Rationalization in the use of irrigation water and reduction of wastage based on the real need of the plant and in a way that ensures avoidance of crop exposure to water stress for the purpose of obtaining economic production. As a result of the deterioration in the quality of irrigation water or the use of groundwater with high salinity, sewage and drainage water, all of this leads to limiting agricultural expansion, which negatively affects soil properties and its productive capacity. Al-Sihi in soil conditions that suffer from a lack of efficient salt leaching and this problem began to appear in large lands in central and southern Iraq. Therefore, it was necessary to use modern irrigation techniques to reduce the deterioration of agricultural lands and to rationalize the use of irrigation water, including drip irrigation, which in turn helps to maintain the physical properties of the soil as well as increases the efficiency of using irrigation water. The drip irrigation system is one of the technologies that has spread widely in most dry and semi-arid areas due to the high efficiency in the use of irrigation water, as well as the positive role in maintaining the physical properties of the soil. As for the most important problems of the drip irrigation system, it is the accumulation of salts at the borders of the wetting area of the drippers. And the area of plant roots spreading is limited in a certain soil volume, which is the area wet with irrigation water but the efficiency of the drip irrigation system by washing the salts and collecting them at the outer borders of the wetting front prompted some studies to use the high drainage of the drippers at the end of the irrigation cycle, which achieved an improvement in the physical properties of the soil Increasing washing efficiency, reducing salt levels and yield growth [1]. For the purpose of benefiting from the advantages of the drip irrigation system in reducing the osmotic tension that occurs between irrigations by adopting a proposed method, which is changing the discharge of drippers as a result of changing the operating pressure of the irrigation system and its impact on soil properties and plant growth [2].

The experiment was carried out in one of the fields of Al-Hayy District-Wasit Governorate, located at longitude 0” 12’ 320 east and latitude 0” 0’ 460. The region is characterized by a dry climate and the soil of the experiment is sedimentary with a clay-silty texture classified as Typic Torrifluvent [3]. Soil samples were taken from a depth of 0-30 cm after digging a trench in the soil of the site with the dimensions (1×2×1), then they were air dried and passed through 2 mm sieve holes and the bulk density was estimated using the Russell method mentioned by Black (source). The true density was also estimated using the Pycnometer Method proposed by Barsher and mentioned in Black [4]. The total porosity was calculated from the common relation between bulk density and true density and as stated in the method presented in Black [4]. The field capacity was calculated in the field by conveying an area of (1) m² from the field to the saturation level, then the soil surface was covered with polyethylene to prevent water evaporation and after (48) hours of saturation, samples were taken from a depth of (0-30) cm to estimate the field capacity. The Nielsen method reported in Black [1].

The pH was measured in the soil suspension 1:1 soil:water using a pH-meter and according to the method mentioned by Jackson [5]. As for the electrical conductivity (Desiemens. M⁻¹), it was measured in the saturated dough extract using the EC-meter and according to the method developed by Page [6]. The Average 
Weighted Diameter (MWD) of soil samples was measured according to the equation proposed by Youker [7]:

(1)

Whereas:

Xi        : The average diameter for any size range of separated assemblies (mm)

Wi       : The weight of the remaining aggregates within the same volumetric range as a ratio to the total dry weight of the soil sample

MWD :   Average Weighted Diameter (mm) (Table 1)

Table 1: Some of the Primary Characteristics of the Soil Used for the Experiment and the Irrigation Water

The experiment included the following factorial transactions:

• Irrigation water level: It included the effect of three irrigation levels represented by 50% EP-75% EP-100% EP depending on the evaporation value measured from the American evaporation basin and this was placed in the experimental site

• The alternating factor in the operating pressure, which included selected combinations of three operating pressures, which are: (20-30-40) kPa

The results shown in Table 2 show the significant effect of the irrigation water levels that were added at the beginning of the growing season, as the 75% EP treatment gave the highest values by 0.3138 mm, compared to the 50 and 100% EP treatments, which recorded (0.2589, 0.2814) mm, respectively. The reason for the superiority of the EP 75% treatment may be due to the rapid wetting resulting from the amount of water added at this level. It was balanced in a way that did not harm the soil structure relatively as a result of the negative impact of the rapid wetting on the soil aggregates and the soil remaining moist and thus maintaining an appropriate soil moisture and not reaching The state of cracking during dry periods between irrigations, which works to demolish and destroy soil aggregates, in addition to the high efficiency in washing salts away from the end of the wetting front compared to the level 50% with slow wetting and the high moisture content given by the level 100%, which leads to the deterioration of soil structure as a result For high hydration speed [8].

Table 2: The Weighted Diameter Average at the Beginning of the Experiment for Both Irrigation Levels Under Different Operating Pressures

As the results showed in Table 2 the significant effect of the alternation coefficients in the operating pressure on the MWD values at the beginning of the growing season, there was a regression in the values of the coefficients in which the operating pressure increased and the highest values were recorded at the 20 kPa operating pressure and were 0.2966 mm compared to the average operating pressure and higher, which gave 0.2829 and 0.2747 mm, respectively. This is due to the effect of irrigation and its relationship to the deterioration of the soil structure and this depends on the speed of hydration and its effect in weakening the bonding forces between the particles within the one soil group and this in turn helped to increase the salt content within the experimental soil and the predominance of the false structure of the soil, which quickly deteriorates during the immersion process and hydration [9].

