Response of Three Barley Cultivars Hordeum vulgare L. to Water Stress Under Field Conditions

A field experiment was conducted in one of the agricultural fields located in the center of Hilla/Babylon, within latitude 32°31’ north and longitude 44°21’ east. During the season 2021-2022 in a soil with a loam silty texture. The aim of the study is to know the effect of water stress on the yield of green feed and grain and its components and the water use efficiency of the barley crop. A split-plot design with RCBD arrangement was used with three replicates. The irrigation treatments that include the comparison treatment (50% depletion of the available water) were occupied and three water depletion treatments (40, 60, 80%) of the amount of water for the control treatment, the main plot, while the cultivars occupied subplot No significant differences appeared between the control treatment and the irrigation treatment, 80% of the control treatment in the yield of green feed and grains, and thus it was possible to save water by 20% without a significant decrease from the control treatment. The irrigation treatments 80 and 60% showed higher efficiency in using water for grain production than the control treatment. The cultivars showed significant differences in yield, as Bohouth 244 gave the highest yield of feed and grain, and it did not differ significantly from cultivar IPA 99. Also, Bohouth 244 showed the best water use efficiency to produce a larger amount of grain, and it did not differ significantly from IPA 99.


Introduction
Barley (Hordeum vulgare L.) is the most important winter feed grain crop in Iraq, where it is used as green feed and for the production of seeds that are used in the manufacture of concentrated feed for large animals and birds.Its seeds are also used in the manufacture of malt and brown bread.Barley is widely grown in developing countries in arid and semi-arid regions, so drought is the most important determinant of crop production in these regions [1].These areas suffer from wide changes in the conditions of the environment and climate and wide changes in the forms of drought in the soil or the atmosphere, In such conditions, productivity and water use efficiency decrease [2].The irrigation process currently used is characterized by randomness in the number of irrigations and in the amount of water added in each irrigation, which was reflected in the decrease in irrigation efficiency as a result of losses, whether by evaporation or infiltration.From here, the importance of the irrigation scheduling process and the study of water consumption becomes clear in order to secure the actual water needs during the growth stages and with a minimum amount of waste, either by giving small amounts of water to moisturize the root zone and thus reduce the number of irrigations or irrigation in critical stages [3].Which will increase the efficiency of water use and enable us to determine the number of actual irrigations that the crop needs to produce the best yield.Grain yield has increased in the past forty years without a significant increase in evaporation-transpiration. That is, the crop management factors that work to reduce growth constraints under conditions of water shortage were appropriate, which increased the efficiency of the crop in the use of water and nutrients [4].Thus, the yield increased.In view of the importance of the barley crop and the lack of studies on water stress, the idea of this study came as an attempt to search for ways to reduce the water consumption of the crop and then reduce the quantities of water.The study also went to test the ability of some cultivars to bear the shortage of irrigation water, determine their efficiency in using water, and study the components of their yield.To find out which cultivars are relatively stable in yield under these conditions.

Materials and Methods
This experiment was applied in a farmer's field in the center of Hilla district / Babylon during the season 2021-2022.For the purpose of studying the irrigation water shortage in green feed yield, grain yield and its components, water consumption and water use efficiency of three barley cultivars, Hordeum vulgare L. The split-plot design was used in the randomized complete block design(RCBD) arrangement with three replicates.The irrigation treatments occupied the main plot and were given the Symbol S1, S2, S3, S4, which is the control treatment (50% of the available water drained) and irrigation by 40,60,80% of the amount of water for the control treatment.While the cultivars were occupied by Bohouth 244, IPA 99, Samir )occupied the secondary treatments.The seeds were sown on 28/11/2021, with a seeding rate of 120 kg ha -1 .The experimental land was divided into sub plot, each area (3 x 3 m), which included 10 lines of 3 m in length for each line, with a planting distance of 20 cm between the lines, and the distance between the experimental units 1 m.A separation distance of 2 m was left between the main treatments and the replicates to prevent water leakage between the plots.The experimental land was fertilized according to the recommendations.The crop was harvested on May 1, 2022.The relationship between the structural tension of the soil sample taken from a depth of 0-40 cm and sifted with a sieve with a diameter of 2 mm and the moisture content for the purpose of estimating the water-holding capacity of the soil was estimated.(Figure 1).The available water content of the soil was calculated from the difference in the volumetric moisture content at the field capacity and wilting point.The moisture content of the soil was monitored by taking samples continuously from different depths to be dried in an electric oven at a temperature of 105 °C for 24 hours, and the moisture content was extracted according to the equation contained in [5].
Since Pw = weight percent moisture Msw = mass of soil when wet Ms = mass of soil dry The irrigation process was repeated after depleting 50% of the available water to a depth of 0.40 m.An amount of water was added to restore moisture to the field capacity and for each experimental unit according to Kohnke's equation.
w Pw = Percentage of soil moisture before irrigation.D = the depth of the soil to be irrigated in meters Seasonal water use.Seasonal water use was calculated for a depth of 40 cm from the following equation [7].

