The effect of riser height in a fixed sprinkler irrigation system, irrigation interval, and addition of emulsified spent engine oil conditioner on soil moisture content and salt distribution in clay soil

Introduction

Appropriate irrigation is considered the fundamental pillar for the sustainability and management of soil and water resources. This process is not limited to merely supplying water to the soil but also aims to preserve the physical, chemical, and fertility properties of The chance of water droplets being exposed to wind effects and evaporation before reaching the soil surface increases with higher sprinkler riser height (Mohamed et al., 2019) [19] . Therefore, the appropriate selection of sprinkler nozzle sizes, operating pressure, sprinkler riser height, and spacing in sprinkler irrigation, in addition to the optimal amount of irrigation water required for the crop root zone, can be made. This selection should neither cause surface runoff nor damage the crop, while providing the best possible water distribution under prevailing wind conditions (Pawlak and Kołodziejczak, 2020; Sharma, 2022) [23,31] . Dehkordi, (2014) [10] indicated that water distribution uniformity improves with increased sprinkler riser height under moderate wind speeds; however, under high wind speeds, increasing the riser height has a negative effect on distribution uniformity. For the purpose of sustaining and efficiently managing soil and water environmental resources under water scarcity and the degradation of soil physical, chemical, and fertility properties, the irrigation interval has emerged as a successful technique. It maintains soil moisture within optimal limits for plant growth, prevents water stress, and reduces irrigation water evaporation from the soil surface (Bian et al., 2024) [7] . Using the optimal irrigation interval allows for supplying the root zone with appropriate moisture without excessively saturating the soil. This improves the soil's water retention capacity and reduces losses through deep percolation, which otherwise causes nutrient leaching. To improve soil properties and limit their degradation, some innovative solutions have appeared to enhance the soil's water-holding capacity. These include the use of petroleum derivative emulsions, which can form a thin water-repellent layer around particle surfaces and aggregates, as well as coat water-conducting capillary pores. This works to slow the rate of water loss through evaporation, thereby enhancing the soil's ability to retain water, increasing plant-available water, and improving water use efficiency (Hasan et al., 2019) [14] . It also reduces direct evaporation from the soil surface, which lessens the phenomenon of salt ascent and accumulation on the soil surface via capillary rise, thereby helping to mitigate the severity of topsoil salinity (Shabeeb, 2016; Dheyab, 2020) [30,11] . This study aims to evaluate the effect of sprinkler riser height, irrigation interval, the addition of emulsified spent engine oil, and their interactions on soil water retention capacity and salt leaching efficiency. These are important characteristics for assessing irrigation system efficiency and their impact on plant water stress.

Materials and Methods

A field experiment was conducted at the Research Station of the College of Agriculture -University of Basrah, located at latitude 30°.53" N and longitude 74°.47" E during winter season 2023-2024, on a clay soil texture, on an area of 25000 m². The soil was classified as Typic Torrifluvent Hyperthermic, Calcareous, Clayey, Mixed (Al-Atab, 2008) [3] . Composite soil samples were collected from the field for three depths (0-30) cm, then dried and passed through a 2 mm sieve for chemical analyses, while some samples were passed through an 8 mm sieve and and retained on a 4 mm sieve to estimate the physical properties of the study soil as shown in Table (1). Methods described in Black et al., (1965) [8] , Jackson, (1958) [16] , Page et al., (1982) [22] , and Richards, (1954) [25] were used to determine the physical and chemical characteristics. The experiment included four factors: the first factor: Sprinkler riser height at three proposed heights: 1m (h₁), 1.25 m (h₂), and 1.5m (h₃) at a pressure of 3.5 bar. The second factor: Irrigation interval, irrigating every 5 days (I₅) and 9 days (I₉), calculated from a US Class-A -evaporation pan. The third factor: conditioner factor with two treatments: emulsified spent engine oil treatment at a concentration of 0.3% (O₁) and a control treatment (Oc). the fourth factor: Horizontal distance from the sprinkler center, divided into three equal distances from the sprinkler center to the end of the spray diameter depending on the wetted area according to sprinkle riser height, represented by the first third near the sprinkler center (X₁), the middle third (X₂), and the last third (X₃). The experimental soil was plowed