Effect of Addition Nitrogen Fertilizer at Different Irrigation Levels on Saturated Hydraulic Conductivity by Using Two System of Irrigation

A field study was conducted in the province of Wasit - Kut, in a semi-arid region with a clay loam texture, for the purpose of studying the effect of adding nitrogen fertilizer, which included the level of 300 kg H-1 (N1) and 150 kg H-1 (N2) and the comparison treatment without adding fertilizer (N0) and using two levels of irrigation, which included EP (P1) 75%, EP (P2) 100% under drip irrigation (DI) and surface irrigation (SI) systems on saturated Hydraulic conductivity (Ks). The results showed that the addition of nitrogen fertilizer N1 had a significant effect by increasing the nitrogen availability using (DI), as the N1 gave the highest value of conductivity and a significant difference from the rest of the treatments, by increase 154.3% While the increase were 103.7% and 56.79% for the treatment N2 and N0, respectively. The results indicated that there were significant differences due to the effect of different irrigation levels on the Ks values, as P1 treatment gave the highest Ks value of 2.21 m day-1 compared with P2 treatment, which amounted to 1.94 m day-1, With the presence of significant differences for the two irrigation systems on the Ks values, as the values increased compared with the values before planting, with an increase of 129.6% and 38.27% for the (DI) and (SI) system. The study also showed that there were significant differences for the effect of the interaction between nitrogen fertilizer treatments and the irrigation levels, as well as the presence of significant differences for the effect of the interaction between the nitrogen fertilizer treatments and the irrigation system used on the Ks values.


Introduction
The arid and semi-arid regions, including Iraqi soils, are characterized by low rainfall and low content of organic matter, which is the main source of organic nitrogen in the soil, which is reflected in the need for irrigation and nitrogen fertilization to increase the productivity of these soils.However, the addition of water and nitrogen in large quantities exposes a large part of it to loss through leaching outside the root zone, as the movement of irrigation water outside the root zone and the high solubility of nitrogen fertilizer lead to leaching of nitrates away from this zone.Therefore, the movement of 1259 (2023) 012008 IOP Publishing doi:10.1088/1755-1315/1259/1/012008 2 water and the rate of leaching of nitrates depends on the soil properties, the amount of water added, the irrigation system, and the amount and type of fertilizer added.In order to reach the optimal use of irrigation systems and the addition of nitrogen fertilizer under the conditions of arid and semi-arid regions, an appropriate amount of water must be stored in the soil, This can be achieved through conducting many agricultural operations related to moisture levels and the used irrigation system, and its impact on water and hydrological properties such as saturated Hydraulic conductivity in the soil [1].
One of the challenges facing water resources after scarcity is the low efficiency of using these resources.The large expansion of traditional surface irrigation in the Arab world is the first influencing the level of low efficiency of using these resources.From the foregoing, it can be said that the need has become urgent and necessary to rationalize and raise the efficiency of water use and Fertilizers by using modern irrigation methods, which contribute to reducing the percentage of waste in water, and the drip irrigation method is the most important modern irrigation method that contributes to achieving this goal.The use of fertilization by irrigation with this method leads to an increase in the efficiency of using water and nutrients, which is reflected in the increase in production [2].Determining the Hydraulic conductivity in the unsaturated area of the soil profile above a stable ground water level is of great importance in the design, construction and management of irrigation systems, soil use and the possibility of contamination of surface water and ground water sources and the movement of nutrients.The importance of water distribution in this region as a function of time does not only stem from the role of water as a basic component of all living organisms, but also as the main means through which nutrients are transported through the soil.The field studies to determine, estimate or predict the movement and source of water in the unsaturated area and the study of irrigation and drainage projects and the investment of water resources are concerned with the necessary attention by those concerned in the agricultural and engineering specialties, and depend mainly on the physical characteristics of the soil, especially those related to the efficiency of water transmission and distribution and fertilizer [3,4].