ET= I+R+∑((P w1 -P w2 )/100)×lb×D
As: ET = seasonal water use (mm).I = total irrigation added (mm).R = rainfall (mm) and its amount was 60.31 mm during the growing season.P W1 = Moisture percentage by weight at the beginning of the season at the irrigated layer.P W2 = Percentage of moisture by weight at the end of the season at the irrigated layer.lb = bulk density (mcg.m -3 ).D = soil depth (cm).The irrigation process was conducted when 50% of the available water was drained to a depth of 40 cm, and the quantities of water per irrigation for treatments S1, S2, S3, and S4 were 384, 269, 230,154 liters per experimental unit, .Irrigation was done using plastic tubes connected to a diesel pump, and a counter was installed on the tube To measure the water passing through the pipe in liters

Studied Traits
 Green feed yield: the plants were stuffed when they reached a height of 40 cm and then left to form grains.  Number of spikes /m -2 : calculated by randomly harvesting one line from the guarded middle lines. The number of grains per spike: it was calculated from the average of 10 spikes taken randomly from the experimental unit. Weight of 1000 grains (g): A thousand grains were taken randomly from the grain yield of each secondary experimental unit and weighed with a sensitive scale to represent the weight of a thousand grains, then returned to the yield. Grain yield, ton ha -1 : It was calculated by harvesting three median lines with a length of 3 m, then converted to ton.ha -1 .The water use efficiency of the grain yield was estimated according to the equation [8].
WUE g = GY/ET WUE = water use efficiency.GY = grain yield.ET = total water use (mm).An analysis of variance was conducted for the studied traits according to the analysis of variance method and using the least significant difference at a significant level of 0.05 [9].

Yield of Green Feed ton ha -1
The results in Table (1) showed that there were significant differences for this traits according to the irrigation water treatments and cultivars.The highest average green feed yield in treatment S1 was 18.56 tons ha -1 and did not differ significantly from S2, while irrigation treatment S4 gave the lowest average that reached 8.38 tons.ha -1 .The decrease in the yield of green feed under conditions of water stress can be due to the closure of stomata, which leads to a reduction in the diffusion of CO 2 gas, which is followed by a decrease in the photosynthesis process, so the percentage of dry matter produced from the leaves decreases, and thus a decrease in the yield of green feed.These results confirmed the findings of [10,11], that water stress and drought reduced feed yield.The cultivars showed a significant difference in this trait, as bohouth 244 cultivar gave the highest average for this trait amounted to 15.07 ton ha -1 and did not differ significantly from IPA 99, and Samir gave the lowest average of 13.43 ton ha -1 .These results agree with [10], who found that cultivars differed in green feed yield due to the difference in their genetic ability to produce tillers.Table 1.Effect of irrigation water quantities and cultivars on green feed yield, ton ha -1 .

The Number of spikes.m -2
The results in Table (2) show that the irrigation treatment S1 (control treatment) gave the highest average number of spikes m -2 , amounting to 522.10 spikes m -2 , while treatment 4S gave the lowest average of 440.36 spikes m -2, and it did not differ significantly from S2 and 3S.water for S4 treatment This led to a decrease in the photosynthesis products as a result of the decrease in the leaf area, which led to a competition between the stem, which began with rapid elongation, and the production of shoots, as well as between the shoots themselves over these products, which led to reducing the chance of their survival and reaching the stage of the beginning of chaff formation.As the cuttings that do not reach this stage do not have a great chance of bearing spikes [12], in addition to that the lack of water reduced the number of buds formed on the stem nodes below the soil surface, which was reflected negatively on the number of cuttings, and then the number of spikes per unit area.These results are consistent with what was found by [1,[13][14][15], that exposure of barley plants to water stress in the preflowering stages leads to a decrease in the number of spikes per unit area.The cultivars also showed a significant difference in the number of spikes.The cultivar IPA 99 excelled by producing the highest number of m -2 spikes, with an average of 485.59 m -2 spikes, while the bohouth 244 cultivar gave the lowest number of spikes.m - .Their exposure to water stress, as well as due to the difference in their ability to produce representative materials that support the shoots to turn them into fertile tillers bearing spikes.These results agree with [14,16,17], who indicated that cultivars with a high ability to tillering have the ability to produce more number of spikes of low-tillering cultivars.

