Enhancing the Growth and Quality of Alfalfa Fodder in Aridisols through Wise Utilization of Saline Water Irrigation, Adopting a Strategic Leaching Fraction Technique

Abstract

An experiment was conducted to investigate the optimal use of high-salt water for alfalfa fodder growth and quality in Aridisol. The experiment included five treatments and was performed using a completely randomized design (CRD) as factorial design with three replications. We used a leaching fraction technique (LF), which is a mitigating technique (MT). The five treatments were T1 = MT1 as normal irrigation (control), T2 = MT2 as a leaching fraction (LF) of 15% with the same quality of water, T3 = MT3 as a LF of 30% with the same quality of water, T4 = MT4 as a LF of 15% with good-quality water (as percentage of total water), in the form of 2–3 irrigations every 3 months, and T5 = MT5 as a LF of 30% with good-quality water (as percentage of total water), in the form of 2–3 irrigations every 3 months. The duration of the experiment was three years and normal soil (non-saline, non-sodic) was used in the current study. Results showed that saline water irrigation negatively affected the growth traits, but the application of the LF technique with same-quality or good-quality water mitigated such negative effects. The fodder quality traits such as crude protein (CP), crude fiber (CF) and ashes were also affected in a negative way with the use of saline irrigation water. This negative impact was more intensified in the third year as the concentration of salts increased in saline water during the three years of the current investigation. A LF with canal water at 15 or 30% reduced the negative effects of salt stress and improved fodder biomass production and quality traits. For examples, using a LF with canal water at 30% increased the biomass production to 33.30 g and 15.87 g when plants were irrigated with W1 and W5, respectively. In addition, it improved quality traits such as crude protein content (5.54% and 3.73%) and crude fiber content (14.55% and 12.75%) when plants were irrigated with W1 and W5, respectively. It was concluded that the LF technique can be recommended for practice in the case of saline water irrigation for the optimized growth and quality of alfalfa fodder.

1. Introduction

Water is a vital element supporting life on Earth, and its distribution primarily controls plant growth across the planet’s surface. Water scarcity significantly impacts crop productivity, posing a major challenge to agricultural economies worldwide. To achieve sustainable agriculture, various water conservation techniques are being employed to mitigate water-related stress [1,2,3]. The increasing global population and dwindling water sources threaten food security, exacerbating the issue [4,5]. The scenario of water stress becomes worse in areas with low rainfall [6] because good-quality water is in short supply and the use of water with compromised quality is the only option for employing in agriculture [7,8,9].

Pakistan’s water security is under severe threat, placing it 14th among 17 countries facing ‘extremely high water risk’ globally [10]. The Indus Basin in Pakistan spans approximately 16 million hectares (Mha). Indus River and its tributaries serve as the primary sources of surface water, with an estimated 122 km³ diverted annually through an extensive canal system for irrigation. However, surface water supplies fall short of meeting crop water requirements for the intensive cropping system. To bridge this gap, approximately 62 km³ of groundwater is pumped annually by 1.36 million private and public tube wells nationwide. Pakistan’s irrigated agriculture faces significant challenges such as inequitable water distribution leading to waterlogging, inefficient water use resulting in soil salinity, low crop yields and water use efficiency, increasing soil salinization, deteriorating water quality, and inefficient drainage effluent disposal [11].

Agriculture faces numerous global challenges. These challenges are comprising the requirement to yield 70% extra foodstuff by 2050 to feed an extra 2.3 billion individuals. This is only possible through preserving limited natural resources and mitigating the impacts of extreme environmental changes, which are critical for combating poverty and hunger [12]. Abiotic stress is a main issue preventing vegetal development and yield when coupled with salinity [13]. It is projected that abiotic stresses, including salinity, will cause over 50% reduction in crop yields [14].

Pakistan’s agriculture is severely impacted by water scarcity, which significantly limits crop yields. Due to the short supply of good-quality water, optimizing water use efficiency in water-deficient areas is crucial for enhanced plant production. This can be attained by utilizing all available water sources [15,16]. Water conservation has become a critical issue in arid and semi-arid regions, where the shortage of good-quality water and rising temperatures due to global environmental changes are primary factors restricting plant growth and development [17]. Therefore, it is essential to develop effective management strategies to utilize poor-quality water with high salt content, ensuring crop water demands are met amidst the scarcity of good-quality water for irrigation [18,19].