Materials and Methods
A field experiment was carried out in the province of Wasit -Kut in a semi-arid area with a clay loam texture.Soil samples were taken from the study site, then air dried and passed through a 2 mm sieve to estimate some initial physical and chemical properties as shown in Table (1).The soil experiment was prepared by plowing, smoothing and leveling, and the soil was divided into marrows, and then a drip irrigation system was installed in the field on water tanks equipped with water, and the surface irrigation process was carried out by opening the main and secondary channels.Irrigation was carried out according to the total water requirement of the plant based on the evaporation value measured directly from the American evaporation basin (Evap.pan class -A-) which was installed at the study site.Implemented the Factorial Experiment, The treatments were distributed randomly according to the Randomized Complete Block Design (RCBD) with three replicates:- The saturated Hydraulic conductivity of the soil was measured by following the static water column method proposed by Klute and described in [5], by stabilizing a column of water five cm high above the soil column, then the amount of water passing through the column was calculated for specific periods of time until the values were fixed with time, as the calculation was calculated The values of the saturated Hydraulic conductivity of the soil through the application of Darcy's law.

Results and Discussion
The results indicated in Figure (1) that there are significant differences in the Ks values when adding nitrogen fertilizers, there was a rise in the Ks values compared with the initial values before planting, which was 0.81 m on Day-1, as the N1 gave the highest value of conductivity and a difference Significant compared to the rest of the treatments, with an increase 154.3%, while the increase rates 103.7% and 56.79% for N2 and N0 treatments, respectively.The significant increase in the Ks values when the N1 treatment is attributed to the increase in nitrogen availability in an ideal way, as it works to increase the growth, elongation and effective depth of the roots for water absorption, which will save irrigation water, especially in the corn crop, as most of the water absorbed by the roots is in the surface layer But when the water is depleted, the roots extend to the bottom and thus increase the large inter-pores, which improve soil structure and porosity which raise soil permeability and increase Ks values on the other hand [6].Also, the nitrogen fertilizers increase the growth of the root system of the plant and the increase in the number of root hairs that in turn prepare tracts and waterways in the soil body that helps the movement and influence of water through it during the measurement of the saturated Hydraulic conductivity of the soil and then raise its values, as the progress of the plant with growth is accompanied by an improvement in soil structure as a result of the development of root growth and complexity in the soil and its positive effects in increasing the soil Porosity and then increasing KS values [7,8].The results of Figure (2) showed a significant different for the influence of different irrigation levels in KS values, as the P1 gave the highest value of KS 2.21 m days -1 compared to the P2, which amounted 1.94 m days -1 .The results also indicate a high KS values compared to the initial values before planting, as the P1 gave the highest value with an increase 172.8% compared to the P2.This is due to the impact of the irrigation water level added to the soil on its construction through the effect of the mechanical action of excess quantities of irrigation water in destroying soil aggregate continuously, as it is noted that the decrease of KS when the P2 treatment is to block most of the inter -pores responsible for the effective channels in the delivery of water as a result of the process Repeated irrigation [9].This may be attributed to the high bulk density values and the decrease in the mean weight diameter as a result of the deterioration of soil construction due to the crash of soil aggregate as a result of moisturizing and drying operations during the irrigation process for the high levels of irrigation, and the P1 level led to an increase in the growth of the root system of the plant and its contribution to preparing waterways during the pores Which in turn helped the movement and penetration of water through it better than the case in the rest of the irrigation levels [10,11].