The Number of Grains spike -1
This traits was significantly affected by the different irrigation water treatments.The irrigation treatment S1 (control treatment) gave the highest average number of grains per spike, amounting to 54.29 grains.spike - which did not differ significantly from 4S (Table 3).The reason for the decrease in the number of grains in the spike in the treatments that were exposed to water deficiency may be due to the fact that water stress led to a decrease in photosynthesis outputs in plants exposed to stress, which increased the competition between the main stem that undergoes a rapid elongation stage with the formation of indentations of spikelets, and this led to a decrease in their number and less The number of grains formed.The reason may also be due to the occurrence of water stress in the late growth stages of elongation and in the endothelium phase, which will affect the growth of florets in the spikelets, which may cause abortion of the florets.And that the maximum number of spikelets in barley is determined at the stage of emergence of spikelets that precedes the emergence of the flag leaf from ZGS30 to ZGS37 [18].These results are consistent with [19,20], who noted that the decrease in photosynthetic rate due to drought or shading during the stages before flowering is related to a decrease in the number of grains in the spike [21,22] that water stress reduces the number of grains in the spike.The results showed that there were significant differences between the cultivars in this trait, as the bohouth 244 cultivar gave the highest average of 58.99 grain.spikes - , while the Samir cultivar gave the lowest average of 44.16 grain.spikes - .This may be due to the fact that bohouth 244 gave the lowest number of spikes.m2, which contributed to an increase in the number of grains per spike (Table 3, 2).Table 3.Effect of irrigation water quantities and cultivars on the number of grains of spike -1 .

Weight of 1000 grain (g)
The results of Table (4) show that there are significant differences for this characteristic according to the irrigation water treatments and cultivars.The highest average weight of 1000 grains in the S2 treatment reached 38.64 g, while the S4 treatment gave the lowest average weight of 36.64 g.The reason for the decrease is due to the short duration of the grain filling, as well as to the rapid drying of the leaves and stem, which was accompanied by the lack of water, which reduced the dry matter accumulated in the grain due to the reduction in the length of the photosynthesis of the flag leaf, which is the basis for supplying the grain with the representative materials.[23], indicated that 61-81% of the variation in grain yield was due to the efficiency and length of photosynthesis of the flag leaf.These results are consistent with what was shown by a number of researchers that lack of water and high temperature lead to a shorter period of grain filling, which is negatively reflected in its weight.That reducing irrigation water quantities led to a significant decrease in grain weight.The cultivars showed a significant difference in grain weight, as bohouth 244 gave the highest average of 38.47 g for this trait, while IPA 99 gave the lowest average of 36.41 g.The decrease in the number of spikes in the bohouth 244 resulted in an increase in grain weight according to the principle of compensation in the components of the crop (Table 4, 2).These results agree with [24], who found that the genotypes of wheat differed in the grain weight traits.
Table 4. Effect of irrigation water quantities and cultivars on an average of 1000 grains (gm).

Grain Yield (ton ha -1 )
The quantities of irrigation water significantly affected the grain yield, Table (5), as the irrigation treatment S1 (control treatment) gave an average of 6.56 tons ha -1 It did not differ significantly from the irrigation treatment S2, while the yield decreased significantly by 4.6 and 30.0%for the quantities of irrigation water S3 and S4, respectively, compared with the complete irrigation treatment S1.The decrease in yield when reducing the amount of irrigation is attributed to a decrease in one or more of the components of the yield.The decrease in the number of spikes (Table 2), the number of grains per spike (Table 3), and the weight of 1000 grains (Table 4) are all reasons for this.This result agrees with [1], who emphasized the necessity of Irrigation during the period of grain saturation to ensure optimum productivity and [25], confirmed that water stress caused a decrease in grain yield and that this is related to the growth stage in which the plant goes through and that the effect was more on the reproductive stages than on the vegetative stages.Significant differences appeared between the cultivars in grain yield, as Bohouth 244 gave the highest yield of 6.07 tons ha -1 , and it did not differ significantly from IPA 99, and its excelled is due to the fact that it gave the highest number of grains per spike and weight of 1000 grains.
Table 5.Effect of irrigation water quantities and cultivars on grain yield (tons ha -1 ).

