The climatic conditions of the main problem in increasing agricultural production and water resources are limited. These factors turning more and more to the pressurized irrigation systems. Among these systems, Subsurface drip irrigation. The design and proper management of these enterprises to reduce water loss and optimal use of water and soil nutrients, soil moisture distribution around the dropper knowing how to demand.Shape (diameter and depth of wet soil) and the wetting front in the soil on many factors including texture and layers of soil, soil homogeneity, intensity of water, soil moisture content, slope of the land and water volume depends. The study of the distribution of moisture in the loam and silt loam Subsurface Emitters taken. The results showed that the moisture in the soil with loam, silty loam texture will appear later. And because of the shallow depth of the pipes in both the garden, the moisture in the soil surface appearance. According to soil texture and appearance of moisture on the soil surface is recommended depth will increase tubes.

Information on water soil content and its distribution is vital for field water management in Subsurface irrigation. The objective followed in this study was to simulate the extent of wastewater distribution taking into account root water uptake and evaporation from the soil surface under, Subsurface drip irrigation system. In this regard, a field experiment was conducted with lettuce as the crop, to collect the required data. soil hydraulic properties were obtained through an assessment of in-situ soil water pressure heads as well as water contents. soil matric potentials, under tensiometery range, were obtained by use of tensiometers and the related water contents by a TDR instrument. For the simulation purposes, the HYDRUS-2D model was made use of. The model performance was evaluated by comparing the measured us the predicted values using Root Mean Square Error (RMSE) statistics. The results of the spatial simulation revealed that this model provides more appropriate results in locations farther away, and deeper than The drippers (RMSE=0.03) as compared with the points adjacent to the droppers and less deeper ones (RMSE=0.008). The results of the temporal simulation showed that the model worked more accurately within 48 hrs after irrigation (RMSE=0.005) rather than one following the start of irrigation (RMSE=0.029). Therefore, it can be concluded that soil water content in Subsurface drip irrigation system can be reasonably simulated while root water uptake and evaporation processes are both actively going on.

To design drip irrigation system, the distribution and changes in soil moisture should be determined in situ that it is very costly and time consuming. This study evaluated the performance of HYDRUS-2D model to estimate soil moisture after irrigation under Subsurface line source was in a heterogeneous heavy soil. Irrigation was done at three tape installation depths of 10, 20 and 30 cm with three volumes of 10, 15 and 20 litters in silty clay soil with three repeating. Observed and simulated data were compared using statistical indices i.e. RMSE, nRMSE and CRM. Results showed that the minimum and maximum of RMSE values were 0.013 and 0.045 cm3.cm-3, respectively. nRMSE of all treatments except of one, the second replication of 10 liters of irrigation water with installation depth of 20 cm, were less than 10% categorized in the excellent class of soil moisture simulation. Maximum and minimum values of CRM were 0.100 and -0.065, respectively. Results from the model showed this model can be used in the design and management of Subsurface drip irrigation systems in heterogeneous soils with heavy texture.

A problem that hinders the development of Subsurface drip irrigation systems is the clogging of drippers as a result of sucking soil into drippers during pump turn-off. Using an envelope around the drippers may lessen the problem. However, the dripper envelope may also change the wetting pattern. The objective of this research was to investigate the effect of unwoven and woven geotextile dripper envelopes on the depth and width of wetting profile. Five 60-cm probes each containing 10-cm spaced moisture sensor were used for specifying the wetting profile. A factorial experiment with 9 treatment comprising the 3 levels of the dripper depth (0, 15 and 30 centimeters) and 3 levels of the envelope, (no envelope as control, unwoven envelope and woven envelope) in a complete randomized blocks structure with 3 replicates was carried out in the research greenhouse at University of Shahrekord. Results showed that the unwoven geotextile had more effect on the wetting pattern compared to woven geotextile. Unwoven geotextile increased the width of wetting profile from 27 to 37 centimeters after 30 minutes and from 37 to 45 centimeters after 60 minutes. Overall, using geotextile increased the width and decreased the depth of wetting significantly (P<0.01). Meanwhile the influence of unwove geotextile was more pronounced than that of the woven geotextile.

In designing and implementing irrigation systems, it is essential to know how Wetting Pattern form soils and their components. Simulation for each design and management scenario, in addition to highly acceptable results, saves time. The main purpose of this study was to provide equations for determination of soil moisture pattern in Subsurface irrigation from point source. For this purpose, by applying dimensional analysis, the Schwartzman and zur equation for Subsurface drip irrigation from point source was modified. By constructing a physical model and using three types of sand, loam and silty clay loam texture, the equations coefficients were extracted and 9 equations were obtained. For the developed simulation model in three soil type, RMSE values was smaller than 2. 47, 1. 27 and 3. 01 cm for wetted width, upper and lower trickle placement respectively. It was found that performance of model was good with model efficiency greater than 81% for all cases. Therefore, it can be used to describe wetted depths and widths of soil under SDI system with point source of water application.