twice orthogonal using a moldboard plow, then the land was divided into three blocks with a distance of 2 m between each two blocks. Afterwards, each block was divided into experimental units according to the wetted diameter based on sprinkle riser height and distributed randomly to match the number of factorial treatment combinations of the factors included in the experiment (3 sprinkle riser heights × 2 irrigation intervals × 2 conditioner addition levels × 3 distances). Then, the factorial treatments were randomly distributed to the experimental units in each block. The spent engine oil conditioner was added after emulsification using an anionic emulsifying agent to the soil surface and to a depth of 0-30 cm. Composite soil samples were taken at the end of the experiment from all experimental units and for the three distances from the sprinkler center before the subsequent irrigation and for the addition depth of 0-30 cm, and placed in polyethylene containers for the purpose of estimating gravimetric moisture content (PW%) by the gravimetric method and electrical conductivity (EC) determined extraction 1:1 soil to water. The results were statistically analyzed using the Genstat DE10.3 statistical program. 32.694 Na +1 18.329 K +1 19.717 HCO3 -2 0.00 CO3 -2 83.821 Cl - 1 26.207 SO4 -2 Results and Discussion 1. Soil moisture content (%) The results in table (6) showed a highly significant effect of the sprinkle riser height factor on Pw% values. Significant differences were found between all treatments (Figure 1), moisture content increases with decreasing sprinkle riser height, the highest values are recorded at sprinkle riser height 1m (h₁), followed by 1.25 m (h₂), then 1.5 m (h₃), with values of 25.44%, 24.52%, and 23.11% respectively, this is attributed to the lower sprinkler riser height is the Uniform distribution of irrigation water at nearly constant depths over the entire irrigated field area, achieving a better wetted area compared to treatments with higher sprinklers, in addition to reducing irrigation water loss through evaporation due to its shorter time spent in the air during its release from the sprinkler nozzle until it falls onto the soil surface. These results agree with Kuti et al., (2019) [17] , where they found that the depth of irrigation water added to the wetted area within the effective wetted radius was greater at sprinkler riser heights of 2 and 3 m compared to a height of 4 m. This is consistent with Mohamed et al., (2019) [19] and Sulaiman and Khalaf, (2022) [32] , who found that the best values for soil moisture content and uniformity of water distribution were achieved at low sprinkle riser heights under conditions of low wind speed, high relative humidity, and low temperatures. Table (6) showed a highly significant effect of the irrigation interval factor on soil Pw % values. There was a significant difference between the two irrigation interval treatments (Figure 2), where the irrigation interval every 5 days (I₅) treatment excelled in achieving the highest moisture content, which reached 25.28%, compared to the irrigation interval every 9 days (I₉) which reached 23.43%, this is attributed to the closer irrigation periods may increase Pw% values in the soil and maintain a high Pw %, compared to the I₉ irrigation interval where moisture loss through evaporation increases due to the longer irrigation interval and the occurrence of cracks in the soil surface layer, this leads to increased, irregular water movement through the formed cracks in the surface layer in three directions, especially downward movement due to gravity, These results consistent with reached by Abdul-Rahman and Al-Sheikhly (2009) [2] that Pw % values for treatments irrigated every three days is higher than the treatments irrigated every five days, due to greater exposure of these treatments to evaporation and moisture depletion processes, as the change in Pw % values between two consecutive irrigations was smaller in the 3day irrigation interval compared to the 5-day interval. The results in table (6) showed a highly significant effect of adding emulsified spent engine oil on soil moisture content values (Pw %) for the addition depth of 0-30 cm. The addition of the conditioner (O₁) led to an increase in Pw % values significantly compared to the control treatment (Oc) (Figure 3), with averages (25.49%, 23.22%) for O1 and OC treatments respectively, with an increase percentage of 9.80% compared to the control treatment. The effect of conditioner addition in increasing Pw% values is attributed to the ease of Infiltration of the emulsified petroleum conditioner into the soil profile, led to partially or completely coat soil particles and aggregates, making their surfaces hydrophobic, also plays a role in coating the internal surfaces of pores, limiting the capillary rise of water to the soil surface, thereby reducing the loss process through surface