The consistent use of high-salt water for irrigation has been reported to increase soil’s electrical conductivity (EC), which is important to salt buildup in plant growing medium [20]. Continued acquaintance with high-EC water can cause salt toxicity, damaging plant roots and negatively impacting growth and yields [21]. To mitigate this issue, it is essential to adopt effective management strategies to overcome salt toxicity and ensure sustainable agricultural practices [3,22,23].

Plants are usually exposed to diverse environmental factors (biotic and abiotic) that reduce crop yields, thereby reducing worldwide crop production by up to 70% due to the effect of temperatures, salinity in soils, and drought [24]. One of the most significant stresses among these is salinity especially in low rainfall areas of the world [25]. Plants are victims of salinity stress at every stage of growth cycle, but this stress is more detrimental at germination and seedling development stages that differ among crop [26]. Possible outcomes of plant exposure to a high concentration of salts include difficulty in germination, difficult root penetration, water stress associated with high osmotic potential of water, toxicity due to presence of ions in excessive concentrations [11]. All these factors reduce the photosynthetic ability of plant [27] with subsequent reduced biomass [28]. The negative effect of such toxic concentrations of salts on crop yield can be avoided by to time flushing out salts from the root zone time to time, applying a quantity of water greater than the crop delta of water. Technically, the extra water above the crop need is the leaching fraction (LF). This addition of extra water resulted in the leaching of salts [29].

Crops have been classified based on their ability to tolerate salinity [30]. Alfalfa is a vital winter seasonal fodder crop in Pakistan, renowned globally as a perennial forage legume offering sustained yields. However, its cultivation in Pakistan remains limited, occupying only 7% of the country’s total forage cultivation area. Under optimal environmental conditions, it has the potential to produce 120–200 kg/acre of seed, highlighting its significant yield potential [31,32]. Alfalfa is recognized as moderately delicate to salt, but its actual tolerance varies depending on factors such as environment, soil characteristics, agronomic measures [33], growth stage [34], and varietal differences [35]. Research has exposed that certain alfalfa varieties exhibit enhanced salt tolerance due to their ability to exclude sodium ions from shoots and restrict chloride ion uptake [36].

Keeping in view the above ability of alfalfa, a three-year research trial was conducted to investigate the optimal use of high-salt water for alfalfa fodder growth and quality in Aridisol.

2. Materials and Methods

2.1. Plant Materials, Treatments and Design

A pot research trial was conducted at the College of Agriculture, University of Sargodha, Punjab, Pakistan, to investigate the optimal use of high-salt water for alfalfa fodder growth and quality in Aridisol. The experimental site is located at latitude: 32.08°N—longitude: 72.67°E—elevation: 193 m above sea level. In Sargodha, the climate is characterized as dry, with a low precipitation rate and extremely high temperatures during summer months (i.e., reaching up to 49 °C).

Treatments are described as follows below and in Table 1:

Factor A: Irrigation water qualities (W)

W1. Water with EC less than 1.0 dS m⁻¹,

W2. Water with EC 2.0 dS m⁻¹,

W3. Water with EC 3.0 dS m⁻¹,

W4. Water with EC 4.0 dS m⁻¹, and

W5. Water with EC 5.0 dS m⁻¹.

Factor B: Mitigating Techniques (MT)

MT1. Normal irrigation (control);

MT2. Leaching fraction of 15% with the same quality of water;

MT3. Leaching fraction of 30% with the same quality of water;

MT4. Leaching fraction of 15% with good-quality water (as percentage of total water), in the form of 2–3 irrigations every 3 months;

MT5. Leaching fraction of 30% with good-quality water (as percentage of total water), in the form of 2–3 irrigations every 3 months.

Preparation of saline waters (W1–W5) for different treatments

• W1. Water with EC less than 1.0 dS m⁻¹

Groundwater was analyzed (Table 2) and used for control treatment as it fulfills the criteria of the control treatment (T1) indicating a value (0.78) of EC < 1.0 dS m⁻¹.

