Introduction

Alfalfa (Medicago sativa L.), of the Fabaceae family, ranks as one of the most significant perennial plants and forage crops around the world1 owing to its capacity to yield abundant green forage protein and plentiful nutrients, which support animal growth and productivity. Qualitatively and quantitatively hay and silage are prepared out of, it has been name “ The king of Fodder” due to its never-ending ability throughout the years 3-4) the time growth period so, in soil just spill out (cruise) for longer or shorter from it depending on the agricultural environment situation which placed with.

Iraq is suffering from a worrying situation about the water scarcity after some of its waters in the Tigris and Euphrates rivers as well as their joints have been reduced due to building dam by neighboring countries, on one hand, and global warming that faces all the world, on the other. The best use of water is very important to manage the number of days between an irrigation and the other according to its stage of growth in order to get a maximum yield. Moreover, water plays a crucial role in the plant body as it acts as a vehicle for nutritive and diluted materials and also facilitates energy transfer required for the process of carbon metabolism involved in the synthesis of organic food, as well as serving to regulate plant temperature [1]. The spread of the root system at its front also depends on water distribution in the soil surface layer, which subsequently affects growth of stem, leaves as well as other organs [2]. This variation in moisture tension at the vicinity of the plant root-system, causes variations on the growth of plants in response to differences in internal differences on this tension [3].

The concept of the inhibition of apical dominance was first developed with growth retardants which provoke or induce one of those processes when applied to appropriate concentrations. Growth regulators of different types are applied, including Ethephon, which has a suppressive effect on growth and controls the source sink relationship by destruction of metabolic products [4] . It decreases the cellular elongation and cell division because of sub-apical meristem region, thus reduce the main stem elongation and reduce vegetative plant. In addition, It is acting as an antagonist for auxins in stem tissues thereby having important role to manage the equilibrium of distribution pattern of photosynthesis products between the source and the sink which gives more yield 5, since plant growth and formation are not happening randomly, there are regulate hormone in plants work to balance source/sink ratio in transfer photosynthesis materials happen and they working on make canopy architecture of plant also influence with rate grow, that make plant feel its environment then interact with it tell be state balance between available factor for grow plant essential water or genetic factor born with it automatic i.e., of course other non-genetic factors but that have huge rule. The removal of apical dominance is associated with the activation of lateral buds and an increase in leaf area, which increases light interception, leads to a higher efficiency for CO(2) assimilation and more accumulation as well. The objective of the current study was to evaluate growth, green forage yield (GFY), and quality of alfalfa under various irrigation intervals and ethephon spray concentrations.(Medicago sativa L.).

Materials and Methods

A field experiment was conducted during the winter season of 2022-2023 in Basra Governorate at the Agricultural Research Station affiliated with the College of Agriculture, University of Basra (Karmat Ali site, University of Basra) in a loamy-textured soil. The study aims to know the effect of irrigation periods and ethephon spray concentrations on the growth, green forage yield, and quality of alfalfa (Medicago sativa L.). The experiment was conducted as a factorial experiment using a randomized complete block design (RCBD) with three replicates. The different factorial treatments were randomly distributed within each block, resulting in a total of 27 experimental units (3 x 3 x 3).

The experiment included two factors: the first factor was three irrigation periods (5, 10, and 15 days), symbolized I1, I2, and I3. The second factor was three ethephon concentrations (0, 0.5, and 1) ml L^-1, symbolized E1, E2, and E3.

A composite sample was also taken from different locations in each replicate from a depth of (0-30 cm), and mixed together. Chemical and physical analyses were carried out on the soil as shown in (Table 1).

Figure 1. Table (1): Shows the physical and chemical characteristics of the study field before planting

The experimental land was harrowed and leveled, then divided then divided into three blocks according to the design used, which were then divided into panels measuring (1.5 x 2). The experimental unit area was 3 m², and each sector contained nine experimental units a distance of 1.5 meters was left between each sector.

Planting was carried out in mid-October using the broadcasting method and after which the seeds were covered with a thin soil layer. An initial irrigation was applied for germination, while subsequent irrigations were carried out according to the experimental treatments.Harvesting was carried out based on reaching a flowering rate of 20-22%. This is because harvesting at this stage produces the highest quantity of green forage yield and the best quality, in addition to maintaining the vitality and ability of the plants to regrow from the crown buds in the subsequent stage.

The data were analyzed statistically using the GenStat program, and the averages were compared according to the least significant difference method at the 0.05% level, as stated in [7] . The following traits were measured:

2.1. Plant height (cm):

plant height was measured from the soil surface to the end of the stem for ten random plants from each experimental unit. After that the average plant height for each experimental unit was measured.

