Response Water Productivity and Sorghum Yield to Deficit Irrigation Under Surface Drip Irrigation System

A field experiment was conducted during the spring season of 2022 in a clay loam soil at the experimental station of the College of Agricultural Engineering Sciences, University of Baghdad - Al-Jadriya, in order to study the effect of deficit irrigation on the growth and productivity of Sorghum, using the surface drip irrigation system, the experiment included irrigation treatments with six levels of full irrigation treatment FI100 When 50% of the available water is depleted, it is compensated by the American evaporation basin class A, from which the deficit irrigation treatments 80, 70, 60, 50, and 40% of the complete irrigation were applied, using the RCBD with three replications. The treatments were applied during the included plant growth stages (vegetative growth, flowering and maturity). Crop growth indicators were measured at the end of the season. Sorghum seeds were sown on 3-13-2022 and harvested on 7-15-2022. The results showed that the seasonal water consumption of corn reached its highest value when the full irrigation treatment was 487.24 mm when 50% of the available water was depleted, then it decreased to 413.59, 376.94, 340.29, 303.63, and 266.98 mm for the deficit irrigation treatments (80, 70, 60, 50, and 40%) calculated from the control treatment (FI%100). Irrigation treatment (FI 100%) gave the highest values for average plant height, leaf area, chlorophyll content, total root dry weight and yield. Water consumption amounted to 413.59 and 376.94 mm compared to the full irrigation treatment, while the treatments (60, 50 and 40) % of the full irrigation were superior in that they saved an amount of water at the expense of low crop productivity. The highest water productivity was recorded at two irrigation treatments minus 80 and 70% for the Sorghum bicolorcrop. It amounted to 13.71 and 15.13 kg m3, as the lack of 20 and 30% of the irrigation water did not affect the productivity. It is recommended to irrigate at a rate of 80 and 70% of the total ETa, which indicates the possibility of providing 20 and 30% of the full irrigation needs without affecting the grain yield.


Introduction
The Arab region is one of the regions most exposed to water shortage in the world and is experiencing very great pressures in terms of the availability of fresh water.The use of water on a global scale has increased sixfold over the past 100 years and is still growing at a rate of 1% per annum due to population growth, economic development and change.Consumption patterns.[1] The situation will be exacerbated in areas currently experiencing water stress due to climate change, which is associated 1259 (2023) 012029 IOP Publishing doi:10.1088/1755-1315/1259/1/012029 2 with irregular and uncertain water supplies.Climate change will affect the availability, quality and quantity of water to meet basic human needs.Hydrological changes caused by climate change will increase the difficulties associated with the sustainable management of water resources, which are already under severe pressure in many regions of the world.Water quality will be negatively affected by high water temperatures and low dissolved oxygen.The risk of water pollution and disease-causing contamination from floods or high concentrations of pollutants during droughts also increases.Climate change will also generate water stress in areas where water and other resources are still present.Physical scarcity of water is often a seasonal rather than a chronic phenomenon, and climate change is likely to cause shifts in the seasonal availability of water throughout the year in many places [2].The continuous availability of water is critical to daily life and sustainable societies.Being the basis of economic growth, food security, poverty alleviation, energy security, conflict resolution, biodiversity loss, and adaptation to climate change depends on water.Iraq is a developing country located in an arid to semi-arid region, and it is one of the most vulnerable countries in the Middle East to climate change.Iraq faces a water shortage that is likely to grow in the future as a result of the impact of several causes including climate change, the oil industry, urbanization, and the high rate of population growth.Deficit irrigation is economically feasible and justified in the case of limited water resources, as it is the process of adding irrigation water on a regular and studied basis at a level less than the optimum water needs of crops, in order to increase the efficiency of using water allocated for irrigation to obtain the highest productivity per water unit, by exposing crops to a level a certain amount of water stress during a particular period of the season or during the entire season [3].Sorghum bicolar L. is one of the important grain crops belonging to the Poaceae family and grown in arid and semi-arid regions.It is classified as the fifth major cereal crop globally.Its grains are used as a food source for humans in some poor countries, were feed for animals, pastures, fiber, fuel, bioethanol, alcoholic beverages, as well as building materials [4].The aim of study to find the effect of deficit irrigation on water productivity and sorghum yield under surface drip irrigation system.