evaporation, which increases the soil's water-holding capacity (Shabeeb et al., 2019 and Dheyab, 2020) [29,11] . Husham and Abd Al Gabar, (2013) [15] also indicated that emulsified engine oil leads to an increase in the soil's waterholding capacity through the mechanism of redistributing the pore volume between and within soil aggregates, in addition to increasing total porosity, which positively reflects on increasing water retention in the soil. The results table (6) showed a highly significant effect of the horizontal distance from the sprinkler center factor on soil moisture content values (Pw %). significant differences were found in Pw% values (Figure 4), where an increase in Pw % values is observed when approaching the sprinkler center and decreasing with distance from it. The highest Pw % values appeared at the first distance close to the sprinkler center, (X₁), with an average of 25.67%, followed by the middle distance X₂ (24.24%), and the lowest at the far distance from the sprinkler center X₃ (23.16%). this is attributed to the water droplets exiting the sprinkler nozzle different in exit angle and speed, therefore, small and medium droplets tend to fall in places close to the sprinkler center due to air resistance overcoming their kinetic energy, while larger and heavier droplets travel farther from the sprinkler center, covering a longer distance in the air to the end of the wetted circle or the edges, due to it has greater momentum (Suryanarayana et al., 2013) [33] , this makes them susceptible to drift and evaporation processes due to wind speed and high temperatures (Martinez-cob et al., 2008; Sanchez et al., 2011; Arunadevi et al., 2021) [18,26,5] , in addition to the low uniformity coefficient at those distances. This agrees with what AbdulKarem and Dheyab, (2022) [1] found, a decrease in % Pw values with increasing distance from the sprinkler center, attributing it to the dispersion of irrigation water droplets exiting the sprinkler nozzle due to wind speed and high temperatures. Furthermore, the high kinetic energy (Momentum) of large droplets results in high impact energy on the soil surface, negatively affecting soil structure and the formation of a soil crust that reduces water infiltration and increases the retention of free water on the soil surface for a longer period, increasing loss through direct surface evaporation. The results in table (6) showed a significant effect of the interaction between the irrigation interval factor and the addition of emulsified spent engine oil conditioner factor. The results in table 2 show the significant increase in Pw% between I5 and I9 treatments varies depending on the addition of conditioner, the highest variance was observed when the conditioner was added (O1) compared to the control treatment (Oc), so the highest value of Pw % recorded at I5O1(26.54%) and the lowest values recorded at I9Oc factorial treatment (22.41%), this is attributed to the treatments irrigated every 5 days with conditioner addition retain higher moisture content until the subsequent irrigation compared to treatments irrigated every 9 days without conditioner addition. the addition of emulsified spent engine oil as a conditioner had sufficient time for the process of Surrounding soil particles and aggregates, improving soil structure, and closing ends of the pore, which reduces evaporation from the soil surface by reducing the capillary International Journal of Agriculture and Food Science https://www.agriculturaljournals.com rise of soil water (Dheyab, 2020) [11] . These results agree with what Al-mehmdy and Al-Hashemi, (2025) [4] found regarding the decrease in % Pw for soil under treatments irrigated with longer time intervals compared to those irrigated with shorter intervals. The results in table (6) showed a significant effect of the interaction between the factors of adding emulsified spent engine oil conditioner and the horizontal distance from the sprinkler center on Pw % values ،the table (2) shows the significant superiority of the treatment of the horizontal distance close to the center of the sprinkler (X₁) and its interaction with the addition of spent engine oil conditioner, with a significant difference compared to the other studied treatments, and this varies according to the variation in conditioner addition. Generally, the highest % Pw values were 26.96% at the horizontal distance treatment (X₁) with conditioner addition (O₁), represented by treatment X₁O₁, while the lowest values were at the horizontal distance treatment far from the sprinkler center X₃ and its interactions with control treatment (Oc), represented by treatment X₃Oc, with a value of 22.01%, this is attributed to the impact of closer [14] and this enhanced by the role of the conditioner in reducing evaporation-transpiration potential and water loss at that distance or irrigated area, which is the last third from the sprinkler center.