2.2. Number of branches (branch m ^{- 2} ) :

It was measured randomly by harvesting 0.5 m2 of each experimental unit and converted to square meters.

2.3. Green forage yield (tons ha⁻¹):

green forage yield was measured from a random 0.5 m2 harvest for each experimental unit. The sample was weighed directly using an automated balance and converted tons ha⁻¹.

2.4. Dry forage yield (tons ha⁻¹):

Dry forage yield (tons ha⁻¹) = Green forage yield (tons ha⁻¹) × % dry matter.

2.5. protein percentage in leaves ( %):

= percentage of Nitrogen x 6.25 [8]

2.6. protein yield (tons ha⁻ ¹ ) : was calculated using this formula:

Protein yield = % protein × dry forage yield (tons ha⁻¹)

Results and discussion

3.1. plant height (cm):

The increase in the Ethophon concentrations (shown in table 1) significantly affected the plant height by reducing it in alfalfa. Plants treated with E₃ concentrations recorded the lowest average of 43.78 cm, compared to E₂ treatment which recorded the highest average of 65.11 cm. The decreased rate of 32.75% might be attributed to the action of ethylene released from Ethophon in the plant tissues that specially functions to decrease the auxin rate, reduces its transport, or binds it to other compounds, in order to make it bound. This results in reduced height, as the hormone responsible for apical dominance.

Table (1) shows how the irrigation treatment I recorded the highest average plant height of 55.00 cm. Meanwhile, the irrigation treatment I₃ recorded the lowest height average of alfalfa (52.06 cm). This reduction of plant height might be attributed to water stress, which likely reduced the natural auxin levels that are responsible for cell elongation, thus affecting plant height. These results are consistent with those reported by [9] [10].

Figure 2. Table (1) effect of irrigation Intervals Ethophon spray concentration and their interaction on plant height (cm)

3.2. Number of branches ( branche m ^-2 )

Table 2 shows that the spraying treatment E₂ achieved the highest mean for number of branches per square meter amounting to 434.22 branches m^-2, while E₁ recorded the lowest mean of 400.67 branches m^-2, which did not differ significantly from the spraying treatment E₃, with an increase percentage of 8.37%.

Figure 3. Table (2) The effect of irrigation Intervals, ethephon spray concentrations, and their interaction on the number of branches m^-2

The reason for that is that spraying with ethephon stimulates the emergence of branches after its application as a result of the occurrence of a state of hormonal balance, as the released ethylene works on hindering the biosynthesis of auxin and inhibiting its movement in the stem tissues, which increased the proportion of cytokinin, so the growth of branch buds was stimulated. These results agree with [11] .

The irrigation treatments differed significantly among themselves in this trait (Table 2), as the irrigation treatment I₂ gave the highest mean for number of branches (435.67 branches), while the irrigation treatment I₃ recorded the lowest mean for number of branches amounting to 389.78 branches, and the reason for the decrease in number of branches is attributed to the decrease in vegetative growth represented by plant height, which leads to inhibition of the photosynthesis process and thus affects the number of branches.

As for the interaction, Table 2 shows the superiority of irrigation treatment I₂ with ethephon spray concentration E₂ over most interactions, recording the highest mean for number of branches amounting to 455.00 branches m⁻², while the interaction between irrigation treatment I₃ and ethephon concentration E₁ gave the lowest mean for number of branches amounting to 365.67 branches.

3.3. Green forage yield (tons ha ^-1 )

Table 3 shows that ethephon spray concentration E₂ achieved the highest green forage yield amounting to 14.91 tons ha^-1, surpassing the other concentrations with an increased percentage of 51.83% compared with E₃. The reason for that is its superiority in number of branches and plant height, which has the greatest effect in increasing green forage yield [12] [13].

Figure 4. Table (3) The effect of irrigation intervals, ethephon spray concentrations, and their interaction on the green forage yield (tons ha^-1)

And this is confirmed by the highly significant correlation values between green forage yield and plant height and number of branches (r = 0.4112* and r = 0.6535**, respectively) (Table 7). The table also shows the presence of a significant decrease in forage yield with the increase of irrigation intervals, as irrigation treatment I₃ recorded the lowest mean for forage yield amounting to 11.14 tons compared with the other irrigation treatments with a decrease percentage of 19.16, Table 3 shows the significant effect of the interaction between ethephon spray concentrations and irrigation treatments in green forage yield, as concentration E₂ under irrigation treatment I₂ achieved the highest mean for forage yield amounting to 17.55 tons ha^-1.