2.

W2. Water with EC 2.0 dS m⁻¹

For W2, sodium chloride (71.305 g) was dissolved in 100 mL of groundwater.

Similarly, saline waters of desired EC 2, 3, 4, and 5 dS m⁻¹ (W2, W3, W4, and W5) were prepared in large drums of 100-L capacity (Table 2). Such prepared water was applied to respective pots according to each treatment. Irrigation with saline water was started two weeks after the seeds germination.

Table 1. Schematic layout of treatments.

W1 = EC < 1.0 dS m−1					W2 = EC = 2.0 dS m−1					W3 = EC = 3.0 dS m−1					W4 = EC = 4.0 dS m−1					W5 = EC = 5.0 dS m−1
MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4= Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5= Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months
With 03 Replications

Table 1. Schematic layout of treatments.

W1 = EC < 1.0 dS m−1					W2 = EC = 2.0 dS m−1					W3 = EC = 3.0 dS m−1					W4 = EC = 4.0 dS m−1					W5 = EC = 5.0 dS m−1
MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4= Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5= Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months	MT1 = Normal irrigation (control)	MT2 = Leaching fraction = 15%	MT3 = Leaching fraction = 30%	MT4 = Leaching fraction = 15% with 2–3 irrigation after every 3 months	MT5 = Leaching fraction = 30% with 2–3 irrigation after every 3 months
With 03 Replications

Table 2. Analysis of soil used in the current study.

Determinations	Units	Value
pHs	-	8.1
ECe	dS m−1	2.89
Carbonates	meq/L	Nil
Bicarbonates	meq/L	5.36
Chloride	meq/L	7.15
Sulfate	meq/L	16.39
Calcium + magnesium	meq/L	7.11
Sodium	meq/L	16.35
SAR	-	8.65
N	%	0.32
P	ppm	8.1
K	ppm	121.5
Soil textural class	-	Clay loam

Note(s): EC_e = electrical conductivity; N = nitrogen; P = phosphorus; K = potassium; SAR = sodium adsorption ratio.

Table 2. Analysis of soil used in the current study.

Determinations	Units	Value
pHs	-	8.1
ECe	dS m−1	2.89
Carbonates	meq/L	Nil
Bicarbonates	meq/L	5.36
Chloride	meq/L	7.15
Sulfate	meq/L	16.39
Calcium + magnesium	meq/L	7.11
Sodium	meq/L	16.35
SAR	-	8.65
N	%	0.32
P	ppm	8.1
K	ppm	121.5
Soil textural class	-	Clay loam

Note(s): EC_e = electrical conductivity; N = nitrogen; P = phosphorus; K = potassium; SAR = sodium adsorption ratio.

2.2. Sowing and Crop Husbandry

To initiate the experiment, normal soil (non-sodic, non-saline) was collected and analyzed (Table 2). The soil was then dried, ground, and sieved before filling pots (20 kg of soil per pot). All pots were irrigated with tap water to create uniform soil conditions. Alfalfa seeds were sown in each pot at a rate of 155 mg/pot (equivalent to 16 kg/ha). A uniform dose of NPK fertilizer (50, 150, 0 kg/ha) was applied to all pots to meet the nutritional requirements of alfalfa plants.

Urea and phosphorus fertilizers were used as sources of N and P, respectively. The estimated dose of urea and single super phosphate (SSP) fertilizers for each pot was 1.04 g and 8.00 g, respectively. The entire P dose was applied at the start of the experiment, along with the first N dose. Subsequent N doses were split into 2–3 applications to meet the total crop requirement during the growing seasons. Weeds were manually removed when needed, and other agronomic practices were applied as required according to the national recommendations. Irrigation water was applied according to the treatment plan.

Alfalfa fodder was grown for three consecutive years, with three cuttings taken each year. The plants were harvested at 100 days after sowing (DAS) and in total 3 cuttings were harvested yearly.

