04 unit/mg protein, and 22.81%, respectively. Nevertheless, in the second season, the highest values varied among the three irrigation systems, where the subsurface irrigation system exhibited the highest values for total chlorophyll, peroxidase activity, and fiber with 41.58 SPAD, 1493.92 units/mg protein, and 1.55%, respectively, while the drip irrigation system manifested the highest values for vitamin C, proline, and total protein with 19.74 mg/100 g FW, 73.38 mol/100g FW, and 21.97%, respectively, and the surface irrigation demonstrated the highest values by catalase activity and superoxide dismutase activity with 0.33 unit/mg protein and 12.21 unit/mg protein, respectively.

The 90% nitrogen level displayed the highest values for the mean of irrigation systems, as well as the most utilized irrigation systems, at the measurements of vitamin C, fiber, catalase activity, and superoxide dismutase activity, with values of 19.26 mg/100 g FW, 1.67%, 0.39 unit/mg protein, and 13.81 unit/mg protein, respectively, at the first season, and with values of 19.35 mg/100 g FW, 1.54%, 0.4 unit/mg protein, and 14.18 unit/mg protein, respectively, at the second season. While only the fiber share showed its highest value at the standard nitrogen level for the second season. Moreover, the total protein in green pods presented its highest value at the standard nitrogen level in the first and second seasons, with 22.97% and 22.67%, respectively.

The peroxidase activity exhibited the highest value at the highest nitrogen levels, with a peroxidase activity of 1458.68 and 1458.02 units/mg protein, respectively, for the first and second seasons. Nonetheless, total chlorophyll and proline revealed their highest amounts by divergent nitrogen levels at the studied season, with the highest values at the first season being 43.16 SPAD and 71.54 mol/100g FW for nitrogen levels of 70% and 100%, respectively, and the highest values at the second season being 40.66 SPAD and 71 mol/100g FW for nitrogen levels of 110%, respectively.

Several measurements exhibited their highest values by the applied excess nitrogen levels (110% and 120%), such as proline, peroxidase activity, fiber, catalase activity, and superoxide dismutase activity, with values of 6.31 mol/100g FW, 1665.85 unit/mg protein, 1.64%, 0.36 unit/mg protein, and 12.63 unit/mg protein, respectively, for the surface irrigation. Nevertheless, other measurements revealed their highest amounts at the lowest applied nitrogen levels (60% and 70%) such as proline, peroxidase activity, and total protein content in green pods for the subsurface irrigation system with 82.78 μmol/100g FW, 1811.77 unit/mg protein, and 24.34%, respectively, at the first season, and 79.22 μmol/100g FW, 1733.86 unit/mg protein, and 23.29%, respectively, at the second season, while the total chlorophyll manifested higher values by the lowest applied nitrogen levels for the measurement total chlorophyll with 44.11 and 42.40 SPAD at the drip and surface irrigation, respectively, at the first season.

3.4. Water Use Efficiency

The water use efficiency (WUE) was calculated for all the applied irrigation and fertilization treatments at the first and second seasons (

Table 6. Water use efficiency (WUE) at the different irrigation systems and nitrogen treatments in seasons 2019 and 2020.

	1st Season								2nd Season
Irrigation System	Nitrogen Level (%)
	60	70	80	90	100	110	120	Mean	60	70	80	90	100	110	120	Mean
	WUE (kg/m3)
Surface (control)	0.93 l	0.95 l	1.09 jk	1.08 k	1.09 jk	1.14 jk	1.14 jk	1.06 C	0.70 l	0.78 kl	0.85 j	0.84 jk	0.99 i	1.00 i	1.01 i	0.88 C
Drip	1.74 i	2.04 g	2.02 h	2.05 g	2.08 fg	2.17 e	2.12 ef	2.03 B	1.53 h	1.73 g	1.71 g	1.84 f	1.94 d	1.91 de	1.86 ef	1.79 B
Subsurface	2.35 d	2.41 c	2.53 a	2.38 c	2.47 b	2.37 c	2.03 gh	2.36 A	2.22 c	2.28 bc	2.39 a	2.26 c	2.33 ab	2.25 c	1.91 de	2.23 A
Mean	1.67 D	1.80 BC	1.88 A	1.84 B	1.88 A	1.90 A	1.77 C		1.48 D	1.60 BC	1.65 B	1.65 B	1.76 A	1.72 A	1.59 C