Water Scarcity in arid and semi-arid regions is the major concern for water and agricultural authorities. To confront this problem, high performance irrigation systems, such as drip irrigation and or Subsurface drip irrigation, are recommended. In designing a Subsurface drip irrigation system for row crops, geometry and dimension of wetted volume are the main factors needed for determining laterals' installation depth as well as emitters' spacings. For this purpose several models were developed to demonstrate a good prediction of wetting pattern using emitter discharge, volume of applied water and hydraulic properties of soil. In this paper dimensional analysis method, developed by Singh et al. (2006) was employed due to its simplicity and less input data requirement. Measured data of wetting pattern under Subsurface drip irrigation system (Z+, Z- and W, lower, upper and horizontal displacement, respectively) in a clay loam soil with 30 cm emitter depth were compared with output data estimated through the model. A good agreement (R2 = 0.97, 0.99 and 0.97 for z+, z- and r, respectively.) was obtained between measured and estimated data.

Salt accumulation in the soil profile is a challenge for irrigated agriculture and the study of salt concentration and its variation in the soil profile under different irrigation systems and management is needed. In this study, Sodium, magnesium, calcium and SAR concentration were studied under three irrigation regimes; farmer management (I1), Irrigation requirement (I2) and I2 plus leaching requirement (I3) in Safaeyeh in Kerman during two cultivation years (1391-1392). According to the results sodium, magnesium, and SAR deceased after irrigation but calcium did not affect by irrigation time. In development growth period, the highest values of SAR, sodium and magnesium were found to be corresponded to 75, 50 and 75 cm soil depth, respectively. The highest values of sodium and magnesium in I3 treatment were 123. 4 and 43. 6 meq/lit which were corresponded to the soil depth of 75cm. The highest value of calcium in I3 treatment was correspond to the soil depth of 25cm which was 52meq/lit. The highest value of SAR (12. 4) was belong to the soil depth of 75 cm which indicates calcium has moved upward and toward the emitter. The interaction effect of irrigation regimes, soil depth, and recording time (before and after irrigation) showed that the highest concentrations of sodium, magnesium and SAR were 131. 8, 74. 4 and 54. 3 meq/lit respectively, which were belong to I3 and 75 cm soil depth before irrigation. The highest amount of SAR was 12. 8 which were belonging to I3 treatment, too. Calcium variations in the soil under I2 and I3 irrigation regimes shows the important of irrigation management for salinity control. The results showed that I2 have better performance than the other irrigation regimes due to less salt accumulation and SAR values in the root zone.

Irrigation management is effective on soil salinity variation. Salinity pattern was studied in different soil layer under different irrigation regimes in a pistachio garden equipped to Subsurface drip irrigation system. The treatments were three irrigation regimes; control (I1), Irrigation based on irrigation requirement (I2) and I2 plus leaching requirement (I3), three soil depth of 25, 50, and 75 cm from soil surface and before and after irrigation event. According to the results soil salinity change by irrigation regime, time and soil depth layer. The I2 irrigation regime were more effective to move the salinity (ECe) to margin of wetted zone compared to other irrigation regimes. Salinity increased by soil depth and that was higher in 75 cm soil depth with 14. 5 dS/m. Irrigation regimes were not effective in moving the salinity to upper part of dripper lateral line. Bilateral impact of irrigation regimes, soil depth, and time before and after irrigation event was also resulted in higher soil salinity in 75 cm soil depth with 14. 2 dS/m. The I3 irrigation regime applied more salt to the soil by higher irrigation depth but was not effective to leach out the salt.

Because of decreasing the value and availability of water resources, we have to use water resources in a best way. The new irrigation systems like Subsurface drip irrigation can improve irrigation efficiency and water use efficiency. To properly manage SDI systems, the precise distribution of water around the emitter must be known.Several models have been developed to simulate soil moisture pattern and wetting front by using soil hydraulic parameters, the emitter’s discharge and the volume of discharged water. In this paper, HYDRUS-2D model was used so simulation results were compared with two sets of experiments involving SDI with emitters installed at two different depth (40 & 50 cm) while the emitters space was 75 cm with 3.5 l/h emitter discharge. The RMSE at different locations around emitter varied between 0.014 and 0.033 for volumetric water content in 40 cm installation depth and 0.009 and 0.025 for 50 cm installation depth. The continuous horizontal wetting profile was achieved so the space of emitter was suitable. With due attention to our results, 75 cm distance between emitters and 50 cm installation depth with 3.5 l/hr emitter discharge is proposed to be applied in loamy soil.