2.3. Measurements

Agronomic parameters such as plant height (cm), fresh biomass weight, and oven-dry weight were recorded. Plant samples were dried, ground, and prepared for chemical analysis to determine fodder quality parameters such as crude protein (CP), crude fiber (CF), and ash content. Laboratory analysis followed the described methods in Handbook 60 of the U.S. Laboratory Staff [37].

Soil analysis: Different properties of soils were analyzed (

Table 3. Analysis of groundwater used for developing EC.

Determinations	Units	Value
EC	dS m−1	0.78
Total soluble salts (TSS)	meq/L	7.8
Carbonates	meq/L	Nil
Bicarbonates	meq/L	5.5
Chlorides	meq/L	2.1
Sulphates	meq/L	0.2
Calcium + magnesium	meq/L	4.4
Sodium	meq/L	3.4
Residual adsorption ratio (SAR)	-	2.30
Residual sodium carbonates (RSC)	meq/L	1.1

) using protocols mentioned in handbook 60 [37].

Analysis of irrigation water: All parameters for irrigation water testing were the same as for soil except RSC. For which the formula given by [38] was used.

$$\mathrm{R}\mathrm{S}\mathrm{C}=({\mathrm{C}\mathrm{O}}_3+{\mathrm{H}\mathrm{C}\mathrm{O}}_3)-(\mathrm{C}\mathrm{a}+\mathrm{M}\mathrm{g})$$

(1)

The relative growth rate (RGR): The formula described by [39] was used to calculate RGR in g m⁻² day⁻¹.

$$RGR={\displaystyle \frac{W_2-W_1}{T_2-T_1}}$$

(2)

where W₁ and W₂ indicated the total dry weights taken at time intervals T₁ and T₂, respectively.

Crude protein in plant biomass:

The mineral nitrogen content was analyzed using the Kjeldahl procedure and then multiplied with a factor of 6.25 to obtain the crude protein values.

$$\mathrm{C}\mathrm{r}\mathrm{u}\mathrm{d}\mathrm{e} \mathrm{p}\mathrm{r}\mathrm{o}\mathrm{t}\mathrm{e}\mathrm{i}\mathrm{n} \mathrm{c}\mathrm{o}\mathrm{n}\mathrm{t}\mathrm{e}\mathrm{n}\mathrm{t} \left(\mathrm{\%}\right)=\mathrm{N}\mathrm{i}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{g}\mathrm{e}\mathrm{n} \mathrm{c}\mathrm{o}\mathrm{n}\mathrm{t}\mathrm{e}\mathrm{n}\mathrm{t}\times 6.25$$

(3)

Crude fiber in plant biomass was calculated using following formula:

$$\mathrm{C}\mathrm{r}\mathrm{u}\mathrm{d}\mathrm{e} \mathrm{f}\mathrm{i}\mathrm{b}\mathrm{e}\mathrm{r}\left(\mathrm{\%} \mathrm{o}\mathrm{f} \mathrm{f}\mathrm{a}\mathrm{t}-\mathrm{f}\mathrm{r}\mathrm{e}\mathrm{e} \mathrm{D}\mathrm{M}\right)={\displaystyle \frac{\left(weight crucible+dried residue\right)-(weight crucible+ashed residue)}{Weight of sample}}\times 100$$

(4)

Ashes in plant biomass were calculated using following formula:

$$\mathrm{A}\mathrm{s}\mathrm{h}(\mathrm{\%})={\displaystyle \frac{Weight of ash}{Weight of sample}}\times 100$$

(5)

2.4. Statistical Analysis

All collected data were statistically analyzed using Statistix 10.1 software to perform analysis of variance (ANOVA) and mean comparisons [40]. The means of treatments were compared using Tukey’s multiple range test, and p-values ≤ 0.05 were considered significant.

3. Results

3.1. Plant Height (cm)

Plant height, a crucial factor contributing to crop yield, was significantly affected by the use of saline water with different irrigation strategies. Alfalfa fodder plants were grown in pots for three years, and three cuttings were collected yearly. The trend of plant height was consistent across the three cuttings, with similar results observed in the third year (Figure 1). The continuous irrigation with saline water resulted in a reduction in plant height due to the salt accumulation. In the third year, plant height was decreased from 117.78 cm (W1) to 50.00 cm (W5) under normal irrigation. However, by combining saline water with leaching fraction (LF) techniques, plant height was improved. The highest plant heights (127 cm and 128 cm) were recorded with 15% and 30% LF, respectively, when coupled with the normal water irrigation, although these treatments were statistically equivalent.