The results in table (6) showed a highly significant effect of the Triple interaction between sprinkle riser height, irrigation interval, and addition of spent engine oil conditioner on Pw% values, results in the table 2 shows that % Pw values for the Triple interactions vary significantly among themselves according to the levels and interactions of these studied factors. Generally, they increase with a decrease in each of sprinkle riser height and irrigation interval with addition conditioner (O1). The highest values were at the distance close to the sprinkler center, irrigation interval of 5 days, and conditioner addition in treatment (h₁I₅O₁), with a average of 27.71%, while the lowest average was at the treatment with high sprinkle riser heights (h₃), irrigation interval of 9 days, and no conditioner addition (h₃I₉Oc), which reached 20.99%. The results in table (6) showed a highly significant effect of the triple interaction between the factors of sprinkle riser height, addition of emulsified spent engine oil conditioner, and distance from the sprinkler center on Pw % values. The results in table 2 show the highest values were recorded at sprinkle riser height (h₁), conditioner addition (O₁), and horizontal distance from the sprinkler center (X₁), represented by the factorial treatment h₁O₁X₁, with average of 28.49%, followed by the factorial treatment h₂O₁X₂ with a average 27.09%. The increase in % Pw values is due to the cumulative effect of the interaction of the factors: sprinkle riser height, spent engine oil conditioner, and horizontal distance from the sprinkler center, with a significant difference between treatments. While, the lowest % Pw values were at sprinkle riser height (h₃), control treatment (Oc), and the far horizontal distance from the sprinkler center (X₃) in treatment (h₃OcX₃), with average of 20.42%.

Salt Distribution in Soil

The results in table (6) show a high significant effect of the sprinkle riser height factor on soil electrical conductivity values (EC). There are significant differences found between all treatments (Figure 5). the EC values decrease with decreasing sprinkle riser height, so the lowest values at sprinkle riser height 1m (h₁), followed by 1.25 m (h₂), then 1.5 m (h₃), with average of 6.86 dS m⁻¹, 7.91 dS m⁻¹, and 9.15 dS m⁻¹ respectively. This is attributed to the increase sprinkler riser height led to decrease the moisture uniformity coefficient within the wetted circle, reducing Moisture distribution efficiency, in addition to its effect on increasing the Dispersion Index and its relationship with the kinetic energy of sprinkler water droplets and their negative impact at high heights. Furthermore, increasing sprinkler riser height contributes to increased direct loss of irrigation water droplets through evaporation due to the longer time period droplets remain in the air from exiting the sprinkler nozzle until arrive to the soil surface, which led to a decrease in soil moisture content (Figure 1 in the research) and reduced water movement within the soil profile, negatively reflecting on salt leaching efficiency. These results agree with Kuti et al., (2019) [17] and Fordjour et al., (2020) [12] , who found an increase in electrical conductivity values with increased sprinkler riser height in a sprinkler irrigation system. Sehsah et al., (2014) [28] confirmed that sprinkle riser height is the most influential factor on EC values, which decrease with a decrease in sprinkle riser height from 120 cm to 100 cm then 60 cm.

The results in table (6) showed a highly significant effect of the irrigation interval factor on soil electrical conductivity values (EC). The result in figure 6 showed there was a significant difference between the two irrigation interval treatments, the irrigation interval every 5 days treatment (I₅) excelled in achieving the lowest EC values 6.92 dS m⁻¹, compared to the irrigation interval every 9 days (I₉) which reached 9.02 dS m⁻¹, with a decrease percentage of 23.28%. This is attributed to the shorter irrigation intervals to adding irrigation water quantities at closer intervals, with a 5-day irrigation interval, leads to maintaining optimum moisture content, contributing to filling most pores with irrigation water. This led to decrease in salt concentration and their displacement from the surface layer to sub surface layers away from the root zone, limiting capillary water movement towards the soil surface which causes salt accumulation and the dominance of upward movement in soil columns. These results agree with AbdulKarem and Dheyab (2022) [1] , who found a decrease in EC values with a decrease in irrigation interval due to adding irrigation water at closer intervals, helping the soil remain moist most of the time, and that most soil pores are filled with water, increasing the process of dissolving and leaching salts and their vertical movement within the soil profile. The results in table (6) showed a highly significant effect of adding emulsified spent engine oil on (EC) values for the soil at the addition depth of 0-30 cm, the addition of the conditioner (O₁) led to a decrease in EC values