Note: Means followed by the same letter within column are not significantly different (p < 0.05)—capital letters indicate the significances for means; small letters indicate the significances for interactions.

; Figure 2). The highest WUE was significantly displayed at the subsurface irrigation systems at the first and second seasons with mean values 2.36 and 2.23 kg/m³, respectively, followed by the drip irrigation system with the values 2.03 and 1.79 kg/m³, respectively. The lowest WUE was revealed by the surface irrigation system with mean values 1.06 and 0.88 kg/m³, respectively. The WUE showed its highest performance with the nitrogen levels of 80%, 90%, 100%, and 110% for the mean applied irrigation systems with the values 1.88, 1.84, 1.88, and 1.90 kg/m³, respectively, at the first season, and 1.65, 1.65, 1.76, and 1.72 kg/m³, respectively, at the second season. While the lowest amounts of WUE was manifested significantly by 60% nitrogen level with 1.67 and 1.48 kg/m³ at the first and second seasons, respectively. For the interaction impact between the irrigation systems and nitrogen levels, the subsurface irrigation system significantly exhibited the highest amount by the first and second seasons at the 80% nitrogen level with 2.53 and 2.39 kg/m³, respectively. While the lowest WUE was presented by the highest nitrogen level (120%) with amounts of 2.03 and 1.91 kg/m³ in the first and second seasons, respectively. However, the drip and surface irrigation systems showed different behaviors, where in the first season, the drip and surface irrigation systems appeared to have their highest WUE by the excess applied nitrogen levels (110% and 120%), with the values of 2.17 and 2.12 kg/m³ for the drip irrigation system and 1.14 and 1.14 kg/m³ for the surface irrigation system, respectively. The lowest WUE was revealed at the lowest nitrogen level (60%) with the amounts of 1.74 and 0.93 kg/m³ for the drip surface irrigation systems, respectively. In the second season, the drip irrigation significantly exhibited the highest WUE at the standard nitrogen level (100%) with 1.94 kg/m³, whereas similar higher values of WUE were presented by the surface irrigation system at the nitrogen levels of 100%, 110%, and 120% with 0.99, 1.00, and 1.01 kg/m³, respectively. The lowest WUE amounts were significantly also shown by the lowest nitrogen levels, with 1.53 and 0.70 kg/m³ for the drip and surface irrigation systems, respectively.

3.5. Greenhouse Gas Emission from Nitrogen Fertilization

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

Table 7. Greenhouse gas emissions (CO₂ equivalent) from nitrogen fertilization as affected by total yield per hectare.

Nitrogen Level (%)	Mass of N Rate Applied	Total Yield		Total N2O	Total CO2 Equivalent	CO2 Equivalent
		kg ha−1		Emissions	Emissions	g/kg Yield
	Kg/ha−1	First Season	Second Season	kg/ha−1	kg/ha−1	First Season	Second Season
60	123	9432	8328	4.24	1264	134	152
70	144	10128	9000	4.57	1363	135	151
80	164	10632	9312	4.89	1456	137	156
90	185	10440	9336	5.22	1555	149	167
100 (control)	205	10680	10056	5.53	1648	154	164
110	226	10800	9888	5.86	1747	162	177
120	246	10176	9288	6.18	1840	181	198