3.4. Dry forage yield (tons ha ^-1 )

The results of Table 4 show that ethephon spray concentration E₂ achieved the highest dry forage yield with a mean of 5.14 Mg, surpassing significantly the other concentrations with an increase percentage of 51.62% compared with concentration E₃, which recorded the lowest mean of 3.39 tons for dry forage yield.

Figure 5. Table (4) The effect of irrigation intervals, ethephon spray concentrations, and the interaction between them on the dry forage yield (tons ha^-1)

The reason for that is its superiority in increasing green forage yield, and these results are confirmed by the highly significant correlation values between dry forage yield with each of green forage yield, number of branches, and plant height (r = 1.0000, r = 0.6535, and r = 0.4112*, respectively) (Table 7). The table also shows a significant superiority in dry forage yield under irrigation treatment I₂, as it recorded the highest mean for forage yield amounting to 4.75 tons compared with the other irrigation treatments, with an increase percentage of 23.70% over duration I3, which recorded the lowest mean amounting to 3.84 tons' ha⁻¹, and this agrees with what was reached by [14]. As for the effect of the interaction, Table 4 shows that ethephon spray concentration E₂ under irrigation treatment I₂ gave the highest mean for dry forage yield 6.05 tons' ha⁻¹, while ethephon spray concentration E₃ under irrigation treatment I₃ gave the lowest mean amounting to 2.76 tons ha^-1.

3.5. protein percentage%

Table 5 indicates the significant effect of ethephon spray concentrations. E2 achieved the highest protein percentage in the plant, amounting to 21.23%, compared to E₃, which recorded the lowest average protein percentage, amounting to 18.48%. This is due to the role of ethephon, when sprayed at the appropriate concentration, in protein synthesis by controlling RNA synthesis and the production of some protein enzymes, thus increasing the protein percentage.

Figure 6. Table (5) Effect of irrigation Intervals, ethephon concentrations and their interaction on the protein percentage.

These results are also supported by the highly significant correlation values ​​between protein percentage and dry forage yield (r = 0.6920**) (Table 7). This is consistent with the findings of [15][16] The table also shows a significant effect on protein percentage, as the I₂ irrigation treatment recorded the highest average protein percentage, amounting to 20.68%, compared to the other irrigation durations, and an increase of 20% over the irrigation treatment, which recorded the lowest average, amounting to 17.23%. Table 5 shows the effect of the interaction between ethephon spray concentrations and irrigation treatments on the protein percentage. Concentration E₂ with irrigation treatment I₂ achieved the highest percentage of 24.07%, while the lowest percentage was recorded when interacting between concentration E₁ and irrigation treatment I₃, reaching 16.63%, which did not differ significantly from the interaction between E₃ and irrigation treatment I₃, which gave 17.10%.

3.6. protein yield (tons h^-1)

E₂ concentration significantly outperformed the other concentrations, yielding 1.107 tons h^-1, while E₃ concentration yielded a lower average of 0.632 tons ha^-1. This may be due to the superiority of E₂ concentration in dry feed yield (Table 4) and protein percentage (Table 5). These results are confirmed by the correlation values ​​between protein yield and dry feed yield (r = 0.9459) and between protein yield and protein percentage (r = 0.8797).

Figure 7. Table (6) Effect of irrigation intervals, ethephon concentrations and their interaction on crude protein yield (tons h^-1)

Irrigation treatments differed significantly in protein yield, with irrigation treatment I₂ yielding the highest average of 1.008 tons ha^-1, a 51.67% increase over the other irrigation treatments, in which irrigation treatment I₃ recorded the lowest average protein yield of 0.664 tons ha^-1. Table 6 shows the significant effect of the interaction between spray concentrations and irrigation treatments on protein yield. Concentration E₂ with irrigation treatment I₂ achieved the highest average protein yield of 1.459 tons ha^-1, while concentration E₃ and irrigation treatment I₃ gave the lowest average of 0.470 tons ha^-1.

conclusion

In conclusion, ethephon was effective in increasing the number of branches, green and dry forage yield, protein percentage, and protein yield. The most important stage for spraying ethephon is the beginning of flowering, as it yielded significant results for most of the study traits. Variations in irrigation treatments also yielded excellent results for growth traits, yield, and protein percentage. Therefore, we recommend spraying ethephon at a concentration of 1 ml per liter at the beginning of flowering to give encouraging results for yield

Figure 8. Table (7) Correlation among the studied traits