Materials and Methods
A field experiment was conducted during the spring season of 2022, at the Experimental Station of the College of Agricultural Engineering Sciences, University of Baghdad _ Al-Jadriya (Station F, located at latitude 16 `28` 33 °N, and longitude `25` 23` 44° E, and at an altitude of 34 meters above sea level, the soils were morphologically described and classified into sub-major aggregates according to Topic Torrifluvent [5].Soil samples were taken from the soil at a depth of 0-0.30 m, and 0.30-0.60m air dried, and passed through a sieve with an opening diameter of 2 mm to determine some physical and chemical properties according to standard methods [6].(Table 1).

Experiment Treatments and Statistical Design
 Fill Irrigation 100% treatment (control treatment) when 50% of the available water is depleted and compensated in terms of the cumulative evaporation from the evaporation basin class A, from which the incomplete irrigation parameters are calculated. FI 80% of the full irrigation treatment. FI 70% of the full irrigation treatment. FI 60% of the full irrigation treatment. FI 50% of the full irrigation treatment. FI 40% of the full irrigation treatment.With three replicates, the Randomized Complete Block Design (RCBD) was used.The experiment was conducted on a land area of 1000 m 2 , its dimensions are 25 m 2 × 40 m 2 , and the land was plowed with a perpendicular plow, and the smoothing operations were conducted using the rotary hoes.The area for each experimental unit was (5m × 6m = 30m 2 ), and the distance between the experimental units was 1.5m 2 .The field was divided into three blocks, and the distance between block was 2m 2 , and the sector was divided into six experimental units representing irrigation levels.Irrigation water samples were taken to determine the chemical properties of this water, which are shown in Table (2) according to the FAO classification of irrigation water [7].

----SAR
The seeds of the Sorghum bicolor crop (Enqaz) were sown on 3/13/2022, the distance between one line was 75.7 cm, at a rate of seven lines per experimental unit.The distance between plant was 20 cm.The experimental land was fertilized with triple superphosphate fertilizer at planting (30% P) according to the fertilizer recommendation of 70 kg P ha -1 .I added urea fertilizer (25 %N), according to the fertilizer recommendation, 320 kg N ha -1 , in two times, the first after 20 days of planting and the second after 32 days of the first batch.Potassium sulfate fertilizer was added in two batches, the first after 03 days of emergence and the second after 40 days of the first times, according to Fertilizer potassium treatments 83 kg Kha -1 [8].Weed control was coundected by manual weeding whenever needed, and the corn stalk borer, Sesamia cretica, was controlled with diazinon granular 10% effective substance, 6 kg diazinon ha -1 , by pruning the growing top, for two times, the first as a preventive control in the stage of 4-5 leaves, and the second after 15 years.days from the first control [9].The crop was harvested manually on 7/15/2022.

Crop Growth Indicators
 Plant height (cm): The plant height was measured at the stage of physiological maturity for each treatment, starting from the point of contact of the stem with the soil up to the top of the head with a measuring tape [10]. Leaf area (cm 2 ): The leafy area of ten randomly selected plants was measured at the end of the season through the following equation [11]: The length of the fourth leaves × its maximum width × 6.18  Dry weight of root system (g plant -1 ): The weight of the roots was calculated for ten plants for each experimental unit at the harvesting stage after drying them in the electric oven at 65°C until the weight stabilized. Estimation of the chlorophyll content in the leaves: The chlorophyll content in the leaves of the sorghum plant was estimated as an average of six plants for the experimental unit, as the readings were taken for the fourth leaf of each plant from the top using a chlorophyll meter of the type 50-SPAD [12]. Grain yield (ton ha -1 ): Ten fifteen plants were harvested from each experimental unit at the stage of full maturity of the crop, and after separating, drying and discharging the grain according to the dry weight of the grain after adjusting the weight on the basis of 15.5% moisture and the amount of the total production.