A similar trend in plant height was observed for the average of three cuttings in the second year of the current study (Figure 2). Irrigation with saline water continued to reduce plant height of alfalfa in the second year as a result of the accumulation of salts. Under the normal irrigation system, plant height was decreased from 113.98 cm (W1) to 54 cm (W5) in the second year. However, when the leaching fraction (LF) technique was combined with saline water, a significant increment in plant height was recorded. The highest plant, 125.66 cm and 127 cm, were recorded with 15% and 30% LF, respectively, when coupled with canal water irrigation.

In the first year of the current study, similar results were observed for alfalfa plant height (Figure 3). The data indicated that using saline water significantly impaired plant height under normal irrigation conditions. The highest plants (i.e., 117.78 cm) were recorded when plants were irrigated using W1 (control), while the shortest plants (i.e., 50 cm) were observed when plants were irrigated using W5 (EC = 5 dS/m). However, when saline water was used in combination with the leaching fraction (LF) technique at 15% and 30%, plant height was significantly improved compared to normal irrigation. The plant height was increased to 119.00 cm and 125.66 cm for W1, and 54.00 cm and 57.88 cm for W5, respectively, with 15% and 30% LF. Using canal water with a LF at 15% and 30% resulted in the highest plants of 127.00 cm and 128 cm for W1, and 67.68 cm and 83.68 cm for W5, respectively. These treatments showed the most promising results in the current study.

3.2. Fresh Weight/Biomass

The ultimate goal of growing fodder crops is to produce fresh weight or biomass. In the third year of our experiment, the fresh biomass of alfalfa was decreased as a result of water saline application that negatively affected plant growth (Figure 4). However, when all treatments were combined with the leaching fraction (LF) of canal water at 15% and 30%, the fresh biomass was improved. The fresh biomass was maximized to 33.30 g when W1 was coupled with a 30% LF and canal water, followed by 32.56 g when W1 was coupled with 15% LF. On the other hand, the lowest fresh biomass of alfalfa, 15.87 g and 18.10 g, was obtained when W5 coupled with 15% and 30% LF, respectively.

A similar trend in fresh biomass was observed in the second year of the current investigation, and the highest fresh biomass of 32.56 g was obtained from plants irrigated with W1 in combination with a 30% LF and canal water (Figure 5). However, the lowest fresh biomass (i.e., 15.11 g and 15.87 g) was obtained from plants treated with W5 in combination with 15% and 30% LF, respectively. A consistent trend was also observed in the first year of the current study (Figure 6), where fresh weight was decreased from 26.87 g when plants were irrigated with W1 to 10.00 g when plants were irrigated with W5. However, a significant improvement in fresh biomass was obtained when treatments were combined with a LF at 15% and 30%, with values increasing to 27.02 g and 31.67 g, respectively. Nevertheless, the lowest fresh biomass of alfalfa were recorded when plants were grown with W5 and coupled with a 15% LF (13.25 g) or a 30% LF (14.00 g). The use of the LF technique with normal water can positively enhance fresh biomass of alfalfa, with a maximum value of 33.30 g that was achieved from plants irrigated with W1 and coupled with a 30% LF and canal water, when compared with the lowest fresh biomass (i.e., 18.10 g) that was recorded from plants irrigated W5 under the same LF technique.

3.3. Oven Dry Weight/Biomass

The dry weight of alfalfa plants irrigated with different saline water was negatively affected due to the salt accumulation, particularly in the 3rd year of the current study (Figure 7). As salt concentration increased, the fodder production as dry weight of alfalfa was decreased. Statistical analysis showed significant differences among different treatments for water types, but using a leaching fraction (LF) at 15% or/and 30% resulted in an improvement in dry weight of fodder production.