). After neglecting the irrigation system factor and working only with the applied nitrogen levels and the mean yield of the irrigation systems at each nitrogen level, the highest amount of the total N₂O and total CO₂ equivalent were revealed at the highest applied nitrogen level (120%) with 6.18 and 1840 kg/ha, respectively, as well as the CO₂ equivalent per kg yield at the first and second seasons with 181 and 198 g/kg yield, respectively. Nevertheless, the mean highest yield was exhibited by the 110% nitrogen level with 10,800 kg/ha in the first season and by the 100% nitrogen level with 10,056 kg/ha in the second season. However, the lowest GHG emissions, total N₂O and CO₂ equivalent (kg/ha), and CO₂ equivalent per kg yield at the first and second seasons (g/kg yield) were manifested at the lowest applied nitrogen level (60%) with 4.24, 1264, 134, and 152, respectively, as well as the lowest mean yield, which was also presented at the 60% nitrogen level with 9432 and 8328 kg/ha at the first and second seasons, respectively.

4. Discussion

Modern irrigation technologies, such as subsurface and drip irrigation systems, aim to provide sufficient water to replenish depleted soil water in time and avoid physiological water stress in growing plants [24,52]. The efficient management of irrigation water by modern irrigation systems can save 20–30% of the utilized water [53], whereas the surface irrigation system can suffer from a water deficit due to insufficient irrigation water management.

The results in Figure 3 showed that the subsurface irrigation system presented the highest values, followed by the drip irrigation system, while the surface irrigation system revealed the lowest values. On the other hand, improved vegetative growth such as plant height, number of leaves, and fresh and dry weight of green bean plants under subsurface irrigation system may be due to proper moisture balance in plants, which creates favorable conditions for nutrient absorption, photosynthesis and metabolite transmission.

Another possibility was increasing the available water and nutrient uptake, which eventually accelerated the rate of vegetative growth. Additionally, improving the environmental conditions of the soil around the roots of plants to become more suitable for encouraging plant growth was another possibility. Water acts as a solvent in which all plant nutrients are dissolved; it is the agent of transporting nutrients to all parts of the plant as well as controlling plant and soil temperatures at a level suitable for plant growth and development. It maintains the swelling of the plant cell, helps the plant root to penetrate into the soil, and finally is responsible for soil activity as it is responsible for the activity of micro- and macro-organisms in the soil [52,53]; thus, increasing vegetative characteristics with subsurface irrigation could be attributed to the suitable irrigation quantity, especially in the early stage of crop growth, which enhanced a deeper and more extensive root system.

The higher observed yield by the modern irrigation system was significantly higher than that by the surface irrigation (Table 4), which agreed with [54], who obtained a higher yield of hot pepper cultivated under the drip irrigation system, even with reduced irrigation water up to 40%. As well, the significantly higher pod yield under the modern irrigation system than the surface one (Table 4) is matched with [12,55], who approved the linear relationship between the pod yield and the efficient use of the supplied irrigation water. The same results were related to the vegetative measurements (Table 3), where the more efficient irrigation systems manifested the higher results than the surface ones, due to the more efficient water management with modern irrigation systems.

In general, it was evident that the best results were obtained from the total yield of green bean fruits by applying the subsurface irrigation system. These results may be due to adequate soil moisture content, which may lead to an increase in various physiological processes, better absorption of plant nutrients, and higher rates of photosynthesis, which may be reflected in an increase in the number of pods and an increase in crop yield [55].

The decline in the chlorophyll content and the leaf greenness appeared clearly due to the irrigation deficit, and that explained the significant lowest chlorophyll content amount by the surface irrigation system compared to the modern ones, where with the surface irrigation system the irrigation efficiency is less than 93% compared with the modern irrigation systems [56]. The appropriate irrigation system (subsurface irrigation) gave the highest content of chlorophyll in plant leaves compared to any other irrigation system tested in this study. These results might be due to the condensed cell sap in which the concentration of chlorophyll would be denser [24].