The results in Figure (3) showed a significant different for the irrigation system on KS values, as values increased compared to the values before planting with an increase 129.6% and 38.27% for the DI and SI systems respectively.As the use of the surface irrigation system in the clay soil causes the exposure of the soil surface layer constantly to change in the physical properties as a result of the deterioration that occurs in the soil construction resulting from the increase in the compact process as a result of the continued surface irrigation process and the lack of large and medium pores or noncontinuous of its paths which leads to water penetration or continuity in the pores compared to slow wetting and regular distribution of water in the drip irrigation system [12].In addition, the decrease in Ks values when surface irrigation is due to the rapid envelopment of water in the soil aggregates and its sudden submergence, which led to the speed of its destruction and the transmission and sedimentation of individual particles in the pore between the particles and the aggregates, which causes a decrease in the proportion of large pore responsible for the movement of water [13].
The results showed in Figure ( 4) that there were significant different due to the effect of interaction between the two nitrogen fertilizer treatments and the irrigation levels on the Ks values.The Ks values increased when compared with the beginning of the season and for all irrigation levels, as the highest increase was noted at P1 and for fertilizer treatments N1 and N2, with an increase of 176.5% and 138.2%, respectively.While it was lower at the P2 level, with an increase 144.4%, 116.1%, and 44.5% for the N1, N2 and N0 treatments, respectively.This is due to the effect of fertilizers at P1 and their ability to improve soil structure, root growth and elongation through the regularization of the particles in the form of aggregates with high stability against the effect of water action to suit this level of irrigation in increasing soil porosity and raising its Ks values [13].Whereas, at P2 the effect of fertilizer action decreases through the displacement of nutrients from the surface of soil particles as a result of high water runoff and soil immersion at high amounts of irrigation levels.Also, the Hydraulic conductivity is greatly affected by the geometry of the soil pores and its sizes distribution in them.
The results showed in Figure ( 5) that there were significant different between the nitrogen fertilizer and the used irrigation system.It was found that the Ks values increased when compared with the beginning of the season and for all irrigation systems, as the highest increase was observed at DI and for fertilizer treatments N1, N2, with an increase rate of 160.5% and 114.8%, respectively.While it was lower at SI, with an increase 141.9%, 104.9%, and 58.1% for fertilizer treatments N1, N2 and N0, respectively.This is due to the fact that the continuation of irrigation operations, especially when surface irrigation leads to soil compaction and deterioration of its structure due to sudden inundation, compared to slow wetting by drip which causes a decrease in Ks values at the end of the season.
Figure 5.The effect of the interaction between nitrogen fertilizers and irrigation systems on saturated Hydraulic conductivity(m day -1 ).
In addition, the spread of the root system of the treatments with added nitrogen fertilizers, which are irrigated with water levels and required irrigation systems, as well as the increase in the activity of microorganisms that work to decompose organic matter and bind soil aggregates through their secretions, which increases the Ks values compared to the treatments that are irrigated with other irrigation levels and systems Others fertilizers are not added to it.In the drip irrigation system, water and nutrients present in nitrogen fertilizers are added near the root zone at a low rate so that a suitable soil structure can be maintained around the roots [14].

Conclusions and Recommendations
 The addition of nitrogen fertilizers at the required levels using drip irrigation systems improved the water and hydrological properties of the soil by increasing the root growth, elongation and effective depth as a result of the availability of nutrients at the root zone and thus improving the soil porosity and increasing the saturated water conductivity. The use of appropriate moisture levels calculated within the actual needs of the plant improves the soil's physical and hydrological characteristics through the effect of the mechanical action of the irrigation water in breaking down the agglomerations and increasing the bulk density of the soil by continuing the irrigation processes that affect the volume distribution of the interfacial pores that transmit water and the saturated Hydraulic conductivity values.

Figure 1 .
Figure 1.The relationship between nitrogen fertilizer levels and saturated Hydraulic conductivity (m day -1 ).

Figure 2 .
Figure 2. The relationship between irrigation levels and saturated Hydraulic conductivity(m day -1 ).

Figure 3 .
Figure 3.The relationship between irrigation systems and saturated Hydraulic conductivity(m day -1 ).

Figure 4 .
Figure 4.The effect of the interaction between nitrogen fertilizers and irrigation levels on saturated Hydraulic conductivity(m day -1 ).

Table 1 .
Some chemical and physical characteristics of the study soil before planting.