The same tendency in oven-dry weight/fodder production was observed in the second-year (Figure 8) where salt was increased. In the first year, using good-quality water (W1) proved to be the optimal treatment when it was used an individual or combined with a leaching fraction (LF) at 15% or/and 30% with either the same water or canal water (Figure 9). Oven dry weight increased from 11.65 g (normal water) to 12.05 g or 12.06 g when coupled with 15% and 30% LF, respectively. In contrast, using W5 treatment produced the lowest dry biomass, with values of 7.4 g, 7.77 g, and 7.88 g for normal mode and LF with the same water at 15% and 30%, respectively. These values were increased to 8.17 g and 8.73 g when a LF was applied with canal water at 15% or/and 30%, respectively.

3.4. The Relative Growth Rate

The relative growth rate of alfalfa was significantly affected with saline water irrigation. During the third year, using good-quality water (W1) proved to be the best treatment, whether used alone or combined with a leaching fraction (LF) at 15% and 30% with either the same water or canal water (Figure 10). The relative growth rate increased from 0.43 g kg⁻¹ day⁻¹ (normal irrigation) to 0.44 g kg⁻¹ day⁻¹ and 0.46 g kg⁻¹ day⁻¹ when coupled with 15% and 30% LF, respectively, and further improved to 0.48 g kg⁻¹ day⁻¹ and 0.49 g kg⁻¹ day⁻¹ when the LF technique was performed with canal water at the same rates. In contrast, the W5 treatment showed the lowest relative growth rate of 0.16 g kg⁻¹ day⁻¹, 0.18 g kg⁻¹ day⁻¹, and 0.19 g kg⁻¹ day⁻¹ for normal mode and the LF technique with the same water at 15% and 30%, respectively. These increased to 0.20 g kg⁻¹ day⁻¹ and 0.21 g kg⁻¹ day⁻¹ when the LF technique was performed with canal water at 15% and 30%, respectively.

During the second year, increased salt concentration in the soil led to reduced fodder production and lower relative growth rates in alfalfa (Figure 11). In the first year, using good-quality water (W1) proved to be the best treatment, whether used alone or combined with a leaching fraction (LF) at 15% and 30% with either the same water or canal water (Figure 11). The relative growth rate increased from 0.4 g kg⁻¹ day⁻¹ (normal irrigation) to 0.43 g kg⁻¹ day⁻¹ and 0.48 g kg⁻¹ day⁻¹ when coupled with 15% and 30% LF, respectively, and further improved to 0.5 g kg⁻¹ day⁻¹ and 0.52 g kg⁻¹ day⁻¹ when the LF technique was performed with canal water at the same rates. In contrast, the W5 treatment showed the lowest relative growth rate of 0.2 g kg⁻¹ day⁻¹, 0.21 g kg⁻¹ day⁻¹, and 0.22 g kg⁻¹ day⁻¹ for normal mode and a LF with the same water at 15% and 30%, respectively. These increased to 0.23 g kg⁻¹ day⁻¹ and 0.24 g kg⁻¹ day⁻¹ when the LF technique was performed with canal water at 15% and 30%, respectively.

3.5. Alfalfa Fodder Quality Parameters

Crude protein: The application of W1 proved to be the optimal treatment, whether used alone or combined with a leaching fraction (LF) at 15% and 30% with either the same water or canal water (Figure 12). The crude protein content of alfalfa was increased from 5.31% when irrigated with W1 to 5.36% and 5.46% when W1 was coupled with 15% or/and 30% LF, respectively, and further improved to 5.50% and 5.54% when W1 LF was applied with canal water at the same rates. In contrast, the W5 treatment showed the lowest crude protein content, with values of 3.5%, 3.56%, and 3.65% for normal mode and a LF with the same water at 15% and 30%, respectively. These values increased to 3.71% and 3.73% when the LF technique was performed with canal water at 15% and 30%, respectively. Similarly, in the second year, increased salt concentration in the soil led to reduced fodder production and lower crude protein content in alfalfa (Figure 13). During the first year, the concentration of crude protein was determined in alfalfa plants after applying irrigation with saline waters of various levels, it was noted that the salt concentration of waters impaired the crude protein content of alfalfa plants in a significant way when compared in terms of statistics. Application of good-quality water (W1) proved the best treatment even when used alone or coupled with a LF of the same or canal water at 15 and 30%. The crude protein content (5.25%) of alfalfa noted for normal mode of irrigation increased to the level of 5.31% and 5.36% when coupled with 15 and 30% LF, respectively, and it was further enhanced to the values of 5.46% and 5.50% when the LF technique at the same rates was performed with canal water (Figure 13). The similar observation was made for W5 treatment, which indicated the lowest crude protein content of alfalfa indicating 3.65, 3.71 and 3.73% for normal mode and a LF with same water at 15 and 30%, respectively. These reached 3.81 and 3.88% when the LF technique was performed with canal water at 15 and 30%, respectively.