significantly compared to the control treatment (Oc) (Figure 7), where the average EC values were (6.80 dS m⁻¹) and (9.13 dS m⁻¹) respectively, With decrease percentage of 34.26% compared to the control treatment (Oc), this is attributed to role of emulsified spent engine oil in coating the soil particles and aggregates that's lead to enhancing physical properties, represented by reduced upward water movement, increasing Soil moisture retention (Moisture conservation figure), which increases water movement and salt leaching efficiency, enhanced through improved soil structure, thus decreasing EC values. These results agree with Shabeeb, (2016) [30] and Dheyab (2020) [11] , who found a decrease in EC values when adding the petroleum emulsion, attributing it to coating the internal surfaces of pores, limiting capillary rise of water to the soil surface, thereby reducing water loss through surface evaporation. The results in table (6) showed a high significant effect of the horizontal distance from the sprinkler center factor on soil electrical conductivity values (EC). A significant difference are found in EC values between all distances from the sprinkler center (Figure 8), generally, observed that EC values decrease when approaching the sprinkler center and increase with distance from it. The lowest EC values were at the first third (X₁) 6.33 dS m⁻¹, followed by the second third (X₂) 8.03 dS m⁻¹, then the far distance from the sprinkler center represented by the last third (X₃) 9.55 dS m⁻¹. This is due to the variation in irrigation water distribution over the field area with different horizontal distances from the sprinkler center, which decreases with increasing distance, in addition to the increase in kinetic energy of irrigation water droplets with increased distance from the sprinkler center and its effect on reducing moisture content and water movement through the soil profile, reflecting on the efficiency of salt movement and leaching from the soil Profile. These results agree with AbdulKarem and Dheyab (2022) [1] , who found an increase in electrical conductivity values with increasing distance from the sprinkler center in a fixed sprinkler irrigation system. The results in table (6) showed a high significant effect of the interaction between sprinkle riser height and irrigation interval on electrical conductivity values (EC), table 3 shows that the differences in EC values between sprinkle riser height treatments varies depending to the difference in irrigation interval.the smallest variations between h₁, h₂, and h₃ appeared at irrigation interval I₅ compared to I₉. This variation is due to the role of irrigation interval I₅ in increasing moisture content between irrigations and its effect on improving soil structure, which enhances salt leaching efficiency despite the variation in sprinkle riser height. In the same context, irrigation interval I₉ at the low sprinkle riser height h₁ and at the factorial treatment h₁I₉ decrease the EC values to 8.18 dS m⁻¹, outperforming heights h₂ and h₃ at the same mentioned irrigation interval, which gave higher values of (8.86) dS m⁻¹ and (10.01) dS m⁻¹ respectively.

The results in table (6) showed a significant effect of the interaction between sprinkle riser height and addition of emulsified spent engine oil on (EC) values. Table 3 shows that the variations in EC values between treatments O₁ and Oc vary according to the variation in sprinkle riser height, the highest variations appeared at height h₁ and decrease with increasing riser height to h₂ then h₃. The reason for this variation is that the addition of the petroleum emulsion enhanced the soil's ability to retain water for the longest period depending on the level of water added to the soil, which was affected by sprinkle riser height and its role in uniform water distribution and other soil properties related to soil structure and water and salt movement. the highest EC values were recorded in treatment Oc at height h₃ in treatment OCh₃, with average 10.21 dS m⁻¹, while the lowest EC values were recorded at the addition level O₁ and height h₁ in treatment O₁h₁, with average 5.67 dS m⁻¹, this is due to the role of the emulsified spent engine oil conditioner in reducing soil salinity for the aforementioned reasons related to its effect on improving soil physical properties. This agrees with Ogbeide and Eriyamremu, (2023) [21] and Dheyab, (2020) [11] , who found a decrease in EC values when adding the emulsified petroleum conditioner compared to the control treatment and non-emulsified petroleum additions. The results in table (6) showed a high significant effect of the interaction between irrigation interval and distance from the sprinkler center on (EC) values. Table 3 shows that the variations in EC values between the mentioned distances from the sprinkler center X₁, X₂, and X₃ vary according to the difference in irrigation interval. The highest differences between the mentioned distances appeared at irrigation interval I₉ compared to irrigation interval I₅, this is due to a shorter irrigation interval enhances increased salt leaching efficiency despite the