Nevertheless, the antioxidant elements, such as peroxidase activity (POD), superoxide dismutase (SOD), and catalase (CAT), were also presented in higher amounts by the modern irrigation systems than the surface ones, although [57,58,59,60] mentioned that the antioxidant elements tend to increase their production under drought stress to eliminate yield reduction. The chemical measurements in fruits (vitamin C, fiber, total protein) decreased under the surface irrigation system, the increase in irrigation amounts in surface irrigation led to a significant decrease in the percentage of nutrients in leaves and fruits. The results may show that under lower soil moisture, soil ion concentration increases and vice versa if soil moisture content increases.

On the other hand, this decrease in nutrient concentration on fruit is observed under surface irrigation for two reasons: the first is due to the dilution effect (increased plant biomass in a fixed food stock) and the second is the nutrient movements towards fruit or otherwise. Plant members, emphasized El-Noemani et al. [12], on green beans, was found that the concentration of fruit nutrients increases with proper irrigation regimen. They added that the lowest concentration of nutrients occurred in irrigated plants with the highest soil moisture content.

As resulted in Table 6 and Figure 2, the highest WUE values were shown significantly by the modern irrigation systems (subsurface irrigation system then drip irrigation system) and the surface irrigation system presented lower amounts. Which were half lower than the modern irrigation system, where modern irrigation system can increase irrigation efficiency up to 93% and reduce water usage by 20–30% [53].

On the other hand, excessive water volume can also reduce the growth rate of plants. Moreover, too much water in the soil is detrimental to plant growth, due to oxygen deprivation in the plant roots. Furthermore, the additional water should reflect the same rate of increase in yield, due to additional costs, based on the law of diminishing yield (WUE). However, the type of soil must also be taken into account. For example, El-Noemani et al. [12] recorded a linear relationship between green bean yield and water use up to 120% IR. It was found that vegetative growth factors and crop components responded favorably to water that increased by up to 120% of IR in newly reclaimed sandy soils. This was due to sandy soils having a small water-holding capacity compared to clay soils. With irrigation, we maintained the conditions for optimal plant growth during all stages. Consequently, higher yields and better WUE can be achieved by using suitable irrigation systems and optimizing water management. The total yield is also positively correlated with WUE (Figure 4), where any additional water must reflect the same increase rate in yield, because of the additional costs, based on the law of diminishing returns (WUE) [26,61].

On the other hand, the highest measurements amounts were revealed mostly at the fertilization levels of 90–110% (Figure 2), and for the yield, the highest values were exhibited at the nitrogen levels of 80–110% (Table 7). At the applied nitrogen levels of 80–110%, not only the yield was higher, but also the GHG emissions (Table 7), but the rate of the GHG emissions increase was higher than the rate of the yield increase, and this result was agreed with by [21], who reported that the increase in the application rate of fertilizer revealed a double increase in GHG emissions compared to the increase in yield. In general, as in Table 7, 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 [62,63,64]. However, the increase in N₂O emissions caused by the applied nitrogen levels was met with an increase in total yield and WUE until the nitrogen level reached 100% in the first season and 110% in the second season, after which they declined by 120% nitrogen level (Figure 4).

5. Conclusions

The subsurface irrigation system presided over the highest values of the plant measurements, yield, and WUE of green beans (Phaseolus vulgaris L.), compared with the other irrigation systems, where the yield under the subsurface irrigation system reached 4.93 with an average of 4.72 ton/acre in the first season and 4.52 ton/acre in the second season. The drip irrigation system also showed high values that sometimes were close to the subsurface irrigation system value or even higher, as indicated by the pods’ fresh weight in the second season. However, the surface irrigation system revealed the lowest values, especially with the WUE values, which were less than 50% of the subsurface and drip irrigation systems. The WUE presented a highly positive correlation with the total yield, while the WUE did not show a correlation with the change due to applied N fertilizer. The GHG emissions increased with the increase of the applied N fertilizer; nevertheless, the total yield started to decrease at the 120% nitrogen level in the first season and 110% in the second season. 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 irrigation management will contribute to obtaining the highest yield while preserving the environment.