3.6. Crude Fiber

In the 3rd year, crude fiber content of alfalfa was increased from 14.35% (normal irrigation) to 14.45% with 15% LF, 14.49% with 30% LF, 14.54% with a 15% LF and canal water, 14.55% with a 30% LF and canal water (Figure 14). A similar observation was recorded from plants irrigated with W5, which indicated the lowest crude fiber content of alfalfa indicating values of 12.46, 12.56 and 12.64% for normal mode and a LF with the same water at 15 and 30%, respectively. The same values reached 12.71% and 12.75% when a LF was applied with the canal water at 15 and 30%, respectively.

During the second year, the increased salt concentration in the soil reduced the fodder production and consequently reduced the crude fiber content in alfalfa (Figure 15). In contrast, during the first year, the W1 proved to be the optimal treatment, whether used alone or combined with a leaching fraction (LF) at 15% and 30% with either the same water or canal water. The crude fiber content of alfalfa was increased from 14.25% (normal irrigation) to: 14.31% with 15% LF, 14.36% with 30% LF, 14.46% with a 15% LF and canal water, 14.50% with a 30% LF and canal water (Figure 15). A similar observation was made for W5 treatment, which indicated the lowest crude fiber content of alfalfa indicating values of 12.65, 12.71, and 12.73% for normal mode and a LF with the same water at 15 and 30%, respectively. The same values reached 12.81 and 12.88% when the LF technique was performed with canal water at 15 and 30%, respectively.

3.7. Total Ash

In the 3rd year, total ash content of alfalfa increased from 7.35% (normal irrigation) to: —7.45% with 15% LF—7.49% with 30% LF—7.54% with a 15% LF and canal water—7.59% with a 30% LF and canal water (Figure 16). In contrast, the W5 treatment showed the lowest total ash content, with values of: —5.54% (normal irrigation)—5.56% (15% LF)—5.64% (30% LF)—5.71% (a 15% LF with canal water)—5.75% (a 30% LF with canal water).

A similar trend in total ash content was observed in the second-year data, with increased soil salt concentration leading to reduced fodder production and lower total ash content (Figure 17). In the first year, good-quality water (W1) was the best treatment, alone or with a leaching fraction (LF) at 15% and 30% with same or canal water. Total ash content increased from 7.25% (normal irrigation) to: —7.31% with 15% LF—7.36% with 30% LF—7.46% with a 15% LF and canal water—7.50% with a 30% LF and canal water These values showed a non-significant increase when compared (Figure 17). The similar observation was made for W5 treatment, which indicated the lowest total ash content of alfalfa indicating values of 5.65, 5.71 and 5.73% for normal mode and a LF with same water at 15 and 30%, respectively. The same values reached the level of 5.81 and 5.88% when the LF technique was performed with canal water at 15 and 30%, respectively.

4. Discussion

One of the most significant plant stresses among abiotic stresses is salinity, particularly in arid and semi-arid regions. Salinity can be defined as the amount of soluble salts present in soil or water. The quantity and quality of the plant’s yield can be negatively affected by salinity [41]. Sodium (Na⁺), calcium (Ca²⁺), magnesium (Mg²⁺), chloride (Cl⁻), sulfur (SO₄²⁻), and bicarbonate (HCO₃⁻) are the most important ions that play an essential role in salinity [42]. Three stages of alfalfa growth can be influenced by salinity; germination, seedling, and maturity stages [35] with germination being the most sensitive stage in this regard [43]. Possible reasons for the survival of alfalfa under salt stress include complex mechanisms such as photosynthesis, detoxification, production of antioxidants, secondary metabolism, and ion transport [44]. Salinity can reduce the photochemical activity of alfalfa due to its effect on the plant chlorophyll content [45]. The stability of the membrane and relative water content in plants can also be reduced due to salinity stress [46].