difference in distance from the sprinkler center. The highest values appeared at treatment I₉X₃, reaching 10.65 dS m⁻¹, and the lowest at the factorial treatment I₅X₁, recorded 5.54 dS m⁻¹. The results in table (6) showed a high significant effect of the interaction between the addition of emulsified spent engine oil and the horizontal distance from the sprinkler center on (EC) values. Table 3 shows that the variations between distances from the sprinkler center X₁, X₂, and X₃ vary according to the treatment of adding the emulsified petroleum conditioner. The highest differences between the mentioned distances appeared at the emulsified oil conditioner addition treatment O₁ and the lowest at the control treatment Oc, this is due to salt leaching efficiency increases with increased soil moisture content, which is enhanced by adding the emulsified conditioner. The results show that the highest values appeared at the factorial treatment OcX₃ with average of 10.51 dS m⁻¹ and the lowest at treatment O₁X₁ with average 5.36 dS m⁻¹. The results in table (6) showed a high significant effect of the interaction between sprinkle riser height and horizontal distance from the sprinkler center on (EC) values. The results in table 3 show the increase in EC values with increasing distance from the sprinkler center from X₁ to X₂ then X₃ varies according to sprinkle riser height, the smallest differences appeared at sprinkle riser height h₁ and increase with increasing sprinkle riser height h₂ then h₃, this is due to the uniformity coefficient of moisture distribution is higher at low sprinkle riser height and decreases with increasing sprinkle riser height, reflecting on differences in moisture content and the effect on salt leaching efficiency through the soil profile, so EC values increased with increasing sprinkle riser height and horizontal distance from the sprinkler center, with the highest values recorded at height h₃ and distance X₃, which recorded 11.00 dS m⁻¹, while height h₁ achieved the lowest values at distance X₁ with a value of 5.61 dS m⁻¹. [6] . The results in table (6) showed a high significant effect of the triple interaction between sprinkle riser height, irrigation interval, and horizontal distance from the sprinkler center on EC values. Table 4 shows that EC values vary with different horizontal distances from the sprinkler center according to sprinkle riser height and irrigation interval. Factorial treatments close to the sprinkler center showed a decrease in EC values at distance X₁, followed by distance X₂, while a significant increase in EC values occurred at distance X₃ compared to the mentioned distances, this variation increases with increasing sprinkle riser height from h₁ to h₃. The highest values were recorded at treatment h₃I₉X₃, which reached 11.87 dS m⁻¹, while factorial treatments close to the sprinkler center showed a evident decrease in EC values at heights h₂ and h₁, with a significant difference compared to height h₃, this effect increases with a decrease in irrigation interval from I₉ to I₅, where the lowest values were recorded at treatment h₁I₅X₁, which reached 4.61 dS m⁻¹. This effect is attributed to the resultant effect of the influencing factors and their interaction on increased soil salinity with increased irrigation interval due to the longer period between irrigations, increasing the amount of evaporated water leaving high salt concentrations, while increased soil salinity with increased distance from the sprinkler center is due to the non-uniform distribution of water emitted from the sprinkler within the wetted circle and the decrease in the uniformity coefficient as we move away from the sprinkler center due to the effect of temperature and wind speed on water droplets exiting the sprinkler (Santra, 2021) [27] . The results in table (6) The results in table (6) showed a high significant effect of the four-way interaction between sprinkle riser height, irrigation interval, addition of emulsified spent engine oil conditioner, and horizontal distance on EC values. It is observed that EC values vary with increasing horizontal distance from the sprinkler center according to sprinkle riser height, irrigation interval, and addition level (Table 5). Factorial treatments that used the emulsified spent engine oil conditioner showed a decrease in EC values at distance X₁, followed by distance X₂, then distance X₃. This variation increases at treatment Oc. Meanwhile, factorial treatments that received the conditioner addition showed a decrease in EC values at heights h₁ and h₂, with a significant difference compared to height h₃. This effect increases with a decrease in irrigation interval from I₉ to I₅. The lowest EC values were recorded at the factorial treatment h₁I₅O₁X₁, reaching 4.12 dS m⁻¹, while treatment h₃I₉OcX₃ gave the highest EC values, reaching 12.17 dS m⁻¹. These results clarify the aforementioned reasons related to the specific effect of each of sprinkler riser height, irrigation interval, addition of emulsified spent engine oil, and horizontal distance from the sprinkler center.

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