The results in Table 2 indicate that there is a significant effect of the overlap between the irrigation levels and the operational pressure one month after the start of the experiment, as it is noted from the results that the highest significant differences were between the irrigation level 75% compared to the other irrigation levels 50 and 100% for all operational pressures, due to The amount of water that was added to the soil was balanced in a manner that did not negatively affect soil structure compared to rapid wetting and its effect on the deterioration of soil structure.

It is clear from the results in Table 3 the effect of alternating operating pressures on the values of the weighted average diameter at the end of the growing season. The operating pressure coefficients showed an increase in the MWD values compared to a month after planting, as the values were recorded as 0.3528, 0.3444 and 0.3343 mm and for the operating pressures 20, 30 and 40 kPa, respectively. This is due to the positive role of the root system of the cultivated economic plant, which contributed to increasing the stability of the agglomerations during the growth period through the formation of organic materials that are carnivorous to the agglomerations and this is a result of the decomposition of the roots as well as their secretions, as well as the activity of the activity of soil revival, which in turn contributes to improving the stability of the soil. As well as a decrease in the rates of evaporation from the soil surface as a result of the decrease in temperature and this in turn led to an increase in the soil’s retention of moisture between irrigation and the next, which reflected positively in reducing the effects of the wetting and drying process and its role in the deterioration of the soil sector.

Table 3: The Weighted Diameter Average at the End of the Experiment for Both Irrigation Levels Under Different Operating Pressures

The results showed in Table 3 that there is a variation in the effect of the irrigation level treatments on the values of the average weighted diameter at the end of the season than at the beginning of the growing season. 0.3712 mm compared to the two treatments 75, 50%, which recorded 0.3505 and 0.3098 mm, respectively. And this increase in the level of irrigation caused an increase in the movement of irrigation water in both the horizontal and vertical directions and this in turn increased the process of washing salts and pushed them away towards the borders of the front of the wetting area, in addition to increasing the growth and spread of roots in a larger area of the soil sector [10].

The results showed in Table 3 that there is a significant effect of the interaction between operational pressures and irrigation levels at the end of the growing season. The operational pressure was 40 kPa, as it gave the highest value and was 0.3776 mm, while the lowest value was recorded for the interference EP50% overlapping with the operational pressure of 20 kPa and was 0.2983 mm. This is due to the aforementioned reasons associated with the increase in the spread of the root system and its interfering role with microorganisms in the soil, which was enhanced by raising the efficiency of salt leaching at a high irrigation level.

1. Hussein, A.S. and H.R. Nayyef. “Effect of Cutting Periods on the Concentration of Hydrocyanic Acid for Five Cultivars of Sorghum (Sorghum bicolor L.).” Plant Archives, vol. 19, suppl. 1, 2019, pp. 1373-1377.

2. Zhou, L. et al. “Effects of Lateral Spacing for Drip Irrigation and Mulching on the Distributions of Soil Water and Nitrate, Maize Yield, and Water Use Efficiency.” Agricultural Water Management, vol. 199, Feb. 2018, pp. 190-200.

3. Al-Ani, A.N. et al. “Physical and Chemical Properties of Some Marsh Soils in Iraq.” Iraqi Agriculture Journal, vol. 5, no. 1, 2000, pp. 1-14.

4. Black, C.A. et al. Method of Soil Analysis. American Society of Agronomy, Madison, Wisconsin, USA, 1965. No. 9, parts I and II.

5. Jackson, M.L. Soil Chemical Analysis. Prentice-Hall, Inc., 1958. Cited in Engle, L.F.R. “Design and Management Considerations for Subsurface Drip Irrigation System.” Central Plains Irrigation Short Course, Kearney, Nebraska, Feb. 7-8, 1994, USA.

6. Page, A.L. et al. Methods of Soil Analysis, Part 2, 2nd ed. American Society of Agronomy, Madison, Wisconsin, USA, 1982.

7. Youker, R.E. and J.L. McGuinness. “A Short Method of Obtaining Mean Weight Diameter Values of Aggregate Analysis of Soil.” Soil Science, vol. 83, 1956, pp. 291-294.

8. Shami, Y.O.A. “The Effect of Adding Soil Conditioners on Some Soil Properties Using Drip Irrigation and Flood Irrigation Methods in Clay Soil and the Growth of Corn (Zea mays L.).” Master’s thesis, Faculty of Agriculture, University of Basrah, Republic of Iraq, 2013.

9. Janabi, I.A.M. and A.S. Aati. “Effect of Type and Level of Organic Residues in Interaction with Saline Water on Some Soil Properties in Calcareous Soil.” Iraqi Journal of Soil Sciences, vol. 6, no. 1, 2006, pp. 53-62.

10. Tayel, M.Y. et al. “Effect of Irrigation Systems on: I-Some Soil Physical Characteristics.” Journal of Applied Sciences Research, vol. 5, no. 5, 2009, pp. 573-578.