Water Yield (kg m -3 )
Water use efficiency was calculated using the equation [13].

Plant Height (cm)
Figure (1) shows the effect of deficit irrigation levels on the average plant height measured at the end of the season, which amounted to 132.43 cm when the full irrigation treatment was FI 100 (%).While the deficit irrigation treatments gave 70, 60, 50, and 40% highly significant differences, the average plant heigh was 126.24, 116.82, 101.03, and 98. .31cm, with decrease rates of 4.90, 13.37, 31.08, and 34.71%, respectively, for the full irrigation treatment (100%).The deficit irrigation treatment, FI80%, did not differ significantly from the full irrigation treatment, as the average plant height was 130.31cm.

Root Dry Reight (g)
The results shown in Figure (3) showed the effect of deficit irrigation on the average dry weight of the root system, as the highest average root dry weight was 277.73 g for the control treatment (100% FI) and 272.82 and 269.06 g for the 08 and 70% incomplete irrigation treatments, which did not differ significantly compared to the irrigation treatment.The irrigation treatments of 60, 50, and 40%, which showed high significant differences in root weight, where the average dry weight decreased by 229.85, 296.66, and 298.24%, compared to the full irrigation treatment, to reach 84.2, 70.12, and 69.74 g, respectively.

Chlorophyll Content
The results shown in Figure (3) indicate the effect of irrigation water quantities on the chlorophyll content, where its highest value was SPAD67.87 in the full irrigation treatment (comparison treatment), then the average chlorophyll decreased to SPAD 55.77, 49.74, and 45.33 in the deficit irrigation treatments of 60, 50, and 40%, with lower rates.21.70, 36.44, and 49.71%, respectively, for the full irrigation treatment, and the mean of the chlorophyll index was 65.83 and 61.43 for the two irrigation treatments minus 80 and 70%, which did not show a significant difference between them for the full irrigation treatment.

Grain Yield
In Figure (5), which shows the effect of deficit irrigation on the average grain yield of the Sorghum bicolor crop, it is noted that the full irrigation treatment (100 FI%) was significantly excelled by giving the highest average grain yield of 5.792 Ton ha -1 , with significant increases of 140.03, 252.74, and 286.39% for the incomplete irrigation treatments 60, 50, and 40%, which gave the lowest average yield of 2.413, 1.642, and 1.499 Ton ha -1 , and that the two treatments of 80 and 70% incomplete irrigation gave grain yields of 5.018 and 4.817 tons' ha -1 , and thus they did not differ significantly from complete irrigation treatment.It is clear from the presented results in figures (1 and 2), which included growth indicators for the Sorghum bicolor crop, that the deficit irrigation led to a decrease in the plant height, leaf area when the plant was exposed to stress in its growth stages, When reduced the amount of the supplied water in case of applying deficit irrigation of sorghum, especially in the vegetative growth stage, it was seen that a clear reduction in the elongation and expansion of the leaves as a result of the loss of bulging pressure exerted on the cell walls.In Photosynthesis process which caused the destruction of oxygen that did not have the opportunity to work on the elongation of the internodes, which also affected on the height of the plant as a result of the small leafy area.The action of auxin reduced plant height.This is consistent with the results obtained by [14 and 15].The exposure of the plant to moisture stress also reduces the amounts of irrigation water that the plant receives, which has a significant effect on the leaf area, where it leads to a reduction in the number of leaves and reduces the ability of the plant to elongate, this agrees with [16].It can be inferred from figures (3,4) the effect of reducing water quantities on the dry weight of the root, as the full irrigation treatment (FI 100%) gave the highest value for the root weight amounting to 277.73 g.It reached 272.82 and 269.06 g.Because of the deficit water and the water stress to which it was exposed, the stress reduced the average dry weight of root for the deficient irrigation treatments of 60, 50, and 40%, in which the dry weight values of the roots decreased, reaching 84.20, 70.12, and 69.74 g for the treatments, in order, since 70% of the root weight of the grain Sorghum bicolor crop is concentrated in the layer from 0-15 cm, Where the root spread is in the layer with high moisture content and the decrease in the amount of irrigation, the number of spreading roots decreases [17].
The results showed a decrease in the average values of the dry weight of the root as a result of the lack of irrigation.The quantities of irrigation water also affected significantly the chlorophyll content in the leaf, as its highest value was SPAD 67.87 at the full irrigation treatment (FI 100%), then it gradually decreased to SPAD 55.77, 49.74, and 45.33 at the deficit irrigation treatments of 60, 50, and 40%, respectively.The reason for this is due to the lack of leaf content of photosynthetic pigments, which were affected by the water stress to which the plant was exposed, where it led to a deficit irrigation absorption as well as oxidation of chlorophyll pigments [18,19].As for the two treatments of incomplete irrigation 80 and 70% of full irrigation they did not differ significantly from the full irrigation treatment (FI 100%) with a value of chlorophyll content of SPAD 65.83 and 61.43.The results of Figure ( 5) also showed that the lack of irrigation gave high significant differences in the average grain yield.This decrease coincided with the decrease in the average plant height, leaf area and chlorophyll content due to the decrease in the photosynthesis process, which also causes a decrease in dry matter from the stems to the upper leaves of the plant for the purpose of producing and the formation of the grain-bearing head.As the stress that the plant is exposed to in the stage of formation of the head and the flag leaf, as well as the occurrence of a defect in the physiological and biological processes of the plant, affects the ability of the plant head to create a spike and its growth, which affects the lack of good pollination and the formation of grains.The grain yield decreases and increases with the number of grains and their weight, and the grain yield is determined by environmental, genetic and administrative factors, and the decrease in the amount of water received at each treatment affected the amount of grain yield, as the yield decreases with the decrease in the amount of irrigation water [20,16].