Plant height is a crucial factor that can contribute to crop yield. In this study, saline water irrigation with different strategies significantly affected height of alfalfa plants. However, plant height declined in the third year due to continuous salt accumulation as a result of saline water irrigation. On the other hand, fresh biomass is considered the main objective of fodder crop growth, but it was negatively affected by saline water irrigation in the current study. This can be due to the addition of salts that can negatively affect plant growth, and consequently can reduce fresh biomass. Nevertheless, coupling treatments of saline water with the LF technique and the canal water at 15% and 30% resulted in an improvement in plant fresh biomass in the current study. For example, the highest biomass was obtained from plants irrigated with W1 that was coupled with a 30% LF and canal water.

Alfalfa is considered moderately sensitive to salts, tolerating an EC level of up to 2 dS m⁻¹. Beyond this threshold, any increase in EC can result in a 7.3% decrease in the crop yield [47]. Consistently, our study showed a decline in alfalfa biomass over three years when plants were irrigated with saline water without effective leaching. The decrease in plant growth can be attributed to osmotic stress caused by the high salt content in water, making it difficult for plant roots to absorb water, thereby hindering plant growth. Similarly, the accumulation of salts in leaves can lead to leaf senescence, causing aged leaves to fall, reducing photosynthetic ability, and limiting food translocation to growing parts, ultimately restricting overall plant growth [48]. These results are also in accordance with the findings of some researchers [35,49,50,51] that reported a reduction in growth and biomass of alfalfa when grown under salt stress. The possible reason for the negative effect of high salinity levels on alfalfa growth and related parameters could be an increase in salt concentration due to continuous irrigation with saline water for three years. Ahmed et al. [20] also reported that long-term irrigation with saline water may lead to salt accumulation in the root zone, leading to reduced yield and deteriorating of natural soil resources.

The prolonged use of saline water for irrigation increases soil electrical conductivity [20]. Long-term saline water irrigation can lead to salt accumulation in the root zone, causing yield reduction and soil degradation [21]. To mitigate these effects, adopting appropriate management practices is crucial [22]. One effective technique is the use of leaching fraction, which maintains a balance between salt entering and leaving the root zone, preventing salt damage to crops [52]. Continuous saline water irrigation significantly damages roots and reduces their water uptake capacity. However, mixing saline water with good-quality water helps plants survive by keeping salt concentrations within tolerable limits [53,54]. This approach enables plants to maintain their water uptake capacity and reduces the risk of salt damage.

The increase in protein content in the current study may be attributed to a higher leaf-to-stem ratio caused by salinity as stated by Robinson et al. [55]. Plant leaves have a higher concentration of chlorophyll and nitrogen compared to stems [56]. Other researchers also reported similar results and suggested an increase in leaf to stem ratio as a result of irrigation with highly saline water being responsible for this increase in protein content [57,58]. On the other hand, the reduction in the fiber content could be a consequence of reduced growth due to stress caused by continuous salt buildup for three years in the current study.

5. Conclusions

Based on three years of agronomic, growth, and quality traits, it is concluded that: 1. Saline water irrigation negatively affected alfalfa plant growth. 2. Using the leaching fraction (LF) technique with the same quality of canal water can contribute to the mitigation of such negative effects. 3. Comparing 15% and 30% LF, the data were non-significant for both water types, consequently the single application of a 15% LF can be sufficient. 4. The negative impact intensified over time, particularly in the second and third years, as salt concentrations increased in the saline irrigation water. 5. Saline irrigation water negatively affected fodder quality traits such as crude protein (CP), crude fiber (CF), and ash content, with more pronounced effects in the third year during the current study. Therefore, based on three years of the current investigation, the leaching fraction technique is recommended for saline water irrigation in alfalfa fodder production.