Total Water Consumption
The data of Table (6) shows that the water consumption in control treatment S1 was the highest, reaching 367.51 mm in the season.As the percentage of moisture in it was closest to the field capacity, which increased the amount of water lost through evaporation and transpiration.These results agree with [26], who indicated an increase in water consumption in the control treatment (when 50% of the available water was drained).The values of water consumption decreased with a decrease in the amounts of irrigation water.Despite this, the irrigation treatment S2 (irrigation by 80% of the control treatment) gave a grain yield that did not differ significantly from the yield of the treatment S1 (the control treatment), in addition to an increase in the efficiency of water consumption by 18.7% and a decrease in Grain yield was insignificantly increased by 2% compared to the control treatment (irrigation when 50% of the field capacity was depleted).While the percentage of decrease in grain yield for irrigation treatments S3 and S4 was (11.7 and 30%).From this it is clear that it is possible to provide 20% of the full irrigation needs without affecting the grain yield in treatment S2.These results agree with what was shown by [2], that the addition of 50% of the full irrigation needs led to a decrease in yield by 10%.Irrigation by 50% of the available water.Table 6.Shows the number of irrigations, the depth of water added (mm), the amount of water used, and the efficiency of water use for irrigation water quantities during the growing season.

Water Use Efficiency for Grain Yield
The treatments of irrigation water quantities and cultivars significantly affected the water use efficiency of grain yield (Table 7).Irrigation treatment S4 gave the highest average water use efficiency of 3.13 kg m -3 , while irrigation treatment S1 gave the lowest average of 1.78 kg m -3 for this traits.The reason for the high water use efficiency in S4 is that the decrease in the quantities of added water constituted a greater percentage of the decrease in grain yield, in addition to the conditions of the beginning of the season in the vegetative growth stage of high relative humidity and the availability of rain.Low temperatures and wind speed helped the plant to form a dry substance that mainly contributed to filling the grain during the period of rain interruption in the flowering and filling stage of the grain, which was accompanied by a decrease in air humidity and an increase in temperature and wind speed.As for the low water use efficiency in S1, it came as a result of increased evaporation-transpiration, especially under conditions of high temperatures and low relative humidity, which led to low water use efficiency even at high irrigation levels.An increase in the amount of water may not always be reflected in an increase in grain yield [1].The results also showed that there were significant differences between the cultivars in the efficiency of water use, where the cultivar Bohouth 244 gave the highest average of 2.51 kg m -3 and did not differ significantly from the cultivar IPA 99, while the cultivar Samir gave the lowest water use efficiency by 2.34 kg.m -3 due to the excelled of the two cultivars.These results agree with what was found by [27,28], regarding the emergence of differences between wheat cultivars in water use efficiency with different irrigation levels.

Conclusion
 The seasonal water consumption of the barley crop was about 367.51 mm distributed over 8 irrigations per season, which produced the maximum grain yield under full irrigation conditions (depletion of 50% of the available water) amounting to 6.56 tons -1 . The possibility of providing 20% of the total irrigation needs without a significant decrease in grain yield.It is possible to use this amount of water to cultivate a larger area when the amount of water is a determining factor. The S1 treatment gave the highest yield of green feed, amounting to 18.56 tons ha -1 , and it did not differ significantly from the treatment S2, and the cultivar bohouth 244 was superior in the yield of green feed, as it gave 15.07 tons ha -1 , and it did not differ significantly from the cultivar IPA99. It was also found that Bohouth 244 gave the highest grain yield and water use efficiency and did not differ significantly from IPA 99.

Figure 1 .
Figure 1.Moisture description curve for field soil.

Table 2 .
Effect of irrigation water quantities and cultivars on the number of spikes/m -2 .

Table 7 .
Effect of irrigation water quantities and cultivars on water use efficiency of grain yield kg.m -3 .