Water Yield (kg m 3 )
The results of the statistical analysis shown in Figure (6) showed were significant differences in the average water productivity for the irrigation levels, as the full irrigation treatment it gave the highest average water productivity 16.48 kg m -3 and the irrigation treatment 40% of the full irrigation had the lowest average water productivity 4.26 kg m -3 .The increase percentage for the full irrigation treatment of water consumption efficiency was 8.19, 16.81, 58.37,71.66and74.15%compared to the incomplete irrigation treatments of 80, 70, 60, 50, and 40% of the complete irrigation, respectively.80 and 70% when compared to the full irrigation treatment, it excelled in water use efficiency reaching 13.71 and 15.13 kg m 3 .The reason for the low water use efficiency of the mentioned irrigation deficiency treatments is due to the significant decrease in grain yield.Also, the statistical analysis showed that there were no significant differences between the averages of water productivity for two irrigation treatments.The addition of 80 and 70% of the irrigation water gave a higher efficiency of water use for the Sorghum crop, as the lack of 20 and 30% of the irrigation water did not affect the productivity, and because of the low amount of irrigation water supplied to the plant, the plant by its physiological nature, it will make a great effort to try to take advantage of all the supplied water to give its natural productivity and thus obtain high water consumption efficiency.Drip irrigation systems will improve water productivity and increase crop production under conditions of water shortage compared to other irrigation methods [21].

Figure 1 .
Figure 1.Effect of deficit irrigation on sorghum plant height.3.2.Leaves Area (cm 2 )Figure(2) shows that deficit irrigation had a significant effect on the mean leaf area values of Sorghum bicolor crop, where the full irrigation treatment (100 FI%) gave the highest value for the mean leaf area of 4580.14 cm 2 , which decreased by 27.56, 58.85, and 66.14% to become 3598.27and 2883.4 and 2756.87 cm 2 for under-irrigation treatments of 60, 50 and 40%, respectively.While it did not differ significantly from the other irrigation treatments 80% and 70%, whose leaf area values were 4535.97 and 4468.95cm 2 .

Figure 2 .
Figure 2. Effect of deficit irrigation on sorghum Leaves area.

Table 1 .
Some physical and chemical properties of field soil before planting. 3

Table 2 .
Chemical properties of irrigation water.